WorldWideScience

Sample records for chepes famatinian orogen

  1. Evolución del orógeno Famatiniano en la Sierra de San Luis: magmatismo de arco, deformación y metamorfismo de bajo a alto grado Evolution of the Famatinian orogen in the Sierra de San Luis: arc magmatism, deformation, and low to high-grade metamorphism

    Directory of Open Access Journals (Sweden)

    AM Sato

    2003-12-01

    muy bien todos los procesos pampeanos.In this geological review of the igneous-metamorphic basement of the Sierra de San Luis we recognize the following three-stage evolution: (1 Pre-Famatinian processes: Initial siliciclastic sedimentation of possible Precambrian age, with interbedded mafic to ultramafic lavas and banded iron formations. Only a few isotopic dates constrain the remnant northwest-trending deformation and associated metamorphism within the Pampean cycle. An additional sedimentary process is also identified within this cycle. (2 Famatinian orogenic cycle, main phase: this was responsible for delineating the most important features of the Sierra de San Luis basement. The Famatinian magmatic arc had already been active since Mid-Cambrian times (507 Ma, and the Ordovician was the climax of the magmatism, tectonism and metamorphism. The granitoids were deformed together with the country rock, and the entire Sierra de San Luis was affected by penetrative NNE-trending foliations. (3 Famatinian cycle, late- to post-orogenic phase: the orogenic activity decreased during Silurian to Early Carboniferous times. Final compression was concentrated through ductile shear zones that led to the juxtaposition and exhumation of metamorphic rock strips. The late- to postorogenic granitoids were also emplaced at this stage. From the regional viewpoint, the Ordovician deformation in Sierras Pampeanas was associated with terrane collision. The Sierra de San Luis was located at the proto-Andean margin of the Gondwana autochthon, where the magmatic arc was emplaced. The Ordovician deformation affected both the Gondwana margin and the Mesoproterozoic basement of the accreted Cuyania terrane, located to the west. To the east of Sierra de San Luis, the Sierra de Córdoba was not directly involved in the main famatinian orogenic axis, and therefore, all the Pampean processes were well preserved there.

  2. Hallazgo de granitoides fuertemente peraluminosos en la sierra de Famatina, orógeno famatiniano Discovery of strongly peraluminous granitoids in the Sierra de Famatina, Famatinian orogeny

    Directory of Open Access Journals (Sweden)

    J.A. Dahlquist

    2005-06-01

    Full Text Available La unidad fuertemente peraluminosa Cerro Toro, formada por rocas graníticas con cordierita y granate, constituye uno de los afloramientos más occidentales de la sierra de Famatina. Estudios combinados de petrología, geoquímica de roca total y química mineral indican que el magma primordial de esta unidad fue derivada a partir de la fusión parcial de metasedimentos en condiciones de alta temperatura (762°C y presión media (4,1 Kb. Las elevadas relaciones de Rb/Sr, Rb/Ba y las bajas relaciones de CaO/NaO2 (The strongly peraluminous Cerro Toro unit is formed of cordierite- and garnet-bearing granitic rocks and constitutes one of the most western outcrops of the Sierra de Famatina. Combined petrology, chemistry/mineralogy and whole-rock geochemistry studies indicate that the parental magma of this igneous unit was derived from the partial melting of metasediments under high temperature (762°C and moderate pressure (4,1 Kb conditions. The higher Rb/Sr, Rb/Ba and lower CaO/NaO2 ratios (< 0.34 suggest that the parental magma was derived from a metasedimentary source of psamopelitic plagioclase-rich composition (metagreywacke, suggesting anatexis of metasediments from an immature continental platform. This paper presents the first report of strongly peraluminous granitic rocks in the Sierra de Famatina. These granitic rocks are very similar to those of the Tuaní Granite peraluminous unit of the Sierra de Chepes, formed of typical Famatinian granitoids, suggesting that similar petrogenetic processes occurred in both regions of the magmatic arc during the Famatinian orogeny.

  3. Depósitos polimetálicos en el orógeno famatiniano de las Sierras Pampeanas de San Luis y Córdoba: fluidos, fuentes y modelos de emplazamiento Polymetallic deposits in the Famatinian orogen of the Sierras Pampeanas of San Luis and Córdoba: fluids, sources and emplacement model

    Directory of Open Access Journals (Sweden)

    D. Mutti

    2007-11-01

    .The famatinian cycle determined a mineralising episode between ~ 385 and ~ 292 Ma into the Sierras Pampeanas of San Luis and Córdoba. This episode, related to N - S first order shear zones and granitoids, formed polymetallic linear domains with W, Ag, Pb, Zn, Au and associated metals, within metamorphites and subordinated granitoids. d18Ofluid(H2O and dDfluid(H2O values obtained in representative deposits of San Luis and Córdoba suggest a magmatic and evolved meteoric water origin for the mineralising fluid. Likewise, d34Sfluido (H2S determinations in sulphides suggest that the sulphur was incorporated by thermoreduction from the crustal metasedimentites. 208Pb/204Pb - 207Pb/204Pb - 206Pb/204Pb relations point to a lead source from the homogenised phanerozoic continental crust, although a mantle component has been proved in La Fortuna (Las Aguadas district, La Aspereza (San Martín district and Fischer (Cerro Áspero district. Tensional mineralised structures between 250º and 319º major direction, and en echelón and stepped internal geometry, respond to the Riedel model in simple shear zones. These secondary structures had been developed in a brittle - ductile and brittle transpressive regimen in an extensional environment, during a maximum principal NW-SE s1 stress and the regional uplift. Investigated features highlight that the sinorogenic to posorogenic magmatism caused thermal anomalies that implicated hydrothermal convective systems. These systems channeled the aqueous flow through the Tres Árboles 1st order structure and secondary lineaments. No proof was found that the granitic magmatism would have contributed significantly with the sulphur and metallic elements, at least for this kind of ore deposits with stressed structural control.

  4. Deciphering orogenic evolution

    OpenAIRE

    Rolland, Yan; Lardeaux, Jean-Marc; Jolivet, Laurent

    2012-01-01

    Deciphering orogenic evolution requires the integration of a growing number of geological and geophysical techniques on various spatial and temporal scales. Contrasting visions of mountain building and lithospheric deformation have been proposed in recent years. These models depend on the respective roles assigned to the mantle, the crust or the sediments. This article summarizes the contents of the Special Issue dedicated to 'Geodynamics and Orogenesis' following the 'Réunion previous termde...

  5. Generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the famatinian magmatic Arc, Argentina

    OpenAIRE

    Juan E. Otamendi; Mihai N. Ducea; Alina M Tibaldi; Bergantz, Geoerge W.; Rosa Díaz, Jesús de la; Graciela I Vujovich

    2009-01-01

    The source regions of dioritic and tonalitic magmas have been identified in a deep crustal section of the Famatinian arc (Sierras Pampeanas of western Argentina). The source zones of intermediate igneous rocks are located at the transition between a gabbro-dominated mafic unit and a tonalite-dominated intermediate unit. In the upper levels of the mafic unit mafic magmas intruded into metasedimentary wall-rocks, crystallized mainly as amphibole gabbronorite and caused the partial melting of th...

  6. Los granitoides famatinianos del sector suroccidentalde la Sierra de San Luis: clasificación y geotermometría TheFamatinian granitoids of the southwestern sector of Sierra de San Luis: Classification and geothermometry

    Directory of Open Access Journals (Sweden)

    Augusto Morosini

    2009-06-01

    Full Text Available En el sector suroccidental dela sierra de San Luis se reconocen varios plutones pertenecientes a un antiguoarco magmático, emplazados en rocas metamórficas de facies esquistos verdes aanfibolitas bajas e interpretados como pre-oclóyicos, dentro del cicloorogénico famatiniano. El estudio cartográfico, petrográfico y de microanálisisquímicos en feldespatos ha permitido realizar una clasificación de las rocasplutónicas del área y ha sido la base para realizar una propuesta de lahistoria de enfriamiento y emplazamiento de las diferentes facies. Losresultados de microanálisis químicos en feldespatos muestran que existe unagran variación en el contenido de An de las plagioclasas de la serie máfica conrespecto a las de la serie félsica, indicando una variación de temperaturas enun rango que va desde los 1.100° a 748°C respectivamente, y un probable origendiferente de los magmas. Los datos fueron modelizados y ajustados a diagramasteóricos preexistentes de isotermas para el sistema or-ab-an y para una presióninterna de H2O de 5.000 barias, es decir, se consideró unpseudo-sistema isobárico.Several plutons belonging to an old magmatic arc arerecognized in the southwestern of the Sierra de San Luis. They are emplaced inmetamorphic rocks of greenschist to lower amphibolites facies, and interpretedas pre-ocloyic, older than 460 Ma, within the Famatinian orogenic cycle. Themapping, petrographic study, and chemical microanalysis in feldspars, haveenabled a classification of the plutonics roks of the area and have revealedpart of the history of cooling and emplacement of the different facies. Also,the chemical microanalysis in feldspars shows that there is great variation inthe An content of plagioclase in the mafic series, in comparison with those ofthe felsic series, indicating a variation in the range of temperatures from1100° to 748° C respectively, and a probably different origin of magmas. Thedata were modeled and adjusted to

  7. And the Variscan Orogen Buckled

    Science.gov (United States)

    Pastor-Galán, D.; Groenewegen, T.; Gutiérrez-Alonso, G.; Langereis, C. G.

    2013-12-01

    Oroclines are the largest scale folds in nature, and as folds can be produced by bending or by buckling. The most commonly invoked bending mechanisms are indentation (the Himalayan syntaxes) and slab roll-back (The Calabria Arc) whereas buckling usually are commonly related with collision of the apex of ribbon continents along strike (Alaskan oroclines). In Western Europe the tectonostratigraphic zonation of Variscan orogen shows a complex 'S' shape pattern recently interpreted as a double orocline consisting of a northern and southern arc. The northern arc, known as Cantabria-Asturias Arc or Cantabrian Orocline, was developed after closure of the Rheic Ocean and the building and collapse of the Variscan orogenic edifice and, therefore, is considered post-Variscan in age. On the other hand, neither the geometry nor the kinematics of the so-called Central Iberian orocline, situated at the south of the Iberian peninsula are properly known. However, it seems reasonable to think that both oroclines developed at the same time as other coupled oroclines, such as the New England oroclines or the Carpathian oroclines. The particular paleogeography of the Variscan belt in Pangea and the kinematics of the oroclinal formation make impossible the mechanisms of indentation or buckling of a ribbon continent. The occurrence of an intense syn- and slightly post-Cantabrian orocline magmatic event (310-290 Ma) has been linked to the development of the orocline(s) due to the particular spatial-temporal distribution of these post-tectonic granitoids and its isotopic signature which would imply that the oroclines (if synchronous) are thick-skinned. This magmatic pulse has also been interpreted as due to slab roll-back. We present widespread evidences of buckling around the whole orocline at different lithospheric levels and new insights of the particular geometry of the southern orocline which is difficult to reconcile with a roll-back related origin. Therefore, a major change in the

  8. Orogenic Response to Augmented Erosion Associated with Northern Hemisphere Glaciation: The St. Elias Orogen of Alaska

    Science.gov (United States)

    Berger, A. L.; Gulick, S. P.; Spotila, J. A.; Worthington, L. L.; Upton, P.; Jaeger, J. M.; Pavlis, T. L.

    2009-12-01

    Active orogens are thought to behave as internally deforming critical-taper wedges that are in rough long-term equilibrium with regional boundary conditions. Deformation, kinematics, and the thermal evolution of orogenic systems are therefore believed to be significantly influenced by spatial and temporal variations in climate. The exact role of cryosphere-geosphere interactions in natural systems, however, continues to be elusive. Here we quantify the spatial patterns of denudation and deformation, and their temporal variations, in the heavily glaciated St Elias orogen in southern Alaska. The tractable size and high latitude of the St. Elias orogen provides an ideal setting to address the real world orogenic response to focused denudation and climate change. Independent of any known change in regional tectonic convergence rate, the St. Elias orogen was subjected to the most severe transition in climate during Cenozoic time, the Late Neogene and Pleistocene onset and advance of glaciers. Low-temperature bedrock thermochronometry, thermokinematic modelling, and offshore seismic reflection and borehole data demonstrate an association between augmented glacial denudation and orogenic evolution. Coeval with the onset of enhanced glacier coverage in mid-Pleistocene time, onshore denudation and offshore sedimentation accelerated ~ten-fold, with the highest rates of exhumation (4 km/Myr (±25%)) located around a narrow zone where the mean Quaternary glacial equilibrium line altitude (ELA) intersects mean topography on the windward flank of the orogen. This climatically driven mass redistribution coincided with the transfer of strain away the seaward deformation front as well as accelerated motion along both a backthrust running the length of the orogen and a series of forethrusts that lie beneath the zone of highest glacial flux. In a cause and effect response, the expansion of glaciers thus appears to have driven an orogen scale structural reorganization leading to the

  9. Evolución tectonotermal ordovícica del borde occidental del arco magmático Famatiniano: metamorfismo de las rocas máficas y ultramáficas de la Sierra de la Huerta de Las Imanas (Sierras Pampeanas, Argentina Tectonothermal ordovician evolution of the western margin of the Famatinian magmatic arc: metamorphism of the mafic and ultramafic rocks of Sierra de la Huerta -Las Imanas (Pampean Ranges, Argentina

    Directory of Open Access Journals (Sweden)

    Juan A Murra

    2006-07-01

    énicosAn important magmatic and tectonometamorphic activity of Early and Middle Ordovician age is registered in the pre-Andean basement of the Sierras Pampeanas of Argentina. These were linked to the development of a continental magmatic arc during the Famatinian Orogeny, resulting from the approach and attachment of an alleged exotic terrane (the Precordillera Terrane, to the south western Gondwana's margin (present coordinates. A suit of meta-mafic and ultramafic rocks are exposed in the Sierras de La Huerta and Las Imanas, at the western limit of the famatinian orogen. Metaperidotites (Ol-Opx-Cpx-Am-Spl, coronitic metapyroxenites (Opx-Cpx-Spl-Am-Pl, metaquartz-norites (Opx-Pl-Am-Qtz-Bt±Grt and metadiorites (Pl-Am-Qtz-Bt-Ep are associated with metasedimentary rocks (marbles, gneisses and migmatites with Sil+Kfs+Grt that reached the peak and post-peak conditions of metamorphism at middle Ordovician time. The meta-mafic rocks record a first high-grade metamorphic event (M1-730ºC and 8.4±0.5 kbar and a second lower pressure event (M2, 720ºC and 4.5 kbar with Cum+Hbl+Mag in a coronitic assemblage. The meta-ultramafic rocks also record the two metamorphic events, but only for the second one it was possible to calculate the P-T conditions. At latitude 32º30'S, the Famatinian magmatic arc shows a systematic compositional variation normal to its trend, i.e. in an east-west direction, which could be related to present erosion levels. In this context, the mafic and ultramafic units of Sierras de La Huerta and Las Imanas, probably represent the deepest levels of the magmatic arc which is consistent with the position that they show marginal to the orogenic belt, i.e., where the uplift and erosion rates were larger

  10. Orogenic Tertiary magmatism on the Macedonian Dinarides: a Review

    OpenAIRE

    Boev, Blazo; Yanev, Yotzo

    2001-01-01

    Widespread Tertiary magmatism of orogenic signature developed on the Macedonian part of the Dinarides, essentially in the Serbo-Macedonian massif and in the Vardar zone (KARAMATA et al., 1992). Orogenic magmatic rocks (predominantly volcanic) are presented in 5 areas (from east to west): the Osogovo-Besna Kobila, Kratovo-Zletovo, BuCim-Borov Dol, Dojran and Kozuf.

  11. La deformación famatiniana del Granito La Escalerilla, sierra de San Luis The Famatinian deformation of La Escalerilla Granite, Sierra de San Luis

    Directory of Open Access Journals (Sweden)

    Augusto Morosini

    2010-12-01

    Full Text Available En el presente trabajo se analizan las estructuras post-magmáticas del Granito La Escalerilla y se propone una interpretación sobre los mecanismos regionales de esfuerzos correspondientes al ciclo famatiniano en el sector suroccidental de la sierra de San Luis. Se considera que el plutón La Escalerilla condicionó el estilo de deformación de las unidades litológicas en su periferia. Ésta deformación estuvo ligada al contraste reológico producido entre el intrusivo y las metamorfitas de la roca de caja. La estructura del plutón está caracterizada por la presencia de: a una foliación interna de orientación meridiana particularmente marcada en los sectores de borde, así como al norte y sur del cuerpo, b una faja milonítica de rumbo NNE, en el contacto oriental, c cizallas dúctiles conjugadas de tipo Riedel (NNO y anti-Riedel (NE, estructuras interpretadas como parte de una tectónica de escape bajo un régimen transpresivo sinestral, y d fracturas tensionales de orientación ONO. Todas estas estructuras se considera que responden a esfuerzos compresivos de dirección ONO, que generan una componente real de esfuerzo tangencial sinestral,de módulo variable, como consecuencia de la oblicuidad general del plutón, respecto al eje de máximo esfuerzo (σ1. Sin embargo en algunos sectores esta componente tangencial es mínima debido a las diferentes orientaciones de los límites del cuerpo respecto al vector de máximo esfuerzo (σ1.In this paper post-magmatic structures of La Escalerilla Granite are analyzed and an interpretation of regional deformation mechanisms is proposed for cycle Famatinian of the Southwestern sector of the Sierra de San Luis. It is thought that La Escalerilla pluton has conditioned the style of deformation of the lithologic units at its periphery. This deformation was linked to the rheological contrast which occurred between the intrusive and metamorphic country rocks. The structure of the pluton is characterized

  12. Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

    Science.gov (United States)

    Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

    2013-08-01

    The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

  13. Remagnetizations in the Variscan orogen and foreland in Czech Republic and Poland: timing, origin and links with orogenic processes

    Czech Academy of Sciences Publication Activity Database

    Grabowski, J.; Bábek, O.; Hladil, Jindřich; Narkiewicz, M.

    [Postdam] : [International Assotiation of Geomagnetism and Aeronomy], [2009]. 506- SAT -P1445-1102-506- SAT -P1445-1102. [International Assotiation of Geomagnetism and Aeronomy (IAGA) Scientific Assembly /11./. 24.08.2009-29.09.2009, Sopron] Institutional research plan: CEZ:AV0Z30130516 Keywords : remagnezations * orogenic processes * Variscan orogen Subject RIV: DB - Geology ; Mineralogy http://www.iaga2009sopron.hu/

  14. Linking magmatism with collision in an accretionary orogen

    Science.gov (United States)

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-05-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  15. Strong imprint of past orogenic events on the thermochronological record

    Science.gov (United States)

    Braun, Jean

    2016-06-01

    Using a simple solution to the heat conduction equation, I show how, at the end of an orogenic event, the relaxation of isotherms from a syn-orogenic advection-dominated geometry to a post-orogenic conduction-dominated geometry leads to the creation of a thick iso-age crustal layer. Subsequent erosion of this layer yields peculiar age-elevation profiles and detrital age distributions that cannot be easily interpreted using traditional techniques. I illustrate these points by using a simple analytical solution of the heat equation as well as a transient, three-dimensional numerical model. I also demonstrate that the age of the end of an orogenic event is so strongly imprinted in the thermochronological record that it erases most of the information pertaining to the orogenic phase itself and the subsequent isostatically-driven exhumation. The concept is used to explain two thermochronological datasets from the Himalayas and demonstrate that their most likely interpretation involves the sudden interruption of extremely fast exhumation accommodated by movement along the South Tibetan Detachment in the Higher Himalayas around 15 Ma.

  16. Evolución metalogenética de las Sierras Pampeanas de Córdoba y sur de Santiago del Estero: Ciclos famatiniano, gondwánico y ándico Metallogenic evolution of the Sierras Pampeanas of Córdoba and south of Santiago del Estero: Famatinian, Gondwanic and Andean cycles

    Directory of Open Access Journals (Sweden)

    D. Mutti

    2005-09-01

    Full Text Available Se propone la evolución metalogenética de las Sierras Pampeaneas de Córdoba y sur de Santiago del Estero en cinco estadios, de los cuales los dos primeros se expusieron en un trabajo anterior. El estadio metalogenético 3, que corresponde al segundo ciclo orogénico del Pampeano-Famatiniano, se caracterizó por la migración de fluidos hidrotermales y la generación y reactivación de estructuras. Durante el mismo sucedieron transformaciones en depósitos de Cr (Fe-Ti, Cu (Au-Ag, Pb-Zn (Ag-Cu-Au, Fe y Cu- Fe (Zn-Au-Ag-Co, y se originaron pegmatitas portadoras de Be-Nb-Ta-W-P-U-ETR, depósitos biextendidos de W-Bi (Mo-Cu-Sn- Zn-Au-B-F-Te y de U asociados a granitoides, depósitos metasomáticos de Fe-Cu (Ti-Au y vetas de Au (Cu-Zn-Pb-As y polimetálicas de Ag-Pb-Zn (V-Sn-Mn-Cd-Au-Cu-As-Bi-Sb-Co. Para este estadio se establece una correlación con depósitos en cinturones orogénicos. El estadio metalogenético 4, correspondiente al ciclo extensional gondwánico y vinculado con la apertura del rifting Atlántico, formó depósitos de Mn (Fe-F-Ba en vetas y de F (Fe-Mn en vetas asociados con granitos. El estadio metalogenético 5 se desarrolló durante el ciclo compresional Ándico y generó manifestaciones de Au epitermal y depósitos y manifestaciones de U-V (Mn-Fe en sedimentitas. Los sucesivos estadios de depositación y movilización de elementos metálicos definieron fajas mineralizadas que otorgan a este sector de las Sierras Pampeanas un carácter de dominio especializado en Cr, W, Fe, Cu, Zn, Pb, Ti, Au, Bi, Be, Li, U, Mn, F y B y subordinado en Sn, Mo, ETR, Ta, Nb, V, Cd, Ag, Sb, Co, P, As, S, Te, Se y Ba.Five metallogenic stages are proposed for the metallogenic evolution of the Sierra Pampeaneas of Córdoba and south of Santiago del Estero, havin. having already been exposed the first two previous work. Metallogenic stage 3, corresponding to the second orogenic cycle of the Pampean-Famatinian compressive cycle, was characterized by

  17. Pn anisotropic tomography under the entire Tienshan orogenic belt

    Science.gov (United States)

    Zhou, Zhigang; Lei, Jianshe

    2015-11-01

    We present a new anisotropic tomography of the uppermost mantle under the Tienshan orogenic belt and surrounding regions using a number of Pn arrival-time data hand-picked from portable seismic stations and chosen from the Xinjiang provincial observation bulletins and the EHB datasets. Our results exhibit prominent lateral heterogeneities in the study region. Distinct low-velocity anomalies are visible under the tectonically active regions, such as the Tienshan orogenic belt and western Kunlun Mountains, whereas pronounced high-velocity anomalies are imaged beneath the stable blocks, such as the Kazakh shield, the Junggar, Tarim, Qaidam, and Turpan-Hami basins, and the Tajik depression. Most strong earthquakes (Ms > 7.0) are mainly distributed along the transition zone of high to low velocity anomalies, suggesting a possible correlation between the strong earthquakes and the upper mantle structure. The fast directions of Pn anisotropy beneath the Tienshan orogenic belt are generally parallel to its striking orientation, whereas those beneath Pamir show a northward arc-shaped distribution. The Pn fast-velocity directions on the boundaries of the Kazakh shield and the Tarim and Junngar basins are approximately perpendicular to the strike of the Tienshan orogenic belt. By integrating with previous findings, our results suggest that the Tarim and Kazakh lithospheric materials could have underthrusted beneath the Tienshan orogenic belt that leads to the hot mantle material upwelling under the Tienshan orogenic belt, which is attributable to the Indo-Asian collision. These dynamic processes could play important roles in the Tienshan mountain building.

  18. Economic implications of plate tectonic models of the Damara orogen

    International Nuclear Information System (INIS)

    The enviroment of the Damara orogen is typical for placer gold and uranium deposits. The alkaline extrusives may also have potential for subaqueous volcano-exhalative mineralisation. Deposits of carbonate, phibolites, ferruginous and pyritic quartzites, lead, zinc, copper and iron occur in this environment. There is also a possibility of tin and tungsten mineralization

  19. Lateral constrictional flow of hot orogenic crust: Insights from the Neoarchean of south India, geological and geophysical implications for orogenic plateaux

    OpenAIRE

    Chardon, Dominique; Jayananda, Mudlappa; Peucat, Jean-Jacques

    2011-01-01

    This study provides an in situ geological perspective on fabrics produced by synconvergence lateral crustal flow of hot orogens. It is based on the example of the Neoarchean orogen of the Dharwar craton (India) and combines structural analysis and ion microprobe U!Pb zircon geochronology. We document a pervasive, three!dimensional flow mode of the lower crust, called lateral constrictional flow (LCF), which combines orogen!normal shortening, lateral constrictional stretching, and transtension...

  20. Petrology of mafic and ultramafic layered rocks from the Jaboncillo Valley, Sierra de Valle Fértil, Argentina: Implications for the evolution of magmas in the lower crust of the Famatinian arc

    Science.gov (United States)

    Otamendi, J. E.; Cristofolini, E.; Tibaldi, A. M.; Quevedo, F. I.; Baliani, I.

    2010-04-01

    This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and peridotitic layered body that is lens-shaped and surrounded by gabbronorites, diorites, and metasedimentary migmatites. This body exposed at Jaboncillo Valley is one among several examples of mafic and ultramafic layered sequences in the Sierras Valle Fértil and La Huerta, which formed as part of the lower crust of the Ordovician Famatinian magmatic arc in central-western Argentina. The layered sequence grew at deep crustal levels (20-25 km) within a mafic lower crust. The base of the layered body was detached during the tectonic uplift of the Famatinian lower crust, whereas the roof of the layered body is exposed in the eastern zone. In the inferred roof, olivine-bearing rocks vanish, cumulate textures are less frequent, and the igneous sequence becomes dominated by massive or thinly banded gabbronorites. Mainly based on the petrographic relationships, the inferred order of crystallization in the gabbroic and peridotitic layered sequence is: (1) Cr-Al-spinel + olivine, (2) Cr-Al-spinel + olivine + clinopyroxene + magnetite, (3) Cr-Al-spinel + olivine + plagioclase + magnetite ± orthopyroxene, and (4) Al-spinel + orthopyroxene + amphibole. A strong linear negative correlation between olivine and plagioclase modal proportions combined with field, petrographic and geochemical observations are used to demonstrate that the physical separation of olivine and plagioclase results in rock diversity at scales of a few centimeters to tens of meters. However, the composition of olivine (Fo ˜ 0.81) and plagioclase (An > 94%) remains similar throughout the layered sequence. Spinels are restricted to olivine-bearing assemblages, and display chemical trends characteristic of spinels found in arc-related cumulates. Gabbroic and peridotitic layered rocks have trace element concentrations reflecting cumulates of early crystallizing minerals. The trace element patterns still retain the

  1. Structural inversion of the Tamworth Belt: Insights into the development of orogenic curvature in the southern New England Orogen, Australia

    Science.gov (United States)

    Phillips, G.; Robinson, J.; Glen, R.; Roberts, J.

    2016-05-01

    The middle to late Permian Hunter Bowen Event is credited with the development of orogenic curvature in the southern New England Orogen, yet contention surrounds the structural dynamics responsible for the development of this curvature. Debate is largely centred on the roles of orogen parallel strike-slip and orogen normal extension and contraction to explain the development of curvature. To evaluate the dynamic history of the Hunter Bowen Event, we present new kinematic reconstructions of the Tamworth Belt. The Tamworth Belt formed as a Carboniferous forearc basin and was subsequently inverted during the Hunter Bowen Event. Kinematic reconstructions of the Tamworth Belt are based on new maps and cross-sections built from a synthesis of best-available mapping, chronostratigraphic data and new interpretations of depth-converted seismic data. The following conclusions are made from our study: (i) the Hunter Bowen Event was dominantly driven by margin normal contraction (east-west shortening; present-day coordinates), and; (ii) variations in structural style along the strike of the Tamworth Belt can be explained by orthogonal vs. oblique inversion, which reflects the angular relationship between the principal shortening vector and continental-arc margin. Given these conclusions, we suggest that curvature around the controversial Manning Bend was influenced by the presence of primary curvature in the continental margin, and that the Hastings Block was translated along a sinistral strike-slip fault system that formed along this oblique (with respect to the regional east-west extension and convergence direction) part of the margin. Given the available temporal data, the translation of the Hastings Block took place in the Early Permian (Asselian) and therefore preceded the Hunter Bowen Event. Accordingly, we suggest that the Hunter Bowen Event was dominantly associated with enhancing curvature that was either primary in origin, or associated with fault block translation

  2. The Cenozoic Tectonic History of the Calabrian Orogen, Southern Italy

    OpenAIRE

    Shimabukuro, David Haruo

    2011-01-01

    The Cenozoic accretionary wedge of Calabria, Southern Italy, consists of several units of continental and oceanic affinity accreted beneath the former continental margin of the Sardinia-Corsica block. Each of these units bears the imprint of blueschist-facies metamorphism, indicating that it has been subducted to high-pressure/low-temperature conditions during the Alpine Orogeny. Structurally higher units, having been accreted first, record the early metamorphic history of the orogen; lower...

  3. The crust-mantle interaction in continental subduction channels: Zircon evidence from orogenic peridotite in the Sulu orogen

    Science.gov (United States)

    Li, Hai-Yong; Chen, Ren-Xu; Zheng, Yong-Fei; Hu, Zhaochu

    2016-02-01

    A combined secondary ion mass spectrometer and laser ablation-(multicollector)-inductively coupled plasma mass spectrometer study of zircon U-Pb ages, trace elements, and O and Hf isotopes was carried out for orogenic peridotite and its host gneiss in the Sulu orogen. Newly grown zircon domains exhibit weak zoning or no zoning, relatively low Th/U ratios (earth element (HREE) contents, steep middle rare earth element-HREE patterns, negative Eu anomalies, and negative to low δ18O values of -11.3 to 0.9‰ and U-Pb ages of 220 ± 2 to 231 ± 4 Ma. Thus, these zircons would have grown from metasomatic fluids during the early exhumation of deeply subducted continental crust. The infiltration of metasomatic fluids into the peridotite is also indicated by the occurrence of hydrous minerals such as amphibole, serpentine, and chlorite. In contrast, relict zircon domains exhibit magmatic zircon characteristics. Their U-Pb ages and trace element and Hf-O isotope compositions are similar to those for protolith zircons from ultrahigh-pressure metamorphic rocks in the Dabie-Sulu orogenic belt. Thus, these relict magmatic zircons would be physically transported into the peridotite by metasomatic fluids originated from the deeply subducted continental crust. Therefore, the peridotite underwent metasomatism by aqueous solutions derived from dehydration of the deeply subducted continental crust during the early exhumation. It is these crustally derived fluids that would have brought not only such chemical components as Zr and Si but also tiny zircon grains from the deeply subducted crustal rocks into the peridotite at the slab-mantle interface in continental subduction channels. As such, the orogenic peridotite records the crust-mantle interaction at the deep continental subduction zone.

  4. Orogenic structural inheritance and rifted passive margin formation

    Science.gov (United States)

    Salazar Mora, Claudio A.; Huismans, Ritske S.

    2016-04-01

    Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

  5. Dynamic Settings and Interactions between Basin Subsidence and Orogeny in Zhoukou Depression and Dabie Orogenic Belt

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This paper presents a study of the geo-dynamic setting and the relation between orogenic uplift and basin subsidence in the inland Zhoukou depression and Dabie orogenic belt. Since the Mesozoic the evolution of Zhoukou depression can be divided into three stages: (1) foreland basin, (2) transitional stage, (3) fault depression. Formation and variations of basin were not only related to the orogenesis, but also consistent with the orogenic uplift.

  6. Palaeoproterozoic adakite- and TTG-like magmatism in the Svecofennian orogen, SW Finland

    OpenAIRE

    Väisänen, M. (Maria); Johansson, Å; Andersson, U.B.; O. Eklund; Hölttä, P.

    2012-01-01

    The Palaeoproterozoic Svecofennian orogen in the Fennoscandian shield is an arc accretionary orogen that was formed at c. 1.92-1.86Ga. Arc accretion, magmatism and the subsequent continent-continent collision thickened the crust up to c. 70km, forming one of the thickest Palaeoproterozic orogens. At the end stage of accretionary tectonics, voluminous synorogenic magmatism occurred in southwestern Finland leading to the intrusion of intermediate to felsic plutonic rocks. Ion microprobe single ...

  7. Exhumation at orogenic indentor corners under long-term glacial conditions: Example of the St. Elias orogen, Southern Alaska

    Science.gov (United States)

    Spotila, James A.; Berger, Aaron L.

    2010-07-01

    Syntaxial bends in convergent plate boundaries, or indentor corners, display some of the most intriguing deformation patterns on Earth and are type localities for "aneurysms" of coupled erosion, thermal weakening, and strain. The St. Elias orogen in Alaska is a small, young convergent system that has been dominated by a glacial climate for much of its history and exhibits two prominent indentor corners that are not well understood. We have added 40 new apatite (U-Th)/He ages to the already extensive dataset for the low-temperature cooling history of this orogen to constrain the pattern of exhumation in these indentor corners. Ages from the western syntaxis show minor variation across the structural hinge, suggesting that the bend has little effect on the pattern of exhumation and that structures, including the Bagley fault, connect smoothly from the orogen core to the subduction zone to the southwest. Rock uplift on the north flank of the range appears to increase steadily towards the eastern syntaxis, which represents the apex in the right-angle bend between a transform fault in the south and the collision zone in the west. Based on age-elevation relationships, zones of relative rock uplift can be defined in which the Mt. Logan massif, or the area just north of the eastern syntaxis, experienced ˜ 4.8 km greater rock uplift than background levels northwest of the western syntaxis. A bulge in relative rock uplift is symmetric about the hinge in the eastern indentor corner. However, rates of denudation in this bulge are not as rapid as the core of the fold and thrust belt and are lower than those implied by detrital cooling ages from beneath the Seward Glacier. This implies that a large bull's eye of ultra-rapid (˜ 5 mm/yr) exhumation does not occur and that the subpopulation of young detrital ages may be sourced from a narrow transpressional zone along the Fairweather fault. Unlike the Himalayan syntaxes, it thus appears that an aneurysm of coupled erosion

  8. Thermo-kinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The Composite Orogenic System

    Science.gov (United States)

    Parsons, A. J.; Law, R. D.; Lloyd, G. E.; Phillips, R. J.; Searle, M. P.

    2016-04-01

    The Himalayan orogen represents a "Composite Orogenic System" in which channel flow, wedge extrusion, and thrust stacking operate in separate "Orogenic Domains" with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >700°C to 550-650°C), to rigid wedge extrusion (Stage 2, 400-600°C) and duplexing (Stage 3, <280-400°C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems.

  9. Late-orogenic, post-orogenic, and anorogenic granites: Distinction by major-element and trace-element chemistry and possible origins

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, J.J.W.; Greenberg, J.K. (Univ. of North Carolina, Chapel Hill (USA))

    1990-05-01

    Granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different among groups. Orogenically related granites include late-orogenic varieties (LO) associated with calc-alkaline batholiths, and post-orogenic varieties (PO), which occur in broad zones of isolated diapiric plutons in recently deformed orogenic belts. Inclined REE patterns, moderate Sr contents, and K{sub 2}O-SiO{sub 2} relationships show that late-orogenic granites formed by fractionation of plagioclase, clinopyroxene, and amphibole from calcalkaline magmas. Flatter REE patterns and K{sub 2}O contents near 5%, plus the absence of associated magmatic rocks, indicate that the post-orogenic granites developed by partial melting of subduction-produced mafic/intermediate magmatic rocks. Both the late- and post-orogenic granites can be part of material newly added to continental crust as a result of orogeny. Anorogenic granites in anorthosite/rapakivi complexes (AR) or alkaline ring complexes (RC) have LIL contents too high to have been equilibrated with a mafic mineral assemblage. These anorogenic rocks probably formed by partial melting of preexisting sialic crust and do not represent new crustal increment.

  10. Qinling Orogenic Belt: Its Palaeozoic- Mesozoic Evolution and Metallogenesis

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The formation, development and evolution of the Qinling orogenic belt can be divided into three stages: (1) formation and development of Precambrian basement in the Late Archaean- Palaeoproterozoic (3.0- 1.6 Ga), (2) plate evolution (0.8- 0.2 Ga), and (3) intracontinental orogeny and tectonic evolution in the Mesozoic. The Devonian (D) and Triassic (T) were the key transition period of the tectonic evolution of the Qinling orogenic belt. That is to say, in the Devonian, the Qinling micro-plate was separated from the northern margin of the Yangtze plate (passive continental margin). This period witnessed transition of the micro-plate from the compressional to extensional state, and consequently three types of sedimentary basins were formed, namely, the rift hydrothermal basin in the micro-plate, restricted ocean basin in the south, and residual ocean basin resulting from collision on the northern margin. In the Triassic the Qinling area was turned into the intracontinental orogen.The Devonian and Triassic were the main periods of enrichment of large amounts of metals. In the Devonian, many sedex-type massive Pb-Zn- (Cu)-Ag deposits were formed in the hydrothermal basins. In the Triassic (Indosinian-Yanshanian movements), many sediment-hosted disseminated gold deposits and reworked sedimentary type Pb-Zn-Hg-Sb (Au) deposits were formed in the rift hydrothermal basins. Many ductile shear zone-related gold deposits were formed in the restricted ocean basins and residual ocean basins on the two sides of the Qinling micro-plate. The above-mentioned discussion indicates that metallogenesis is not only consistent with geological events, but also controlled by them.

  11. Occurrence and significance of blueschist in the southern Lachlan Orogen

    International Nuclear Information System (INIS)

    Serpentinite/talc-matrix melanges, bearing blocks of blueschist metavolcanics, occur within the Heathcote and Governor Fault Zones of the southern Lachlan Orogen. In the Heathcote Fault Zone, serpentinite-matrix melange consists of blocks or small pods of boninite, andesite, ultramafic rocks, chert and volcanogenic sandstone variably metamorphosed to prehnite-pumpellyite, greenschist, or greenschist to blueschist facies. In the Governor Fault Zone, blueschist metavolcanics occur as blocks within serpentinite/talc matrix that is interleaved with prehnite-pumpellyite to greenschist facies, intermediate pressure slate and phyllite. Ar/Ar dating of white mica from slaty mud-matrix (broken formation) indicates that the main fabric development occurred at 446 ± 2 Ma. U-Pb (SHRIMP) dating of titanite from blueschists in the Governor Fault Zone indicates that metamorphism occurred at approximately 450 Ma, close to the time of melange formation. Previously published, Ar/Ar dating of white mica from phyllite and biotite from metadiorite in the Heathcote Fault Zone suggest that blueschist metamorphism occurred at a similar time. These ages are supported by field relationships. Illite crystallinity and b0 data from white mica, and the preservation of blueschist blocks indicate that these fault zones maintained low temperatures both during and after intermediate- to high-pressure metamorphism. Occurrences of blueschists in the Arthur Lineament of the Tyennan (Delamerian) Orogen in Tasmania, and in the New England Orogen, have different ages, and in conjunction with the occurrences described here, suggest that subduction-accretion processes contributed significantly to the development of the Tasmanides from Cambrian through to Carboniferous times. Copyright (2002) Geological Society of Australia

  12. Linking magmatism with collision in an accretionary orogen

    OpenAIRE

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma al...

  13. Geometry, kinematics and evolution of the Tongbai orogenic belt

    Institute of Scientific and Technical Information of China (English)

    HUANG Shaoying; XU Bei; WANG Changqiu; ZHAN Sheng; DENG Rongjing

    2006-01-01

    The Tongbai orogenic belt (TOB) is composed of six tectonic units. From south to north these units are: Tongbai gneiss rise (TGR); Hongyihe-Luozhuang eclogite belt (HLE); Maopo-Hujiazhai igneous rock belt (MHI); Zhoujiawan flysch belt (ZFB); Yangzhuang greenschist belt (YGB); and Dongjiazhuang marble belt (DMB).The geometry and kinematic images of the TOB include: the antiformal structures caused by a later uplift process, the top-to-north ductile shear structure that related to a process that the ultrahigh pressure rocks are brought to surface, the top-to-south ductile shear thrust and the sinistrial shear structures related to a south-north direction compression, and the east-west direction fold structures in the upper crust. In the view of the multistage subduction-collision orogenic belt, according to the characters of petrology and its distribution, geometry, kinematics and structural chronology in these tectonic units, tectonic evolution of the TOB can be divided into four stages: oceanic crust subduction during 400-300 Ma, continental collision during 270-250 Ma, continental deep subduction and uplift during 250-205 Ma and doming deformation during 200-185 Ma.

  14. Stress Dynamics of Magma Activity during Orogenic Evolution: An Example from Kinmen Island, SE China

    Science.gov (United States)

    Chen, Ping-Chuan; Yeh, En-Chao; Lin, Jian-Wei; Lee, Chi-Yu; Chen, Rou-Fei; Lin, Wayne; Hsieh, Pei-Shan; Lin, Cheng-Kuo; Iizuka, Yoshiyuki

    2016-04-01

    During orogeny, a mountain belt experienced different orogenic stages with various conditions of temperature, pressure, stress and fluid pressure. The speculation, that the orogenic stresses evolve from reverse faulting via strike-slip faulting to normal faulting stress regimes corresponding to syn-orogenic, post-orogenic and an-orogenic stage respectively, has been proposed but has not been proved yet. Here we report the study of dikes from Kinmen Island can shed light on understanding the stress evolution of orogeny. The Kinmen Island, located in the southeastern continental margin of Mainland China, cropped out the middle to lower crust of NE structural grain, which was experienced deformation and metamorphism during Late Yenshanian Orogeny(LYO). Based on previous studies of geochemistry, geochronology, and P-T conditions, various types of dike have been identified. They are syn-orognic dikes of amphibolite (130-110Ma), post-orogenic dikes of pegmatite and aplite (110-100Ma), and an-orogenic dike of gabbro (94-76Ma). During syn-orogenic stage of LYO, dike intrusion appeared as low-angle dip, which reflected that reverse faulting regime and horizontal maximum stress direction in E-W orientation. In post-orogenic stage, stress would be divided into two sub-stages. The early one was strike-slip faulting regime and horizontal maximum stress was in NW-SE orientation. The late one was normal faulting regime and horizontal maximum stress direction returned to E-W orientation. Finally, an-orogenic dike intrusion striked NE-SW with vertical dip, which displayed that normal faulting regime and NE-SW horizontal maximum stress direction. Our observation is consistent with the expected stress evolution during orogeny. Deviatoric stresses from new findings were decreased at early post-orogenic stage but increased after late post-orogenic stage, indicating the change of fluid pressure ratio with time. The spatiotemporal variation of stress field might be suggested the change

  15. Regional Fault Systems of Qaidam Basin and Adjacent Orogenic Belts

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The purpose of this paper is to analyze the regional fault systems of Qaidam basin and adjacent orogenic belts. Field investigation and seismic interpretation indicate that five regional fault systems occurred in the Qaidam and adjacent mountain belts, controlling the development and evolution of the Qaidam basin. These fault systems are: (1)north Qaidam-Qilian Mountain fault system; (2) south Qaidam-East Kunlun Mountain fault system; (3)Altun strike-slip fault system; (4)Elashan strike-slip fault system, and (5) Gansen-Xiaochaidan fault system. It is indicated that the fault systems controlled the orientation of the Qaidam basin, the formation and distribution of secondary faults within the basin,the migration of depocenters and the distribution of hydrocarbon accumulation belt.

  16. Architecture and Kinematics of the Dabie Orogen, Central Eastern China

    Institute of Scientific and Technical Information of China (English)

    XU Shutong; LIU Yican; CHEN Guanbao; WU Weiping

    2005-01-01

    The geometry of the Dabie Mountains is manifested in terms of the distribution of petro-tectonic units in three dimensions. It is identified into three segments from east to west, four horizons in vertical profiles and eight petrotectonic units from north to south. Three segments are the east, middle and west segments. Four horizons, from top to bottom, are two different meta-tectonic melange in the uppermost part, underthrust basement and cover below them, and mantle at the bottom of the profiles. Eight petro-tectonic units from north to south are: (1) the hinterland basin, (2) the meta-flysch, (3) the ultramafic rock belt (UM) + Sujiahe eclogite belt (SH), (4) eclogite belt 2 (Ec2) with most eclogites of continental affinity, (5) eclogite belt 1 (Ecl1) with some eclogite of oceanic affinity, (6) the Dabie complex or underthrust basement of the Yangtze continent, (7) the Susong and Zhangbaling Groups or underthrust cover of the Yangtze continent and (8) the foreland belt. The (3), (4) and (5) units belong to meta-tectonic melange. Some ultrahigh pressure metamorphic minerals such as coesite and micro-diamonds have been found in (3) and (4) units; a possible ultrahigh pressure mineral,clinozoisite aggregate pseudomorph after lawsonite, was found in unit (5). The three tectonic units are speculated to be coherent initially; the UM and SH units are suggested to be the root belt in the east, middle and west segments respectively.The kinematics of the Dabie orogen is divided into three stages: top-to-south thrusting during the eclogite-granulite facies metamorphism, top-to-north extension during the amphibolite metamorphic stage, and faults or shear bands of brittle deformation and greenschist facies metamorphism were formed in the post-orogenic stage since the Late Jurassic and the movement pictures of these faults is different from each other.

  17. Late-stage orogenic processes: How to link surface motion with distinct lithospheric processes

    Science.gov (United States)

    Neubauer, F.; Heberer, B.

    2009-04-01

    There is still a lack of knowledge of surface expression caused by deep-seated lithospheric processes, and how such processes could be distinguished from other, e.g. climate-induced, surface processes like denudation. Surface expressions of deep-seated lithospheric processes in convergent settings are expected to have been long-lived and to show large wave-length structures creating a dynamic topography (Wortel and Spakman, 2000; Cloetingh and Ziegler, 2007). Resulting continent-continent collisional orogens are bivergent, and the principal vergency of collisional orogens is controlled by the previous subduction of oceanic lithosphere (Beaumont et al., 1996). A number of tectonic processes are shown to be active during late orogenic phases and these processes particularly result in specific patterns of surface uplift and denudation of the evolving orogens as well as subsidence in the associated foreland basin. A number of these processes are not fully understood. Late-stage orogenic processes include, among others, slab break-off, slab delamination respectively of lithospheric roots, back-thrusting, tectonic indentation and consequent orogen-parallel lateral extrusion and formation of Subduction-Transform Edge Propagator (STEP) faults acting on the subducting lithosphere (Molnar and Tapponnier, 1975; Wortel and Spakman, 2000; Ratschbacher et al., 1991; Govers and Wortel, 2005). Here, we discuss these processes mainly in terms of their near-surface geological expressions within the orogen and the associated foreland basins, and how these processes could be distinguished by such geological features. We also show distinct theoretical models applied to the arcuate Alpine-Balkan-Carpathian-Dinaric system, which is driven by the oblique convergence of Africa-Europe. Slab-break-off results in lateral orogen-parallel migration of sharp subsidence in a linear belt in front of the slab window, coupled subsidence and subsequent uplift/basin inversion of peripheral foreland

  18. ON THE SPECIFIC STATE OF CRUSTAL STRESSES IN INTRACONTINENTAL OROGENS

    Directory of Open Access Journals (Sweden)

    Yu. L. Rebetsky

    2015-12-01

    Full Text Available The article presents a systematic review of the available tectonophysical data on the state of crustal uplifts and basins in intracontinental orogens. Based on results of the tectonophysical analysis of data on earthquake focal mechanisms for the Altai-Sayan and Northern Tien Shan regions, it is established that in many cases the crust in the basins and uplifts has antipodal structures, considering various types of the state of stresses. In the crust of the uplifts, maximum compression axes are usually sub-horizontal; in the crust of the basins, only the axis of the principal stress of minimum compression (i.e. maximum deviatoric extension is sub-horizontal. These observations correlate well with estimations of deformations on the surface of the crust on the basis of the GPS-geodesy data, as well as with stress measurements taken directly on mining sites. The antipodal structures and physical fields in the crust of the uplifts and basins are not a random phenomenon. This suggests a common mechanism of deformation at the stage of active formation of the uplifts and basins. However, results of a similar tectonophysical analysis performed for the crust of the Pamir plateau and Tibet show that minimum compression stresses are subhorizontal in these regions, and the geodynamic type of the state of stresses is determined as horizontal extension or horizontal shearing. This pattern contrasts sharply with the type of the state of stresses of horizontal compression in the crust of the mountain ranges around the plateau (the Himalayas, Kunlun, Tsilian Shan, Hindu Kush, as well as with the state of stresses of active orogenic structures of the Tien Shan and Altai-Sayan regions.Based on the stress values estimated for a range of geodynamic types of the state of stresses, it is estimated that additional compression stresses of the order of 5.4 kbar are required for the transition from horizontal extension to horizontal compression. If the regional strain

  19. Seismic tomography beneath the orogenic belts and adjacent basins of northwestern China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Three-dimensional velocity images of the crust and upper mantlebeneath orogenic belts and adjacent basins of the northwestern continent of China are reconstructed by seismic tomography, based on arrival data of P wave recorded in seismic networks in Xinjiang, Qinghai, Gansu of China and Kyrgyzstan. The velocity images of upper crust demonstrate the tectonic framework on the ground surface. High velocities are observed beneath orogenic belts, and low velocities are observed in the basins and depressions that are obviously related to unconsolidated sediments. The velocity image in mid-crust maintains the above features, and in addition low velocities appear in some earthquake regions and a low velocity boundary separates the western Tianshan Mts. from eastern Tianshan Mts. The orogenic belts and the northern Tibetan plateau have a Moho depth over 50 km, whereas the depths of the Moho in basins and depressions are smaller than 50 km. The velocity images of upper mantle clearly reveal the colliding relationship and location of deep boundaries of the continental blocks in northwestern China, indicating a weakness of the upper mantle structure of orogenic belts. The top depth of upper mantle asthenosphere varies from place to place. It seems shallower under the northern Tibetan plateau, Altay and Qilian Mts., and deeper under the Tarim and Tianshan regions. Hot mantle probably rose to the bottom of some orogenic belts along tectonic boundaries when continental blocks collided to each other. Therefore their dynamic features are closely correlated to the formation and evolution of orogenic belts in northwestern China.

  20. Continental Growth and Recycling in Convergent Orogens with Large Turbidite Fans on Oceanic Crust

    Directory of Open Access Journals (Sweden)

    Ben D. Goscombe

    2013-07-01

    Full Text Available Convergent plate margins where large turbidite fans with slivers of oceanic basement are accreted to continents represent important sites of continental crustal growth and recycling. Crust accreted in these settings is dominated by an upper layer of recycled crustal and arc detritus (turbidites underlain by a layer of tectonically imbricated upper oceanic crust and/or thinned continental crust. When oceanic crust is converted to lower continental crust it represents a juvenile addition to the continental growth budget. This two-tiered accreted crust is often the same thickness as average continental crustal and is isostatically balanced near sea level. The Paleozoic Lachlan Orogen of eastern Australia is the archetypical example of a tubidite-dominated accretionary orogeny. The Neoproterozoic-Cambrian Damaran Orogen of SW Africa is similar to the Lachlan Orogen except that it was incorporated into Gondwana via a continent-continent collision. The Mesozoic Rangitatan Orogen of New Zealand illustrates the transition of convergent margin from a Lachlan-type to more typical accretionary wedge type orogen. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of turbidite and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism recorded in these rocks reflects the crustal thickening phase, whereas post-tectonic magmatism constrains the timing of chemical maturation and cratonization. Cratonization of continental crust is fostered because turbidites represent fertile sources for felsic magmatism. Recognition of similar orogens in the Proterozoic and Archean is important for the evaluation of crustal growth models, particularly for those based on detrital zircon age patterns, because crustal growth by accretion of upper oceanic crust or mafic underplating does not readily result in the addition of voluminous zircon

  1. Tectono-metamorphic evolution of the internal zone of the Pan-African Lufilian orogenic belt (Zambia): Implications for crustal reworking and syn-orogenic uranium mineralizations

    Science.gov (United States)

    Eglinger, Aurélien; Vanderhaeghe, Olivier; André-Mayer, Anne-Sylvie; Goncalves, Philippe; Zeh, Armin; Durand, Cyril; Deloule, Etienne

    2016-01-01

    The internal zone of the Pan-African Lufilian orogenic belt (Zambia) hosts a dozen uranium occurrences mostly located within kyanite micaschists in a shear zone marking the contact between metasedimentary rocks attributed to the Katanga Neoproterozoic sedimentary sequence and migmatites coring domes developed dominantly at the expense of the pre-Neoproterozoic basement. The P-T-t-d paths reconstructed for these rocks combining field observations, microstructural analysis, metamorphic petrology and thermobarometry and geochronology indicate that they have recorded burial and exhumation during the Pan-African orogeny. Both units of the Katanga metasedimentary sequence and pre-Katanga migmatitic basement have underwent minimum peak P-T conditions of ~ 9-11 kbar and ~ 640-660 °C, dated at ca. 530 Ma by garnet-whole rock Lu-Hf isochrons. This suggests that this entire continental segment has been buried up to a depth of 40-50 km with geothermal gradients of 15-20 °C.km- 1 during the Pan-African orogeny and the formation of the West Gondwana supercontinent. Syn-orogenic exhumation of the partially molten root of the Lufilian belt is attested by isothermal decompression under P-T conditions of ~ 6-8 kbar at ca. 530-500 Ma, witnessing an increase of the geothermal gradients to 25-30 °C·km- 1. Uranium mineralizations that consist of uraninite and brannerite took place at temperatures ranging from ~ 600 to 700 °C, and have been dated at ca. 540-530 Ma by U-Pb ages on uraninite. The main uranium deposition thus occurred at the transition from the syn-orogenic burial to the syn-orogenic exhumation stages and has been then partially transposed and locally remobilized during the post-orogenic exhumation accommodated by activation of low-angle extensional detachment.

  2. Crustal Architecture along BABEL and FIRE profiles - Insight in the Growth of the Svecofennian Orogen

    Science.gov (United States)

    Korja, Annakaisa

    2016-04-01

    The Precambrian Svecofennian orogen is characterized by LP- HT metamorphism and voluminous granitoid magmatism that usually develop in transitional to plateau stages of a collisional orogeny. Deep seismic reflection profiles BABEL and FIRE have been interpreted using PURC concepts: prowedge, retrowedg, uplifted plug, subduction conduit and elevated plateau. BABEL profiles image a transitional orogen with several nuclei displaying prowedge-uplifted plug-retrowedge architecture above paleo-subduction conduits. Prowedge and -continent are on the south-southwestern side and retrowedge and -continent on the north-northwestern side. This implies a long-lived southwesterly retreating convergent margin, where transitional accretionary orogens have developed. FIRE1-3 profiles images a hot orogen with a pronounced super-infra structure, typical of an elevated plateau stage, below the Central Finland Granitoid Complex. Large volumes of granitoid intrusions suggest large scale melting of the middle and/or lower crust. Reflection structures, analogue and numerical modeling suggest midcrustal flow. The plateau is flanked by prowedges that are characterized by HT-LP migmatite belts. The Svecofennian orogeny has progressed to an elevated plateau stage in the thickest core of the orogen, west of the arc-continent collision zone.

  3. Confirmation of pelitic granulite in the Altai orogen and its geological significance

    Institute of Scientific and Technical Information of China (English)

    WANG Wei; WEI ChunJing; WANG Tao; LOU YuXing; CHU Hang

    2009-01-01

    The existence of pelitic granulite in the Altai orogen was confirmed for the first time by detailed petro-graphic research and P-T pseudosection modeling. The pelitic granulite has the assemblage of garnet + cordierite + K-feldspar + biotite + sillimanite + plagioclase + quartz with some samples containing the paragenesis of cordierite + spinel. Peak conditions of the pelitic granulite determined from the P-T pseudosection involved P= 0.5-0.6 GPa, T= 780-800?*, belonging to medium-to low-pressure type. SHRIMP U-Pb dating of zircon presented a metamorphic age of 292.8 ± 2.3 Ma. The discovery of pelitic granulite reflects an extensional environment with high heat flow in the southern margin of the Altai orogen during the Early Permian, which provides an important petrological constraint on the evolution of the Altai orogen.

  4. Neogene coupling between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China.

    Science.gov (United States)

    He, Guang-Yu; Chen, Han-Lin

    2004-08-01

    Based on the sedimentary and subsiding features of Kuqa foreland basin, this paper presents the following characteristics of Neogene coupling relationship between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China: (1) The Southern Tien Shan Orogen underwent Neogene uplifting of 4 km in height and the Kuqa Basin underwent Neogene subsidence of 4-6 km in depth accordingly beginning in 25 Ma; (2) The Southern Tien Shan Orogen moved continuously toward the Kuqa Basin, with largest structural shortening rate of greater than 53.7%, and the north boundary of the Kuqa Basin retreated continuously southward accordingly since the Miocene; (3) There are two subsidence centers with high subsiding rates and large subsiding extent, located in the eastern and western Kuqa Basin respectively, with the subsiding maximizing in the deposition period of Kuqa Formation. PMID:15236483

  5. Neogene coupling between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China

    Institute of Scientific and Technical Information of China (English)

    何光玉; 陈汉林

    2004-01-01

    Based on the sedimentary and subsiding features of Kuqa foreland basin, this paper presents the following characteristics of Neogene coupling relationship between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China:(l) The Southern Tien Shan Orogen underwent Neogene uplifting of 4 km in height and the Kuqa Basin underwent Neogene subsidence of 4-6 km in depth accordingly beginning in 25 Ma; (2) The Southern Tien Shan Orogen moved continuously toward the Kuqa Basin, with largest structural shortening rate of greater than 53.7%, and the north boundary of the Kuqa Basin retreated continuously southward accordingly since the Miocene; (3) There are two subsidence centers with high subsiding rates and large subsiding extent, located in the eastern and western Kuqa Basin respectively, with the subsiding maximizing in the deposition period of Kuqa Formation.

  6. Orogenic plateau magmatism of the Arabia-Eurasia collision zone

    Science.gov (United States)

    Allen, M. B.; Neill, I.; Kheirkhah, M.; van Hunen, J.; Davidson, J. P.; Meliksetian, Kh.; Emami, M. H.

    2012-04-01

    generally applicable as melt triggers. Enigmatic lavas are erupted over the thick lithosphere of Kurdistan Province, Iran. These alkali basalts and basanites have the chemical characteristics of small degree (<1%) melts in the garnet stability field. Most possess supra-subduction zone chemistry (La/Nb = 1-3), but this signature is highly variable. Similar La/Nb variability occurs in the basic lavas of Damavand volcano in the Alborz Mountains of northern Iran. Modelling suggests the depletion of residual amphibole during the progression of partial melting can explain the observed La/Nb range. This melting may occur as the result of lithospheric thickening. At depths of ~90 km, amphibole-bearing peridotite crosses an experimentally-determined "backbend" in its solidus. Melting can continue while the source remains hydrated. Such "compression" melting may apply to parts of other orogenic plateaux, including Tibet.

  7. Reconciling the detrital zircon record and crustal growth within juvenile accretionary orogens

    Science.gov (United States)

    Spencer, C. J.; Cawood, P. A.; Roberts, N. M. W.

    2014-12-01

    Ancient cratons are generally characterised by Archaean cores surrounded by Proterozoic accretionary belts with large volumes of juvenile crust. Their crustal growth histories provide important insights into the genesis of continents and orogenic evolution. Whole-rock and detrital zircon isotopic studies are often used to deduce those histories, but the extent to which representative lithologies within the orogens are reliably sampled for such studies is not well established. This is especially true in cases where juvenile, zircon-poor mafic crust comprises a significant proportion of an orogen such as the East African (0.8-0.5 Ga), Namaqua-Natal (1.2-1.0 Ga), Trans-Hudson (1.9-1.8 Ga), and Kola (2.5 Ga). In particular, the Mesoproterozoic Namaqua-Natal orogenic belt (NNO) fringing the Kalahari Craton is a case in point in which Nd isotopic studies of whole-rock outcrop samples and U-Pb-Hf isotopic studies of detrital zircons from sediments of the Orange River (which drains the NNO) show different crust-formation ages and proportions of new and reworked crustal material. We hypothesise that this discrepancy is due to biasing of the detrital zircon record towards felsic rocks. Understanding the representative nature of the crustal archive preserved in detrital zircons remains critical for many studies of crustal evolution. We present data that: (a) addresses the scale of potential bias within an accretionary orogen containing large proportions of juvenile material, (b) demonstrates how the whole-rock and detrital zircon records can be reconciled for the Namaqua-Natal orogen to start, and (c) can be used to evaluate the effect of zircon bias on previous crustal growth models.

  8. Plate tectonics and orogenic research after 25 years: Synopsis of a Tethyan perspective

    Science.gov (United States)

    Şengör, A. M. Celâl

    1991-02-01

    Orogeny, the process by which the earth's prominent mountain ranges are constructed, is herein defined as a collective term for convergent margin processes. The recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt has grown gradually during the last two centuries. Investigation of orogenic belts along cross-sections reveals that there are a large number of types of orogenic belts. These are divided into four main orders ( transpressional, subduction-controlled, obduction-controlled, and collision-controlled) consisting of two superfamilies, eight families, and twenty genera. Cross-sectional studies of orogenic belts show that the cross-sectional area during orogeny is not conserved. Similarly, map-view studies of orogenic belts reveal that an absolute minimum of 60% (by length) of them display significant strike-slip motion along their trend which leads also to a non-conservation of the cross-sectional area during orogeny. Thus, rigorous line and area balancing across orogenic belts now is not possible. Large orogenic belts are commonly made up of tectonic collages of microcontinents, island arcs, and accretionary complexes, generally disrupted to form smaller, fault-bounded tectonic entities of diverse sorts. The recently developed "terrane analysis" was developed to aid the study of these but it resembles the early concepts of Alpine nappes and is found to be a retrogressive step in tectonic research mainly because of its disclaim of most genetic connotations. The temporal aspects of orogeny have been debated for over 200 years in terms of continuous vs. world-wide, synchronously episodic orogeny. Plate tectonics has provided a rigorous rationale and something approaching a consensus for continuous orogeny. I conclude that there are as yet no shortcuts to establishing the kinematics of continental deformation except by the traditional methods of field geology aided by relevant

  9. Reconciling competing models for the tectono-stratigraphic zonation of the Variscan orogen in Western Europe

    Science.gov (United States)

    Murphy, J. Brendan; Quesada, Cecilio; Gutiérrez-Alonso, Gabriel; Johnston, Stephen T.; Weil, Arlo

    2016-06-01

    The Late Paleozoic Variscan orogen in Europe is the result of convergence and collision between Laurussia and Gondwana during closure of the Rheic Ocean. The orogen is divided into tectonostratigraphic zones that have a distinct curvature (Ibero-Armorican Arc, IAA) and record the Late Cambrian-Early Ordovician opening of the Rheic Ocean, the migration of terranes from the Gondwanan margin towards Laurussia, as well as the closure of that ocean and development of the IAA. Three models have emerged to explain the distribution of tectonostratigraphic zones:

  10. Shear Zone Development and Rheology in the Deep Orogenic Crust

    Science.gov (United States)

    Marsh, J. H.; Johnson, S. E.; Gerbi, C. C.; Culshaw, N. G.

    2008-12-01

    Within the Central Gneiss Belt (CGB) of the southwestern Grenville Province, Ontario, Canada, a number of allocthonous lithotectonic domains are juxtaposed along crustal-scale shear zones. Extensive exposure of variably reworked granulites of the interior Parry Sound domain (iPSD) has enabled investigation of the structural and petrologic character of domain-bounding shear zones within the deep orogenic crust. Recent detailed mapping and structural data collected along the southwestern margin of the iPSD is consistent with the suggestion of Culshaw et al. (in prep) that spaced outcrop-scale shear zones have coalesced and progressively reworked layered granulites into a transposed amphibolite-facies tectonite. The tectonites comprise the Twelve Mile Bay Shear Zone (TMBSZ), which separates the iPSD from para-autocthonous rocks to the south. This study investigates the grain- and outcrop-scale mechanisms involved in shear zone development and attempts to quantify the associated changes in rock rheology. Northwest of TMBSZ, samples collected across individual outcrop-scale shear zones (i.e., across large strain gradients) have distinct differences in mineralogy and microstructure. In mafic layers the original granulite texture and cpx + opx + pl + hbl +/- grt assemblage is commonly retained away from the shear zones within unsheared "panels". With proximity to the shear zones pyroxenes and garnet are progressively consumed in hydration reactions producing hornblende and biotite, which define a new planar foliation within the highly attenuated and deflected layering. Felsic layers generally have only minor mineralogical changes across the zones, but develop an increasingly intense and recrystallized structural fabric into the sheared margin. The shear zones are commonly cored by variably deformed pegmatite dikes that were emplaced prior to, or during the early stages of shearing. Evidence for incipient shear zone formation along mineralized fracture sets that cut

  11. Relating orogen width to shortening, erosion, and exhumation during Alpine collision

    Science.gov (United States)

    Rosenberg, C. L.; Berger, A.; Bellahsen, N.; Bousquet, R.

    2015-06-01

    We investigate along-strike width changes of the thickened, accreted lower plate (TALP) in the Central and in the Eastern Alps. We set the width of the TALP in relation to the inferred amount of collisional shortening and exhumation along six orogen-scale cross sections. Taking the present-day, along-strike gradients in the amount of collisional shortening to represent the temporal evolution of the collisional wedge, it may be concluded that the cross-sectional area of the TALP diminishes during ongoing shortening, indicating that the erosional flux outpaced the accretionary flux. Higher amounts of collisional shortening systematically coincide with smaller widths of the TALP and dramatic increases of the reconstructed eroded rock column. Higher amounts of shortening also coincide with larger amplitudes of orogen-scale, upright folds, with higher exhumation and with higher exhumation rates. Hence, erosion did play a major role in reducing by >30 km the vertical crustal thickness in order to accommodate and allow shortening by folding. Long-term climate differences cannot explain alternating changes of width by a factor of almost 2 along straight segments of the orogen on length scales less than 200 km, as observed from the western Central Alps to the easternmost Eastern Alps. Sedimentary or paleontological evidences supporting such paleo-climatic differences are lacking, suggesting that erosional processes did not directly control the width of the orogen.

  12. Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

    Science.gov (United States)

    Goodenough, K.M.; Thomas, Ronald J.; De Waele, B.; Key, R.M.; Schofield, D.I.; Bauer, W.; Tucker, R.D.; Rafahatelo, J.-M.; Rabarimanana, M.; Ralison, A.V.; Randriamananjara, T.

    2010-01-01

    Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U-Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen. ?? 2009 Natural Environment Research Council.

  13. Visualizing the sedimentary response through the orogenic cycle using multi-dimensional scaling

    Science.gov (United States)

    Spencer, C. J.; Kirkland, C.

    2015-12-01

    Changing patterns in detrital provenance through time have the ability to resolve salient features of an orogenic cycle. Such changes in the age spectrum of detrital minerals can be attributed to fluctuations in the geodynamic regime (e.g. opening of seaways, initiation of subduction and arc magmatism, and transition from subduction to collisional tectonics with arrival of exotic crustal material). These processes manifest themselves through a variety of sedimentary responses due to basin formation, transition from rift to drift sedimentation, or inversion and basement unroofing. This generally is charted by the presence of older detrital zircon populations during basement unroofing events and is followed by a successive younging in the detrital zircon age signature either through arrival of young island arc terranes or the progression of subduction magmatism along a continental margin. The sedimentary response to the aforementioned geodynamic environment can be visualized using a multi-dimensional scaling approach to detrital zircon age spectra. This statistical tool characterizes the "dissimilarity" of age spectra of the various sedimentary successions, but importantly also charts this measure through time. We present three case studies in which multi-dimensional scaling reveals additional useful information on the style of basin evolution within the orogenic cycle. The Albany-Fraser Orogeny in Western Australia and Grenville Orogeny (sensu stricto) in Laurentia demonstrate clear patterns in which detrital zircon age spectra become more dissimilar with time. In stark contrast, sedimentary successions from the Meso- to Neoproterozoic North Atlantic Region reveal no consistent pattern. Rather, the North Atlantic Region reflects a signature consistent with significant zircon age communication due to a distal position from an orogenic front, oblique translation of terranes, and complexity of the continental margin. This statistical approach provides a mechanism to

  14. Alkali-calcic and alkaline post-orogenic (PO) granite magmatism: petrologic constraints and geodynamic settings

    Science.gov (United States)

    Bonin, Bernard; Azzouni-Sekkal, Abla; Bussy, François; Ferrag, Sandrine

    1998-12-01

    The end of an orogenic Wilson cycle corresponds to amalgamation of terranes into a Pangaea and is marked by widespread magmatism dominated by granitoids. The post-collision event starts with magmatic processes still influenced by subducted crustal materials. The dominantly calc-alkaline suites show a shift from normal to high-K to very high-K associations. Source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle, affected by dehydration melting and generating more and more K- and LILE-rich magmas. In the vicinity of intra-crustal magma chambers, anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves. The post-collision event ends with emplacement of bimodal post-orogenic (PO) suites along transcurrent fault zones. Two suites are defined, (i) the alkali-calcic monzonite-monzogranite-syenogranite-alkali feldspar granite association characterised by [biotite+plagioclase] fractionation and moderate [LILE+HFSE] enrichments and (ii) the alkaline monzonite-syenite-alkali feldspar granite association characterised by [amphibole+alkali feldspar] fractionation and displaying two evolutionary trends, one peralkaline with sodic mafic mineralogy and higher enrichments in HFSE than in LILE, and the other aluminous biotite-bearing marked by HFSE depletion relative to LILE due to accessory mineral precipitation. Alkali-calcic and alkaline suites differ essentially in the amounts of water present within intra-crustal magma chambers, promoting crystallisation of various mineral assemblages. The ultimate enriched and not depleted mantle source is identical for the two PO suites. The more primitive LILE and HFSE-rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere. Present rock compositions are a mixture of major mantle contribution and various crustal components

  15. Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands

    Science.gov (United States)

    Bradley, D.C.; Leach, D.L.

    2003-01-01

    Most of the world's Mississippi Valley-type (MVT) zinc-lead deposits occur in orogenic forelands. We examine tectonic aspects of foreland evolution as part of a broader study of why some forelands are rich in MVT deposits, whereas others are barren. The type of orogenic foreland (collisional versus Andean-type versus inversion-type) is not a first-order control, because each has MVT deposits (e.g., Northern Arkansas, Pine Point, and Cevennes, respectively). In some MVT districts (e.g., Tri-State and Central Tennessee), mineralization took place atop an orogenic forebulge, a low-amplitude (a few hundred meters), long-wavelength (100-200 km) swell formed by vertical loading of the foreland plate. In the foreland of the active Banda Arc collision zone, a discontinuous forebulge reveals some of the physiographic and geologic complexities of the forebulge environment, and the importance of sea level in determining whether or not a forebulge will emerge and thus be subject to erosion. In addition to those on extant forebulges, some MVT deposits occur immediately below unconformities that originated at a forebulge, only to be subsequently carried toward the orogen by the plate-tectonic conveyor (e.g., Daniel's Harbour and East Tennessee). Likewise, some deposits are located along syn-collisional, flexure-induced normal and strike-slip faults in collisional forelands (e.g., Northern Arkansas, Daniel's Harbour, and Tri-State districts). These findings reveal the importance of lithospheric flexure, and suggest a conceptual tectonic model that accounts for an important subset of MVT deposits-those in the forelands of collisional orogens. The MVT deposits occur both in flat-lying and in thrust-faulted strata; in the latter group, mineralization postdated thrusting in some instances (e.g., Picos de Europa) but may have predated thrusting in other cases (e.g., East Tennessee).

  16. SVM-based base-metal prospectivity modeling of the Aravalli Orogen, Northwestern India

    Science.gov (United States)

    Porwal, Alok; Yu, Le; Gessner, Klaus

    2010-05-01

    The Proterozoic Aravalli orogen in the state of Rajasthan, northwestern India, constitutes the most important metallogenic province for base-metal deposits in India and hosts the entire economically viable lead-zinc resource-base of the country. The orogen evolved through near-orderly Wilson cycles of repeated extensional and compressional tectonics resulting in sequential opening and closing of intracratonic rifts and amalgamation of crustal domains during a circa 1.0-Ga geological history from 2.2 Ga to 1.0 Ga. This study develops a conceptual tectonostratigraphic model of the orogen based on a synthesis of the available geological, geophysical and geochronological data followed by deep-seismic-reflectivity-constrained 2-D forward gravity modeling, and links it to the Proterozoic base-metal metallogeny in the orogen in order to identify key geological controls on the base-metal mineralization. These controls are translated into exploration criteria for base-metal deposits, validated using empirical spatial analysis, and used to derive input spatial variables for model-based base-metal prospectivity mapping of the orogen. A support vector machine (SVM) algorithm augmented by incorporating a feature selection procedure is used in a GIS environment to implement the prospectivity mapping. A comparison of the SVM-derived prospectivity map with the ones derived using other established models such as neural-networks, logistic regression, and Bayesian weights-of-evidence indicates that the SVM outperforms other models, which is attributed to the capability of the SVM to return robust classification based on small training datasets.

  17. Paleozoic Orogens of Mexico and the Laurentia-Gondwana Connections: an Update

    Science.gov (United States)

    Ortega-Gutierrez, F.

    2009-05-01

    The present position of Mexico in North America and the fixist tectonic models that prevailed prior to the seventies of the past century, have considered the main Paleozoic tectonic systems of Mexico as natural extensions of the orogens that fringed the eastern and southern sides of the Laurentian craton. Well known examples of pre-Mesozoic orogens in Mexico are the Oaxacan, Acatlan, and Chiapas polymetamorphic terranes, which have been correlated respectively with the Grenville and Appalachian-Ouachitan orogens of eastern North America. Nonetheless, several studies conducted during the last decade in these Mexican orogenic belts, have questioned their Laurentian connections, regarding northwestern Gondwana instead as the most plausible place for their birth and further tectonic evolution. This work pretends to approach the problem by briefly integrating the massive amount of new geological information, commonly generated through powerful dating methods such as LA-ICPM-MS on detrital zircon of sedimentary and metasedimentary units in the Paleozoic crustal blocks, which are widely exposed in southern and southeastern Mexico. The Acatlan Complex bears the closest relationships to the Appalachian orogenic system because it shows thermotectonic evidence for opening and closure of the two main oceans involved in building the Appalachian mountains in eastern Laurentia, whereas two other Paleozoic terranes in NW and SE Mexico, until recently rather geologically unknown, may constitute fundamental links between the Americas for the last-stage suturing and consolidation of western Pangea. The buried basement of the Yucatan platform (400,000 squared km) on the other hand, remains as one of the most relevant problems of tectonostratigraphic correlations across the Americas, because basement clasts from the Chicxulub impact ejecta reveal absolute and Nd-model ages that suggest close Gondwanan affinities. Major changes in the comprehension of the Paleozoic orogens in Mexico

  18. Testing models of orogen exhumation using zircon (U-Th)/He thermochronology: Insight from the Ligurian Alps, Northern Italy

    Science.gov (United States)

    Maino, Matteo; Dallagiovanna, Giorgio; Dobson, Katherine J.; Gaggero, Laura; Persano, Cristina; Seno, Silvio; Stuart, Finlay M.

    2012-08-01

    Testing models of orogen exhumation requires precise constraint of the time-temperature paths of the exhumed rocks. The zircon (U-Th)/He (ZHe) thermochronometer has a closure temperature of ~ 140-210 °C, and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen. We performed ZHe analyses to test the existing contradictory models for the exhumation of the Ligurian Alps. The ZHe ages indicate a very rapid (1.3-6.8 mm/yr) and southward migrating exhumation of the orogen between ~ 32 and 25 Ma. These high exhumation rates are unique within the Alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the Ligurian Alps. We propose a model of tectonic denudation via detachment accomplished in the shallowest crust (< 5 km) as a result of the last orogenic phase of extension.

  19. Axial Belt Provenance: modern river sands from the core of collision orogens

    Science.gov (United States)

    Resentini, A.; Vezzoli, G.; Paparella, P.; Padoan, M.; Andò, S.; Malusà, M.; Garzanti, E.

    2009-04-01

    Collision orogens have a complex structure, including diverse rock units assembled in various ways by geodynamic processes. Consequently, orogenic detritus embraces a varied range of signatures, and unravelling provenance of clastic wedges accumulated in adjacent foreland basins, foredeeps, or remnant-ocean basins is an arduous task. Dickinson and Suczek (1979) and Dickinson (1985) recognized the intrinsically composite nature of orogenic detritus, but did not attempt to establish clear conceptual and operational distinctions within their broad "Recycled Orogenic Provenance". In the Alpine and Himalayan belts, the bulk of the detritus is produced by focused erosion of the central backbone of the orogen, characterized by high topography and exhumation rates (Garzanti et al., 2004; Najman, 2006). Detritus derived from such axial nappe pile, including slivers of thinned continental-margin lithosphere metamorphosed at depth during early collisional stages, has diagnostic general features, which allows us to define an "Axial Belt Provenance" (Garzanti et al., 2007). In detail, "Axial Belt" detrital signatures are influenced by metamorphic grade of source rocks and relative abundance of continental versus oceanic protoliths, typifying distinct subprovenances. Metasedimentary cover nappes shed lithic to quartzolithic detritus, including metapelite, metapsammite, and metacarbonate grains of various ranks; only amphibolite-facies metasediments supply abundant heavy minerals (e.g., almandine garnet, staurolite, kyanite, sillimanite, diopsidic clinopyroxene). Continental-basement nappes shed hornblende-rich quartzofeldspathic detritus. Largely retrogressed blueschist to eclogite-facies metaophiolites supply albite, metabasite and foliated antigorite-serpentinite grains, along with abundant heavy minerals (epidote, zoisite, clinozoisite, lawsonite, actinolitic to barroisitic amphiboles, glaucophane, omphacitic clinopyroxene). Increasing metamorphic grade and deeper

  20. Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

    Science.gov (United States)

    Wu, Xiaozhi; He, Dengfa; Qi, Xuefeng

    2016-04-01

    Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas

  1. History of tectono-magmatic evolution in the Western Kunlun Orogen

    Institute of Scientific and Technical Information of China (English)

    毕华; 王中刚; 王元龙; 朱笑青

    1999-01-01

    Based on the statistical and analytical data on more than 170 isotopic ages published since the 1980s of magmatic rocks, metamorphic rocks, tectonites and ores from the Western Kunlun Orogen, and the characteristics of sedimentation, magmatism, metamorphism and tectonic activities in the region studied in conjunction with geological field investigations and necessary supplementary isotope data, five stages of tectono-magmatic evolution, i.e. Ar3-Pt21 tectono-magmatic active stage (Ⅰ) , Pt22 stable stage (Ⅱ), Pt31-P2 active stage (Ⅲ), T1-T2 stable stage (Ⅳ) , and T3-Q active stage (Ⅴ) can be distinguished in the Western Kunlun Orogen. Moreover, the tectono-magmatic active style and general trend, the characteristics of tectonic settings, etc. of each stage and substage in the region studied are also discussed .

  2. Recent advances about of the orogenic modern belt (1000-500 M.A.) in Uruguay

    International Nuclear Information System (INIS)

    Progress in lithologic, structural, tectonic and geo tectonic data about a 1000-500 m.y.orogenic belt developed at the East of Uruguay, arrived in the 80, are here described. Conclusions are mainly based on the 1/100.000 scale geologic map of a 6000 sq. km comprised between Sierra Ballena, Sierra de Animas, Pan de Azucar and Mariscala. These new data clearly states the lithological distribution and contribute to guide strategic prospect ion.

  3. Seismic Studies of Paleozoic Orogens in SW Iberia and the Middle Urals

    OpenAIRE

    Kashubin, Artem

    2008-01-01

    Controlled source seismic methods were employed in this study to investigate the reflectivity and velocity structure of two Hercynian orogens – the Uralides and Variscides. Conventional common depth point (CDP) sections from five reflection seismic campaigns and a velocity model obtained from tomographic inversion of wide-angle observations were the main datasets studied from the Middle Urals. These were complemented with the near-vertical seismic sections and velocity models from the Souther...

  4. The role of lateral lithospheric strength heterogeneities in orogenic plateau growth: Insights from 3-D thermo-mechanical modeling

    Science.gov (United States)

    Chen, Lin; Gerya, Taras V.

    2016-04-01

    Preexisting lateral variations in crustal thickness and lithospheric thermal state are documented for the formation of some orogenic plateaux. Here we use high-resolution 3-D thermo-mechanical simulations to investigate the influence of preexisting lateral lithospheric strength heterogeneity on the growth of orogenic plateau. The modeling results illustrate an episodic scenario for plateau growth: (1) an early rapid growth stage, characterized by rapid surface uplift and intensive crustal buckling and thickening; (2) an outward spreading stage, characterized by significant lateral expansion of the plateau edges; and (3) a mature stage, characterized by the development of the intracrustal partial melting and subduction of the surrounding lithosphere under the plateau. Sensitivity analyses indicate that lateral variation in crustal thickness favors outward spreading of orogenic plateau, while lateral variation in geothermal gradient favors crustal buckling. The model in absence of lateral strength heterogeneity leads to progressive migration of orogenic belt. Our models show that the plateau's lower crust is largely coupled with underlying lithospheric mantle and does not flow into the surrounding lithospheres, casting doubt on the lower crust flow model. We suggest that the Himalayan-Tibetan orogenic system can be best understood within the framework that the proto-southern Asian margin was fairly weak prior to the India-Asia collision to steer the formation of a large hot orogenic plateau there.

  5. The tectonic frame of the Variscan Alleghanian orogen in Southern Europe and Northern Africa

    Science.gov (United States)

    Simancas, J. Fernando; Tahiri, Abdelfatah; Azor, Antonio; Lodeiro, Francisco González; Martínez Poyatos, David J.; El Hadi, Hassan

    2005-04-01

    By confronting different geological and geophysical data, we attempt to reconstruct the Variscan-Alleghanian orogenic belt, with especial emphasis on the links between Iberia, northwest Africa, and northeast America. The northern Iberia transect corresponds to the rifted margin of Gondwana, inverted during the Variscan orogeny and overthrust in its westernmost sector by a pile of allochthonous units, some of them with oceanic affinity and witnessing an orogenic suture. The southern Iberia section reveals two sutures at both boundaries of a terrane closely tied to Gondwana, namely the Ossa-Morena Zone. The southern boundary of this zone (i.e., the contact with the South Portuguese Zone) is enhanced by amphibolites with oceanic affinity and probably represents the suture of the Rheic Ocean. The Moroccan Variscides can be divided into: (i) a western external zone, namely the Coastal Block and the Central Massif; (ii) an internal zone, namely the Eastern Meseta; (iii) an eastern external zone represented in the Anti Atlas region; and (iv) the African cratonic foreland. Since neither ophiolites nor eclogites crop out along this transect of the orogen, we consider it to be an incomplete transect, lacking the main suture zone (Rheic Ocean). Stratigraphic and faunal affinities between the Moroccan Meseta, on the one hand, and the Central Iberian, Western Asturian-Leonese, and Cantabrian zones of Iberia, on the other hand, suggest that they may well have been part of a common pre-orogenic domain at the margin of Gondwana. On the contrary, there are no counterparts in Morocco for the Ossa-Morena Zone. Thus, the northern Iberia palaeogeographic zones would prolong in the Moroccan Meseta through an eastward arcuate structure, while the suture of the Rheic Ocean would do so offshore Morocco. In our reconstruction, an Avalonian spur (Grand Banks indentor), which included the Caledonian Sehoul block in northern Morocco and the crust of the South Portuguese Zone in SW Iberia

  6. Molybdenite Re Os dating constrains gravitational collapse of the Sveconorwegian orogen, SW Scandinavia

    Science.gov (United States)

    Bingen, Bernard; Stein, Holly J.; Bogaerts, Michel; Bolle, Olivier; Mansfeld, Joakim

    2006-04-01

    Re-Os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the Sveconorwegian orogen in SW Scandinavia. A 1019 ± 3 Ma planar quartz vein defines a minimum age for brittle behaviour in central Telemark. In Rogaland-Vest Agder, molybdenite associated with deformed quartz and pegmatite veins formed between 982 ± 3 and 947 ± 3 Ma in the amphibolite-facies domain (three deposits) and between 953 ± 3 and 931 ± 3 Ma west of the clinopyroxene-in isograd (two deposits) in the vicinity of the 0.93-0.92 Ga Rogaland anorthosite complex. The data constrain the last increment of ductile deformation to be younger than 0.95 and 0.93 Ga in these two metamorphic zones, respectively. Molybdenite is the product of an equilibrium between biotite, oxide and sulfide minerals and a fluid or hydrated melt phase, after the peak of 1.03-0.97 Ga regional metamorphism. Molybdenite precipitation is locally episodic. A model for gravitational collapse of the Sveconorwegian orogen controlled by lithospheric extension after 0.97 Ga is proposed. In the west of the orogen, the Rogaland-Vest Agder sector is interpreted as a large shallow gneiss dome, formed slowly in two stages in a warm and structurally weak crust. The first stage at 0.96-0.93 Ga was associated with intrusion of the post-collisional hornblende-biotite granite suite. The second stage at 0.93-0.92 Ga, restricted to the southwesternmost area, was associated with intrusion of the anorthosite-mangerite-charnockite suite. Most of the central part of the orogen was already situated in the brittle upper crust well before 0.97 Ga, and did not undergo significant exhumation during collapse. In the east of the orogen, situated against the colder cratonic foreland, exhumation of high-grade rocks of the Eastern Segment occurred between 0.97 and 0.95 Ga, and included preservation of high-pressure rocks but no plutonism.

  7. Window into the Caledonian orogen: Structure of the crust beneath the East Shetland platform, United Kingdom

    Science.gov (United States)

    McBride, J.H.; England, R.W.

    1999-01-01

    Reprocessing and interpretation of commercial and deep seismic reflection data across the East Shetland platform and its North Sea margin provide a new view of crustal subbasement structure beneath a poorly known region of the British Caledonian orogen. The East Shetland platform, east of the Great Glen strike-slip fault system, is one of the few areas of the offshore British Caledonides that remained relatively insulated from the Mesozoic and later rifting that involved much of the area around the British Isles, thus providing an "acoustic window" into the deep structure of the orogen. Interpretation of the reflection data suggests that the crust beneath the platform retains a significant amount of its original Caledonian and older architecture. The upper to middle crust is typically poorly reflective except for individual prominent dipping reflectors with complex orientations that decrease in dip with depth and merge with a lower crustal layer of high reflectivity. The three-dimensional structural orientation of the reflectors beneath the East Shetland platform is at variance with Caledonian reflector trends observed elsewhere in the Caledonian orogen (e.g., north of the Scottish mainland), emphasizing the unique tectonic character of this part of the orogen. Upper to middle crustal reflectors are interpreted as Caledonian or older thrust surfaces that were possibly reactivated by Devonian extension associated with post-Caledonian orogenic collapse. The appearance of two levels of uneven and diffractive (i.e., corrugated) reflectivity in the lower crust, best developed on east-west-oriented profiles, is characteristic of the East Shetland platform. However, a north-south-oriented profile reveals an interpreted south-vergent folded and imbricated thrust structure in the lower crust that appears to be tied to the two levels of corrugated reflectivity on the east-west profiles. A thrust-belt origin for lower crustal reflectivity would explain its corrugated

  8. What Happened in the Trans-North China Orogen in the Period 2560-1850 Ma?

    Institute of Scientific and Technical Information of China (English)

    Guochun ZHAO; LIU Shuwen; Min SUN; LI Sanzhong; Simon WILDE; Xiaoping XIA; Jian ZHANG; Yanhong HE

    2006-01-01

    The Trans-North China Orogen (TNCO) was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton (NCC). Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greenstone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages.Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic (TTG) magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, ~2250 Ma 2110-21760 Ma and ~2050 Ma granites in the orogen.Contemporary volcano-sedimentary rocks developed in the back-arc or intra-arc basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge,leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and

  9. High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

    Science.gov (United States)

    Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

    2015-09-01

    New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

  10. BASIN-RANGE SYSTEM EVOLUTION OF QINLING-DABIE OROGENIC BELT AND ITS IMPACT ON REGIONAL ENVIRONMENT

    Institute of Scientific and Technical Information of China (English)

    HU Baoqing; ZENG Qiaosong; LIU Shunsheng; WANG Shijie

    2004-01-01

    As the structural body related to temporal-spatial evolution and tectonic dynamic system, the orogenic belt and basin are not only dependent on each other in space but also closely related with each other in terms of infrastructure, matter transference and dynamic mechanisms. By using apatite fission-track method, the authors firstly analyze the uplift and denudation ratios of the Qinling-Dabie orogenic belt, and by using tectonically deformed combination analysis and tectonic-thermal simulation the main geological occurrences are also illustrated. It is found that there must have had multi-phase differential uplift and denudation phenomena in the Qinling-Dabie orogenic belt during the Mesozoic-Cenozoic. Then, the regional evolution pattern of qualitative and quantitative denudation process is obtained during the post-orogenic period. On the basis of summarizing evolution process of the basin-range system in the Qinling-Dabie orogenic belt during the Mesozoic-Cenozoic and its effects on regional environment, the influence of evolution process on geomorphologic landscapes change, water system vicissitude, eco-environment succession and drainage basin system evolution is discussed.

  11. Erosion and Sediment Transport Across Pronounced Topographic and Climatic Gradients in the Himalayan Orogen

    Science.gov (United States)

    Strecker, M. R.; Bookhagen, B.

    2014-12-01

    The interaction between the NW-directed trajectories of moisture transport associated with the Indian Summer Monsoon circulation and the high topography of the Himalayan orogen results in one of the most efficient orographic barriers on Earth. The steep topographic gradients, the impact of focused rainfall along the southern flank of the range, and northward shifts of rainfall during frequent intensified Indian Summer Monsoons are responsible for an efficient erosional regime, with some of the highest known erosion rates. The spatiotemporal correlation between various topographic, tectonic, climatic, and exhumational phenomena in this region has resulted in the formulation of models of possible long-term erosional and tectonic feedback processes that drive the lateral expansion and vertical growth of the mountain belt. However, despite an increase in thermochronologic, cosmogenic radionuclide, and sedimentological datasets that help explain the underlying mechanisms, the true nature of these relationships is still unclear and controversies particularly exist concerning the importance of the different forcing factors that drive exhumation and, ultimately, deformation. Here, we synthesize and assess these controversies with observations from studies conducted perpendicular to and along strike of the orogen, and combine them with our new basin-wide erosion-rate data from the Sutlej Valley in the NW Himalaya. In our regional comparison we highlight the importance of large river systems and climate-controlled aspects of weathering concerning fluvial mass distribution as there appear to be positive feedbacks between tectonics and surface processes. In contrast, observations from smaller catchments along the orogenic front suggest a negative correlation. Similar to other environments with steep topographic and climatic gradients, our observations from the Sutlej catchments emphasize that erosional processes in the Himalayan realm are most efficient in geomorphic

  12. Noble gases fingerprint a metasedimentary fluid source in the Macraes orogenic gold deposit, New Zealand

    Science.gov (United States)

    Goodwin, Nicholas R. J.; Burgess, Ray; Craw, Dave; Teagle, Damon A. H.; Ballentine, Chris J.

    2016-04-01

    The world-class Macraes orogenic gold deposit (˜10 Moz resource) formed during the late metamorphic uplift of a metasedimentary schist belt in southern New Zealand. Mineralising fluids, metals and metalloids were derived from within the metasedimentary host. Helium and argon extracted from fluid inclusions in sulphide mineral grains (three crush extractions from one sample) have crustal signatures, with no evidence for mantle input (R/Ra = 0.03). Xenon extracted from mineralised quartz samples provides evidence for extensive interaction between fluid and maturing organic material within the metasedimentary host rocks, with 132Xe/36Ar ratios up to 200 times greater than air. Similarly, I/Cl ratios for fluids extracted from mineralised quartz are similar to those of brines from marine sediments that have interacted with organic matter and are ten times higher than typical magmatic/mantle fluids. The Macraes mineralising fluids were compositionally variable, reflecting either mixing of two different crustal fluids in the metasedimentary pile or a single fluid type that has had varying degrees of interaction with the host metasediments. Evidence for additional input of meteoric water is equivocal, but minor meteoric incursion cannot be discounted. The Macraes deposit formed in a metasedimentary belt without associated coeval magmatism, and therefore represents a purely crustal metamorphogenic end member in a spectrum of orogenic hydrothermal processes that can include magmatic and/or mantle fluid input elsewhere in the world. There is no evidence for involvement of minor intercalated metabasic rocks in the Macraes mineralising system. Hydrothermal fluids that formed other, smaller, orogenic deposits in the same metamorphic belt have less pronounced noble gas and halogen evidence for crustal fluid-rock interaction than at Macraes, but these deposits also formed from broadly similar metamorphogenic processes.

  13. Constraints from rocks in the Taiwan orogen on crustal stress levels and rheology

    OpenAIRE

    Kidder, Steven B.; Avouac, Jean-Philippe; Chan, Yu-Chang

    2012-01-01

    Taiwan's Hsüehshan range experienced penetrative coaxial deformation within and near the brittle-plastic transition between ∼6.5 and 3 Ma. This recent and short-lasting deformation in an active, well-studied orogen makes it an ideal natural laboratory for studying crustal rheology. Recrystallized grain size piezometry in quartz and Ti-in-quartz thermobarometry yield peak differential stresses of ∼200 MPa at 250–300°C that taper off to ∼80 MPa at ∼350°C and ∼14 MPa at ∼400–500°C. Stress result...

  14. Three evolutionary stages of the collision orogenic deformation in the Middle Yangtze Region

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A discussion of collision orogenic deformation has been made for the Middle Yangtze Region. Based on its deformation assemblage orders, three developing stages are classified successively as compression thrust uplift, strike-slip escape rheology and tension extension inversion. The collision orogenesis of the studied region has been divided into three developing periods of initial, chief and late orogeny. Based on the data from Wugong Mts., Jiuling Mts. and Xuefeng Mts.,for each stage, its variation of stress and strain axes, the conversion of joint fractures and their relative tectonic evolution are described, models are plotted and corresponding explanations are made for the rock chronology dating value in the same tectonic period.

  15. The contorted New England Orogen (eastern Australia): New evidence from U-Pb geochronology of early Permian granitoids

    Science.gov (United States)

    Rosenbaum, Gideon; Li, Pengfei; Rubatto, Daniela

    2012-02-01

    A series of sharp bends (oroclines) are recognized in the Paleozoic to early Mesozoic New England Orogen of eastern Australia. The exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated. Here we present zircon U-Pb ages that confirm the lateral continuation of early Permian (296-288 Ma) granitoids and shed new light on the oroclinal structure. Orogenic curvature is defined by the alignment of early Permian granitoids parallel to the structural grain of the orogen, as well as the curved geometry of sub-vertical deformation fabrics, forearc basin terranes, and serpentinite outcrops. Alternative geometrical interpretations may involve two bends (Texas and Coffs Harbour Oroclines), three bends (+Manning Orocline), or even four bends (+Nambucca Orocline). We argue that the model involving four bends is most consistent with available data, although further kinematic constraints are required to confirm the existence of the Manning and Nambucca Oroclines. A subsequent phase of younger magmatism (Bowen orogeny.

  16. A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

    Science.gov (United States)

    Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

    2000-01-01

    We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

  17. Geochronological Significance of the Post-Orogenic Mafic-Ultramafic Rocks in the Hongqiling Area of Jilin Province, Northeast China

    Institute of Scientific and Technical Information of China (English)

    Zhang Guangliang; Wu Fuyuan

    2006-01-01

    Mafic-ultramafic complexes are widespread in Hongqiling in central Jinlin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-ultramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-ultramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-ultramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-ultramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-ultramafic complexes in the Xing'an-Mongolia Orogenic Belt

  18. Modelling the thermal evolution of orogens: where’s the heat?

    Science.gov (United States)

    Healy, D.; Clark, C.

    2009-12-01

    Our understanding of heat transfer during orogenesis has largely been shaped by the seminal work of England & Thompson (1984). These authors explored P-T-t paths in thickened crust as a function of radiogenic heat production, mantle heat flow, thermal conductivity and rates of erosion. In this contribution we incorporate recent experimental data on the temperature dependence of thermal conductivity and field observations of heat producing elements in exposed orogenic roots into 1D thermal models of regional metamorphism. We identify distinct tectonic processes responsible for heat flow perturbations in thickened crust and compare the temporal evolution of temperature with depth (pressure) for each case. Several recent papers have presented ad hoc combinations of these processes and we seek to clarify the contribution of each process to the total heat orogenic heat budget. We present sensitivity analyses to key model parameters for each case and discuss the scope for separating the relative contribution of each process from field data such as metamorphic field gradients and pressure-temperature-time paths.

  19. An important form of basin-mountain coupling:Orogenic belt and flank basin

    Institute of Scientific and Technical Information of China (English)

    WANG Erchie

    2004-01-01

    Orogeny is always associated with the erosion and sediments carried by both transverse and longitudinal river systems. Those two river systems transport sediments into foreland or hinterland basin and flank basin. Longitudinal river systems prevail in and around the Tibetan Plateau due to the fact that they flow parallel to the strike of structures within the developing mountain belt. The flank basins surrounded the Tibetan Plateau and adjacent areas are developed in different tectonic settings, including inland,continental margin and deep ocean, most of them containing oil and natural gas. Those basins not only have longer evolution histories than foreland basins but also are more complete in their records of deposition. Coupling of orogeny and flank basin deposition also occurred widely in pre-Cenozoic time, in particular, the coupling between the Qinling orogenic belt and Songpan-Ganzi flysch flank basin is the most distinctive. The evolution of ancient latitudinal rivers derived from the Qinling orogenic belt during periods of mountain building was controlled not only by landforms but also by the lateral extrusion of the crustal fragments.

  20. Sediment-hosted/orogenic gold mineral systems exploration using PALSAR remote sensing data in Peninsular Malaysia

    Science.gov (United States)

    Beiranvand Pour, Amin; Hashim, Mazlan

    2016-06-01

    The Bentong-Raub Suture Zone (BRSZ) is genetically related to the sediment-hosted/orogenic gold deposits associated with the major lineaments and form-lines in the Central Gold Belt of Peninsular Malaysia. In this investigation, the Phased Array type L-band Synthetic Aperture Radar (PALSAR) satellite remote sensing data were used to analyse major geological structures in Peninsular Malaysia and provide detailed characterization of lineaments and form-lines in the BRSZ, as well as its implications for sediment-hosted/orogenic gold exploration in tropical environments. The pervasive array of N-S faults in the study area and surrounding terrain is mainly linked to the N-S trending of the BRSZ Suture Zone. N-S striking lineaments are often cut by younger NE-SW and NW-SE-trending lineaments. Three generations of folding event have been discerned from remote sensing structural analysis. Gold mineralized trends lineaments are associated with the intersection of N-S, NE-SW, NNW-SSE and ESE-WNW faults and curvilinear features in shearing and alteration zones. Compressional tectonics structures such as NW-SE trending thrust, ENE-WSW oriented faults in mylonite and phyllite, recumbent folds and asymmetric anticlines in argillite are high potential zones for gold prospecting.

  1. The early Cretaceous orogen-scale Dabieshan metamorphic core complex: implications for extensional collapse of the Triassic HP-UHP orogenic belt in east-central China

    Science.gov (United States)

    Ji, Wenbin; Lin, Wei; Faure, Michel; Shi, Yonghong; Wang, Qingchen

    2016-03-01

    The Dabieshan massif is famous as a portion of the world's largest HP-UHP metamorphic belt in east-central China that was built by the Triassic North-South China collision. The central domain of the Dabieshan massif is occupied by a huge migmatite-cored dome [i.e., the central Dabieshan dome (CDD)]. Origin of this domal structure remains controversial. Synthesizing previous and our new structural and geochronological data, we define the Cretaceous Dabieshan as an orogen-scale metamorphic core complex (MCC) with a multistage history. Onset of lithospheric extension in the Dabieshan area occurred as early as the commencement of crustal anatexis at the earliest Cretaceous (ca. 145 Ma), which was followed by primary (early-stage) detachment during 142-130 Ma. The central Dabieshan complex in the footwall and surrounding detachment faults recorded a consistently top-to-the-NW shearing. It is thus inferred that the primary detachment was initiated from a flat-lying detachment zone at the middle crust level. Removal of the orogenic root by delamination at ca. 130 Ma came into the extensional climax, and subsequently isostatic rebound resulted in rapid doming. Along with exhumation of the footwall, the mid-crustal detachment zone had been warped as shear zones around the CDD. After 120 Ma, the detachment system probably experienced a migration accommodated to the crustal adjustment, which led to secondary (late-stage) detachment with localized ductile shearing at ca. 110 Ma. The migmatite-gneiss with HP/UHP relicts in the CDD (i.e., the central Dabieshan complex) was product of the Cretaceous crustal anatexis that consumed the deep-seated part of the HP-UHP slices and the underlying para-autochthonous basement. Compared with the contemporaneous MCCs widely developed along the eastern margin of the Eurasian continent, we proposed that occurrence of the Dabieshan MCC shares the same tectonic setting as the "destruction of the North China craton". However, geodynamic trigger

  2. Late Mesozoic deformations of the Verkhoyansk-Kolyma orogenic belt, Northeast Russia

    Science.gov (United States)

    Fridovsky, Valery

    2016-04-01

    The Verkhoyansk-Kolyma orogenic belt marks the boundary between the Kolyma-Omolon superterrane (microcontinent) and the submerged eastern margin of the North Asian craton. The orogenic system is remark able for its large number of economically viable gold deposits (Natalka, Pavlik, Rodionovskoe, Drazhnoe, Bazovskoe, Badran, Malo-Tarynskoe, etc.). The Verkhoyansk - Kolyma orogenic belt is subdivided into Kular-Nera and the Polousny-Debin terranes. The Kular-Nera terrane is mainly composed of the Upper Permian, Triassic, and Lower Jurassic black shales that are metamorphosed at lower greenschist facies conditions. The Charky-Indigirka and the Chai-Yureya faults separate the Kular-Nera from the Polousny-Debin terrane that is predominantly composed of the Jurassic flyschoi dturbidites. The deformation structure of the region evolved in association with several late Mesozoic tectonic events that took place in the north-eastern part ofthe Paleo-Pacific. In Late Jurassic-Early Cretaceous several generations of fold and thrust systems were formed due to frontal accretion of the Kolyma-Omolon superterrane to the eastern margin of the North Asian craton.Thrusting and folding was accompanied by granitic magmatism, metamorphic reworking of the Late Paleozoic and the Early Mesozoic sedimentary rocks, and formation of Au-Sn-W mineralization. Three stages of deformation related to frontal accretion can be distinguished. First stage D1 has developed in the north-eastern part of the Verkhoyansk - Kolyma orogenic belt. Early tight and isoclinal folds F1 and assosiated thrusts are characteristic of D1. Major thrusts, linear concentric folds F2 and cleavage were formed during D2. The main ore-controlling structures are thrust faults forming imbricate fan systems. Frontal and oblique ramps and systems of bedding and cross thrusts forming duplexes are common. It is notable that mineralized tectonized zones commonly develop along thrusts at the contacts of rocks of contrasting competence

  3. Leucogranito pumayaco: anatexis cortical durante el ciclo orogénico en el extremo norte de la sierra molino, provincia de Salta Pumayaco leucogranite: crustal anatexis during the Famatinian cycle in the northern end of the Sierra de Molinos, Salta Province

    Directory of Open Access Journals (Sweden)

    Alfonso M Sola

    2010-03-01

    Early Ordovician age. These are folded sheetlike bodies of small dimensions (less than 10 km², emplaced synchronously within deformation at mid-crustal levels. They are intimately linked with migmatic rocks and characterized by the presence of accessory minerals such as garnet, cordierite, sillimanite and tourmaline. The Pumayaco leucogranite is the largest of theses plutons and is located in the center of the Molinos range. Here we present a detailed mapping of the main granite, and separate different facies using petrographic and geochemical data. The alumina contents (ASI>1.1 and the narrow silica variations (72-76 %wt, as well as the petrographic features, allow to classify them as S-type granitoids derived from crustal anatexis. The processes that would have been involved in the generation and differentiation of these granitoids include different melting reactions of metapelite and metagreywacke protoliths, and an influence of restite phases in the segregated melt compositions. The association with ductile shear zones and the field relation with migmatic units suggest an important participation of deformation during segregation, migration and emplacement of these melts under a convergent tectonic regime (Famatinian Cycle.

  4. Sand fairway mapping as a tool for tectonic restoration in orogenic belts

    Science.gov (United States)

    Butler, Rob

    2016-04-01

    geomorphology. The stratigraphic records are preserved in many parts of the Alpine-Mediterranean region. Examples are drawn from the Eo-Oligocene of the western Alps and the early Miocene of the Maghreb-Apennine system to illustrate how turbidite sedimentology, linked to studies of basin structure, can inform understanding of tectonic processes on regional and local scales. In both examples, sediment was delivered across deforming basin arrays containing contractional structures, sourced from beyond the immediate orogenic segments. The depositional systems show that multiple structures were active in parallel, rather than develop in any particular sequence. Both systems show that significant deformation occurs, emerging to the syn-orogenic surface ahead of the main orogenic wedge. The cycling of uplift and subsidence of "massifs" can be significantly more complex that the histories resolved from thermochronological data alone.

  5. Hydrothermal alteration styles in ancient and modern orogenic gold deposits, New Zealand

    International Nuclear Information System (INIS)

    Orogenic hydrothermal systems in the South Island of New Zealand were active during Mesozoic and late Cenozoic collisional deformation and metamorphism of greywacke/schist terranes. Observations on the currently active mountain-building environment yield insights on processes occurring in the upper 5-15 km of the crust, and observations on an adjacent lithologically identical exhumed ancient mountain belt provide information on processes at 10-20 km in the crust. Hydrothermal fluids were mainly derived from metamorphic dehydration reactions and/or circulating topographically driven meteoric water in these mountain belts. Three geochemically and mineralogically different types of hydrothermal alteration and vein mineralisation occurred in these orogenic belts, and gold enrichment (locally economic) occurred in some examples of each of these three types. The first type of alteration involved fluids that were in or near chemical equilibrium with their greenschist facies host rocks. Fluid flow was controlled by discontinuous fractures, and by microshears and grain boundaries in host rocks, in zones from metres to hundreds of metres thick. Vein and alteration mineralogy was similar to that of the host rocks, and included calcite and chlorite. The second type of alteration occurred where the fluids were in distinct disequilibrium with the host rocks. Fracture permeability was important for fluid flow, but abundant host rock alteration occurred as well. The alteration zones were characterised by decomposition of chlorite and replacement by ankeritic carbonate in zones up to tens of metres thick. The mineralising fluid was deep-sourced and initially rock-equilibrated, with some meteoric input. The third type of mineralisation was controlled almost exclusively by fracture permeability, and host rock alteration was minor (centimetre scale). This mineralisation type commonly involved calcite and chlorite as vein and alteration minerals, and mineralisation fluids had a major

  6. Lawsonite Blueschists in Recycled Mélange Involved in K-Rich Orogenic Magmatism

    Science.gov (United States)

    Wang, Y.; Prelevic, D.; Foley, S. F.; Buhre, S.; Galer, S. J. G.

    2014-12-01

    The origin of K-rich orogenic magmatism in the Alpine-Himalayan belt and its relationship to the large-scale elevations in several massifs of the orogen is controversial, particularly the significance of the widespread presence of a geochemical signal typical for recycled continental crust. Two competing scenarios invoke direct melting of continental crust during deep intercontinental subduction and removal of heavily metasomatised mantle lithosphere by delamination into the convecting mantle. Here we investigate the coupling of high Th/La ratio with crustal isotopic signatures in K-rich orogenic lavas that does not occur in volcanic rocks from other collisional environments to distinguish between these two models. High-pressure experimental results on a phyllite representing upper crustal composition and a detailed mineral and geochemical study of blueschists from Tavşanlı mélange, Turkey, indicate that this geochemical fingerprint originates by melting of subducted mélange. Melting of crust at the top of the subducted continental lithosphere cannot produce observed fingerprint, whereas lawsonites, especially those with terrigenous sediment origin from blueschists with high Th/La can. Lawsonites that grow in various components of a subduction mélange inherit the geochemical characteristics of either oceanic or continental protoliths. It is currently uncertain whether those carrying the high Th/La signature originate by direct melting of continental blocks in the mélange or by the introduction of supercritical fluids from lawsonite blueschist of continental origin that infiltrate oceanic sediment blocks. Either way, the high Th/La is later released into subsequently formed melts. This confirms the supposition that lawsonite is the main progenitor of the high Th/La and Sm/La ratio. However, lawsonite must break down completely to impart this unique feature to subsequent magmas. The source regions of the potassic volcanic rocks consist of blueschist facies m

  7. Tectonic Subdivision of Dabie Orogenic Belt, Central China: Evidence from Pb Isotope Geochemistry of Late Mesozoic Basalts

    Institute of Scientific and Technical Information of China (English)

    匡少平; 张本仁

    2002-01-01

    It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesozoic granitoid K-feldspar (revealing the crust Pb) in combination with Meso-Cenozoic basalts (revealing the mantle Pb), being divided into the North China and Yangtze Pb isotopic provinces, where the crust and mantle of the Yangtze craton are characterized by more radiogenic Pb. In this sense, previous researchers suggested that the pro-EW-trending Dabie orogenic belt with less radiogenic Pb in the crust was part of the North China craton. In this paper, however, the Late Cretaceous basalts in the central and southern parts of the Dabie orogenic belt are characterized by some more radiogenic Pb (206pb/204pb = 17. 936 - 18. 349, 207pb/204pb = 15. 500 - 15. 688, 208pb/204pb = 38. 399 - 38. 775 )and a unique U-Th-Pb trace element system similar to those of the Yangtze craton, showing that the Mesozoic mantle is of the Yangtze type. In addition, the decoupled Pb isotopic compositions between crust and mantle were considerably derived from their rheological inhomogeneity, implying a complicated evolution of the Dabie orogenic belt.

  8. Preservation and Recycling of Crust during Accretionary and Collisional Phases of Proterozoic Orogens: A Bumpy Road from Nuna to Rodinia

    Directory of Open Access Journals (Sweden)

    Kent C. Condie

    2013-05-01

    Full Text Available Zircon age peaks at 2100–1650 and 1200–1000 Ma correlate with craton collisions in the growth of supercontinents Nuna and Rodinia, respectively, with a time interval between collisions mostly <50 Myr (range 0–250 Myr. Collisional orogens are two types: those with subduction durations <500 Myr and those ≥500 Myr. The latter group comprises orogens with long-lived accretionary stages between Nuna and Rodinia assemblies. Neither orogen age nor duration of either subduction or collision correlates with the volume of orogen preserved. Most rocks preserved date to the pre-collisional, subduction (ocean-basin closing stage and not to the collisional stage. The most widely preserved tectonic setting in Proterozoic orogens is the continental arc (10%–90%, mean 60%, with oceanic tectonic settings (oceanic crust, arcs, islands and plateaus, serpentinites, pelagic sediments comprising <20% and mostly <10%. Reworked components comprise 20%–80% (mean 32% and microcratons comprise a minor but poorly known fraction. Nd and Hf isotopic data indicate that Proterozoic orogens contain from 10% to 60% of juvenile crust (mean 36% and 40%–75% reworked crust (mean 64%. Neither the fraction nor the rate of preservation of juvenile crust is related to the collision age nor to the duration of subduction. Regardless of the duration of subduction, the amount of juvenile crust preserved reaches a maximum of about 60%, and 37% of the volume of juvenile continental crust preserved between 2000 and 1000 Ma was produced in the Great Proterozoic Accretionary Orogen (GPAO. Pronounced minima occur in frequency of zircon ages of rocks preserved in the GPAO; with minima at 1600–1500 Ma in Laurentia; 1700–1600 Ma in Amazonia; and 1750–1700 Ma in Baltica. If these minima are due to subduction erosion and delamination as in the Andes in the last 250 Myr; approximately one third of the volume of the Laurentian part of the GPAO could have been recycled into the mantle

  9. Paleozoic accretionary orogenesis in the eastern Beishan orogen: constraints from zircon U-Pb and 40Ar/39Ar geochronology

    Science.gov (United States)

    Ao, Songjian; Xiao, Wenjiao; Windley, Brian; Mao, Qigui

    2016-04-01

    The continental growth mechanism of the Altaids in Central Asia is still in controversy between models of continuous subduction-accretion versus punctuated accretion by closure of multiple oceanic basins. The Beishan orogenic belt, located in the southern Altaids, is a natural laboratory to address this controversy. Key questions that are heavily debated are: the closure time and subduction polarity of former oceans, the emplacement time of ophiolites, and the styles of accretion and collision. This paper reports new structural data, zircon ages and Ar-Ar dates from the eastern Beishan Orogen that provide information on the accretion process and tectonic affiliation of various terranes. Our geochronological and structural results show that the younging direction of accretion was northwards and the subduction zone dipped southwards under the northern margin of the Shuangyingshan micro-continent. This long-lived and continuous accretion process formed the Hanshan accretionary prism. Our field investigations show that the emplacement of the Xiaohuangshan ophiolite was controlled by oceanic crust subduction beneath the forearc accretionary prism of the Shuangyingshan-Mazongshan composite arc to the south. Moreover, we address the age and terrane affiliation of lithologies in the eastern Beishan orogen through detrital zircon geochronology of meta-sedimentary rocks. We provide new information on the ages, subduction polarities, and affiliation of constituent structural units, as well as a new model of tectonic evolution of the eastern Beishan orogen. The accretionary processes and crustal growth of Central Asia were the result of multiple sequences of accretion and collision of manifold terranes. Reference: Ao, S.J., Xiao, W., Windley, B.F., Mao, Q., Han, C., Zhang, J.e., Yang, L., Geng, J., Paleozoic accretionary orogenesis in the eastern Beishan orogen: Constraints from zircon U-Pb and 40Ar/39Ar geochronology. Gondwana Research, doi: http://dx.doi.org/10.1016/j

  10. Genesis of Yangla Banded Skarn-Hosted Copper Deposit in Tethys Orogenic Belt of Southwestern China

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Yangla copper deposit is the largest banded skarn-hosted copper deposit found recently in the Tethys orogenic belt of Southwestern China. On the basis of the study of distribution, petrology and mineralogy as well as major element, REE and isotope geochemistry, the authors find that the banded skarn, which hosts the deposit, was precipitated from hydrothermal solutions in the form of exhalate sediment. Therefore, the banded skarn-hosted copper deposit is a Sedex-type deposit, with a series of stacked, conformable lenses underlain by at least one stringer zone. The deposit, intercalated at the contact of lower clastic rock and upper carbonate rock of Gajinxueshan Group, was formed in the Carboniferous ((296.1±7.0) Ma), contemporary to the host Gajinxueshan Group. The interpretation of the genesis of Yangla banded skarn-hosted copper deposit is of fundamental exploration significance for the discovery of Sedex-type copper deposit in the region.

  11. Precise timing of the Early Paleozoic metamorphism and thrust deformation in the Eastern Kunlun Orogen

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In Dulan County, Qinghai Province NW China, the arc volcanic sequences in the northern side of the Central Fault of the East Kunlun were metamorphosed progressively from upper greenschist facies in the south to epidote-amphibolite facies in the north. High-angle thrust deforma-tion was developed synchronously with the peak metamor-phim and superimposed with later low-angle striking-slip deformation. Zircon U-Pb dating yields a concordant age of (448 ± 4) Ma for the metavolcanics. Syn-kinematic horn-blende and muscovite separated from the high-angle thrust-ing belt give 40Ar-39Ar plateau age of (427 ± 4) Ma and 408 Ma, respectively. These results precisely constrain the timing of the closure of early Paleozoic volcanic basin (Proto-Tethys) over the eastern portion of the East Kunlun Orogen, and the thrust tectonic slice had a cool rate of ca. 9℃/Ma.

  12. Cross-sectional anatomy and geodynamic evolution of the Central Pontide orogenic belt (northern Turkey)

    Science.gov (United States)

    Hippolyte, J.-C.; Espurt, N.; Kaymakci, N.; Sangu, E.; Müller, C.

    2016-01-01

    Geophysical data allowed the construction of a ~250-km-long lithospheric-scale balanced cross section of the southern Black Sea margin (Espurt et al. in Lithosphere 6:26-34, 2014). In this paper, we combine structural field data, stratigraphic data, and fault kinematics analyses with the 70-km-long onshore part of the section to reconstruct the geodynamic evolution of the Central Pontide orogen. These data reveal new aspects of the structural evolution of the Pontides since the Early Cretaceous. The Central Pontides is a doubly vergent orogenic wedge that results from the inversion of normal faults. Extensional subsidence occurred with an ENE-trend from Aptian to Paleocene. We infer that the Black Sea back-arc basin also opened during this period, which was also the period of subduction of the Tethys Ocean below the Pontides. As in the Western Pontides, the Cretaceous-Paleocene subsidence was interrupted from Latest Albian to Coniacian time by uplift and erosion that was probably related to a block collision and accretion in the subduction zone. The restoration of the section to its pre-shortening state (Paleocene) shows that fault-related subsidence locally reached 3600 m within the forearc basin. Structural inversion occurred from Early Eocene to Mid-Miocene as a result of collision and indentation of the Pontides by the Kırşehir continental block to the south, with 27.5 km (~28 %) shortening along the section studied. The inversion was characterized by NNE-trending shortening that predated the Late Neogene dextral escape of Anatolia along the North Anatolian Fault and the modern stress field characterized by NW-trending compression within the Eocene Boyabat basin.

  13. Active Tectonics in crossroads of an evolving orogen and morphological consequences: Anatolia

    Science.gov (United States)

    Koral, Hayrettin

    2016-04-01

    Anatolia lies in a curved setting of the active Alpine Mountain Range and is located in crossroads of the European and Asian terrains. It is one of the fastest deforming land in the world, manifested by seismicity, characteristic landforms and GPS measurements. Active tectonics in Anatolia provides not only a comparable geological model for the past orogens, but also a laboratory case for morphological consequences of an orogenic processes. Anatolia comprise different tectonic subsettings with its own characteristics. Northern part is influenced by tectonic characteristics of the Black Sea Basin, the Pontides and the Caucasian Range; northwestern part by the Balkanides; eastern-southeastern part by the Bitlis-Zagros suture; and south-southwestern part by the eastern Mediterranean subduction setting. Much of its present tectonic complexity was inherited from the convergence dominant plate tectonic setting of the platelets prior to the Middle-Neogene. Beginning about 11 Ma ago, the deformed and uplifted landmass unable to accommodate further deformation in Anatolia and ongoing tectonic activity gave rise to rearrangement of tectonic forces and westerly translational movements. Formation of major strike-slip faults in Anatolia including the North and East Anatolian Faults and a new platelet called the Anatolian Plate are the consequences of this episode. Such change in the tectonic regime has led to modification of previously-formed landscape, modification and sometimes termination of previously-formed basins. Evidence is present in the Plio-Quaternary stratigraphy, tectonic characteristics and morphology of the well-studied areas. This presentation will discuss active tectonic features of the northwestern, southwestern and eastern Anatolian subsettings and their influence on morphology that is closely related to sites of pre-historical human settlement.

  14. Zircon dating of Neoproterozoic and Cambrian ophiolites in West Mongolia and implications for the timing of orogenic processes in the central part of the Central Asian Orogenic Belt

    Science.gov (United States)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Tomurhuu, Dondov; Liu, Dunyi

    2014-06-01

    We present new isotopic and trace element data to review the geochronological/geochemical/geological evolution of the central part of the Central Asian Orogenic Belt (CAOB), and find a fundamental geological problem in West Mongolia, which has traditionally been subdivided into northwestern early Paleozoic (formerly Caledonian) and southerly late Paleozoic (formerly Hercynian) belts by the Main Mongolian Lineament (MML). We resolve this problem with SHRIMP zircon dating of ophiolites and re-evaluation of much published literature. In Northwest Mongolia the Dariv-Khantaishir ophiolite marks the boundary between the Lake arc in the west and the Dzabkhan-Baydrag microcontinent in the east. Zircons from a microgabbro and four plagiogranites yielded weighted mean 206Pb/238U ages of 568 ± 5 Ma, 567 ± 4 Ma, 560 ± 8 Ma (Dariv), 573 ± 8 Ma and 566 ± 7 Ma (Khantaishir) that we interpret as reflecting the time of ophiolite formation (ca. 573-560 Ma). Metamorphic zircons from an amphibolite on a thrust boundary between the Khantaishir ophiolite and the Dzabkhan-Baydrag microcontinent formed at 514 ± 8 Ma, which we interpret as the time of overthrusting. In South Mongolia the Gobi Altai ophiolite and the Trans-Altai Gurvan Sayhan-Zoolen forearc with an ophiolite basement were investigated. Zircons of a layered gabbro (lower ophiolite crust) and a leucogabbro (mid-upper crust) of the Gobi Altai ophiolite yielded crystallization ages of 523 ± 5 Ma and 518 ± 6 Ma. The age data constrain the formation time of ophiolite within ca. 523-518 Ma. Zircons from four samples of the Gurvan Sayhan-Zoolen forearc, with similar hybrid adakite-boninite affinities, yielded 519 ± 4 Ma for an anorthosite, ≥ 512 ± 4 Ma for a hornblendite and 520 ± 5 and 511 ± 5 Ma for two diorites. The ophiolite basement has an upper age limit of 494 ± 6 Ma, determined by dating a tonalite dike cutting the Zoolen ophiolite. Integrating available zircon ages as well as geochemical and geological data

  15. Mianlüe tectonic zone and Mianlüe suture zone on southern margin of Qinling-Dabie orogenic belt

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    The Mianlue tectonic zone (Mianlue zone), an ancient suture zone in addition to theShangdan suture in the Qinling-Dabie orogenic belt, marks an important tectonic division geo-logically separating north from south and connecting east with west in China continent. To de-termine present structural geometry and kinematics in the Mianlue tectonic zone and to recon-struct the formation and evolution history involving plate subduction and collision in theQinling-Dabie orogenic belt, through a multidisciplinary study, are significant for exploring themountain-building orogenesis of the central orogenic system and the entire process of the majorChinese continental amalgamation during the Indosinian.

  16. The boundary between the eastern and western domains of the Pyrenean Orogen: a Cenozoic triple junction zone in Iberia?

    Directory of Open Access Journals (Sweden)

    S. Tavani

    2012-04-01

    Full Text Available The Cantabrian Transitional Area (CTA is located in the eastern portion of the Cantabrian Mountain Range of the northern Spain. It represents the most important internal boundary within the Upper Cretaceous to Cenozoic E–W elongated Pyrenean Orogen. In the south-verging portion of this orogen, the CTA divides the western thick-skinned Cantabrian Domain, which accommodated for a limited portion of the total N–S oriented orogenic shortening, from the Pyrenean realm to the east, where the south-verging frontal structures are characterised by a marked thiN–Skin style of deformation, and significantly contributed to accommodate the total shortening. In the Cantabrian Transitional Area, Cenozoic syn-orogenic left-lateral, right-lateral and reverse dip-slip movements have occurred along different directions, postdating early-orogenic extensional structures. The latter indicate that the southern portion of the study area formed the eastern termination of the northward concave roughly E–W oriented proto Duero Foreland Basin. This basin was flanked to the north by the thick-skinned proto Cantabrian Belt, which included in its easternmost part the northern portion of the Cantabrian Transitional Area. Onset of right-lateral strike-slip tectonics along the WNW-ESE striking Ubiernal-Venatniella Fault System, which locates to the SW of the CTA and crosses the entire Cantabrian Belt and its formerly southern foreland basin, caused the dislocation of the belt-foredeep system. Contextually, thiN–Skinned structures belonging to the eastern domain of the Pyrenean Orogen laterally propagated and incorporated the eastern part of the proto Duero Foreland Basin. Coexistence of right-lateral and reverse movements to the west and to the east, respectively, determined the onset of an intrabelt compression at the boundary between the Cantabrian and Pyrenean domains, which was the ultimate act of the fusion of the two domains into a single orogen.

  17. North Qinling Paleozoic granite associations and their variation in space and time: Implications for orogenic processes in the orogens of central China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Integrated zircon U-Pb dating and whole rock geochemical analyses have been carried out for two typical S-and I-type granitoids in the north Qinling. Zircon dating by SIMS of the Piaochi S-type grani- toids yields an emplacement age of 495±6 Ma. The granitoids show whole-rock εNd(t)=-8.2--8.8, zircon εHf(t)=-6―-39. The Huichizi I-type granitoids have emplacement ages of 421±27 Ma and 434±7 Ma es- tablished by LA-ICP-MS and SIMS methods, respectively. Their whole-rock εNd(t)=-0.9-0.9 and zircon εHf(t)=-11-8.4. Combined with statistical analyses of 28 zircon ages of granitoid plutons collected from the literature, Paleozoic magmatism in the north Qinling can be divided into three stages. The first-stage magmatism (~505-470 Ma) mainly occurred in the east part of the north Qinling and has features of an I-type arc, associated with which are S-type granitoids such as Piaochi pluton. The early granitoids (~505-490 Ma) have close spatio-temporal relations to ultra-high-pressure (UHP) rocks, and thus are interpreted as an oceanic subduction system along a continental margin. The second-stage magmatism (~450-422 Ma) occured through the whole north Qinling, and is characterized by I-type granitoids represented by the Huichizi pluton. The magma is interpreted as partial melting of lower crust mixed by mantle-derived magma in a collisional setting with the uplift of terranes. The third-stage magmatism (~415-400 Ma) is dominated by I-type granitoids and only took place in the middle part of the north Qinling, and is regarded as a late-stage collision. The spatial and temporal variations of the Qinling Paleozoic magmatism reveal protracted subduction/collision. The subduction was initiated from the east part of the north Qinling, earlier than that in the Qilian-northern Qaidam, Kunlun, and northern Dabie regions. This demonstrates variations in time of subduction, accretion and collision of separate blocks or terranes in the orogenic systems in central China.

  18. Sediment budgets by detrital geochronology and new perspectives in understanding orogenic erosion (solicited)

    Science.gov (United States)

    Malusà, Marco Giovanni

    2014-05-01

    Low-temperature thermochronological data provide an estimate of the average exhumation rate from the partial retention zone to the surface. The timescale the rate is referred to largely depends on the distribution of thermochronological ages in the study area, which may be inadequate to constrain fast orogenic processes. New perspectives to investigate orogenic erosion and its linkage with climate and tectonics are provided by quantitative sediment budgets based on detrital geochronological analyses, which allows a much greater time resolution chiefly depending on available biostratigraphic constraints. Detrital samples derived from the mixing of geochronologically distinguishable detrital sources are expected to yield polymodal grain-age distributions that include different grain-age populations. The relative size between populations depends on (i) the relative size of the catchment areas, (ii) the mineral fertility of the parent bedrock, and (iii) the erosion rate in each catchment. If we know two of these factors, then we can calculate the third (Resentini & Malusà, 2012). A reliable approach to mineral fertility quantification thus represents a fundamental prerequisite for any sediment budget based on single-mineral data. In a temperate/cold climate where chemical weathering is minor, mineral fertility in the source rocks can be effectively determined by measuring the mineral concentration in the sediment they produce, provided that a range of potential sources of bias are properly accounted for and minimized (Malusà et al., 2013). Specifically, this approach requires that no significant modification has been induced by hydrodynamic processes in the natural environment (as tested by basic principles of hydraulic sorting), and that no bias is later introduced during mineral separation. Orogen-scale fertility maps are thus easily produced for different minerals thanks to the analysis of a reasonably low number of modern sand samples. Potentials and pitfalls of

  19. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: A lead isotope study of an Archaean gold prospect in the Attu region, Nagssugtoqidian orogen, West Greenland

    OpenAIRE

    Stendal, Henrik; Frei, Robert; Stensgaard, Bo Møller

    2006-01-01

    This paper presents a lead isotope investigation of a gold prospect south of the village Attu in the northern part of the Nagssugtoqidian orogen in central West Greenland. The Attu gold prospect is a replacement gold occurrence, related to a shear/mylonite zone along a contact between orthogneissand amphibolite within the Nagssugtoqidian orogenic belt. The mineral occurrence is small, less than 0.5 m wide, and can be followed along strike for several hundred metres. The mineral assemblage is ...

  20. Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

    Science.gov (United States)

    Whitney, D.L.; Tepper, J.H.; Hirschmann, M.M.; Hurlow, H.A.

    2008-01-01

    The Skymo Complex in the North Cascades, Washington, is a layered mafic intrusion within the Ross Lake fault zone, a major orogen-parallel structure at the eastern margin of the Cascades crystalline core. The complex is composed dominantly of troctolite and gabbro, both with inclusions of primitive olivine gabbro. Low-pressure minerals in the metasedimentary contact aureole and early crystallization of olivine + plagioclase in the mafic rocks indicate the intrusion was emplaced at shallow depths (magmatism. The Skymo mafic complex and the Golden Horn granite were emplaced during regional extension and collapse of the North Cascades orogen and represent the end of large-scale magmatism in the North Cascades continental arc. ?? 2008 Geological Society of America.

  1. Uranium cycle and tectono-metamorphic evolution of the Lufilian Pan-African orogenic belt (Zambia)

    International Nuclear Information System (INIS)

    Uranium is an incompatible and lithophile element, and thus more concentrated in silicate melt produced by the partial melting of the mantle related to continental crust formation. Uranium can be used as a geochemical tracer to discuss the generation and the evolution of continental crust. This thesis, focused on the Pan-African Lufilian belt in Zambia, combines structural geology, metamorphic petrology and thermos-barometry, fluid inclusions, geochemistry and geochronology in order to characterize the uranium cycle for this crustal segment. Silici-clastic and evaporitic sediments have been deposited within an intra-continental rift during the dislocation of the Rodinia super-continent during the early Neo-proterozoic. U-Pb ages on detrital zircon grains in these units indicate a dominant Paleo-proterozoic provenance. The same zircon grains show sub-chondritic εHf (between 0 and -15) and yield Hf model ages between ∼2.9 and 2.5 Ga. These data suggest that the continental crust was generated before the end of the Archean (< 2.5 Ga) associated with uranium extraction from the mantle. This old crust has been reworked by deformation and metamorphism during the Proterozoic. Uranium has been re-mobilized and reconcentrated during several orogenic cycles until the Pan-African orogeny. During this Pan-African cycle, U-Pb and REY (REE and Yttrium) signatures of uranium oxides indicate a first mineralizing event at ca. 650 Ma during the continental rifting. This event is related to late diagenesis hydrothermal processes at the basement/cover interface with the circulation of basinal brines linked to evaporites of the Roan. The second stage, dated at 530 Ma, is connected to metamorphic highly saline fluid circulations, synchronous to the metamorphic peak of the Lufilian orogeny (P=9±3 kbar; T=610±30 deg. C). These fluids are derived from the Roan evaporite dissolution. Some late uranium re-mobilizations are described during exhumation of metamorphic rocks and their

  2. Polyphase deformation of a Paleozoic metamorphosed subduction-accretionary complex in Beishan Orogen, southern Altaids

    Science.gov (United States)

    Song, Dongfang; Xiao, Wenjiao

    2014-05-01

    The Lebaquan Complex in central Beishan plays a significant role in understanding the subduction-accretion-collision processes of the Beishan orogenic collage, southern Altaids. This complex is a polyphase deformed upper greenschist to lower amphibolite facies metamorphic rock assemblages composed of metasedimentary sequence, gneissic plutons, metacherts, amphibolites and marbles, with multiple generations of syn-tectonic leucogranite-pegmatite and post-tectonic mafic dykes. Lithologic and geochemical characteristics show the Lebaquan Complex is a forearc-arc complex. Four stages of deformation can be recognized for the Lebaquan Complex. The D1 deformation is defined by pervasively developed foliations (S1) defined by alternative metamorphic layering and intrafolia isoclinal folds of quartz veins (F1). The D2 deformation is indicated by crenulation cleavage (S2) mainly developed in the schists, extensively-developed tight to open folds and asymmetric folds (F2) and pinch and swell structures. The D3 deformation is characterized by high-strain ductile shearing, which modified earlier structures. Small-scale asymmetric folds, σ-type porphyroclasts and S-C fabrics indicate dextral sense of shearing in east-west direction. The D4 deformation is represented by ductile to brittle structures including open/gentle folds, kink folds and small scale thrust faults which overprint earlier deformations. The overall deformation of this complex indicates a geodynamic setting change from initial north-south directed strong compression to later east-west directed transpression and finally extension. LA-ICP-MS zircon U-Pb dating was performed on key lithologies. Youngest age peak of detrital zircons from a garnet-mica-quartz schist is ~424 Ma, constraining the depositional age for the protolith of the metasedimentary sequence. A syn-deformation leucogranitic dyke that underwent D2 but did not experience D1 and a post-deformation mafic dyke that intrudes all the lithologies were

  3. A Late Cretaceous Orogen Triggering the Tertiary Rifting of the West Sunda Plate; Andaman Sea Region

    Science.gov (United States)

    Sautter, B.; Pubellier, M. F.; Menier, D.

    2015-12-01

    Rifted Basins often develop in internal zones of orogenic belts, although the latter may not be easy to unravel. We chose the example of the super-stretched Andaman sea region affected by several stages of rifting in the internal zone of a composite collage of allochthonous terranes. We made use of a set of geophysical, geochronological and structural data to analyze the rifting evolution and reconstruct the previous compressional structures. - Starting in the late Oligocene the East Andaman Basin opened as a back arc in a right-lateral pull- apart. The rifting propagated Westward to the central Andaman basin in the Middle Miocene, and to the oceanic spreading stage in the Pliocene. - An early extension occurred in the Paleogene, marked by widespread opening of isolated continental basins onshore Malay Peninsula and offshore Andaman Shelf and Malacca Straits. The rifting was accommodated by LANF's along preexisting weakness zones such as hinges of folds and granitic batholiths. Continuous extension connected the isolated basins offshore, whereas onshore, the grabens remained confined. There, AFT data show an uplift phase around 30Ma. In the Late Cretaceous, a major deformation occurred oblique to the pre-existing Indosinian basement fabrics. The convergence was partitioned into thrusting and uplift of the Cretaceous volcanic arc in Thailand and Myanmar, inversion of Mesozoic basins, and coeval wrenching responsible for large phacoid-shaped crustal slivers bounded by wide strike slip fault zones. The slivers share similar characteristics: a thick continental core of lower Paleozoic sedimentary basins units surrounded by Late Cretaceous granitoids. Radiometric data and fission tracks indicate a widespread thermal anomaly in all West Sunda Plate synchronous to a strong uplift. In the Latest Mesozoic, the Western Margin of Sunda plate was subjected to a major E-W compression, accommodated by oblique conjugate strike slip faults, leading to the formation of a large

  4. Magnetic signatures of the orogenic crust of the Patagonian Andes with implication for planetary exploration

    Science.gov (United States)

    Díaz Michelena, Marina; Kilian, Rolf

    2015-11-01

    The Patagonian Andes represent a good scenario of study because they have outcrops of diverse plutonic rocks representative of an orogenic crust on Earth and other planets. Furthermore, metamorphic surface rocks provide a window into deeper crustal lithologies. In such remote areas, satellite and aerial magnetic surveys could provide important geological information concerning exposed and not exposed rocks, but they integrate the magnetic anomalies in areas of kilometres. For the southernmost Andes long wavelength satellite data show clear positive magnetic anomalies (>+100 nT) for the Patagonian Batholith (PB), similar as parts of the older martian crust. This integrated signal covers regions with different ages and cooling histories during magnetic reversals apart from the variability of the rocks. To investigate the complex interplay of distinct magnetic signatures at short scale, we have analysed local magnetic anomalies across this orogen at representative sites by decimeter-scale magnetic ground surveys. As expected, the investigated sites have positive and negative local anomalies. They are related to surface and subsurface rocks, and their different formation and alternation processes including geomagnetic inversions, distinct Curie depths of the magnetic carriers, intracrustal deformation among other factors. Whole rock chemistry (ranging from 45 to >80 wt.% SiO2 and from 1 to 18 wt.% FeOtot.), magnetic characteristics (susceptibilities, magnetic remanence and Königsberger ratios) as well as the composition and texture of the magnetic carriers have been investigated for representative rocks. Rocks of an ultramafic to granodioritic intrusive suite of the western and central PB contain titanomagnetite as major magnetic carrier. Individual magnetic signatures of these plutonic rocks reflect their single versus multidomain status, complex exolution processes with ilmenite lamella formations and the stoichiometric proportions of Cr, Fe and Ti in the oxides. At

  5. A combined noble gas and halogen study of orogenic gold mineralisation in the Alpine and Otago Schists, New Zealand

    OpenAIRE

    Goodwin, Nicholas Robert John

    2010-01-01

    Quartz and pyrite samples from Pliocene-recent, sub-economic orogenic gold mineralisation in the Southern Alps and Mesozoic economic deposits in the Otago Schist Belt have been analysed for noble gases and halogens. Palaeo-hydrothermal fluids preserved in fluid inclusions were released by crushing and analysed by mass spectrometry. Helium isotope measurements confirm the absence of a mantle-derived fluid component in gold-bearing veins from the Southern Alps and at the large gold deposit at M...

  6. Interactions between tectonics, erosion, and sedimentation during the recent evolution of the alpine orogen: analogue modeling insights

    OpenAIRE

    Bonnet, Cécile; Malavieille, Jacques; Mosar, Jon

    2008-01-01

    On the basis of a section across the northwestern Alpine wedge and foreland basin, analogue modeling is used to investigate the impact of surface processes on the orogenic evolution. The basis model takes into account both structural and lithological heritages of the wedge. During shortening, erosion and sedimentation are performed to maintain a critical wedge. Frontal accretion leads to the development of a foreland thrust belt; underplating leads to the formation of an antiformal nappe stac...

  7. Early Mesozoic granitoid and rhyolite magmatism of the Bureya Terrane of the Central Asian Orogenic Belt: Age and geodynamic setting

    Science.gov (United States)

    Sorokin, A. A.; Kotov, A. B.; Kudryashov, N. M.; Kovach, V. P.

    2016-09-01

    Early Mesozoic granitoids and volcanic rocks are widespread throughout the structures of all of the continental massifs in the eastern part of the Central Asian Orogenic Belt, although its tectonic setting is not yet clear. Generally, they are associated with subduction and plume processes or rifting. Such uncertainty is mostly explained by the unequal investigation of Early Mesozoic magmatism. This paper presents the results of geochemical, Sm-Nd isotope, and U-Pb geochronologic (ID-TIMS) studies of "key-type" Early Mesozoic magmatic rock complexes of the Bureya Terrane. This is one of the largest continental massifs in the eastern Central Asian Orogenic Belt and knowledge of its geological structure is of fundamental importance in understanding the history of its formation. It has been established that the leucogranites of the Altakhtinsky Complex and the trachyrhyolites of the Talovsky Complex are practically coeval (~ 209-208 Ma). The subalkaline leucogranites of the Kharinsky Complex have a slightly younger age of ~ 199 Ma. These data correspond to the general stage of Early Mesozoic magmatic and metamorphic events (236-180 Ma) in most continental massifs in the eastern Central Asian Orogenic Belt. We believe that large-scale Early Mesozoic events were related to the amalgamation of the continental massifs of the eastern Central Asian Orogenic Belt into a single continental structure (the Amur superterrane or microcontinent Amuria) and collision with the North Asian Craton. It should be noted that the collision processes were followed by crustal thickening, thus creating the conditions for metamorphism and formation of magmatic rock complexes of various geochemical types.

  8. Role of Neogene Exhumation and Sedimentation on Critical-Wedge Kinematics in the Zagros Orogenic Belt, Northeastern Iraq, Kurdistan

    Science.gov (United States)

    Koshnaw, R. I.; Horton, B. K.; Stockli, D. F.; Barber, D. E.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The Zagros orogenic belt and foreland basin formed during the Cenozoic Arabia-Eurasia collision, but the precise histories of shortening and sediment accumulation remain ambiguous, especially at the NW extent of the fold-thrust belt in Iraqi Kurdistan. This region is characterized by well-preserved successions of Cenozoic clastic foreland-basin fill and deformed Paleozoic-Mesozoic hinterland bedrock. The study area provides an excellent opportunity to investigate the linkage between orogenic wedge behavior and surface processes of erosion and deposition. The aim of this research is to test whether the Zagros orogenic wedge advanced steadily under critical to supercritical wedge conditions involving in-sequence thrusting with minimal erosion or propagated intermittently under subcritical condition involving out-of-sequence deformation with intense erosion. These endmember modes of mountain building can be assessed by integrating geo/thermochronologic and basin analyses techniques, including apatite (U-Th)/He thermochronology, detrital zircon U-Pb geochronology, stratigraphic synthesis, and seismic interpretations. Preliminary apatite (U-Th)/He data indicate activation of the Main Zagros Fault (MZF) at ~10 Ma with frontal thrusts initiating at ~8 Ma. However, thermochronometric results from the intervening Mountain Front Flexure (MFF), located between the MZF and the frontal thrusts, suggest rapid exhumation at ~6 Ma. These results suggest that the MFF, represented by the thrust-cored Qaradagh anticline, represents a major episode of out-of-sequence deformation. Detrital zircon U-Pb analyses from the Neogene foreland-basin deposits show continuous sediment derivation from sources to the NNE in Iraq and western Iran, suggesting that out-of-sequence thrusting did not significantly alter sedimentary provenance. Rather, intense hinterland erosion and recycling of older foreland-basin fill dominated sediment delivery to the basin. The irregular distribution of

  9. Syn- and post-orogenic exhumation of metamorphic rocks in North Aegean

    Directory of Open Access Journals (Sweden)

    R. Lacassin

    2007-11-01

    Full Text Available The Olympos-Ossa-Pelion (OOP ranges, in NW Aegean, encompass Greece highest summit and are located near the extremity of the North Anatolian Fault (NAF. Structural and thermochronological data gathered in the OOP ranges show that the main exhumation of metamorphic nappes occurred in the Eocene, at ca. 43–39 Ma. This early exhumation, associated with ductile, then brittle-ductile normal faulting with northeastward transport, is coeval with orogenic shortening in the close area. Cooling rates, and likely exhumation, have been low between ~40 Ma and ~20 Ma. 40Ar/39Ar crystallization ages (between 20 and 15 Ma appears related to brittle-ductile normal faulting and likely associated with Neogene Aegean back-arc extension. The dating of a diabase dyke, and the geometry of associated brittle jointing, of onshore and offshore active normal faults suggest a shift in extension direction after 4Ma, possibly in relation with the propagation of the NAF in northern Aegean.

  10. Polyphase Neoproterozoic orogenesis within the east Africa- Antarctica orogenic belt in central and northern Madagascar

    Science.gov (United States)

    Key, R.M.; Pitfield, P.E.J.; Thomas, Ronald J.; Goodenough, K.M.; Waele, D.; Schofield, D.I.; Bauer, W.; Horstwood, M.S.A.; Styles, M.T.; Conrad, J.; Encarnacion, J.; Lidke, D.J.; O'connor, E. A.; Potter, C.; Smith, R.A.; Walsh, G.J.; Ralison, A.V.; Randriamananjara, T.; Rafahatelo, J.-M.; Rabarimanana, M.

    2011-01-01

    Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid- Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana. ?? The Geological Society of London 2011.

  11. New isotopic ages and the timing of orogenic events in the Cordillera Darwin, southernmost Chilean Andes

    International Nuclear Information System (INIS)

    A well-constrained Rb-Sr isochron age of 157 +- 8 m.y. and an initial 87Sr/86Sr ratio of 0.7087 obtained from a pre-tectonic granitic suite suggest a genetic relation between this suite and Upper Jurassic silicic volcanic rocks in the cover sequence (Tobifera Formation), and also suggest involvement of continental crust in formation of these magmas. A poorly constrained Rb-Sr isochron age of 240 +- 40 m.y. obtained from supposed basement schists is consistent with field relations in the area which suggest a late Paleozoic/early Mesozoic metamorphism for these pre-Late Jurassic rocks. However, because of scatter in the data and the uncertainties involved in dating metasedimentary rocks, the significance of the isotopic age is dubious. Compilation of previously published ages in the area [9] with new mineral ages reported here indicate that early Andean orogenic events occurred between 100 and 84 m.y. ago, and that subduction-related magmatism has contributed, probably discontinuously, to the crustal evolution of the region throughout the Mesozoic. (orig.)

  12. Contrasting Metamorphic Record of Heat Production Anomalies in the Penokean Orogen of Northern Michigan.

    Science.gov (United States)

    Attoh

    2000-05-01

    It is proposed that the contrasting metamorphic mineral assemblages of the isolated amphibolite facies metamorphic highs in the Penokean orogen of northern Michigan may be caused by different heat production rates in the Archean basement. This hypothesis is based on concentrations of K, U, and Th in the Archean basement gneisses and Paleoproterozoic metasediments that indicate significant contribution of radiogenic heating during Penokean metamorphism. Heat production was anomalously high ( approximately 10.6 µWm-3) where andalusite-bearing mineral assemblages indicate that high temperatures were attained at shallow crustal levels ( approximately 550 degrees -600 degrees C at approximately 3 kbar). In contrast, where exposed metamorphic rocks indicate peak temperatures of 600 degrees -650 degrees C at 6-7 kbar, heat production in the Archean basement was lower ( approximately 3.7 µWm-3). The effect of heat production rates on the metamorphic pressure-temperature paths was tested with numerical thermal models. The calculations show (1) that if the heat production rate, where andalusite-bearing assemblages formed, was significantly sillimanite or kyanite stability fields; and (2) differences between PTmax estimates for the metamorphic highs based on thermobarometry can be reproduced if thermal history involved significant crustal thickening as well as moderate unroofing rates. PMID:10769161

  13. Exhumation of an eclogite terrane as a hot migmatitic nappe, Sveconorwegian orogen

    Science.gov (United States)

    Möller, Charlotte; Andersson, Jenny; Dyck, Brendan; Antal Lundin, Ildiko

    2015-06-01

    We demonstrate a case of eclogite exhumation in a partially molten, low-viscosity fold nappe within high-grade metamorphosed crust in the Eastern Segment of the Sveconorwegian orogen. The nappe formed during tectonic extrusion, melt-weakening assisted exhumation and foreland-directed translation of eclogitized crust, and stalled at 35-40 km depth within the collisional belt. The eclogites are structurally restricted to a regional recumbent fold in which stromatic orthogneiss with pods of amphibolitized eclogite make up the core. High-temperature mylonitic gneiss with remnants of kyanite eclogite (P > 15 kbar) composes a basal shear zone 50 km long and eclogite and stromatic orthogneiss constrain the time of eclogitization at 988 ± 6 Ma and 978 ± 7 Ma. Migmatization, concomitant deformation, and exhumation are dated at 976 ± 6 Ma, and crystallization of post-kinematic melt at 956 ± 7 Ma. Orthogneiss protoliths are dated at 1733 ± 11 and 1677 ± 10 Ma (stromatic gneiss) and 1388 ± 7 Ma (augen gneiss in footwall), demonstrating origins indigenous to the Eastern Segment. Eclogitization and exhumation were coeval with the Rigolet phase of the Grenvillian orogeny, reflecting the late stage of continental collision during construction of the supercontinent Rodinia.

  14. A tear fault boundary between the Taiwan orogen and the Ryukyu subduction zone

    Science.gov (United States)

    Lallemand, Serge E.; Liu, Char-Shine; Font, Yvonne

    1997-06-01

    More than twenty seismic lines were analysed across the intersection of the Taiwan orogen and the Ryukyu arc-forearc system. The main results of this study concern the recognition of two superposed sedimentary basins that were previously unknown. We have named the recent one the Hoping Basin and the older, tectonized one the Suao Basin. The Suao Basin, containing sediments more than 3 km thick, records subsidence of about 3 km on its southwestern portion after being shortened in the direction of plate convergence. On the basis of seismicity, gravity, present-day plate kinematics as well as seismic reflection data, we relate the dramatic subsidence of the Suao Basin to the initiation of a WNW-trending tear fault within the Philippine Sea plate. This tear fault decouples the subducting Philippine Sea plate to the northeast and the apparent overthrusting Philippine Sea plate in the Coastal Range to the southwest. Back-arc rifting may thus occur in the westernmost section of the Okinawa trough above the sinking Philippine Sea slab while lithospheric shortening prevails south of Hualien. As a consequence, the triangular area located southwest of the tear fault, between the Taiwan coastline and the toe of the Yaeyama ridge, no longer belongs to the Ryukyu forearc. It is now passively transported with the non-subducting portion of the Philippine Sea plate. We propose an evolutionary model for the relative chronology of tectono-sedimentary events in this region over the last 5 m.y.

  15. Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran

    Directory of Open Access Journals (Sweden)

    Taghipour Batoul

    2015-03-01

    Full Text Available The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ, within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist and footwall (meta-limestone rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO42- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG type shear zone and orogenic type gold mineralisation.

  16. Three-dimensional thermoluminescence spectra of different origin quartz from Altay Orogenic belt, Xinjiang, China

    Energy Technology Data Exchange (ETDEWEB)

    Tan Kaixuan [School of Nuclear Resource and Safety Engineering, University of South China, Hengyang, Hunan 421001 (China)], E-mail: nhtkx@126.com; Liu Zehua; Zeng Sheng; Liu Yan; Xie Yanshi [School of Nuclear Resource and Safety Engineering, University of South China, Hengyang, Hunan 421001 (China); Rieser, Uwe [School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington (New Zealand)

    2009-05-15

    Three-dimensional thermoluminescence spectra are measured for different types of geological origin quartz from the Altay orogenic belt, northern Xinjiang, China. The results show striking differences which appear to be characteristic of their geological origin. Granitic quartz is dominated by emission bands at 420-430 nm, 550-560 nm, at a temperature of 170 deg. C. Pegmatite quartz is characterized by an intense 480 nm emission band at 170 deg. C. Volcanic quartz has exclusive UV (340-360 nm) and violet (410-430 nm) emission bands. Hydrothermal quartz exhibits very different TL spectral characteristics because of different hydrothermal activity and mineralization. Only one TL peaks at 485 nm/170 deg. C was observed in sedimentary quartz. An intense 730 nm emission band observed at 170 deg. C considered generally to be characteristics of feldspar was observed in quartz from granite and hydrothermal Au-bearing quartz. This TL peak is probably related to the centre of [FeO{sub 4}]{sup 0} on an Si site. All samples show an intense 990-1000 nm emission band at 330 deg. C. Identical types of quartz formed in different regions or different geological and tectonic settings can also exhibit striking differences in TL spectra.

  17. Modelling of current crustal tectonic deformation in the Chinese Tianshan orogenic belt constrained by GPS observations

    International Nuclear Information System (INIS)

    It is important to discover the deformation characteristics of the Tianshan mountain range for a better understanding of the geodynamics of the Tianshan orogenic belt. Constrained by the GPS-derived velocity vectors of crustal movement, the current velocity field, stress field and strain rate in the Tianshan mountains have been retrieved from a three-dimensional numerical model presented in this paper by using the finite-element code ANSYS, on the basis of geological structures, tectonic regimes, active fault belts and seismic velocity structures of the crust and upper mantle. The results suggest that: (1) the general direction of crustal movement is NNE, and yet gradually turns to NE from west to east; (2) the regional stress field is characterized by near N–S tectonic compression, resulting in crustal shortening in the near N–S direction as well; and (3) the shortening strain rate is ∼10−8 a−1 and decreases gradually from west to east. Our results support the opinion that the crustal deformation of the Tianshan mountain range is controlled by the clockwise rotation of the Tarim basin

  18. Partial melting of deeply subducted eclogite from the Sulu orogen in China.

    Science.gov (United States)

    Wang, Lu; Kusky, Timothy M; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2014-01-01

    We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U-Pb dating and petrological analyses, that partial melting occurred at 228-219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619

  19. Strong Lg-wave attenuation in the Middle East continental collision orogenic belt

    Science.gov (United States)

    Zhao, Lian-Feng; Xie, Xiao-Bi

    2016-04-01

    Using Lg-wave Q tomography, we construct a broadband crustal attenuation model for the Middle East. The QLg images reveal a relationship between attenuation and geological structures. Strong attenuation is found in the continental collision orogenic belt that extends from the Turkish and Iranian plateau to the Pamir plateau. We investigate the frequency dependence of QLg in different geologic formations. The results illustrate that QLg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions. An average QLg value between 0.2 and 2.0 Hz, QLg (0.2-2.0 Hz), may be a critical index for crustal attenuation and is used to infer the regional geology. Low-QLg anomalies are present in the eastern Turkish plateau and correlate well with low Pn-velocities and Cenozoic volcanic activity, thus indicating possible partial melting within the crust in this region. Very strong attenuation is also observed in central Iran, the Afghanistan block, and the southern Caspian Sea. This in line with the previously observed high crustal temperature, high-conductivity layers, and thick marine sediments in these areas, suggests the high Lg attenuation is caused by abnormally high tectonic and thermal activities.

  20. Finding of Neoproterozoic low-18O igneous rocks in the northern margin of the Dabie orogen

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yongfei; WU Yuanbao; ZHAO Zifu; GONG Bing

    2004-01-01

    @@ It has been one of the most intriguing questions in the earth sciences whether the snowball Earth event is genetically associated with mantle superwelling, supercontinent assemblage and breakup, and rift magmatism during the Neoproterozoic[1-4]. In order to demonstrate the occurrence of significant interaction in energy and matter between the earth's interior and exterior in this period, it is critical to find coeval igneous rocks that contain the signature of surface water and thus form low-18O magma.Several investigations of U-Pb dating and O isotope analysis were carried out for zircons from ultrahigh pressure (UHP) metamorphic rocks in the Dabie-Sulu orogen,east-central China[5-8]. The results indicate that low δ18O zircons have U-Pb ages of 700-800 Ma as dated by either TIMS discordia upper-intercept or SIMS in-situ magmatic core, and the origin of low δ18O water is related to cold paleoclimate during the Sturtian ice age.

  1. Partial melting of deeply subducted eclogite from the Sulu orogen in China

    Science.gov (United States)

    Wang, Lu; Kusky, Timothy M.; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2014-01-01

    We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619

  2. Tip to midpoint observations on syntectonic veins, Ouachita orogen, Arkansas: Trading space for time

    Science.gov (United States)

    Cervantes, Pablo; Wiltschko, David V.

    2010-08-01

    By examining a vein from its tip to center, we have established the transition from a single filled fracture at the vein tip to typical 'crack-seal' textures observed in fibered, laminated veins. The vein is contained in the boudin neck of a sandstone layer within the Lower Ordovician Mazarn Formation, Benton Uplift, Ouachita orogen. The tip of the vein is composed of one or more isolated veinlets, defined as quartz-filled narrow (5-25 μm) fractures parallel to the larger vein's long dimension. Scanned SEM-based cathodoluminescence shows that quartz laminae of the same orientation and thickness are found throughout the vein. Wall-normal fibers first appear in the vein where detrital grains are cut by multiple veinlets, each veinlet mimicking the crystallographic orientation of the detrital grain, whereas later veinlets reflect the established crystallographic orientation of the fiber. Fibers throughout the vein retain evidence of having been formed by repeated fracturing and filling of a pre-existing grain (at the vein walls) or fiber. However, recrystallization later modified the fibers by obliterating some evidence of the veinlets and moving fiber walls. Boudin formation provided the extension site that localized fracturing and vein filling. The vein grows by the repeated addition of veinlets in the neck region. Recrystallization altered the shape of previously formed fibers.

  3. Low-temperature thermochronology of the northern Thomson Orogen: Implications for exhumation of basement rocks in NE Australia

    Science.gov (United States)

    Verdel, Charles; Stockli, Daniel; Purdy, David

    2016-01-01

    The Tasmanides of eastern Australia record much of the Phanerozoic tectonic development of the retreating Pacific-Australia plate boundary and are an oft-cited example of an orogen that has undergone "tectonic mode switching." To begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the NE Tasmanides, we measured apatite and zircon (U-Th)/He ages from the Thomson Orogen and overlying Paleozoic strata in the back-arc of the New England Orogen in NE Australia. Zircon (U-Th)/He ages from basement samples (including those recovered from boreholes at depths of up to 1.1 km) are characterized by large inter- and intra-sample variability and range from approximately 180 Ma (Early Jurassic) to 375 Ma (Late Devonian). (U-Th)/He zircon ages from several individual samples are negatively correlated with effective uranium (eU), a pattern that is also true of the dataset as a whole, suggesting that variations in U and Th zoning and radiation damage are partially responsible for the age variability. The oldest zircon (U-Th)/He cooling ages coincide with the formation of regionally extensive Late Devonian-early Carboniferous back-arc basins, suggesting that Late Devonian extension played a significant role in exhumation of parts of the northern Thomson Orogen. Apatite (U-Th)/He ages from a basement sample and a late Permian sandstone in the overlying Bowen Basin, which are also marked by intra-sample variability and age-eU correlations, span from the Early Cretaceous through Oligocene, in general agreement with previous apatite fission track data. In conjunction with observations of key geologic relationships and prior K-Ar and 40Ar/39Ar data, our results suggest four overall phases in the thermal history of the northern Thomson Orogen: (1) Cambrian-early Silurian metamorphism during the Delamerian and Benambran Orogenies; (2) protracted cooling during the Late Devonian through mid-Permian that likely resulted from extensional

  4. Cambro-Ordovician Granites in the Araçuaí Belt, in Brazil: snapshots from a late orogenic collapse

    Science.gov (United States)

    De Campos, Cristina P.; Mendes, Júlio Cesar; de Medeiros, Silvia Regina; Ludka, Isabel P.

    2014-05-01

    Along the Brazilian Coast, surrounding the São Francisco Craton and adjacent mobile belts, deep segments of a Neoproterozoic orogen (Araçuaí-West Congo) generated over 120 Ma of successive magmatic episodes of granitic magmatism. The c.630-585 Ma calc-alkaline magmatic arc consists of metatonalite to metagranodiorite, with metadioritic to noritic facies and enclaves. During the syn-collisional and crustal thickening stage (c. 585 to 560 Ma) S-type metagranites have been built by dehydration melting of a diverse package of sediments. Around 545-525 Ma late orogenic crustal remelting formed mostly non-foliated garnet-cordierite leucogranites. In the post-orogenic stage (c. 510-480 Ma) inversely zoned calc-alkaline to alkaline plutons intruded previous units. This work will focus on the youngest post-orogenic magmatism. It will present the state of the art by reviewing structural measurements, detailed mapping of flow patterns and additional geochemical and isotopic data. The architecture of around 10 plutons, ranging from c. 20 to 200 km2 in surface area, unravels deep mushroom- to funnel-like magma chambers and/or conduits. Available data point towards different compositional domains, which are interfingered in complex concentric layers, so that, each pluton depicts a unique internal flow pattern. In the silica-richer structures concentric fragmented or folded layers of granite, in a hybrid K-gabbroic/dioritic matrix, contrast with predominantly homogeneous K-basaltic to gabbroic regions. These may be separated by magmatic shear zones where mixing is enhanced, also resulting in hybrid compositions. Sharp and pillow-like contacts between granitic and K-basaltic rocks locally depict a frozen-in situation of different intrusive episodes. In the silica-poorer plutonic bodies gradational contacts are more frequent and may be the result of convection enhanced diffusion. For all plutons, however, mostly sub-vertical internal contacts between most- and least

  5. Microstructural analysis of the Greater Himalayan Sequence, Annapurna-Dhaulagiri Himalaya, central Nepal: Channel Flow and Orogen-parallel deformation.

    Science.gov (United States)

    Parsons, A. J.; Phillips, R. J.; Lloyd, G. E.; Searle, M. P.; Law, R. D.

    2014-12-01

    Knowledge of deformation processes that occur in the lithosphere during orogenesis can be gained from microstructural analysis of exhumed terranes and shear zones. Here, we use Crystallographic Preferred Orientation (CPO) and Anisotropy of Magnetic Susceptibility (AMS) data to reveal the kinematic evolution of the metamorphic core of the Himalayan orogen, the Greater Himalayan Sequence (GHS). The Himalayan orogen is commonly explained with models of channel flow, which describe the GHS as a partially molten, rheologically weak mid crustal channel. Extrusion of the channel was facilitated by coeval reverse- and normal-sense shear zones, at the lower and upper channel margins respectively. Whilst many thermobarometric studies support the occurrence of channel flow, the spatial and temporal distribution of strain within the GHS is one aspect of the model that is yet to be fully resolved. We present a quantified strain proxy profile for the GHS in the Annapurna-Dhaulagiri region of central Nepal and compare our results with the kinematic predictions of the channel flow model. Samples were collected along a NS transect through the Kali Gandaki valley of central Nepal for CPO and AMS analysis. Variations in CPO strength are used as a proxy for relative strain magnitude, whilst AMS data provide a proxy for strain ellipsoid shape. Combining this information with field and microstructural observations and thermobarometric constraints reveals the kinematic evolution of the GHS in this region. Low volumes of leucogranite and sillimanite bearing rocks and evidence of reverse-sense overprinting normal-sense shearing at the top of the GHS suggest that channel flow was not as intense as model predictions. Additionally, observed EW mineral lineations and oblate strain ellipsoid proxies in the Upper GHS, indicative of three dimensional flattening and orogen parallel stretching, cannot be explained by current channel flow models. Whilst the results do not refute the occurrence of

  6. New assemly model of Jiangnan Orogen: insight from detrital zircon geochronology of pre-Cretaceous strata, South China

    Science.gov (United States)

    Su, J.; Dong, S.

    2013-12-01

    The Jiangnan Orogen separates the Yangtze and Cathaysian Blocks in South China and provokes a longstanding debate on the amalgamation history between the two Blocks. The assembly of the two Blocks is termed Sibao orogeny marked by undeformed Late Neoproterozoic strata (Banxi Group) overlying on the deformed Early Neoproterozoic strata (Lengjiaxi Group) in China. Detrital zircons can provide critical links in recognizing the source history of a deposit, sedimentary dispersal systems and tectonic reconstructions. Therefore, fifteen sandstone samples taken from pre-Cretaceous strata of Yangtze Block are analyzed to constrain the evolution of the South China Block (SCB), especially the assembly between Yangtze and Cathaysia Blocks. The results show that the detrital zircons from the Neoproterozoic Lengjiaxi Group (ca. 830 Ma) near the boundary of large detachment fault of Hengshan have similar age populations with that in the other sites of the Jiangnan Orogen, different from that of the Kunyang and Dahongshan Groups (>960 Ma) in the southwestern margin of the Yangtze Block. The detrital zircons from Paleozoic samples have similar age populations with that in the Cathaysia Block. We infer that they originate from the Cathaysia Block, together with paleogeography, paleocurrent and former research. The detrital zircons of middle-late Jurassic sandstones in southwestern and central Yangtze yield dominant populations at 2.0-1.7 Ga and subordinate Groups of 2.6-2.4Ga, 0.7-0.8Ga and 0.6-0.4Ga. The provenance of late Triassic strata may be derived from southern Yangtze and North China Block due to the collisions among the Indosina, South China and North China Blocks, whereas the Jurassic sediments may be partly derived from uplift erosion of Jiangnan Orogen due to intra-continental orogeny induced by pacific subduction towards Eurasia Plate. The tectothermal event occurred at ca. 1.1-0.8 Ga has long been attributed to the assembly or breakup of Yangtze and Cathaysia Blocks

  7. Linking orogen and peripheral foreland basin: conceptual model and application to the Southalpine-Dinaric (Friuli) orocline

    Science.gov (United States)

    Heberer, Bianca; Neubauer, Franz

    2010-05-01

    Surface uplift and rock exhumation within an orogen are generally a consequence of convergence, and can often be linked with subsidence in a peripheral foreland. Since vertical loads act on the entire lithosphere, these processes can, therefore, be considered as plate-scale processes. Here, we propose a conceptual model for this linkage for the Friuli orocline and its surrounding units. The Friuli orocline stretches from the ENE-trending Southern Alps to the SE-trending Dinarides. There, two Neogene stages of convergence and associated deformation can be differentiated: (1) a Mid-Late Miocene phase of increased surface uplift and intra-orogenic subsidence of sedimentary basins reflecting intra-orogenic crustal-scale folding. Depocentres are e.g. the flexural Belluno, Ljubljana and Klagenfurt basins. (2) A second stage of convergence during Late Pliocene-Pleistocene times led to overall surface uplift in the orogen and contemporaneous pronounced subsidence in the peripheral foreland basin (Venetian platform and the northern Adriatic Sea). We propose, that the spatially variable extent of subsidence originates in variably strong orogen-basin coupling, i.e. weak coupling during stage 1 vs. strong coupling during stage 2. This interpretation is based on the apatite fission track age pattern, the distribution of intra-orogenic Neogene sediment basins and subsidence analyses in the foreland basin (Barbieri et al., 2007). Available low-temperature thermochronological data for the Southern Alps and the NW Dinarides are sparse, in contrast to a dense network of primarily apatite fission track ages north of the Periadriatic lineament (e.g. summarized by Luth & Willingshofer, 2008). AFT ages adjacent to the eastern Periadriatic Lineament mainly range from 15 to 25 Ma (Hejl, 1997; Fodor et al., 2008). Detrital studies on Oligocene to Miocene sediments from the Venetian foreland basin yielded dominant age groups clustering roughly around 20 and 30 Ma (Stefani et al., 2008

  8. Chepe Metralla semblanza empresarial y política de José María Bernal Bernal

    Directory of Open Access Journals (Sweden)

    Luis Fernando Molina Londoño

    2014-03-01

    Full Text Available El objetivo de este trabajo es relacionar y descubrir algunos hechos que muestran las motivaciones de la intervención de los industriales en política mediante el caso del ingeniero, empresario y político José María Bernal Bernal, muy activo entre 1918 y 1958. Sus actuaciones, durante el denominado periodo de la Violencia en las décadas de 1940 y 1958, influyeron sobre los negocios, el gremio de los industriales, el Partido Conservador, la seguridad interna, la infraestructura energética y la hacienda pública en este complejo periodo de la historia colombiana.

  9. Patterns of glaciation and topographic hypsometry across semi-arid western Himalayan-Tibetan orogen (Invited)

    Science.gov (United States)

    Dortch, J.; Hughes, P.; Owen, L. A.; Murari, M. K.; Caffee, M. W.

    2013-12-01

    It has been hypothesized that the reduction of mountain glacier extent throughout late Quaternary glacial cycles may reflect adjustment of topographic hypsometry and lowering of accumulation area via glacial erosion. The Himalayan-Tibetan orogen represents a good test case due to high relief, fast rates of erosion, and recently developed regional glacial chronologies. In particular, analysis of all terrestrial cosmogenic nuclide ages of moraines in the drylands of the western Himalayan-Tibetan orogen show 16 regional glacial stages extending back >300 ka; stages older than the global Last Glacial Maximum (gLGM) broadly correlate with strong monsoons, while younger stages correlate with northern hemisphere climatic events. These patterns suggest that frequent glacial advances are driven by mid-latitude westerlies within each glacial cycle, but that each cycle is punctuated by more extensive advances driven by the monsoon. This raises the question of which style of glaciation has the greatest effect on the shaping and incision of topography: frequent, less-extensive variations in glaciation, or infrequent more-extensive advances (the latter being akin to punctuated equilibrium)? To investigate this question, changes in glacier position based on moraines and climatic proxies are used to model changes in equilibrium line altitude (ELA), which is then compared to topographic hypsometry in catchments were the glacial buzzsaw hypothesis has been previously invoked. The loss in resolution due to the decrease in moraine preservation through time must be accounted for. Thus, the MIS curve and monsoon index are combined to fit to the regional chronology with the view that ages represents the minimum age of deglaciation. A best fit curve is used as a proxy for glacial extent to estimate higher-frequency fluctuations for the pre-gLGM portion of the regional chronology. ELAs are then calculated for selected glaciers at various extents to enable the determination of the average

  10. Geochemistry of metavolcanics from the Neoproterozoic Tuludimtu orogenic belt, western Ethiopia

    Science.gov (United States)

    Tadesse, Gebremedhin; Allen, Alistair

    2004-06-01

    The 200 km wide Tuludimtu Belt of Western Ethiopia is one of a series of N-S trending Neoproterozoic orogenic belts of the East African Orogenic Province in southeastern Sudan and western and southern Ethiopia. The Tuludimtu Belt consists of deformed greenschist facies metasediments and metavolcanics, flanked to the east and west by gneissic terranes, all of which are invaded by pre-, syn- and post-tectonic intrusives ranging from ultramafic to felsic in composition. The Tuludimtu Belt has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka Domains. On the basis of lithological associations, the three domains in the core of the belt, the Kemashi, Dengi and Sirkole Domains, are respectively interpreted to represent an ophiolitic terrane of oceanic crustal origin, a volcanic arc, and a fold-thrust terrane composed of interleaved thrust sheets of gneissic basement and cover strata. The Didesa and Daka Domains are composed of moderate- to high-grade gneisses, possibly representing the basement forelands to the belt. Major and trace element geochemistry for metavolcanics of predominantly basaltic and andesitic composition from the Kemashi, Dengi and Didesa Domains, are presented, and a preliminary analysis of the data undertaken. Two suites of metavolcanics are clearly differentiated by the discrimination diagrams. The samples from all three domains are predominantly tholeiitic, subalkaline basalts and andesites. Bivariate plots reveal weak negative correlations of SiO 2 and Al 2O 3 with MgO, and a positive correlation of CaO with MgO, indicating that magmas evolved by fractionation of clinopyroxene, orthopyroxene and olivine from the parent liquids. Trace element spider diagrams show a tight coherence of patterns for the Dengi and Sirkole samples, suggestive that alteration did not accompany metamorphic processes to any great extent, and a slight depletion of HFS elements possibly due to fractionation

  11. Arsenic mobility in mildly alkaline drainage from an orogenic lode gold deposit, Bralorne mine, British Columbia

    International Nuclear Information System (INIS)

    Highlights: • As concentrations in flooded anoxic mine workings in range of 6000 μg/L. • Sorbed As released in workings by reductive dissolution of accumulated HFO. • As concentrations in portal effluent in range of 3000 μg/L. • Limited natural attenuation of As due to high pH and the lack of Fe sorbent. • Partitioning of As in effluent described by a field-scale distribution coefficient. - Abstract: The historical (1932–1971) Bralorne mine produced over 87 million grams of Au from an archetypal orogenic lode gold deposit in southwest British Columbia. High concentrations of As in mine drainage, however, represent an on-going environmental concern prompting a detailed study of effluent chemistry. The discharge rate at the mine portal was monitored continuously over a fourteen-month period during which effluent samples were collected on a quasi-weekly basis. Water samples were also collected on synoptic surveys of the adit between the portal and the main source of flow in the flooded workings. Total concentrations of As in the mildly alkaline (pH = 8.7) portal drainage average 3034 μg/L whereas at the source they average 5898 μg/L. As emergent waters from the flooded workings flow toward the portal, their dissolved oxygen content and pH increase from 0 to 10 mg/L and from 7.7 to 9, respectively. Near the emergence point, dissolved Fe precipitates rapidly, sorbing both As(III) and As(V). With increasing distance from the emergence point, dissolved As(III) concentrations drop to detection limits through sorption on hydrous ferric oxide and through oxidation to As(V). Concentrations of dissolved As(V), on the other hand, increase and stabilize, reflecting lower sorption at higher pH and the lack of available sorbent. Nonetheless, based on synoptic surveys, approximately 35% of the source As load is sequestered in the adit resulting in As sediment concentrations averaging 8.5 wt%. The remaining average As load of 1.34 kg/d is discharged from the portal

  12. Origin of Relief in a Collisional Orogen: the Case of the Canadian Rockies

    Science.gov (United States)

    Osborn, G.; Stockmal, G.; Haspel, R.

    2005-12-01

    Contrary to popular assumption, the mountainous local relief of the Canadian Rockies probably did not originate with the thrusting that characterized the Laramide Orogeny; rather, that relief is a post-orogenic phenomenon. The magnitude of present local relief in the Rockies thrust-and-fold belt (TFB) depends the relative erosional resistance of rocks exposed at the surface. The mountains consist of high ridges of well-indurated Paleozoic and Proterozoic rocks carried by thrust faults, alternating with valleys developed in softer Mesozoic clastic rocks, whereas in the foothills, where the less-resistant Mesozoic rocks are at the surface, relief is subdued. Mesozoic rocks originally blanketed the entire width of what is now the TFB, and local physiography of the belt at the end of Laramide (EOL) time must have depended on whether the Mesozoic rocks had been erosionally removed to expose the underlying, resistant Paleozoic rocks. A reconstruction of the TFB using critical-taper theory generally agrees with reconstructions from earlier stratigraphic and paleothermometry studies: what are now the front ranges in the eastern Rockies were still covered with Mesozoic rocks at the EOL. Hence this part of the belt may have comprised a high-elevation upland of relatively low relief, perhaps broadly similar to the Tibetan Plateau. Generation of modern relief, including the escarpment at the mountain front, had to await stripping of Mesozoic rocks and incision of rivers into harder substrates in post-EOL time. In the 'main ranges' in the western part of the TFB, thrusting and consequent erosion began earlier. Mesozoic cover was partly stripped off by EOL time, and probably locally in early Cretaceous time, so that part of the belt probably displayed 'mountainous' relief then. But the evolution there probably was the same, from original high-elevation, low-relief plateau to later rugged mountains.

  13. Post-collisional lithosphere delamination of the Dabie-Sulu orogen

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    two sides of the orogen.

  14. Transpressional deformation, strain partitioning and fold superimposition in the southern Chinese Altai, Central Asian Orogenic Belt

    Science.gov (United States)

    Li, Pengfei; Sun, Min; Rosenbaum, Gideon; Cai, Keda; Chen, Ming; He, Yulin

    2016-06-01

    Transpressional deformation has played an important role in the late Paleozoic evolution of the western Central Asian Orogenic Belt (CAOB), and understanding the structural evolution of such transpressional zones is crucial for tectonic reconstructions. Here we focus on the transpressional Irtysh Shear Zone with an aim at understanding amalgamation processes between the Chinese Altai and the West/East Junggar. We mapped macroscopic fold structures in the southern Chinese Altai and analyzed their relationships with the development of the adjacent Irtysh Shear Zone. Structural observations from these macroscopic folds show evidence for four generations of folding and associated fabrics. The earlier fabric (S1), is locally recognized in low strain areas, and is commonly isoclinally folded by F2 folds that have an axial plane orientation parallel to the dominant fabric (S2). S2 is associated with a shallowly plunging stretching lineation (L2), and defines ∼NW-SE tight-close upright macroscopic folds (F3) with the doubly plunging geometry. F3 folds are superimposed by ∼NNW-SSE gentle F4 folds. The F3 and F4 folds are kinematically compatible with sinistral transpressional deformation along the Irtysh Shear Zone and may represent strain partitioning during deformation. The sub-parallelism of F3 fold axis with the Irtysh Shear Zone may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation (F3) in fold zones. The strain partitioning may have become less efficient in the later stage of transpressional deformation, so that a fraction of transcurrent components was partitioned into F4 folds.

  15. CHIME dating method and its application to the analysis of evolutional history of orogenic belts

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Kazuhiro; Adachi, Mamoru; Kato, Takenori; Yogo, Setsuo [Nagoya Univ. (Japan)

    1999-03-01

    This paper outlines the CHIME (chemical Th-U-total Pb isochron method: Suzuki and Adachi, 1991a, b; Adachi and Suzuki, 1992) dating method and reviews its application to the event analysis of orogenic belts. The reviewed examples of the CHIME geochronology include (1) the electron microprobe observations of Pb diffusion in metamorphosed detrital monazites from high-grade Ryoke paragneisses (Suzuki et al., 1994), (2) the recycled Precambrian clastic materials from the Mino terrane (Adachi and Suzuki, 1993, 1994), (3) the late Permian-early Triassic metamorphism and plutonism in the Hida terrane (Suzuki and Adachi, 1991b, 1994), (4) the relationship between the Hikami Granite and Siluro-Devonian clastic rocks in the South Kitakami terrane (Suzuki et al, 1992; Adachi et al., 1994), and (5) the denudation history of the high T/P Ryoke metamorphic belt (Suzuki and Adachi, 1998). The CHIME dating method is based on precise electron microprobe analyses of Th, U and Pb as low as 0.01wt.% in an area of 5 {mu}m across within a single grain of compositionally ununiformed Th-and U-bearing accessory minerals like monazite and zircon. This method has an advantage of high spatial resolution, and provides a new vista on the study of igneous, metamorphic and sedimentary rocks that underwent complex thermo-tectonic history. Monazite is most suitable to the CHIME dating, since it shows a concordant Th-U-Pb relation, contains 5-20 wt.% ThO{sub 2} and 0.1-1.5wt.% UO{sub 2} that can produce 0.01-0.06wt.% PbO during 50 Myr, and remains immune to significant Pb-loss during the sillimanite grade metamorphism; it has great chronological potential for the analysis of the detailed sequence of geologic events. (author)

  16. Post-orogenic exhumation history of a Variscan mid-crustal basement in Galicia (NW Spain)

    Science.gov (United States)

    Grobe, Rene; Alvarez-Marrón, Joaquina; Glasmacher, Ulrich A.; Stuart, Finlay; Castañeda-Zarauz, A.

    2010-05-01

    The present study aims to quantify the complex post-orogenic history of cooling, denudation, and long-term landscape evolution of a mid-crustal section of Variscan basement in Galicia (NW Spain). We use apatite fission-track and apatite (U-Th)/He thermochronological techniques combined with time-temperature (t-T) path modelling using the software code HeFTy©. The topography is characterized by an extensive, low relief area at ~500 m elevation in central Galicia, and a WNW-ESE ridge that reaches up to 1000 m to the North. The area experienced two major tectonic events since the end of the Variscan orogeny in the Late Palaeozoic: 1) continental break-up and Mesozoic rifting leading to the opening of the Atlantic Ocean and the Bay of Biscay, and 2) limited convergence between Iberia and Eurasia since Middle Eocene times. Apatite fission-track ages range from 68.1 ± 5.0 Ma to 174.5 ± 7.7 Ma and apatite (U-Th)/He ages range from 73.6 ± 5.4 to 147.1 ± 16.6 Ma. Age-elevation plots and t-T path modelling suggest a tectonothermal evolution with faster exhumation associated to faulting during Mesozoic rifting. In particular, two major fault systems trending WNW-ESE and NNE-SSW, the As Pontes and the Lugo faults respectively separate areas with the fastest exhumation around 115 Ma from areas with overall slow exhumation since 200-150 Ma. A landscape of subdued topography in central Galicia was acquired prior to Eocene convergence. The higher elevation areas along the northern ridge formed since Middle Eocene times due to fault reactivation and minor exhumation occurred along the fault escarpment.

  17. From orogenic collapse to rifting ; structures of the South China Sea

    Science.gov (United States)

    Pubellier, M.; Chan, L. S.; Chamot Rooke, N.; Shen, W.; Ringenbach, J. C.

    2009-04-01

    The opening of the South China Sea has been a matter of debate for many years because of its internal structure, the differences between the conjugate margins and the variations of rifting and spreading directions. Although it is considered as being a back-arc basin, it is not sitting directly above a subduction zone, and the rifting process lasted for an unusually long duration. Among the specific characteristics is the early phase of rifting which took place early in place of the former Yanshanian andean-type mountain range. This stage is marked by narrow basins filled with deformed conglomerate, and initiated around 70My ago within a framework where the oblique subduction marked by igneous activity and ductile wrench faults, was replaced by orogenic collapse. The rifting stage is marked by Eocene syntectonic normal faults and occasional volcanics centres and has proceeded from NW-SE to NS extension. The NW stretching created at least two aborted basins which remained at rift stage. Extension was followed by spreading from 33 to ~20 Ma in the South China Sea. The ocean floor spreading also changed direction to NW-SE with a propagator inside the Sunda shelf from 20 to 17My ago. However the propagator opening implies that deformation is also taken by rifting around a southern wedge which in turn created strain inside the thinned crust. Another extension parallel to the margin is also observed althought the spreading was in process. The southward motion of the southern conjugate margin was later accommodated by its subduction beneath the NW Borneo wedge until completion of the Proto South China Sea subduction. Variations of rifting spreading through time and variations of structural styles are discussed in terms of boundary forces acting to the SE.

  18. CHIME dating method and its application to the analysis of evolutional history of orogenic belts

    International Nuclear Information System (INIS)

    This paper outlines the CHIME (chemical Th-U-total Pb isochron method: Suzuki and Adachi, 1991a, b; Adachi and Suzuki, 1992) dating method and reviews its application to the event analysis of orogenic belts. The reviewed examples of the CHIME geochronology include (1) the electron microprobe observations of Pb diffusion in metamorphosed detrital monazites from high-grade Ryoke paragneisses (Suzuki et al., 1994), (2) the recycled Precambrian clastic materials from the Mino terrane (Adachi and Suzuki, 1993, 1994), (3) the late Permian-early Triassic metamorphism and plutonism in the Hida terrane (Suzuki and Adachi, 1991b, 1994), (4) the relationship between the Hikami Granite and Siluro-Devonian clastic rocks in the South Kitakami terrane (Suzuki et al, 1992; Adachi et al., 1994), and (5) the denudation history of the high T/P Ryoke metamorphic belt (Suzuki and Adachi, 1998). The CHIME dating method is based on precise electron microprobe analyses of Th, U and Pb as low as 0.01wt.% in an area of 5 μm across within a single grain of compositionally ununiformed Th-and U-bearing accessory minerals like monazite and zircon. This method has an advantage of high spatial resolution, and provides a new vista on the study of igneous, metamorphic and sedimentary rocks that underwent complex thermo-tectonic history. Monazite is most suitable to the CHIME dating, since it shows a concordant Th-U-Pb relation, contains 5-20 wt.% ThO2 and 0.1-1.5wt.% UO2 that can produce 0.01-0.06wt.% PbO during 50 Myr, and remains immune to significant Pb-loss during the sillimanite grade metamorphism; it has great chronological potential for the analysis of the detailed sequence of geologic events. (author)

  19. Geological setting and tectonic subdivision of the Neoproterozoic orogenic belt of Tuludimtu, western Ethiopia

    Science.gov (United States)

    Allen, Alistair; Tadesse, Gebremedhin

    2003-05-01

    The N-S trending Tuludimtu Belt in the extreme west of Ethiopia has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka domains. The Kemashi, Dengi and Sirkole Domains, forming the core of the belt, contain volcano-sedimentary successions, whilst the Didesa and Daka Domains are gneiss terranes, interpreted to represent the eastern and western forelands of the Tuludimtu Belt. The Kemashi Domain, which consists of an ophiolitic sequence of ultramafic and mafic volcanic and plutonic rocks together with sedimentary rocks of oceanic affinity, is interpreted as oceanic crust and is considered to represent an arc-continent suture zone. The Dengi Domain, composed of mafic to felsic volcanic and plutonic rocks, and a sequence of volcanoclastic, volcanogenic, and carbonate sediments, is interpreted as a volcanic arc. The Sirkole Domain consists of alternating gneiss and volcano-sedimentary sequences, interpreted as an imbricated basement-cover thrust-nappe complex. All the domains are intruded by syn- and post-kinematic Neoproterozoic granitoids. Structural analysis within the Didesa and Daka Domains indicate the presence of pre-Pan African structures, upon which Neoproterozoic deformation has been superimposed. The gneissic rocks of these two domains are regarded as pre-Pan African continental fragments amalgamated to West Gondwana during Neoproterozoic collision events. Unconformably overlying all of the above are a series of tilted but internally undeformed conglomerate-sandstone-shale sequences, regarded as post-accretionary molasse-type deposits, formed during gravitational collapse of the Tuludimtu Belt. The Tuludimtu Belt is interpreted as a collision orogenic belt formed during the assembly of West Gondwana prior to final closure of the Mozambique Ocean.

  20. Tectonic, magmatic, and metallogenic evolution of the Late Cretaceous arc in the Carpathian-Balkan orogen

    Science.gov (United States)

    Gallhofer, Daniela; Quadt, Albrecht von; Peytcheva, Irena; Schmid, Stefan M.; Heinrich, Christoph A.

    2015-09-01

    The Apuseni-Banat-Timok-Srednogorie Late Cretaceous magmatic arc in the Carpathian-Balkan orogen formed on the European margin during closure of the Neotethys Ocean. It was subsequently deformed into a complex orocline by continental collisions. The Cu-Au mineralized arc consists of geologically distinct segments: the Apuseni, Banat, Timok, Panagyurishte, and Eastern Srednogorie segments. New U-Pb zircon ages and geochemical whole rock data for the Banat and Apuseni segments are combined with previously published data to reconstruct the original arc geometry and better constrain its tectonic evolution. Trace element and isotopic signatures of the arc magmas indicate a subduction-enriched source in all segments and variable contamination by continental crust. The magmatic arc was active for 25 Myr (~92-67 Ma). Across-arc age trends of progressively younger ages toward the inferred paleo-trench indicate gradual steepening of the subducting slab away from the upper plate European margin. This leads to asthenospheric corner flow in the overriding plate, which is recorded by decreasing 87Sr/86Sr (0.70577 to 0.70373) and increasing 143Nd/144Nd (0.51234 to 0.51264) ratios over time in some segments. The close spatial relationship between arc magmatism, large-scale shear zones, and related strike-slip sedimentary basins in the Timok and Pangyurishte segments indicates mild transtension in these central segments of the restored arc. In contrast, the Eastern Srednogorie segment underwent strong orthogonal intraarc extension. Segmental distribution of tectonic stress may account for the concentration of rich porphyry Cu deposits in the transtensional segments, where lower crustal magma storage and fractionation favored the evolution of volatile-rich magmas.

  1. The Ust-Belaya ophiolite terrane, West Koryak Orogen: Isotopic dating and paleotectonic interpretation

    Science.gov (United States)

    Palandzhyan, S. A.

    2015-03-01

    The Ust-Belaya ophiolite terrane in the West Koryak Orogen, which is the largest in northeastern Asia, consists of three nappe complexes. The upper Ust-Belaya Nappe is composed of a thick (>5 km) sheet of fertile peridotites and mafic rocks (remnants of the proto-Pacific lithosphere); its upper age boundary is marked by Late Neoproterozoic plagiogranites. In the middle Tolovka-Otrozhny Nappe, the Late Precambrian lherzolite-type ophiolites are supplemented by fragments of tectonically delaminated harzburgite-type ophiolites, which make up the Tolovka rock association. The isotopic age of metadacite (K-Ar method, whole-rock sample) and zircons from plagiogranite porphyry (U-Pb method, SHRIMP) determines the upper chronological limit of the Tolovka ophiolites as 262-265 Ma ago. It is suggested that igneous rocks of these ophiolites were generated in a backarc basin during the Early Carboniferous and then incorporated into the fold-nappe structure in the Mid-Permian. This was the future basement of the Koni-Taigonos arc, where the Early Carboniferous ophiolites together with Late Neoproterozoic precursors were subject to low-temperature metamorphism and intruded by plagiogranite porphyry dikes in Permian-Triassic. The polymicte serpentinite mélange, which was formed in the accretionary complex of the Koni-Taigonos arc comprises rock blocks of the upper units of Late Precambrian ophiolites (in particular, plagiogranite), the overlying Middle to Upper Devonian and Early Carboniferous deposits, as well as Early Carboniferous (?) Tolovka ophiolites and meta-ophiolites. Mélange of this type with inclusions of Late Precambrian "oceanic" granitoids also developed in the lower Utyosiki Nappe composed of Middle Jurassic-Lower Cretaceous sedimentary and volcanic sequences, the formation of which was related to the next Uda-Murgal island-arc systems.

  2. Partial melting of the South Qinling orogenic crust, China: Evidence from Triassic migmatites and diorites of the Foping dome

    Science.gov (United States)

    Zhang, He; Ye, Ri-Sheng; Liu, Bing-Xiang; Wang, Yan; Zhang, Yuan-Shuo; Siebel, Wolfgang; Chen, Fukun

    2016-09-01

    The Qinling orogen was ultimately formed by suturing of the South Qinling and Yangtze blocks, but the exact timing of the final amalgamation of the two blocks has not been well established so far. Partial melting of the Qinling orogenic continental crust resulted in the generation of migmatites, and such rocks may help to decipher the chronology of such event. In this paper, we report U-Pb ages, trace element, and Hf isotopic compositions of zircons from migmatites and diorite gneisses of the Foping dome, South Qinling. Zircons from migmatites form anhedral grains of variable sizes that are characterized by complex trace element compositions. Based on zircon U-Pb ages, the migmatites can be subdivided into two groups: Group 1 migmatites mainly retain Triassic zircons with U-Pb ages of 214-211 Ma and Hf model ages of ~ 1.46 Ga in core and rim domains; zircons from Group 2 migmatites record both Triassic (~ 210 Ma) and Neoproterozoic U-Pb ages, analogous to igneous rocks of the Wudang and Yaolinghe Groups exposed in South Qinling. Zircons from the diorite gneisses yield U-Pb ages of 216-210 Ma with Hf isotopic composition (TDM2 ages of ~ 1.46 Ga) similar to the migmatites. Evidence from whole-rock Nd isotopic analyses also points to a similar genesis between migmatites and diorite gneisses. It is proposed that Group 1 migmatites were derived by melting of Triassic diorites, while Group 2 migmatites were derived from Neoproterozoic igneous rocks, a major basement lithology of South Qinling. Partial melting of the orogenic crust took place at ~ 214-210 Ma, approximately consistent with the retrograde metamorphism of granulites exposed along the suture zone between the South Qinling and Yangtze blocks. We suggest that the collision of these two blocks occurred prior to ~ 215 Ma and that the Foping dome resulted from rapid collapse of an overthickened crust followed by partial melting enhanced by asthenospheric influx.

  3. The genesis of gold mineralisation hosted by orogenic belts: A lead isotope investigation of Irish gold deposits

    OpenAIRE

    Standish, CD; Dhuime, B.; Chapman, RJ; Hawkesworth, CJ; Pike, AWG

    2014-01-01

    Lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 Irish gold occurrences, including 27 placers, and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts. The Pb isotope ratios of lode and placer gold range from 206Pb/204Pb=17.287-18.679, 207Pb/204Pb=15.382-15.661, and 208Pb/204Pb=37.517-38.635, consistent with the Pb isotopic data on previously reported Irish sulphide mineralisation...

  4. The Influence of Glacial-Interglacial Cycles on the Erosion of Orogens

    Science.gov (United States)

    Yanites, Brian; Ehlers, Todd

    2010-05-01

    The evolution of mountain topography and sediment flux to adjacent basins is dictated by variations in the rates of rock-uplift, climate, lithology, and vegetation. Currently, many mountainous settings are in a state of a ‘glacial hangover' whereby Quaternary glaciation has dramatically altered catchment morphology and produced non-equilibrium conditions with respect to the environmental conditions preceding this major climatic transition. In this study, we investigate transients in mountain erosion and morphology due to glacial-interglacial cycles imposed on landscapes previously dominated by fluvial and hillslope processes. In our approach, we use a surface process model to produce an equilibrium fluvial landscape for rock uplift rates between 0.25-1.0 mm/yr. The landscapes are then subjected to repeated glacial cycles of different periodicity and intensity. Variations in predicted glacial basal sliding velocity, erosion, topography and sediment flux are tracked. Results indicate that glacial processes increase rates of valley bottom erosion by one to two orders of magnitude higher than fluvial processes, a result consistent with low-temperature thermochronological data from a number of glaciated catchments worldwide. Increased rates of hillslope and ridgetop erosion occur in response to increased glacial erosion and lag behind the onset of glaciation, thereby producing a complicated history of local relief. The timescale of this lag can vary by orders of magnitude and depends on model parametrization. We also find that two broad effects compete to control the evolution of sediment leaving such an orogen: 1) the topographic disequilibrium with glacial processes acts to initially increase sediment production, but as the topography readjusts, the disequilibrium wanes; 2) the initial geometry of the drainage basin is inefficient at providing ice to the sliding portions of the glaciers, thus impeding erosion early on, but as the topography becomes more

  5. Orogenic gold mineralization at the Chah Bagh deposit, Muteh gold district, Iran

    Science.gov (United States)

    Kouhestani, Hossein; Rashidnejad-Omran, Nematollah; Rastad, Ebrahim; Mohajjel, Mohammad; Goldfarb, Richard J.; Ghaderi, Majid

    2014-09-01

    The Chah Bagh gold deposit, in the Muteh gold district, is located in the central part of the Sanandaj-Sirjan zone (SSZ), Iran. Gold mineralization at Chah Bagh is hosted by a Paleozoic sequence of rocks that is dominated by deformed schist, metarhyolite, and amphibolite that exhibits a greenschist- to lower amphibolite-facies metamorphism. Three deformation events are recognized in the Chah Bagh area, D1, D2, and D3. The major NW-trending (N280-N290) dextral strike-slip shear zone in the area was formed during D2 ductile events. Gold mineralization at Chah Bagh occurred over a prolonged deformation history, but is closely related to alteration, retrograde greenschist-facies assemblages, and ductile and brittle deformation during D2 and D3. The geometry of the Au-bearing quartz veins indicates that they are temporally related to the S2 foliation and therefore to the D2 flattening and shearing. Some veins, however, are spatially and temporally related to D3 brittle normal faults and are brecciated and boudinaged during the associated shear movement. The presence of deformed Au-bearing quartz veins, and their concordant and discordant relation with respect to the main mylonitic foliation and the shear zone, indicates continuous mineralization during the D2 and D3 episodes. The Au-hosting shear zones are characterized by extensive development of heterogeneous mylonitic rocks that enhanced the permeability within the shear zones. This gave rise to further extensive dilatancy within major dilational jogs and produced a suitable structural regime for vein-hosted Au mineralization. The epigenetic Au mineralization resulted from metamorphic hydrothermal fluids circulating through major shear zones and associated structures during the late stages of orogeny. Our investigation shows that granitic intrusions have no genetic link with gold mineralization and we propose an orogenic gold model for Chah Bagh deposit, similar to Qolqoleh and Kervian in the northwestern part of the

  6. Late Devonian Anoxia Events in the Central Asian Orogenic Belt: a Global Phenomenon

    Science.gov (United States)

    Carmichael, S. K.; Waters, J. A.; Suttner, T. J.; Kido, E.; DeReuil, A. A.; Moore, L. M.; Batchelor, C. J.

    2013-12-01

    Atmospheric CO2 values decreased dramatically during the Middle Devonian due to the rapid rise of land plants. These changing environmental conditions resulted in widespread anoxia and extinction events throughout the Late Devonian, including the critical Kellwasser and Hangenberg anoxia events, which are associated with major mass extinctions at both the beginning and end of the Famennian Stage of the Late Devonian. Fammenian sediments in northwestern Xinjiang Province, China, represent a highly fossiliferous shallow marine setting associated with a Devonian oceanic island arc complex. Analysis of multiple geochemical proxies (such as U/Th, Ba, normalized P2O5, V/Cr, Zr), magnetic susceptibility, and mineralogical data (biogenic apatite and pyrite framboids) indicates that these Famennian sequences record not only the Upper Kellwasser Anoxic Event at the Frasnian/Famennian (F/F) boundary but also the rebound from the F/F extinction event. Preliminary evidence suggests that the Hangenberg Anoxic Event can also be recognized in the same sequence, although our biostratigraphic control is less precise. Previous studies of the Kellwasser and Hangenberg Events have been performed on continental shelf environments of Laurussia, Gondwana, Siberia, and South China. The Devonian formations of northwest Xinjiang in this study, however, are part of the Central Asian Orogenic Belt (CAOB), which is thought to have formed as part of a complex amalgamation of intra-oceanic island arcs and continental fragments prior to the end of the latest Carboniferous. These results allow us to confirm the presence of the Kellwasser and Hangenberg Events in the open oceanic part of Paleotethys, indicating that both events were global in scope. The presence of an abundant diverse Famennian fauna between these anoxia/extinction events suggests that the shallow marine ecosystems in the CAOB were somewhat protected due to their tectonic location and relative isolation within an open ocean system

  7. Orogenic-type copper-gold-arsenic-(bismuth) mineralization at Flatschach (Eastern Alps), Austria

    Science.gov (United States)

    Raith, Johann G.; Leitner, Thomas; Paar, Werner H.

    2015-10-01

    high Hg content (up to 11 mass %). The Cu-Au deposits in the Flatschach area show similarities with meso- to epizonal orogenic lode gold deposits regarding the geological setting, the structural control of mineralization, the type of alteration, the early (stage 1) sulfide assemblage and composition of gold. Unique about the Flatschach district is the lower-temperature overprint of copper arsenides (domeykite and koutekite) and copper sulfides (djurleite, yarrowite/spionkopite) on earlier formed sulfide mineralization. Based on mineralogical considerations temperature of stage 2 mineralization was between about 70 °C and 160 °C. Gold was locally mobilized during this low-temperature hydrothermal overprint as well as during stage 3 supergene oxidation and cementation processes.

  8. Early Yanshanian post-orogenic granitoids in the Nanling region——Petrological constraints and geodynamic settings

    Institute of Scientific and Technical Information of China (English)

    陈培荣; 陆建军; 范春方; 华仁民; 章邦桐

    2002-01-01

    Early Yanshanian magmatic suites predominate absolutely in the Nanling granite belt. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late oroge

  9. Pan-African granulites of central Dronning Maud Land and Mozambique: A comparison within the East-African-Antarctic orogen

    Science.gov (United States)

    Engvik, A.K.; Elevevold, S.; Jacobs, J.; Tveten, E.; de Azevedo, S.; Njange, F.

    2007-01-01

    Granulite-facies metamorphism is extensively reported in Late Neoproterozoic/Early Palaeozoic time during formation of the East-African-Antarctic orogen (EAAO). Metamorphic data acquired from the Pan-African orogen of central Dronning Maud Land (cDML) are compared with data from northern Mozambique. The metamorphic rocks of cDML are characterised by Opx±Grt-bearing gneisses and Sil+Kfs-bearing metapelites which indicate medium-P granulite-facies metamorphism. Peak conditions, which are estimated to 800-900ºC at pressures up to 1.0 GPa, were followed by near-isothermal decompression during late Pan-African extension and exhumation. Granulite-facies lithologies are widespread in northern Mozambique, and Grt+Cpx-bearing assemblages show that high-P granulite-facies conditions with PT reaching 1.55 GPa and 900ºC were reached during the Pan-African orogeny. Garnet is replaced by symplectites of Pl+Opx+Mag indicating isothermal decompression, and the subsequent formation of Pl+amphibole-coronas suggests cooling into amphibolite facies. It is concluded that high-T metamorphism was pervasive in EAAO in Late Neoproterozoic/Early Paleozoic time, strongly overprinting evidences of earlier metamorphic assemblages.

  10. Extreme mass flux from the glaciated, collisional St. Elias Orogen: Preliminary results from IODP Expedition 341 (Invited)

    Science.gov (United States)

    Gulick, S. P.; Jaeger, J. M.

    2013-12-01

    Integrated Ocean Drilling Program Expedition 341 drilled a cross-margin transect to investigate the linkages between global climate change, modification of the dynamics of surficial processes, and subsequent tectonic responses. The Gulf of Alaska (GoA) borders the St. Elias orogen, the highest coastal mountain range on Earth. Exp. 341 drilled five sites within a regional seismic reflection grid that spans from the distal Surveyor Fan to the continental shelf. More than 3000 m of high-quality core coupled with seismic reflection profiles collected with nested vertical resolution allows us to address the major objectives of drilling in the GoA. These objectives were to: 1) document the tectonic response of an active orogenic system to late Miocene to recent climate change; 2) establish the timing of advance/retreat phases of the northern Cordilleran ice sheet to test its relation to dynamics of other global ice sheets; 3) implement an expanded source-to-sink study of the interactions between glacial, tectonic, and oceanographic processes responsible for creation of one of the thickest Neogene high-latitude continental margin sequences; 4) understand the dynamics of productivity, nutrients, freshwater input to the ocean, and ocean circulation in the northeast Pacific and their role in the global carbon cycle, and 5) document the spatial and temporal behavior of the geomagnetic field at extremely high temporal resolution in an under-sampled region of the globe. The Exp. 341 cross-margin transect discovered transitions in sediment accumulation rates from >100 m/Ma at the distal site to > 1000 m/Ma in the proximal fan, slope and on the continental shelf that provide a telescoping view of strata formation from the Miocene to the Holocene. Complete recovery and development of spliced sedimentary records of the Pleistocene through Holocene were achieved at the distal, proximal, and slope Sites U1417, U1418, and U1419, respectively, because of exceptional piston core

  11. Deep Seismic Reflection Profiles Reveal The Crust Structures Beneath Xing'an-Mongolian Orogenic Belt and Its Neighboring Area

    Science.gov (United States)

    Hou, H.; Gao, R.; Keller, R. G.; Li, Q.; Li, W.; Li, H.; Xiong, X.; Guo, L.

    2012-12-01

    The Xing'an-Mongolia orogenic belt (XMOB) as the eastern part of the CAOB (Central Asian Orogenic Belt) is one of the remarkably reworked and crustal accretionary belts during the Phanerozoic in the world. It is located between the northern margin of the North China craton and the southern margin of the Siberia craton and is characterized by large-scale Mesozoic magmatism, and forms a key part of the NE-trending Mesozoic magmatic belt in East China. Therefore, it will be of great importance to study the contact relationship between these blocks, which will prodive important information on the study of mineralization and assessment of earthquake disaster. A major problem with all previous publications on Xing'an-Mongolian Orogenic belt was the lack of a seismic section which could potentially image the zone or the dominant vergence of crustal structures at depth. In the view of above, deep seismic profiling data acquisition finished in last three years and the newly processing seismic reflection profiles in this belt were possible under the support of SinoProbe project and China Geological Survey. As we not only focuse on the deep structures of crust, but also carry about the relationships between the shallow reflection fabrics with surface geology. Therefore, different with oil industrial data accquistion, we develop some deep seismic reflection techniques such as three levels of explosive shots were adopted for enough energy reflected from all crust, long offset with single side length of 15 km on symmetrical for the modeling of shallow crust by use of tomographic method, meanwhile we share the shots large than 500 kg with seismic refraction survey line providing more rays for modeling deep velocity strucutre. The seismic reflection data were mainly using the seismic processing package ProMAX and the CGG processing system, following the processing steps with special methods such as tomographic inversion static corrections, surface-consistent amplitude compensation

  12. Large landslides lie low: Vertical domains of denudation processes in the arid Himalaya-Karakoram orogen

    Science.gov (United States)

    Blöthe, Jan Henrik

    2014-05-01

    Large bedrock landslides (defined here as affecting >0.1 km2 in planform area) are thought to substantially contribute to denuding active mountain belts, and limiting the growth of topographic relief produced by concurrent tectonic uplift and fluvial or glacial incision. While most research on large landslides has focused on tectonically active, humid mountain belts with varying degrees of rainstorm and earthquake activity, lesser attention has been devoted to arid mountain belts. Especially in the Himalaya, where high denudation rates are commonly associated with high landslide activity, previous work has largely ignored landslide processes in the arid compartments of the orogen. This was motivation for us to compile a landslide inventory covering the arid Himalaya-Karakoram of NW India and N Pakistan within the Indus catchment. Our data set contains 493 rock-slope failures that we compiled from published studies and mapping from remote sensing imagery. Using an empirical volume-area scaling approach we estimate the total landslide volume at >250 km3. This is more than thousand times the contemporary annual sediment load in the Indus River. We analyse the distribution of these volumetrically significant landslides with respect to the regional hypsometry, contemporary glacier cover, and the distribution of rock glaciers. We find that large bedrock landslides in the arid Himalaya-Karakoram region preferentially detach near or from below the study area's median elevation, while glaciers and rock glaciers occupy higher elevations almost exclusively. This trend holds true for both the study area and parts thereof. The largest and highest-lying landslides occur in the Karakoram mountains, where local relief exceeds 6 km, and >90% of the landslide areas lie below the region's median elevation. Our analysis reveals a hitherto unrecognized vertical layering of denudation processes, with landslides chiefly operating below the median elevation, whereas mass transport by

  13. Miocene magmatism and tectonics within the Peri-Alboran orogen (western Mediterranean)

    Science.gov (United States)

    El Azzouzi, M.; Bellon, H.; Coutelle, A.; Réhault, J.-P.

    2014-07-01

    The aim of this paper concerns Miocene igneous activity in the Alboran Sea and Peri-Alboran area (northern Morocco, western Algeria and Betic Cordilleras in Spain), considering its age and its location with regard to major tectonics structures. We have compiled previous K-Ar isotopic ages of lavas and plutonic boulders and intrusives with an error of ±1σ and completed this set by a new K-Ar isotopic age for andesitic tuffites from Alboran Island. Geochemistry of most of these samples has been considered after previous analyses completed with new data for Spain magmatism. These two sets of data allow us to place the magmatic activity within the regional stratigraphy and tectonics and their chronological framework of the three major tectonic phases of the Maghrebian orogen, at 17 Ma (Burdigalian), 15 Ma (Langhian) and 9 Ma (Tortonian). Petro-geochemical characteristics are compared through time and geographical locations. A major goal of this coupled approach is to help the elaboration of possible geodynamical processes. As an application, we present the case study of the Dellys, Djinet and Thenia region (east of Algiers) where the successive magmatic events between 19.4 ± 1 and 11.6 ± 0.5 Ma are closely related to the local tectonics and sedimentation. The Peri-Alboran igneous activity is placed in a multidisciplinary framework. Timing of activity is defined according to the ages of the neighbouring sedimentary units and the K-Ar ages of igneous rocks. In Spain, the Cabo de Gata-Carboneras magmatic province displays late Oligocene and early Miocene leucogranitic dikes, dated from 24.8 ± 1.3 to 18.1 ± 1.2 Ma; three following andesitic to rhyolitic events took place around 15.1 ± 0.8 to 14.0 ± 0.7 Ma, 11.8 ± 0.6 to 9.4 ± 0.4 Ma, 8.8 ± 0.4 to 7.9 ± 0.4 Ma; this last event displays also granitic rocks. Lamproitic magmas dated between 8.4 ± 0.4 and 6.76 ± 0.04 Ma were emplaced after the Tortonian phase. In Morocco, after the complex building of the Ras Tarf

  14. Deep Crustal Metamorphic Carbon Cycling in Collisional Orogens: What do we Really Know?

    Science.gov (United States)

    Ague, J.

    2012-12-01

    fluxes. The key problem is whether or not this CO2 can reach the surface. CO2 can be stripped from cooling, decompressing fluids ascending toward the surface by a variety of mechanisms; retrograde carbonation reactions will be very important but direct deposition of carbonate minerals or graphite are also likely to be significant. We have modeled coupled flow and retrograde carbonation reaction using both "standard" Darcian fluid flow and "two-phase" flow incorporating matrix compaction and porosity waves (Tian and Ague, 2012). In either case, the CO2 sequestration potential is great, and depends on a variety of geologic factors including rock reactivity, buffer capacity, and layer thickness. High-grade metacarbonate rocks as well as ultramafic rocks/serpentinites are particularly reactive sinks for orogenic carbon. A fundamental problem, however, is whether or not retrograde reaction closes off porosity, thus limiting fluid flow and CO2 transfer. Petrologists have traditionally concentrated on prograde metamorphism, but renewed focus on retrogression at the regional scale is now warranted to better understand how much CO2 is trapped and how much can actually escape from mountain belts during orogensis.

  15. Kinematics of the Torcal Shear Zone: transpressional tectonics shaping orogenic curves in the northern Gibraltar Arc.

    Science.gov (United States)

    Barcos, Leticia; Balanyá, Juan Carlos; Díaz-Azpiroz, Manuel; Expósito, Inmaculada; Jiménez-Bonilla, Alejandro

    2014-05-01

    Structural trend line patterns of orogenic arcs depict diverse geometries resulting from multiple factors such as indenter geometry, thickness of pre-deformational sequences and rheology of major decollement surfaces. Within them, salient-recess transitions often result in transpressive deformation bands. The Gibraltar Arc results from the Neogene collision of a composite metamorphic terrane (Alboran Domain, acting as a relative backstop) against two foreland margins (Southiberian and Maghrebian Domains). Within it, the Western Gibraltar Arc (WGA) is a protruded salient, 200 km in length cord, closely coinciding with the apex zone of the major arc. The WGA terminates at two transpressional zones. The main structure in the northern (Betic) end zone is a 70 km long and 4-5 km wide brittle deformation band, the so-called Torcal Shear Zone (TSZ). The TSZ forms a W-E topographic alignment along which the kinematic data show an overall dextral transpression. Within the TSZ strain is highly partitioned into mainly shortening, extensional and strike-slip structures. The strain partitioning is heterogeneous along the band and, accordingly, four distinct sectors can be identified. i) The Peñarrubia-Almargen Transverse Zone (PATZ), located at the W-end of the TSZ presents WNW-ESE folds and dextral faults, together with normal faults that accommodate extension parallel to the dominant structural trend. WNW ESE dextral faults might be related with synthetic splays at the lateral end of the TSZ. ii) The Sierra del Valle de Abdalajís (SVA) is characterized by WSW-ENE trending folds and dextral-reverse faults dipping to SSE, and NW-SE normal faults. The southern boundary of the SVA is a dextral fault zone. iii) The Torcal de Antequera Massif (TAM) presents two types of structural domains. Two outer domains located at both margins characterized by E-W trending, dextral strike-slip structures, and an inner domain, characterized by en echelon SE-vergent open folds and reverse shear

  16. Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

    Science.gov (United States)

    Taghipour, Batoul; Ahmadnejad, Farhad

    2015-03-01

    The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ), within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO42- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu) are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG) type shear zone and orogenic type gold mineralisation. Based on the number of phases observed at room temperature and their microthermometric behaviour, three fluid inclusion types have been recognised in quartz-sulphide and quartz-calcite veins: Type I monophase aqueous inclusions, Type II two-phase liquid-vapour (L-V) inclusions which are subdivided into two groups based on the homogenisation temperature (Th): a) L-V inclusions with Th from 205 to 255°C and melting temperature of last ice (Tm) from -3 to -9°C. b) L-V inclusions with higher Th from 335 to 385

  17. Geodynamics of oceanic plateau and plume head accretion and their role in Phanerozoic orogenic systems of China

    Institute of Scientific and Technical Information of China (English)

    Peter G. Betts; Louis Moresi; Meghan S. Miller; David Willis

    2015-01-01

    We present three 3D numerical models of deep subduction where buoyant material from an oceanic plateau and a plume interact with the overriding plate to assess the influence on subduction dynamics, trench geometry, and mechanisms for plateau accretion and continental growth. Transient instabilities of the convergent margin are produced, resulting in:contorted trench geometry;trench migration parallel with the plate margin; folding of the subducting slab and orocline development at the convergent margin;and transfer of the plateau to the overriding plate. The presence of plume material beneath the oceanic plateau causes flat subduction above the plume, resulting in a“bowed”shaped subducting slab. In plateau-only models, plateau accretion at the edge of the overriding plate results in trench migration around the edge of the plateau before subduction is re-established directly behind the trailing edge of the plateau. The plateau shortens and some plateau material subducts. The presence of buoyant plume material beneath the oceanic plateau has a profound influence on the behaviour of the convergent margin. In the plateau þ plume model, plateau accretion causes rapid trench advance. Plate convergence is accommodated by shearing at the base of the plateau and shortening in the overriding plate. The trench migrates around the edge of the plateau and subduction is re-established well behind the trailing edge of the plateau, effectively embedding the plateau into the overriding plate. A slab window forms beneath the accreted plateau and plume material is transferred from the subducting plate to the over-riding plate through the window. In all of the models, the subduction zone maintains a relatively stable configuration away from the buoyancy anomalies within the downgoing plate. The models provide a dynamic context for plateau and plume accretion in Phanerozoic accretionary orogenic systems such as the East China Orogen and the Central Asian Orogen (Altiads), which

  18. Multiple fluid sources/pathways and severe thermal gradients during formation of the Jílové orogenic gold deposit, Bohemian Massif, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Zachariáš, J.; Žák, Karel; Pudilová, M.; Snee, L. W.

    2013-01-01

    Roč. 54, October (2013), s. 81-109. ISSN 0169-1368 Institutional research plan: CEZ:AV0Z30130516 Institutional support: RVO:67985831 Keywords : Orogenic gold deposits * Carbon isotopes * Oxygen isotopes * Bismuth * Age * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.383, year: 2013

  19. Bicarbonate-rich fluid inclusions and hydrogen diffusion in quartz from the Libčice orogenic gold deposit, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Hrstka, Tomáš; Dubessy, J.; Zachariáš, J.

    2011-01-01

    Roč. 281, 3-4 (2011), s. 317-332. ISSN 0009-2541 Institutional research plan: CEZ:AV0Z30130516 Keywords : bicarbonate * fluid inclusions * hydrogen diffusion * orogenic gold deposits * raman spectroscopy Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.518, year: 2011

  20. Subsidence, stress regime and rotation(s) of a tectonically active sedimentary basin within the western Alpine Orogen: the Tertiary Piedmont Basin (Alpine domain, NW Italy)

    NARCIS (Netherlands)

    Carrapa, B.; Bertotti, G.; Krijgsman, W.

    2003-01-01

    The Oligocene to Miocene Tertiary Piedmont Basin (TPB) is located in the NW part of Italy at the junction between the Apennine and the Alpine thrust belts. The position of the TPB on top of the Alpine/Apennine Orogen poses fundamental questions as to the tectonics of the basin subsidence. Having und

  1. Crustal structure in the junction of Qinling Orogen, Yangtze Craton and Tibetan Plateau: implications for the formation of the Dabashan Orocline and the growth of Tibetan Plateau

    Science.gov (United States)

    Jiang, Chengxin; Yang, Yingjie; Zheng, Yong

    2016-03-01

    The crust at the junction of Qinling Orogen, Yangtze Craton and NE Tibetan Plateau bears imprints of the Triassic collision and later intra-continental orogeny between the Qinling Orogen and the Yangtze Craton, and the Cenozoic growth of Tibetan Plateau. Investigating detailed crustal structures in this region helps to better understand these tectonic processes. In this study, we construct a 3-D crustal Vs model using seismic ambient noise data recorded at 321 seismic stations. Ambient noise tomography is performed to generate Rayleigh wave phase velocity maps at 8-50 s periods, which are then inverted for a 3D isotropic Vs model using a Bayesian Monte-Carlo method. Our 3D model reveals deep-rooted high velocities beneath the Hannan-Micang and Shennong-Huangling Domes, which are located on the west and east sides of the Dabashan Orocline. Similar high velocities are observed in the upper/mid crust of the western Qinling Orogen. We suggest the crustal-scale bodies with high velocity beneath the two domes and the western Qinling Orogen may represent mechanically strong rocks, which not only assisted the formation of the major Dabashan Orocline during late Mesozoic intra-continental orogeny, but also have impeded the northeastward expansion of the Tibetan Plateau during the Cenozoic era.

  2. Crustal structure in the junction of Qinling Orogen, Yangtze Craton and Tibetan Plateau: implications for the formation of the Dabashan Orocline and the growth of Tibetan Plateau

    Science.gov (United States)

    Jiang, Chengxin; Yang, Yingjie; Zheng, Yong

    2016-06-01

    The crust at the junction of Qinling Orogen, Yangtze Craton and NE Tibetan Plateau bears imprints of the Triassic collision and later intracontinental orogeny between the Qinling Orogen and the Yangtze Craton, and the Cenozoic growth of Tibetan Plateau. Investigating detailed crustal structures in this region helps to better understand these tectonic processes. In this study, we construct a 3-D crustal Vs model using seismic ambient noise data recorded at 321 seismic stations. Ambient noise tomography is performed to generate Rayleigh wave phase velocity maps at 8-50 s periods, which are then inverted for a 3-D isotropic Vs model using a Bayesian Monte Carlo method. Our 3-D model reveals deep-rooted high velocities beneath the Hannan-Micang and Shennong-Huangling Domes, which are located on the west and east sides of the Dabashan Orocline. Similar high velocities are observed in the upper/mid crust of the western Qinling Orogen. We suggest the crustal-scale bodies with high velocity beneath the two domes and the western Qinling Orogen may represent mechanically strong rocks, which not only assisted the formation of the major Dabashan Orocline during late Mesozoic intracontinental orogeny, but also have impeded the northeastward expansion of the Tibetan Plateau during the Cenozoic era.

  3. Disclosing the Paleoarchean to Ediacaran history of the São Francisco craton basement: The Porteirinha domain (northern Araçuaí orogen, Brazil)

    Science.gov (United States)

    Silva, Luiz Carlos da; Pedrosa-Soares, Antonio Carlos; Armstrong, Richard; Pinto, Claiton Piva; Magalhães, Joana Tiago Reis; Pinheiro, Marco Aurélio Piacentini; Santos, Gabriella Galliac

    2016-07-01

    This geochronological and isotopic study focuses on one of the Archean-Paleoproterozoic basement domains of the São Francisco craton reworked in the Araçuaí orogen, the Porteirinha domain, Brazil. It also includes a thorough compilation of the U-Pb geochronological data related to the adjacent Archean and Rhyacian terranes from the São Francisco craton and Araçuaí orogen. The main target of this study is the TTG gneisses of the Porteirinha complex (Sample 1). The gneiss dated at 3371 ± 6 Ma unraveled a polycyclic evolution characterized by two metamorphic overprinting episodes, dated at 3146 ± 24 Ma (M1) and ca. 600 Ma (M2). The former (M1) is so far the most reliable evidence of the oldest metamorphic episode ever dated in Brazil. The latter (M2), in turn, is endemic in most of the exposed eastern cratonic margin within the Araçuaí orogen. Whole-rock Sm-Nd analysis from the gneiss provided a slightly negative εNd(t3370) = - 0.78 value, and a depleted mantle model (TDM) age of 3.5 Ga, indicating derivation mainly from the melting of a ca. 3.5 Ga tholeiitic source. Sample 2, a K-rich leuco-orthogneiss from the Rio Itacambiriçu Complex, was dated at 2657 ± 25 Ma and also presents a ca. 600 Ma M2 overprinting M2 age. The other two analyses were obtained from Rhyacian granitoids. Sample 3 is syn-collisional, peraluminous leucogranite from the Tingui granitic complex, showing a crystallization age of 2140 ± 14 Ma and strong post-crystallization Pb*-loss, also ascribed to the Ediacaran overprinting. Accordingly, it is interpreted as a correlative of the late Rhyacian (ca. 2150-2050 Ma) collisional stage of the Mantiqueira orogenic system/belt (ca. 2220-2000 Ma), overprinted by the Ediacaran collage. Sample 4 is a Rhyacian post-orogenic (post-collisional), mixed-source, peralkaline, A1-type suite, with a crystallization age of 2050 ± 10 Ma, presenting an important post-crystallization Pb*-loss related to Ediacaran collision. The focused region records some

  4. The Sikhote-Alin orogenic belt, Russian South East: Terranes and the formation of continental lithosphere based on geological and isotopic data

    Science.gov (United States)

    Khanchuk, A. I.; Kemkin, I. V.; Kruk, N. N.

    2016-04-01

    The Sikhote-Alin orogenic belt, Russian South East, consists of folded terranes made up of Jurassic and Early Cretaceous accretionary prisms, turbidite basins, and island arc terranes that are overlapped unconformably by undeformed upper Cenomanian to Cenozoic volcanic deposits. The Jurassic and Early Cretaceous accretionary prisms, together with the Early Cretaceous island arc, are related to subduction of the Paleo-Pacific plate. The turbidite basin, which began to form at the beginning of the Early Cretaceous, is related to left-lateral movement of the Paleo-Pacific plate along the Paleo-Asian continental margin. The collage of terranes that make up the Sikhote-Alin orogenic belt was amalgamated in two stages. The first began after Jurassic subduction beneath the Asian continent was terminated, and the second took place in the late Albian, when the Early Cretaceous island arc collided with the continental margin. Intense deformation of the terranes took place along the continental margin in the form of large-scale translations from south to north, together with oroclinal folding. The deformation resulted in rapid thickening of sediments in the upper crust, resulting in turn in the formation of granitic-metamorphic material in the continental lithosphere. In the southwestern part of the Sikhote-Alin orogen, granites were intruded during the Hauterivian-Aptian, while the entire orogenic belt was affected by intrusions in the late Albian-early Cenomanian. Synorogenic intraplate volcanic rocks and alkaline ultramafic-mafic intrusions also testify to the fact that the orogenic processes in the Sikhote-Alin were related to a transform continental margin, and not to subduction. Geochemical and Nd isotopic data indicate, the primary continental crust of the Sikhote-Alin was of a "hybrid" nature, consisting of juvenile basic components accreted from an oceanic plate and recycled sedimentary material derived from the erosion of ancient blocks.

  5. Early Cretaceous Erlangmiao Metaluminous A-type Granite in the Eastern Qinlin Orogen, central China: Geochronological and Geochemical Constraints

    Science.gov (United States)

    Zhang, J.; Ma, C.; Sher, Z.; Wang, S.; Wang, L.; Cao, Y.

    2007-12-01

    It is possible to study the Mesozoic lithospheric thinning and crust-mantle interaction due to Early Cretaceous intensive magmatism widely developed in the North China Block. As an important part of the Early Cretaceous magmatism in the North China Block, the widespread Early Cretaceous granites in the Dabieshan-Qinlin Orogen, situated in the southern margin of the North China Block, contain hornblende and/or biotite and are I-type granites, but other type granites are less reported. Early Cretaceous Erlangmiao garnet granite (EGG) with garnet and biotite found recently near Erlangmiao in Fangcheng County, Henan Province, China, has provided new constraints for evolvement of the Dabie-Qinlin Orogen. This abstract reports results of zircon U-Pb dating, elemental geochemistry, and Sr-Nd isotopic compositions of the EGG and its wall rocks in an attempt to constrain its petrogenesis and the Early Cretaceous tectonic evolution of the Dabie-Qinlin Orogen. The EGG, located in the eastern Qinlin Orogen, was emplaced in gneissic monzogranites (GG). There are abundant GG xenoliths and surmicaceous enclaves in the eastern margin of the stock. LA-ICPMS zircon U-Pb dating of the EGG suggests its crystallization at 118 ±2 Ma, whole-rock Rb-Sr isochron age, represented the cooling age of the EGG, is 110±1 Ma. The EGGs are syenogranites with almandine-Spessartine garnet and biotite. The EGGs are characterized by high SiO2 and alkali contents, high FeOt/MgO ratio, low Al2O3 and CaO contents, and display high-K calc-alkaline and metaluminous characteristics. They show low total Rare Earth Element content (ΣREE), strong negative Eu anomaly, are generally enriched in Rb, Th, Ta, Nb, Zr, Hf, Y, Yb and depleted in Sr, Ba, Ce, P, Ti, and have high Rb, Rb/Sr and Ga/Al ratios. Al2O3, Fe2O3, K2O, Zr, Rb, Pb of the EGGs decrease with increasing SiO2 content. Initial 87Sr/86Sr ratios of the whole rocks range in 0.706-0.708, while the ɛNd(110Ma) values vary from -6.6 to -9.0 and Nd

  6. Isotopic composition, sources of crustal magmatism, and structure of caledonian crust in the lake zone, Central Asian orogenic belt

    International Nuclear Information System (INIS)

    New estimates of Caledonian crust composition in the lake zone (Western Mongolia) of the Central Asian orogenic belt, made on the basis of isotopic and geochemical studies of both magmatic and sedimentary rocks, including different-age granitoids that emerged at the continental stage of the zone evolution are presented. According to data obtained by Sm-Nd- and Ar-Ar-dating the age of the rocks from different masses of the zone made up 570 and 545 bill. years respectively. Relying on U-Pb-dating of the granitoids by zircons, the age groups of acid continental magmatism of the territory in the range of 494 - ∼200 bill. years were determined

  7. Expansion of the granitic post-orogenic magmatism in the formation of Serrinha (Northeastern Bahia, B R), Sao Francisco craton

    International Nuclear Information System (INIS)

    The Pedra Vermelha Granitic Massif, located at the North area of Serrinha Nucleus, presents a circular shape, being intrusive at the Archaean geoscience-magmatic basement rocks and the Paleoproterozoic volcano sedimentary sequences. The single zircon U-Pb dating yield a crystallization age of 2080 ± 8 Ma. The geological, petrographic al and litogeochemical characteristics of the studied rocks are similar to those of the Morro do Lopes granitic magmatism (2076 ± 6 a 2071 ± 6 Ma), which is located at the South area of this nucleus. These allow us to infer that those post-orogenic alkaline bodies are widespread throughout the Serrinha Nucleus and constitute its last Paleoproterozoic magmatic expression. (author)

  8. Whole-rock Ar-Ar dating for low-grade metavolcanics within the Dabie orogen and its geological significance

    Institute of Scientific and Technical Information of China (English)

    GAO Tianshan; TANG Jiafu; SANG Haiqing; HU Shiling; QIAN Cunchao

    2006-01-01

    The genetic relationship between low- grade and ultrahigh-pressure (UHP) metamorphic units in the interior of the Dabie orogen has been controversial with respect to preservation of volcanic texture during continental subduction to mantle depths. In order to resolve this issue, whole-rock Ar-Ar dating was carried out for greenschist-facies metatuff that is in contact with UHP eclogite in Yuexi County, Anhui Province. One sample gave a plateau age of 784.4±2.0 Ma and an isochron age of 785.0± 4.7 Ma, and the other sample a plateau age of 770.9± 2.0 Ma and an isochron age of 769.5±3.1 Ma. It appears that the Ar isotopic system was not disturbed since the volcanic eruption at the middle Neoproterozoic. Because of the low closure temperature of Ar diffusion in volcanic rocks, retention of the Neoproterozoic ages indicates that the low-grade metavolcanics did not experience high-grade metamorphism up to eclogite-facies conditions during the Triassic subduction of continental crust. Furthermore, the Neoproterozoic Ar-Ar ages are also in agreement with protolith ages of UHP metaigneous rocks in the Dabie orogen. Therefore, the metatuff is interpreted as a tectonic relict that was scraped off during the Triassic subduction and thus was not subducted to mantle depths like the adjacent eclogite. This lends support to the model for crustal detachment between cover and basement during continental collision. A tectonic mélange model is proposed to explain the occurrence of contrasting grades of metamorphic rock within the UHP metamorphic zone.

  9. Paleomagnetic and geochronological study of Carboniferous forearc basin rocks in the Southern New England Orogen (Eastern Australia)

    Science.gov (United States)

    Pisarevsky, Sergei A.; Rosenbaum, Gideon; Shaanan, Uri; Hoy, Derek; Speranza, Fabio; Mochales, Tania

    2016-06-01

    We present results of a paleomagnetic study from Carboniferous forearc basin rocks that occur at both limbs of the Texas Orocline (New England Orogen, eastern Australia). Using thermal and alternating field demagnetizations, two remanence components have been isolated from rocks sampled from the Emu Creek terrane, in the eastern limb of the orocline. A middle-temperature Component M is post-folding and was likely acquired during low-temperature oxidation at 65-35 Ma. A high-temperature Component H is pre-folding, but its comparison with the paleomagnetic data from coeval rocks in the northern Tamworth terrane on the other limb of Texas Orocline does not indicate rotations around a vertical axis, as expected from geological data. A likely explanation for this apparent discrepancy is that Component H postdates the oroclinal bending, but predates folding in late stages of the 265-230 Ma Hunter Bowen Orogeny. The post-Kiaman age of Component H is supported by the presence of an alternating paleomagnetic polarity in the studied rocks. A paleomagnetic study of volcanic and volcaniclastic rocks in the Boomi Creek area (northern Tamworth terrane) revealed a stable high-temperature pre-folding characteristic remanence, which is dated to c. 318 Ma using U-Pb zircon geochronology. The new paleopole (37.8°S, 182.7°E, A95 = 16.2°) is consistent with previously published poles from coeval rocks from the northern Tamworth terrane. The combination of our new paleomagnetic and geochronological data with previously published results allows us to develop a revised kinematic model of the New England Orogen from 340 Ma to 270 Ma, which compared to the previous model, incorporates a different orientation of the northern Tamworth terrane at 340 Ma.

  10. Mesozoic basin-fill records in south foot of the Dabie Mountains: Implication for Dabie Orogenic attributes

    Institute of Scientific and Technical Information of China (English)

    李忠; 李任伟; 孙枢; 张雯华

    2003-01-01

    Five evolutional phases are found from Mesozoic basin-fill sequences in the northern Jianghan basin, the south foot of the Dabie Mountains: (i) Early Triassic to the early period of Late Triassic showing continental shelf marine and paralic deposits; (ii) the middle-late period of Late Triassic indicating the uplift and erosion in compressional tectonic setting; (iii) the late period of Late Triassic to Early-Middle Jurassic showing peneplain terrestrial and fluvial clastic deposits interlayered with coal-seams; (iv) Late-Jurassic to Early-Cretaceous characterized by cycle fills of acidic volcanic rocks interstratified with pyroclastic rocks in intracontinental extension tectonic regime; (v) a lot of coarse clastic deposits similar to molasses occur in Late-Cretaceous mainly. Based on the compositions of detrital sandstones and conglomerates, combined with the analysis of sedimentary facies, it is indicated that most clasts sourced from the Yangtze continent from phase one to phase three, whose provenances are attributed to "recycled orogenic belt" types. On the other hand, detrital assemblages of the fifth phase deposits are mainly related with pre- Mesozoic metamorphic rocks of the Dabie Mountains, subjected to "arc orogenic belt" provenance types. In the Mesozoic basins of the south foot of the Dabie Mountains, it is proved that there are no direct depositional records corresponding to "Late Triassic syn-collisional orogenesis". Molasse depositional records of Upper Cretaceous distinctly reflect post-collisional orogenesis of the Dabie Mountains (intracontinental orogenesis) and intensive exhumation in extensional tectonic regime. This paper further discusses the inconsistent relations existing between basin-fill records at the south and north feet of the Dabie Mountains and the uplift models of the Dabie Mountains published, and indicates their key problems.

  11. Metamorphic Rock-Hosted Orogenic Gold Deposit Type as a Source of Langkowala Placer Gold, Bombana, Southeast Sulawesi

    Directory of Open Access Journals (Sweden)

    Arifudin Idrus

    2014-06-01

    Full Text Available DOI: 10.17014/ijog.v6i1.114In 2008, placer gold was discovered in Langkowala area (Bombana Regency, Southeast Sulawesi, Indonesia, and more than 60,000 traditional gold miners in the early 2009 have been operating by digging vertical pits and panning active stream sediments. The grade of placer gold ranges from 50 to 140 g/t. Local geological framework indicates that the placer gold is not related to volcanic rock-related hydrothermal gold deposit, e.g. epithermal, skarn or porphyry. This paper describes a preliminary study on possible primary deposit type as a source of the Langkowala (Bombana secondary placer gold. A field study indicates that the Langkowala (Bombana placer/paleoplacer gold is possibly related to gold-bearing quartz veins/veinlets hosted by metamorphic rocks particularly mica schist and metasediments in the area. These quartz veins/veinlets are currently recognized in metamorphic rocks at Wumbubangka Mountains, a northern flank of Rumbia Mountain Range. Sheared, segmented quartz veins/veinlets are of 2 cm to 2 m in width and contain gold in a grade varying between 2 and 61 g/t. At least, there are two generations of the quartz veins. The first generation of quartz vein is parallel to foliation of mica schist and metasediments with general orientation of N 300oE/60o; the second quartz vein generation crosscut the first quartz vein and the foliation of the wallrock. The first quartz veins are mostly sheared/deformed, brecciated, and occasionally sigmoidal, whereas the second quartz veins are relatively massive. The similar quartz veins/veinlets types are also probably present in Mendoke Mountain Range, in the northern side of Langkowala area. This primary gold deposit is called as ‘orogenic gold type’. The orogenic gold deposit could be a new target of gold exploration in Indonesia in the future.

  12. The Permian Dongfanghong island-arc gabbro of the Wandashan Orogen, NE China: Implications for Paleo-Pacific subduction

    Science.gov (United States)

    Sun, Ming-Dao; Xu, Yi-Gang; Wilde, Simon A.; Chen, Han-Lin; Yang, Shu-Feng

    2015-09-01

    The Dongfanghong hornblende gabbro is located in the western part of the Wandashan Orogen and to the east of the Jiamusi Block in NE China. It was emplaced into Early Paleozoic oceanic crust (i.e. Dongfanghong ophiolite) at ~ 275 Ma and both later collided with the eastern margin of the Jiamusi Block. The Dongfanghong gabbro is sub-alkaline with high Na2O contents and is characterized by enrichment in light rare earth elements (LREE), large ion lithosphile elements (LILE), Sr, Eu, and Ba, and depletion in high field strength elements (HFSE). The enriched isotopic signatures (87Sr/86Sri = ~ 0.7065, εNd(t) = ~- 0.5, 208Pb/204Pbi = ~ 38.05, 207Pb/204Pbi = ~ 15.56, 206Pb/204Pbi = ~ 18.20 and zircon εHf(t) = ~+ 5.8) indicate an enriched mantle (EM2) source, with some addition of continental material. It has arc geochemical affinities similar to Permian arc igneous rocks in the eastern margin of the Jiamusi Block, the Yakuno Ophiolite in SW Japan, arc rocks along the western margin of the North America Craton, and also the Gympie Group in eastern Australia. All these features, together with information from tectonic discrimination diagrams, suggest that the Dongfanghong gabbro formed in an immature island arc. The spatial configuration of ~ 290 Ma immature continental arc rocks in the eastern part of the Jiamusi Block and the ~ 275 Ma immature island arc Dongfanghong gabbro in the Wandashan Orogen to the east is best explained by eastward arc retreat and slab roll-back of the Paleo-Pacific Plate. This model is also supported by the Carboniferous-Permian stratigraphic transition in the Jiamusi Block from oceanic carbonate rocks to coal-bearing terrestrial clastic rocks and andesites. We thus suggest that both Paleo-Pacific subduction and roll-back occurred in the Early Permian along the eastern margin of Asia.

  13. Three evolutionary stages of the collision orogenic deformation in the Middle Yangtze Region

    Institute of Scientific and Technical Information of China (English)

    SUN; Yan

    2001-01-01

    13]Sun Yan Sbu Liangshu, Faure, M. et al., Tectonic development of the metamorphic core complex of Wugongshan in the Northern Jiangxi Province, Jour. of Nanjing University, 1997, 33: 447-449.[14]Faure. M., Sun Yah, Shu Liangshu et al., Extensional tectonics within a subduction-type orogen, the case study of the Wugongshan dome, Tectonophysics, 1996, 263: 77- 106.[15]Shu Liangshu, Shi Yangshen, Guo Lingzhi et al., Plate Tectonic Evolution and the Kinematics of Collisional Orogeny in the Middle Jiangnan, Eastern China, Nanjing: Publishing House of Nanjing University, 1995, 14-149.[16]Sun Yan, Shi Zejin Study on mechanical parameters of rocks and regional layerslip system in Hunan-Jiangxi area, Science in China, Ser. B. 1993, 36(8): 962-975.[17]Xu Zhiqin, Chui Junwen, Tectonic Dynamics of the Continental China, Beijing: Metallurgical Industry Publishing House, 1996, 89-178.[18]Sun Yan, Tectonics and mineralization of Lachlan Fold Belt, Canberra, Geol. Soc. of Australia, 1991, 29: 52-53.[19]Faure, M., The geodynamic evolution of the Eastern Eurasian margin in Mesozoic times, Tectonophysics, 1992, 208: 97-411.[20]Herwegh, M., Handy, M. R., Heilbronner, R., Evolution of mylonitic microfabric (EMM), a computer application for educational purposes, Tectonophysics, 1999, 303: 141-146.21.Wiens, D. A., Sliding skis and slipping faults, Nature, 1998, 279: 824-825.[21]Sun Yan, Suzuki, T., Study on the ductile deformation domain of the simple shear in rocks, Science in China, Ser. B, 1992,35(12): 1512-1520.[22]Molnar, P., Tapponnier, P., Cenozoic tectonics of Asia: effects of a continental collision, Science, 1975, 189: 419-426.[23]Buke, K.. Sengor, A. B. C., Tectonic escape in evolution of the continenental crust, in Reflection Seismology, The Continental Crust, Geodynamics Series (14). (eds. Barazangi, M., Brown, L.), Washington D.C.: American Geophysical Union,1986. 41 -53.[24]Shan Yanjun, Xia Bangdong, A preliminary discussion on

  14. Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

    Science.gov (United States)

    Offler, R.; Fergusson, C. L.

    2016-04-01

    The Early Palaeozoic proto-Pacific Pacific margin of Gondwana was characterised by a huge turbidite submarine fan with abundant clastic detritus derived from unknown sources within Gondwana. These deposits are widespread in the Lachlan Orogen of southeast Australia and include the Ordovician Adaminaby Group. Here we show that the mudstones and sandstones of the Adaminaby Group have chemical compositions that indicate the detritus in them was derived from a felsic, continental source similar in composition to Post Archean Australian Shales (PAAS). Chondrite normalised REE patterns showing LREE enrichment, flat PAAS normalised patterns and elemental ratios La/Sc, Cr/Th, Cr/V, Th/Sc and Th/U, have been used to support this interpretation. The dominance of quartz, and to a lesser degree plagioclase and biotite in the sandstones, suggests that the source was mainly granodioritic to tonalitic in composition. Th/Yb and Ta/Yb ratios indicate that the source was probably calc-alkaline, continental and shoshonitic. In addition, the presence of detrital muscovite, low-grade metamorphic and felsic volcanic clasts, demonstrates that a low-grade metamorphic terrane and volcanic arc contributed to the detritus observed in the samples. The presence of well-rounded zircons and tourmalines, very high Zr contents, high Zr/Sc and higher Cr/V ratios in some samples particularly in the Shoalhaven River area, indicate that some of the detritus was recycled. SiO2 versus (Al2O3 + K2O + Na2O) plots suggest the source areas experienced conditions varying from humid/semi-humid to semi-arid. Textural features and weathering trends of samples from all locations follow a curved pathway on Al2O3 - (CaO* + Na2O) - K2O (ACNK) diagrams, and indicate that the clays formed from weathering had been K-metasomatised prior to penetrative deformation. Chemical indices of alteration (CIA) reveal that even the freshest sandstones are altered and others are moderately to strongly altered. Discrimination

  15. Contrasting zircon morphology and UPb systematics in peralkaline and metaluminous post-orogenic granite complexes of the Arabian Shield, Kingdom of Saudi Arabia

    Science.gov (United States)

    Aleinikof, J.N.; Stoeser, D.B.

    1989-01-01

    Uzircon ages are reported for seven metaluminous-to-peralkaline post-orogenic granites from the Late Proterozoic Arabian Shield of Saudi Arabia. Zircons from the metaluminous rocks are prismatic, with length-to-width ratios of ??? 2-4: 1 and small pyramidal terminations. In contrast, zircons from three of the four peralkaline complexes either lack well-developed prismatic faces (are pseudo-octahedral) or are anhedral. Some zircons from the peralkaline granites contain inherited radiogenic Pb and have very high common Pb contents (206Pb/204Pb Zircons in the metaluminous granites do not contain inheritance and yield well-defined concordia intercepts. The span of ages of the seven complexes (670-470 Ma) indicates that post-orogenic granitic magmatism was not a singular event in the Arabian Shield but rather occurred as multiple intrusive episodes from the Late Proterozoic to the Middle Ordovician. ?? 1989.

  16. The Kharapeh orogenic gold deposit: Geological, structural, and geochemical controls on epizonal ore formation in West Azerbaijan Province, Northwestern Iran

    Science.gov (United States)

    Niroomand, Shojaeddin; Goldfarb, Richard J.; Moore, Farib; Mohajjel, Mohammad; Marsh, Erin E.

    2011-01-01

    The Kharapeh gold deposit is located along the northwestern margin of the Sanandaj–Sirjan Zone (SSZ) in the West Azerbaijan province, Iran. It is an epizonal orogenic gold deposit formed within the deformed zone between central Iran and the Arabian plate during the Cretaceous–Tertiary Zagros orogeny. The deposit area is underlain by Cretaceous schist and marble, as well as altered andesite and dacite dikes. Structural analysis indicates that the rocks underwent tight to isoclinal recumbent folding and were subsequently co-axially refolded to upright open folds during a second deformation. Late- to post-tectonic Cenozoic granites and granodiorites occur northeast of the deposit area. Mineralization mainly is recognized within NW-trending extensional structures as veins and breccia zones. Normal faults, intermediate dikes, and quartz veins, oriented subparallel to the axial surface of the Kharapeh antiform, indicate synchronous extension perpendicular to the fold axis during the second folding event. The gold-bearing quartz veins are >1 km in length and average about 6 m in width; breccia zones are 10–50 m in length and ≤1 m in width. Hydrothermal alteration mainly consists of silicification, sulfidation, chloritization, sericitization, and carbonatization. Paragenetic relationships indicate three distinct stages—replacement and silicification, brecciation and fracture filling, and cataclastic brecciation—with the latter two being gold-rich. Fluid inclusion data suggest mineral deposition at temperatures of at least 220–255°C and depths of at least 1.4–1.8 km, from a H2O–CO2±CH4 fluid of relatively high salinity (12–14 wt.% NaCl equiv.), which may reflect metamorphism of passive margin carbonate sequences. Ore fluid δ18O values between about 7‰ and 9‰ suggest no significant meteoric water input, despite gold deposition in a relatively shallow epizonal environment. Similarities to other deposits in the SSZ suggest that the deposit formed as

  17. Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple Magma Types During Orogenic Collapse

    Science.gov (United States)

    Freeman, M.; Owen, J. P.; Hoskin, P. W.

    2009-05-01

    Eocene dyke swarms in southeastern British Columbia provide an important record of the tectonic and magmatic history of the Cordillera following orogenic collapse. New field mapping, petrographic, and geochemical data is presented for a swarm of more than thirty dykes located near the mining town of Trail, B.C. Detailed field mapping revealed that individual dykes are highly diverse, both in composition and morphology. As a group, the dykes trend northwest (average strike of 338 degrees) and dip steeply to the southwest. Their average thickness is approximately 1.5m, with a range from 4.5m to less than 1cm. Three sub-parallel dykes were mapped for a length of 2km, and exhibit irregularities in their form such as branching and offshoots that follow fractures in the country rock. Thin-section analysis shows a wide variety of rock types within the swarm, including: micro-quartz syenite, micro-syenite, micro-monzonite, latite, basalt, basaltic andesite, and lamprophyre. Texturally, these samples are consistently porphyritic and partially altered to chlorite and sericite. This alteration commonly occurs in concentric rims around phenocrysts. The samples are typically intergranular, although some display trachytic texture. Whole-rock geochemistry shows that the dykes have a wide range in composition, with SiO2 between 76.45 wt.% and 45.15 wt.% and MgO between 0.13 wt.% and 13.16 wt.%. The results also revealed that one dyke has very high values of Ni (430 ppm), Cr (1420 ppm), and Co (50 ppm), giving it a fairly primitive composition. Harker diagrams and trace element plots show three distinct groups: mafic calc-alkaline dykes, felsic calc- alkaline dykes, and minette lamprophyres. The felsic dykes are characterized by negative Eu and Sr anomalies suggesting fractionation of plagioclase feldspar, as well as pronounced negative P and Ti anomalies. The minettes are enriched in LILE and depleted in HSFE relative to the mafic dykes. The three groups do not appear to be

  18. Post-orogenic evolution of the coupled foreland megafan/mountainous catchment system : the Lannemezan megafan and its cactchment in the Northern Pyrenees (SW France)

    OpenAIRE

    Mouchené, Margaux

    2016-01-01

    This thesis aims at deciphering the respective roles of autogenic processes and allogenic forcing in the post-orogenic evolution of a coupled mountain catchment/foreland megafan system, with a focus on the Lannemezan megafan and its mountainous catchment in the northern Pyrenees (France). AFT data are consistent with previously published thermochronological data, showing (i) the main exhumation phase of the Axial Zone (AZ; ~50-30 Ma) with lateral variations in the exhumation rates, (ii) a lat...

  19. Aeromagnetic study of the Hengshan-Wutai-Fuping region: Unraveling a crustal profile of the Paleoproterozoic Trans-North China Orogen

    Science.gov (United States)

    Zhang, Jian; Zhao, Guochun; Shen, Wenlue; Li, Sanzhong; Sun, Min

    2015-11-01

    An integrated crustal profile of the intervening Trans-North China Orogen (TNCO) is one of the key issues to understanding the tectonic evolution of the North China Craton. However, the existing geological studies focus only on the surface-mapping based petrological, geochemical and structural analysis, but lack subsurface geophysical evidence and thus make the crustal profile interpretations ambiguous. In contrast, the current geophysical data covers a very large-scale lithospheric mantle and fails to image the detailed structural pattern of the orogenic crust. To achieve this goal, we present high-resolution aeromagnetic data for the Hengshan-Wutai-Fuping region, the largest exposure of the central TNCO. The reduced-to-pole magnetic anomaly map firstly verifies the regional tectonic subdivision that the high-grade metamorphic terranes (i.e. Hengshan and Fuping Complexes) are consistent with high-magnetic responses and long-wavelength anomalies, intervened by a low-grade terrane (Wutai Complex) characterized by low-magnetic responses and short-wavelength anomalies. 3D Euler deconvolution reveals that the tendencies of the clustered solutions show large consistence with the major structural pattern of the region which is characterized by a fan-shaped doubly-vergent orogenic wedge. Upward continuation further shows that the northwest part of the orogen yields a thicker crust and is most likely located closer to the paleosubduction zone. The new aeromagnetic data, combined with structural, petrological and metamorphic data indicate that an eastward-dipping subduction zone was most possibly active before the collision of the Western and Eastern Blocks, leading to the formation of the TNCO and the final amalgamation of the North China Craton.

  20. Subsidence, stress regime and rotation(s) of a tectonically active sedimentary basin within the western Alpine Orogen: the Tertiary Piedmont Basin (Alpine domain, NW Italy)

    OpenAIRE

    Carrapa, B.; Bertotti, G.; Krijgsman, W.

    2003-01-01

    The Oligocene to Miocene Tertiary Piedmont Basin (TPB) is located in the NW part of Italy at the junction between the Apennine and the Alpine thrust belts. The position of the TPB on top of the Alpine/Apennine Orogen poses fundamental questions as to the tectonics of the basin subsidence. Having undergone little deformation, the TPB sediments provide an insight into the stress regime and rotations in the kinematically very complex area surrounding the basin itself. In this study we integrate ...

  1. Influence of syn-sedimentary faults on orogenic structures in a collisional belt: Insights from the inner zone of the Northern Apennines (Italy)

    Science.gov (United States)

    Brogi, Andrea

    2016-05-01

    This paper discusses the possible influence of syn-sedimentary structures on the development of orogenic structures during positive tectonic inversion in the inner Northern Apennines (Italy). Examples from key areas located in southern Tuscany provided original cartographic, structural and kinematics data for Late Oligocene-Early Miocene thrusts, organized in duplex systems, verging in the opposite direction of the foreland propagation (back-thrusts), which affected the Late Triassic-Oligocene sedimentary succession of the Tuscan Domain, previously affected by pre-orogenic structures. These latter consist of mesoscopic-to cartographic-scale Jurassic syn-sedimentary normal faults and extensional structures, which gave rise to effective stratigraphic lateral variation and mechanical heterogeneities. Structural analysis of both syn-sedimentary faults and back-thrusts were therefore compared in order to discuss the possible role of the pre-existing anisotropies in influencing the evolution of the back-thrusts. As a result, it can be reasonably proposed that back-thrusts trajectories and stacking pattern were controlled by relevant syn-sedimentary normal faults; these latter were reactivated, in some cases, if properly oriented. Such an issue adds new inputs for discussing the potential role of structural inheritance during tectonic inversions, and helps to better understand the processes suitable for the development of back-thrusts in the inner zones of orogenic belts, as it is the case of the inner Northern Apennines.

  2. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: A lead isotope study of an Archaean gold prospect in the Attu region, Nagssugtoqidian orogen, West Greenland

    Directory of Open Access Journals (Sweden)

    Stendal, Henrik

    2006-12-01

    Full Text Available This paper presents a lead isotope investigation of a gold prospect south of the village Attu in the northern part of the Nagssugtoqidian orogen in central West Greenland. The Attu gold prospect is a replacement gold occurrence, related to a shear/mylonite zone along a contact between orthogneissand amphibolite within the Nagssugtoqidian orogenic belt. The mineral occurrence is small, less than 0.5 m wide, and can be followed along strike for several hundred metres. The mineral assemblage is pyrite, chalcopyrite, magnetite and gold. The host rocks to the gold prospect are granulite facies ‘brown gneisses’ and amphibolites. Pb-isotopic data on magnetite from the host rocks yield an isochron in a 207Pb/204Pb vs. 206Pb/204Pb diagram, giving a date of 3162 ± 43 Ma (MSWD = 0.5. This date is interpreted to represent the age of the rocks in question, and is older than dates obtained from rocks elsewhere within the Nagssugtoqidian orogen. Pb-isotopic data on cataclastic magnetite from the shear zone lie close to this isochron, indicating a similar origin. The Pb-isotopic compositions of the ore minerals are similar to those previously obtained from the close-by ~2650 Ma Rifkol granite, and suggest a genetic link between the emplacement of this granite and the formation of the ore minerals in the shear/mylonite zone. Consequently, the age of the gold mineralisation is interpreted tobe late Archaean.

  3. U-Pb zircon ages for the Luzhenguan Complex in northern part of the eastern Dabie orogen

    Institute of Scientific and Technical Information of China (English)

    JIANG; Laili; Wolfgang; Siebe; CHEN; Fukun; LIU; Yican

    2005-01-01

    The study presents U-Pb zircon ages for granitic gneiss and amphibolite from the Luzhenguan Complex (LZC) in northern part of the eastern Dabie Orogen and their geological significance. Two granitic gneisses and one amphibolite give protolith zircon U-Pb ages of 740 Ma and 725 Ma, respectively. The ages show that the LZC is composed mainly of Neoproterzoic acid and basic igneous rocks, suggesting that there is no Paleozoic active continental marginal rock association in the southern margin of the North China Block in northern part of the eastern Dabie Mountain. Based on the ages and combining the geological and geophysical analyses, the middle-low grade metamorphic rocks in the North Huiyang Belt (NHB) can be divided into three parts, which are the LZC composed mainly of the Neoproterzoic acid and basic igneous rocks, the Neoproterzoic Xianrechong Formation and Xiangyunzhai Formation and the Devonian Zhufoan Formation and Pangjialing Formation of the Foziling Group, and the suture zone between the Yongtze Block and the North China Block is inferred to be thrust under the NHB.

  4. EMP chemical ages of monazites from Central Zone of the eastern Kunlun Orogen: Records of multi-tectonometamorphic events

    Institute of Scientific and Technical Information of China (English)

    CHEN NengSong; SUN Min; WANG QingYan; ZHAO GuoChun; CHEN Qiang; SHU GuiMing

    2007-01-01

    Two generations of monazite were identified in one mica schist sample from the central zone of the eastern Kunlun Orogen at the northern margin of the Qinghai-Tibet Plateau.The first generation was found in the cores of garnet porphyroblasts with relatively high Y2O3 contents (averaging 1.012±0.088 wt%).The second generation occurs either as inclusions in the rims of garnet porphyroblasts, matrix kyanite, plagioclase and quartz, or as separate crystals associated with matrix biotite and muscovite mostly having a relatively low Y2O3 content (averaging 0.479±0.100 wt%).Electron microprobe (EMP) Th-U-Pbtotal chemical dating for two grains of the first generation monazite yields average ages of 455 ± 18 Ma and 420 ± 20 Ma, respectively; six grains of the second generation gave an average age of 246.1 ± 3.8 Ma.These ages suggest that the core and rim of the garnet porphyroblasts and their associated assemblages record two events of significant tectonometamorphism.The formation of the Ordovician monazite is related to the tectonometamorphic event responsible for continuous amalgamation of the Gondwanaland in the Late Pan-African period or for consumption of the Proto-Tethys, whereas the development of the Triassic monazite is related to the tectonometamorphic event for consumption of the Paleo-Tethys.

  5. The Ediacaran Rio Doce magmatic arc revisited (Araçuaí-Ribeira orogenic system, SE Brazil)

    Science.gov (United States)

    Tedeschi, Mahyra; Novo, Tiago; Pedrosa-Soares, Antônio; Dussin, Ivo; Tassinari, Colombo; Silva, Luiz Carlos; Gonçalves, Leonardo; Alkmim, Fernando; Lana, Cristiano; Figueiredo, Célia; Dantas, Elton; Medeiros, Sílvia; De Campos, Cristina; Corrales, Felipe; Heilbron, Mônica

    2016-07-01

    Described half a century ago, the Galiléia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Araçuaí-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galiléia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Araçuaí orogen. Meanwhile, the name Rio Doce magmatic arc was applied to calc-alkaline plutons found in the Araçuaí-Ribeira boundary. After those pioneer studies, the calc-alkaline plutons showing a pre-collisional volcanic arc signature and age between 630 Ma and 585 Ma have been grouped in the G1 supersuite, corresponding to the Rio Doce arc infrastructure. Here, we revisit the Rio Doce arc with our solid field knowledge of the region and a robust analytical database (277 lithochemical analyses, and 47 U-Pb, 53 Sm-Nd, 25 87Sr/86Sr and 7 Lu-Hf datasets). The G1 supersuite consists of regionally deformed, tonalitic to granodioritic batholiths and stocks, generally rich in melanocratic to mesocratic enclaves and minor gabbroic to dioritic plutons. Gabbroic to dioritic enclaves show evidence of magma mixing processes. The lithochemical and isotopic signatures clearly reveal a volcanic arc formed on a continental margin setting. Melts from a Rhyacian basement form the bulk of the magma produced, whilst gabbroic plutons and enclaves record involvement of mantle magmas in the arc development. Tonalitic stocks (U-Pb age: 618-575 Ma, εNd(t): -5.7 to -7.8, Nd TDM ages: 1.28-1.68 Ga, 87Sr/86Sr(t): 0.7059-0.7118, and εHf(t): -5.2 to -11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Araçuaí orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galiléia, Muniz Freire, São Vítor) record a long-lasting magmatic history (632-580 Ma; εNd(t): -5.6 to -13.3; Nd TDM age: 1.35-1.80 Ga; 87Sr/86Sr(t): 0.7091-0.7123). At arc western border, the magmatic

  6. The structure of the Temsamane fold-and-thrust stack (eastern Rif, Morocco): Evolution of a transpressional orogenic wedge

    Science.gov (United States)

    Jabaloy-Sánchez, Antonio; Azdimousa, Ali; Booth-Rea, Guillermo; Asebriy, Lahcen; Vázquez-Vílchez, Mercedes; Martínez-Martínez, José Miguel; Gabites, Janet

    2015-11-01

    The structure of the Temsamane fold-and-thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds. This ductile stack was formed in an inclined left-handed transpressional zone at the North African paleomargin during Chattian to Langhian times producing two main deformational events. The first event (Dp) produced a Sp/Lp planar linear fabric generated in a non-coaxial deformation with a top-to-the-WSW sense of movement and was associated to metamorphic P-T conditions varying from late diagenesis in the southernmost Temsamane outcrops to epizone in the north. According to the 40Ar/39Ar ages, this deformation occurred at Chattian-Aquitanian times. The second deformational event (Dc event) generated ENE-WSW trending folds with SSE vergence and a set of anastomosing shear zones with Sm/Lm planar linear fabric. The latter units were generated at around 15 Ma (Langhian), and indicate a strong localization of the simple shear component of the transpression. Moreover, this orientation is compatible with the kinematics of the Temsamane detachment, which can explain most of the uplift of the Temsamane rocks from the middle to the uppermost crust. The described evolution indicates that collision between the western Mediterranean terranes and the North African paleomargin and the formation of the Rifean orogenic wedge occurred at Chattian to Langhian times.

  7. Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet

    Science.gov (United States)

    Zhang, Zeming; Xiang, Hua; Dong, Xin; Ding, Huixia; He, Zhenyu

    2015-01-01

    The Namche Barwa Complex exposed in the Eastern Himalayan Syntaxis, south Tibet, underwent high-pressure (HP) and high-temperature (HT) granulite-facies metamorphism and associated anatexis. The HP pelitic granulites contain garnet, kyanite, sillimanite, cordierite, biotite, quartz, plagioclase, K-feldspar, spinel, ilmenite and graphite. These minerals show composite reaction texture and varying chemical compositions and form four successive mineral assemblages. Phase equilibrium modeling constrains the P-T conditions of 10-12 kbar and 550-700 °C for the prograde stage, 13-16 kbar and 840-880 °C for the peak-metamorphic stage, and 5-6 kbar and 830-870 °C for the late retrograde stage, indicating that the HP granulites recorded a clockwise P-T path involving the early heating burial and anatexis through dehydration melting of both muscovite and biotite, and the late isothermal decompression and gradual melt crystallization under HT granulite-facies conditions. The zircon U-Pb dating reveals that the HT granulite-facies metamorphism probably initiated at ca. 40 Ma, and lasted to ca. 8 Ma. Therefore, the present study provides robust evidence for a long-lived HT metamorphism and associated anatexis in the deeply buried Indian continent and important constraints on the leucogranite generation and tectonic evolution of the Himalayan orogen.

  8. Evolution, source and tectonic significance of Early Mesozoic granitoid magmatism in the Central Asian Orogenic Belt (central segment)

    Science.gov (United States)

    Li, Shan; Wang, Tao; Wilde, Simon A.; Tong, Ying

    2013-11-01

    Numerous Early Mesozoic granitoids have been recognized from the central segment of the Central Asian Orogenic Belt (CAOB). They can be broadly classified into two groups according to zircon U-Pb ages: an early-stage group covering the time span from Early to Middle Triassic (250-230 Ma) and a late-stage group emplaced during Late Triassic to Early Jurassic (ca. 230-190 Ma). Early-stage (250-230 Ma) granitoids are mainly distributed in the western Central Mongolia-Erguna Belt (CMEB), the western Altai Belt (AB), the South Mongolia-Xing'an Belt (SMXB) and the Beishan-Inner Mongolia-Jilin Belt (BIJB). They consist mainly of quartz-diorites, granodiorites and monzogranites, mostly of I-type, with minor mafic intrusions, with some of them showing adakite-like signatures and some with S-type features. Late-stage (230-190 Ma) granitoids mainly occur in the North Mongolia-Transbaikalia Belt (NMTB), the eastern CMEB (Erguna massif) and the eastern Altai Belt (AB). They are predominately syenogranites, monzogranites and syenites, associated with many alkaline granites and mafic intrusions and are A-type and transitional I-A type or highly fractionated I-type granites.

  9. Detrital zircon provenance analysis in the Zagros Orogen, SW Iran: implications for the amalgamation history of the Neo-Tethys

    Science.gov (United States)

    Zhang, Zhiyong; Xiao, Wenjiao; Majidifard, Mahmoud Reza; Zhu, Rixiang; Wan, Bo; Ao, Songjian; Chen, Ling; Rezaeian, Mahnaz; Esmaeili, Rasoul

    2016-03-01

    The Zagros Orogen developed as a result of Arabia-Eurasia collision. New in situ detrital zircon U-Pb and Hf isotopic analyses from a Cenozoic sedimentary sequence in SW Iran are used to unravel the amalgamation history of Neo-Tethys. Data indicate that: (1) Paleocene and Eocene strata (58 and 45 Ma, respectively) were sourced from obducted ophiolite and Triassic volcanics, (2) Lower Miocene (~18 Ma) strata indicate mixed provenance from obducted ophiolite and Iranian magmatic rocks, (3) Mid to Upper Miocene sediments (~14 to 11.2 Ma) were mainly sourced from Sanandaj-Sirjan zone granitoids to the north, and (4) Lower Pliocene (~5 Ma) sediments mainly show Arabian age characteristics, with a minor Eurasian affinity component. Two hypotheses are outlined to highlight the key events: Hypothesis A, previously published by several workers, suggests that the sequence studied lay on the Arabia passive margin and that initial collision occurred prior to 18 Ma; Hypothesis B, modified from the Makran model, which is here preferred, suggests that Paleogene to Upper Miocene sediments were sourced from the northern Neo-Tethyan accretionary complex or Eurasia, and carry no input from Arabia, whereas the Lower Pliocene sample shows a mixed provenance from both Arabia and Eurasia, suggesting that collision occurred between ~11.2 and 5 Ma.

  10. An interpretation of the aeromagnetic data covering the western portion of the Damara orogen in South West Africa/Namibia

    International Nuclear Information System (INIS)

    A study of the aeromagnetic data covering the western portion of the Damara Orogen was undertaken in order to determine whether any additional information relating to the occurrence of uraniferous granite in the area could be derived from these data. The study included palaeomagnetic surveys and an interpretation of the regional structure, coupled with computer modelling of a geomagnetic section across the belt. A number of features are evident from this study, viz: (i) All currently known uraniferous alaskitic granite occurrences of economic interest are hallmarked, on a semi-regional basis, by prominent negative geomagnetic anomalies. (ii) A number of structural lineaments and broader lineament zones are apart from the Okahandja Lineament, recognised and named for the first time. Computer modelling studies support the hypothesis that these geomagnetic lineament zones are in fact fault-controlled geanticlinal ridges bounded by relatively rapid monoclinal downfolding of the stratigraphy: (iii) A post-F3 (north-east) structural phase, F4, oriented north-north-east is concluded to be of particular significance to the emplacement of uraniferous granite since, firstly, the major fold axes of the domes and structures with which these occurrences are associated mostly have this orientation and, secondly, the currently known occurrences are exposed along the north-north-easterly trending Welwitschia lineament zone

  11. Distribution, Microfabric, and Geochemical Characteristics of Siliceous Rocks in Central Orogenic Belt, China: Implications for a Hydrothermal Sedimentation Model

    Directory of Open Access Journals (Sweden)

    Hongzhong Li

    2014-01-01

    Full Text Available Marine siliceous rocks are widely distributed in the central orogenic belt (COB of China and have a close connection to the geological evolution and metallogenesis. They display periodic distributions from Mesoproterozoic to Jurassic with positive peaks in the Mesoproterozoic, Cambrian—Ordovician, and Carboniferous—Permian and their deposition is enhanced by the tensional geological settings. The compressional regimes during the Jinning, Caledonian, Hercynian, Indosinian, and Yanshanian orogenies resulted in sudden descent in their distribution. The siliceous rocks of the Bafangshan-Erlihe ore deposit include authigenic quartz, syn-depositional metal sulphides, and scattered carbonate minerals. Their SiO2 content (71.08–95.30%, Ba (42.45–503.0 ppm, and ΣREE (3.28–19.75 ppm suggest a hydrothermal sedimentation origin. As evidenced by the Al/(Al + Fe + Mn, Sc/Th, (La/YbN, and (La/CeN ratios and δCe values, the studied siliceous rocks were deposited in a marginal sea basin of a limited ocean. We suggest that the Bafangshan-Erlihe area experienced high- and low-temperature stages of hydrothermal activities. The hydrothermal sediments of the former stage include metal sulphides and silica, while the latter was mainly composed of silica. Despite the hydrothermal sedimentation of the siliceous rocks, minor terrigenous input, magmatism, and biological activity partly contributed to geochemical features deviating from the typical hydrothermal characteristics.

  12. Sediment yield along the Andes: continental budget, regional variations, and comparisons with other basins from orogenic mountain belts

    Science.gov (United States)

    Latrubesse, Edgardo M.; Restrepo, Juan D.

    2014-07-01

    We assess the sediment yield at 119 gauging stations distributed from Colombia to Patagonia, covering the different morphotectonic and morphoclimatic settings of the Andes. The most productive areas are the Meta River basin within the northern Andes and the Bolivian and northern Argentina-Chaco systems, which produce an average of 3345, 4909 and 2654 t km2 y- 1 of sediment, respectively. The rivers of the northern and central Andes (excluding the Pacific watersheds of Peru, northern Chile, and central Argentina) have a weighted mean sediment yield of 2045 t km- 2 y- 1 and produce 2.25 GTy- 1 of total sediment. A major constraint estimating the Andean continental budget of sediment yield lies in the lack of gauging data for the Peruvian region. Using the available gauge stations, the regional sediment yield appears underestimated. Assuming a higher value of sediment yield for the Peruvian Andes, the total budget for the whole central Andes could range between 2.57 GT y- 1 and 3.44 GT y- 1. A minimum of ~ 0.55 GT y- 1 and a probable maximum of ~ 1.74 GT y- 1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins. The magnitude of sediment yield in the Andes is comparable to other rivers draining orogenic belts around the world.

  13. Pre- and syn-Ross orogenic granitoids at Drake Head and Kartografov Island, Oates Coast, northern Victoria Land, East Antarctica

    International Nuclear Information System (INIS)

    The majority of the Oates Coast, northern Victoria Land granitoids, typified by those at Drake Head and Kartografov Island (Harald Bay), are monzogranites with lesser granodiorites and minor quartz-monzodiorite and syenogranite. All are plagioclase-K-feldspar-biotite granitoids with additional muscovite, garnet and/or hornblende, and are subalkaline and peraluminous. Berg Granite typifies the early Ordovician, Granite Harbour Instrusive (GHI) suite of the Ross Orogen at the Oates Coast. Granitoids from Kartografov Island have higher amounts of Fe+Mg+Ti and an ambiguous Rb-Sr geochronology: they could be either pre-Ross Orogeny in age, or syn-Ross Orogeny and representing a lower structural level of GHI. The Drake Head granite gneiss has a fractionated leuco-granite composition similar to Berg Granite, and is intruded by granite and granodiorite. Rb-Sr ages indicate that all are Neoproterozoic, although the granite gneiss result is probably an errorchron age, reflecting its less uniform nature (granodiorite:649 ± 30 Ma, initial ratio 0.7065 +/- 6; granite gneiss: 682 ± 140 Ma, initial ratio 0.7107 ± 50). These late Neoproterozoic granitoids provide a source for distinctive detrital zircon age components in extensive early Paleozoic turbidites of Australia-New Zealand-Antarctica. (author). 24 refs., 5 figs., 1 tab

  14. Altered crystalline rock distributed along groundwater conductive fractures and the retardation capacity in the orogenic field of Japan - 16332

    International Nuclear Information System (INIS)

    In the orogenic field Japanese islands, there are wide areas of crystalline rocks that inevitably contain groundwater conductive fractures associated with alteration zones. However, little attention has been given to the formation process and possible influence on the radionuclides migration from radioactive waste repository that might be sited within crystalline rock. In particular, the influences of alteration minerals and micro-fractures, due to chemical sorption and/or physical retardation are required to assess the realistic barrier function. In order to understand the alteration process and the retardation capacity, detailed mineralogical and physico-chemical characterization of altered crystalline rocks have been carried out. Mineralogical analysis reveals that the altered crystalline rocks have been formed through basically two stages of water-rock interaction during and after uplift. Physico-chemical characteristics including laboratory sorption experiments show that altered crystalline rock has a certain volume of accessible porosity, particularly in plagioclase grains, which would influence on nuclide retardation more than the accessible porosity in other minerals present, such as biotite. These results provide confidence that even altered and fractured parts of any crystalline rock that might be encountered in a site for the disposal of high-level radioactive waste may still play a role of barrier function. (authors)

  15. A mineralogical, petrological and geochemical study of a suite of rocks from the Damara Orogenic Belt South West Africa

    International Nuclear Information System (INIS)

    This work was a pilot study in which the petrology, mineralogy and geochemistry of a suite of rocks from the Khan/Swakop area of the Damara Orogen were investigated. Petrographic and mineralogical data are presented for about 140 samples. This data (1) assisted in the selection of suitable samples for chemical analysis; (2) aided in the classification of the samples as a basis for geochemical classification; (3) allowed the samples to be correlated with the regional geology of the area. It was found that petrographic examination alone cannot be used to distinguish between mineralised and unmineralised alaskites. Certain features although not exclusive to mineralised and unmineralised alaskites are nevertheless in general characteristic of these rocks types. the X-ray diffraction analysis indicated that mineralised alaskites, even from different localites, produced characteristic X-ray diffractograms which separated them from the rest of the rock-types including the unmineralised alaskites. The geochemical interpretation of the data showed that it was possible to distinguish between the main rock groups using both the major and trace elements. With using the trace elements only this distinction was not possible. Mineralogical relationships within the rock groups could be inferred from the geochemical results thereby complementing the petrographic investigation. It was established that in the main, mineralised alaskites are K-feldspar rich with biotite and no muscovite and that the thorium and rare-earth contents should be high

  16. Mineralization Zoning in Yindongzi—Daxigou Barite—Siderite,Silver—Polymetallic Deposits in the Qinling Orogen,China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 等

    2001-01-01

    The Yindongzi-Daxigou strata-bound barite-siderite,silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate.The orebodies occur in a series of hydrothermal depositonal rocks.Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ab→Cu-Ag→Pb→Au.This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization.In this gradational transition between Chefanggou and Yindongzi,vent-proximal mineralization consists of silver-polymetallic orebodies(Pb-Ag),which is the center of hydrothermal mineralization.The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization.Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in te east is represented by the Pb ore district.Thick massive,laminated barren albite chert and jasperite,sometimes with minor silver-ploymetallic mineralization of commercial importance,and pyritization in rocks feature more distal mineralization.Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually,Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  17. Mineralization Zoning in Yindongzi-Daxigou Barite-Siderite, Silver-Polymetallic Deposits in the Qinling Orogen, China

    Institute of Scientific and Technical Information of China (English)

    方维萱; 胡瑞忠; 黄转莹

    2001-01-01

    The Yindongzi-Daxigou strata-bound barite-siderite, silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate. The orebodies occur in a series of hydrothermal depositional rocks. Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ag→Cu-Ag→Pb→Au. This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization. In this gradational transition between Chefanggou and Yindongzi, vent-proximal mineralization consists of silver-polymetallic orebodies (Pb-Ag), which is the center of hydrothermal mineralization. The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization. Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in the east is represented by the Pb ore district. Thick massive, laminated barren albite chert and jasperite, sometimes with minor silver-ploymetallic mineralization of commercial importance, and pyritization in rocks feature more distal mineralization. Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually, Au deposits are dominantly controlled by the late brittle-ductile shear zone.

  18. Middle Miocene paleoaltimetry of southern Tibet: Implications for the role of mantle thickening and delamination in the Himalayan orogen

    Science.gov (United States)

    Currie, Brian S.; Rowley, David B.; Tabor, Neil J.

    2005-03-01

    The stable isotope composition of pedogenic and early diagenetic carbonates from the Oiyug Basin of southern Tibet allows model estimates of the paleoaltimetry of the Tibetan Plateau for the middle Miocene. Pedogenic calcium carbonate nodules have average δ18Occ values of -19.6‰, whereas nodular lacustrine dolomites range in composition from -7.6‰ to -5.5‰. The most negative of the carbonate isotope values can be used to constrain the oxygen isotope composition of paleoprecipitation, from which model estimates of paleoaltimetry can be made. Model results indicate that the southern Tibetan Plateau achieved elevations of ˜5200 +1370/-605 m by at least 15 Ma. Our results are identical within uncertainty to previous workers' paleoelevation estimates based on Oiyug Basin fossil floral physiognomy. This is the first time that two paleoaltimeters have been directly compared and are in accord. Collectively, these data strongly support tectonic models in which thickening of mantle lithosphere beneath the domain of crustal thickening and subsequent detachment of the mantle lithosphere plays an indiscernible role in the elevation history of this part of the Himalaya-Tibet orogenic system.

  19. Structural evolution of the Irtysh Shear Zone (northwestern China) and implications for the amalgamation of arc systems in the Central Asian Orogenic Belt

    Science.gov (United States)

    Li, Pengfei; Sun, Min; Rosenbaum, Gideon; Cai, Keda; Yu, Yang

    2015-11-01

    The NW-SE Irtysh Shear Zone is a major tectonic boundary in the Central Asian Orogenic Belt (CAOB), which supposedly records the amalgamation history between the peri-Siberian orogenic system and the Kazakhstan/south Mongolia orogenic system. However, the tectonic evolution of the Irtysh Shear Zone is not fully understood. Here we present new structural and geochronological data, which together with other constraints on the timing of deformation suggests that the Irtysh Shear Zone was subjected to three phases of deformation in the late Paleozoic. D1 is locally recognized as folded foliations in low strain areas and as an internal fabric within garnet porphyroblasts. D2 is represented by a shallowly dipping fabric and related ˜ NW-SE stretching lineations oriented sub-parallel to the strike of the orogen. D2 foliations are folded by ˜ NW-SE folds (F3) that are bounded by a series of mylonite zones with evidence for sinistral/reverse kinematics. These fold and shear structures are kinematically compatible, and thus interpreted to result from a transpressional deformation phase (D3). Two samples of mica schists yielded youngest detrital zircon peaks at ˜322 Ma, placing a maximum constraint on the timing of D1-D3 deformation. A ˜ NE-SW granitic dyke swarm (˜252 Ma) crosscuts D3 fold structures and mylonitic fabrics in the central part of the shear zone, but is displaced by a mylonite zone that represents the southern boundary of the Irtysh Shear Zone. This observation indicates that the major phase of D3 transpressional deformation took place prior to ˜252 Ma, although later phases of reactivation in the Mesozoic and Cenozoic are likely. The late Paleozoic deformation (D1-D3 at ˜322-252 Ma) overlaps in time with the collision between the Chinese Altai and the intra-oceanic arc system of the East Junggar. We therefore interpret that three episodes of late Paleozoic deformation represent orogenic thickening (D1), collapse (D2), and transpressional deformation (D3

  20. Origin of Silurian gabbros and I-type granites in central Fujian, SE China: Implications for the evolution of the early Paleozoic orogen of South China

    Science.gov (United States)

    Zhang, Qiao; Jiang, Yao-Hui; Wang, Guo-Chang; Liu, Zheng; Ni, Chun-Yu; Qing, Long

    2015-02-01

    The early Paleozoic orogen of South China is possibly one of the few examples of intraplate orogeny in the world. It is characterized by an angular unconformity between post-Silurian cover and pre-Devonian strata and by the intensive and extensive early Paleozoic granitic plutonism. However, synchronous mafic-ultramafic rocks have not been well-studied, but they are crucial for understanding the nature and evolution of the orogen. In this paper, we present the first detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical and Sr-Nd-Hf isotopic data for a Silurian gabbroic pluton (Dakang) and a coeval granitic pluton (Guiyang), that have recently been identified in central Fujian, in the southeastern part of the orogen. We assess the origin of these mafic and granitic rocks and their relationship to the evolution of the early Paleozoic orogen in South China. LA-ICP-MS zircon U-Pb dating shows that the Dakang and Guiyang plutons were emplaced at 441-438 Ma and 431 Ma, respectively. The Dakang pluton consists of gabbros and minor intermediate rocks (diorite, monzodiorite and monzonite). These rocks are all metaluminous and potassic, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They have initial 87Sr/86Sr of 0.7066-0.7098, εNd (T) of - 7.0 to - 3.3 and εHf (T) (in-situ zircon) of - 5.2 to - 4.4. Geochemical data suggest that the Dakang gabbroic magmas were derived by partial melting of previously subduction-modified lithospheric mantle in the spinel-garnet transition zone at a high temperature (~ 1300 °C). These primary magmas underwent fractionation crystallization of clinopyroxene and amphibole, forming the evolved gabbros and intermediate rocks. The Guiyang pluton consists of weakly peraluminous granites, which show low Ga/Al ratios (10,000*Ga/Al < 2.6) and so can be classed as I-type granites. They have initial 87Sr/86Sr of 0.7095-0.7113, εNd (T) of - 6.7 to - 5.9 and εHf (T

  1. Porphyry copper assessment of the Central Asian Orogenic Belt and eastern Tethysides: China, Mongolia, Russia, Pakistan, Kazakhstan, Tajikistan, and India: Chapter X in Global mineral resource assessment

    Science.gov (United States)

    Mihalasky, Mark J.; Ludington, Stephen; Hammarstrom, Jane M.; Alexeiev, Dmitriy V.; Frost, Thomas P.; Light, Thomas D.; Robinson, Gilpin R., Jr.; Briggs, Deborah A.; Wallis, John C.; Miller, Robert J.; Bookstrom, Arthur A.; Panteleyev, Andre; Chitalin, Andre; Seltmann, Reimar; Guangsheng, Yan; Changyun, Lian; Jingwen, Mao; Jinyi, Li; Keyan, Xiao; Ruizhao, Qiu; Jianbao, Shao; Gangyi, Shai; Yuliang, Du

    2015-01-01

    The U.S. Geological Survey collaborated with international colleagues to assess undiscovered resources in porphyry copper deposits in the Central Asian Orogenic Belt and eastern Tethysides. These areas host 20 known porphyry copper deposits, including the world class Oyu Tolgoi deposit in Mongolia that was discovered in the late 1990s. The study area covers major parts of the world’s largest orogenic systems. The Central Asian Orogenic Belt is a collage of amalgamated Precambrian through Mesozoic terranes that extends from the Ural Mountains in the west nearly to the Pacific Coast of Asia in the east and records the evolution and final closure of the Paleo-Asian Ocean in Permian time. The eastern Tethysides, the orogenic belt to the south of the Central Asian Orogenic Belt, records the evolution of another ancient ocean system, the Tethys Ocean. The evolution of these orogenic belts involved magmatism associated with a variety of geologic settings appropriate for formation of porphyry copper deposits, including subduction-related island arcs, continental arcs, and collisional and postconvergent settings. The original settings are difficult to trace because the arcs have been complexly deformed and dismembered by younger tectonic events. Twelve mineral resource assessment tracts were delineated to be permissive for the occurrence of porphyry copper deposits based on mapped and inferred subsurface distributions of igneous rocks of specific age ranges and compositions. These include (1) nine Paleozoic tracts in the Central Asian Orogenic Belt, which range in area from about 60,000 to 800,000 square kilometers (km2); (2) a complex area of about 400,000 km2 on the northern margin of the Tethysides, the Qinling-Dabie tract, which spans central China and areas to the west, encompassing Paleozoic through Triassic igneous rocks that formed in diverse settings; and (3) assemblages of late Paleozoic and Mesozoic rocks that define two other tracts in the Tethysides, the 100

  2. Apatite fission-track thermochronological constraints on the pattern of late Mesozoic-Cenozoic uplift and exhumation of the Qinling Orogen, central China

    Science.gov (United States)

    Chen, Hong; Hu, Jianmin; Wu, Guoli; Shi, Wei; Geng, Yingying; Qu, Hongjie

    2015-12-01

    The Qinling Orogen of central China was formed by intracontinental collision between the North and South China Blocks. The orogen comprises several micro-blocks bounded by sutures and faults, and has undergone long-term intracontinental deformation since the Late Triassic. The micro-blocks include the southern margin of the North China Block (S-NCB), the Northern Qinling Belt (NQB), the Southern Qinling Belt (SQB), and the northern margin of the South China Block (N-SCB). Under a uniform tectonic setting in late Mesozoic-Cenozoic, these micro-blocks have been subjected to a range of deformation styles, as demonstrated by their structural deformation, history of magmatism, and the development of sedimentary basins. To investigate the differences among the micro-blocks and to quantify their uplift and exhumation, we obtained 45 rock samples from eight Mesozoic granites in these micro-blocks, and conducted apatite fission-track (AFT) thermochronological modeling. The results reveal that the Qinling Orogen underwent four distinct stages of rapid cooling histories during the late Mesozoic-Cenozoic, and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south (the N-SCB) and propagated to the north (S-NCB). In the first stage, during the Late Jurassic-Early Cretaceous (ca. 160-120 Ma), rock cooling occurred mainly in the N-SCB, attributed to the clockwise rotation and northward subduction of the South China Block beneath the Qinling Orogen. In the second stage, compression- and extension-related uplift was initiated during the late Early Cretaceous-early Late Cretaceous (ca. 120-90 Ma) in the SQB, consistent with the southward subduction of the North China Block and broadly extensional deformation in the eastern China continent. In the third stage, a gentle regional-scale cooling event that occurred during the latest Cretaceous-Paleocene (ca. 90-50 Ma) started in the NQB and became widespread in the Qinling Orogen. This

  3. Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

    Science.gov (United States)

    Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

    2016-05-01

    The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion-collision processes in NW China, and hosts Paleozoic Cu-Pb-Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U-Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U-Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9-213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67-1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere. In contrast, the

  4. Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

    Science.gov (United States)

    Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

    2016-01-01

    The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion–collision processes in NW China, and hosts Paleozoic Cu–Pb–Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U–Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U–Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9–213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67–1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and

  5. Orogenic development of the Adrar des Iforas (Tuareg Shield, NE Mali): New geochemical and geochronological data and geodynamic implications

    Science.gov (United States)

    Bosch, Delphine; Bruguier, Olivier; Caby, Renaud; Buscail, François; Hammor, Dalila

    2016-05-01

    Laser-ablation U-Th-Pb analyses of zircon and allanite from magmatic and metamorphic rocks of the Adrar des Iforas in Northern Mali allow re-examining the relationships between the different crustal units constituting the western part of the Tuareg Shield, as well as the timing of magmatic and metamorphic events in the West Gondwana Orogen. Granulite-facies metamorphism in the Iforas Granulitic Unit (IGU) and at In Bezzeg occurred at 1986 ± 7 Ma and 1988 ± 5 Ma respectively. This age is slightly younger, but consistent with that of the HT granulite facies event characterizing the In Ouzzal granulitic unit (IOGU), thereby substantiating the view that these units once formed a single granulitic belt of c. 800 km long. High-grade metamorphic basement units of the Kidal terrane surrounding the IGU contain Paleoproterozoic magmatic rocks crystallized between 1982 ± 8 Ma and 1966 ± 9 Ma. Inherited components in these rocks (2.1 Ga and 2.3-2.5 Ga) have ages similar to that of detrital zircons at In Bezzeg and to that of basement rocks from the IGU. This is taken as evidence that the Kidal terrane and the IGU formed a single crustal block at least until 1.9 Ga. East of the Adrar fault, the Tin Essako orthogneiss is dated at 2020 ± 5 Ma, but escaped granulite facies metamorphism. During the Neoproterozoic, the Kidal terrane underwent a long-lived continental margin magmatism. To the west, this terrane is bounded by the Tilemsi intra-oceanic island arc, for which a gneissic sub-alkali granite was dated at 716 ± 6 Ma. A synkinematic diorite extends the magmatic activity of the arc down to 643 ± 4 Ma, and, along with literature data, indicates that the Tilemsi arc has a life span of about 90 Ma. Backward docking to the western margin of the Kidal terrane is documented by migmatites dated at 628 ± 6 Ma. Subduction related processes and the development of the Kidal active margin was responsible for the development of a back-arc basin in the Tafeliant area, with

  6. Structural evolution of the early Permian Nambucca Block (New England Orogen, eastern Australia) and implications for oroclinal bending

    Science.gov (United States)

    Shaanan, Uri; Rosenbaum, Gideon; Li, Pengfei; Vasconcelos, Paulo

    2014-07-01

    The Paleozoic to early Mesozoic southern New England Orogen of eastern Australia exhibits a remarkable ear-shaped curvature (orocline), but the geodynamic processes responsible for its formation are unclear. Oroclinal bending took place during the early Permian, simultaneously with the deposition of the rift-related Sydney, Gunnedah, and Bowen basins, which bound the oroclines to the west. The Nambucca Block is another early Permian rift basin, but it is situated in the core of the oroclinal structure. Here we present new stratigraphic, structural, and geochronological data from the Nambucca Block in an attempt to better understand its tectonic history and relationships to the formation of the oroclines. We recognized four phases of folding and associated structural fabrics (S1-4), with the second phase (S2) dated at 275-265 Ma by 40Ar/39Ar geochronology of muscovite. This age overlaps with independent constraints on the timing of oroclinal bending, suggesting that the earlier two phases of deformation in the Nambucca Block (F1 and F2) were associated with orocline formation. We propose that oroclinal bending involved three major stages. The first stage (basins in a hot extensional back-arc setting. This was followed by a second stage of oroclinal bending, possibly linked to dextral wrench faulting, which involved ~ N-S contraction (F1). Subsequent deformation at 275-265 Ma involved formation of nappe-style structures (F2). This phase of contractional deformation may have resulted from an increased plate coupling that was possibly linked to flat-slab subduction.

  7. From folding to transpressional faulting: the Cenozoic Fusha structural belt in front of the Western Kunlun Orogen, northwestern Tibetan Plateau

    Science.gov (United States)

    Wang, Cong; Cheng, Xiao-Gan; Chen, Han-Lin; Li, Kang; Fan, Xiao-Gen; Wang, Chun-Yang

    2016-03-01

    Fusha structural belt (FSB) is one of the most important tectonic units in front of the Western Kunlun Orogen, northwestern Tibetan Plateau (NW China), in which the Kekeya oil field was discovered in 1971. However, there is no new oil field discovered since then due to the unclarity of the intense and complex Cenozoic deformation in this area. Based on field investigation, seismic interpretation and Continuous Electromagnetic Profile data, we analyze in detail the Cenozoic deformation history, emphasizing on the spatial and temporal variation of the deformation of the FSB in this paper. The result suggests that the FSB was dominated by two deformation events, (1) early (Miocene-early Pliocene) folding event expressed by anticline, with the western segment E-W orienting, while the eastern segment NWW-SEE orienting and (2) later (since late Pliocene) transpressional faulting event that destroyed and divided the earlier anticline into a number of fault blocks. The transpressional faulting caused dextral strike-slip reverse fault, with the dip angles decreasing eastward from ~90° to <45°. The dextral strike-slip reverse fault developed in the core of the anticline in the western part which caused the anticline into several fault blocks, while in the eastern part, the fault developed in the north limb of the anticline with the core of the anticline reserved. Based on the spatial variation of structural characteristics, we propose that the fault block traps and anticline traps in the eastern segment and fault block traps in western segment are favorable for hydrocarbon accumulation.

  8. Petrogenesis of the Dengzhazi A-type pluton from the Taihang-Yanshan Mesozoic orogenic belts, North China Craton

    Science.gov (United States)

    Xiaolu, Niu; Bin, Chen; Xu, Ma

    2011-05-01

    The voluminous Mesozoic monzonitic to monzogranitic rocks in the north China craton (NCC) mostly show high-K calc-alkaline and I-type granitoids features. The Dengzhazi granitic pluton, however, shows features typical of A-type granites. The A-type pluton was emplaced in the Taihang-Yanshan orogenic belts of the northern margin of the NCC, with zircon U-Pb ages of around 140 Ma. The Dengzhazi A-type granites are characterized by high SiO 2 (70.2-77.7 wt.%), K 2O + Na 2O, Zr, Nb, Ga, Zn, and Y contents as well as high Ga/Al ratios, and extremely low CaO, Ba, Sr. In addition, they show high zircon saturation temperatures (870-950 °C), low water and low oxygen fugacity. All these features are consistent with the A-type affinity of the pluton. In situ Hf isotopic analyses for the dated zircons show relatively small range of ɛHf( t) (-13 to -17). They also have homogeneous initial Nd isotopic compositions with ɛNd( t) ranging from -15.1 to -16.3. The Hf and Nd isotopic data suggest that the Dengzhazi A-type granites originated from a homogeneous crustal source, probably the Archean mafic-intermediate granulites. Taking into account the high temperatures, the low H 2O and fO 2 of the magma system, we believe that partial melting of the granulites should have been triggered by underplating of mantle-derived magmas at the base of the mafic lower crust in an extensional regime. The Dengzhazi A-type granite is the oldest pluton of the Taihang-Yanshan Mesozoic magma belts, signifying the commencement of extensive underplating of mafic magmas, and thus of lithospheric thinning in the northern NCC.

  9. Pressure-temperature-deformation-time of the ductile Alpine shearing in Corsica: From orogenic construction to collapse

    Science.gov (United States)

    Rossetti, Federico; Glodny, Johannes; Theye, Thomas; Maggi, Matteo

    2015-03-01

    Definition of the Tertiary tectono-metamorphic history of Alpine Corsica is a key task to decipher the space-time linkage between the Alpine and Apennine subduction systems in the Mediterranean region. Alpine Corsica exposes a nappe stack of oceanic- and continental-derived units, structurally juxtaposed onto the former European continental margin (Hercynian Corsica). Still uncertain is the timing of involvement of the continental-derived units in orogenic construction and shift to regional extension. This paper focuses on reconstruction of the pressure-temperature-deformation-time evolution of selected ductile shear zones activated during transition from the tectonic underplating to the extensional reworking stages. New Rb-Sr mineral age data, integrated with structural and thermobarometric investigations constrain the waning stages of the high-pressure (from blueschist to greenschist facies metamorphic conditions) top-to-the-W thrusting of the HP, oceanic-derived realm (Schistes Lustrés Complex) onto the Hercynian Corsica along the East Tenda Shear Zone in the early Oligocene (from ~ 32 to ~ 27 Ma). This early compressional evolution is overprinted by a major phase of retrogressive, syn-greenschist top-to-the-E extensional shearing in the Schistes Lustrés Complex with the last episode of deformation-related ductile recrystallization recorded during the early Miocene at ~ 20-21 Ma, in a continuum transition from ductile to brittle shearing. The same early Miocene Rb-Sr deformation ages are recovered from the ductile-to-brittle top-to-the-E reactivation domains within the East Tenda Shear Zone, documenting that transition from compression to extension in Alpine Corsica occurred during the late Oligocene-early Miocene time lapse. Implications of these data are discussed in the broader context of the Tertiary geodynamic evolution of the Central Mediterranean region.

  10. From folding to transpressional faulting: the Cenozoic Fusha structural belt in front of the Western Kunlun Orogen, northwestern Tibetan Plateau

    Science.gov (United States)

    Wang, Cong; Cheng, Xiao-Gan; Chen, Han-Lin; Li, Kang; Fan, Xiao-Gen; Wang, Chun-Yang

    2016-07-01

    Fusha structural belt (FSB) is one of the most important tectonic units in front of the Western Kunlun Orogen, northwestern Tibetan Plateau (NW China), in which the Kekeya oil field was discovered in 1971. However, there is no new oil field discovered since then due to the unclarity of the intense and complex Cenozoic deformation in this area. Based on field investigation, seismic interpretation and Continuous Electromagnetic Profile data, we analyze in detail the Cenozoic deformation history, emphasizing on the spatial and temporal variation of the deformation of the FSB in this paper. The result suggests that the FSB was dominated by two deformation events, (1) early (Miocene-early Pliocene) folding event expressed by anticline, with the western segment E-W orienting, while the eastern segment NWW-SEE orienting and (2) later (since late Pliocene) transpressional faulting event that destroyed and divided the earlier anticline into a number of fault blocks. The transpressional faulting caused dextral strike-slip reverse fault, with the dip angles decreasing eastward from ~90° to <45°. The dextral strike-slip reverse fault developed in the core of the anticline in the western part which caused the anticline into several fault blocks, while in the eastern part, the fault developed in the north limb of the anticline with the core of the anticline reserved. Based on the spatial variation of structural characteristics, we propose that the fault block traps and anticline traps in the eastern segment and fault block traps in western segment are favorable for hydrocarbon accumulation.

  11. Highly refractory peridotites in Songshugou, Qinling orogen: Insights into partial melting and melt/fluid-rock reactions in forearc mantle

    Science.gov (United States)

    Cao, Yi; Song, Shuguang; Su, Li; Jung, Haemyeong; Niu, Yaoling

    2016-05-01

    The Songshugou ultramafic massif is located in the eastern segment of the Qinling orogenic belt, central China. It is a large spinel peridotite body dominated by coarse-grained, porphyroclastic, and fine-grained dunite with minor harzburgite, olivine clinopyroxenite, and banded/podiform chromitite. The compositions of the bulk-rock dunite and harzburgite, and the constituent olivine and spinel, together with the textures and chemical characteristics of multiphase mineral inclusions, point to the highly refractory nature of these rocks with complex histories of high-temperature boninite melt generation and boninitic melt-rock reaction, probably in a young, warm, and volatile-rich forearc lithospheric mantle setting. Additionally, a subsequent low-temperature fluid-rock reaction is also recorded by TiO2-rich spinel with Ti solubility/mobility enhanced by chloride- or fluoride-rich subduction-zone fluids as advocated by Rapp et al. (2010). The olivine clinopyroxenite, on the other hand, was likely crystallized from a residual boninitic melt that had reacted with harzburgitic residues. The ubiquitous occurrences of hydrous minerals, such as anthophyllite, tremolite, Cr-chlorite, and serpentine (stable at lower P-T crustal conditions) in the matrix, suggest that further low-temperature fluid-rock reaction (or retrograde metamorphism) has affected the original volatile-poor peridotites either in a mature and cool subduction zone, or in a continental crust during their exhumation into the Qinling collisional orogeny at early Paleozoic era, or both. The prolonged and intense ductile/brittle deformation can decrease the mineral grain size through dynamic recrystallization and fracturing, and thus aid the fluid-rock reaction or retrograde metamorphism and mineral chemical re-equilibration processes. Therefore, the Songshugou peridotites present a good example for understanding the petrogenesis and evolution of the mantle wedge, with the emphasis on the complex partial

  12. Post-Orogenic Granites in Pingwu Region, Northwest Sichuan: Evidence for North China Block and Yangtze Block Collision during Triassic

    Institute of Scientific and Technical Information of China (English)

    Pei Xianzhi; Li Zuochen; Ding Saping; Feng Jianyun; Li Ruibao; Sun Yu; Zhang Yafeng; Liu Zhanqing

    2009-01-01

    The Nanyili (南一里), Laohegou (老河沟), and Shaiziyan (筛子岩) granitic intrusions are located in the southern margin of the Bikou (碧口) block in Pingwu (平武) area, Northwest Sichuan (四川). The petrography and geochemical characteristics of the granitic intrusions as well as their source and tectonic settings are reported and discussed in this article. The Laohegou and Shaiziyan granites are with high SiO2 (69.89 wt.%-73.05 wt.%) and Al2O3 contents, and A/CNK=1.04-1.12. They are typi-cal strongly peraluminous granites, with supersaturation in Al and Si. The abundance of ∑REE varies in the range of (33.13-89.12)×106. The rocks show an LREE enrichment pattern and obvious Eu nega-tive anomaly. The trace element geochemistry is characterized evidently by a negative anomaly of Ta, Nb, Ti, etc. and a positive anomaly of Rb, Ba, Sr, etc.. Zircons of the Nanyili granite have higher Th/U ratios, and their CL images have internal oscillatory zoning, suggesting that the zircons of the samples are igneous in origin. The LA ICP-MS zircon U-Pb isotopic concordia diagram yields an age of 223.1±2.6 Ma (MSWD=1.4), which indicates that the granodiorite intrusions formed in the early Late Triassic. The Nanyili, Laohegou, and Shaiziyan granites have the characteristics of post-eollisional granites and are regarded as post-orogenic granites. Thus, the granite intrusions are interpreted as syn-collisional granites that resulted from the crustal thickening caused by the collisions between the North China plate and the Yangtze plate during the Indosinian. The granitic intrusions formed in a transitional environment from syn- (compres-slonal environment) to post-collision (extensionalenvironment).

  13. The Modi Taung-Nankwe gold district, Slate belt, central Myanmar: mesothermal veins in a Mesozoic orogen

    Science.gov (United States)

    Mitchell, A. H. G.; Ausa, C. A.; Deiparine, L.; Hlaing, T.; Htay, N.; Khine, A.

    2004-07-01

    The recently discovered quartz-gold veins comprising the Modi Taung-Nankwe gold district in central Myanmar are largely hosted by mudstones of the late Palaeozoic Slate belt. Mesozoic rocks of the Paunglaung-Mawchi zone separate the Slate belt from the Shan Scarp and Shan Plateau to the east. At Modi Taung 5 km of exploration adits indicate that the veins, within steeply dipping oblique reverse-slip shear zones, are displaced by movements along the shears, intruded by late Jurassic calc-alkaline dykes, and offset on conjugate cross-faults. Drill intercepts show that mineralization extends vertically for more than 500 m. Coarse visible gold, book-and-ribbon texture and stylolitic laminations, and trace metal values are consistent with mineralization at mesothermal depths of several kilometres in the brittle-ductile regime. Our field observations suggest that mineralization took place in the early Jurassic following collision of Myanmar on the passive western margin of a Greater Shan-Thai continental block with an oceanic arc on the overriding plate to the west. Collision generated intra-continental thrusting in and east of the Paunglaung-Mawchi zone, metamorphism of Plateau rocks thrust west beneath the Slate belt to form the Mogok Metamorphics, and ascent of mineralizing fluids expelled from dehydrating underthrust rocks. Reversal in orogenic polarity initiated late Jurassic eastward subduction of oceanic crust beneath Myanmar, and generation of a magmatic arc with dykes cutting the quartz-gold veins. Renewed east-directed thrusting translated the Slate belt over arc clastics, and probably resulted in exhumation of the Mogok Metamorphics and offsets of the veins on conjugate faults. Young K/Ar, Rb 87/Sr 86 and Ar 40/Ar 39 ages on the Mogok Metamorphic belt imply renewed Tertiary uplift and possibly intrusion of mid-Tertiary or Palaeogene granites.

  14. Precambrian Processes, the Trans-Hudson Orogen, and Cratonic Keels: Insights From Teleseismic Tomography in Northern Hudson Bay, Canada

    Science.gov (United States)

    Liddell, M. V.; Bastow, I. D.; Gilligan, A.; Kendall, J. M.; Darbyshire, F. A.

    2015-12-01

    Earth conditions in the Precambrian, and their effect upon the formation of cratons and orogenies from that era, are not fully understood. For example, the precise onset of modern plate tectonics remains ambiguous; it has been hypothesised to have begun anywhere from ~4.1Ga (Hopkins, 2008) to ~1Ga (Stern, 2005). Also, the exceptional depth to which fast wave-speed and geoid anomalies extend beneath some cratons points to the existence of thick "cratonic keels", the origin of which remains unexplained. To improve our understanding of the early Earth processes, geological evidence preserved within ancient plates that have remained largely unchanged since the Precambrian can be used. The rocks of northern Hudson Bay include Archean domains, the Paleoproterozoic Trans-Hudson Orogen (THO), and lie atop one of the largest cratonic keels on Earth (Bastow et al., 2013), making this region an ideal laboratory for study of Precambrian processes. Here, we use seismological data recorded at Canadian POLARIS and Hudson Bay Lithospheric Experiment (HuBLE) stations to perform a relative arrival-time study of northern Hudson Bay region and the THO. Waveforms are aligned using the adaptive stacking routine of Rawlinson et al. (2004), and inversions are produced using the Fast Marching Tomography (FMTOMO) inversion code of Rawlinson et al. (2006). Our inversions provide an improved velocity model of the lithosphere and upper mantle of northern Canada, suggesting updated boundaries between lithospheric blocks at mantle depths and constituting new body-wave constraints on their structure. The results are used to address a number of outstanding questions regarding the processes that formed the THO and the Laurentian Keel of North America.

  15. Buildup of a dynamically supported orogenic plateau: Numerical modeling of the Zagros/Central Iran case study

    Science.gov (United States)

    François, T.; Burov, E.; Agard, P.; Meyer, B.

    2014-06-01

    Iranian plateau is a vast inland region with a smooth average elevation of c. 1.5 km formed at the rear of the Zagros orogen as a result of the Arabia-Eurasia collision (i.e., over the last 30-35 Myr). This collision zone is of particular interest due to its disputed resemblance to the faster Himalayan collision, which gave birth to the Tibetan plateau around 50 Myr ago. Recent studies have suggested that a recent (10-5 Ma) slab break-off event below Central Iran caused the formation of the Iranian plateau. Here, we test several hypotheses through large-scale (3082 × 590 km) numerical models of continental subduction models that incorporate a free upper surface erosion, rheological stratification, brittle-elastic-ductile rheologies, and metamorphic phase changes (density and physical properties) and account for the specific crustal and thermal structure of the Arabian and Iranian continental lithospheres. We test the impact of the transition from oceanic to continental subduction and the topographic consequences of the progressive slowdown of the convergence rate during continental subduction. Our results demonstrate the role of mantle flow beneath the overriding plate, initiated as an indirect consequence of slab break-off. This flow creates a dynamic topography support during continental subduction and results in delamination of the overriding plate lithospheric mantle followed by isostatic readjustment, hence of further uplift and maintenance of a plateau-like topography without significant crustal thickening. The slowdown of the convergence rate during the development of the continental subduction/collision phase largely contributes to this process by controlling the timing and depth of slab break-off.

  16. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Presentation and interpretation of structural data from the Nagssugtoqidian orogen using a GIS platform: general trends and features

    Directory of Open Access Journals (Sweden)

    van Gool, Jeroen A.M.

    2006-12-01

    Full Text Available In this contribution we present data collected by more than 50 international geologists involved ingeological mapping and research projects in the Nagssugtoqidian orogen of West Greenland, organised by the Geological Survey of Denmark and Greenland and the Danish Lithosphere Centre. Using a geographical information system (GIS as a framework for visualisation and analysis of structural and lithological data, it is now possible to give a unique overview of thousands of data points, employedhere within a study area of approximately 160 × 180 km in the central and northern Nagssugtoqidian orogen. The GIS methodology allows comparison, integration and analysis of datasets interms of subject, space, and scale. This is extremely helpful in the recognition of geological patterns,such as terrain or domain boundaries and map-scale structures. Analysis of the available structuraldata shows clear differences in deformation patterns between the core and the northern segment ofthe Nagssugtoqidian orogen. One of the most prominent features is the ENE-striking Nordre Strømfjord shear zone, which transects the orogen from the coast to the Inland Ice. The data also clearly document a change from predominantly steeply dipping, ENE–WSW-trending fabrics and large,elongate structural domains in the core of the orogen, to large, open fold patterns and moderately to shallowly dipping fabrics in smaller structural domains in the north.

  17. Common Pb isotope mapping of UHP metamorphic zones in Dabie orogen, Central China: Implication for Pb isotopic structure of subducted continental crust

    Science.gov (United States)

    Shen, Ji; Wang, Ying; Li, Shu-Guang

    2014-10-01

    We report Pb isotopic compositions for feldspars separated from 57 orthogneisses and 2 paragneisses from three exhumed UHPM slices representing the North Dabie zone, the Central Dabie zone and the South Dabie zone of the Dabie orogen, central-east China. The feldspars from the gneisses were recrystallized during Triassic continental subduction and UHP metamorphism. Precursors of the orthogneisses are products of Neoproterozoic bimodal magmatic events, those in north Dabie zone emplaced into the lower crust and those in central and south Dabie zones into middle or upper crust, respectively. On a 207Pb/204Pb vs. 206Pb/204Pb diagram, almost all orthogneisses data lie to the left of the 0.23 Ga paleogeochron and plot along the model mantle evolution curve with the major portion of the data plotting below it. On a 208Pb/204Pb vs. 206Pb/204Pb diagram the most of data of north Dabie zone extend in elongate arrays along the lower crustal curve and others extend between the lower crustal curve to near the mantle evolution curve for the plumbotectonics model. This pattern demonstrates that the Pb isotopic evolution of the feldspars essentially ended at 0.23 Ga and the orthogneiss protoliths were principally dominated by reworking of ancient lower crust with some addition of juvenile mantle in the Neoproterozoic rifting tectonic zone. According to geological evolution history of the locally Dabie orogen, a four-stage Pb isotope evolution model including a long time evolution between 2.0 and 0.8 Ga with a lower crust type U/Pb ratio (μ = 5-6) suggests that magmatic emplacement levels of the protoliths of the orthogneisses in the Dabie orogen at 0.8 Ga also play an important role in the Pb evolution of the exhumed UHPM slices, corresponding to their respective Pb characters at ca. 0.8-0.23 Ga. For example, north Dabie zone requires low μ values (3.4-9.6), while central and south Dabie zones require high μ values (10.9-17.2). On the other hand, Pb isotopic mixing between

  18. Mesozoic tectonic evolution of the Daba Shan Thrust Belt in the southern Qinling orogen, central China: Constraints from surface geology and reflection seismology

    Science.gov (United States)

    Li, Jianhua; Dong, Shuwen; Yin, An; Zhang, Yueqiao; Shi, Wei

    2015-08-01

    The Daba Shan Thrust Belt is located along the southern margin of the Qinling orogen that separates the north China block in the north from the south China block in the south. Despite decades of research, the total magnitude of shortening accommodated by continent-continent convergence across the Qinling orogen after Triassic ocean closure between north and south China remains poorly constrained. The lack of knowledge on the shortening magnitude in turn limits our ability to test a wide array of tectonic models for the development of the Qinling orogen and thus the convergence history between north and south China. In order to address this issue, we construct a balanced cross section and develop a new kinematic model for the evolution of the Daba Shan Thrust Belt. This work was accomplished by integrating (1) surface geologic mapping, (2) detailed kinematic analysis of key structures, (3) existing geochronologic and thermochronological data, and (4) a recently obtained lithospheric-scale seismic reflection profile. Restoration of the cross section indicates that the minimum shortening strain increases northward from ~10% in the foreland to >45% in the thrust belt interior. The estimated amount of upper crustal shortening across the Daba Shan Thrust Belt is >130 km, which is sufficient to allow the inferred mafic lower crust of the subducted south China lithosphere to have experienced eclogite phase transition. Thus, our work supports that the development of the Daba Shan Thrust Belt may have been driven by slab pull of the subducted mafic lower crust at the leading edge of the down-plunging south China continental lithosphere.

  19. The Pyhäntaka formation, southern Finland: a sequence of metasandstones and metavolcanic rocks upon an intra-orogenic unconformity

    Directory of Open Access Journals (Sweden)

    Mikko Nironen

    2011-08-01

    Full Text Available Detrital zircon studies suggest that the few quartzite occurrences in southern Finland are younger than 1.87 Ga and express sedimentation after 1.89–1.87 Ga accretional deformation and metamorphism in the Svecofennian orogenic belt. Detailed field work in the high-grade metamorphic Pyhäntaka area allowed to distinguish an overturnedformation within metagraywackes (cordierite paragneisses and psammites. The Pyhäntaka formation has a maximum thickness of 1000 meters and consists of quartzite overlain by meta-arkose, metatuff, and metabasalt on top. An uncorformity, expressed by aweathering surface, separates the quartzite from underlying metagraywacke. The metavolcanic rocks within, stratigraphically underlying and overlying the Pyhäntaka formation are mostly basalts and basaltic andesites, but a felsic volcanic rock and dacitic fragments in volcaniclastic rocks imply bimodal affinity. The quartzite was deposited during a stable intra-orogenic period probably after accretion but before 1.83–1.80 Ga collisionaldeformation and metamorphism in the Svecofennian orogen. Rifting during the intraorogenic period and accumulation of variable material in the rift from nearby sources by fluvial processes is a viable scenario for deposition and preservation of the Pyhäntakaformation. Geochemical diagrams of the metavolcanic rocks show a scatter that is best explained by source heterogeneity and crustal contamination. Despite their (likely postaccretion setting the basaltic rocks show arc-type characteristics due to subduction-modified lithospheric mantle sources. Because of recycling, also the paragneisses in the Pyhäntaka area are geochemically similar in spite that they represent different tectonic settings. The use of elemental geochemistry alone appears to be insufficient for discriminatingtectonic settings of basalts or graywackes in the Svecofennian of southern Finland where accretion and post-accretion settings were largely obliterated by late

  20. Key role of Upper Mantle rocks in Alpine type orogens: some speculations derived from extensional settings for subduction zone processes and mountain roots

    Science.gov (United States)

    Müntener, Othmar

    2016-04-01

    Orogenic architecture and mountain roots are intrinsically related. Understanding mountain roots largely depends on geophysical methods and exhumed high pressure and high temperature rocks that might record snapshots of the temporal evolution at elevated pressure, temperatures and/or fluid pulses. If such high pressure rocks represent ophiolitic material they are commonly interpreted as exhumed remnants of some sort of 'mid-ocean ridge' processes. Mantle peridotites and their serpentinized counterparts thus play a key role in understanding orogenic architecture as they are often considered to track suture zones or ancient plate boundaries. The recognition that some mantle peridotites and their serpentinized counterparts are derived from ocean-continent transition zones (OCT's) or non-steady state (ultra-)slow plate separation systems question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. Among these are: (i) the commonly held assumption of a simple genetic link between mantle melting and mafic (MORB-type) magmatism, (ii) the commonly held assumption that mélange zones represent deep subduction zone processes at the plate interface, (iii) that pre-collisional continental crust and oceanic crust can easily be reconstructed to their original thickness and used for reconstructions of the size of small subducted oceanic basins as geophysical data from rifted margins increasingly indicate that continental crust is thinned to much less than the average 30-35 kilometers over a large area that might be called the 'zone of hyperextension', and (iv) the lack of a continuous sheet of mafic oceanic crust and the extremely short time interval of formation results in a lack of 'eclogitization potential' during convergence and hence a lack of potential for subsequent slab pull and, perhaps, a lack of potential for 'slab-breakoff'. Here we provide a synopsis of mantle rocks from the

  1. An interpretation of the aeromagnetic data covering portion of the Damara orogenic belt, with special reference to the occurrence of uraniferous granite

    International Nuclear Information System (INIS)

    This thesis comprises primarily palaeomagnetic studies within the Damara orogenic belt of South West Africa (Namibia), as well as an interpretation of the regional structure, utilizing published aeromagnetic data. The prime objectives of the study were to aid uranium exploration programmes in this area by establishing any possible magnetic relationships associated with the uraniferous granites in the area, and to interpret regional structure from the aeromagnetic data. Cursory interpretation of the airborne radiometric data is also undertaken. Gravity traverses, conducted across three dome structures with which uranium mineralisation is intimately associated, are interpreted in order to determine the origin of these structures

  2. Nappe-Bounding Shear Zones Initiated On Syn-Tectonic, Pegmatite-Filled Extensional Shear Fractures During Deep-Crustal Nappe Flow In A Large Hot Orogen

    Science.gov (United States)

    Culshaw, Nicholas; Gerbi, Christopher; Marsh, Jeffrey; Regan, Peter

    2014-05-01

    The Central Gneiss Belt (CGB) of the Proterozoic western Grenville Province is an extensive exposure of the mid-crustal levels (upper amphibolite facies, lesser granulites) of a large hot orogen. Numerical models give a credible prediction of structure and metamorphism accompanying CGB deep-crustal nappe flow and define a temporal framework based on four developmental phases: thickening, heating, nappe-flow and post convergence extensional spreading. These phases are diachronous in direction of orogen propagation and imply a spatial framework: externides (close to orogen-craton boundary) containing moderately inclined thickening and/or extensional structures, and internides containing thickening structures overprinted by sub-horizontal nappe flow structures, which may be locally overprinted by those due to extensional spreading. Although on average of granitoid composition, CGB nappes differ in rheology, varying from fertile and weak (unmetamorphosed before Grenville, meltable) to infertile and strong (metamorphosed at high grade before Grenville, unmeltable) or mixed fertile-infertile protoliths. Deformation style varies from diffuse in fertile nappes, weakened by pervasive melting, to localised in shear zones on boundaries or interiors of infertile nappes. Specifically, in terms of deformation phase and location within the orogen, shear zones occur as: thickening structures of externides, early thickening- and later overprinting nappe-flow structures of infertile internide nappes, and extension-related shear zones in externides and internides. Many of the nappe-flow shear zones of the internides are associated with pegmatites. One example has been recognized of a preserved progression from small-scale fracture arrays to regional shear zone. The sequence is present on a km-scale and initiates in the interior of a nappe of layered granulite with arrays of pegmatite filled extensional-shear fractures (mm to cm width) displaying amphibolized margins. The fracture

  3. Mineralogical and geochemical constraints on contribution of magma mixing and fractional crystallization to high-Mg adakite-like diorites in eastern Dabie orogen, East China

    Science.gov (United States)

    Zhang, Chao; Ma, Changqian; Holtz, Francois; Koepke, Jürgen; Wolff, Paul Eric; Berndt, Jasper

    2013-07-01

    The Liujiawa pluton which is located near the eastern boundary of the Dabie orogen is composed of multiple lithologic units including mainly gabbronorites, diorites, granodiorites and hornblende gabbros. Gabbronorites and hornblende gabbros occur as enclaves in dioritic hosts which show gradual contact with granodiorites. Zircon U-Pb dating indicates that gabbronorites and diorites formed coevally at ~ 128 Ma, but they have distinct zircon Hf isotopes with εHf(t) of - 26 to - 23 (gabbronorite) and of - 32 to - 27 (diorite) respectively. Petrographic observations and rock-forming mineral compositions clearly show mixing between mafic and felsic magma end-members, which might have formed the homogeneous whole-rock Sr-Nd isotopes with εNd(t) of - 17 to - 25 and initial 87Sr/86Sr of 0.707 to 0.709. As revealed by zircon Hf isotopes, F concentrations in amphibole and biotite and thermodynamic modeling of crystallization, the gabbronorites represent enriched lithospheric mantle-derived magmas which evolved by fractional crystallization of orthopyroxene, clinopyroxene, magnetite and/or amphibole, whereas the granodiorites may be derived from the Dabie Archean basement. Mineralogical and geochemical data as well as major and trace element modeling show that the origin of diorites, previously interpreted as high-Mg adakites, can be explained by magma mixing between the crust-derived granodioritic magmas and the differentiation products of mantle-derived gabbronoritic magmas. As a result, the high-Mg adakite-like geochemistry of the diorites is a consequence of magma differentiation at a crustal depth, involving fractional crystallization and magma mixing, rather than an intrinsic feature of primitive melts. The mantle upwelling in the adjacent central Middle-Lower Yangtze River metallogenic (MLYR) belt during Late Jurassic-Early Cretaceous belt might have acted as a precursor and triggered the partial melting of lithospheric mantle beneath the eastern Dabie orogen and the

  4. Multiple sources of the Upper Triassic flysch in the eastern Himalaya Orogen, Tibet, China: Implications to palaeogeography and palaeotectonic evolution

    Science.gov (United States)

    Li, Xianghui; Mattern, Frank; Zhang, Chaokai; Zeng, Qinggao; Mao, Guozheng

    2016-01-01

    The Upper Triassic flysch-Langjiexue Group (tentatively named the "Shannan Terrane") of the eastern Himalaya Orogen has been tectonically assigned either to the Tethys Himalaya or the Yarlung Zangbo Suture Zone (YZSZ). In this work, geochronology of detrital zircon U-Pb isotope shows that the Shannan Terrane is characterized by the population of ~ 260-200 Ma (peak ca. 240 Ma), strongly supporting the view of no affinity to the Tethys Himalaya. The detrital zircons dated as ~ 400-290 Ma display relatively positive εHf(t) values of - 5.0 to + 15.0 with TDMC ages of 2.6-1.3 Ga for the Shannan Terrane, whereas highly negative are of - 20.0 to - 5.0 for the Lhasa Terrane, indicating that the two terranes have different Devonian-Carboniferous sources. Numerous Cr-spinels found in the Shannan Terrane but not in the Lhasa Terrane, exhibit contents in Cr2O3 and Cr# of mainly 44-100% and 48-95%, in TiO2 of 0.01-1.0%, and in Al2O3 of 5-257%, respectively, denoting several parent lithologies. These differences suggested that the Shannan Terrane has multiple sources, not only from the Lhasa Terrane, but also from oceanic (island) arc/seamount and mid-ocean ridge areas as well as likely from Greater India and Australia. Considering the Early Cretaceous diabase dykes within the Upper Triassic flysch defined to the Comei-Bunbury Large Igneous Province, we propose that the Langjiexue Group could have been deposited on the ocean between India and Australia, and would have not stopped till the Lhasa Terrane was separated from Australia during the terminal Triassic. According to the Cenozoic deformation and metamorphic history and palaeogeography of the Langjiexue Group, we postulate that the Shannan Terrane could have been loaded onto the Greater India during the middle Early Cretaceous, and subsequently drifted northward to the collision zone of India and Asia, implying that it does not represent an accretionary prism within the YZSZ.

  5. Upper Paleozoic tectonics in the Tien Shan (Central Asian Orogenic Belt): insight from new structural data (Kyrgyzstan)

    Science.gov (United States)

    Jourdon, Anthony; Petit, Carole; Rolland, Yann; Loury, Chloé; Bellahsen, Nicolas; Guillot, Stéphane; Ganino, Clément

    2016-04-01

    Due to successive block accretions, the polarity of structures and tectonic evolution of the Central Asian Orogenic Belt (CAOB) are still a matter of debate. There are several conflicting models about the polarity of subduction during the Paleozoic, the number of microplates and oceanic basins and the timing of tectonic events in Kyrgyz and Chinese Tien Shan. In this study, we propose new structural maps and cross-sections of Middle and South Kyrgyz Tien Shan (MTS and STS respectively). These cross-sections highlight an overall dextral strike-slip shear zone in the MTS and a north verging structure related to south-dipping subduction in the STS. These structures are Carboniferous in age and sealed by Mesozoic and Cenozoic deposits. In detail, the STS exhibits two deformation phases. The first one is characterized by coeval top-to-the north thrusting and top-to-the-South normal shearing at the boundaries of large continental unit that underwent High-Pressure (Eclogite facies) metamorphism. We ascribe this phase to the exhumation of underthrusted passive margin units of the MTS. The second one corresponds to a top to the North nappe stacking that we link to the last collisional events between the MTS and the Tarim block. Later on, during the Late Carboniferous, a major deformation stage is characterized by the deformation of the MTS and its thrusting over the NTS. This deformation occurred on a large dextral shear zone between the NTS and the MTS known as Song-Kul Zone or Nikolaiev Line as a "side effect" of the Tarim/MTS collision. Based on these observations, we propose a new interpretation of the tectonic evolution of the CAOB. The resulting model comprises the underthrusting of the MTS-Kazakh platform beneath the Tarim and its exhumation followed by the folding, shortening and thickening of the internal metamorphic units during the last collisional events which partitioned the deformation between the STS and the MTS. Finally, the docking of the large Tarim Craton

  6. Continental growth through accreted oceanic arc: Zircon Hf-O isotope evidence for granitoids from the Qinling orogen

    Science.gov (United States)

    Wang, Hao; Wu, Yuan-Bao; Gao, Shan; Qin, Zheng-Wei; Hu, Zhao-Chu; Zheng, Jian-Ping; Yang, Sai-Hong

    2016-06-01

    The continental crust is commonly viewed as being formed in subduction zones, but there is no consensus on the relative roles of oceanic or continental arcs in the formation of the continental crust. The main difficulties of the oceanic arc model are how the oceanic arcs can be preserved from being subducted, how we can trace the former oceanic arcs through their high-Si products, and how the oceanic arcs can generate the high-Si, K-rich granitoid composition similar to the upper continental crust. The eastern Qinling orogen provides an optimal place to address these issues as it preserves the well-exposed Erlangping oceanic arc with large amounts of granitoids. In this study, we present an integrated investigation of zircon U-Pb ages and Hf-O isotopes for four representative granitoid plutons in the Erlangping unit. In situ zircon SIMS U-Pb dating indicated that the Zhangjiadazhuang, Xizhuanghe, and Taoyuan plutons formed at 472 ± 7, 458 ± 6 and 443 ± 5 Ma, respectively, all of which postdated the deep subduction of the Qinling microcontinent under the Erlangping oceanic arc. The Zhangjiadazhuang, Xizhuanghe, and Taoyuan plutons are sodic granitoid and have highly positive εHf(t) (+7.6 to +12.9) and relatively low δ18O (4.7-5.0‰) values, which were suggested to result from prompt remelting of hydrothermally altered lower oceanic crust of the accreted Erlangping oceanic arc. The zircon grains from the Manziying monzogranitic pluton show similar Hf-O isotopic compositions to those of the Xizhuanghe pluton, and thus the Manziying monzogranitic pluton was likely derived from the dehydration melting of previous tonalites as exemplified by the Xizhuanghe pluton. The deep subduction of Qinling microcontinent resulted in the accretion of the Erlangping oceanic arc, which implies that arc-continent collision provides an effective way for preventing oceanic arcs from being completely subducted. The highly positive εHf(t) and relatively low δ18O values of zircon

  7. Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Aracuai Orogen, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Queiroga, Glaucia Nascimento; Martins, Maximiliano de Souza; Castro, Marco Paulo de; Jordt-Evangelista, Hanna; Silva, Ana Lucia da, E-mail: glauciaqueiroga@yahoo.com.br, E-mail: maximilianomartins@yahoo.com.br, E-mail: marco_pcastro@yahoo.com, E-mail: hanna@degeo.ufop.br, E-mail: alucia.silva@hotmail.com [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Pedrosa-Soares, Antonio Carlos, E-mail: pedrosa@igc.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Instituto de Geociencias. Departamento de Geologia; Schulz, Bernhard, E-mail: bernhard.schulz@mineral.tu-freiberg.de [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)

    2016-01-15

    The Capelinha Formation (Macaubas Group) consists of a lower quartzitic unit with metamafic intercalations and an upper metapelitic sequence. It occurs in a complex tectono-metamorphic sector of the Aracuai orogen, where post-collisional collapse-related structures superimposed collisional structures. The garnet-bearing assemblages started crystallization in the collisional deformation stage that formed the main regional foliation around 570 Ma. Garnet porphyroblasts display a well developed growth zonation of Fe-Mg-Ca-Mn and show, from core to rim, increasing almandine and pyrope contents in contrast with decreasing grossular and spessartine contents. Mineral relations and microstructures provide criteria for local equilibria and a structurally controlled application of geothermobarometry based on cation exchange and net transfer reactions. The P-T values calculated from cores to rims of garnets, aligned along clockwise trends, resulted in increasing temperatures (from 500 deg C up to 620 deg C) under decompression conditions (from 8.0 kbar to 4.5 kbar). The Th-UPb dating of homogeneous monazites by electron microprobe revealed a recrystallization period at around 490 - 480 Ma. These ages can be related to the tectono-thermal event associated with the gravitational collapse, constraining the youngest time limit for metamorphic processes in the Aracuai orogen. (author)

  8. U-Pb SHRIMP and 40Ar/39Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, Sao Luis cratonic fragment, Brazil

    International Nuclear Information System (INIS)

    Caxias is an orogenic gold deposit in the Sao Luis cratonic fragment, which is correlated with the Rhyacian terranes of the West-African Craton. The deposit postdates peak metamorphism (estimated at 2100 ± 15 Ma) and is hosted in a shear zone that cuts across schists of the Aurizona Group (2240 ± 5 Ma) and the Caxias Microtonalite. The emplacement age of the microtonalite, as determined in this work by SHRIMP U-Pb zircon dating, is 2009 ± 11 Ma and represents a latest age magmatic event in the Sao Luis cratonic fragment. Older zircon age of 2139 ± 10 Ma is interpreted as due to inheritance from the older granitoid or volcanic suites (magmatic sources?) or to contamination during emplacement. Lead isotope compositions indicate that the Pb incorporated in ore-related pyrite was probably sourced from regional, orogenic calc-alkaline granitoids of ca. 2160 Ma. Hydrothermal sericite from Caxias yielded a 40Ar/39Ar plateau age of 1990 ± 30 Ma, which combined with the emplacement age of the Caxias Microtonalite brackets the age of gold mineralization between 2009 ± 11 and 1990 ± 30 Ma. (author)

  9. Distinct magnetic fabric in weakly deformed sediments from extensional basins and fold-and-thrust structures in the Northern Apennine orogenic belt (Italy)

    Science.gov (United States)

    Caricchi, Chiara; Cifelli, Francesca; Kissel, Catherine; Sagnotti, Leonardo; Mattei, Massimo

    2016-02-01

    We report on results from anisotropy of magnetic susceptibility (AMS) analyses carried out on weakly deformed fine-grained sediments from the Northern Apennine orogenic system (Italy). We sampled 63 sites from preorogenic, synorogenic, and postorogenic sequences, which differ in age, composition, depositional environment, degrees of deformation, and tectonic regimes. The magnetic fabric is typical of weakly deformed sediments, with a magnetic foliation subparallel to the bedding plane and a magnetic lineation well defined in this plane. Northern Apennine chain deposits are characterized by strongly oblate magnetic susceptibility ellipsoids, indicating that the magnetic fabric is the result of both compaction process and tectonic load experienced by the sediments during diagenesis and orogenic events. The orientation of magnetic lineation is significantly different depending whether the studied sites underwent extensional or compressional tectonic regimes. In the Northern Apennine chain, the magnetic lineation is mostly oriented NNW-SSE, parallel to the main compressional structures. It suggests a tectonic origin of the magnetic lineation with an acquisition related to the Apennines compressional phases. In the extensional Tuscan Tyrrhenian margin, magnetic lineation is oriented ENE-WSW, almost perpendicular to the main extensional faults, which represent the main deformation elements of the area. Our results demonstrate a close relationship between the shape and orientation of magnetic fabric and the tectonic history of rocks, confirming that AMS represents a valuable tool to investigate the tectonic history of weakly deformed sedimentary rocks.

  10. Science Letters: Discovery of ultrahigh-T spinel-garnet granulite with pure CO2 fluid inclusions from the Altay orogenic belt, NW China

    Institute of Scientific and Technical Information of China (English)

    厉子龙; 陈汉林; SANTOSHM.; 杨树锋

    2004-01-01

    We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the orthopyroxenes have high XMg and Al2O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around -56.7℃, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3-23.8℃ translating into CO2 densities of the order of 0.86-0.88g/cm3. Based on preliminary mineral paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions.

  11. Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Aracuai Orogen, Brazil

    International Nuclear Information System (INIS)

    The Capelinha Formation (Macaubas Group) consists of a lower quartzitic unit with metamafic intercalations and an upper metapelitic sequence. It occurs in a complex tectono-metamorphic sector of the Aracuai orogen, where post-collisional collapse-related structures superimposed collisional structures. The garnet-bearing assemblages started crystallization in the collisional deformation stage that formed the main regional foliation around 570 Ma. Garnet porphyroblasts display a well developed growth zonation of Fe-Mg-Ca-Mn and show, from core to rim, increasing almandine and pyrope contents in contrast with decreasing grossular and spessartine contents. Mineral relations and microstructures provide criteria for local equilibria and a structurally controlled application of geothermobarometry based on cation exchange and net transfer reactions. The P-T values calculated from cores to rims of garnets, aligned along clockwise trends, resulted in increasing temperatures (from 500 deg C up to 620 deg C) under decompression conditions (from 8.0 kbar to 4.5 kbar). The Th-UPb dating of homogeneous monazites by electron microprobe revealed a recrystallization period at around 490 - 480 Ma. These ages can be related to the tectono-thermal event associated with the gravitational collapse, constraining the youngest time limit for metamorphic processes in the Aracuai orogen. (author)

  12. Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt--On deep-seated xenoliths in Minggang region of Henan Province

    Institute of Scientific and Technical Information of China (English)

    LU; Fengxiang; WANG; Chunyang; ZHENG; Jianping

    2004-01-01

    Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.

  13. Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

    Science.gov (United States)

    Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

    2005-01-01

    During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

  14. Two-stage formation model of the Junggar basin basement: Constraints to the growth style of Central Asian Orogenic Belt

    Science.gov (United States)

    He, Dengfa

    2016-04-01

    Junggar Basin is located in the central part of the Central Asian Orogenic Belt (CAOB). Its basement nature is a highly controversial scientific topic, involving the basic style and processes of crustal growth. Some researchers considered the basement of the Junggar Basin as a Precambrian continental crust, which is not consistent with the petrological compositions of the adjacent orogenic belts and the crust isotopic compositions revealed by the volcanic rocks in the basin. Others, on the contrary, proposed an oceanic crust basement model that does not match with the crustal thickness and geophysical characteristics of the Junggar area. Additionally, there are several viewponits, such as the duplex basement with the underlying Precambrian crystalline rocks and the overlying pre-Carboniferous folded basement, and the collaged basement by the Precambrian micro-continent block in the central part and the Hercynian accretionary folded belts circling it. Anyway, it is necessary to explain the property of basement rock, its strong inhomogeneous compositions as well as the geophysical features. In this paper, based on the borehole data from more than 300 industry wells drilled into the Carboniferous System, together with the high-resolution gravity and magnetic data (in a scale of 1:50,000), we made a detailed analysis of the basement structure, formation timing and processes and its later evolution on a basis of core geochemical and isotopic analysis. Firstly, we defined the Mahu Pre-Cambrian micro-continental block in the juvenile crust of Junggar Basin according to the Hf isotopic analysis of the Carboniferous volcanic rocks. Secondly, the results of the tectonic setting and basin analysis suggest that the Junggar area incorporates three approximately E-W trending island arc belts (from north to south: Yemaquan- Wulungu-Chingiz, Jiangjunmiao-Luliang-Darbut and Zhongguai-Mosuowan- Baijiahai-Qitai island arcs respectively) and intervened three approximately E-W trending

  15. The tectonic transition from oceanic subduction to continental subduction: Zirconological constraints from two types of eclogites in the North Qaidam orogen, northern Tibet

    Science.gov (United States)

    Zhang, Long; Chen, Ren-Xu; Zheng, Yong-Fei; Li, Wan-Cai; Hu, Zhaochu; Yang, Yueheng; Tang, Haolan

    2016-02-01

    In the plate tectonics theory, continental subduction is pulled by subduction of dense oceanic crust. In practice, however, it is not easy to demonstrate that preceding oceanic crust exposes as oceanic-type eclogite together with continental-type eclogite in collisional orogens. The North Qaidam orogen in northern Tibet is an ultrahigh-pressure (UHP) metamorphic belt that contains the two types of eclogites, providing us with an excellent opportunity to study the tectonic transition from oceanic subduction to continental subduction. In order to constrain the protolith nature and metamorphic evolution of eclogites, we performed a combined study of zircon U-Pb ages, trace elements, mineral inclusions and O-Hf isotopes for various eclogites from the orogen. We discriminate the two types of eclogites by their differences in zircon U-Pb ages and O-Hf isotopes. CL-dark zircon domains exhibit high Th/U ratios, steep HREE patterns and significantly negative Eu anomalies, indicating that they are protolith zircons of magmatic origin with different extents of metamorphic recrystallization. Relict magmatic zircon domains in Type I eclogites yield Neoproterozoic protolith ages of > 830 Ma and Hf model ages of 850-1100 Ma, whereas those in Type II eclogites yield Cambrian protolith U-Pb ages of > 489 Ma and Hf model ages of 500-650 Ma. Most of the CL-bright zircon domains show low Th/U ratios, flat HREE patterns and no negative Eu anomalies, and contain mineral inclusions of garnet, omphacite and rutile, indicating their growth under eclogite-facies metamorphic conditions. These metamorphic domains have consistent eclogite-facies metamorphic ages of 433-440 Ma throughout the North Qaidam orogen, regardless of the eclogite types and locations. The metamorphic zircon domains in Type I eclogites mostly exhibit δ18O values higher than normal mantle values, whereas Type II eclogites mostly have δ18O values lower than the normal mantle values. The difference in the δ18O values

  16. Syn- to post-orogenic exhumation of metamorphic nappes: Structure and thermobarometry of the western Attic-Cycladic metamorphic complex (Lavrion, Greece)

    Science.gov (United States)

    Scheffer, Christophe; Vanderhaeghe, Olivier; Lanari, Pierre; Tarantola, Alexandre; Ponthus, Léandre; Photiades, Adonis; France, Lydéric

    2016-05-01

    The Lavrion peninsula is located along the western boundary of the Attic-Cycladic metamorphic complex in the internal zone of the Hellenic orogenic belt. The nappe stack is well exposed and made, from top to bottom, of (i) a non-metamorphic upper unit composed of an ophiolitic melange, (ii) a middle unit mainly composed of the Lavrion schists in blueschist facies, (iii) and a basal unit mainly composed of the Kamariza schists affected by pervasive retrogression of the blueschist facies metamorphism in greenschist facies. The middle unit is characterized by a relatively steep-dipping foliation associated with isoclinal folds of weakly organized axial orientation. This foliation is transposed into a shallow-dipping foliation bearing a N-S trending lineation. The degree of transposition increases with structural depth and is particularly marked at the transition from the middle to the basal unit across a low-angle mylonitic to cataclastic detachment. The blueschist facies foliation of the Lavrion schists (middle unit) is underlined by high pressure phengite intergrown with chlorite. The Kamariza schists (basal unit) contains relics of the blueschist mineral paragenesis but is dominated by intermediate pressure phengite also intergrown with chlorite and locally with biotite. Electron probe micro-analyzer chemical mapping combined with inverse thermodynamic modeling (local multi-equilibrium) reveals distinct pressure-temperature conditions of crystallization of phengite and chlorite assemblages as a function of their structural, microstructural and microtextural positions. The middle unit is characterized by two metamorphic conditions grading from high pressure (M1, 9-13 kbar) to lower pressure (M2, 6-9 kbar) at a constant temperature of ca. 315 °C. The basal unit has preserved a first set of HP/LT conditions (M1-2, 8-11 kbar, 300 °C) partially to totally transposed-retrogressed into a lower pressure mineral assemblage (M3, 5-8.5 kbar) associated with a slight but

  17. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events

    Science.gov (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    .4 Ma (i.e. Guadalupian-Permian) for N750E trending granitic dykes; and 261.4±1.7 Ma (i.e. Guadalupian-Permian) for N800W trending andesite dykes. New radiometric ages from the dykes cross-cutting the Demirci metamorphics-paragneisses in the İstanbul-Zonguldak Tectonic Unit imply several consecutive orogenic phases. The Cambro-Ordovician and Ordovician-Silurian ages are concordant with the Caledonian Orogeny-first and second closure phase of the Tersseyre-Tornquist Sea, a branch of the Iapetus; the Upper Carboniferous age with the Variscan Orogeny-late closure phase of the Rheic Ocean, and Permian ages with the Hercynian Orogeny-initial closure phase of Palaeo-Tethys Ocean.

  18. Tectonic evolution and crustal-scale structure of Kyrgyz Central Asian Orogenic Belt: new insights from the Darius programme

    Science.gov (United States)

    Rolland, Yann; Loury, Chloé; Guillot, Stéphane; Mikolaichuk, Alexander

    2014-05-01

    Mechanisms and history of the Late Palaeozoic accretion followed by formation of trunscurrent strike-slip faults were studied in the southern segment of the Central Asian Orogenic Belt (CAOB) within Kyrgyz South Tianshan. 1. South Tianshan Suture: ending accretion process after docking of Tarim craton This study gives insights into the crustal-scale structure and Upper Paleozoic history of this mountain belt, currently intensely reactivated by the India-Asia collision. Structural, petrological and geochronological studies were carried out within South Tianshan suture east of the Talas-Ferghana Fault (TFF). New data highlight a south-dipping structure featured by a HP metamorphic core complex comprised of c. 320 Ma continental and oceanic eclogites exhumed by top-to-North motion. A large massif (10 x 50 km) of continental HP rocks in the Atbashi Range is comprised of hectometric boudins of eclogites embedded in metapelites and gneissesMetamorphic units exhibit blueschist to eclogite facies conditions, with oceanic (MORB) rocks in the blueschist facies representing the accretionary oceanic prism being thrusted by oceanic rocks and a continental unit in the eclogite facies (510 ± 50°C and 24 ± 2 kbar). Evidence for eclogite facies both in metasediments and mafic lithologies and geological structure are in agreement with a previously thinned continental margin. Subduction of this thinned COT (Continent-Ocean Transition) probably occurred by slab pull in a south-dipping subduction zone, while another north-dipping subduction was active below Middle Tianshan. Final stacking of Middle and South Tianshan occurred at 320-310 Ma. These opposite subduction zones are still reflected in the main structures of Tianshan. Reactivation of the South-dipping structures since 30-25 Ma is ascribed to explain the current Tianshan intra-continental subduction from seismology. 2. Talas-Ferghana Fault (TFF) activity & Basin formation After this accretionary episode, the South Tianshan

  19. Geochronological and geochemical constraints on the Lüliang Group in the Lüliang Complex: Implications for the tectonic evolution of the Trans-North China Orogen

    Science.gov (United States)

    Liu, Chaohui; Zhao, Guochun; Liu, Fulai; Shi, Jianrong

    2014-06-01

    The Lüliang Complex is located at the western margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks amalgamated to form the basement of the North China Craton. The complex consists of the late Neoarchean to Paleoproterozoic granitic plutons and meta-supracrustal rocks, of which the latter are subdivided into the Jiehekou, Lüliang, Yejishan, and Heichashan/Lanhe Groups. The Lüliang Group is composed mainly of siliciclastic rocks in the lower part and volcanic rocks in the upper part, all of which have been metamorphosed from greenschist- to amphibolite-facies. U-Pb ages of detrital zircons from meta-sedimentary rocks in the Lüliang Group yield four populations of 3061-2920 Ma, 2790-2600 Ma, 2599-2280 Ma and 2211-2202 Ma, suggesting that their provenances were derived mainly from the Lüliang and Taihua Complexes in the Trans-North China Orogen. The meta-volcanic rocks give igneous zircon U-Pb ages of 2209-2178 Ma and εHf(t) values of - 0.8 to + 3.6. Geochemically, they are subalkaline basalts and andesites that can be classified into two groups, of which one group has flat LREEs, weak enrichment in LREEs relative to HREEs and flat HREEs and displays E-MORB-like spider diagrams with the exception of insignificantly negative Nb-Ta, Zr-Hf and Ti anomalies. In contrast, the other group displays stronger LREE fractionation, stronger enrichment in LREEs relative to HREEs and mildly fractionated HREEs and is characterized by “spiky” spider diagrams similar to arc volcanic rocks. The first group is interpreted to have originated from a Neoarchean E-MORB source, whereas the second group shows inputs of newly subduction-derived fluids in the mantle source. These geochronological and geochemical signatures indicate the existence of an 2.2-2.1 Ga continental back-arc system in the Lüliang Complex of the Trans-North China Orogen, which is consistent with the model that the collision between the Eastern and Western

  20. Reconstructing deep crustal dynamics in a large, hot orogen: Application of integrated zircon petrochronology and petrological modeling to the Canadian Grenville Province

    Science.gov (United States)

    Marsh, Jeffrey; Culshaw, Nicholas

    2014-05-01

    The timing and conditions of high pressure (HP) metamorphism, crustal anatexis, and shear zone formation are of primary importance in understanding lithosphere-scale dynamics of collisional orogens. Within the western Grenville Province, Ontario, Canada, a number of structural and metamorphic relationships are preserved that represent specific orogenic stages or processes. Lower allochthonous domains contain variably retrogressed mafic complexes that typically retain vestages of earlier HP metamorphic assemblages (e.g. garnet porphyroblasts, kyanite, and rutile) within a matrix dominated by incomplete decompression reactions (e.g. pseudomorphous diopside + sodic plagioclase intergrowths after omphacite and concentric coronas of aluminous minerals surrounding kyanite). Zircon from these samples yield U-Pb ages between 1085-1097 Ma, and exhibit REE characteristics consistent with crystallization in an eclogite-facies (garnet-rich, plagioclase-poor) mineral assemblage. REE partitioning between zircon and garnet suggests zircon growth coincided with the latter stages of garnet growth. Titanium concentrations in zircon constrain crystallization temperatures between ~678-736 °C, whereas Zr concentration in rutile yield crystallization temperatures of ~705-740 °C (for rutile inclusions in garnet) and 742-764 °C (for rutile in the matrix). Intersection of zircon and rutile crystallization temperature with the calculated stability field for the HP assemblage (Grt+Cpx+Ky+Rt+Zrn±Hbl) yields minimum pressures of ~15 kbar. Thus, HP metamorphism apparently occurred at ca. 1090 Ma across the orogen, at minimum depths of ~53 km and T ~700±50 °C, yielding a geothermal gradient of pegmatite-rich, amphibolite-facies shear zones by ca. 1100 Ma. Thus, petrochronological data constrain a sequence of nappe emplacement, HP metamorphism, and migmatization evolving over ~15-20 Myrs, apparently marking a transition in the deep crustal dynamics from a predominantly thickening phase to a

  1. Magma Mixing for the Origin of the Granites. Geochemistry, Sr-Nd Isotopic, Zircon U-Pb Dating and Hf Isotopic Evidences from the Triassic Mishuling Monzonitic Granite and Its Enclaves, Qinling Orogen (Central China)

    Institute of Scientific and Technical Information of China (English)

    QIN Jiang-feng; LAI Shao-cong; DIWU Chun-rong; JU Yin-juan; LI Yong-fei

    2008-01-01

    @@ Major and trace element, whole rock Sr-Nd isotope, mineral chemistry, zircon U-Pb and Hf isotope compositions are reported for a suite of I-type monzogranite and its marie microgranular enclaves from the Triassic (210±2 Ma) Mishuling pluton, Qinling orogen, central China, with the aim of investigating the sources and petrogenesis of I-type granites.

  2. From hyper-extended rifts to orogens: the example of the Mauléon rift basin in the Western Pyrenees (SW France)

    Science.gov (United States)

    Masini, E.; Manatschal, G.; Tugend, J.

    2011-12-01

    An integral part of plate tectonic theory is that the fate of rifted margins is to be accreted into mountain belts. Thus, rift-related inheritance is an essential parameter controlling the evolution and architecture of collisional orogens. Although this link is well accepted, rift inheritance is often ignored. The Pyrenees, located along the Iberian and European plate boundary, can be considered as one of the best places to study the reactivation of former rift structures. In this orogen the Late Cretaceous and Tertiary convergence overprints a Late Jurassic to Lower Cretaceous complex intracontinental rift system related to the opening of the North Atlantic. During the rifting, several strongly subsiding basins developed in the axis of the Pyrenees showing evidence of extreme crustal extension and even locale mantle exhumation to the seafloor. Although the exact age and kinematics of rifting is still debated, these structures have an important impact in the subsequent orogenic overprint. In our presentation we discuss the example of the Mauléon basin, which escaped from the most pervasive deformations because of its specific location at the interface between the western termination of the chain and the Bay of Biscay oceanic realm. Detailed mapping combined with seismic reflection, gravity data and industry wells enabled to determine the 3D rift architecture of the Mauléon basin. Two major diachronous detachment systems can be mapped and followed through space. The Southern Mauléon Detachment (SMD) develops first, starts to thin the crust and floors the Southern Mauléon sub-Basin (SMB). The second, the Northern Mauléon Detachment (SMD) is younger and controls the final crustal thinning and mantle exhumation to the north. Both constitute the whole Mauléon basin. Like at the scale of the overall Pyrenees, the reactivation of the Mauléon Basin increases progressively from west to east, which enables to document the progressive reactivation of an aborted hyper

  3. Geological and geochemical character and genesis of the Jinlongshan-Qiuling gold deposits in Qinling orogen: Metallogenic mechanism of the Qinling-pattern Carlin-type gold deposits

    Institute of Scientific and Technical Information of China (English)

    张复新,陈衍景,李超Department; of; Geology,; Peking; University,; Beijing; 100871,; China; ,张静Department; of; Geology,; Peking; University,; Beijing; 100871,; China; ,马建秦,李欣Department; of; Geology,; Peking; University,; Beijing; 100871,; China

    2000-01-01

    The Qinling Carlin-type gold deposit belt is the second largest Carlin-type gold ore concentrated area in the world and occurs in Mesozoic intracontinental collisional orogen, contrasting to the Carlin-type gold deposits in the Basin and Range province in Cenozoic active continental margin of West America. With ore-forming ages focussed at the range of 197.45-129.45 Ma, its metallogenic geodynamic background was the decornpression-pyrogenation regime at the transition stage from collisional compression to extension, indicating that gold mineralization synchronized with the Mesozoic continental collision. Geochemical studies discover that ore fluids and materials mainly came from the Hercynian-lndosinian tectonic layer. Mesozoic intracontinental subduction of Hercynian-lndosinian association along the Shuanghe-Gongguan fault led to the formation of Jinlongshan-Qiuling gold deposits. Accordingly, the tectonic metallogenic model is established for Qinling-pattern Carlin-type gold deposits.

  4. The role of partial melting and syn-orogenic deformation in the pre-concentration of uranium and thorium. The example of the CAGE District (Northern Quebec).

    Science.gov (United States)

    Trap, Pierre; Goncalves, Philippe; Durand, Cyril; Marquer, Didier; Feybesse, Jean-Louis; Richard, Yoann; Lacroix, Brice; Caillet, Yoann; Paquette, Jean-Louis

    2015-04-01

    This contribution aims to discuss the relationships between metamorphism, deformation and U-Th mineralization within the orogenic crust, from millimeter to kilometer scale and during the whole P-T-t evolution. The study area is the CAGE district along the paleoproterozoic Torngat orogen (Northern Quebec) made of 2.1 Ga metasedimentary rocks, marbles and paragneisses, deposited upon a 2.5 Ga orthogneissic basement. Several types of U-Th mineralizations have been reported within the middle crust highly metamorphosed and deformed during the Torgnat orogeny (1.9-1.8 Ga). An integrated study with field, geophysical, structural, petrological, geochemical and thermochronological analyses enable a reconstitution of the tectono-metamorphic setting of these U-Th mineralizations and of the mechanism responsible for their pre-concentration into the orogenic crust. The petrological analysis allows us to build a clockwise P-T-t-D evolution with peak pressure conditions at 7.5 - 10 kbar and 725 - 750 ° C and peak temperature conditions at 5-6 kbar and 800-850°C. This high grade metamorphism and widespread partial melting developed within a single dextral transpressive regime. The structural analysis suggests strain partitioning responsible for a S-C-C' like architecture observed at all scales. Aeromagnetic, radiometric and field observations revealed that U-Th mineralizations are mainly focused along the kilometer scale C and C'-type shear zones. The age of crustal partial melting was constrained by U-Pb LA-ICP-MS analyses on zircon and monazite within migmatitic paragneiss and orthogneiss between 1841 ± 5 and 1828 ± 7 Ma. Younger U-Pb ages at around 1810-1750 Ma have been reported on monazite and titanites within the crustal scale shear bands (C and C' like). Results obtained on mylonitic metacarbonaceous and metapelites within kilometer scale shear zones suggest that late shearing formed during retrograde evolution at decreasing temperature after peak metamorphism. The δ13

  5. Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen into the Yangtze craton, central China

    Science.gov (United States)

    Hu, Shengbiao; Raza, Asaf; Min, Kyoungwon; Kohn, Barry P.; Reiners, Peter W.; Ketcham, Richard A.; Wang, Jiyang; Gleadow, Andrew J. W.

    2006-12-01

    Cretaceous and Cenozoic reactivation of the Triassic Qinling-Dabie orogen between the north China and Yangtze cratons resulted from the combined effects of Pacific subduction-back-arc extension in east China and collisions in west China. We report new apatite fission track and apatite and zircon (U-Th)/He data from east Qinling along a >400-km-long N-S transect from Huashan through the Qinling orogen to Huangling. The ages show a general pattern of younging northward. Three major cooling phases are defined by modeling the multiple thermochronologic data sets. The first phase occurred locally in the North and South Qinling during the late Triassic to early Jurassic, following heating associated with the Triassic Yangtze subduction and exhumation of the Wudang metamorphic core complex on the cratonal edge. A second phase represents regional exhumation between 100 and 60 Ma, coeval with rifting marked by the Late Cretaceous-Eocene (K2-E) red bed deposition in eastern China and possibly indicating a link with Pacific subduction-back-arc extension in eastern China; however, it may also have been superimposed by eastward tectonic escape resulting from the Lhasa-West Burma-Qiangtang-Indochina collision. The third cooling phase was initiated at ˜45 Ma exclusively in the north Qinling and in the footwall of the graben-bounding normal fault of the Weihe graben in the Lesser Qinling. We suggest the third phase was related to reactivation of the Qinling fault system as a result of eastward tectonic escape imposed by the India-Asia collision at ˜50 Ma.

  6. Detrital zircon provenance constraints on the initial uplift and denudation of the Chinese western Tianshan after the assembly of the southwestern Central Asian Orogenic Belt

    Science.gov (United States)

    Han, Yigui; Zhao, Guochun; Sun, Min; Eizenhöfer, Paul R.; Hou, Wenzhu; Zhang, Xiaoran; Liu, Dongxing; Wang, Bo

    2016-06-01

    U-Pb and Lu-Hf isotopic data of detrital zircons from late Paleozoic and Mesozoic strata along the southern flank of the Chinese western Tianshan enable to identify provenance changes and reconstruct early stage uplift and denudation history of the Tianshan range. Detrital zircons from Permian and Early-Middle Triassic siliciclastic rocks show two prominent age populations at 500-390 Ma and 310-260 Ma, and subordinate Precambrian ages at ~ 2.5 Ga, 2.0-1.7 Ga, 1.2-0.9 Ga and 900-600 Ma, with rare ages between 390 and 310 Ma. These characteristics and zircon εHf(t) data consistently suggest a sediment source predominantly from the Tarim Craton, rather than the Central Tianshan-Yili Block. In contrast, Late Triassic to Cretaceous strata additionally contain abundant 390-310 Ma and 260-220 Ma detrital zircons, implying multiple source regions from the Central Tianshan-Yili Block, Tarim Craton, and Western Kunlun Orogen. A significant switch of sedimentary provenances occurred in the mid-Triassic and is consistent with contemporaneous change of paleocurrent directions and the onset of intense tectonothermal events in the broad region of the Chinese western Tianshan and Kyrgyz Tianshan. These data collectively indicate that the significant surface uplift and denudation of the Tianshan range were probably initiated in the mid-Triassic (~ 240 Ma) after the assembly of the southwestern Central Asian Orogenic Belt. This uplifting event represents an intracontinental orogeny most likely in response to the collision between the Qiangtang Block and southern Eurasia, following the closure of the western part of the Paleo-Tethys Ocean.

  7. Palaeozoic synorogenic sedimentation in central and northern Australia: a review of distribution and timing with implications for the evolution of intracontinental orogens

    International Nuclear Information System (INIS)

    The Palaeozoic Alice Springs Orogeny was a major intraplate tectonic event in central and northern Australia. The sedimentological, structural and isotopic effects of the Alice Springs Orogeny have been well documented in the northern Amadeus Basin and adjacent exhumed Arunta lnlier, although the full regional extent of the event, as well as lateral variations in timing and intensity are less well known. Because of the lack of regional isotopic data, we take a sedimentological approach towards constraining these parameters, compiling the location and age constraints of inferred synorogenic sedimentation across a number of central and northern Australian basins. Such deposits are recorded from the Amadeus, Ngalia, Georgina, Wiso, Eastern Officer and, possibly, Warburton Basins. Deposits are commonly located adjacent to areas of significant basement uplift related to north-south shortening. In addition, similar aged orogenic deposits occur in association with strike-slip tectonism in the Ord and southern Bonaparte Basins of northwest Australia. From a combination of sedimentological and isotopic evidence it appears that localised convergent deformation started in the Late Ordovician in the eastern Arunta lnlier and adjacent Amadeus Basin. Synorogenic style sedimentation becomes synchronously widespread in the late Early Devonian and in most areas the record terminates abruptly close to the end of the Devonian. A notable exception is the Ngalia Basin in which such sedimentation continued until the mid-Carboniferous. In the Ord and Bonaparte Basins there is evidence of two discrete pulses of transcurrent activity in the Late Devonian and Carboniferous. The sedimentological story contrasts with the isotopic record from the southern Arunta lnlier, which has generally been interpreted in terms of continuous convergent orogenic activity spanning most of the Devonian and Carboniferous, with a suggestion that rates of deformation increased in the mid-Carboniferous. Either

  8. Tectonic evolution of the Western Kunlun orogenic belt in northern Qinghai-Tibet Plateau: Evidence from zircon SHRIMP and LA-ICP-MS U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    ZHANG ChuanLin; LU SongNian; YU HaiFeng; YE HaiMin

    2007-01-01

    The Western Kunlun Range in northern Qinghai-Tibet Plateau is composed of the North Kunlun Terrane,the South Kunlun Terrane and the Karakorum-Tianshuihai Terrane. Here we report zircon SHRIMP and LA-ICP-MS U-Pb ages of some metamorphic and igneous rocks and field observations in order to provide a better understanding of their Precambrian and Palaeozoic-early Mesozoic tectonic evolution.Based on these data we draw the following conclusions: (1) The paragneisses in the North Kunlun Terrane are likely of late Mesoproterozoic age rather than Palaeoproterozoic age as previously thought,representing tectonothermal episodes at 1.0-0.9 Ga and ~0.8 Ga. (2) The North Kunlun Terrane was an orogenic belt accreted to the southern margin of Tarim during late Mesoproterozoic to early Neoproterozoic, the two episodes of metamorphisms correspond to the assemblage and breakup of Rodinia respectively. (3) The Bulunkuole Group in western South Kunlun Terrane, which was considered to be the Palaeoproterozoic basement of the South Kunlun Terrane by previous studies, is now subdivided into the late Neoproterzoic to early Palaeozoic paragneisses (khondalite) and the early Mesozoic metamorphic volcano-sedimentary series; the paragneisses were thrust onto the metamorphic volcano-sedimentary series from south to north, with two main teconothermal episodes (i.e., Caledonian,460-400 Ma, and Hercynian-Indosinian, 340-200 Ma), and have been documented by zircon U-Pb ages.(4) In the eastern part of the South Kunlun Terrane, a gneissic granodiorite pluton, which intruded the khondalite, was crystallized at ca. 505 Ma and metamorphosed at ca. 240 Ma. In combination with geochronology data of the paragneiss, we suggest that the South Kunlun Terrane was a Caledonian accretionary orogenic belt and overprinted by late Paleozoic to early Mesozoic arc magmatism.

  9. Tectonic evolution of the Western Kunlun orogenic belt in northern Qinghai-Tibet Plateau:Evidence from zircon SHRIMP and LA-ICP-MS U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Western Kunlun Range in northern Qinghai-Tibet Plateau is composed of the North Kunlun Terrane,the South Kunlun Terrane and the Karakorum-Tianshuihai Terrane. Here we report zircon SHRIMP and LA-ICP-MS U-Pb ages of some metamorphic and igneous rocks and field observations in order to pro-vide a better understanding of their Precambrian and Palaeozoic-early Mesozoic tectonic evolution. Based on these data we draw the following conclusions: (1) The paragneisses in the North Kunlun Terrane are likely of late Mesoproterozoic age rather than Palaeoproterozoic age as previously thought,representing tectonothermal episodes at 1.0―0.9 Ga and ~0.8 Ga. (2) The North Kunlun Terrane was an orogenic belt accreted to the southern margin of Tarim during late Mesoproterozoic to early Neopro-terozoic,the two episodes of metamorphisms correspond to the assemblage and breakup of Rodinia respectively. (3) The Bulunkuole Group in western South Kunlun Terrane,which was considered to be the Palaeoproterozoic basement of the South Kunlun Terrane by previous studies,is now subdivided into the late Neoproterzoic to early Palaeozoic paragneisses (khondalite) and the early Mesozoic metamorphic volcano-sedimentary series; the paragneisses were thrust onto the metamorphic vol-cano-sedimentary series from south to north,with two main teconothermal episodes (i.e.,Caledonian,460―400 Ma,and Hercynian-Indosinian,340―200 Ma),and have been documented by zircon U-Pb ages. (4) In the eastern part of the South Kunlun Terrane,a gneissic granodiorite pluton,which intruded the khondalite,was crystallized at ca. 505 Ma and metamorphosed at ca. 240 Ma. In combination with geochronology data of the paragneiss,we suggest that the South Kunlun Terrane was a Caledonian accretionary orogenic belt and overprinted by late Paleozoic to early Mesozoic arc magmatism.

  10. Petrogenesis of the early Cretaceous volcanic rocks in the North Huaiyang tectono-magmatic unit of the Dabie Orogen, eastern China: Implications for crust-mantle interaction

    Science.gov (United States)

    Gao, Xin-Yu; Zhao, Tai-Ping; Zhao, Jun-Hong

    2016-03-01

    New elemental and isotopic data are presented for the early Cretaceous felsic to mafic volcanic rocks in the North Huaiyang tectono-magmatic unit (NHY) of the Dabie Orogen, in order to investigate their petrogenesis and provide insights into the nature of the late Mesozoic lithosphere mantle beneath the region and its tectonic relationship with neighboring blocks. LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Jingangtai Formation erupted in a quite short interval about 5 Mys during the Early Cretaceous (128-123 Ma). The rocks have wide ranges of SiO2 (48-68 wt.%) and MgO (0.6-5.6 wt.%) contents. They are enriched in large-ion-lithophile-elements (LILE) (e.g. Rb, Ba) and light rare-earth-elements (LREE), and depleted in high field strength elements (e.g. Nb, Ta and Ti) with weak negative Eu anomalies (Eu/Eu∗ = 0.71-0.94). Meanwhile, the rocks show relatively high whole-rock initial 87Sr/86Sr ratios (0.7074-0.7094), strong negative εNd(t) (-19.1 to -15.8) and zircon εHf values (-20.7 to -14.1). Such typical "continental" geochemical characteristics did not result from crustal contamination during magma ascent, but from an enriched mantle source modified by materials from the subducted Yangtze Craton during the Triassic continental collision. We propose that the petrogenesis of the large-scale contemporaneous magmatism of Dabie Orogen including felsic to mafic volcanic rocks in the NHY reflects an intensive lithospheric thinning and extension during the early Cretaceous as a tectonic response to the change of plate motion of westward subducted Pacific Plate beneath the Eurasian continent.

  11. Geochronology, geochemistry and Sr-Nd-Hf isotopes of mafic dikes in the Huicheng Basin: Constraints on intracontinental extension of the Qinling orogen

    Science.gov (United States)

    Li, Wei; Dong, Yunpeng; Guo, Anlin; Liu, Xiaoming; Wang, Yuejun; Liu, Wenhang; Yang, Yuanzhen

    2015-05-01

    The diabase dikes intruded the Lower Cretaceous sandstone in the Huicheng Basin are key to understanding the Mesozoic tectonic evolution of the Qinling orogen. LA-ICP-MS zircon U-Pb dating yields a crystallization age of 107 ± 1 Ma for them. The dikes have low contents of SiO2 (42.46-50.16 wt.%), MgO (3.47-5.59 wt.%) with low Mg# of 49-59, and TiO2 (1.35-1.63 wt.%), high TFe2O3 (8.15-9.36 wt.%), Al2O3 (14.75-17.23 wt.%) and K2O (0.87-3.61 wt.%). Their Ni and Cr contents are in range of 16.8-111 and 45.7-315 ppm, respectively. They are significantly enriched in light rare earth elements and large ion lithophile elements (e.g., Cs, Pb and Ba), and depleted in Rb, K, P, and Ti. The dikes show relatively high whole-rock initial 87Sr/86Sr ratios (0.7071-0.7079) and negative εNd (t) values (-1.5 to -4.8) with single-stage Nd model ages of 941-1186 Ma. In addition, they have low zircon εHf (t) values (-8.6 to +3.5) with single-stage Hf model ages of 674-1117 Ma. Both elemental and isotopic geochemistry suggests that the magma of these dikes has undergone significant crystallization fractionation of olivine and pyroxene but weak crustal contamination during magma evolution. They were derived from partial melting of an enriched lithospheric mantle source. Together with regional geological data, these results suggest that the Qinling orogen experienced an intracontinental extension during the late Early Cretaceous.

  12. Evaluation of structural and geological factors in orogenic gold type mineralisation in the Kervian area, north-west Iran, using airborne geophysical data

    Science.gov (United States)

    Almasi, Alireza; Jafarirad, Alireza; Kheyrollahi, Hasan; Rahimi, Mana; Afzal, Peyman

    2014-03-01

    The Piranshahr-Sardasht-Saqqez Zone (PSSZ) in the north-west of the Sanandaj-Sirjan metamorphic zone (SSZ) hosts some major Iranian gold deposits. In the south-east of PSSZ, there is a north-east trending orogenic gold belt which contains three gold deposits/occurrences (Qolqoleh, Kervian and Ghabaghloujeh). In this research, studies are focused on processing and analysing airborne magnetic and radiometric data in order to find applicable indicators for prospecting gold in this area. Former studies on the gold deposits/occurrences in the study area suggest three essential factors in local orogenic gold mineralisation: (1) intersecting deep bending structures/shear zones, (2) Fe-rich mafic meta-volcanic lithologies (primary source and host rocks) and (3) altered mylonitic granites (secondary host rock). Geological structures and lithological contacts can be mapped based on locating edges in the magnetic field at different depths. In this study, we extracted the structure from aeromagnetic data by reduction to the pole, upward continuation and applying a tilt derivative filter to the horizontal derivative of the upward continued data. Upward continuation was to several levels from 500 to 4000 m. Afterwards, a 3D architecture was built based on extracted subsurface lineaments in different levels. This 3D model can assist in the visualisation of the underground shape of structures that may influence gold mineralisation. Moreover, mafic meta-volcanic rocks in the study area, which contain magnetic minerals such as magnetite, titanomagnetite and ilmenite, can be mapped using aeromagnetic data. Mylonitic granites, which are the other host rock in the deposits, were mapped using airborne radiometric data.

  13. Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: an in situ SIMS study with implications for the source of sulfur

    Science.gov (United States)

    Chen, Lei; Li, Xian-hua; Li, Jian-wei; Hofstra, Albert H.; Liu, Yu; Koenig, Alan E.

    2015-08-01

    High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)), and sulfur isotopic (secondary ion mass spectrometry (SIMS)) analyses of pyrite from the Qiuling sediment-hosted gold deposit (232 ± 4 Ma) in the West Qinling orogen, central China were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids. The results reveal an enormous variation (-27.1 to +69.6 ‰) in sulfur isotopic composition of pyrite deposited during three paragenetic stages. Pre-ore framboidal pyrite, which is characterized by low concentrations of As, Au, Cu, Co, and Ni, has negative δ34S values of -27.1 to -7.6 ‰ that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predominant lithologies in the deposit area, and the most important hosts of many sediment-hosted gold deposits throughout the West Qinling orogen. The ore-stage hydrothermal pyrite contains high concentrations of Au, As, Cu, Sb, Tl, and Bi and has a relatively narrow range of positive δ34S values ranging from +8.1 to +15.2 ‰. The sulfur isotope data are comparable to those of ore pyrite from many Triassic orogenic gold deposits and Paleozoic sedimentary exhalative (SEDEX) Pb-Zn deposits in the West Qinling orogen, both being hosted mainly in the Devonian sequence. This similarity indicates that sulfur, responsible for the auriferous pyrite at Qiuling, was largely derived from the metamorphic devolatization of Paleozoic marine sedimentary rocks. Post-ore-stage pyrite, which is significantly enriched in Co and Ni but depleted in Au and As, has unusually high δ34S values ranging from +37.4 to +69.6 ‰, that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying Cambrian sedimentary rocks with very

  14. Mantle Response to Collision, Slab Breakoff & Lithospheric Tearing in Anatolian Orogenic Belts, and Cenozoic Geodynamics of the Aegean-Eastern Mediterranean Region

    Science.gov (United States)

    Dilek, Yildirim; Altunkaynak, Safak

    2010-05-01

    The geochemical and temporal evolution of the Cenozoic magmatism in the Aegean, Western Anatolian and peri-Arabian regions shows that plate tectonic events, mantle dynamics, and magmatism were closely linked in space and time. The mantle responded to collision-driven crustal thickening, slab breakoff, delamination, and lithospheric tearing swiftly, within geologically short time scales (few million years). This geodynamic continuum resulted in lateral mantle flow, whole-sale extension and accompanying magmatism that in turn caused the collapse of tectonically and magmatically weakened orogenic crust. Initial stages of post-collisional magmatism (~45 Ma) thermally weakened the orogenic crust in Tethyan continental collision zones, giving way into large-scale extension and lower crustal exhumation via core complex formation starting around 25-23 Ma. Slab breakoff was the most common driving force for the early stages of post-collisional magmatism in the Tethyan mountain belts in the eastern Mediterranean region. Magmatic rocks produced at this stage are represented by calc-alkaline-shoshonitic to transitional (in composition) igneous suites. Subsequent lithospheric delamination or partial convective removal of the sub-continental lithospheric mantle in collision-induced, overthickened orogenic lithosphere caused decompressional melting of the upwelling asthenosphere that in turn resulted in alkaline basaltic magmatism (punctuated by the collisional accretion of several ribbon continents (i.e. Pelagonia, Sakarya, Tauride-South Armenian) to the southern margin of Eurasia, and by related slab breakoff events. Exhumation of middle to lower crustal rocks and the formation of extensional metamorphic domes occurred in the backarc region of this progressively southward-migrated trench and the Tethyan (Afro-Arabian) slab throughout the Cenozoic. Thus, slab retreat played a major role in the Cenozoic geodynamic evolution of the Aegean and Western Anatolian regions. However

  15. Ongoing compression triggered exhumation of the orogenic crust in the Variscan Maures-Tanneron Massif, France - Geological arguments and thermo-mechanical tests

    Science.gov (United States)

    Gerbault, Muriel; Schneider, Julie; Reverso-Peila, Alexandre; Corsini, Michel

    2016-04-01

    The Maures-Tanneron Massif (MTM), together with Corsica and Sardinia, hosted the South-Eastern Variscan belt and record a continuous evolution from continental collision to exhumation. We present a synthesis of the available geological and geochronogical data that explores the transition from convergence to perpendicular Permean extension in the MTM (at ~ 325 Ma ± 25 My). The migmatitic Internal Zone that composes the Western MTM displays structural clues such as backthrusting and magmatic foliations, and metamorphic data indicating exhumation of deep seated partially molten rocks at an apparent heating rate of 1-2 °C/km/My from ca. 345 Ma to 320 Ma. This suggests vertical advective heat transport during continued N140° convergence (D2 phase). In contrast at the same time, the low grade External zone composing the Eastern part of the MTM recorded exhumation of more conductive patterns at an apparent rate of 0.3-0.6 °C/km/My. It is only from ca. 320 Ma that transcurrent motion dominates in the Internal zone and progressively leaves way to N-S strecthing (D3 phase), indicative of orogenic collapse and extension and in asociation with emplacement of larger volumes of magmatism in the crust. Thermo-mechanical modeling complements this synthesis in order to highlight the conditions under which deep seated HP units could melt and massively start to exhume during maintained convergence (phase D2). Accounting for temperature dependent elasto-visco-plastic rheologies, our models explore the dynamics of an orogenic prism starting from a dis-equilibrated state just after slab break-off or delamination, at ca. 350 Ma. We simulate the development of gravitational instabilities in partially melting crust, a process that is already well known to depend on strain-rate, heat sources and strength layering. In order to reproduce the exhumation patterns of rocks from ~50 km depth over the appropriate time-scale (>20 My) and spatial extent (>100 km), a best fit was obtained with a

  16. Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence

    Science.gov (United States)

    Wang, Lu; Kusky, Timothy; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2015-04-01

    Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence Numerous studies have described partial melting processes in low-high pressure meta-sedimentary rocks, some of which may generate melts that coalesce to form plutons. However, migmatized ultrahigh pressure (UHP) eclogite has never been clearly described from the microscale to macroscale, though experimental studies prove dehydration partial melting of eclogite at high pressure condition1 and low degrees of partially melted eclogite have been reported from the Qaidam UHP orogenic belt in NW China2,3 or inferred from multiphase solid (MS) inclusions within eclogite4 in the Sulu UHP belt. We present field-based documentation of decompression partial melting of UHP eclogite from Yangkou and General's Hill, Sulu Orogen. Migmatized eclogite shows successive stages of anatexis, initially starting from intragranular and grain boundary melt droplets, which grow into a 3D interconnected intergranular network, then segregate and accumulate in pressure shadow areas, and finally merge to form melt channels and dikes that transport melts to upper lithospheric levels. In-situ phengite breakdown-induced partial melting is directly identified by MS inclusions of Kfs+ barium-bearing Kfs + Pl in garnet, connected by 4-10 μm wide veinlets consisting of Bt + Kfs + Pl next to the phengite. Intergranular veinlets of plagioclase + K-feldspar first form isolated beads of melt along grain boundaries and triple junctions of quartz, and with higher degrees of melting, eventually form interconnected 3D networks along grain boundaries in the leucosome, allowing melt to escape from the intergranular realm and collect in low-stress areas. U-Pb (zircon) dating and petrological analyses on residue and leucocratic rocks shows that partial melting occurred at 228-219 Ma, shortly after peak UHP metamorphism (~230 Ma), and at depths of 30-90 km

  17. Lead and barium sources in Cambrian siliciclastics and sediment provenance of a sector of the Taconic Orogen, Quebec: a mixing scenario based on Pb-isotopic evidence

    Science.gov (United States)

    Schrijver, K.; Zartman, R.E.; Williams-Jones, A. E.

    1994-01-01

    To test the hypothesis that siliciclastic rocks constituted the major source of Pb and Ba in barite-galena deposits of the Taconic Orogen, we determined Pb-isotope ratios in galena, barren rocks and contained minerals, as well as concentrations of Pb, U, Th and Ba in the latter (detrital feldspars, sandstones, mudstones, rock clasts and carbonate cements and clasts). Ranges in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of 28 galena samples are 17.96-18.05, 15.56-15.59 and 37.75-37.93, respectively; ranges for 41 barren rocks and minerals are 16.17-23.31, 15.26-15.86 and 35.98-42.51, respectively. The lowest ratios are in feldspar, and the highest in carbonate and mudstone. Values of the mudstones samples overlap those of galena when corrected for in situ decay of U and Th since galena precipitation (???450 Ma). We thus propose that mudstones constituted a source of lead. Corrected ratios for anomalously Pb-rich mudstones are virtually identical to galena-Pb ratios and may be due to contamination by lead-bearing brines. Assuming that burial diagenesis did not disturb the Pb-isotope values of sandstones, these rocks contributed only a minor fraction of lead to the galena, estimated at ???20% for one deposit. The source of barite-Ba was probably perthite. Low Ba and Pb concentrations of sandstone adjacent to this deposit, compared to high concentrations remote from it, support leaching of barium (and minor lead) from feldspar penecontemporaneous with feldspar dissolution. Geological data indicate that the provenance of the siliciclastic rocks was mainly from Grenville terrane. A comparison of our Pb-isotopic data for Taconic perthite with those of Grenville K-feldspar, as well as ratios of trace elements, support this provenance for both sandstones and mudstones. The presence of carbonate platforms peripheral to the orogen, and the Middle Ordovician-Middle Devonian depositional range of the studied and Mississippi Valley type deposits north (Newfoundland) and south (U

  18. Origin of Middle Cambrian and Late Silurian potassic granitoids from the western Kunlun orogen, northwest China: a magmatic response to the Proto-Tethys evolution

    Science.gov (United States)

    Liu, Zheng; Jiang, Yao-Hui; Jia, Ru-Ya; Zhao, Peng; Zhou, Qing; Wang, Guo-Chang; Ni, Chun-Yu

    2014-02-01

    This paper presents new SHRIMP zircon U-Pb chronology, major and trace element, and Sr-Nd-Hf isotopic data of two Early Paleozoic granitic plutons (Yierba and North Kudi) from the western Kunlun orogen, in attempt to further constrain the Proto-Tethys evolution. SHRIMP zircon U-Pb dating shows that the Yierba pluton was emplaced in the Middle Cambrian (513 ± 7 Ma) and the North Kudi pluton was emplaced in the Late Silurian (420.6 ± 6.3 Ma). The Yierba pluton consists of quartz monzodiorite, quartz monzonite and granodiorite. These granitoids are metaluminous and potassic, with initial 87Sr/86Sr ratios of 0.7072-0.7096, ɛNd (T) of -0.2 to -1.6 and ɛHf (T) (in-situ zircon) of -1.2. Elemental and isotopic data suggest that they were formed by partial melting of subducted sediments, with subsequent melts interacting with the overlying mantle wedge in an oceanic island arc setting in response to the intra-oceanic subduction of Proto-Tethys. The North Kudi pluton consists of syenogranite and alkali-feldspar granite. These granites are metaluminous to weakly peraluminous and potassic. They show an affinity of A1 subtype granite, with initial 87Sr/86Sr ratios of 0.7077-0.7101, ɛNd (T) of -3.5 to -4.0 and ɛHf (T) (in-situ zircon) of -3.9. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metamorphic basement at a shallow depth (<30 km) during the post-orogenic regime caused by Proto-Tethyan oceanic slab break-off. Our new data suggest that the subduction of the Proto-Tethyan oceanic crust was as early as Middle Cambrian (˜513 Ma) and the final closure of Proto-Tethys was not later than Late Silurian (˜421 Ma), most probably in Middle Silurian.

  19. The syncollisional granitoid magmatism and continental crust growth in the West Kunlun Orogen, China - Evidence from geochronology and geochemistry of the Arkarz pluton

    Science.gov (United States)

    Zhang, Yu; Niu, Yaoling; Hu, Yan; Liu, Jinju; Ye, Lei; Kong, Juanjuan; Duan, Meng

    2016-02-01

    The West Kunlun orogenic belt (WKOB) at the northwest margin of the Greater Tibetan Plateau records seafloor subduction, ocean basin closing and continental collision with abundant syncollisional granitoids in response to the evolution of the Proto- and Paleo-Tethys Oceans from the early-Paleozoic to the Triassic. Here we present a combined study of detailed zircon U-Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotopic geochemistry on the syncollisional Arkarz (AKAZ) pluton with mafic magmatic enclaves (MMEs) exposed north of the Mazha-Kangxiwa suture (MKS) zone. The granitoid host rocks and MMEs of the AKAZ pluton give the same late Triassic age of ~ 225 Ma. The granitoid host rocks are metaluminous granodiorite and monzogranite. They have initial 87Sr/86Sr of 0.70818 to 0.70930, εNd(225 Ma) = - 4.61 to - 3.91 and εHf(225 Ma) = - 3.01 to 0.74. The MMEs are more mafic than the host with varying SiO2 (51.00-63.24 wt.%) and relatively low K2O (1.24-3.02 wt.%), but have similar Sr-Nd-Hf isotope compositions to the host ((87Sr/86Sr)i = 0.70830-0.70955, εNd(225 Ma) = - 4.88 to - 4.29, εHf(225 Ma) = - 2.57 to 0.25). Both the host and MMEs have rare earth element (REE) and trace element patterns resembling those of bulk continental crust (BCC). The MMEs most likely represent cumulate formed from common magmas parental to the granitoid host. The granitoid magmatism is best explained as resulting from melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional similarity to the BCC and the inherited mantle-like isotopic compositions. Simple isotopic mixing calculations suggest that ~ 80% ocean crust and ~ 20% continental materials contribute to the source of the AKAZ pluton. Thus, the hypothesis "continental collision zones as primary sites for net continental crust growth" is applicable in the WKOB as shown by studies in southern Tibet, East Kunlun and Qilian orogens. In

  20. Geochronology and geochemistry of the Eastern Erenhot ophiolitic complex: Implications for the tectonic evolution of the Inner Mongolia-Daxinganling Orogenic Belt

    Science.gov (United States)

    Zhang, Zhicheng; Li, Ke; Li, Jianfeng; Tang, Wenhao; Chen, Yan; Luo, Zhiwen

    2015-01-01

    The Eastern Erenhot ophiolitic complex (EOC) is one of the numerous fragments of oceanic lithosphere in southeastern Central Asian Orogenic Belt. It is composed dominantly of serpentinized ultramafic rocks with subordinate gabbros, mafic lavas and minor plagiogranite dikes. Zircons from two gabbros and one plagiogranite yielded weighted mean 206Pb/238U ages of 354.2 ± 4.5 Ma, 353.3 ± 3.7 Ma and 344.8 ± 5.5 Ma. These ages suggest that the oceanic crust of the EOC formed in a maximum time period of 10 Ma, and that the plagiogranite may have formed later than the gabbroic section. An undeformed and unmetamorphosed dioritic porphyry dike intruded in the Carboniferous strata near the EOC has an intrusive age of 313.6 ± 2.9 Ma and provides a possible younger minimum time limit for the formation of the early Carboniferous ophiolitic complex. All the mafic rocks have similar chondrite normalized REE patterns characterized by moderate depletion in LREE with (La/Yb)N (0.20-0.75) similar to normal middle oceanic ridge basalt (N-MORB). The PM-normalized trace element patterns of the gabbros and massive basalts are also reasonably consistent, essentially similar to those of N-MORB except for some enrichment in LILE (e.g. Rb, Ba) and slightly negative Ti anomalies. The plagiogranite samples are characterized by lower K2O (0.45-0.73 wt%) comparable with oceanic plagiogranite. They have LREE-enriched, chondrite-normalized REE patterns with varying Eu anomalies and the trace elements (e.g. Rb, Y, Nb) show similarity to volcanic arc granite. These geochemical features of the EOC show a similar volcanic arc affinity, suggesting that they form in a back-arc-type environment. Their origin is attributed to asthenospheric upwelling and further lithospheric extension during early Carboniferous, formed as a consequence of slab breakoff on collision of the northern early to mid-Paleozoic orogenic terrane and the Hunshandake Block.

  1. Evolution of crustal stress, pressure and temperature around shear zones during orogenic wedge formation: a 2D thermo-mechanical numerical study

    Science.gov (United States)

    Markus Schmalholz, Stefan; Jaquet, Yoann

    2016-04-01

    We study the formation of an orogenic wedge during lithospheric shortening with 2D numerical simulations. We consider a viscoelastoplastic rheology, thermo-mechanical coupling by shear heating and temperature-dependent viscosities, gravity and erosion. In the initial model configuration there is either a lateral temperature variation at the model base or a lateral variation in crustal thickness to generate slight stress variations during lithospheric shortening. These stress variations can trigger the formation of shear zones which are caused by thermal softening associated with shear heating. We do not apply any kind of strain softening, such as reduction of friction angle with progressive plastic strain. The first major shear zone that appears during shortening crosscuts the entire crust and initiates the asymmetric subduction/underthrusting of mainly the mechanically strong lower crust. After some deformation, the first shear zone in the upper crust is abandoned, the deformation propagates towards the foreland and a new shear zone forms only in the upper crust. The shear zone propagation occurs several times where new shear zones form in the upper crust and the mechanically strong top of the lower crust acts as detachment horizon. We calculate the magnitudes of the maximal and minimal principal stresses and of the mean stress (or dynamic pressure), and we record also the temperature for several marker points in the upper and lower crust. We analyse the evolution of stresses and temperature with burial depth and time. Deviatoric stresses (half the differential stress) in the upper crust are up to 200 MPa and associated shear heating in shear zones ranges between 40 - 80 °C. Lower crustal rocks remain either at the base of the orogenic wedge at depths of around 50 km or are subducted to depths of up to 120 km, depending on their position when the first shear zone formed. Largest deviatotric stresses in the strong part of the lower crust are about 1000 MPa and

  2. Geochronology and geochemistry of the Early Cretaceous Jigongshan and Qijianfeng batholiths in the Tongbai orogen, central China: implications for lower crustal delamination

    Science.gov (United States)

    Zhang, Jinyang; Ma, Changqian; Li, Jianwei; She, Zhenbing; Zhang, Chao

    2013-06-01

    The Jigongshan and Qijianfeng batholiths in the Tongbai orogen consist mainly of porphyritic hornblende-biotite monzogranite, biotite monzogranite, and biotite syenogranite, which are variably intruded by lamprophyre, diorite, and syenogranite dykes. Mafic microgranular enclaves commonly occur in the hornblende-biotite monzogranite, whereas surmicaceous enclaves are found in the biotite monzogranite. Both batholiths have zircon U-Pb ages ranging from ca. 139 to 120 Ma, indicating their emplacement in the Early Cretaceous. The hornblende-biotite monzogranite has an adakitic affinity marked by relatively high Sr/Y and (La/Yb) N ratios, lack of Eu anomalies, low MgO and Ni contents, and Na2O > K2O. Its chemical compositions, combined with enriched Sr-Nd isotopic signatures, suggest formation by dehydration melting of mafic rocks in a thickened lower crust. This thickened crust resulted from the Permo-Triassic subduction-collision between the North China and South China blocks and persisted until the Early Cretaceous. The biotite monzogranite and biotite syenogranite have low Al2O3, CaO, and Sr contents, low Rb/Sr, FeOt/MgO, and (Na2O + K2O)/CaO ratios, and flat HREE patterns with moderate to weak Eu anomalies. They were produced by partial melting of crustal materials under relatively low pressure. Partial melting at different crustal levels could have significantly contributed to mechanical weakening of the crust. The diorite and lamprophyre dykes show linear trends between SiO2 and major or trace elements on Harker diagrams, with two lamprophyre samples containing normative nepheline and olivine. These rocks have high La/Yb and Dy/Yb ratios, both displaying co-variation with contents of Yb. They were originated from relatively deep lithospheric mantle followed by fractionation of olivine + clinopyroxene + apatite + Fe-Ti oxides. Extensive partial melting in the lithospheric mantle indicates relatively high temperatures at this level. We suggest that the presence of

  3. Neoproterozoic diamictite-bearing sedimentary rocks in the northern Yili Block and their constraints on the Precambrian evolution of microcontinents in the Western Central Asian Orogenic Belt

    Science.gov (United States)

    He, Jingwen; Zhu, Wenbin; Zheng, Bihai; Wu, Hailin; Cui, Xiang; Lu, Yuanzhi

    2015-12-01

    The origin and tectonic setting of Precambrian sequences in the Central Asian Orogenic Belt (CAOB) have been debated due to a lack of high resolution geochronological data. Answering this question is essential for the understanding of the tectonic framework and Precambrian evolution of the blocks within the CAOB. Here we reported LA-ICP-MS detrital zircon U-Pb ages and in-situ Hf isotopic data for Neoproterozoic sedimentary cover in the northern Yili Block, an important component of the CAOB, in order to provide information on possible provenance and regional tectonic evolution. A total of 271 concordant U-Pb zircon ages from Neoproterozoic sedimentary cover in the northern Yili Block define three major age populations of 1900-1400 Ma, 1300-1150 Ma and 700-580 Ma, which are quite different from cratons and microcontinents involved in the CAOB. Although it is not completely consistent with the local basement ages, an autochthonous provenance interpretation is more suitable. Some zircon grains show significant old Hf model ages (TDMC; 3.9-2.4 Ga) and reveal continental crust as old as Paleoarchean probably existed. Continuous Mesoproterozoic zircon age populations exhibit large variations in the εHf(t) ratios, suggesting the long-time involvement of both reworked ancient crust and juvenile material. Similar Mesoproterozoic evolution pattern is identified in many continental terranes involved in the CAOB that surround the Tarim Craton. Based on our analysis and published research, we postulate that the northern Yili Block, together with Chinese Central Tianshan, Kyrgyz North Tianshan and some other microcontinents surrounding the Tarim Craton, once constituted the continental margin of the Tarim Craton in the Mesoproterozoic, formed by long-lived accretionary processes. Most of the late Neoproterozoic zircons exhibit significant positive εHf(t) ratios, suggesting the addition of juvenile crust. It is consistent with the tectonic event related to the East Africa

  4. Little and Large: Implications for Preservation of Radiogenic-Pb in Titanite. An example from the Albany-Fraser Orogen, Australia

    Science.gov (United States)

    Kirkland, C.

    2015-12-01

    Titanite typically contains more non-radiogenic Pb than zircon, nonetheless it can preserve useful age information that complements geochronology from other datable phases. Titanite is more reactive than zircon and it interacts more readily with other major phases. As a result titanite dates frequently indicate the time of cooling below a blocking temperature (in reality an interval). The role of titanite grain size is important as it has a bearing on the extent to which titanite U-Pb ages reflect diffusive Pb loss or pristine formation ages. We demonstrate that titanite collected through the Albany-Fraser Orogen, across an uplifted refractory lower crustal block, can record thermal overprints apparently lacking in the zircon record. Two zones of the Albany-Fraser Orogen are the Biranup and Fraser Zones, each with a distinctive Proterozoic history but unequivocally part of the reworked margin of the Archean Yilgarn Craton. A dichotomy exists in the zircon geochronology record of this area, in that within the older Biranup Zone, Stage II overprinting (1225-1140 Ma) is widespread whereas in the younger Fraser Zone, Stage I (1345-1260 Ma) is dominant, with Stage II apparently absent. Although, most metamorphic titanite in the Fraser Zone records an age of 1307 ± 17 Ma, reflecting closure to radiogenic-Pb mobility after Stage I metamorphism, small titanite grains reveal Stage II overprinting with a mean reset age of 1205 ± 16 Ma. In contrast, titanite from metasediments within the Biranup Zone principally record ages of 1203 ± 6 Ma and 1153 ± 27 Ma reflecting cooling after prolonged Stage II metamorphism. Thermochronological modelling indicates that small titanite grains in the Fraser Zone would be reset during Stage II overprinting at temperatures of 695-725°C. Larger titanite crystals would not be reset by this thermal overprint. This result is similar to phase equilibrium modelling from the Biranup Zone that indicates temperatures of 670-680 °C during Stage II

  5. Tomographic images of subducted oceans matched to the accretionary records of orogens - Case study of North America and relevance to Central Asia

    Science.gov (United States)

    Sigloch, Karin; Mihalynuk, Mitchell G.; Hosseini, Kasra

    2016-04-01

    Accretionary orogens are the surface record of subduction on the 100-million-year timescale; they aggregate buoyant crustal welts that resisted subduction. The other record of subduction is found in the deep subsurface: oceanic lithosphere preserved in the mantle that records ocean basin closure between successive generations of arcs. Seismic tomography maps out these crumpled paleo-oceans down to the core-mantle boundary, where slab accumulates. One such accumulation of enormous scale is under Eastern Asia, recording the assembly of the Central Asian Orogenic Belt (CAOB). Deep CAOB slab has hardly been explored because tomographic image resolution in the lowermost mantle is limited, but this is rapidly improving. We present new images of the CAOB slabs from our P-wave tomography that includes core-diffracted waves as a technical novelty. The previous slab blur sharpens into the type of elongated geometries expected to trace paleo-trench lines. Since the North American Cordillera is younger than the CAOB (mostly 10,000 km long. North America converged on the two microcontinents by westward subduction of two intervening basins (which we name Mezcalera and Angayucham oceans), culminating in diachronous suturing between ~150 Ma and ~50 Ma. Hence geophysical subsurface evidence negates the widely accepted "Andean-style" model of Farallon-beneath-continent subduction since at least 180 Ma, and supports a Jura-Cretaceous paleogeography closer to today's Southwestern Pacific, or to the Paleozoic CAOB. Though advocated since the 1970's by a minority of geologists, this scenario had not gained wide acceptance due to a record obscured by overprinting, margin-parallel translation, and oroclinal bending. The new subsurface evidence provides specific indications where to seek the decisive Mezcalera-Angayucham suture. The suture is evident in a trail of collapsed Jura-Cretaceous basin relics that run the length of the Cordillera. Reference: Sigloch, K., & Mihalynuk, M. G. (2013

  6. I-type granitoids associated with the early Paleozoic intracontinental orogenic collapse along pre-existing block boundary in South China

    Science.gov (United States)

    Yu, Yang; Huang, Xiao-Long; He, Peng-Li; Li, Jie

    2016-04-01

    the block boundary by mantle-derived melt during the orogenic collapse. The pre-existing block boundary might have promoted asthenosphere upwelling and basaltic underplating during the intracontinental orogenic collapse.

  7. U Pb, Hf and O isotope evidence for two episodes of fluid-assisted zircon growth in marble-hosted eclogites from the Dabie orogen

    Science.gov (United States)

    Wu, Yuan-Bao; Zheng, Yong-Fei; Zhao, Zi-Fu; Gong, Bing; Liu, Xiaoming; Wu, Fu-Yuan

    2006-07-01

    A combined study of internal structure, U-Pb age, and Hf and O isotopes was carried out for metamorphic zircons from ultrahigh-pressure eclogite boudins enclosed in marbles from the Dabie orogen in China. CL imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain, respectively. The metamorphic zircons have low Th and U contents with low Th/U ratios, yielding two groups of 206Pb/ 238U age at 245 ± 3 to 240 ± 2 Ma and 226 ± 4 to 223 ± 2 Ma, respectively. Anomalously high δ 18O values were obtained for refractory minerals, with 9.9 to 21.4‰ for garnet and 16.9‰ for zircon. This indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction-zone metamorphism. Most of the zircons are characterized by very low 176Lu/ 177Hf ratios of 0.000001-0.000028, indicating their growth in association with garnet recrystallization. A few of them falling within the older age group have comparatively high 176Lu/ 177Hf ratios of 0.000192-0.000383, suggesting their growth prior to the formation of garnet in the late stage of subduction. The variations in the Lu/Hf ratios for zircons can thus be used to correlate with garnet growth during eclogite-facies metamorphism. In either case, the zircons have variable ɛHf ( t) values for individual samples, suggesting that their protolith is heterogeneous in Hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle. Nevertheless, a positive correlation exists between 206Pb/ 238U ages and Lu-Hf isotope ratios for the metamorphically recrystallized zircons, suggesting that eclogite-facies metamorphism in the presence of fluid has the identical effect on zircon Lu-Hf and U-Th-Pb isotopic systems. We conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh-pressure metamorphism, whereas the younger zircons

  8. Petrogenesis and tectonic significance of the late Triassic mafic dikes and felsic volcanic rocks in the East Kunlun Orogenic Belt, Northern Tibet Plateau

    Science.gov (United States)

    Hu, Yan; Niu, Yaoling; Li, Jiyong; Ye, Lei; Kong, Juanjuan; Chen, Shuo; Zhang, Yu; Zhang, Guorui

    2016-02-01

    We present zircon U-Pb ages and geochemical data on the late Triassic mafic dikes (diabase) and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in the East Kunlun Orogenic Belt (EKOB). These rocks give a small age window of 228-218 Ma. The mafic dikes represent evolved alkaline basaltic melts intruding ~ 8-9 Myrs older and volumetrically more abundant A-type granite batholith. Their rare earth element (REE) and multi-element patterns are similar to those of the present-day ocean island basalts (OIBs) except for a weak continental crustal signature (i.e., enrichment of Rb and Pb and weak depletion of Nb, Ta and Ti). Their trace element characteristics together with the high 87Sr/86Sr (0.7076-0.7104), low εNd(t) (- 2.18 to - 3.46), low εHf(t) (- 2.85 to - 4.59) and variable Pb isotopic ratios are consistent with melts derived from metasomatized subcontinental lithospheric mantle with crustal contamination. The felsic volcanic rocks are characterized by high LREE/HREE (e.g., [La/Yb]N of 5.71-17.00) with a negative Eu anomaly and strong depletion in Sr and P, resembling the model upper continental crust (UCC). Given the high 87Sr/86Sr (0.7213-0.7550) and less negative εNd(t) (- 3.83 to - 5.09) and εHf(t) (- 3.06 to - 3.83) than the UCC plus the overlapping isotopes with the mafic dikes and high Nb-Ta rhyolites, the felsic volcanic rocks are best interpreted as resulting from melting-induced mixing with 45-50% crustal materials and 50-55% mantle-derived mafic melts probably parental to the mafic dikes. Such mantle-derived melts underplated and intruded the deep crust as juvenile crustal materials. Partial melting of such juvenile crust produced felsic melts parental to the felsic volcanic rocks in the EKOB. We hypothesize that the late Triassic mafic dikes and felsic volcanic rocks are associated with post-collisional extension and related orogenic collapse. Such processes are probably significant in causing asthenospheric upwelling, decompression melting

  9. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: 207Pb-206Pb dating of magnetite, monazite and allanite in the central and northern Nagssugtoqidian orogen, West Greenland

    Directory of Open Access Journals (Sweden)

    Frei, Robert

    2006-12-01

    Full Text Available Pb-isotopic data for magnetite from amphibolites in the Nagssugtoqidian orogen, central West Greenland, have been used to trace their source characteristics and the timing of metamorphism. Analyses of the magnetite define a Pb-Pb isochron age of 1726 ± 7 Ma. The magnetite is metamorphic in origin, and the 1726 Ma age is interpreted as a cooling age through the closing temperature of magnetite at ~600°C. Some of the amphibolites in this study come from the Naternaq supracrustal rocks in the northern Nagssugtoqidian orogen, which host the Naternaq sulphide deposit and may be part ofthe Nordre Strømfjord supracrustal suite, which was deposited at around 1950 Ma ago.Pb-isotopic signatures of magnetite from the Arfersiorfik quartz diorite in the central Nagssugtoqidian orogen are compatible with published whole-rock Pb-isotopic data from this suite; previous work has shown that it is a product of subduction-related calc-alkaline magmatism between 1920 and 1870 Ma. Intrusion of pegmatites occurred at around 1800 Ma in both the central and the northernparts of the orogen. Pegmatite ages have been determined by Pb stepwise leaching analyses of allanite and monazite, and source characteristics of Pb point to an origin of the pegmatites by melting of the surrounding late Archaean and Palaeoproterozoic country rocks. Hydrothermal activity took place after pegmatite emplacement and continued below the closure temperature of magnetite at 1800–1650 Ma. Because of the relatively inert and refractory nature of magnetite, Pb-isotopic measurements from this mineral may be of help to understand the metamorphic evolution of geologicallycomplex terrains.

  10. Detrital zircon U-Pb ages and Hf isotopes of Permo-Carboniferous sandstones in central Inner Mongolia, China: Implications for provenance and tectonic evolution of the southeastern Central Asian Orogenic Belt

    Science.gov (United States)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan

    2016-03-01

    The tectonic setting of the southeastern Central Asian Orogenic Belt (CAOB) during the Late Paleozoic has been debated for many years. Provenance analysis of Permo-Carboniferous sedimentary rocks can effectively address this issue. In this study, eight sandstone samples were collected for zircon U-Pb and Lu-Hf isotopic analyses combined with petrographic analysis. Framework petrography and zircon morphology suggest that the samples were from recycled orogen of an igneous origin. Carboniferous rocks, with a significant age peak at 432 Ma and εHf (t) values of - 9.0 to 13.6, were mainly derived from Early to Mid-Paleozoic magmatic rocks and deposited in a piedmont zone, namely, the margin of an inland sea. Permian rocks, mostly with age peaks at 445 Ma and/or 280 Ma and εHf (t) values of - 25.2 to 11.4, dominantly originated from a pre-existing Early to Mid-Paleozoic magmatic arc and Late Paleozoic igneous rocks. These rocks formed in restricted basins of the piedmont and intermountain zones. Based on zircon spectral discrimination, sedimentary environmental analysis, and previous studies, this study supports the interpretation that the southeastern CAOB entered stages of extension and rifting during the Late Paleozoic. In the end, this study proposes a tectonic-paleogeographic reconstruction to explain the tectonic evolution of the southeastern CAOB and the exhumation-transportation-deposition processes between the basins and ranges developed in this orogen.

  11. Compositional change of granitoids from Eastern Pontides Orogenic Belt (NE Turkey) at ca. 84 Ma: Response to slab rollback of the Black Sea

    Science.gov (United States)

    Liu, Ze; Zhu, Di-Cheng; Eyuboglu, Yener; Wu, Fu-Yuan; Rızaoǧlu, Tamer; Zhao, Zhi-Dan; Xu, Li-Juan

    2016-04-01

    Magma generation and evolution is a natural consequence of mantle dynamics and crust-mantle interaction. As a result, changes of magma compositions in time and space can be used, in turn, to infer these deep processes. In this paper we report new zircon U-Pb age and Hf isotope, whole-rock major and trace element, and Nd isotope data for the granitoids from Kürtün in Eastern Pontides. These data, together with the data in the literature, reveal the occurrence of magma compositional variations at ca. 84 Ma in the region, providing new insights into the mantle dynamics responsible for the generation of the extensive Late Cretaceous felsic magmatism in Eastern Pontides Orogenic Belt (NE Turkey) (Eyuboglu et al., 2015). Group I samples (SiO2 = 77-62 wt.%) were concentrated in 91-86 Ma and are characterized by their low CaO (1.6-1.5 wt.%) and Th (8.2-3.0 ppm) contents and low K2O/Na2O (0.7-0.1) and Th/La (0.4-0.2) ratios. Group II samples (SiO2 = 71-63 wt.%) were concentrated in 82-72 Ma and include high concentrations of CaO (5.2-3.0 wt.%) and Th (29.6-14.3), high K2O/Na2O (1.5-1.1) and varying Th/La (1.0-0.5) ratios. Group I samples have positive zircon eHf(t) (+9.6 to +7.6) and whole-rock eNd(t) (+3.5 to +2.5), significantly differing from those of Group II samples with eHf(t) of +1.9 to -1.5 and whole-rock eNd(t) of -3.6 to -3.8. Modeling results indicate that the Nd-Hf isotopic compositions of Group I and II samples can be interpreted as having derived from partial melting of the low-K amphibolite within the juvenile lower crust beneath the Eastern Pontides Orogenic Belt that incorporated into 15-20% and 70-75% enriched components from the basement rocks represented by the Carboniferous granites exposed in the region, respectively. In combination with the geological observations that indicate the occurrence of regional thermal subsidence (Bektaş et al., 1999) and extensional structure (Bektaş et al., 1999, 2001) during the Campanian (83.6-72.1 Ma), the coeval

  12. New insights into Phanerozoic tectonics of south China: Part 1, polyphase deformation in the Jiuling and Lianyunshan domains of the central Jiangnan Orogen

    Science.gov (United States)

    Li, Jianhua; Dong, Shuwen; Zhang, Yueqiao; Zhao, Guochun; Johnston, Stephen T.; Cui, Jianjun; Xin, Yujia

    2016-04-01

    The central Jiangnan Orogen, genetically formed by the Proterozoic Yangtze-Cathaysia collision, presents as a composite structural feature in the Phanerozoic with multiple ductile and brittle fabrics whose geometries, kinematics, and ages are crucial to decipher the tectonic evolution of south China. New structural observations coupled with thermochronological and geochronological studies of these fabrics document four main stages of deformation. The earliest stage in early Paleozoic time (460-420 Ma) corresponds to combined E-trending dextral and northwest directed thrust shearing that was variably partitioned in anastomosing high-strain zones under greenschist-facies conditions (~400-500°C), related to the continued Yangtze-Cathaysia convergence externally driven by the suturing of south China with Australia. This event was heterogeneously overprinted by the second stage characterized by ~E-oriented folding in middle Triassic time, geodynamically resulting from the continental collision of south China with Indochina and North China. The third stage was locally developed by northwest and southeast vergent thrusts that truncated ~E-oriented folds in the Late Jurassic, due to northwestward subduction of the Paleo-Pacific plate. The latest stage involved normal faulting and tectonic unroofing in Cretaceous time, which resulted in basin opening and reset footwall 40Ar/39Ar ages in proximity to the Hengshan detachment fault, associated with roll-back of the subducting Paleo-Pacific plate.

  13. Lithospheric structure beneath the central and western North China Craton and the adjacent Qilian orogenic belt from Rayleigh wave dispersion analysis

    Science.gov (United States)

    Wei, Zigen; Chen, Ling; Jiang, Mingming; Ling, Yuan

    2015-04-01

    We used surface wave tomography to image the lithospheric S-wave velocity structure along a linear seismic array across the central and western North China Craton (NCC) and the adjacent Qilian orogenic belt (QB). Using waveform data from 8 earthquakes collected at 60 broadband stations, Rayleigh wave phase velocities were measured at periods of 20-120 s and subsequently inverted for reliable S-wave velocities from 60 to 200 km depth. Distinct lithospheric structures and marked lateral variations were revealed beneath the study region, correlating well with regional geological and tectonic features. The average S-wave velocity from 60 to 200 km depth beneath the array is ~ 4.45 km/s, ~ 1% lower than that in model AK135. High velocities of > 4.45 km/s are most pronounced beneath the stable Ordos Block (western NCC). However, the depth to which the observed high velocity body extends varies significantly laterally. It is deepest (~ 200 km) under eastern Ordos, and becomes shallower on both sides along the array. The maximum depth of the high velocity body gradually shallows westward and reaches ~ 110 km near the western edge of Ordos. This depth variation suggests a coexistence of both preserved and modified lithosphere in Ordos. The depth of high velocities decreases rapidly eastward by > 80 km over a lateral distance of evolution of NCC.

  14. Oxygen, carbon, and strontium isotopic constraints on timing and sources of crustal fluids in an active orogen : South Island, New Zealand

    International Nuclear Information System (INIS)

    Active deformation on New Zealand's South Island can be divided into four tectonic zones: Inboard, Main Divide, Outboard, and Marlborough strike-slip. On the basis of stable isotope data (δ13C and δ18O) we suggest that calcite veins are formed from a mixed meteoric and metamorphic water in the Inboard and Main Divide tectonic zones, as well as the Alpine-Wairau Fault of the Marlborough strike-slip zone. We suggest that the metamorphic waters are derived from the breakdown of biotite at c. 25 km, a depth which corresponds to a conductive zone identified by a recent magnetotelluric study across central South Island. These metamorphic fluids exit the orogen along the steep faults that border the Southern Alps. 87Sr/86Sr ratios of vein and fault-zone calcite suggest that calcite formation is associated with young tectonically driven hydrothermal fluid flow in the Inboard, Main Divide, and Wairau Fault zones. The age of calcite formation in the Outboard, Awatere, and Hope Fault zones could not be explicitly determined. (author). 49 refs., 4 figs., 1 tab

  15. K-Ar age determinations from the northern Damara branch and their implications for the structural and metamorphic evolution of the Damara Orogen, South West Africa/Namibia

    International Nuclear Information System (INIS)

    K-Ar age determination on the fine mineral fractions (< 2 μm) of phyllites and schists were carried out on samples from two separate areas of the north-south-trending coastal branch of the Damara Orogen and additionally from the Tsumeb region. From the northern Damara branch (Sesfontein area), two groups of ages were obtained. One group, around 490 m.y., is interpreted as the cooling age of a regional metamorphism having its peak in this region around 530 m.y. The second, younger group of ages around 460 m.y. seems to be influenced by the mineral composition of the samples taken for determination and as yet is not interpreted in the sence of a second regional metamorphic event. In the southern part of the northern branch (Brandberg West area), the main regional metamorphic event appears to have occurred around 490 m.y. Younger ages in this region may also have been influenced by the mineral composition of the samples or may have been rejuvenated by the intrusion of late to post-tectonic granites. The K-Ar age determinations on the rocks of the Tsumeb area can be related to a main regional metamorphic event dated at about 460 m.y. in this region

  16. An interpretation of the aeromagnetic data covering portion of the Damara orogenic belt, with special reference to the occurance of uraniferous granite

    International Nuclear Information System (INIS)

    This thesis comprises primarily palaeomagnetic studies within the Damara orogenic belt of South West Africa (Namibia), as well as an interpretation of the regional structure, utilizing published aeromagnetic data. Cursory interpretation of the airborne radiometric data is also undertaken. Gravity traverses, conducted across three dome structures with which uranium mineralisation is intimately associated, are interpreted in order to determine the origin of these structures. A number of features, having an important bearing on both the uraniferous granite occurrences and the regional structure of the area, are recognised for the first time in this study, viz.: a) all currently known uraniferous alaskitic granite occurences of economic interest are hallmarked. b) Virtual geomagnetic poles were derived for the 500 Ma tectonothermal event and for the basement rocks in the area. c) A close correlation exists between positive magnetic anomalies and high radiometric responses over the red granites, reactivated basement and over the Salem Granite Suite and other late- to post-tectonic granites. d) a number of structural lineaments and broader lineament zones are, apart from the Okahandja lineament, identified and named for the first time. e) A post-F3 (northeast) structural phase, F4, is recognised as being a major structural event of particular significance to the emplacement of uraniferous granite. f) The gravity studies indicate that the investigated dome structures result from an interplay between both vertical and lateral stress components

  17. Associations between sulfides, carbonaceous material, gold and other trace elements in polyframboids: Implications for the source of orogenic gold deposits, Otago Schist, New Zealand

    Science.gov (United States)

    Hu, Si-Yu; Evans, Katy; Fisher, Louise; Rempel, Kirsten; Craw, Dave; Evans, Noreen J.; Cumberland, Susan; Robert, Aileen; Grice, Kliti

    2016-05-01

    Intimately intergrown micron-scale framboidal pyrite, carbonaceous material (CM), chalcopyrite, sphalerite and cobaltite form polyframboids in prehnite-pumpellyite facies rocks of the Otago Schist, New Zealand. This study quantifies the metal contents of these polyframboids using synchrotron X-ray fluorescence (SXRF) and laser ablation inductively coupled plasma spectrometry (LA-ICP-MS). Trace elements Au, Zn, As, Mo, Co, Ni, Cu, Ag and Pb are significantly enriched in the polyframboids. The distribution of Zn most closely follows that of CM, and was probably absorbed into the structure of the polyframboids during biogenic processes. The concentrations of Au and Ag are positively corrected with the Zn concentration in the polyframboids (R2 of Au-Zn and Ag-Zn are 0.81 and 0.89, respectively.). The concentration of other trace elements, such as As, Co and Cu, which occur adjacent to Zn on elemental maps, show a weak relationship with Zn and may have been incorporated into the polyframboids during later processes. These polyframboids are a probable source for gold and other elements in the orogenic gold mineralization system of the Otago Schist. Metamorphic transformation of the polyframboids may have released the metallic elements into the mineralizing fluid during prograde metamorphism of the schist belt.

  18. The tectono-magmatic evolution of the occidental terrane and the Paraiba do Sul Klippe within the Neoproterozoic Ribeira orogenic Belt, Southeastern Brazil

    International Nuclear Information System (INIS)

    The occidental Terrane is envisaged as the eastern/southeastern reworked margin of the Sao Francisco/Rio de la Plata plate associated with and E-trending subduction under the Congo plate. The Paraiba do Sul Klippe is part of the Oriental Terrane, envisaged as a portion of the Congo plate. A collisional-stage resulted in intense westward deformation of the Occidental Terrane under intermediate pressure metamorphism (syn-D1+D2 events). A late-collisional stage resulted in subvertical folding and steep shear zones (D3 event). Both stages were associated with voluminous crustal-derived granites. U-Pb and Sm-Nd geochronology as well as geochemical and structural data point to three magmatic episodes: a syn-collisional stage 1; a syn-collisional stage 2; and a late-collisional stage. This paper presents a magmatic evolutionary model for this crustal segment of the Ribeira orogenic belt based on new geological data of Brasiliano granites and data available in the literature. (author)

  19. Gondwanan basement terranes of the Variscan-Appalachian orogen: Baltican, Saharan and West African hafnium isotopic fingerprints in Avalonia, Iberia and the Armorican Terranes

    Science.gov (United States)

    Henderson, Bonnie J.; Collins, William Joseph; Murphy, James Brendan; Gutierrez-Alonso, Gabriel; Hand, Martin

    2016-06-01

    Iberia, Avalonia and the "Armorican" terranes form key constituents of the Variscan-Appalachian orogen, but their Neoproterozoic origins along the northern Gondwanan margin continue to be strongly debated. Here, we present a new detrital zircon U-Pb-Hf dataset from Neoproterozoic-Silurian sedimentary sequences in NW Iberia and Avalonia, in conjunction with the comprehensive existing datasets from potential source cratons, to demonstrate that the provenance of each terrane is relatively simple and can be traced back to three major cratons. The enigmatic Tonian-Stenian detrital zircons in autochthonous Iberian rocks were derived from the Saharan metacraton in the latest Neoproterozoic-early Cambrian. Avalonia is commonly considered to have been derived from the Amazonian margin of Gondwana, but the hafnium isotopic characteristics of the detrital zircon grains in early Neoproterozoic rocks bear much stronger similarities to Baltica. The hafnium isotopic array also suggests the early Avalonian oceanic arc was built on a sliver of "Grenvillian-type crust" (~ 2.0-1.0 Ga) possibly of Baltican affinity at ~ 800 Ma, prior to accretion with a continental margin at ~ 640 Ma. The Upper Allochthon of Iberia is frequently linked to the West African Craton in the late Neoproterozoic-early Cambrian, however the hafnium isotopic array presented here does not support this connection; rather it is more similar to the hafnium array from Avalonia. The Armorican terranes have strong detrital zircon isotopic links to the West African Craton during the late Neoproterozoic-Cambrian.

  20. Early Paleozoic magmatic history of central Inner Mongolia, China: implications for the tectonic evolution of the Southeast Central Asian Orogenic Belt

    Science.gov (United States)

    Wu, Chen; Liu, Changfeng; Zhu, Yan; Zhou, Zhiguang; Jiang, Tian; Liu, Wencan; Li, Hongying; Wu, Chu; Ye, Baoying

    2016-07-01

    To provide insights into the Early Paleozoic tectonic evolution of the southern portion of the long-lived Central Asian Orogenic Belt, we have conducted major and trace element analyses and zircon U-Pb dating of granitoid samples from central Inner Mongolia. Our study area covers three pre-Mesozoic tectonic units from north to south: the Wenduermiao subduction-accretionary complex, the Bainaimiao magmatic belt, and the northern margin of the North China craton. Our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units. Accordingly, we suggest that the Wenduermiao subduction-accretionary complex developed in the Middle Cambrian-Late Silurian (509-421 Ma), comprising of coeval oceanic crust, arc magmatism, and forearc deposits. The Bainaimiao continental arc was developed during the Late Cambrian to Early Silurian (501-437 Ma), which superposed on the basement with the affinity of the North China craton. The back-arc basin opened prior to Early Silurian and lasted to the Late Silurian, which is slightly younger than Bainaimiao island arc. The Wenduermiao Ocean, between the Wenduermiao subduction-accretionary complex and the Bainaimiao continental arc, existed in Early Paleozoic.

  1. Regional contemporaneity of eustatic, subsidence, and tectonic events in the Middle-Upper Ordovician of the Appalachians and Ouachita orogens and the southern Oklahoma aulacogen

    Energy Technology Data Exchange (ETDEWEB)

    Finney, S.C.; Bergstroem, S.M.

    1985-01-01

    On-going graptolite and conodont studies in the Southern Appalachians, the Ouachitas, and the Arbuckle Mountains have revealed contemporaneity of important geological events of regional significance. Reassessment of previous graptolite biostratigraphy has resulted in a revised zonation that has solved some correlation problems and is tied to the Midcontinent and North Atlantic conodont zonations. These zonations are used to date significant geological events in geographically separate regions during two time intervals in the Middle-Upper Ordovician. The base of the graptolite shale succession (Athens) in the Southern Appalachians (Alabama-Tennessee) belongs to the G. teretiusculus Zone, or locally (Georgia) possibly a slightly older unit, and marks the initial shelf-basin development and uplift of source areas to the east reflecting a phase of the Taconic Orogeny. The bases of the Womble and Woods Hollow shales in the Ouachita Orogen represent about the same level. Slightly younger N. gracilis Zone strata tend to be transgressive throughout the world and appear to represent a global eustatic event. In the Arbuckle Mountains this event is reflected by the Tulip Creek Shale. A major subsidence event in the Oklahoma aulacogen, contemporaneous with the regression, produced a transgressive lithofacies sequence represented by the lower Viola Springs Formation in the Arbuckle Mountains. The regressive and subsidence events appear to have been coeval with the emplacement of the Taconic allochthon and Hamburg Klippe in the Northern Appalachians.

  2. Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes

    Science.gov (United States)

    Chen, Wei; Xu, Zhaowen; Qiu, Wenhong; Li, Chao; Yu, Yang; Wang, Hao; Su, Yang

    2015-05-01

    The Dabie orogen is among the most famous continent-continent collisional orogenic belts in the world, and is characterized by intensive post-collisional extension, magmatism and Mo mineralization. However, the genetic links between the mineralization and the geodynamic evolution of the orogen remain unresolved. In this paper, the Yaochong Mo deposit and its associated granitic stocks were investigated to elucidate this issue. Our new zircon U-Pb ages yielded an Early Cretaceous age (133.3 ± 1.3 Ma) for the Yaochong granite, and our molybdenite Re-Os dating gave a similar age (135 ± 1 Ma) for the Mo deposit. The Yaochong stock is characterized by high silica and alkali but low Mg, Fe and Ca. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta, Ti and Y). The Yaochong granite has initial 87Sr/86Sr ratios of 0.7087-0.7096, and Pb isotopic ratios of (206Pb/204Pb)i = 16.599-16.704, (207Pb/204Pb)i = 15.170-15.618 and (208Pb/204Pb)i = 36.376-38.248. The granite has εNd(t) of -18.0 to -16.3 and εHf(t) values of -26.5 to -20.0. All these data indicate that the Yaochong granite is a high-K calc-alkaline fractionated I-type granite, and may have originated from partial melting of the thickened Yangtze continental crust. The Mo ores also show low radiogenic Pb isotopes similar to the Yaochong stock. Medium Re content in molybdenite (21.8-74.8 ppm) also suggests that the ore-forming materials were derived from the thickened lower crust with possibly minor mixing with the mantle. Similar to the Eastern Dabie orogen, the thickened crust beneath the Western Dabie orogen may also have experienced tectonic collapse, which may have exerted fundamental geodynamic controls on the two-stage Mo mineralization in the region.

  3. Geochemical and Sr-Nd-Hf isotopic constraints on the origin of Late Triassic granitoids from the Qinling orogen, central China: Implications for a continental arc to continent-continent collision

    Science.gov (United States)

    Jiang, Yao-Hui; Jin, Guo-Dong; Liao, Shi-Yong; Zhou, Qing; Zhao, Peng

    2010-06-01

    The Qinling-Dabie-Sulu orogen marks the junction between the North and South China Blocks. However, the exact timing of the final coalescence of the North and South China Blocks in the Qinling orogen is poorly constrained. This paper presents new SHRIMP zircon U-Pb chronology, major and trace elements, and Sr-Nd-Hf isotope data for five early Mesozoic granitic plutons across the Qinling orogen. SHRIMP zircon U-Pb dating shows that four plutons were emplaced in the Carnian (227-218 Ma) of Late Triassic with a southward-younging trend and one pluton was emplaced in the Norian (˜ 211 Ma) of Late Triassic. The Carnian plutons consist of high-K calc-alkaline granitoids (quartz monzodiorite, quartz monzonite, granodiorite and monzogranite) and calc-alkaline diorite. These rocks are mainly metaluminous and are characterized by high Sr and low Y and Yb contents, with high Sr/Y and La/Yb ratios, and by high Mg#, higher than pure crustal melts. The Norian pluton is composed of high-K calc-alkaline two-mica granites, which are peraluminous. These granites have low Sr and high Y and Yb contents and show similar Mg# to pure crustal melts. Detailed elemental and isotopic data suggest that the Carnian plutons were emplaced in a continental arc setting coupled with the northward subduction of the Paleo-Tethyan oceanic crust. Partial melting of subducted sediments triggered by dehydration of the underlying igneous oceanic crust, with subsequent melts interacting with the overlying mantle wedge, formed the high-K calc-alkaline granitic magmas. Partial melting of the hybridized peridotitic mantle wedge induced by slab melts generated the calc-alkaline dioritic magma. The Norian pluton was emplaced during continental collision between the South Qinling terrane and South China Block, which marks the final integration of the North and South China Blocks. Partial melting of subducted sediments at a shallow depth (origin of the Norian peraluminous granites. Our new data suggest that the

  4. Late Paleozoic tectono-metamorphic evolution of the Altai segment of the Central Asian Orogenic Belt: Constraints from metamorphic P-T pseudosection and zircon U-Pb dating of ultra-high-temperature granulite

    Science.gov (United States)

    Li, Zilong; Yang, Xiaoqiang; Li, Yinqi; Santosh, M.; Chen, Hanlin; Xiao, Wenjiao

    2014-09-01

    Ultra-high-temperature (UHT) granulite-facies rocks offer important constraints on crustal evolution processes and tectonic history of orogens. UHT granulites are generally rare in Phanerozoic orogens. In this study, we investigate the late Paleozoic pelitic UHT granulites from Altai in the western segment of the Central Asian Orogenic Belt (CAOB). The diagnostic minerals in these rocks include high alumina orthopyroxene (Al2O3 up to 9.76 wt.%, and y(opx) = AlVI in orthopyroxene up to 0.21) coexisting with sillimanite and quartz, and low Zn spinel (ZnO = 1.85-2.50 wt.%) overgrowth with quartz. Cordierite corona separates sillimanite from orthopyroxene. The high alumina orthopyroxene is replaced by symplectites of low-alumina orthopyroxene (~ 5.80 wt.% Al2O3) and cordierite. These textural observations are consistent with a significant decompression following the peak UHT metamorphism. Phase equilibrium modeling using pseudosections and the y(opx) isopleths indicate an anti-clockwise P-T path for the exhumation of the Altai orogenic belt. The pre-peak assemblage of spinel + quartz in garnet is stable at high- to ultra-high-temperature and low-pressure conditions (P 940 °C and 7.8 to 10 kbar. Subsequent near-isothermal decompression occurred at 890 to 940 °C and 5 to 6 kbar. The final-stage cooling is recorded at 750 and 800 °C and 4 to 5 kbar accompanied by a decrease in the y(opx) values (0.11-0.12). In the UHT granulite, zircon grains are commonly enclosed within cordierite. The overgrowth rims of the zircon grains yield a weighted mean 206Pb/238U age of 277 ± 2 Ma using LA-ICP-MS zircon dating, which is interpreted to mark the timing of decompression and cooling. We propose that the anti-clockwise P-T path of the UHT granulite in the Altai orogenic belt could be related to an extensional event related to the sinistral strike-slip along the Irtish tectonic belt after the subduction and slab detachment during the convergence of the Kazakhstan-Junggar plate and

  5. Re-Os molybdenite ages and zircon Hf isotopes of the Gangjiang porphyry Cu-Mo deposit in the Tibetan Orogen

    Science.gov (United States)

    Leng, Cheng-Biao; Zhang, Xing-Chun; Zhong, Hong; Hu, Rui-Zhong; Zhou, Wei-De; Li, Chao

    2013-06-01

    The Miocene porphyry Cu-(Mo) deposits in the Gangdese orogenic belt in southern Tibet were formed in a post-subduction collisional setting. They are closely related to the Miocene adakite-like porphyries which were probably derived from a thickened basaltic lower crust. Furthermore, mantle components have been considered to have played a crucial role in formation of these porphyry deposits (Hou et al. Ore Geol Rev 36: 25-51, 2009; Miner Deposita doi:10.1007/s00126-012-0415-6, 2012). In this study, we present zircon Hf isotopes and molybdenite Re-Os ages on the newly discovered Gangjiang porphyry Cu-Mo deposit in southern Tibet to constrain the magma source of the intrusions and the timing of mineralization. The Gangjiang porphyry Cu-Mo deposit is located in the Nimu ore field in the central Gangdese porphyry deposits belt, southern Tibet. The copper and molybdenum mineralization occur mainly as disseminations and veins in the overlapped part of the potassic and phyllic alteration zones, and are predominantly hosted in the quartz monzonite stock and in contact with the rhyodacite porphyry stock. SIMS zircon U-Pb dating of the pre-mineral quartz monzonite stock and late intra-mineral rhyodacite porphyry yielded ages of 14.73 ± 0.13 Ma (2 σ) and 12.01 ± 0.29 Ma (2 σ), respectively. These results indicate that the magmatism could have lasted as long as about 2.7 Ma for the Gangjiang deposit. The newly obtained Re-Os model ages vary from 12.51 ± 0.19 Ma (2 σ) to 12.85 ± 0.18 Ma (2 σ) for four molybdenite samples. These Re-Os ages are roughly coincident with the rhyodacite porphyry U-Pb zircon age, and indicate a relatively short-lived episode of ore deposition (ca. 0.3 Ma). In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS indicate that the ɛ Hf( t) values of zircons from a quartz monzonite sample vary from +2.25 to +4.57 with an average of +3.33, while zircons from a rhyodacite porphyry sample vary from +5.53 to +7.81 with an average of +6.64. The

  6. Continental crust subducted deeply into lithospheric mantle: the driving force of Early Carboniferous magmatism in the Variscan collisional orogen (Bohemian Massif)

    Science.gov (United States)

    Janoušek, Vojtěch; Schulmann, Karel; Lexa, Ondrej; Holub, František; Franěk, Jan; Vrána, Stanislav

    2014-05-01

    The vigorous Late Devonian-Early Carboniferous plutonic activity in the core of the Bohemian Massif was marked by a transition from normal-K calc-alkaline, arc-related (~375-355 Ma), through high-K calc-alkaline (~346 Ma) to (ultra-)potassic (343-335 Ma) suites, the latter associated with mainly felsic HP granulites enclosing Grt/Spl mantle peridotite bodies. The changing chemistry, especially an increase in K2O/Na2O and 87Sr/86Sri with decrease in 143Nd/144Ndi in the basic end-members, cannot be reconciled by contamination during ascent. Instead it has to reflect the character of the mantle sources, changing over time. The tectonic model invokes an oceanic subduction passing to subduction of the attenuated Saxothuringian crust under the rifted Gondwana margin (Teplá-Barrandian and Moldanubian domains). The deep burial of this mostly refractory felsic metaigneous material is evidenced by the presence of coesite/diamond (Massonne 2001; Kotková et al. 2011) in the detached UHP slices exhumed through the subduction channel and thrusted over the Saxothuringian basement, and by the abundance of felsic HP granulites (> 2.3 GPa), some bearing evidence for small-scale HP melt separation, in the orogen's core (Vrána et al. 2013). The subduction channel was most likely formed by 'dirty' serpentinites contaminated by the melts/fluids derived from the underlying continental-crust slab (Zheng 2012). Upon the passage through the orogenic mantle, the continental crust-slab derived material not only contaminated the adjacent mantle forming small bodies/veins of pyroxenites (Becker 1996), glimmerites (Becker et al. 1999) or even phlogopite- and apatite-bearing peridotites (Naemura et al. 2009) but the felsic HP-HT granulites also sampled the individual peridotite types at various levels. Eventually the subducted felsic material would form an (U)HP continental wedge under the forearc/arc region, to be later redistributed under the Moldanubian crust by channel flow and crustal

  7. Multi-stage barites in partially melted UHP eclogite: implications for fluid/melt activities during deep continental subduction in the Sulu orogenic belt

    Science.gov (United States)

    Wang, Songjie; Wang, Lu

    2015-04-01

    Barite (BaSO4) is well-known from deep-sea sedimentary environments but has received less attention to its presence in high-grade metamorphic rocks. Recently, barite in ultrahigh pressure (UHP) eclogite has drawn increasing attention from geologists, especially in the Dabie-Sulu orogen, since it is an important indicator for high-salinity fluid events, thus aiding in further understanding HP-UHP fluid / melt evolution. However, its formation time and mechanism in UHP eclogite are still controversial, with three representative viewpoints: (1) Liu et al. (2000) found barite-anhydrite-coesite inclusions in zircon and interpreted them to have formed by UHP metamorphic fluids; (2) Zeng et al. (2007) recognized isolated barite within K-feldspar (Kfs) and Quartz (Qz) surrounded by radial cracks in omphacite, and interpreted Kfs+Qz to be reaction products of potassium-rich fluid/melt and coesite, with the barite formed by prograde metamorphic fluids; (3) Gao et al. (2012) and Chen et al. (2014) found barite-bearing Multiphase Solid (MS) inclusions within garnet and omphacite and assumed that the barite formed by phengite breakdown possibly caused by eclogite partial melting during exhumation, though no direct evidence were proposed. The controversy above is mainly due to the lack of direct formation evidence and absence of a clear link with the metamorphic evolution of UHP eclogite along the subduction-exhumation path. We report detailed petrological and micro-structural analyses revealing four types of barites clearly linked with (1) the prograde, (2) earlier stage of partial melting and (3) later stage of crystallization differentiation, as well as (4) high-grade amphibolite-facies retrogression of a deeply subducted and partially melted intergranular coesite-bearing eclogite from Yangkou Bay, Sulu Orogen. Round barite inclusions (type-I) within UHP-stage garnet and omphacite are formed by internally buffered fluids from mineral dehydration during prograde metamorphism

  8. Upper Triassic turbidites of the northern Tethyan Himalaya (Langjiexue Group): the terminal of a sediment-routing system sourced in the Gondwanide Orogen

    Science.gov (United States)

    Wang, Jian-Gang; Wu, Fu-Yuan; Garzanti, Eduardo; Hu, Xiu-Mian; Ji, Wei-Qiang; Liu, Zhi-Chao; Liu, Xiao-Chi

    2016-04-01

    zircons with uniform ɛHf(t) values from -5 to +10 are incompatible with any nearby source, including the Qiantang Block, the Lhasa Block or the India subcontinent, and indicate instead supply from a long-lived magmatic-arc terrane. Considering what is known about Late Triassic paleogeography, a plausible source for Langjiexue sediments is represented by the Gondwanide Orogen, generated during subduction of the pan-Pacific oceanic lithosphere beneath southeastern Gondwana. This scenario is supported by the age range and Hf isotopic signatures of Late Paleozoic-Early Mesozoic zircons contained in Langjiexue turbidites as in coeval turbidites exposed in western Myanmar (Sevastjanova et al., 2016). New data are needed to confirm/falsify the existence of a thousands-km-long sediment-routing system similar to the modern Amazon, which - sourced in a cordillera-type orogen rising along the southeastern margin of Gondwana - crossed an entire continent to feed turbiditic fans now exposed from western Myanmar to the northern Tethys Himalaya.

  9. Age, tectonic evolution and origin of the Aswa Shear Zone in Uganda: Activation of an oblique ramp during convergence in the East African Orogen

    Science.gov (United States)

    Saalmann, K.; Mänttäri, I.; Nyakecho, C.; Isabirye, E.

    2016-05-01

    . Early Aswa Shear Zone activation is linked to underthrusting of the Congo Craton and coeval high-grade metamorphism and intense deformation in the orogen interior. During E-W convergence between ca. 690 and 650 Ma, the NE-dipping ASZ was activated as an oblique ramp leading to deflection of the transport direction and concentration of non-coaxial strain and sinistral shear along the shear zone system. During progressive convergence, between ca. 645 and 620 Ma, sinistral shearing along ASZ changed to ductile-brittle deformation mechanisms, while thrusting took place in Pan-African belts in eastern and western Uganda. Late-orogenic brittle sinistral reactivation of the ASZ can be regarded as the result of continent collision and closure of the Mozambique ocean further to the east, that potentially caused lateral escape manifested in NW-SE striking sinistral shear zones in Kenya and the southern Arabina-Nubian Shield between 620 and 570 Ma.

  10. P- T conditions of crystallization and origin of plagioclase-mantled alkali feldspar megacrysts in the Mesozoic granitoids in the Qinling orogen (China)

    Science.gov (United States)

    Wang, Xiaoxia; Wang, Tao; Haapala, Ilmari; Mao, Jingwen

    2008-07-01

    The Qinling orogen between the North China and South China cratons was intruded at 211-217 Ma by calc-alkaline quartz monzonitic to monzogranitic plutons characterized by I- to A-type geochemistry and in many places contain plagioclase-mantled alkali feldspar megacrysts (rapakivi texture sensu lato). The felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas. The P- T conditions of crystallization have been determined for early mineral assemblages (inner parts of alkali feldspar megacrysts and their plagioclase, quartz, amphibole and biotite inclusions) and late assemblages (matrix minerals) of the rapakivi-textured granitoids. Al contents in amphibole from the early and late mineral assemblages yield pressures of 1.2-3.0 and 0.7-3.0 kbar, respectively, and indicate only minor pressure change between the crystallization of the early and late assemblages. Amphibole-plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 °C for both the early and late assemblages indicating nearly isothermal conditions. Feldspar thermometers yield lower temperatures. Relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in MgO, Na 2O and CaO than the early assemblages. Rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas. Small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts.

  11. New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil

    Science.gov (United States)

    Gonçalves, Leonardo; Farina, Federico; Lana, Cristiano; Pedrosa-Soares, Antônio C.; Alkmim, Fernando; Nalini, Hermínio A.

    2014-07-01

    The Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclave-rich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HT-melting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.

  12. Petrological and geochemical features of the Jingtieshan banded iron formation (BIF): A unique type of BIF from the Northern Qilian Orogenic Belt, NW China

    Science.gov (United States)

    Yang, Xiu-Qing; Zhang, Zuo-Heng; Duan, Shi-Gang; Zhao, Xin-Min

    2015-12-01

    The Jingtieshan banded iron formation (BIF) is located in the Northern Qilian Orogenic Belt (NQOB) in NW China. The BIFs are hosted in Mesoproterozoic Jingtieshan Group, a dominantly clastic-carbonate sedimentary formation, and was metamorphosed to lower greenschist facies. The Jingtieshan BIFs include oxide-, carbonate- and mixed carbonate-oxide facies, and consist of alternating iron-rich and silica-rich bands. The BIFs are composed essentially of specularite and jasper, with minor carbonate minerals and barite. The SiO2 + Fe2O3 content is markedly high in the oxide facies BIF, followed by FeO, CO2 and Ba, with the other elements usually lower than 1%, suggesting that the original chemical sediments were composed of Fe, Si, CO32- and Ba. The positive correlation between Al2O3, TiO2 and Zr in the BIFs indicates that these chemical sediments incorporate minor detrital components. Oxide facies BIF shows low HFSE, low ∑REE and low Y/Ho. The Post Archean Australian Shale-normalized REE patterns for Jingtieshan BIFs are characterized slight LREE depletion, strong positive Eu anomalies and lack of significant negative Ce anomalies. Siderite in the carbonate- and mixed carbonate-oxide facies BIF shows negative δ13C values varying from -8.4‰ to -3.0‰, and δ18O values show a range of -16.6‰ to -11.7‰. The geochemical signatures and carbon-oxygen isotopes suggest origin from high-temperature hydrothermal fluids with weak seawater signature for the sediments of Jingtieshan BIFs. The absence of negative Ce anomalies and the high Fe3+/∑Fe ratios of the oxide facies BIF do not support ocean anoxia. In contrast to the three main types (Algoma-, Superior- and Rapitan-type) of global BIFs, the Jingtieshan BIFs represent a unique type with features similar to those of sedimentary-exhalative mineralization.

  13. Intermediate P/T-type regional metamorphism of the Isua Supracrustal Belt, southern west Greenland: The oldest Pacific-type orogenic belt?

    Science.gov (United States)

    Arai, Tatsuyuki; Omori, Soichi; Komiya, Tsuyoshi; Maruyama, Shigenori

    2015-11-01

    The 3.7-3.8 Ga Isua Supracrustal Belt (ISB), southwest Greenland, might be the oldest accretionary complex on Earth. Regional metamorphism of the ISB has a potential to constrain the tectonothermal history of the Earth during the Eoarchean. Chemical and modal analyses of metabasite in the study area (i.e., the northeast part of the ISB) show that the metamorphic grade increases from greenschist facies in the northern part of the study area to amphibolite facies in the southern part. To determine the precise metamorphic P-T ranges, isochemical phase diagrams of minerals of metabasite were made using Perple_X. A synthesis of the estimated metamorphic P-T ranges of the ISB indicates that both the metamorphic pressure and temperature increase systematically to the south in the study area from 3 kbar and 380 °C to 6 kbar and 560 °C. The monotonous metamorphic P-T change suggests that the northeast part of the ISB preserves regional metamorphism resulting from the subduction of an accretionary complex although the ISB experienced metamorphic overprints during the Neoarchean. Both the presence of the regional metamorphism and an accretionary complex having originating at subduction zone suggest that the ISB may be the oldest Pacific-type orogenic belt. The progressive metamorphism can be considered as a record of intermediate-P/T type geothermal gradient at the subduction zone in the Eoarchean. Intermediate-P/T type geothermal gradient is typical at the current zones of subducting young oceanic crust, such as in the case of the Philippine Sea Plate in the southwest part of Japan. Considering the fact that almost all metamorphisms in the Archean are greenschist-amphibolite facies, the intermediate-P/T type geothermal gradient at the ISB might have been worldwide in the Archean. This would indicate that the subduction of young micro-plates was common because of the vigorous convection of hot mantle in the Archean.

  14. Constraints on Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust from a survey of orogenic eclogites and amphibolites

    Science.gov (United States)

    Zirakparvar, N. Alex

    2016-04-01

    To further understand Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust, this paper evaluates all available Lu-Hf garnet isochron ages and initial ɛHf values in conjunction with present-day bulk-rock Lu-Hf isotope and trace element (K, Nb, Ta, Zr, and Ti in addition to Lu-Hf) data from the world's orogenic eclogites and amphibolites (OEAs). Approximately half of OEAs exhibit Lu-Hf and Nb-Ta systematics mimicking those of unsubducted oceanic crust whereas the rest exhibit variability in one or both systems. For the Lu-Hf system, mixing calculations demonstrate that subduction-related phase transformations, in conjunction with open system behavior, can shift subducted oceanic crust toward higher Lu/Hf, or toward lower Lu/Hf that can also be associated with unradiogenic ɛHf values. However, evaluation of potential mechanisms for fractionating Nb from Ta is more complicated because many of the OEAs have Nb-Ta systematics that are decoupled from Lu-Hf and the behavior of K, Zr, and Ti. Nonetheless, the global data set demonstrates that the association between unradiogenic ɛHf and elevated Nb/Ta observed in some kimberlitic eclogite xenoliths can be inherited from processes that occurred during subduction of their oceanic crustal protoliths. This allows for a geologically based estimate of the Nb concentration in a reservoir composed of deeply subducted oceanic crust. However, mass balance calculations confirm that such a reservoir, when considered as a whole, likely has a Nb concentration similar to unsubducted oceanic crust and is therefore not the solution to the problem of the Earth's "missing" Nb.

  15. Crustal nature and origin of the Russian Altai: Implications for the continental evolution and growth of the Central Asian Orogenic Belt (CAOB)

    Science.gov (United States)

    Cai, Keda; Sun, Min; Buslov, M. M.; Jahn, Bor-ming; Xiao, Wenjiao; Long, Xiaoping; Chen, Huayong; Wan, Bo; Chen, Ming; Rubanova, E. S.; Kulikova, A. V.; Voytishek, E. E.

    2016-04-01

    The Central Asian Orogenic Belt is a gigantic tectonic collage of numerous accreted terranes. However, its geodynamic evolution has been hotly debated primarily due to incomplete knowledge on the nature of these enigmatic terranes. This work presents new detrital zircon U-Pb and Hf isotopic data to constrain the crustal nature and origin of the Russian Altai, a critical segment of Altai-Mongolian terrane. The youngest zircon 206Pb/238U ages of 470 Ma constrain that the Terekta Formation, previously envisaged as Precambrian basement, was actually deposited after the Middle Ordovician. As for the three more sedimentary sequences above the Terekta Formation, they have youngest zircon 206Pb/238U ages of 425 Ma, 440 Ma and 380 Ma, respectively, indicating their depositions likely in the Late Silurian to Devonian. From all analyses, it is noted that many zircon U-Pb ages cluster at ca. 520 Ma and ca. 800 Ma, and these zircons display oscillatory zoning and have subhedral to euhedral morphology, which, collectively, suggests that adjacent Neoproterozoic to Paleozoic igneous rocks were possibly dominant in the sedimentary provenance. Additionally, a few rounded Archean to Mesoproterozoic zircon grains are characterized by complex texture, which are interpreted as recycling materials probably derived from the Tuva-Mongolian microcontinent. Precambrian rocks have not been identified in the Russian Altai, Chinese Altai and Mongolian Altai so far, therefore, Precambrian basement may not exist in the Altai-Mongolian terrane, but this terrane probably represents a large subduction-accretion complex built on the margin of the Tuva-Mongolian microcontinent in the Early Paleozoic. Multiple episodes of ridge-trench interaction may have caused inputs of mantle-derived magmas to trigger partial melting of the newly accreted crustal materials, which contributed to the accretionary complex. During accretionary orogenesis of the CAOB, formation of such subduction-accretion complex is

  16. Northwest trending tectonic belt in the middle Yanshan Orogenic Belt of northeast Hebei Province, North China:Tectonic evolution and geochronology

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Changhou; WU; Ganguo; WANG; Genhou; ZHANG; Weijie

    2004-01-01

    The northwest trending tectonic belt in the middle part of the Mesozoic intraplate Yanshan Orogenic Belt, northeast Hebei Province, is composed of thrusts, extensional faults,strike-slip faults and syntectonic sedimentations as well. The northeastward basement-involved major thrusting deformation occurred between 174Ma and 168MaBP and was followed by an intrusion of the granitic plutonic rocks. As a part of the post-thrusting extensional deformations a northwest extending volcano-sedimentation system of Late Jurassic and Early Cretaceous formed in the southwest side of the belt. These volcano-sedimentary sequences are divided into Tuchengzi Formation, Zhangjiakou Formation, Yixian Formation and Jiufotang Formation respectively. They are characterized by southeastward migration as a result of the increasing down-dip slip displacement along the major extensional fault toward the southeast of the belt.The provenance area of the Jiufotang Formation north to it experienced southwestward thrusting during and after its later sedimentation. The thrusting in this stage resulted in the formation of an asymmetric footwall syncline with vergence to SW in the Jiufotang Formation in the NE side of the basin. Finally a dextral strike-slip deformation occurred along the NW tectonic belt. The striking tectono-geomorphological features and present seismic activities along this belt indicate that it has been being active since Cenozoic era and is still in the active state at present. This northwest extending tectonic belt was following the same direction and location as the existing fault systems within the basement as revealed by former geological and geophysical studies. So it is reasonable to infer the Mesozoic deformation along this belt to be a result of reactivation of the basement structures in a favorable tectonic stress field. The reactivation of basement structures might be taken as one of the mechanisms of intraplate deformation and orogeny.

  17. Zirconolite, zircon and monazite-(Ce) U-Th-Pb age constraints on the emplacement, deformation and alteration history of the Cummins Range Carbonatite Complex, Halls Creek Orogen, Kimberley region, Western Australia

    Science.gov (United States)

    Downes, Peter J.; Dunkley, Daniel J.; Fletcher, Ian R.; McNaughton, Neal J.; Rasmussen, Birger; Jaques, A. Lynton; Verrall, Michael; Sweetapple, Marcus T.

    2016-04-01

    In situ SHRIMP U-Pb dating of zirconolite in clinopyroxenite from the Cummins Range Carbonatite Complex, situated in the southern Halls Creek Orogen, Kimberley region, Western Australia, has provided a reliable 207Pb/206Pb age of emplacement of 1009 ± 16 Ma. Variably metamict and recrystallised zircons from co-magmatic carbonatites, including a megacryst ~1.5 cm long, gave a range of ages from ~1043-998 Ma, reflecting partial isotopic resetting during post-emplacement deformation and alteration. Monazite-(Ce) in a strongly foliated dolomite carbonatite produced U-Th-Pb dates ranging from ~900-590 Ma. Although the monazite-(Ce) data cannot give any definitive ages, they clearly reflect a long history of hydrothermal alteration/recrystallisation, over at least 300 million years. This is consistent with the apparent resetting of the Rb-Sr and K-Ar isotopic systems by a post-emplacement thermal event at ~900 Ma during the intracratonic Yampi Orogeny. The emplacement of the Cummins Range Carbonatite Complex probably resulted from the reactivation of a deep crustal structure within the Halls Creek Orogen during the amalgamation of Proterozoic Australia with Rodinia over the period ~1000-950 Ma. This may have allowed an alkaline carbonated silicate magma that was parental to the Cummins Range carbonatites, and generated by redox and/or decompression partial melting of the asthenospheric mantle, to ascend from the base of the continental lithosphere along the lithospheric discontinuity constituted by the southern edge of the Halls Creek Orogen. There is no evidence of a link between the emplacement of the Cummins Range Carbonatite Complex and mafic large igneous province magmatism indicative of mantle plume activity. Rather, patterns of Proterozoic alkaline magmatism in the Kimberley Craton may have been controlled by changing plate motions during the Nuna-Rodinia supercontinent cycles (~1200-800 Ma).

  18. Early-Middle Paleozoic subduction-collision history of the south-eastern Central Asian Orogenic Belt: Evidence from igneous and metasedimentary rocks of central Jilin Province, NE China

    Science.gov (United States)

    Pei, Fu-Ping; Zhang, Ying; Wang, Zhi-Wei; Cao, Hua-Hua; Xu, Wen-Liang; Wang, Zi-Jin; Wang, Feng; Yang, Chuan

    2016-09-01

    To constrain the Early-Middle Paleozoic tectonic evolution of the south-eastern segment of the Central Asian Orogenic Belt (CAOB), we undertook zircon U-Pb dating and analyzed major and trace elements and zircon Hf isotope compositions of Late Cambrian to Middle Devonian igneous and metasedimentary rocks in central Jilin Province, NE China. LA-ICP-MS zircon U-Pb dating indicates that the Early-Middle Paleozoic magmatism in central Jilin Province can be divided into four episodes: Late Cambrian (ca. 493 Ma), Middle Ordovician (ca. 467 Ma), Late Ordovician-Early Silurian (ca. 443 Ma), and Late Silurian-Middle Devonian (425-396 Ma). The progression from subduction initiation to maturity is recorded by Late Cambrian low-K tholeiitic meta-diabase, Middle Ordovician medium-K calc-alkaline pyroxene andesite, and Late Ordovician to Early Silurian low-K tonalite, which all have subduction-related characteristics and formed in an evolving supra-subduction zone setting. Late Silurian to Middle Devonian calc-alkaline igneous rocks, with the lithological association of granodiorite, monzogranite, rhyolite, dacite, and trachydacite, show progressively increasing K2O contents from medium K to shoshonite series. Furthermore, the Early-Middle Devonian monzogranites are characterized by high K2O, Sr/Y, and [La/Yb]N values, indicating they were generated by the melting of thickened lower crust. These results suggest a transition from subduction to post-orogenic setting during the Late Silurian-Middle Devonian. Our interpretation is supported by the maximum age of molasse deposition in the Zhangjiatun member of the Xibiehe Formation. Overall, we suggest that Late Cambrian tholeiitic meta-diabase, Middle Ordovician pyroxene andesite, and Late Ordovician-Early Silurian tonalite formed above the northward-subducting and simultaneously seaward-retreating of Paleo-Asian Ocean plate. Subsequently, the northern arc collided with the North China Craton and post-orogenic extension occurred

  19. Zircons traced from the 700-500 Ma Transgondwanan Supermountains and the Gamburtsev Subglacial Mountains to the Ordovician Lachlan Orogen, Cretaceous Ceduna Delta, and modern Channel Country, central-southern Australia

    Science.gov (United States)

    Veevers, J. J.; Belousova, E. A.; Saeed, A.

    2016-04-01

    We test the hypothesis that the Transgondwanan Supermountains at the collision of East and West Gondwanaland were the provenance of a vast turbiditic fan that stretched alongside the East Gondwanaland margin to eastern Australia which, in turn, became the provenance of sediment shed into interior Australia to the Cretaceous Ceduna Delta in central-southern Australia and the modern Channel Country of central Australia. We employ an integrated analysis (U-Pb, Lu-Hf isotopes and trace elements) of detrital zircons in the Ceduna Delta and Channel Country. The main properties of the detrital zircons are U-Pb ages of 700-500 Ma (model ages TDMC 2.5-1.0 Ga; εHf +10 to -20) and 1300-1000 Ma ages (TDMC 2.7-1.3 Ga; εHf +4 to -17), in hosts of mafic granitoids with alkaline affinity. Zircons with these properties can be traced back through the drainage/paleo-slope to the intermediate provenances of the Ordovician turbidites and S-type granitoids of the Lachlan Orogen, then up-paleoslope to the primary or secondary provenance of the ancestral Gamburtsev Subglacial Mountains, and finally to the primary provenance of the Transgondwanan Supermountains atop the 700-500 Ma East African-Antarctic Orogen. Another primary provenance, the 140-95 Ma Whitsunday Volcanic Province/New Caledonia arc in northeastern Australia, also shed sediment across Australia to the Ceduna Delta. We suggest that the primary sediment from the 700-500 Ma East African-Antarctic Orogen and the ancestral Gamburtsev Subglacial Mountains was shed into a deep-sea super-fan to (1) Ordovician turbidites in southeast Australia, recycled by melting of the turbidites to (2) 450 Ma S-type granites in the Lachlan Orogen, and (3) finally deposited, together with volcanogenic sediment from northeast Australia, in the Ceduna Delta. Zircons in the Channel Country and the Ceduna Delta have essentially the same properties, and indicate that the northeastern Australian provenance was largely unchanged over the past 100 Ma.

  20. Petrogenesis and U-Pb zircon chronology of felsic tuffs interbedded with turbidites (Eastern Pontides Orogenic Belt, NE Turkey): Implications for Mesozoic geodynamic evolution of the eastern Mediterranean region and accumulation rates of turbidite sequences

    Science.gov (United States)

    Eyuboglu, Yener

    2015-01-01

    The Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt, which is one of the key areas of the Alpine-Himalayan system, is still controversial due to lack of systematic geological, geophysical, geochemical and chronological data. The prevailing interpretation is that this belt represents the southern margin of Eurasia during the Mesozoic and its geodynamic evolution is related to northward subduction of oceanic lithosphere. This paper reports the first detailed geological, geochemical and chronological data from felsic tuffs interbedded with late Cretaceous turbidites in the Southern Zone of the Eastern Pontides Orogenic Belt. Individual tuff layers are thin, mostly shards and 10-20% broken quartz crystals, whereas the crystal-rich tuffs consist of > 50% crystals. The zircon U-Pb data show three statistically distinct ages at 84, 81 and 77 Ma, with uncertainties of about 1 Ma, suggesting that tuff-forming late Cretaceous magmatism started about 84 Ma ago and was episodically active over a minimum of 7 Ma. The age data also indicate that the average accumulation rate of the turbiditic sequence that hosts the felsic tuffs remained constant between 36 and 40 cm/10 ky. Their enrichment in LIL and LRE elements relative to HFS and HRE elements, and also strongly negative Nb, Ta and Ti anomalies, are consistent with those of magmas generated by subduction-related processes. The tuffs have relatively low initial ratios of 143Nd/144Nd (0.512296-0.512484; εNd: - 2.1 and - 7.2) and 87Sr/86Sr (0.704896-0.706159). Their initial Pb isotopic compositions range from 18.604 to 18.646 for 206Pb/204Pb, from 15.644 to 15.654 for 207Pb/206Pb and from 38.712 to 38.763 for 208Pb/204Pb. The distribution of Sr-Nd isotopic compositions in the late Cretaceous igneous rocks from different locations of the Eastern Pontides Orogenic Belt is consistent with two-component mixing between depleted mantle and crust. However, the Pb isotopic data are not compatible with two

  1. Geochemical evidence for origin of magma mixing for the Triassic monzonitic granite and its enclaves at Mishuling in the Qinling orogen (central China)

    Science.gov (United States)

    Qin, Jiangfeng; Lai, Shaocong; Grapes, Rodney; Diwu, Chunrong; Ju, Yinjuan; Li, Yongfei

    2009-10-01

    Whole-rock major-trace elements and Sr-Nd isotopes, mineral chemistry, and zircon U-Pb and Lu-Hf isotope compositions are reported for I-type monzogranite and its mafic microgranular enclaves from the Triassic Mishuling granite in the Qinling orogen, central China. Zircon U-Pb dating yields an age of 212 ± 5 Ma for the mafic enclaves and 213 ± 3 Ma for the host monzogranite. Whole-rock major-trace elements, Sr-Nd isotopes and zircon Hf isotopes preclude simple crystal fractionation or restite unmixing for a genetic link between the enclaves and the monzogranite. Mixing between mafic and felsic magmas is compatible with the geochemical data. The monzogranite displays an enriched LILE and LREE pattern, high ( 87Sr/ 86Sr) i ratios of 0.7068 to 0.7071 and low ɛNd( t) values of - 9.2 to - 5.7, suggesting a crustal origin. Its high Mg# (47.6 to 50.7), Cr and Ni contents clearly indicate its derivation from mafic refractory lower crust. Most of the zircons in the monzogranite have negative ɛHf( t) values of - 12.5 to - 0.1 and two-stage Hf model ages of 1049 to 1683 Ma, and some zircons in the host monzogranite have positive ɛHf( t) values of 0.3 to 4.8 and single-stage Hf model ages of 665 to 845 Ma. This indicates that the monzogranite is most likely to be formed by partial melting of a Proterozoic lower continental crust. The mafic enclaves have fine-grained igneous textures and contain abundant acicular apatite that indicates rapid cooling. They also have a high ( 87Sr/ 86Sr) i ratio of 0.7071 and a low ɛNd( t) value of - 6.5, suggesting a derivation from ancient subcontinental lithosphere mantle (SCLM). Zircons in the mafic microgranular enclaves have ɛHf( t) values of - 1.6 to 5.1 and single-stage Hf model ages of 700 to 910 Ma, suggesting a possible origin from partial melting of the Neoproterozoic SCLM that may form in association with contemporaneously supercontinental rifting in the South China Block. Therefore, the Mishuling I-type granite may form by

  2. Paleozoic structure of Middle Tien Shan (Kyrgyzstan Central Asian Orogenic Belt): Insights on the polarity and timing of tectonic motions, subductions, and lateral correlations

    Science.gov (United States)

    Jourdon, Anthony; Loury, Chloé; Rolland, Yann; Petit, Carole; Bellahsen, Nicolas

    2015-04-01

    The structure and Palaeozoic tectonic evolution in Kyrgyz and Chinese Tien Shan Central Asian Orogenic Belt (CAOB) are still a matter of debate. There are numerous and conflicting models about the polarity of tectonic motions in the Paleozoic, the number of continental blocks and oceanic basins involved and the timing of tectonic events. In this study we propose new maps and structural cross-sections of Middle and South Kyrgyz Tien Shan (TS). These cross-sections allow us to highlight an overall South-verging structure in the Middle TS, with a thick-skin style involving the crystalline basement. This deformation occurred during the Early Carboniferous, and is sealed by an Upper Carboniferous unconformity. We ascribe this structure to an Upper Plate deformation linked to north-dipping subduction below Middle TS. In contrast, the South TS exhibits a north-verging structure, linked to south-dipping subduction, which is evidenced by an accretionary prism, a volcanic arc, and high-pressure rocks (Loury et al., 2015), and is correlated to similar structures in the Chinese TS (e.g., Charvet et al., 2011). Based on these observations, we propose a new interpretation of the tectonic evolution of the Middle and South TS CAOB. The resulting model comprises a long-lived north-dipping subduction of the Turkestan Ocean below the Middle TS-Karazakh Platform and a short-lived south-dipping subduction of a marginal back-arc basin below the Tarim. Consequently, the South TS is interpreted as a rifted block from the Tarim. Finally, the docking of the large Tarim Craton to the CAOB corresponds to a rapid collision phase (320-300 Ma). This put an end to the long-lived Paleozoic subduction history in the CAOB. Charvet, J., Shu, L., et al., 2011. Palaeozoic tectonic evolution of the Tianshan belt, NW China. Science China Earth Sciences, 54, 166-184. Loury, C. , Rolland, Y., Guillot S., Mikolaichuk, A.V., Lanari, P., Bruguier, O., D.Bosch, 2015. Crustal-scale structure of South Tien Shan

  3. Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

    Science.gov (United States)

    Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

    2015-12-01

    Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of

  4. The Permian post-orogenic collapse in the Alps: insights from the Campo unit (Austroalpine nappes, N-Italy, SE-Switzerland)

    Science.gov (United States)

    Petri, Benoît; Mohn, Geoffroy; Štípská, Pavla; Manatschal, Gianreto; Schulmann, Karel

    2014-05-01

    the ~290 Ma (U-Pb on zircon) mafic intrusion give conditions of ~6 kbar and > 900°C. Our results bring constrains on the thermal and mechanical relation between the pluton and the host rock in the middle crust and confirm the mid-crustal position of the Campo unit during the Permian. Furthermore, this study highlights the contrasted evolution of mid-crustal levels compared to lower-crustal systems such as the Ivrea zone. Eventually at a larger scale, these results provide insights on the tectonic and magmatic processes and thermal conditions of the continental crust during Variscan post-orogenic evolution.

  5. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia

    Science.gov (United States)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.

    2016-03-01

    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °C, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in the

  6. Timing and nature of the Xinlin-Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing'an Range, eastern Central Asian Orogenic Belt

    Science.gov (United States)

    Feng, Zhiqiang; Liu, Yongjiang; Liu, Binqiang; Wen, Quanbo; Li, Weimin; Liu, Qing

    2016-03-01

    Jifeng ophiolitic mélange (ultramafic rocks, meta-basalts and gabbros) crops out in the northern segment of the Great Xing'an Range, the eastern segment of the Central Asian Orogenic Belt, which marks the closure of the Xinlin-Xiguitu Ocean associated with the collision between the Erguna block and Xing'an block. In order to investigate the formation age and magma source of the Jifeng ophiolitic mélange, the gabbros from newly discovered the Jifeng ophiolitic mélange are studied with zircon U-Pb ages, whole-rock geochemistry and zircon Hf isotopes. Zircon U-Pb dating from the ophiolitic gabbros yields U-Pb age of 647 ± 5.3 Ma, which may represent the formation age of the ophiolitic mélange. The gabbros display low SiO2, TiO2, K2O contents, high Na2O, LREE contents and indistinctive REE fractionation [(La/Yb)N = 1.97-2.98]. It shows an E-MORB-like affinity, while the element concentrations of the Jifeng samples are lower than that of E-MORB. More importantly, Nb displays negative anomaly in comparison with Th, which shows a transitional SSZ-type ophiolite signature. Moreover, the ɛ Hf ( t) values of ~647 Ma zircons in the gabbros range from +8.4 to +13.4, and the corresponding Hf single-stage ages ( T DM1) are between 687 and 902 Ma, which is obviously older than the crystallization age of 647 Ma. These geochemical features can be explained as melts from the partial melting of a depleted mantle source meta-somatized by fluids derived from a subducted slab. Accordingly, we conclude that the Jifeng ophiolitic mélange is probably related to transitional SSZ-type ophiolite and developed in an intra-oceanic subduction, which indicates that an ocean (the Xinlin-Xiguitu Ocean) existed between the Erguna block and Xing'an block. The Ocean's formation might be no later than the Neoproterozoic (647 Ma), and it was closed in the Late Cambrian because of the collision between the Erguna block and Xing'an block.

  7. Crustal melting and magma mixing in a continental arc setting: Evidence from the Yaloman intrusive complex in the Gorny Altai terrane, Central Asian Orogenic Belt

    Science.gov (United States)

    Chen, Ming; Sun, Min; Buslov, Mikhail M.; Cai, Keda; Zhao, Guochun; Kulikova, Anna V.; Rubanova, Elena S.

    2016-05-01

    Granitoids and their hosted mafic enclaves may retain important information on crust-mantle interaction, and thus are significant for study of crustal growth and differentiation. An integrated petrological, geochronological and geochemical study on the granitoid plutons of the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt, was conducted to determine their source nature, petrogenesis and geodynamics. Mafic enclaves are common in the plutons, and a zircon U-Pb age (389 Ma ± 4 Ma) indicates that they are coeval with their granitoid hosts (ca. 393-387 Ma). Petrographic observations reveal that these mafic enclaves probably represent magmatic globules commingled with their host magmas. The relatively low SiO2 contents (46.0-60.7 wt.%) and high Mg# (38.9-56.5) further suggest that mantle-derived mafic melts served as a crucial component in the formation of these mafic enclaves. The granitoid hosts, including quartz diorites and granodiorites, are I-type in origin, possessing higher SiO2 contents (60.2-69.9 wt.%) and lower Mg# (32.0-44.2). Their zircon Hf and whole-rock Nd isotopic compositions indicate that the magmas were dominated by remelting of Neoproterozoic (0.79-1.07 Ga) crustal materials. Meanwhile, the geochemical modeling, together with the common occurrence of igneous mafic enclaves and the observation of reversely zoned plagioclases, suggests that magma mixing possibly contributed significantly to the geochemical variation of the granitoid hosts. Our results imply that mafic magmas from the mantle not only provided substantial heat to melt the lower crust, but also mixed with the crust-derived melts to form the diverse granitoids. The oxidizing and water-enriched properties inferred from the mineral assemblages and compositions imply that the granitoid plutons of the Yaloman intrusive complex were possibly formed in a continental arc-related setting, which is also supported by their geochemistry. The

  8. Permian doleritic dikes in the Beishan Orogenic Belt, NW China: Asthenosphere-lithosphere interaction in response to slab break-off

    Science.gov (United States)

    Zhang, Yunying; Yuan, Chao; Sun, Min; Long, Xiaoping; Xia, Xiaoping; Wang, Xinyu; Huang, Zongying

    2015-09-01

    Extensive Permian mafic-ultramafic intrusions crop out within the Central Asian Orogenic Belt (CAOB). Because the magmatic activity is spatially and temporally associated with the Tarim Large Igneous Province (LIP), a mantle plume has been invoked to explain the petrogenesis of these mafic-ultramafic rocks. In order to test this hypothesis, we present new geochronological and geochemical data for doleritic dike swarms in the Beishan area, southern CAOB. Zircon U-Pb dating of the Yinaoxia and Gubaoquan doleritic dikes indicates that they were emplaced during the Early Permian (ca. 282 Ma). The Yinaoxia doleritic dikes have higher Mg# (52-74) and εNd(t) values (9.0-9.1) than the Gubaoquan dikes (Mg# = 35-56; εNd(t) = 5.8-7.4), indicating that the former are more primitive than the latter. The Gubaoquan dikes are characterized by higher Ba/Nb (15-276), Ba/La (6-103), Th/Yb (0.12-0.24) and Th/Nb (0.20-0.36) ratios, suggesting that their parental magmas contained more subduction-related material. Calculated parental magmatic compositions in equilibrium with Cr-rich clinopyroxenes within the dikes have LREE-depleted to flat REE patterns ((La/Yb)N = 0.57-1.28) and negative to slightly positive Nb anomalies ((Nb/La)PM = 0.33-0.91). These data suggest that their parental magmas may have been generated by interaction between depleted asthenospheric mantle and metasomatized lithospheric mantle. Using clinopyroxene-liquid thermobarometers, we estimate a temperature range of 1142 °C-1276 °C, indicative of an upper asthenospheric mantle source. Although the doleritic dikes in Beishan are coeval with the Tarim LIP, their petrological and geochemical compositions do not suggest the abnormally high mantle temperatures or OIB-like mantle signatures that characterize the mantle source of the Tarim LIP magmas. This means that the Permian Tarim mantle plume cannot account for the formation of the doleritic dikes in the Beishan area, and that the Tarim LIP does not extend to the

  9. Correlation of Coseismic Velocity and Static Volumetric Strain Changes Induced by the 2010 Mw6.3 Jiasian Earthquake under the Southern Taiwan Orogenic Belt

    Science.gov (United States)

    Wu, S. M.; Hung, S. H.

    2015-12-01

    Earthquake-induced temporal changes in seismic velocity of the earth's crust have been demonstrated to be monitored effectively by the time-lapse shifts of coda waves recently. Velocity drop during the coseismic rupture has been explicitly observed in proximity to the epicenters of large earthquakes with different styles of faulting. The origin of such sudden perturbation in crustal properties is closely related to the damage and/or volumetric strain change influenced by seismic slip distribution. In this study, we apply a coda wave interferometry method to investigate potential velocity change in both space and time related to the moderate-sized (Mw6.3) 2010 Jiasian earthquake, which nucleated deeply in the crust (~23 km), ruptured and terminated around the depth of 10 km along a previously unidentified blind thrust fault near the lithotectonic boundary of the southern Taiwan orogenic belt. To decipher the surface and crustal response to this relatively deep rupture, we first measure relative time-lapse changes of coda between different short-term time frames spanning one year covering the pre- and post-seismic stages by using the Moving Window Cross Spectral Method. Rather than determining temporal velocity variations based on a long-term reference stack, we conduct a Bayesian least-squares inversion to obtain the optimal estimates by minimizing the inconsistency between the relative time-lapse shifts of individual short-term stacks. The results show the statistically significant velocity reduction immediately after the mainshock, which is most pronounced at the pairs with the interstation paths traversing through the hanging-wall block of the ruptured fault. The sensitivity of surface wave coda arrivals mainly in the periods of 3-5 s to shear wave speed perturbation is confined within the depth of 10 km, where the crust mostly experienced extensional strain changes induced by the slip distribution from the finite-fault model. Compared with coseismic slip

  10. 40Ar-39Ar and U-Pb ages of metadiorite from the East Kunlun Orogenic Belt: Evidence for Early-Paleozoic magmatic zone and excess argon in amphibole minerals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Single-grain zircon U-Pb and amphibole 40Ar-39Ar dating have beenconducted on a deformed and metamorphosed diorite in the East Kunlun Orogenic Belt, which intruded into the middle Proterozoic Kuhai Group exposed in the south of Xiangride region, Dulan County, NW Qinghai Province. The zircon gives a concordant U-Pb age of (446.5±9.1) Ma. The amphibole yields Ar plateau age of (488.0±1.2) Ma and an isochronal age of (488.9±5.6) Ma. Age results of both stepwise released Ar and conventional K-Ar analysis are remarkably higher than that of zircon U-Pb, suggesting that the amphibole contains excess argon and the amphibole plateau age cannot be taken as the timing of metamorphism or deformation. The zircon age is interpreted to be crystallization age of the diorite pluton, which suggests that an Early-Paleozoic magmatic zone indeed existed in the East Kunlun Orogenic Belt stretching along the region south to the Golmud, Normuhong and Xiangride.

  11. U-Pb SHRIMP and {sup 40}Ar/{sup 39}Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, Sao Luis cratonic fragment, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Evandro Luiz, E-mail: evandro.klein@cprm.gov.br [Servico Geologico do Brasil (CPRM), Belem, PA (Brazil); Tassinari, Colombo Celso Gaeta, E-mail: ccgtassi@usp.br [Universidade de Sao Paulo (USP), SP (Brazil). Instituto de Geociencias. Centro de Pesquisas Geocronologicas; Vasconcelos, Paulo Marcos, E-mail: paulo@earth.uq.edu.au [University of Queensland, School of Earth Sciences, Brisbane (Australia)

    2014-07-01

    Caxias is an orogenic gold deposit in the Sao Luis cratonic fragment, which is correlated with the Rhyacian terranes of the West-African Craton. The deposit postdates peak metamorphism (estimated at 2100 ± 15 Ma) and is hosted in a shear zone that cuts across schists of the Aurizona Group (2240 ± 5 Ma) and the Caxias Microtonalite. The emplacement age of the microtonalite, as determined in this work by SHRIMP U-Pb zircon dating, is 2009 ± 11 Ma and represents a latest age magmatic event in the Sao Luis cratonic fragment. Older zircon age of 2139 ± 10 Ma is interpreted as due to inheritance from the older granitoid or volcanic suites (magmatic sources?) or to contamination during emplacement. Lead isotope compositions indicate that the Pb incorporated in ore-related pyrite was probably sourced from regional, orogenic calc-alkaline granitoids of ca. 2160 Ma. Hydrothermal sericite from Caxias yielded a {sup 40}Ar/{sup 39}Ar plateau age of 1990 ± 30 Ma, which combined with the emplacement age of the Caxias Microtonalite brackets the age of gold mineralization between 2009 ± 11 and 1990 ± 30 Ma. (author)

  12. Nature and evolution of the lithospheric mantle beneath the eastern Central Asian Orogenic Belt: Constraints from peridotite xenoliths in the central part of the Great Xing'an Range, NE China

    Science.gov (United States)

    Pan, Shaokui; Zheng, Jianping; Griffin, W. L.; Xu, Yixian; Li, Xiyao

    2015-12-01

    Our knowledge of the lithospheric mantle beneath the Central Asian Orogenic Belt is still sparse. Petrologic, major- and trace-element studies on the peridotite xenoliths from the Cenozoic volcanic fields in the Aershan area, the central part of the Great Xing'an Range, NE China, provide insights into the nature and evolution of the lithospheric mantle beneath the eastern part of the belt. According to the REE patterns of clinopyroxene, these peridotites can be divided into three groups which show clear differences in microstructure, geochemistry and equilibration temperature. Group 1 xenoliths (LREE-depleted patterns of Cpx) are lherzolites, with protogranular microstructure and high modal Cpx (8-13 wt.%), low Cr# in spinel ( 3300, (La/Yb)N asthenospheric material played a key role in modifying the lithospheric mantle underneath the eastern Central Asian Orogenic Belt, and resulted in mantle heterogeneity, which is characterized by juvenile fertile lithospheric material (e.g. Group 1) mixed with older, moderately refractory relics (e.g. Group 2), with the fertile type dominating the shallower levels.

  13. Fluid Inclusion characteristics of syn-late orogenic Co-Ni-Cu-Au deposits in the Siegerland District of the Rhenish Massif, Germany

    Science.gov (United States)

    Wohlgemuth, Christoph; Hellmann, André; Meyer, Franz Michael

    2013-04-01

    The Siegerland District is located in the fold-and-thrust-belt of the Rhenish Massif and hosts various syn- late orogenic vein-hosted hydrothermal mineralization types. Peak-metamorphism and deformation occurred at 312-316 ± 10 Ma (Ahrendt et al., 1978) at pT-conditions of 280 - 320 °C and 0.7 - 1.4 kbar (Hein, 1993). The district is known for synorogenic siderite-quartz mineralization formed during peak-metamorphic conditions. At least 4 syn-late orogenic mineralization types are distinguished: Co-Ni-Cu-Au, Pb-Zn-Cu, Sb-Au and hematite-digenite-bornite mineralization (Hellmann et al., 2012b). Co-Ni-Cu-Au mineralization of the Siegerland District belongs to the recently defined class of metasediment hosted synorogenic Co-Cu-Au deposits (i.e. Slack et al, 2010). Ore minerals are Fe-Co-Ni sulpharsenides, bearing invisible gold, chalcopyrite, and minor As-bearing pyrite. The gangue is quartz. The alteration mineralogy comprises chlorite, illite-muscovite and quartz. The epigenetic quartz veins are closely related to the formation of reverse faults (Hellmann et al., 2011a). Microthermometric studies of fluid inclusions concerning the relationship between mineralization and microstructures have not been done so far for this deposit-class and this will be addressed here. Fluid inclusions are investigated in hydrothermally formed vein-quartz, selected from Co-Ni-Cu-Au mineralization bearing veins showing only minor overprints by later mineralization types. Two quartz generations are distinguished: subhedral quartz-I showing growth zonation and fine grained, recrystallized- and newly formed quartz-II grains forming irregular masses and fracture fillings in quartz-I. Co-Ni-Fe sulpharsenides and chalcopyrite are closely intergrown with quartz-II, implying their contemperaneous formation. However, fluid inclusions in quartz-II are often small, therefore fluid inclusions in quartz-I have been mostly investigated. In total, 180 inclusions from 4 different deposits have been

  14. Timing and genesis of the adakitic and shoshonitic intrusions in the Laoniushan complex, southern margin of the North China Craton: Implications for post-collisional magmatism associated with the Qinling Orogen

    Science.gov (United States)

    Ding, Li-Xue; Ma, Chang-Qian; Li, Jian-Wei; Robinson, Paul T.; Deng, Xiao-Dong; Zhang, Chao; Xu, Wang-Chun

    2011-10-01

    The NWW-striking Qinling Orogen formed in the Triassic by collision between the North China and Yangtze Cratons. Triassic granitoid intrusions, mostly middle- to high-K, calc-alkaline, are widespread in this orogen, but contemporaneous intrusions are rare in the southern margin of the North China Craton, an area commonly considered as the hinterland belt of the orogen. In this paper, we report zircon U-Pb ages, elemental geochemistry, and Sr-Nd-Hf isotope data for the Laoniushan granitoid complex that was emplaced in the southern margin of the North China Craton. Zircon U-Pb dating shows that the complex was emplaced in the late Triassic (228 ± 1 to 215 ± 4 Ma), indicating that it is part of the post-collisional magmatism in the Qinling Orogen. The complex consists of, from early to late, biotite monzogranite, quartz diorite, quartz monzonite, and hornblende monzonite, which span a wide compositional range, e.g., SiO 2 = 55.9-70.6 wt.%, K 2O + Na 2O = 6.6-10.2 wt.%, and Mg # of 24 to 54. The biotite monzogranite has high Al 2O 3 (15.5-17.4 wt.%), Sr (396-1398 ppm) and Ba (1284-3993 ppm) contents and relatively high La/Yb (mostly 14-30) and Sr/Y (mostly 40-97) ratios, but low Yb (mostly 1.3-1.6 ppm) and Y (mostly14-19 ppm) contents, features typical of adakitic rocks. The quartz monzonite, hornblende monzonite and quartz diorite have a shoshonitic affinity, with K 2O up to 5.58 wt.% and K 2O/Na 2O ratios averaging 1.4. The rocks are characterized by strong LREE/HREE fractionation in chondrite-normalized REE pattern, without obvious Eu anomalies, and show enrichment in large ion lithophile elements but depletion in high field strength elements (Nb, Ta, Ti). The biotite monzogranite (228 Ma) has initial 87Sr/ 86Sr ratios of 0.7061 to 0.7067, ɛNd(t) values of - 9.2 to - 12.6, and ɛ Hf(t) values of - 9.0 to - 15.1; whereas the shoshonitic granitoids (mainly 217-215 Ma) have similar initial 87Sr/ 86Sr ratios (0.7065 to 0.7075) but more radiogenic ɛNd(t) (- 12.4 to

  15. 2090-2070 Ma A-type granitoids in Zanhuang Complex: Further evidence on a Paleoproterozoic rift-related tectonic regime in the Trans-North China Orogen

    Science.gov (United States)

    Du, Lilin; Yang, Chonghui; Wyman, Derek A.; Nutman, Allen P.; Lu, Zenglong; Song, Huixia; Xie, Hangqiang; Wan, Yusheng; Zhao, Lei; Geng, Yuansheng; Ren, Liudong

    2016-06-01

    the Trans-North China Orogen (TNCO), and also present a bimodal character. We propose that 2.2-2.0 Ga bimodal magmas throughout the TNCO were likely formed in a Paleoproterozoic rifting setting. Considering the widespread 2.2-2.0 Ga magmatic rocks in the North China Craton (NCC), we infer that the magmatism likely occurs in tensional environment after the initial amalgamation of the NCC in the late Archean.

  16. Geochronology, mantle source composition and geodynamic constraints on the origin of Neoarchean mafic dikes in the Zanhuang Complex, Central Orogenic Belt, North China Craton

    Science.gov (United States)

    Deng, Hao; Kusky, Timothy; Polat, Ali; Wang, Junpeng; Wang, Lu; Fu, Jianmin; Wang, Zhensheng; Yuan, Ye

    2014-09-01

    Mafic granulitic and amphibolitic boudins dispersed in Archean felsic gneisses are widely distributed in the Central Orogenic Belt (COB) and the Eastern Block of the North China Craton (NCC) and are considered to constitute deformed mafic dike swarms. Previous studies have demonstrated that the mafic dikes in the Zanhuang Complex of the NCC intruded the fabrics of an Archean mélange belt and were boudinaged during younger deformation. Igneous zircons from an undeformed mafic dike yield a 207Pb/206Pb age of 2535 ± 30 Ma, which is interpreted as the crystallization age. In addition, pegmatites cutting across the mafic dikes in the field also yield an igneous zircon 207Pb/206Pb age of 2504 ± 16 Ma, providing strong evidence that the mafic dikes in the NCC intruded during the Neoarchean. Metamorphic zircons from one deformed mafic dike sample yield a metamorphic 207Pb/206Pb age of 2090 ± 83 Ma, and another four samples from deformed mafic dikes have a consistent metamorphic zircon age of ca. 1850 Ma, indicating that the mafic dikes underwent at least two generations of Paleoproterozoic metamorphism of ca. 2.1 Ga and ca. 1.85 Ga. Previously reported trace element systematics of the mafic dikes are consistent with an arc-related lithospheric mantle source region, rather than an ocean island basalt (OIB)-like source region. The new whole rock Nd isotopic composition (ɛNd(t) = + 0.71 to + 3.70) is relatively more evolved compared to that of the depleted mantle at 2.5 Ga, indicating an enriched lithospheric mantle source. Accordingly, the mafic dikes are proposed to have been formed in a subduction-related environment and their enriched mantle source was metasomatized by the melts and fluids derived from the subducted slab. Based on previous studies of the NCC and new geochronological and isotopic data in this contribution, a new comprehensive tectonic model is proposed for the evolution of the NCC between 2.7 Ga and 1.85 Ga: (1) from 2.7 to 2.5 Ga, an oceanic arc

  17. 'Extra-regional' strike-slip fault systems in Chile and Alaska: the North Pacific Rim orogenic Stream vs. Beck's Buttress

    Science.gov (United States)

    Redfield, T. F.; Scholl, D. W.; Fitzgerald, P. G.

    2010-12-01

    The ~2000 km long Denali Fault System (DFS) of Alaska is an example of an extra-regional strike-slip fault system that terminates in a zone of widely-distributed deformation. The ~1200 km long Liquiñe-Ofqui Fault Zone (LOFZ) of Patagonia (southern Chile) is another. Both systems are active, having undergone large-magnitude seismic rupture is 2002 (DFS) and 2007 (LOFZ). Both systems appear to be long-lived: the DFS juxtaposes terranes that docked in at least early Tertiary time, whilst the central LOFZ appears to also record early Tertiary or Mesozoic deformation. Both fault systems comprise a relatively well-defined central zone where individual fault traces can be identified from topographic features or zones of deformed rock. In both cases the proximal and distal traces are much more diffuse tributary and distributary systems of individual, branching fault traces. However, since their inception the DFS and LOFZ have followed very different evolutionary paths. Copious Alaskan paleomagnetic data are consistent with vertical axis small block rotation, long-distance latitudinal translation, and a recently-postulated tectonic extrusion towards a distributary of subordinate faults that branch outward towards the Aleution subduction zone (the North Pacific Rim orogenic Stream; see Redfield et al., 2007). Paleomagnetic data from the LOFZ region are consistent with small block rotation but preclude statistically-significant latitudinal transport. Limited field data from the southernmost LOFZ suggest that high-angle normal and reverse faults dominate over oblique to strike-slip structures. Rather than the high-angle oblique 'slivering regime' of the southeasternmost DFS, the initiation of the LOFZ appears to occur across a 50 to 100 km wide zone of brittly-deformed granitic and gneissic rock characterized by bulk compression and vertical pathways of exhumation. In both cases, relative plate motions are consistent with the hypothetical style, and degree, of offset, leading

  18. Impact of hydrothermal alteration on the U-Pb isotopic system of zircons from the Fangcheng syenites in the Qinling orogen, Henan Province, China

    Institute of Scientific and Technical Information of China (English)

    BAO Zhiwei; WANG Qiang; BAI Guodian; ZHAO Zhenhua

    2009-01-01

    Disturbance of the zircon U-Pb isotopic system has been investigated extensively, but mostly in lab, in the last decades. Here, we reported a field-based study on intensive sericitization, K-feldsparthization and the impacts of mylonitization on zircons from the Fangcheng syenites.The Fangcheng syenites occur in the eastern part of the Qinling orogen and consist mainly of aegirine-augite syenite, aegirine nepheline syenite, biotite syenite and hornblende nepheline syenite. Zircons from the slightly sericitized aegirine augite syenite are colorless, transparent crystals and exhibit well-developed oscillatory and sector zoning on the cathodoluminescence (CL) images which are typical of magmatic zircons from alkaline rocks. Zircon U-Pb determinations by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) showed that the syenite was formed in Neoproterozoic time, the weighted average of 206Pb/238U ages is 844.3±1.6 Ma (MSWD=0.86). In contrast, the hydrothermally altered zircons (hydrothermal zircon) from the intensively sericitized, K-feldsparthized, and weakly mylonitized aegirine augite syenite are conglomerates, yellowish to brown in color, generally translucent and internally textureless. The CL and backscatter electron (BSE) images of hydrothermal zircons exhibit fractured, textureless or mosaic textures, and occasionally show "sponge texture" with the veinlets and inclusions of K-feldspar; however, relicts of magmatic oscillatory zoning can still be discerned locally in individual grains. LA-ICPMS analyses of the hydrothermal zircons demonstrated that the zircons are chemically inhomogeneous, with enhanced and widely varied Pb, U, and Th contents. The U and Th contents of the hydrothermal zircons are estimated to be 32×10-6-1550×10-6 and 188×10-6-4059×10-6, respectively, with Th/U ratios within the range of 0.7-44.9. 206Pb/238U apparent ages of the hydrothermal zircons are negatively correlated with the contents of U, and radiogenic and

  19. Devonian granitoids and their hosted mafic enclaves in the Gorny Altai terrane, northwestern Central Asian Orogenic Belt: crust-mantle interaction in a continental arc setting

    Science.gov (United States)

    Chen, Ming; Sun, Min

    2016-04-01

    Granitoids are a major component in the upper continental crust and hold key information on how did the continental crust grow and differentiate. This study focuses on the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt (CAOB). The association of granitoids and mafic enclaves can provide important clues on the source nature, petrogenetic processes and geodynamic setting of the Yaloman intrusive complex, which in turn will shed light on the crustal evolution in the northwestern CAOB. Zircon U-Pb dating shows that the granitoids, including quartz diorites and granodiorites, were emplaced in ca. 389-387 Ma. The moderate Na2O + K2O contents and low A/CNK values indicate that these rocks belong to the sub-alkaline series with metaluminous to weakly peraluminous compositions. The granitoids yield two-stage zircon Hf model ages of ca. 0.79-1.07 Ga and whole-rock Nd model ages of ca. 0.90-0.99 Ga, respectively, implying that they were mainly sourced from Neoproterozoic juvenile crustal materials. The mafic enclaves show an almost identical crystallization age of ca. 389 Ma. The identification of coarse-grained xenocrysts and acicular apatites, together with the fine-grained texture, makes us infer that these enclaves are likely to represent magmatic globules commingled with the host magmas. The low SiO2 and high MgO contents of the mafic enclaves further suggest that substantial mantle-derived mafic melts were probably involved in their formation. Importantly, the SiO2 contents of the granitoids and mafic enclaves are well correlated with other major elements and most of the trace elements. Also a broadly negative correlation exists between the SiO2 contents and whole-rock epsilon Nd (390 Ma) values of the granitoids. Given the observation of reversely zoned plagioclases within the granitoids and the common occurrence of igneous mafic enclaves, we propose that magma mixing probably played an important role in the formation

  20. Reconstructing multiple arc-basin systems in the Altai-Junggar area (NW China): Implications for the architecture and evolution of the western Central Asian Orogenic Belt

    Science.gov (United States)

    Li, Di; He, Dengfa; Tang, Yong

    2016-05-01

    The Altai-Junggar area in northwestern China is a critical region to gain insights on the tectonic framework and geological evolution of the western Central Asian Orogenic Belt (CAOB). In this study, we report results from integrated geological, geochemical and geophysical investigations on the Wulungu Depression of the Junggar Basin to determine the basement nature of the basin and understand its amalgamation history with the Chinese Altai, within the broad tectonic evolution of the Altai-Junggar area. Based on borehole and seismic data, the Wulungu Depression is subdivided into two NW-trending tectonic units (Suosuoquan Sag and Hongyan High) by southward-vergent thrust faults. The Suosuoquan Sag consists of the Middle-Late Devonian basaltic andesite, andesite, dacite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance (zircon εHf(t) = 6.0-14.9), compared to the Late Carboniferous andesite and rhyolite in the Hongyan High. Zircon SIMS U-Pb ages for dacites and andesites indicate that these volcanics in the Suosuoquan Sag and Hongyan High erupted at 376.3 Ma and 313.4 Ma, respectively. The Middle-Late Devonian basaltic andesites from well LC1 are calc-alkaline and exhibit primitive magma-like MgO contents (7.9-8.6%) and Mg# values (66-68), with low initial 87Sr/86Sr (0.703269-0.704808) and positive εNd(t) values (6.6-7.6), and relatively high Zr abundance (98.2-116.0 ppm) and Zr/Y ratios (5.1-5.4), enrichment in LREEs and LILEs (e.g., Th and U) and depletion in Nb, Ta and Ti, suggesting that they were probably derived from a metasomatized depleted mantle in a retro-arc extensional setting. The well LC1 andesitic tuffs, well L8 dacites, well WL1 dacitic tuffs and well L5 andesites belong to calc-alkaline and metaluminous to peraluminous (A/CNK = 0.8-1.7) series, and display low Mg# values (35-46) and variably positive εNd(t) (4

  1. Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa

    Science.gov (United States)

    Chinnasamy, Sakthi Saravanan; Uken, Ron; Reinhardt, Jürgen; Selby, David; Johnson, Spencer

    2015-08-01

    Gold mineralization in the Klipwal Shear Zone (KSZ) at the Klipwal Gold Mine is confined to laminated quartz-carbonate lodes, stringers, and associated alteration in sandstone and siltstone of the Delfkom Formation in the upper Mozaan Group of the Mesoarchaean Pongola Supergroup. The moderately dipping brittle-ductile KSZ strikes N-S with an oblique-reverse, sinistral sense of shear. The deformational events that are recognized include an early compressional phase that produced anastomosing shears defined by shear fabrics with numerous shear-parallel laminated quartz-carbonate fault-fill veins and, in places, extensional quartz vein stockworks, and a late brittle reactivation phase that produced fault breccias, displacing earlier extensional veins. Three closely spaced economic reefs (lodes) are developed: the main R-reef constitutes the KSZ, while the J- and H-reefs represent footwall splays. Alteration comprises chlorite, muscovite, epidote, feldspar, and carbonates along with pyrite, arsenopyrite, and chalcopyrite ± pyrrhotite. An inner alteration zone is dominated by laminated quartz-carbonate veins with alternating quartz-carbonate-rich and muscovite-chlorite-rich laminae, whereas the proximal zone is characterized by alteration halos of K-feldspar, albite, epidote, chlorite, and muscovite along with carbonates and associated quartz veins. Chlorite thermometry from the inner and proximal zones yielded temperatures of 267 to 312 °C. Arsenopyrite compositions provide temperatures in the same range, 255 to 318 °C. Fluid inclusion microthermometry and Raman spectrometry of quartz veins in the mineralized reefs reveal the presence of metamorphogenic aqueous-gaseous fluid with an average salinity of 6.5 wt% NaCl equiv. Fluid compositions and estimated pressure-temperature (P-T) range (1.1 to 2.5 kbar at 255 to 318 °C) are typical of orogenic gold deposits. Devolatilization during the regional facies metamorphism of the Pongola Supergroup is considered the likely

  2. Implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary (non-collisional) and collisional (suturing) orogens

    Science.gov (United States)

    Scholl, D. W.; Von Huene, R.

    2009-01-01

    Arc magmatism at subduction zones (SZs) most voluminously supplies juvenile igneous material to build rafts of continental and intra-oceanic or island arc (CIA) crust. Return or recycling of accumulated CIA material to the mantle is also most vigorous at SZs. Recycling is effected by the processes of sediment subduction, subduction erosion, and detachment and sinking of deeply underthrust sectors of CIA crust. Long-term (>10-20 Ma) rates of additions and losses can be estimated from observational data gathered where oceanic crust underruns modern, long-running (Cenozoic to mid-Mesozoic) ocean-margin subduction zones (OMSZs, e.g. Aleutian and South America SZs). Long-term rates can also be observationally assessed at Mesozoic and older crust-suturing subduction zone (CSSZs) where thick bodies of CIA crust collided in tectonic contact (e.g. Wopmay and Appalachian orogens, India and SE Asia). At modern OMSZs arc magmatic additions at intra-oceanic arcs and at continental margins are globally estimated at c. 1.5 AU and c. 1.0 AU, respectively (1 AU, or Armstrong Unit,= 1 km3 a-1 of solid material). During collisional suturing at fossil CSSZs, global arc magmatic addition is estimated at 0.2 AU. This assessment presumes that in the past the global length of crustal collision zones averaged c. 6000 km, which is one-half that under way since the early Tertiary. The average long-term rate of arc magmatic additions extracted from modern OMSZs and older CSSZs is thus evaluated at 2.7 AU. Crustal recycling at Mesozoic and younger OMSZs is assessed at c. 60 km3 Ma-1 km-1 (c. 60% by subduction erosion). The corresponding global recycling rate is c. 2.5 AU. At CSSZs of Mesozoic, Palaeozoic and Proterozoic age, the combined upper and lower plate losses of CIA crust via subduction erosion, sediment subduction, and lower plate crustal detachment and sinking are assessed far less securely at c. 115 km3 Ma-1 km-1. At a global length of 6000 km, recycling at CSSZs is accordingly c. 0

  3. 中亚造山带中的燃烧变质事件及其年代学研究%Combustion metamorphic events as age markers of orogenic movements in Central Asia

    Institute of Scientific and Technical Information of China (English)

    Igor S. Novikov; Ellina V. Sokol

    2007-01-01

    Combustion metamorphic (pyrometamorphic) complexes produced by prehistoric natural coal fires are widespread in Central Asia, namely at the interfaces between mountain systems and the flanking sedimentary basins. Large-scale and prolonged fires accompanied the initial orogenic stages as unweathered coal-bearing formations became exposed into the aeration zone.Pyrometamorphic rocks are comparable to sanidinite facies rocks in formation conditions and in alteration of sedimentary material but,unlike these, their protolith underwent different melting degrees to produce either ferrous basic paralavas or glazed clinkers. The phase composition of the newly-formed melted rocks are favorable for 40Ar/39Ar dating of combustion metamorphic events which are coeval to the onset of the main stage of recent orogenic events. We suggest a new algorithm providing correct 40 Ar/39 Ar dating of pyrometamorphic rocks followed by well-grounded geological interpretation. We studied pyrometamorphic rocks in the western Salair zone of the Kuznetsk coal basin where combustion metamorphism under temperatures above 1000℃ acted upon large volumes of coalbearing sediments. Samples of paralavas were dated by the step heating 40 Ar/39 Ar method checked against internal (plateau and isochrone ages) and external ("criterions of couple") mineralogical criterions, and against preliminary dating from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events. The first one (1.2±0.4 Ma) is drawn towards the west boundary of Prokopyevsk-Kiselevsk block of Salair zone, while the second one (0.2±0.3 Ma) is confined to its east boundary. The former ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the latter ages correspond to those in its eastern edge. The dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the

  4. Emplacement age of the post- orogenic A-type granites in Northwestern Lesser Xing'an Ranges, and its relationship to the eastward extension of Suolushan-Hegenshan-Zhalaite collisional suture zone

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A great amount of alkali-feldspar and alkaline granites have been found around Nenjiang, Northwest Lesser Xing'an Ranges, but their forming ages have been a controversial subject due to the lack of reliable geological and isotopic geochronological evidence. The zircon U-Pb isotopic dating results conducted in this note indicate that these granites emplaced at 260-290 Ma, coeval with the late stage of Late Paleozoic. Studies of mineralogy, petrology and geochemistry show that they are post-orogenic A-type granites, and consist of the northeastern extension of huge belt of Late Paleozoic A-type granite along North Xinjiang-Southeast Mongolia-Central Inner Mongolia. Therefore, we can determine that the Suolunshan-Hegenshan-Zhalaite collisional suture zone extends northeastward to Heihe with the collision age of Carboniferous.

  5. Potassic/ultrapotassic magmatism pos a tardi-orogenic (associated to subduction) in the western of Bahia: batolite monzo-syenitic from Guanambi-Urandi and the syenites from Correntina, Brazil

    International Nuclear Information System (INIS)

    The western portion of Bahia State is characterized by polimetamorfic rocks (granulites and gneissic-migmatitics) intruded by great volume of undeformated monzonitic and syenitic rocks. Tectonically, this region is interpreted as an Early Proterozoic mobile belt. Clynopiroxene-syenitic rocks are more conspicuous in the western side of the Sao Francisco river (Correntina Syenites), while amphibole-mica monzonitic and syenitic rocks (Guanambi-Urandi Batholith) occur southeastward. The Guanambi-Urandi, a 6000 km2 batholith, shows a slight sigmoidal shape whereas the Correntina Syenites outcrop along the valleys where the Phanerozoic cover difficults the mapping. The existing geochronological data reveal a contemporaneity between these set of rocks, about 2 Ga. Our geochemical data point to potassic plutonism, with high Ba, Sr, REE and moderate Ti, Zr, Nb and Y. The above characteristics suggest an orogenic environment, probably linked a subduction zone. (author)

  6. Zircon ages and Hf isotopic compositions of Ordovician and Carboniferous granitoids from central Inner Mongolia and their significance for early and late Paleozoic evolution of the Central Asian Orogenic Belt

    Science.gov (United States)

    Shi, Yuruo; Jian, Ping; Kröner, Alfred; Li, Linlin; Liu, Cui; Zhang, Wei

    2016-03-01

    We present zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the evolution of central Inner Mongolia, China, in the early and late Paleozoic. Zircons of a granodiorite yielded a 206Pb/238U age of 472 ± 3 Ma that reflects the time of early Paleozoic magmatism. Zircon ages were also obtained for a tonalite (329 ± 3 Ma), quartz-diorite (320 ± 3 Ma), and granite vein (297 ± 2 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia. The dated samples are mostly granodiorite, tonalite and quartz-diorite in composition with intermediate to high-silica, high Na2O (3.08-4.26 wt.%), low K2O (0.89-2.86 wt.%), and high Na2O/K2O and Sr/Y ratios. Their chondrite-normalized REE patterns are characterized by LREE enrichment. In mantle-normalized multi-element variation diagrams they show typical negative Nb and Ta anomalies, and all samples display positive εHf(t) and εNd(t) values, and low ISr. The Ordovician rocks, however, show higher Sr/Y and La/Yb ratios than the Carboniferous samples, implying that the older granitoids represent adakitic granitoids, and the Carboniferous granitoids are typical subduction-related arc granitoids but also with adakite-like compositions. The results are compatible with the view that the Central Asian Orogenic Belt (CAOB) in Inner Mongolia evolved through operation of several subduction systems with different polarities: an early-middle Paleozoic subduction and accretion system along the northern margin of the North China Craton and the southern margin of the Mongolian terrane, and late Paleozoic northward subduction along the northern orogen and exhumation of a high-pressure metamorphic terrane on the northern margin of the North China Craton.

  7. Kinematic 3-D Retro-Modeling of an Orogenic Bend in the South Limón Fold-and-Thrust Belt, Eastern Costa Rica: Prediction of the Incremental Internal Strain Distribution

    Science.gov (United States)

    Brandes, Christian; Tanner, David C.; Winsemann, Jutta

    2016-03-01

    The South Limón fold-and-thrust belt, in the back-arc area of southern Costa Rica, is characterized by a 90° curvature of the strike of the thrust planes and is therefore a natural laboratory for the analysis of curved orogens. The analysis of curved fold-and-thrust belts is a challenge because of the varying structural orientations within the belt. Based on seismic reflection lines, we created a 3-D subsurface model containing three major thrust faults and three stratigraphic horizons. 3-D kinematic retro-deformation modeling was carried out to analyze the spatial evolution of the fold-and-thrust belt. The maximum amount of displacement on each of the faults is (from hinterland to foreland); thrust 1: 800 m; thrust 2: 600 m; thrust 3: 250 m. The model was restored sequentially to its pre-deformational state. The strain history of the stratigraphic horizons in the model was calculated at every step. This shows that the internal strain pattern has an abrupt change at the orogenic bend. Contractional strain occurs in the forelimbs of the hanging-wall anticlines, while a zone of dilative strain spreads from the anticline crests to the backlimbs. The modeling shows that a NNE-directed transport direction best explains the structural evolution of the bend. This would require a left-lateral strike-slip zone in the North to compensate for the movement and thereby decoupling the South Limón fold-and-thrust belt from northern Costa Rica. Therefore, our modeling supports the presence of the Trans-Isthmic fault system, at least during the Plio-Pleistocene.

  8. Revealing the significance and polyphase tectonothermal evolution of a major metamorphic unit in an orogen: the central Sanandaj-Sirjan zone, Zagros Mts., Iran

    Science.gov (United States)

    Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Liu, Xiaoming; Dong, Yunpeng; Monfaredi, Behzad; Benroider, Manfred; Finger, Fritz; Waitzinger, Michael

    2016-04-01

    The Dorud-Azna region in the central Sanandaj-Sirjan metamorphic belt plays a key role in promoting the tectonic evolution of Zagros orogen, within the frame of the Arabia-Eurasia collision zone. From footwall to hangingwall, structural data combined with the U-Pb zircon and extensive 40Ar-39Ar mineral dating survey demonstrate three metamorphosed tectonic units, which include: (1) The Triassic June complex is metamorphosed within greenschist facies conditions, overlain by (2) the amphibolite-grade metamorphic Galeh-Doz orthogneiss, which is intruded by mafic dykes, and (3) the Amphibolite-Metagabbro unit. To the east, these units were intruded by the Jurassic Darijune gabbro. We present U-Pb detrital zircon ages of a garnet-micaschist from the Amphibolite-Metagabbro unit, which yield six distinctive age groups, including a previously unrecognized Late Grenvillian age population at ~0.93 to 0.99 Ga. We speculate that this unique Late Grenvillian group coupled with biogeographic evidence suggests either relationship with the South China craton or to the "Gondwana superfan". The laser ablation ICP-MS U-Pb zircon ages of 608 ± 18 Ma and 588 ± 41 Ma of the granitic Galeh-Doz orthogneiss reveals a Panafrican basement same as known from the Yazd block of Central Iran. Geochemistry and Sr-Nd isotopes of alkaline and subalkaline mafic dykes within the Galeh-Doz orthogneiss show OIB-type to MORB-type and indicate involvement of both depleted and enriched sources for its genesis. The new 40Ar-39Ar amphibole age of ca. 322.2 ± 3.9 Ma from the alkaline mafic dyke implies Carboniferous cooling age after intrusion. The metagabbros (including the Dare-Hedavand metagabbro with a 206Pb/238U age of 314.6 ± 3.7 Ma) and amphibolites with E-MORB geochemical signature of the Amphibolite-Metagabbro unit represent an Upper Paleozoic rift. The geochemical composition of the Triassic greenschist facies metamorphosed June complex, implying formation in a same, but younger tectonic

  9. Late Palaeozoic magmatism in the northern New England Orogen - evidence from U-Pb SHRIMP dating in the Yarrol and Connors provinces, central Queensland

    International Nuclear Information System (INIS)

    Full text: The northern part of the New England Orogen in central Queensland has been divided into three provinces, which are from east to west, the Wandilla, Yarrol and Connors Provinces. Previous workers suggested that the provinces are elements in an Early Carboniferous west-dipping subduction system with the Wandilla Province representing the accretionary wedge, the Yarrol Province a forearc basin and the Connors Province the volcanic arc. Farther west, a fourth province, the Drummond Basin, is interpreted as a back-arc basin. The Connors Province crops out in two areas, the Auburn Arch in the south and Connors Arch in the north. Prior to the present study, some workers recognised two superimposed volcanic arcs, one in the Late Devonian and a second in the Early Permian. Other workers have challenged this model suggesting that the rocks in the Connors Province were mainly Late Carboniferous to Early Permian and that they recorded a period of continental extension. U-Pb SHRIMP dating in the Connors Province has confirmed the existence of at least episodic Early Carboniferous magmatism from the Tournaisian to Namurian in both the Auburn and Connors Arches. We suggest that the Tournaisian rocks are vestiges of the Early Carboniferous volcanic arc suggested by earlier workers. Ages of ∼350Ma and ∼349Ma in the Connors Province are similar to ages for volcanics in Cycle 1 in the Drummond Basin and to volcanics in the lower part of the Rockhampton Group in the Yarrol Province. Magmatism in the Drummond Basin and Yarrol Province continued into the Visean although no early Visean rocks have yet been recognised in the Connors Province. The mid-Carboniferous (late Visean) may represent an important change in the evolution of the region. East of the Auburn Arch, in the Yarrol Province, this time corresponds to the boundary between the Rockhampton Group and Lorray Formation, and is marked by a sudden increase in regional radiometric response. It represents the start of

  10. Paleomagnetic study on the Neoproterozoic mafic dikes and Early Permian volcanic-sedimentary rocks from NW Yili Block (NW China): Implications for post-orogenic kinematic evolution of the SW CAOB

    Science.gov (United States)

    Zhu, Xin; Wang, Bo; Chen, Yan; Liu, Hongsheng; Shu, Liangshu; Faure, Michel

    2016-04-01

    As one of the largest accretionary orogens of the world, the Central Asian Orogenic Belt (CAOB) has been the focus of geological studies in the last decades. However, several key points are still in hot debate, such as the formation process of the Paleo-Asian Ocean, the intracontinental movements among constituent blocks of the CAOB. In order to better understand these questions, we conducted a paleomagnetic study on the Neoproterozoic (ca. 780 Ma) mafic dikes and Early Permian (ca. 268 Ma) volcanic and sedimentary rocks from NW of the Yili Block (NW China). Ten sites have been sampled from three mafic dikes. The thickness of dikes varies from 10 to 40 meters. At about 15 km west of the mafic dikes, 4 sites were drilled in the Lower Permian basalts and limestones that unconformably overlay the Neoproterozoic mafic dikes. Mineralogical investigations show the titanium-poor magnetite as the major magnetic remanence carrier. Stepwise alternating field (AF) and thermal demagnetizations reveal two-component magnetizations. The low temperature (coercivity) component shows a viscous and unstable magnetic remanence, whereas the high temperature (coercivity) component stably decays toward to the origin and is considered as the characteristic remanent magnetization (ChRM). All ChRMs isolated from both the mafic dikes and volcanic-sedimentary samples exclusively show a reversed magnetic polarity. Based on the following 3 arguments, we suggest that the Neoprotozoic mafic dikes have been remagnetized in the Early Permian. 1. International reference of magnetostratigraphic polarity shows a dominance of the normal polarity for the Neoproterozoic period and a superchron of the reversed polarity for the late Carboniferous-Permian; 2. Two groups of sampling show coherent paleomagnetic poles with an undistinguishable angular difference; and 3. The widespread Early Permian magmatism in the sampling area could be the cause of the remagnetization. Consequently, an Early Permian

  11. Zircon U-Pb geochronology, geochemical and Sr-Nd-Hf isotopic compositions of the Triassic granite and diorite dikes from the Wulonggou mining area in the Eastern Kunlun Orogen, NW China: Petrogenesis and tectonic implications

    Science.gov (United States)

    Ding, Qing-Feng; Jiang, Shao-Yong; Sun, Feng-Yue

    2014-09-01

    The Wulonggou mining area in the Eastern Kunlun Orogen of NW China is characterized by extensive granitoid magmatism, ductile faulting, and skarn-type Cu-Pb-Zn and orogenic gold mineralizations. The Balugou granite dike, which hosts skarn-type Cu-Pb-Zn mineralizations, is located in northeast Wulonggou, whereas the Huanglonggou diorite dike, which is cut by the Huanglonggou gold veins, is located in the central part of the area. This study investigated the major and trace-element compositions, zircon U-Pb dates, and Sr-Nd-Hf isotopic compositions of these rocks. Three Balugou granite dike samples yielded an average zircon U-Pb age of ~ 244 Ma (Anisian), and two Huanglonggou diorite dike samples yielded an average zircon U-Pb age of ~ 215 Ma (Norian). Therefore, the skarn-type mineralizations in the Wulonggou area formed during the early Anisian (~ 244 Ma), and the orogenic gold mineralizations formed after 215 Ma. The Anisian Balugou granite dike is metaluminous to slightly peraluminous and has high alkali contents of 7.19-9.57 wt.%, high Zr + Nb + Ce + Y contents, high Fe2O3T/MgO ratios, and high Rb/Nb and Y/Nb ratios, which suggest an A-type affinity. The Norian Huanglonggou diorite dike is metaluminous and has high Al2O3 contents (15.61-16.40 wt.%), high Mg# values (0.49-0.54), relatively high Sr contents (370-507 ppm), high Sr/Y ratios, high (La/Yb)N ratios, and low HREE and Y contents, which suggest an adakite-like high-Mg diorite. The Anisian granite dike has initial 87Sr/86Sr (ISr) ratios of 0.707289 to 0.708981, εNd(t) values of - 3.6 to - 3.1, and zircon εHf(t) values of - 3.9 to + 1.3. The Norian diorite dike has initial 87Sr/86Sr (ISr) ratios of 0.709166 to 0.709529, εNd(t) values of - 5.7 to - 5.1, and zircon εHf(t) values of - 4.9 to - 1.0. The Sr-Nd-Hf isotopic data suggest that the Anisian granite dike was likely derived from partial melting of dominantly Mesoproterozoic mafic lower crust, whereas the Norian diorite dike was likely derived from

  12. Geochemistry, geochronology and zircon Hf isotopic study of peralkaline-alkaline intrusions along the northern margin of the North China Craton and its tectonic implication for the southeastern Central Asian Orogenic Belt

    Science.gov (United States)

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei; Liao, Wen; Wang, Yanyang

    2016-09-01

    A giant Permian alkaline magmatic belt has recently been identified in southern Inner Mongolia, along the northern margin of the North China Craton (NCC). This belt is mainly composed of syenite, quartz syenite, alkaline granite and mafic microgranular enclaves (MME)-bearing granodiorite. In order to study the petrogenesis and tectonic implications of these rocks, we undertook zircon U-Pb dating and geochemical analysis of two Permian alkaline plutons. The first Guangxingyuan Pluton occurs in the Hexigten area and is composed of MME-bearing tonalite, K-feldspar granite and syenite. The second Durenwuliji Pluton, located in the Xianghuangqi area, comprises syenite, quartz syenite and K-feldspar granite. Zircon U-Pb dating on tonalite, K-feldspar granite, syenite and quartz syenite from the two plutons yielded a tight range of ages from 259 to 267 Ma. The peralkaline-alkaline rocks show high abundance of total alkalis (K2O + Na2O = 7.9-12.9%) and K2O contents (3.9-8.0%), enrichment in large ion lithophile elements (LILE) and light rare earth element (LREE), and depletion of high field strength elements (HFSE). The associated tonalite and MMEs display I-type granitic geochemical affinity, with less total abundance of trace elements than the peralkaline-alkaline rocks. Zircon Hf isotopic analysis of the Guangxingyuan pluton yielded a large range of εHf(t) values from - 15.5 to + 6.7 and model ages (TDMC) from 781 to 2012 Ma. By contrast, the Hf isotopic data of the Durenwuliji pluton shows a small range of εHf(t) from + 6.2 to + 8.9 and TDMC from 667 to 816 Ma. The geochemical and Hf isotopic characteristics indicate that the parental magma was derived from a mixing of metasomatic mantle-derived mafic magma with different amount of crust-derived felsic magma, and followed by fractional crystallization. Considering previous tectonic studies in Inner Mongolia, a Permian post-orogenic extension was proposed to account for these peralkaline-alkaline intrusions following

  13. A turning-point in the evolution of the Variscan orogen: the ca. 325 Ma regional partial-melting event of the coastal South Armorican domain (South Brittany and Vendee, France)

    International Nuclear Information System (INIS)

    By drastically reducing the bulk strength of crustal materials, partial-melting is one of the main parameter controlling the rheological behaviour of the continental crust. With more than ca. 50% of the outcropping surface characterised by migmatites and granites, the coastal South Armorican domain, offers an opportunity to study deep-orogenic processes and more particularly, to understand the role of partial-melting for the late-evolution of the Variscan belt. To date, time-constraints are scarce hindering the understanding of this crucial stage in the Variscan belt evolution. This paper provides 29 new U-Th/Pb chemical ages on monazite collected over five sampling areas consisting in migmatite domes and late regional classic plutons. Based on structural, textural and chemical criteria, three main U-Th/Pb age-groups are distinguished. The first group, settled at ca. 335-330 Ma concerns samples of restites and core-domains of the monazite crystals for most of the granite massifs. Its significance is ascribed to inherited crystallisation ages probably recording the crossing of prograde monazite forming reactions (i.e. metamorphic iso-grads) during increasing P-T conditions in an overall nappe-stacking context. The second group that clusters at ca. 325-320 Ma corresponds to newly formed monazite grains that crystallised from juvenile silicate melts. Ages of this group are interpreted as crystallisation ages of leucosomes after a major partial-melting event that affected the whole domain. The last ca. 320 Ma group corresponds to rim-domains of monazite crystals. It is interpreted as the emplacement age of most of the large-scale granite massifs and therefore fixes the end of the partial-melting event. The inception and drastic generalisation of partial-melting at peak-P conditions therefore coincides with a major change in the tectonic regime recorded at regional-scale. In the lights of these results, this implies that (1) either continuous stacking of continental

  14. Early Silurian (~ 440 Ma) adakitic, andesitic and Nb-enriched basaltic lavas in the southern Altay Range, Northern Xinjiang (western China): Slab melting and implications for crustal growth in the Central Asian Orogenic Belt

    Science.gov (United States)

    Shen, Xiao-Ming; Zhang, Hai-Xiang; Wang, Qiang; Ma, Lin; Yang, Yue-Heng

    2014-10-01

    As an important part of the Central Asian Orogenic Belt (CAOB), the Altay Range contains large-scale Paleozoic magmatic rocks. However, owing to the lack of precise age constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area have been controversial, which has led to the debate on Phanerozoic crustal growth mechanisms and accretionary orogenic processes in the CAOB. Herein, we report geochronological and geochemical data of the Suoerkuduke adakitic, andesitic and Nb-enriched basaltic (NEB) lavas in the southern margin of the southern Altay Range. LA-ICP-MS zircon U-Pb analyses for five adakitic, andesitic and NEB samples indicate that they were coevally generated in the Early Silurian (~ 440 Ma). The adakites and basaltic andesites are geochemically characterized by high Na2O/K2O, Sr/Y, Al2O3, Sr, εNd(t) and zircon εHf(t) values and relatively low (87Sr/86Sr)i ratios. The NEBs are sodium-rich and have higher TiO2, P2O5, Zr, Nb, and Nb/U values than those of typical arc basalts. They also have positive εNd(t) values and positive and variable zircon εHf(t) values. We suggest that the Suoerkuduke adakites were derived by a partial melting of the subducted oceanic crust with minor overlying sediments, and the continuous compositional variations between adakites and basaltic andesites confirm that the interaction between slab melts and mantle peridotite played an important role in the formation of basaltic andesites. The associated NEBs were possibly generated by a partial melting of mantle wedge peridotites metasomatized by slab-derived adakitic melts and minor fluids. In combination with the occurrence of voluminous Silurian-Devonian granitoids, coeval ophiolite mélanges, and a series of intra-arc basins, a slab window model triggered by slab tearing is proposed to account for the formation of the Suoerkuduke adakite-basaltic andesite-NEB suites. The upwelling of the asthenospheric mantle through the slab window probably caused

  15. Geochemistry, zircon U-Pb ages and Sr-Nd-Hf isotopes of an Ordovician appinitic pluton in the East Kunlun orogen: New evidence for Proto-Tethyan subduction

    Science.gov (United States)

    Xiong, Fuhao; Ma, Changqian; Wu, Liang; Jiang, Hong'an; Liu, Bin

    2015-11-01

    Appinite is commonly derived from a mantle source in subduction zones and thus holds a key to constrain the tectonic evolution of ancient orogens. This study presents chronological, mineralogical and geochemical data for one appinitic pluton from the south Tethyan suture zone in the East Kunlun orogen, Northern Tibetan Plateau. The pluton is predominantly composed of hornblende-rich mafic appinites, with minor amounts of granodiorite. Zircon U-Pb age of the granodiorite (466 Ma) is identical to the mafic appinites (447-450 Ma). The mafic appinites are commonly hornblende diorites, which comprise large amounts of magnesio-hornblende [Mg/(Fe + Mg) = 0.61-0.68] and andesine (An43-54). The hornblende diorites have low contents of SiO2 (48.62-54.95 wt.%), high contents of total FeO (7.90-12.84 wt.%) and MgO (4.32-11.89 wt.%) and moderate values of Mg# [Mg# = molar 100 ∗ Mg/(Mg + Fe); 49-69]. Their geochemistry displays: slight enrichment of light rare earth elements ((La/Yb)N = 1.89-6.84) and flat heavy rare earth elements ((Ga/Yb)N = 1.49-2.22); enrichment in large ion lithophile elements and depletion in high field strength elements; less-enriched isotopic compositions with initial 87Sr/86Sr ratios of 0.70536-0.70617, εNd(t) of 0.79-3.02 and zircon εHf(t) of 8.73-12.82. The associated granodiorites comprise plagioclase (45-50 vol.%, An = 26-39), quartz (15-20 vol.%), K-feldspar (5-10 vol.%), ferrohornblende [2-5 vol.%, (Mg/(Fe + Mg) = 0.45-0.49] and epidote (1-5 vol.%). The epidotes have pistacite components ranging from 23 to 28. The granodiorites exhibit calc-alkaline character, and have rare earth and trace element patterns similar to the hornblende diorites. The geochemical compositions and simulations suggest that the parental magma of the mafic appinites was generated by partial melting of one depleted mantle source which was metasomatised by subducted sediment-derived felsic melts (ca. 20-25%). Fractional crystallization of clinopyroxene, hornblende

  16. Mineral potential tracts for orogenic, Carlin-like, and epithermal gold deposits in the Islamic Republic of Mauritania, (phase V, deliverable 69): Chapter H in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

    Science.gov (United States)

    Goldfarb, Richard J.; Marsh, Erin; Anderson, Eric D.; Horton, John D.; Finn, Carol A.; Beaudoin, Georges

    2015-01-01

    The gold resources of Mauritania presently include two important deposits and a series of poorly studied prospects. The Tasiast belt of deposits, which came into production in 2007, is located in the southwestern corner of the Rgueïbat Shield and defines a world-class Paleoproterozoic(?) orogenic gold ore system. The producing Guelb Moghrein deposit occurs along a shear zone in Middle Archean rocks at the bend in the Northern Mauritanides and is most commonly stated to be an iron oxide-copper-gold (IOCG) type of deposit, although it also has some important characteristics of orogenic gold and skarn deposits. Both major deposits are surrounded by numerous prospects that show similar mineralization styles. The Guelb Moghrein deposit, and IOCG deposit types in general are discussed in greater detail in a companion report by Fernette (2015). In addition, many small gold prospects, which are probably orogenic gold occurrences and are suggested to be early Paleozoic in age, occur along the length of Southern Mauritanides. Existing data indicate the gold deposits and prospects in Mauritania have a sulfide assemblage most commonly dominated by pyrrhotite and chalcopyrite, and have ore-related fluids with apparently high salinities.

  17. Mechanical Initiation and Propagation Mechanism of a Thrust Fault: A Case Study of the Yima Section of the Xiashi-Yima Thrust (North Side of the Eastern Qinling Orogen, China)

    Science.gov (United States)

    Cai, Wu; Dou, Linming; Li, Zhenlei; He, Jiang; He, Hu; Ding, Yanlu

    2015-09-01

    Thrust faults exist extensively in nature, and their activities often cause earthquakes and disasters involving underground engineering, such as the May 12, 2008 Wenchuan Earthquake; the April 20, 2013 Ya'an Earthquake; and the Nov. 3, 2011 Yima Qianqiu Coal-Mining Accident in China. In this paper, the initiation and propagation of a thrust are discussed from a mechanical viewpoint using fault mechanics and fault-slip analysis, taking as an example the Yima section of the Xiashi-Yima thrust (north side of the eastern Qinling Orogen, China). The research primarily focuses on the stress field and the formation trajectory of the thrust and the genesis of the large-scale inversion thrust sheet. The results show that the thrust results from failures in the compressive deformation state and that its stress state is entirely compressive shear. The rupture trajectory of the thrust develops upward, and the fault fracture zone forms similarly to a listric fault, up-narrow and down-wide. The model results and the genesis of the large-scale inversion thrust sheet are consistent with in situ exploration observations. This investigation can be extended to other thrust faults with similar characteristics, particularly for the design of mining operations in tectonic-active areas. Moreover, this research can be used to further study the mechanism of thrust faults and provide support for the feasibility of using fault-slip analysis to assess fault stability.

  18. Geochemistry and geochronology of late Mesozoic volcanic rocks in the northern part of the Eastern Pontide Orogenic Belt (NE Turkey): Implications for the closure of the Neo-Tethys Ocean

    Science.gov (United States)

    Özdamar, Şenel

    2016-04-01

    This paper presents 40Ar/39Ar and U-Pb age data, Sr-Nd isotopes, whole-rock and mineral compositions of Upper Cretaceous volcanic rocks from the Ordu area of the Eastern Pontide Orogenic Belt (EPOB) in northeastern Turkey. The volcanic rocks exhibit a wide compositional range: basalt, basaltic-andesites, andesites and a rhyodacite suite; they are characterized by subparallel light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with Eu anomalies and moderate fractionation [average (La/Yb)N = 8.55]. The geochemical results show that the volcanic rocks have calc-alkaline affinity consistent with arc volcanic rocks erupted in an active continental margin. Initial 87Sr/86Sr values vary between 0.70569 and 0.70606, while initial 143Nd/144Nd values lie between 0.51244 and 0.51249. Crustal contamination affected the mantle-originated primary magma, as indicated by increased 87Sr/86Sr and decreased 143Nd/144Nd ratios with increasing SiO2. New precise laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) 206Pb-238U age analyses of zircon and 40Ar/39Ar age data of plagioclase from the volcanics enable a more precise reconstruction of the EBOP. The ages provide insight into the timing of arc formation in this region, constrain the volcanic activity between 86 My (Coniacian) and 75 My (Campanian) and constrain the timing of closure of the Neo-Tethys.

  19. Syn-collisional adakitic granodiorites formed by fractional crystallization: Insights from their enclosed mafic magmatic enclaves (MMEs) in the Qumushan pluton, North Qilian Orogen at the northern margin of the Tibetan Plateau

    Science.gov (United States)

    Chen, Shuo; Niu, Yaoling; Li, Jiyong; Sun, Wenli; Zhang, Yu; Hu, Yan; Shao, Fengli

    2016-04-01

    The Qumushan (QMS) syn-collisional granodiorite, which is located in the eastern section of the North Qilian Orogen at the northern margin of the Greater Tibetan Plateau, has typical adakitic characteristics and also contains abundant mafic magmatic enclaves (MMEs). This recognition offers an unprecedented insight into the petrogenesis of both the adakitic host granodiorite and the enclosed MMEs. The MMEs and their host granodiorites share many characteristics in common, including identical crystallization age (~ 430 Ma), same mineralogy, similar mineral chemistry and whole-rock isotopic compositions, indicating their genetic link. The MMEs are most consistent with being of cumulate origin formed at earlier stages of the same magmatic system that produced the QMS adakitic granodiorite. Subsequent replenishment of adakitic magmas could have disturbed the cumulate piles as "MMEs" dispersed in the adakitic granodiorite host during emplacement. The geochemical data and petrogenetic modeling of trace elements suggest that the QMS adakitic host granodiorite is most consistent with fractional crystallization dominated by the mineral assemblage of the MMEs. The parental magma for the QMS granodiorite is best explained as resulting from partial melting of the ocean crust together with recycled terrigenous sediments during continental collision, which may have also experienced interaction with mantle peridotite during ascent.

  20. Mineral chemistry and geochemistry of the Late Neoproterozoic Gabal Abu Diab granitoids, Central Eastern Dessert, Egypt: Implications for the origin of rare metal post-orogenic A-type granites

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Ahmed, Awaad F.; Mohamed, Haroun A.

    2015-04-01

    within A-type granite worldwide. According to Zhang et al., 2012, the garnet crystallized at the expense of biotite from the MnO-rich evolved melt after fractionation of biotite, plagioclase, K-feldspar, zircon, apatite, and ilmenite. The granitoids are alkali feldspar granites showing distinct geochemical features and most likely, belong to the post-orogenic younger Egyptian granitoids. They are peraluminous A-type alkaline rocks but they have lower Fe2O3, MgO, MnO, CaO, TiO2, P2O5, Sr, Ba, V, and higher SiO2, Na2O, K2O, Nb, Ta, U, Zr, Th, Ga/Al and Rb than the typical rocks of this type. The positive correlation between Ba and Sr, and the negative correlation between Rb and K/Rb reveal fractional crystallization of alkali feldspar. The similarity in most geochemical characteristics suggests that Abu Diab granitoids are genetically related to each other and extremely enrichment in incompatible elements such as Nb and Ta, indicating that they crystallized from extremely differentiated magmas. References: Zhang, J., Ma, C. and She, Z., 2012. An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen, central China: Petrological, mineralogical and geochemical constraints. Geoscience Frontiers 3 (5), 635-646.

  1. 天山造山带深部探测及地球动力学研究进展%Deep probe in the Tianshan orogenic belt and its geodynamics

    Institute of Scientific and Technical Information of China (English)

    雷显权; 陈运平; 赵俊猛; 赵炯洋

    2012-01-01

    In order to study the geodynamics of the Tianshan orogenic belt (TOB), a large amount of works for probing the deep structure of the TOB have been conducted in this area since 1970s, and abundant achievements have been acquired. The purpose of this paper is to summarize these works and achievements. The study results show that; The crust of the TOB is relatively thicker and there is not a clear mountain root. The crustal structure is characterized by the vertically layering and the laterally blocking. The crust-mantle boundary is not clear and the Moho is dislocated beneath the basin-range junction zones. The low-velocity anomalies commonly existing in the crustal interior and the relatively higher crustal Possion's ratio imply the mechanical weakness of the crust Velocity anomalies also exist in the upper mantle, the low ones are likely to be related to the upwelling of the hot mantle materials and the high ones may be the lithospheric detachment fragments of the age-old plates. The dislocation of the Moho, the Q-value structure and the velocity anomalies can be interpreted by the underthrusting of the stable rigid geological blocks to the TOB from the south and the north, and this interpretion is also evidenced by the high-resolutional tomographic images. The shear wave splitting results imply that the upper mantle involved in the orogen movement is considerablely thick. The above knowledge suggests that the deformation and the uplift of the TOB are resulted from the combined actions of the tectonic compression of the southern and northern stable blocks and the complex crust-mantle coupling.%为了研究天山造山带的地球动力学,自1970年代以来,国内外在天山造山带开展了大量的深部探测工作,并取得了丰富的成果,本文对这些工作和成果进行了梳理和综述.已有研究结果表明:天山造山带的地壳厚度较大,但并无明显山根;地壳结构具有垂向分层和横向分块特征;壳幔界面不清晰,

  2. Early Silurian (~ 440 Ma) adakites and high-Nb basaltic rocks in the southern Altay Range (Northern Xinjiang): Slab melting and implications for crustal growth in the Central Asian Orogenic Belt

    Science.gov (United States)

    Shen, X.; Zhang, H.; Wang, Q.; Ma, L.

    2012-12-01

    As an important part of the Central Asian Orogenic Belt (CAOB), the Altay Range contain large-scale Paleozoic magmatic rocks. However, owing to lack of precise age constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area have been controversial, which cause the debate on Phanerozoic crustal growth mechanism and accretionary orogenic processes in CAOB. Here we report geochronological and geochemical data of the Suoerkuduke adakites and associated high-Nb basaltic rocks in the southern margin of the southern Altay Range. LA-ICP-MS zircon U-Pb isotopic data for five adakite and high-Nb basaltic rock samples indicate that they were generated in the Early Silurian (~ 440 Ma). The adakites are geochemically characterized by high Na2O/K2O (1.3 to 16.7), Sr/Y (21 to 117), Al2O3 (13.0 to 18.3 wt.%), Sr (405 to 1813 ppm), ɛNd(t) (+3.6 to +6.5) and zircon ɛHf(t) (+10.8 to +18.9) values and relatively low (87Sr/86Sr)i ratios (0.7046 to 0.7049). The high-Nb basaltic rocks are sodium-rich (Na2O/K2O = 1.5-5.5) and have higher TiO2 (2.99 to 3.49 wt.%), P2O5 (1.09 to 1.56 wt.%), Zr (335 to 431 ppm), Nb (17.7 to 20.9 ppm), and Nb/U (11.7 to 30.2) values than those of typical arc basalts. They also have positive ɛNd(t) values (+5.4 to +8.4) and positive and variable zircon ɛHf(t) values (+0.71 - +16.9). We suggest that the Suoerkuduke adakites were derived by partial melting of subducted oceanic crust with minor overlying sediments, and the high-Nb basaltic rocks were possibly generated by partial melting of mantle wedge peridotite metasomatized by slab-derived adakitic melts and minor fluids. In combination with the occurrence of voluminous Silurian-Devonian granitoids, coeval ophiolite mélanges, and a series of intra-arc basins, a slab window model triggered by slab tearing or breakoff is proposed to interpret the formation of the Suoerkuduke adakite and high-Nb basaltic rock suites. The upwelling of asthenospheric mantle through the slab window

  3. K-Ar dating of late Mesozoic volcanism and geochemistry of volcanic gravels in the North Huaiyang Belt, Dabie orogen: Constraints on the stratigraphic framework and exhumation of the northern Dabie orthogneiss complex

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Two eruption episodes are identified through systematic field investigations and K-Ar dating of the lateMesozoic volcanic rocks in the North Huaiyang belt (NHB),Dabie orogenic belt, of which the earlier volcanic suitetermed Maotanchang Fm. (Fm.) occurring at Jinzhai,Xianhualing and Maotanchang, etc., was erupted from 149Ma to 138 Ma. The other named Xiaotian Fm. mainly dis-tributed at Xiaotian, Shucheng, etc., was formed between132 Ma and 116 Ma. During the eruption gap of the two vol-canic suites deposited a volcano-sedimentary conglomeratelayer, which are composed of the multi-compositional gravels, including the North Dabie orthogneiss complex (NDOC),volcanic gravels, etc. These volcanic gravels in the con-glomerate layer show identical geochemical and isotopic compositions (87Sr/86Sr(t) =0.7084-0.7092, (Nd (t) = 21.8-24.4) to the Maotanchang Fm. volcanic rocks (87Sr/86Sr = 0.7086-0.7102, (Nd = 19.2-24.4), but significantly distinct from those of Xiaotian Fm. (87Sr/86Sr = 0.7076-0.7084, (Nd = 17.2 - 19.2). K-Ar dating results of its underlying andoverlying volcanic sequences indicate that the conglomerate layers were deposite d at ~135 Ma. This suggests that the NDOC was rapidly exhumed to the surface dur ing or shortly before ~135 Ma and became the important provenance of the late Me sozoic volcano-sedimentary basins in the NHB. In combination with the regional v olcano-sedimentary correlation, we divided the Mesozoic stratigraphic sequence i n the NHB from base to top into Fanghushan Fm. (>160 Ma), Yuantongshan Fm. (/mid dle- lower segment of Sanjianpu Fm.) (160-149 Ma), Maotanchang Fm. (/Zhougongsh an Fm./upper segment of Sanjianpu Fm./Fenghuangtai Fm.) (149-135 Ma) and Xiaoti an Fm. (/Baidafan Fm./Heshidu Fm.) (135-116 Ma).

  4. Gold and uranium metallogenesis in the framework of Neo-proterozoic crust growth and differentiation: example of the Mayo-Kebbi Massif (Chad) in the Central Africa Orogenic belt

    International Nuclear Information System (INIS)

    The Mayo Kebbi massif located in southwestern Chad between the Congo craton in the South, the West African craton in the west and the Sahara meta-craton to the east exposes a segment of Neo-proterozoic juvenile crust accreted in the Central African orogenic belt during the Pan African orogeny. It consists of two greenstone belts (Zalbi and Goueygoudoum) separated by the May Kebbi calc-alkaline batholith complexes and intruded by calc-alkaline high-K granitic plutons. The whole is covered by Phanerozoic sedimentary formations. The greenstone belts contain sulphide zones hosted mainly by meta-plutonic rocks (granodiorites) and meta-basalts and meta-volcaniclastics. The mineralization comprises pyrite, pyrrhotite, arsenopyrite, chalcopyrite, pentlandite, pentlandite silver, pentlandite cobaltiferous, sphalerite, cobaltite. These sulphides are disseminated, aggregated in form of layers or are filling veins and cracks. The greenstones also contain quartz veins with calcite and chlorite comprising a mineralization made of pyrite, chalcopyrite, galena and gold. Gold is present both as native crystals and as electrum. The high-K calc-alkaline Zabili granitic pluton hosts uranium mineralization related to a superposition of: (1) ductile deformation and metasomatic alteration implying the interaction between magmatic minerals with a Na-rich fluid, of potential magmatic origin, coeval to the main deposition of uranium oxides, followed by (2) brittle deformation and deposition of secondary hydrated uranium silicates involving a Na-Ca-rich fluid. We propose that these uranium mineralizations represent the extreme expression of crustal differentiation as a result of Pan-African reworking of a Neo-proterozoic juvenile crustal segment. (author)

  5. Anticlockwise P-T evolution at ∼280 Ma recorded from ultrahigh-temperature metapelitic granulite in the Chinese Altai orogenic belt, a possible link with the Tarim mantle plume?

    Science.gov (United States)

    Tong, Laixi; Xu, Yi-Gang; Cawood, Peter A.; Zhou, Xin; Chen, Yibing; Liu, Zhao

    2014-11-01

    An ultrahigh-temperature (UHT) metapelitic granulite assemblage consisting of garnet(g)-spinel(sp)-orthopyroxene(opx)-sillimanite(sil)-cordierite(cd)-ilmenite(ilm)-biotite(bi)-plagioclase(pl)-quartz(q) occurs within migmatitic paragneiss near Kalasu in the Chinese Altai, NW China. Textural relations, mineral compositions and P-T estimates, indicate three stages of mineral assemblages: (1) pre-peak prograde stage (M1) consisting of a sp-sil-bearing or sp-opx-bearing inclusion assemblage, with low-Al2O3 contents (4-5 wt.%) in orthopyroxene and P-T conditions of ∼7 kbar and ∼890 °C, (2) peak UHT stage (M2) comprising a g-opx-cd-bearing coarse-grained assemblage, with high-Al2O3 contents (8-9 wt.%) in orthopyroxene and peak conditions of ∼8 kbar and ∼970 °C, and (3) post-peak HT stage (M3) containing an oriented opx-bi-sil-bearing assemblage in matrix, with moderate amounts of Al2O3 (6-7 wt.%) in orthopyroxene and P-T conditions of 8-9 kbar and ∼870 °C. The three discrete stages define an anticlockwise P-T path involving initial prograde heating and post-peak near isobaric cooling. Such a near isobaric cooling anticlockwise P-T path suggests that UHT metamorphism likely occurred in an overall extensional tectonic setting with associated underplating of mantle-derived mafic magma. A SHRIMP zircon U-Pb age of 278 ± 2 Ma obtained from the metapelitic granulite indicates UHT metamorphism in the Altai orogen occurred during the Permian, coeval with spacially associated mantle-derived mafic intrusions (∼280 Ma) and the Tarim mantle plume (∼275 Ma). Thus, the Permian UHT metamorphism of the Chinese Altai is likely associated with underplating and heating of mantle-derived mafic magma as a result of the Tarim mantle plume.

  6. Monazite U-Th-Pb EPMA and zircon U-Pb SIMS chronological constraints on the tectonic, metamorphic, and thermal events in the inner part of the Variscan orogen, example from the Sioule series, French Massif Central

    Science.gov (United States)

    Do Couto, Damien; Faure, Michel; Augier, Romain; Cocherie, Alain; Rossi, Philippe; Li, Xian-Hua; Lin, Wei

    2016-03-01

    In the northern Variscan French Massif Central, the Sioule metamorphic series exposes from top to bottom the tectonic superposition of the Upper Gneiss Unit (UGU), Lower Gneiss Unit (LGU), and Para-autochthonous Unit (PAU). The nappe stacking developed throughout two prograde syn-metamorphic events: D1 is a top-to-the-SW shearing coeval with a probable Devonian migmatization and D2 is a top-to-the-NW shearing event. Both events were completed before the unconformable deposition of the undeformed and unmetamorphosed "Tufs anthracifères" formation, dated at ca 330 Ma (Late Visean). Furthermore, the UGU experienced a high-pressure metamorphism ascribed to a D0 event during which eclogite or granulite crystallized in several parts of the UGU. Monazite U-Th-Pb and zircon U-Pb SIMS datings were carried out in order to constrain the ages of these D0, D1, and D2 tectono-metamorphic events. These new geochronological results are placed in a P-T-t diagram constructed for the UGU, LGU, and PAU. Monazite sampled in UGU, LGU, and PAU rocks yields similar 365-350 Ma ages consistent with the D2 event dated in other places of the French Massif Central. A zoned monazite grain from a granulitic paragneiss yields 416 ± 15 and 362 ± 14 Ma ages interpreted as those of the D0 and D2 events, respectively. Zircon from the same granulitic paragneiss yields SIMS ages at 343 ± 2 and 328 ± 2 Ma that are interpreted as recrystallization processes associated with post-thickening thermal events, possibly recording the onset of orogenic collapse of the Northern Massif Central. It is worth to note that neither monazite nor zircon recorded the D1 event.

  7. ‘Indicator’ carbonaceous phyllite/graphitic schist in the Archean Kundarkocha gold deposit, Singhbhum orogenic belt, eastern India: Implications for gold mineralization vis-a-vis organic matter

    Indian Academy of Sciences (India)

    P R Sahoo; A S Venkatesh

    2014-10-01

    Carbonaceous rocks in the form of graphitic schist and carbonaceous phyllite are the major host rocks of the gold mineralization in Kundarkocha gold deposit of the Precambrian Singhbhum orogenic belt in eastern India. The detection of organic carbon, essentially in the carbonaceous phyllite and graphitized schist within the Precambrian terrain, is noted from this deposit. A very close relationship exists between gold mineralization and ubiquitous carbonaceous rocks containing organic carbon that seems to play a vital role in the deposition of gold in a Precambrian terrain in India and important metallogenetic implications for such type of deposits elsewhere. However, the role played by organic matter in a Precambrian gold deposit is debatable and the mechanism of precipitation of gold and other metals by organic carbon has been reported elsewhere. Fourier transform infrared spectroscopy (FTIR) results and total organic carbon (TOC) values suggest that at least part of the organic material acted as a possible source for the reduction that played a significant role in the precipitation of gold. Lithological, electron probe analysis (EPMA), fluid inclusions associated with gold mineralization, Total Carbon (TC), TOC and FTIR results suggest that the gold mineralization is spatially and genetically associated with graphitic schist, carbonaceous phyllite/shale that are constituted of immature organic carbon or kerogen. Nano-scale gold inclusions along with free milling gold are associated with sulfide mineral phases present within the carbonaceous host rocks as well as in mineralized quartz-carbonate veins. Deposition of gold could have been facilitated due to the organic redox reactions and the graphitic schist and carbonaceous phyllite zone may be considered as the indicator zone.

  8. Dynamic of an intra-continental orogenic prism: thermo-chronologic (apatite fission tracks) and tectonic evolution of the axial zone and the piedmont of the west-central Pyrenees

    International Nuclear Information System (INIS)

    This work illustrates the application of thermo chronology to the study of the following geologic issue: the tectonic evolution of the Pyrenean oncologic prism. Thermo-chronology gives information on the vertical movements at the scale of geological eras. Thermo-chronology is based on the following principle: the decay of a nucleus gives birth to a daughter nucleus. Above a specific temperature named closure temperature, the daughter element can diffuse outside the system while below the closure temperature, diffusion is not possible. Consequently thermo-chronology can be considered to date the moment when a mineral goes below a a specific closure temperature. Minerals have different closure temperatures and so by using a suite of thermo-chronometers on a single sample, its cooling path through the crust can be reconstructed. This work focuses on apatite fission track (AFT)analysis which is a low temperature thermo-chronometer. In apatites the temperature range between 60 and 120 Celsius degrees corresponds to the partial annealing zone. The spontaneous fission of one U238 nucleus entails the formation of one fission track. The determination of the initial quantity of U238 is based on the natural steady ratio U238/U235 which equals 137.88. The initial quantity of U235 is determined through the neutron irradiation of the sample. The knowledge of the initial quantity of U238 and the number of tracks in the sample allows the dating of the sample. In this work we combine AFT thermo- chronology with a detailed structural analysis to describe vertical movements related to the thrusting system evolution, and to determine the influence of the latter on the sedimentation/burial/exhumation cycle of the syn-orogenic deposits of the southern fore-land basin

  9. Late Permian high-Mg andesite and basalt association from northern Liaoning, North China: Insights into the final closure of the Paleo-Asian ocean and the orogen-craton boundary

    Science.gov (United States)

    Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Lu, Yinghuai; Zong, Keqing

    2016-08-01

    High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U-Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO2 contents ranging from 48.7 to 63.2 wt.%, high Mg# values of 63-75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87Sr/86Sr ratios of 0.70417-0.70457, εNd(t) values from - 0.4 to 5.0, and εHf(t) values from 5.1 to 11, as well as zircon εHf(t) values from - 9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker-Xra Moron-Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian-Early Triassic.

  10. Geochronology, geochemistry, and deformation history of Late Jurassic-Early Cretaceous intrusive rocks in the Erguna Massif, NE China: Constraints on the late Mesozoic tectonic evolution of the Mongol-Okhotsk orogenic belt

    Science.gov (United States)

    Tang, Jie; Xu, Wen-Liang; Wang, Feng; Zhao, Shuo; Li, Yu

    2015-09-01

    This paper presents new zircon and sphene U-Pb ages, biotite and hornblende 40Ar/39Ar ages, Hf isotopic data, and geochemical data for five Mesozoic plutons in the Erguna Massif of NE China. These data are used to constrain the late Mesozoic tectonic evolution of the Mongol-Okhotsk orogenic belt. This new dating, when combined with previously published ages, indicates that the Late Jurassic-Early Cretaceous (J3-K1) intrusive rocks can be subdivided into three stages that represent periods of magmatism during the Late Jurassic (~ 155 Ma), early Early Cretaceous (~ 137 Ma), and late Early Cretaceous (~ 123 Ma). In addition, the rocks have undergone later deformation recorded by peak ages of ~ 137 and ~ 123 Ma. The Late Jurassic and early Early Cretaceous intrusive rocks in the study area are dominantly syenogranites and are either A-type granites or are classified as alkaline series, suggesting that they formed in an extensional environment. The late Early Cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment, along with coeval bimodal volcanics. These data, combined with the presence of regional unconformities in the northern part of Hebei Province and western part of Liaoning Province, and the spatial distribution of coeval volcanic rocks in NE China, suggest the Late Jurassic and early Early Cretaceous magmatisms and the early Early Cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the Mongol-Okhotsk Ocean. In comparison, the late Early Cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the Mongol-Okhotsk tectonic regime or the subduction of the Paleo-Pacific Plate, or the combined influence of these two tectonic regimes.

  11. Calcite Twins, a Tool for Tectonic Studies in Thrust Belts and Stable Orogenic Forelands Les macles de la calcite, un outil pour les études tectoniques dans les chaînes plissées et les avant-pays peu déformés des orogènes

    Directory of Open Access Journals (Sweden)

    Lacombe O.

    2010-10-01

    Full Text Available Calcite twins have been used for a long time as indicators of stress/strain orientations and magnitudes. Recent developments during the last 15 years point toward significant improvements of existing techniques as well as new applications of calcite twin analysis in thrust belts and forelands. This paper summarizes the principles of the most common techniques in this tectonic field and illustrates some aspects of the use of calcite twins to constrain not only stress/strain orientations and magnitudes, but also to some extent paleotemperature or paleoburial in orogenic forelands. This review is based in a large part on the studies that I conducted in various geological settings such as the forelands of Taiwan, Pyrenees, Zagros, Rockies and Albanides orogens. The contribution of calcite twin analysis to the understanding of the intraplate stress transmission away from plate boundaries is also emphasized. Les macles de la calcite sont utilisees depuis longtemps comme indicateurs de paleocontraintes et comme marqueurs de la deformation finie, en orientations comme en grandeurs. Au cours des 15 dernieres annees, des ameliorations importantes des methodes d’analyses existantes ont ete realisees et ont donne lieu a de nouvelles applications dans les chaines plissees et les avant-pays peu deformes des orogenes. Cet article resume le principe des methodes les plus utilisees en tectonique et illustre quelques apports de l’analyse des macles de la calcite pour la caracterisation non seulement des orientations et des grandeurs des paleocontraintes et de la deformation finie, mais egalement dans une certaine mesure de la paleotemperature et du paleoenfouissement. Cette revue se fonde en grande partie sur les etudes regionales que j’ai effectuees dans des contextes geologiques varies, comme les avant-pays des chaines de Taiwan, des Pyrenees, du Zagros, des Rocheuses et des Albanides. Cet article discutera egalement la contribution de l’etude des

  12. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Structural analysis of the northern Nagssugtoqidian orogen, West Greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains

    Directory of Open Access Journals (Sweden)

    Mazur, Stanislaw

    2006-12-01

    Full Text Available Structural analysis of the deeply eroded northern flank of the Palaeoproterozoic Nagssugtoqidian orogen shows marked regional variations in both the orientation and type of fabrics, as is characteristic of Precambrian high-grade terrains subjected to polyphase deformation. Here we investigate the relationship between strain, metamorphic grade, and the resulting structural patterns. The study area south of Aasiaat in West Greenland consists of amphibolite- togranulite-gradeArchaean orthogneisses and relatively thin supracrustal units. The regional foliation displays a WSW–ENE to SW–NE strike associated with steep to moderate dips towards the WNW or SSE. Lineation trends are WSW–ENE and generally plunge gently towards the WSW. Mesoscopic fold hinges are usually colinear with the regional lineation. A systematic change in the plunge of lineations occurs across the south-western part of the study area. Towards the south, the lineation plunge progressively increases, despite the generally uniform strike of foliation. This southward increase of lineation pitch is typically associated with the transition from L > S or L = S shape fabrics in rocks characterised by a low pitch, to S > L or S fabrics in the zone of moderate to high pitch. The structural patterns point to subdivision of the study area into a southern domain mostly characterised by S or S > L shape fabrics and a moderate to high angle of lineation pitch, and a northern domain showing L > S or L = S fabrics and low angles of lineation pitch. This subdivision corresponds well with the map scale boundary between granulite facies rocks in the south and amphibolite facies rocks farther north. The observed structural pattern may be explained by two alternative tectonic models: (1 northward indentation of the previously cooled granulite block into the rheologically weaker amphibolite domain, and (2 strain partitioning within a mid-crustal transpression zone. In model 2 the northern domain

  13. Geochronology and geochemistry of early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China: Implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

    Science.gov (United States)

    Wang, Zhi-wei; Xu, Wen-liang; Pei, Fu-ping; Wang, Feng; Guo, Peng

    2016-09-01

    This paper presents new zircon U-Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China, in order to constrain the early Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB). Zircon U-Pb dating indicates that early Paleozoic magmatic events within the northern Songnen-Zhangguangcai Range Massif (SZM) can be subdivided into four stages: Middle Cambrian (~ 505 Ma), Late Cambrian (~ 490 Ma), Early-Middle Ordovician (~ 470 Ma), and Late Ordovician (460-450 Ma). The Middle Cambrian monzogranites are K-rich, weakly to strongly peraluminous, and characterized by pronounced heavy rare earth element (HREE) depletions, high Sr/Y ratios, low Y concentrations, low primary zircon εHf(t) values (- 6.79 to - 1.09), and ancient two-stage model (TDM2) ages (1901-1534 Ma). These results indicate derivation from partial melting of thickened ancient crustal materials that formed during the amalgamation of the northern SZM and the northern Jiamusi Massif (JM). The Late Cambrian monzonite, quartz monzonite, and monzogranite units are chemically similar to A-type granites, and contain zircons with εHf(t) values of - 2.59 to + 1.78 and TDM2 ages of 1625-1348 Ma. We infer that these rocks formed from primary magmas generated by partial melting of Mesoproterozoic accreted lower crustal materials in a post-collisional extensional environment. The Early-Middle Ordovician quartz monzodiorite, quartz monzonite, monzogranite, and rhyolite units are calc-alkaline, relatively enriched in light REEs (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), depleted in HREEs and high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), and contain zircons with εHf(t) values of - 7.33 to + 4.98, indicative of formation in an active continental margin setting. The Late Ordovician alkali-feldspar granite and rhyolite units have A-type granite affinities that suggest they formed in

  14. Petrogenesis, zircon U–Pb age, and geochemistry of the A-type Mogou syenite, western Henan Province: Implications for Mesozoic tectono-magmatic evolution of the Qinling Orogen

    Indian Academy of Sciences (India)

    Xinyu He; Jionghui Wang; Changming Wang; Emmanuel John M Carranza; Liang Chen; Bin Wu

    2016-04-01

    The Mogou syenite intruded into the Mesoproterozoic Xiong’er Group is the main lithostratigraphic unit, along the southern margin of the North China Craton (NCC). This paper reports zircon LAICP-MS data, whole-rock major and trace element compositions of late Triassic magmatic rocks in the Mogou syenite, in order to constrain the formation age of the Mogou syenite, research the origin and evolution of the magma and analyse the geodynamic setting of the Qinling Orogen (QO) in Late Triassic. These rocks consist of medium- to coarse-grained syenite and fine-grained quartz syenite. Zircon U–Pb dating yields a crystallization age of 226.5±2.7 Ma. The syenites are characterized by highSiO_2 (63.49–72.17%), alkali (K_2O+Na_2O of 11.18–15.38%) and potassium (K_2O/Na_2O of 2.88–28.11), are peralkaline or metaluminous (molar A/CNK of 0.87–1.02) and belong to shoshonite series. The syenites have ΣREE of 33.01–191.30 ppm, LREE/HREE of 14–20, (La/Yb)N of 11–24, with LREE-richdistribution pattern and obvious differentiation between HREE and LREE. Eu anomalies are positive for the medium- to coarse-grained syenite and weakly negative for the fine-grained quartz syenite. In addition, the syenites are enriched in large-ion lithophile elements (Ba, K, Sr, and Pb) but depleted inhigh strength field elements (Ti, Ta, Nb, Zr, and Hf), and have high differentiation indices of 91.69–97.06. These geochemical features indicate that the primary magma of the Mogou syenite most likely originated from a mantle source with minor crustal component, and underwent a fractional crystallizationprocess during its emplacement. The late Triassic A-type Moguo syenite along the southern margin of the NCC was generated in the late stage of the syn-collision event of QO, recording a transition periodfrom compression to extension at around 227 Ma.

  15. Timing, petrogenesis and tectonic setting of the Late Paleozoic gabbro-granodiorite-granite intrusions in the Shalazhashan of northern Alxa: Constraints on the southernmost boundary of the Central Asian Orogenic Belt

    Science.gov (United States)

    Shi, Xingjun; Wang, Tao; Zhang, Lei; Castro, Antonio; Xiao, XuChang; Tong, Ying; Zhang, Jianjun; Guo, Lei; Yang, Qidi

    2014-11-01

    The Late Paleozoic tectonic setting and location of the southernmost boundary of the Central Asian Orogenic Belt (CAOB) with respect to the Alxa Block or Alxa-North China Craton (ANCC) are debated. This paper presents new geochronological, petrological, geochemical and zircon Hf isotopic data of the Late Paleozoic intrusions from the Shalazhashan in northern Alxa and discusses the tectonic setting and boundary between the CAOB and ANCC. Using zircon U-Pb dating, intrusions can be broadly grouped as Late Carboniferous granodiorites (~ 301 Ma), Middle Permian gabbros (~ 264 Ma) and granites (~ 266 Ma) and Late Permian granodiorites, monzogranites and quartz monzodiorites (254-250 Ma). The Late Carboniferous granodiorites are slightly peraluminous and calcic. The remarkably high zircon Hf isotopes (εHf(t) = + 6-+ 10) and characteristics of high silica adakites suggest that these granodiorites were mainly derived from "hot" basaltic slab-melts of the subducted oceanic crust. The Middle Permian gabbros exhibited typical cumulate textures and were derived from the partial melting of depleted mantle. The Middle Permian granites are slightly peraluminous with high-K calc-alkaline and low εHf(t) values from - 0.9 to + 2.9. These granites were most likely derived from juvenile materials mixed with old crustal materials. The Late Permian granodiorites, monzogranites and quartz monzodiorites are characterized as metaluminous to slightly peraluminous, with variable Peacock alkali-lime index values from calc-alkalic to alkali-calcic. These rocks were mainly derived from juvenile crustal materials, as evidenced by their high εHf(t) values (+ 3.3 to + 8.9). The juvenile sources of the above intrusions in the Shalazhashan are similar to those of the granitoids from the CAOB but distinct from the granitoids within the Alxa Block. These findings suggest that the Shalazhashan Zone belongs to the CAOB rather than the Alxa Block and that its boundary with the Alxa block can be

  16. Petrogenesis, zircon U-Pb age, and geochemistry of the A-type Mogou syenite, western Henan Province: Implications for Mesozoic tectono-magmatic evolution of the Qinling Orogen

    Science.gov (United States)

    He, Xinyu; Wang, Jionghui; Wang, Changming; Carranza, Emmanuel John M.; Chen, Liang; Wu, Bin

    2016-04-01

    The Mogou syenite intruded into the Mesoproterozoic Xiong'er Group is the main lithostratigraphic unit, along the southern margin of the North China Craton (NCC). This paper reports zircon LA-ICP-MS data, whole-rock major and trace element compositions of late Triassic magmatic rocks in the Mogou syenite, in order to constrain the formation age of the Mogou syenite, research the origin and evolution of the magma and analyse the geodynamic setting of the Qinling Orogen (QO) in Late Triassic. These rocks consist of medium- to coarse-grained syenite and fine-grained quartz syenite. Zircon U-Pb dating yields a crystallization age of 226.5±2.7 Ma. The syenites are characterized by high SiO2 (63.49-72.17%), alkali (K2O+Na2O of 11.18-15.38%) and potassium (K2O/Na2O of 2.88-28.11), are peralkaline or metaluminous (molar A/CNK of 0.87-1.02) and belong to shoshonite series. The syenites have ΣREE of 33.01-191.30 ppm, LREE/HREE of 14-20, (La/Yb)N of 11-24, with LREE-rich distribution pattern and obvious differentiation between HREE and LREE. Eu anomalies are positive for the medium- to coarse-grained syenite and weakly negative for the fine-grained quartz syenite. In addition, the syenites are enriched in large-ion lithophile elements (Ba, K, Sr, and Pb) but depleted in high strength field elements (Ti, Ta, Nb, Zr, and Hf), and have high differentiation indices of 91.69-97.06. These geochemical features indicate that the primary magma of the Mogou syenite most likely originated from a mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The late Triassic A-type Moguo syenite along the southern margin of the NCC was generated in the late stage of the syn-collision event of QO, recording a transition period from compression to extension at around 227 Ma.

  17. Tu-U-Pb{sub T} ages of monazite and geothermobarometry of high level metapelitic rocks in the orogenic system Itabuna-Salvador-Curaca, state of Bahia, Brazil: a study in electron microprobe; Idades Th-U-Pb{sub T} de monazita e geotermobarometria de rochas metapeliticas de alto grau do sistema orogenico Itabuna-Salvador-Curaca, BA, Brasil: um estudo em microsonda eletronica

    Energy Technology Data Exchange (ETDEWEB)

    Vlach, Silvio Roberto Farias; Lama, Eliane Aparecida del [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica

    2002-12-15

    Electron microprobe Th-U-Pb T dating of monazite was performed on aluminous gneiss samples from the northern Jacurici and southern Ilheus areas of the Itabuna-Salvador-Curuca Orogenic System. Studied samples are spinel-sillimanite-cordierite-garnet gneiss and corundum-spinel-sillimanite-garnet gneiss that equilibrated during a high temperature metamorphism at T-P conditions of about 835 deg C/6,9 kbar and 890 deg C/7.4 kbar, respectively. Microprobe ages of monazite in equilibrium with these mineral associations are interpreted as true crystallization ages and date granulite facies metamorphism. Both samples gave ages of about 2.07 and 2.08 (+-0.02) Ga, in agreement with the known geochronological pattern in this system. The Ilheus sample contain a younger, contrasting monazite generation (e.g., with distinct REE patterns and Th/Gd ratios), dated at ca. 1.97 (+-0.04) Ga. Based on the occurrence of the corundum-sillimanite-quartz association in the sample and information from the literature, we suggest that this age may be related to a regional decompression event and/or a thermal overprint due to late intrusive magmatism (1.9 - 2.0 Ga) in the orogenic system. (author)

  18. The evolving anatomy of a collapsing orogen

    NARCIS (Netherlands)

    Hinsbergen, D.J.J. van

    2004-01-01

    The Tethys Oceans separated Africa and Arabia from Eurasia, and India from Asia. Closure of the Tethys started in the Jurassic and led to the Alpine-Himalayan mountain chain. This thesis will focus on the Aegean segment of this mountain belt. The Aegean region is occupied by a stack of nappes that

  19. Modelo para la variación del volumen orogénico andino y acortamientos en el sector 20°-46°S Model for Andean orogenic volume variation and shortening in the 20°-46°S sector

    Directory of Open Access Journals (Sweden)

    F.A. Pose

    2005-12-01

    Full Text Available El volumen orogénico levantado en los Andes es el resultado del delicado equilibrio entre el levantamiento y la erosión. Los diferentes grados de acortamiento sufridos por el borde occidental del continente americano, desde el codo de Arica hasta Tierra del Fuego, han definido contrastantes rasgos morfotectónicos, desde extensas altiplanicies endorreicas hasta reducidas y simples divisorias. El volumen orogénico a través de los Andes Centrales Australes y Patagónicos Septentrionales (20°-46°S disminuye linealmente de norte a sur. Esta linealidad experimenta un drástico cambio de pendiente, a los 38°S, en la zona de transición entre los Andes Centrales Australes y los Patagónicos Septentrionales. La zona norte (20°-38°S presenta mayor velocidad de variación que la sur (38°-46°S. Este quiebre coincide con un cambio relativo en el gradiente de edades de fondo oceánico, sugiriendo un control en el acortamiento, al menos parcial, por parte de la flotabilidad de la placa oceánica subducida. Esto se contrapone con las hipótesis que postulan que el factor climático sería el principal condicionante de estos contrastes morfológicos. Se presentan además dos ecuaciones empíricas para la obtención de volúmenes orogénicos a una latitud dada, fuera del ámbito de dos anomalías centradas en 27° y 33°S respectivamente. A estas latitudes, otros factores adicionales al acortamiento orogénico están definiendo el relieve observado. Adicionalmente se discute una ley de variación del acortamiento en función de la latitud, calculado a partir de datos gravimétricos, fuera de los entornos de estas anomalías alrededor de las cuales se observan fluctuaciones equivalentes al caso anterior.The orogenic volume of the Andes is the result of the equilibrium between the tectonic uplift and erosion. The different rates of shortening along the western margin of the South American continent have defined contrasting morphostructural settings. The

  20. Recent regional shortening in the interior of the orogenic Puna Plateau of the southern central Andes: New InSAR observations from the Salar de Pocitos, Salta, NW Argentina.

    Science.gov (United States)

    Eckelmann, Felix; Motagh, Mahdi; Bookhagen, Bodo; Strecker, Manfred; Freymark, Jessica; Bekeschus, Benjamin; Alonso, Ricardo

    2013-04-01

    sedimentary units in the western part of the basin are tilted eastward as part of the eastern flank of an anticline. Importantly, the Quaternary lacustrine shorelines along the margins of the basin document protracted tilting associated with an anticline. Our analysis of InSAR-measurements suggests the existence of two deformation signals. (1) As observed in other areas of the Puna there appears to be a seasonal change in elevation in the salt-basin center, which may be caused by volume changes related to the crystallization of evaporate minerals (e.g. Ruch et al., 2012); (2) to the west of the Salar de Pocitos the deformation signals point toward continued shortening associated with the growth of the anticline. This is compatible with observed shortening in the Chilean Salar de Atacama to the west. Combined with published data on the termination of shortening and the onset of extension in the orogen interior, our study emphasizes the diachronous evolution of crustal deformation on the Puna Plateau and the need to reconsider models that suggest coeval plateau-wide extension.

  1. Application of U-Th-Pb phosphate geochronology to young orogenic gold deposits: New age constraints on the formation of the Grass Valley gold district, Sierra Foothills province, California

    Science.gov (United States)

    Taylor, Ryan D.; Goldfarb, Richard J.; Monecke, Thomas; Fletcher, Ian R.; Cosca, Michael A.; Kelly, Nigel M.

    2015-01-01

    The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping east-west (E-W) veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping north-south (N-S) veins hosted by the Grass Valley granodiorite; the latter have yielded about 70 percent of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170-140 Ma and 120-80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. Uranium-lead isotopic dating of hydrothermal xenotime yielded the first absolute age of 162±5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of a Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wallrock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153-151 Ma gold event that was previously reported for the E-W veins. Overlapping U-Pb zircon (159.9±2.2 Ma) and 40Ar/39Ar biotite and hornblende (159.7±0.6 to 161.9±1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient

  2. 40Ar/39Ar geochronology and P-T-t paths constraining tectonic processes in orogenic belts: results from Qilian and Kunlun mountains (Western China) and Radstadt mountains (Eastern Alps, Austria)

    International Nuclear Information System (INIS)

    rifting of the continental crust during the Permian (290 - 250 Ma). Austroalpine Permo-Mesozoic cover rocks were deformed during the Cretaceous (around 80 Ma) and the Paleogene (55 - 50 Ma), the latter ages found in deeper tectonic levels and represent the collision of Austroalpine and Penninic tectonic units. The Penninic nappe complex displays a rather continuous decrease of ages from c. 37 to 25 Ma from high to deep levels. A second age group of c. 22 Ma was found both in low-temperature release steps and as plateau ages in higher parts of the Penninic unit. It is attributed to a thermal overprint due to ductile extension of the over thickened orogenic wedge. These new age data show that tectonic accretion lasted over a period of more than 65 - 50 Ma. (author)

  3. Trace elements in minerals from mafic and ultramafic cumulates of the central Sierra de Valle Fértil, Famatinian arc, Argentina

    Science.gov (United States)

    Otamendi, Juan E.; Tiepolo, Massimo; Walker, Barry A.; Cristofolini, Eber A.; Tibaldi, Alina M.

    2016-01-01

    Trace element abundances in constituent minerals from mafic and ultramafic rocks of a deep arc crustal section are studied to observe their abundance and distribution. Five cumulate rocks were selected from a sequence that consists of pyroxene hornblende peridotite, olivine hornblende gabbronorite, pyroxene hornblende gabbronorite, hornblende gabbronorite, gabbro and anorthosite. Solid/liquid partition coefficients calculated with the equilibrium distribution model indicate that Cr, Ni, Co, Zn and V are highly compatible with an olivine-dominated mineral assemblage from the mafic and ultramafic cumulates. The compatibility of Ti and Sc would be dependent on the stability of clinopyroxene, amphibole and oxides in the magmatic system. With few exceptions, the other trace elements are incompatible with the minerals that form the cumulate. At most half the mass of Sr carried by a primitive arc magma could be stored in anorthite-rich plagioclase from the mafic cumulates. Magmatic amphibole fractionates Y, middle and heavy REE from other incompatible elements during crystal accumulation of mafic cumulates. In contrast, late magmatic to subsolidus amphibole has no effect on the differentiation of a primitive arc magma. In fact, the trace element variability of amphibole and clinopyroxene is easily related to different stages of magmatic evolution within the cumulate pile. The results presented here are helpful for modelling other cases of arc magma petrogenesis where the cumulate rocks with dominant mafic assemblages are not exposed.

  4. New SHRIMP U-Pb data from the Famatina Complex : constraining Early-Mid Ordovician Famatinian magmatism in the Sierras Pampeanas, Argentina

    OpenAIRE

    J.A. Dahlquist; Pankhurst, Robert; C.W. Rapela; C. Galindo; Alasino, P.; Fanning, C. M.; J. Saavedra; Baldo, E.

    2008-01-01

    New SHRIMP U-Pb zircon ages are reported for igneous and sedimentary rocks of the Famatina Complex, constraining the age of the magmatism and the ensialic basins. Together with whole-rock and isotope geochemistry for the igneous rocks from the complex, these ages indicate that the voluminous parental magmas of metaluminous composition were derived by partial melting of an older lithosphere without significant asthenospheric contribution. This magmatism was initiated in the Early Ordovician (4...

  5. 澳大利亚造山型金矿和侵入岩有关金矿系统流体包裹体资料和矿化过程的比较%Comparison of fluid inclusion data and mineralization processes for Australian orogenic gold and intrusion-related gold systems

    Institute of Scientific and Technical Information of China (English)

    T.P.Memagh; E.N.Bastrakov; Khin Zaw; A.S.Wygralak; L.A.I.Wybom

    2007-01-01

    We have examined the fluid inclusion data and fluid chemistry of Australian orogenic and intrusion-related gold deposits to determine if similar mineralization processes apply to both styles of deposits. The fluid inclusion data from the Yilgarn craton, the western subprovince of the Lachlan orogen, the Tanami, Tennant Creek and Pine Creek regions, and the Telfer gold mine show that mineralization involved fluids with broadly similar major chemical components ( i. e. H2O + NsCl + CO2 ± CH4 ± N2 ). These deposits formed over a wide range of temperature-pressure conditions ( < 200 to > 500℃, < 100 ~ 400MPa ). Low salinity, CO2-bearing inclusions and low salinity aqueous inclusions occur in both systems but the main difference between these two types of deposits is that most intrusion-related gold deposits also contain at least one population of high-salinity aqueous brine. Oxygen and hydrogen isotope data for both styles of deposit usually cannot distinguish between a magmatic or metamorphic source for the ore-bearing fluids. However, sulfur and lead isotope data for the intrusion-related gold deposits generally indicate either a magmatic source or mixing between magmatic and sedimentary sources of fluid. The metamorphic geothermal gradients associated with intrusion-related gold deposits are characterized by low pressure, high temperature metamorphism and high crustal geothermal gradients of > 30/km. Where amphibole breakdown occurs in a granite source region, the spatially related deposits are more commonly associated with Cu-Au deposits rather than Au-only deposits that are associated with lower temperature granites. The dominant processes thought to cause gold precipitation in both types of deposits are fluid-rock interaction ( e. g. desulfidation) or phase separation. Consideration of the physical and chemical properties of the H2O-NaCl-CO2 system on the nature of gold precipitation mechanisms at different crustal levels infers different roles of

  6. Neoproterozoic-Paleozoic Sedimentary Basins Evolution of Xing-Meng Orogenic Belt%兴蒙造山系新元古代-古生代沉积盆地演化

    Institute of Scientific and Technical Information of China (English)

    杨文麟; 骆满生; 王成刚; 徐增连

    2014-01-01

    Based on comprehensive analysis of the type,sedimentary formation,biostratigraphy and chronostratigraphy for 24 main sedimentary basins,we study the evolution of sedimentary basins of Xing-Meng orogenic belt in the Neoproterozoic-Paleo-zoic,dividing it into six phases as follows.(1)The epicontinental accretion in the Neoproterozoic to Early Cambrian character-ized by the assembly of Ergun and Xingan blocks,as Huanyu-Xinlin ophiolite accreted to margin of southern Ergun blocks;(2)The stable epicontinental sediment in the Terreneuvian-Serises 2,with the feature of a relatively stable clastic-calciclastic sediment around the blocks while Jiamusi massif affected by Late Pan-African metamorphic event;(3)The formation of archi-pelagic arc-basin systems in the Early and Middle Ordovician,marked by the distribution of arc-basin in the margin of Duobaoshan and the different levels oceanic crust subduction effect among other land masses;(4)The development of archipe-lagic arc-basin systems in the Late Ordovician to Pridoli,as the erosion of the uplifted land masses;(5)The subduction of ar-chipelagic arc-basin systems in the Early Devonian to Early Carboniferous,characterized by the collage of Ergun-Xingan and Songnen blocks and the transformation of western margin of Jiamusi massif from passive to active in the late Early Carbonifer-ous;(6)The oceanic-continental transition in the Late Carboniferous-Lopingian,characterized by the assembly of Jiamusi mas-sif,Songnen massif,and Khanka massif.Massifs of Northeast China completely collaged to a whole.%在系统分析兴蒙造山系新元古代-古生代24个沉积盆地类型、沉积建造、生物地层与年代地层等特征的基础上,划分了6个沉积大地构造演化阶段并对其进行讨论:(1)新元古代-寒武纪早期陆缘增生阶段:额尔古纳地块向南增生并与兴安地块拼贴,形成环宇-新林蛇绿岩拼合带;(2)寒武纪纽芬兰世-第二世陆缘稳定沉积阶段:各地块边

  7. Petrología del magmatismo de arco pre-deformacional en el cordón de El Realito y la zona norte del plutón La Escalerilla. Sierra de San Luis Petrology of the pre-deformational arc magmatism in the Cordón de El Realito and in the northern zone of the La Escalerilla pluton, Sierra de San Luis

    Directory of Open Access Journals (Sweden)

    N. Brogioni

    2005-09-01

    Escalerilla pluton are the most extensive. High-K calcalkaline magmas intrude low- to medium-grade metasedimentary rocks in both areas. The oldest event is represented by arc-type, metaluminous Pl+Bt+Ep±Hbl±Kf granodiorites, tonalites and scarce diorites, carrying numerous enclaves of gabbroic to monzodioritic composition. Chemical abundances and evolutionary trends of these rocks correlate well with those of the metaluminous arcsequence of Sierras de Chepes and Los Llanos in La Rioja province. The youngest event consists of peraluminous and collisionrelated Kf+Pl+Ms±Bt±Grt, leucocratic monzogranites, intruding the arc-sequence. The monzogranites do not appear to be generated as a result of differentiation from the metaluminous sequence, although both magmatic suites are part of the Famatinian subductionrelated arc. The peraluminous magmatism displays the typical vertical evolutionary trend of felsic peraluminous granitoids and is interpreted as derived mainly from partial melting of Ms-metapelites and greywackes. Some geochemical abundances and HREE patterns of the La Escalerilla stock are probably controlled by differences in the source. The Famatinian regional metamorphism and shearing strongly modified the arc-sequence rocks fabrics. However, the magmatic rocks preserved their whole chemical signatures except for the most basic members of the series which display spreading in evolutionary trends and increased peraluminosity. The pre-deformational peraluminous melts in both areas are clearly distinct from those of some syn-kinematic Ms±Bt±Grt leucogranitoids which crop out in the Eastern Basement Complex of the Sierra.

  8. Characteristics of the Late Carboniferious post-orogenic Dayinhe intrusion in the northwest of the Xiao Hinggan Mountains and their geological implications%小兴安岭西北部晚石炭世造山后达音河岩体的特征及其地质意义

    Institute of Scientific and Technical Information of China (English)

    赵院冬; 赵君; 王奎良; 车继英; 吴大天; 许逢明; 李世超

    2013-01-01

    小兴安岭西北部达音河岩体主要由碱长花岗岩、正长花岗岩组成.碱长花岗岩的锆石LA-ICP-MS U-Pb定年结果为304.4±1.3 Ma,时代属于晚石炭世,而不是过去认为的晚侏罗世.该岩体化学组成以高硅、钾、钠,低钙为特征,富集Rb、La、Th等大离子亲石元素,亏损Ba、Sr、Eu等大离子亲石元素和Nb、Ta、Zr高场强元素,反映斜长石作为源区残留相对岩浆地球化学特征的控制.该岩体同区域上十二站、新开岭、龙镇、扎兰屯等岩体构成晚石炭世造山后伸展背景下形成的I型和A型花岗岩带,反映了兴安、松嫩块体在晚石炭世结束块体碰撞造山,转入造山后伸展环境.%The Dayinhe intrusion, located in the northwest of the Xiao Hinggan Mountains, is mainly composed of alkali-feldspar granite and syenogranite. Zircon U-Pb age obtained by LA-ICP-MS analysis of the alkali-feldspar granite is 304.4 ±1.3 Ma, suggesting that it intruded in the Late Carboniferous period rather than the Late Jurassic period as proposed before. Petrochemically, the Dayinhe intrusion is characterized by high Si, Na, K and low Ca. It is enriched in Rb, La, Th and depleted in Ba, Sr. Nb, Ta, Zr, implying the effect of plagio-clase as the stable residual phase in the magma source. Regionally, the Dayinhe intrusion, together with the Shierzhan, Xinkailin, Longzhen and Zhalantun granites that share the same petrologic and geochemical characteristics, forms the Late Carboniferous post-orogenic I-type and A-type granite belt in the Da Hinggan Mountains, implying the end of the collision and orogen between the Hinggan block and the Songnen block and the beginning of post-orogeic extension in this region.

  9. The Analysis of Metamorphism-deformation Sequence for the Paired Metamorphic Belt in West Tianshan Orogen:An Example from Chahanwusu Area,Zhaosu County,Xinjiang%西天山造山带双变质带变质变形序列分析--以新疆昭苏县察汗乌苏一带为例

    Institute of Scientific and Technical Information of China (English)

    程培起

    2015-01-01

    西天山造山带中双变质带以新疆昭苏察汗乌苏一带较为典型,根据变质作用的不同,划分出绿片岩相绢云母绿泥石带、绿片岩相蓝闪石带、角闪岩相黑云母普通角闪石带、角闪岩相矽线石铁铝榴石带等变质相带;按其变质作用以及构造变形程度分为上部层次脆性性构造层、中上部层次、深部层次3种构造层次。根据之间的相互叠加关系,确立了造山带内的岩石主要存在着3期以上构造变形特征;在主要的3期构造变形过程中见有相应的变质矿物,并根据生成的矿物组合与变形之间的相互关系,通过变质矿物先后生成关系与岩石的结构、构造建立了变质与变形序列关系,确立了变质与变形非简单一一对应,而是具有渗透叠加和循环往复的特点。%The paired metamorphic belt of West Tianshan Orogen is more typical in Chahanwusu Area,Xinjiang. According to the difference of metamorphism,this paired metamorphic belt can be divided into several metamorphic facies zone,including sericite-chlorite zone with greeanschist-facies,glaucophane zone with greenschist facies,biotite-hornblende zone with amphibolite facies belt and sillimanite-almandite zone with amphibolite facies. Based on the degree of metamorphism and tectonic deformation,this paired metamorphic belt can be divided into three kinds of structur-al levels:the brittle structural layer in the upper level,the structural layers in the middle-upper level and the ones in the lower level. After analyzing the superimposed relationship among these structural levels,more than threetimes of tectonic deformation characteristics have been distin-guished in the rocks of West Tianshan Orogen. And the corresponding metamorphic minerals for these three tectonic stages in the process of deformation can be observed. And then,the interre-lationship between generated mineral association and deformation has been discussed,the rela

  10. Geometria e evolução do feixe de zonas de cisalhamento Manhuaçu - Santa Margarida, Orógeno Araçuaí, MG Geometry and evolution of the Manhuaçu-Santa Margarida shear zone system, Araçuai Orogen, MG

    Directory of Open Access Journals (Sweden)

    Cláudio Maurício Teixeira da Silva

    2009-03-01

    Full Text Available Feixe de Zonas de Cisalhamento Manhuaçu-Santa Margarida de orientação geral NS estende-se por, aproximadamente, 300 km na região leste de Minas Gerais. Como uma das principais estruturas do núcleo cristalino do Orógeno Araçuaí, é constituído por um conjunto de zonas de cisalhamento dúcteis, que, em mapa, mostram traços sigmoidais. O seu segmento norte é composto por zonas de cisalhamento reversas que promovem o transporte de material em direção a oeste e, subordinadamente, por zonas transcorrentes dextrais. Os segmentos central e sul são dominados por zonas transcorrentes dextrais. O desenvolvimento do feixe deu-se em quatro fases deformacionais neoproterozóicas. A primeira fase promoveu a nucleação do conjunto de zonas reversas, que ficaram parcialmente preservadas no segmento norte do feixe. Durante a segunda fase, as zonas preexistentes experimentaram, de norte para sul, uma rotação progressiva para a vertical e para a direção NE-SW, além de intensa reativação transcorrente dextral. A terceira fase gerou zonas de cisalhamento normais de ocorrência restrita ao segmento norte. Na quarta fase, formaram-se falhas transversais e juntas. Em sua terminação sul, o feixe, dominado por zonas transcorrentes dextrais, rotaciona-se até confundir-se com as estruturas da porção NW da Faixa Ribeira. Tal fato implica que as estruturas dessa porção do feixe são de mesma idade, ou algo mais velhas que as transcorrências dextrais, que marcam o quadro tectônico do segmento NW da Faixa Ribeira.The N-S trending Manhuaçu-Santa Margarida shear zone system extends for ca. 300 km in eastern Minas Gerais. As one of the main structures of the crystalline core of the Neoproterozoic Araçuaí Orogen, the Manhuaçu-Santa Margarida system is made up of a series of ductile shear zones, which show a sigmoidal trace in map view. The northern segment of the system mainly consists of west-verging thrusts and subordinate dextral strike

  11. Las fajas de deformación dúctil de las Sierras Pampeanas de Córdoba: Una reseña general Ductile deformation shear belts at Pampean Ranges near Córdoba, Central Argentina: A Review

    Directory of Open Access Journals (Sweden)

    RD Martino

    2003-12-01

    Ranges near Córdoba are described defining extension, limits, fault rocks, milonitic foliations and stretching lineations. These belts are arranged in four groups based on its tectonic significance. (1 Arc parallel dextral transcurrent shear belts related, to the pampean subduction during Early Cambrian. (2 Cambrian Pampean Orogen unroofing shear belts, essentially reverse with minor dextral movements produced by convergent general shear (transpression, related to late collisional movements between Pampia terrane and Gondwana margin, and famatinian subduction. Deformation is bracketed on these belts at 490-470 Ma. (3 Regional imbrication shear belts developing rheologically controlled thrusts and defining age domains. These thrust producing events are related to the Ocloyic deformation phase (Famatinian Orogeny occurred between Late Ordovician-Early Silurian. Domains are arranged from East to West in: an igneous Precambrian-Cambrian Domain, a metamorphic high-medium grade Cambrian Domain, and a metamorphic high-medium grade Ordovician Domain. This intense contractional deformation would be related with the approaching of the Cuyania terrane to the Gondwana margin, before its emplacement and final collision during Late Ordovician. (4 Achalian contractional shear belts with reverse and transcurrent movements extended up to Lower Devonian in coincidence with Cuyania terrane's final emplacement, and Famatinian magmatism cessation. After these events, around of the Devonian-Carboniferous limits, a new shearing event is developed during the Chanic phase (Famatinian orogeny when Chilenia terrane was emplaced against the Gondwanic margin.

  12. Orogenic Thrust Belt, Gulf of Mexico Basin [gcthrustbg

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — These data provide the general location of the Ouachita and Appalachian structural fronts slightly modified from Plate 4, Natural resources, Gulf of Mexico Basin...

  13. Shaping post-orogenic landscapes by climate and chemical weathering

    OpenAIRE

    Chadwick, OA; Roering, JJ; Heimsath, AM; Levick, SR; Asner, GP; Khomo, L

    2013-01-01

    The spacing of hills and valleys reflects the competition between disturbance-driven (or diffusive) transport on hillslopes and concentrative (or advective) transport in valleys, although the underlying lithologic, tectonic, and climatic controls have not been untangled. Here, we measure geochemical and geomorphic properties of catchments in Kruger National Park, South Africa, where granitic lithology and erosion rates are invariant, enabling us to evaluate how varying mean annual precipitati...

  14. Thermal modelling of orogenic mesothermal deposits : application to Ghana

    OpenAIRE

    Harcouët, Virginie

    2005-01-01

    This thesis deals with thermal processes and fluid flow regimes leading to the genesis of mesothermal gold deposits.Two numerical modelling approaches have been used, a regional one, characterising the conductive thermal regime before mineralisation and a local one adding hydrothermal convection contemporaneous to mineralisation. Models are applied to the Palaeoproterozoic ore deposits of the Ashanti belt in Ghana which are representative of giant mesothermal gold deposits. From the results, ...

  15. The structural, metamorphic and magmatic evolution of Mesoproterozoic orogens

    OpenAIRE

    Roberts, Nick M. W.; Slagstad, Trond; Viola, Giulio

    2015-01-01

    The Mesoproterozoic (1600–1000 Ma) is an Era of Earth history that has been defined in the literature as being quiescent in terms of both tectonics and the evolution of the biosphere and atmosphere (Holland, 2006, Piper, 2013b and Young, 2013). The ‘boring billion’ is an informal term that is given to a time period overlapping the Mesoproterozoic period, extending from 1.85 to 0.85 Ga (Holland, 2006). Orogenesis was not absent from this period however, with various continents featuring active...

  16. The Xilingele complex from the eastern part of the Central Asian-Mongolia Orogenic Belt, China: Products of Early Variscan orogeny other than ancient block: Evidence from zircon SHRIMP U-Pb ages%中亚-蒙古造山带东段的锡林郭勒杂岩:早华力西期造山作用的产物而非古老陆块?——锆石SHRIMP U-Pb年代学证据

    Institute of Scientific and Technical Information of China (English)

    薛怀民; 郭利军; 侯增谦; 周喜文; 童英; 潘晓菲

    2009-01-01

    锡林郭勒杂岩是华北板块北缘古生代褶皱带内出露面积最大的变质岩系,以前多被当着前寒武纪的古老地块.本文通过对该杂岩中副片麻岩和正片麻岩的锆石SHRIMP U-Pb年代学研究发现,副片麻岩中的锆石多为岩浆锆石,其~(206)pb/~(238)U加权平均年龄为406±7Ma,指示它们的原岩主要是由近同期(略早些)的岩浆岩风化后就近沉积的产物,该年龄应代表源区(岛弧型?)花岗岩的形成时间,同时也是副片麻岩原岩沉积的下限年龄.正片麻岩中岩浆锆石的~(206)pb/~(238)U加权平均年龄为382±2Ma,代表花岗片麻岩原岩的侵位年龄.岩石中锆石的变质增生边的形成年龄为337±6Ma,代表锡林郭勒杂岩发生变质和变形的时间,该变质事件可能与贺根山缝合带内所发生的一次主要的碰撞造山作用有关.这些年龄资料充分说明,锡林郭勒杂岩并非古老地块,而是华力西早期岩浆作用、沉积作用和变质作用事件的产物.整个事件是在较短的时间范围内(~70Ma)完成的,推测该杂岩发育在碰撞造山带的弧前环境.中亚-蒙古造山带东南部(内蒙古的中、东部)碰撞前的构造格局可能不是典型的多岛洋体制,由于缺少古老的陆块,造山过程更多的表现为大洋的大陆化过程,即洋内俯冲形成岛弧,岛弧在被动大陆边缘拼贴聚合转化为新的大陆.%The Xilingele complex is one of the maximal series of metamorphic rocks outcropped in the Paleozoic folded region along the northern margin of the North China Craton, has been ever considered as a Precambrian block before. In this work, we acquired zircon SHRIMP U-Pb data of the complex in order to gain the forming ages of their protoliths and metamorphism ages to constrain the orogenic processes of the eastern part of the Central Asian-Mongolia Orogenic Belt. The results are as follows: Most zircon grains from the paragneiss were formed in magma, their weighted mean

  17. 青藏高原东南缘哀牢山构造带泥质高压麻粒岩的发现及其构造意义%Discovery of high-pressure pelitic granulite in Ailaoshan orogenic belt,southeastern Tibet, and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    戚学祥; 赵宇浩; 朱路华; 李志群

    2012-01-01

    High-pressure pelitic granulite containing porphyroblasts of garnet (Grt), sillimanite ( Sil), K-feldspar ( Kf) and plagioclase (PI) , and inclusions of spinel (Spl) , kyanite ( Ky) , sapphirine (Spr) and rutile (Rut) have been found from the Ailaoshan orogenic belt, southeastern Tihet, regarded as a key indicator for identification of the boundary between the Indochina and South China blocks. The temperatures and pressures calculated by garnet-biotite-plagioclase-quartz geothermobarometery and high-temperature equilibrium spinel ± quartz assemblage show the formation and evolution of the graunlite had experienced clockwise P-T path from high-pressurc/-tcmpcrature to mid-temperature and low-pressure metamorphism. That are: 1) the high-pressure/-temperature metamorphism (HP/HT) is characterized by an assemblage of Ky ± Sil ± Grt1 ± Kf1 ± PI1 ± Spr ± Ter( Kf ± PI) ± Bt1 ± Spl ± Qtz ± Ilm1 ± Rut1, and the peak P-T conditions of > 10.4kbar at 850 ~ 919℃ ; 2) the mid-temperature and low-pressure retrogressive metamorphism characterized by an assemblage of Grt2 ± Bt2 ± PI2 ± Ms ± Qtz ± Ilm, ± Rut2, and two stage P-T conditions of 4. 9 ~ 6. 5kbar at 664 -754℃ and 3. 5 -3. 9kbar at 572 -576T respectively. The dynamic metamorphic path was that the metapelitic rock experienced high-pressure/-temperature granulite-facies metamorphism in lower continental crust ( >30 km) exhumated to mid-upper crust rapidly, it might be related to the continental collision and underthrusting between the Indochina and South China blocks, and exhumation and slip shearing lately.%哀牢山构造带泥质高压麻粒岩主要由石榴石、夕线石、钾长石和斜长石变斑晶及尖晶石、铁假蓝宝石、蓝晶石、石英、金红石和钛铁矿包裹体组成,为确定印支地块和华南地块的边界提供了关键性标志.石榴石-黑云母-斜长石-石英地质温压计(GBPQ)计算结果及标志性高温矿物组合(Spl+ Qz)表明泥质高压麻粒岩

  18. The offshore basement of Perú: Evidence for different igneous and metamorphic domains in the forearc

    Science.gov (United States)

    Romero, Darwin; Valencia, Kiko; Alarcón, Pedro; Peña, Daniel; Ramos, Victor A.

    2013-03-01

    As a result of new studies carried out in the offshore of Perú during the exploration and hydrocarbon evaluation of the forearc basins, new U-Pb SHRIMP and TIMS in zircons and some Ar-Ar data were obtained in the metamorphic and igneous basement. The understanding of this basement was critical to evaluate different hypotheses that have been proposed for the tectonic evolution of pre-Andean crust of Perú. Recent research performed in the basement rocks of the Marañón Massif in northern Perú, claimed that west of this area was a basement-free region in the Paleozoic, where the arc and forearc were developed in a mafic quasi-oceanic crust. However, petrographic studies and new preliminary ages indicate, for the first time, the nature and age of this sialic basement. Reconnaissance studies were performed in several offshore islands, as the Las Hormigas de Afuera Island west of Lima, and Macabí and Lobera islands along the edge of the continental platform. These data were complemented with the studies of some cutting samples obtained in recent exploration wells in northern Perú. The results of the present work show two large crustal domains in the Peruvian offshore forearc. A northern domain contains late Paleozoic igneous rocks that appear to be the southern offshore continuation of the Amotape-Tahuin block, which is interpreted as the southernmost remnant of the Laurentia Alleghenian orogen. The central offshore domain, known as the Paracas High, corresponds to the outer shelf high of previous studies. It contains orthogneisses of Grenville-age, probably recrystallized during an Ordovician magmatic episode. The new results show that the central offshore of Perú is an extension of the Grenville-age basement affected by Famatinian, early Paleozoic magmatism, well exposed in the southern domain in the Arequipa Massif along the coast of southern Perú.

  19. The geodynamic evolution of the eastern Sierras Pampeanas based on geochemical, Sm-Nd, Pb-Pb and SHRIMP data

    DEFF Research Database (Denmark)

    Drobe, M; Lopez de Luchi, M; Steenken, A;

    2011-01-01

    , have been carried out to unravel the provenance and the geodynamic history of the Eastern Sierras Pampeanas, Central Argentina. The geochemical and the Sm–Nd data point to a slightly stronger mafic and less-fractionated material in the provenance area of the Sierras de Co´rdoba when compared...... to the other units. The TDM model ages from the Sierras de Chepes (*1.82 Ga) and the Sierra Norte (*1.79 Ga) are significantly older than the data from the Sierras de Córdoba (1.67 Ga). The Pb data are homogeneous for the different units. Only the 208Pb/204Pb ratios of some samples from the Sierras de Co......´rdoba are higher. A late Pampean detrital zircon peak around 520 Ma from the Sierras de Chepes is in accordance with the new data from the San Luis Formation. This is similar to the literature data from the Famatina Belt located to the northwest of the Sierras de Chepes and also fits the detrital zircon peaks...

  20. Oroclinal bending and orogenic asymmetry? A case study from the apex of the Northern Andean orocline

    Science.gov (United States)

    Mora, A.; Parra-Amezquita, M.; Rodriguez, G.

    2013-05-01

    Here we present new thermocronometric analysis from the eastern flank of the Colombian Eastern Cordillera at 7° N lat. which aid in deconvolving the roles of plate tectonics, tectonic inheritance and surface processes in building the Cocuy syntaxis, at the apex of the Northern Andean orocline. The Cocuy syntaxis is the region with higher structural and topographic relief in the Eastern Cordillera. The primary factor controlling that is faster tectonism, apparently related with the most important Panama collision at ca. 4 Ma. This push from behind is focused between two resistant plates and escapes toward a weak foreland plate, which is able to flex. However, we suggest it is an enhanced late Miocene to Recent exhumation episode which is responsible for the limited advance of the deformation front as basement involved blocks. Faster denudation causes faster sedimentation rates in the weak foreland plate east of Cocuy. In this case, the thick pile of synkinematic sediments would make an otherwise possible thin skin deformation migration very difficult.

  1. Tectonic-Climate Interactions in Action Orogenic Belts: Quantification of Dynamic Topography with SRTM data

    Science.gov (United States)

    Burbank, Douglas W.; Oskin, Mike; Niemi, Nathan; Miller, Scott

    2005-01-01

    This project was undertaken to examine the approach to steady state in collisional mountain belts. Although the primary thrust of this grant was to look at larger collisional mountain belts, such as the Himalaya, the Tien Shan, and Southern Alps, we began by looking at smaller structures represented by growing and propagating folds. Like ranges that are evolving toward a topographic steady state, these folds undergo a series of morphologic changes as they are progressively uplifted and eroded. We wanted to document the nature of these changes and to try to discern some of the underlying controls on them. We initially focused on the Wheeler Ridge anticline in southern California. Subsequently, we progressed to looking at the topographic development and the effects of differential uplift and glaciation on the Kyrgyz Range in the northern Tien Shan. This range is unusual inasmuch as it is transformed along its length from a simple uplift with a largely preserved Mesozoic erosion surface arching across it to a highly dissected and heavily glaciated uplift in the region where uplift has been sustained at higher rates over longer intervals. In efforts to understand the distribution of erosion rates at 10(exp 3) - 10(exp 5) year time scales, cosmogenic radionuclide (CRN) concentrations have been gaining increasingly widespread usage (Brown et al., 1995; Riebe et al., 2004; Riebe et al., 2001; Vance et al., 2003). Most studies to date, however, have been conducted in slowly eroding ranges. In rapidly eroding mountains where landslides deliver most of the sediments to the rivers, we hypothesized that CRN concentrations could be highly perturbed by the stochastic processes of landsliding. Therefore, we undertook the development of a numerical model that simulated the effects of both landsliding and grain-by-grain attrition within fluvial catchments. This modeling effort has shown the effects of catchment size and erosion rate on CRN concentrations and allows a prediction of where to sample to obtain the optimal erosion rate estimates using CRN techniques. Finally, we developed computational techniques to operate on DEMs to extract useful information that would enable quantification of climate-erosion interactions. In particular, we worked on rapid techniques to define catchments of any given range of sizes, to extract channel gradients, to combine precipitation information to calculate discharge, and to utilize various stream-power models to determine the erosional energy within any given catchment within a transect. We briefly describe results from Wheeler Ridge, the Kyrgyz Range, the Nepal Himalaya, and our numerical modeling.

  2. Weathering, erosion and fluvial transfers of particulate and dissolved materials from the Taiwan orogen

    Science.gov (United States)

    Hovius, Niels; Galy, Albert; Hilton, Robert; West, Joshua; Chen, Hongey; Horng, Ming-Jame; Chen, Meng-Chiang

    2010-05-01

    Systematic monitoring of river loads helps refine and extend the map of internal dynamics and external feedbacks in Earth's surface and near-surface system. Our focus is on Taiwan where hillslope mass wasting and fluvial sediment transport are driven by earthquakes and cyclonic storms. The biggest trigger events cause instantaneous erosion and seed a weakness in the landscape that is removed over time in predictable fashion. This gives rise to patterns of erosion that can not be understood in terms of bulk characteristics of climate, such as average annual precipitation. Instead, these patterns reflect the distribution and history of seismicity and extreme precipitation. For example, the 1999 Mw 7.6 Chi-Chi earthquake has resulted in elevated rates of sediment transport that decayed to normal values over seven years since the earthquake. Very large typhoons, with enhanced precipitation due to a monsoonal feed, have caused a similar, temporary deviation from normal catchment dynamics. Crucially, these events do not only mobilize large quantities of clastic sediment, but they also harvest particulate organic carbon (POC) from rock mass, soils and the biosphere. In Taiwan, most non-fossil POC is carried in hyperpycnal storm floods. This may promote rapid burial and preservation of POC in turbidites, representing a draw down of CO2 from the atmosphere that is potentially larger than that by silicate weathering in the same domain. Oxidation of fossil POC during exhumation and surface transport could offset this effect, but in Taiwan the rate of preservation of fossil POC is extremely high, due to rapid erosion and short fluvial transfer paths. Meanwhile, coarse woody debris flushed from the Taiwan mountains is probably not buried efficiently in geological deposits, representing a concentrated flux of nutrients to coastal and marine environments instead.

  3. Thermoluminescence et orogenèse. Les Alpes occidentales au Paléogène.

    OpenAIRE

    Ivaldi, Jean-Pierre

    1989-01-01

    Le sujet de ce travail est l'étude du Paléogène marin de la zone alpine externe. Son objet : rechercher par l'analyse détaillée des unités lithostratigraphiques externe. Son objet : rechercher par l'analyse détaillée des unités lithostratigraphiques formelles, des données et des schémas paléogéographiques cohérents qui permettent de préciser l'évolution tectono-sédimentaire de la marge interne de la plaque européenne au cours de la période paléogène. La principale méthode d'investigation util...

  4. Geophysical structure of the Southern Alps orogen, South Island, New Zealand

    OpenAIRE

    Davey, Fred J.; Eberhart-Phillips, Donna; Kohler, Monica D.; Bannister, Stephen; Caldwell, Grant; Henrys, Stuart; Scherwath, Martin; Stern, Tim; Van Avendonk, Harm

    2007-01-01

    The central part of the South Island of New Zealand is a product of the transpressive continental collision of the Pacific and Australian plates during the past 5 million years, prior to which the plate boundary was largely transcurrent for over 10 My. Subduction occurs at the north (west dipping) and south (east dipping) of South Island. The deformation is largely accommodated by the ramping up of the Pacific plate over the Australian plate and near-symmetric mantle shortening. T...

  5. When sink becomes source: Importance of sediment recycling in linked orogen-basin systems

    Science.gov (United States)

    Romans, Brian W.; Fosdick, Julie C.; Hubbards, Stephen M.; Fildani, Andrea

    2013-04-01

    Much of the recent research on sedimentary system dynamics has focused on extant systems where the linkage of sediment production from eroding highlands can be directly linked to deposition in lowlands and/or offshore basins. Studies of such systems, typically late Pleistocene to Holocene in age, are especially valuable for quantitative constraints such as system morphometrics (e.g., longitudinal profiles, basin volumes, etc.) and rates of processes (e.g., erosion/denudation, sediment accumulation, etc.), which can be measured directly or estimated with relatively high certainty. Moreover, information about climate and tectonic forcings that are independent to the system is explicitly known for extant systems. However, an understanding of longer-term (>105 yr) evolution can only be gained through the investigation of ancient systems. Such systems are either buried in the subsurface, which requires geophysical remote sensing and/or drilling, or exposed at the Earth's surface as outcrops as the result of uplift and exhumation. The dynamic linkage of mountain belt and adjacent basin makes foreland basin systems ideal natural laboratories to address long-term sedimentary system evolution. In this presentation, we highlight important issues and challenges that sedimentary systems research is currently facing, with an emphasis on sediment recycling during progressive stages of basin development. In this context, we focus on sedimentary systems in which multiple episodes of uplift and erosion of the primary depocenter led to a history whereby basin material was repeatedly recycled. The spatial and temporal aspects of sediment recycling have implications for how provenance signals (based on composition, crystallization or metamorphic age information, thermal history, etc.) are used. Additionally, improved constraints regarding the timescales and magnitude of sediment recycling have implications for system-scale modeling. Key parameters such as total sediment volumes and differences in rock erodibility between original basement source and sedimentary source must be accounted for in these models if budget closure is to be considered. Sediment recycling has long been considered by basin analysts and recognized using numerous provenance indicators; however, new analytical tools allow us to further quantify the impact of recycled source terranes. The Magallanes Basin of South America provides an appropriate example to discuss these issues because of its long-lived convergent basin history and proximity to distinctive source terranes. A robust and growing database of compositional (e.g., sandstone composition, shale geochemistry), detrital age (zircon geochronology), and time-temperature (detrital thermochronology) information is used to help constrain source-area configuration and evolution. These data are placed within a multi-scale stratigraphic framework that addresses basin geometry and depositional system evolution, thereby enabling us to test geologic models based on sediment transport pathways, maturation of sediment-sources, and post-depositional thermal history.

  6. Recognition of shallow structure of Orogenic area with application of AMT and CSAMT survey

    International Nuclear Information System (INIS)

    Complete text of publication follows. Hydrocarbon deposits in the Carpathians occur at rather shallow depths, but under highly complicated structural and lithological conditions. It is therefore much difficult to detect and recognize such deposits with the use of surface geophysical methods. In 2008, research work commissioned by the Polish Oil and Gas Company and the project 'Development of new methods for detecting hydrocarbon deposits and recognition of their structure and variability during exploitation with the use of deep- and medium-penetration electromagnetic surveys' sponsored by the Minister of Science and Higher Education led to investigations of the Grabownica deposit with the use of two electromagnetic methods: Audio Magnetotellurics (AMT) and Controlled Source Audio-Frequency Magnetotellurics (CSAMT). The objective of the investigations was to evaluate the usefulness of electromagnetic methods in recognition of structural and tectonic conditions of deposits, and particularly to determine hydrocarbon-saturated zones. The Grabownica deposit occurs within a long steep fault that is cut by a number of tectonic zones both running conformably and transversely to the fault strike. The deposit series are formed of rather thin and steep sandstone layers sealed by shales. Due to the direct contact of steep layers with the ground surface, the seal seems to be somewhat problematic in some part of the deposit. Because the structure is fairly good examined by numerous exploitation boreholes, this makes favorable conditions for test investigations. Also, the recognition of zones with no hydrocarbon saturation and deposit zones with different exploitation degree are propitious factors. All this information helps to evaluate how the deposit is reflected in interpreted resistivity distribution along test profiles. A significant impediment to electromagnetic data interpretation is the complex structure of the deposit. It is often difficult in the interpreted resistivity cross-sections to distinguish between anomalies generated by a 'structural factor' and anomalies due to varied lithology and/or hydrocarbon saturation.

  7. Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

    OpenAIRE

    Taghipour Batoul; Ahmadnejad Farhad

    2015-01-01

    The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj–Sirjan Zone (SSZ), within the NE–SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrich -ment in LREE re...

  8. Structural framework of a major intracontinental orogenic termination zone: The easternmost Tien Shan, China

    Science.gov (United States)

    Cunningham, D.; Owen, L.A.; Snee, L.W.; Li, J.

    2003-01-01

    The Barkol Tagh and Karlik Tagh ranges of the easternmost Tien Shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range. Barkol and Karlik Tagh and lesser ranges to the north are bounded by active thrust faults that locally deform Quaternary sediments. Major thrusts in Karlik Tagh connect along strike to the east with the left-lateral Gobi-Tien Shan Fault System in SW Mongolia. From a Mongolian perspective. Karlik Tagh represents a large restraining bend for this regional strike-slip fault system, and the entire system of thrusts and strike-slip faults in the Karlik Tagh region defines a horsetail splay fault geometry. Regionally, there appears to be a kinematic transition from thrust-dominated deformation in the central Tien Shan to left-lateral transpressional deformation in the easternmost Tien Shan. This transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the NNE-directed maximum horizontal stress in the region and the pre-existing basement structural grain, which is northwesterly in the central Tien Shan (orthogonal to SHmax) but more east-west in the eastern Tien Shan (acute angular relationship with SHmax . Ar-Ar ages indicate that major range-bounding thrusts in Barkol and Karlik Tagh are latest Permian-Triassic ductile thrust zones that underwent brittle reactivation in the Late Cenozoic. It is estimated that the modern mountain ranges of the extreme easternmost Tien Shan could have been constructed by only 10-15 km of Late Cenozoic horizontal shortening.

  9. Late Proterozoic Colisional Orogen and Geosuture in Southeastern China:Petrological Evidence

    Institute of Scientific and Technical Information of China (English)

    周新民; 朱云鹤

    1993-01-01

    The Jiangshan-Shaoxing fracture belt(JSFB)is a Late Proterozoic geosuture due to island arc-continent collision in South China,The Cathaysian Block(CT),lying on the southeast side of JSFB,is composed of green schist-amphibolite complexes in the form of a series of tectonic flakes. On the northwest side of JSFB,which is located in the border area of Zheijiang,Jiangxi and Ahhhi provinces(abbreviated as ZJP-JXP-AHP),are distrbuted and ophiolite suite and other rocks,constituting the Jiangnan ancient island arc(JN)on the southeast margin of the Yangtze Block(YZ).The collision between JN and CT at-0.9Ga ago led to the folding of JN.followed by the intrusion(-0.9-0.8Ga ago)of many dioritic and ultramafic stitching plutons along the fracture belt.As a result,the basic Precambrian tectonic framework of southeastern China was shaped.

  10. The nature and location of the suture zone in the Rokelide orogen, Sierra Leone: Geochemical evidence

    Science.gov (United States)

    Lytwyn, Jennifer; Burke, Kevin; Culver, Stephen

    2006-12-01

    The boundaries of the West African Craton mark the location of a continuous suture zone that records Neoproterozoic to Early Cambrian oceanic closure. The western part of the circum-West African suture zone extends through the line of outcrop of the Mauritanide, Bassaride and Rokelide mountain belts. Our geochemical analyses are consistent with the idea that igneous and metamorphic rocks of the Rokelide and Southern Mauritanide mountain belts of West Africa occupy a suture zone that records the closing of a Neoproterozoic to Early Cambrian ocean basin during the Pan-African orogeny and final assembly of Gondwana. The closing of that basin was marked by the collision between Archean rocks of the Leo massif of the West African Craton and reactivated Archean and Paleoproterozoic rocks that now outcrop nearer to the coast of Africa in Sierra Leone and Liberia. Within the Rokelides, the geochemistry of the Kasewe Hills volcanic rocks and Marampa amphibolite indicate that remnants of an arc system are caught up in the suture zone. The geochemistry of Guingan schists that outcrop along strike of the Rokelides is compatible with the idea that the metamorphosed equivalents of the Marampa and Kasewe Hills arc volcanic rocks extend through the Bassarides and into the Southern Mauritanides.

  11. Crustal structure of the eastern Qinling orogenic belt and implication for reactivation since the Cretaceous

    Science.gov (United States)

    Guo, Zhen; Chen, Y. John

    2016-06-01

    A high resolution crustal model of the eastern Qinling belt and central North China Craton (central NCC) is obtained along a N-S trending profile (corridor) by joint inversion of surface wave and receiver function. The NCC is one of the oldest cratons on Earth and the Qinling belt is the suture zone between the NCC and South China block (SCB). The Qinling belt is characterized by low crustal velocity (observed just above the Moho, consistent with the regional high bulk Vp/Vs ratio (> 1.8). The forward gravity modeling supports the presence of a high-density layer (3.05 g/cm3) at the base of the crust beneath the central NCC. We propose that the high velocity in the lowermost crust beneath the central NCC is most likely due to the repeated mafic underplating, which also results in high crustal Vp/Vs ratio and is responsible for the rapid crustal uplift during the late Mesozoic.

  12. Complexity and Geodynamics of Ore-accumulating Basins in the Qinling Orogenic Belt, China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Researches were made of different continental-margin and intraplate basin systems in the Qinling microplate in terms of hydrothermal deposition, geodynamics of basin formation, hydrothermal sedimentary rock facies, syntectonics in the basins, and the styles of ore accumulation in the basins.

  13. Dating emplacement and evolution of the orogenic magmatism in the internal Western Alps

    DEFF Research Database (Denmark)

    Berger, Alfons; Thomsen, Tonny B.; Ovtcharova, Maria;

    2012-01-01

    Miagliano tonalite. The latter is of special interest, because it is located in the south-eastern side of the Canavese Line, in contrast to most Periadriatic Plutons. The dioritic to tonalitic rocks of the Miagliano Pluton represent an intermediate stage of a calc-alkaline differentiation, demonstrated by...... relics of two different pyroxenes as well as the texture of allanite. Hornblende barometry indicates pressures of similar to 0.46 GPa consistent with the presence of magmatic epidote. Field relationships between the two Plutons, the volcanic and volcaniclastic rocks of the Biella Volcanic Suite and......The Canavese Line in the Western Alps represents the position in the Alpine chain, where alkaline and calc-alkaline magmatism occur in close spatial and temporal association. In addition to available data on the alkaline Valle del Cervo Pluton, we present petrological and geochemical data on the...

  14. Engineering Geological and Petrographic Characterization of Migmatites Belonging to the Calabria-Peloritani Orogen (Southern Italy)

    Science.gov (United States)

    Pappalardo, G.; Punturo, R.; Mineo, S.; Ortolano, G.; Castelli, F.

    2016-04-01

    The laboratory characterization of migmatite rocks, affected by tunneling works in southern Calabria (Italy), has been carried out with the purpose of investigating the relationship between some potentially interdependent petrographic and petrophysical features with the mechanical behavior of the excavated rocks. Mineralogical and petrographic investigation allowed estimating the modal composition of the rock and the grain size of the constituting minerals, as well as examining the intergranular contacts and associated microfractures. The velocity of seismic waves within the specimens has been measured and calculated, along with the elastic properties of the rock. Specimens were also characterized from the physical-mechanical point of view and their mode of failure was considered. Results show that the mechanical behavior of migmatites varies within the sample population, although the specimens belong to the same sampling area. It is controlled by both porosity and modal composition of the rock. Thus, primary minerals were grouped with respect to their elastic properties; their abundance/deficiency within the specimen controls its mechanical strength. This is also reflected in the modes of failure associated to different strength values. This is a new consideration in the laboratory characterization of this rock type, largely cropping out in several contexts worldwide. Results should be taken into account before starting engineering works, in order to avoid errors resulting from considering this rock as a homogeneous material from the mechanical and petrographic points of view.

  15. Orogen-parallel Variation in Flexure of the Arabian Plate Beneath the Zagros Mountains

    Science.gov (United States)

    Pirouz, M.; Avouac, J. P.; Simpson, G.; Hassanzadeh, J.; Herman, F.; Sternai, P.

    2014-12-01

    The Zagros Mountains are the part of the Alpine-Himalayan chain that forms the northern margin of the Arabian plate and comprises a Neogene-Recent sedimentary basin that is forming in response to ongoing Arabia-Eurasia collision. Flexure of the Arabian lithosphere beneath the Zagros forms one of largest and most active basins in the world at which a backstripped deflection of a competent layer just below the foreland deposits represents its total amount of tectonic subsidence. As such, the Asmari Fm. can be used to analyze flexural bending and subsequently the amount of loading and elastic thickness of the Arabian lithosphere since the continent-continent collision started. In this study, flexure of the Arabian lithosphere is investigated using more than 100 boreholes and 60 interpreted seismic lines which show that the flexure is shallower (~ 1 km) and wider in the east and deeper (~6 km) and narrower towards the west (Figure 1). The shallow and wide eastern foredeep has little accommodation space due to small tectonic loads and the thick lithosphere in this region. In addition, viscous strength in the eastern sector leads to a wide deformation belt with low topography and low surface slopes. These factors, combined with arid climatic conditions, produce low sediment supply to the foreland basin so that it remains under-filled even though the foreland basin is shallow. In contrast, the western part of the Zagros region shows much larger accommodation space due to the combination of large loads and a relatively thin elastic plate. In the western sector, frictional basal strength and steeper topography along with more humid climatic conditions leading to a large supply of sediment to the foreland which is completely filled even though the foreland basin is deep. Our results also show that the Zagros foreland basin migrated towards south through the Neogene; however, the way of propagation is not fully understood yet. The eastern depocenter of the Zagros foreland migrated towards south about ~400 km during the last 17 Ma, whereas this migration decreases to about ~100 km towards the west. Our preliminary results propose that the western Zagros foreland basin is developing under wedge growing condition and the eastern sector is growing due to thrusting beneath the steady-state wedge (?), but the idea requires further analysis.

  16. Surface Uplift History of the Central Andes: Implications for the Growth of Orogenic Plateaus

    Science.gov (United States)

    Garzione, C. N.; Hoke, G. D.; Libarkin, J. C.; MacFadden, B. J.; Withers, S.

    2007-05-01

    Sedimentation, paleoelevation, and incision histories provide important constraints on the timing and magnitude of regional surface uplift of mountain belts that point to specific processes that led to surface uplift. The sedimentary record and stable isotopic compositions of carbonates are used to reconstruct the late Miocene subsidence history, paleoenvironment, and paleoelevation of the northern Altiplano basin. Multiple paleoelevation proxies, including paleoleaf physiognomy, δ18O paleoaltimetry, and Δ47 paleothermometry, suggest that the Altiplano rose by 2.5±0.5 km to 3.5±0.5 km to its current elevation between ~10 and 7 Ma. Geomorphic evidence from widespread, low-relief paleosurfaces on both the eastern and western flanks of the Andes also shows that the onset of rapid incision of paleosurfaces occurred between ~10 and 6.5 Ma over the entire width of the mountain belt and over at least 5° latitude. Stream profile analysis of the drainage systems that incise these paleosurfaces has been inferred to reflect ~1 to 2 km of surface uplift of the flanks of the Andes. Combining geomorphic evidence with paleoelevation constraints, the paleotopographic evolution of the Andes is reconstructed over the late Miocene. Late Miocene regional surface uplift requires the removal of mantle lithosphere as the dominant geodynamic mechanism for raising the plateau during this time. However, crustal thickening and redistribution of crust by erosion/sedimentation and/or lower crustal flow set the limit of surface uplift. Regional surface uplift of the Andean plateau in the late Miocene predicts a decrease in the horizontal deviatoric stress in the plateau that is consistent with observations of upper crustal shortening, sedimentation rates, and magmatism in the plateau. Shortening ceased across the plateau between 10 and 7 Ma, coincident with widespread ignimbrite eruptions and an abrupt decrease in sedimentation rates. The combination of geodynamic processes that appear to have occurred in the Andes in late Miocene time, including removal of high density lower lithosphere and redistribution of crust by erosion/sedimentation and flow of low density middle-lower crust, are likely mechanisms for building broad, flat, high elevation plateaus in convergent tectonic settings.

  17. Formation of elongated granite–migmatite domes as isostaticaccommodation structures in collisional orogens

    Czech Academy of Sciences Publication Activity Database

    Verner, K.; Žák, J.; Šrámek, F.; Paclíková, J.; Zavřelová, A.; Machek, Matěj; Finger, F.; Johnson, K.

    2014-01-01

    Roč. 73, January (2014), s. 100-117. ISSN 0264-3707 Institutional support: RVO:67985530 Keywords : anisotropy of magnetic susceptibility * Bohemian Massif * granite-migmatite dome * metamorphic core complex * exhumation Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.217, year: 2014

  18. A Model For Syntectonic Fibrous Vein Growth Inferred From Microtextures. Ouachitas Orogen, Arkansas

    Science.gov (United States)

    Cervantes, P.; Wiltschko, D. V.

    2005-12-01

    Veins from the Lower Ordovician Mazarn Formation in the Arkansas' Ouachitas show two processes of vein growth, 1) continuous localized fracturing and filling and 2) recrystallization, tied to the deformation history of the area under study. Evidence for continuous localized fracturing includes the presence of veinlets near or at the vein-host interface. Veinlets are long and narrow features parallel to the main body of the vein, filled mainly with quartz, between 5 and 25 μm wide. Veinlets cut and displaced host grains. Displacement of host grains is evident because the material precipitated on veinlets show different luminescence than host grains. Remnants of these veinlets are observed in completely recrystallized fibers. Evidence for recrystallization includes, 1) wide fibers (more than 100 μm) with fluid inclusion trails parallel to fiber length that span the entire fiber length, 2) luminescence in the central part of the vein is different than luminescence in the external part of the vein (close to host-vein interface), 3) remnants of original luminescence in the central part of the vein suggesting that recrystallization is a later process. We hypothesize that in this region folding followed by flattening gave rise to boudinage of resistant layers accompanying abundant pressure solution providing the vein forming material. Precipitation of material took place along necks of boudins, which fractured repeatedly allowing veins to grow in width and length. Late thrust faults led to open system conditions which gave rise to new vein growth and recrystallization. Recrystallization altered the shape of previously formed veins.

  19. Geology, structure and age of the Nahuel Niyeu Formation in the Aguada Cecilio area, North Patagonian Massif, Argentina

    Science.gov (United States)

    Greco, Gerson A.; González, Pablo D.; González, Santiago N.; Sato, Ana M.; Basei, Miguel A. S.; Tassinari, Colombo C. G.; Sato, Kei; Varela, Ricardo; Llambías, Eduardo J.

    2015-10-01

    The low-grade Nahuel Niyeu Formation in the Aguada Cecilio area (40°50‧S-65°53‧W) shows ultramafic to felsic metaigneous rocks forming a sill swarm intercalated in the metasedimentary sequence and a polyphase deformation which permit an integrated study of the magmatic and tectonometamorphic evolution of this geological unit. In this paper we present a geological characterization of the Nahuel Niyeu Formation in the Aguada Cecilio area combining mapping, structural and metamorphic analysis with a SHRIMP U-Pb age and geochemical data from the metaigneous rocks. The metasedimentary sequence consists of alternating metagreywackes and phyllites, and minor metasandstones and granule metaconglomerates. The sills are pre-kinematic intrusions and yielded one SHRIMP U-Pb, zircon crystallization age of 513.6 ± 3.3 Ma. Their injection occurred after consolidation of the sedimentary sequence. A syn-sedimentary volcanic activity is interpreted by a metaandesite lava flow interlayered in the metasedimentary sequence. Sedimentary and igneous protoliths of the Nahuel Niyeu Formation would have been formed in a continental margin basin associated with active magmatic arc during the Cambrian Epoch 2. Two main low-grade tectonometamorphic events affected the Nahuel Niyeu Formation, one during the Cambrian Epoch 2-Early Ordovician and the other probably in the late Permian at ˜260 Ma. Local late folds could belong to the final stages of the late Permian deformation or be even younger. In a regional context, the Nahuel Niyeu and El Jagüelito formations and Mina Gonzalito Complex show a comparable Cambrian-Ordovician evolution related to the Terra Australis Orogen in the south Gondwana margin. This evolution is also coeval with the late and early stages of the Pampean and Famatinian orogenies of Central Argentina, respectively. The late Permian event recorded in the Nahuel Niyeu Formation in Aguada Cecilio area is identified by comparable structures affecting the Mina Gonzalito

  20. Sucesiones volcánico-sedimentarias tremadocianas y arenigianas en la sierra de las Planchadas-Narváez: registros evolutivos del arco magmático Famatiano Tremadoc and Arenig volcano-sedimentary successions in the Sierra de Las Planchadas, Narváez: Evolutive records of the Famatinian magmatic arc

    Directory of Open Access Journals (Sweden)

    Clara Eugenia Cisterna

    2010-03-01

    Full Text Available Se analizan secciones volcano-sedimentarias ordovícicas del norte del Sistema de Famatina, aportando nuevos datos petrológicos para la comprensión de la naturaleza de sus magmas y de los procesos volcanológicos asociados con la evolución del arco magmático en la región. Información paleontológica previa, apoyada por estudios estructurales y por las relaciones de intrusividad con una granodiorita de 485 ± 7 Ma, asignaron edades del Tremadociano temprano a las sedimentitas de Las Angosturas y del Arenigiano temprano - medio a las de las secciones Vuelta de la Tolas - Chaschuil y quebrada Larga - Punta Pétrea. Los litotipos que integran la sucesión tremadociana son lavas basálticas, andesíticas, dacíticas y riodacíticas, interestratificadas con limolitas y psamitas finas, polideformadas y con importante alteración hidrotermal, habiéndose reconocido paragénesis de metamorfismo de bajo grado y de contacto. Los depósitos arenigianos, afectados por plegamiento y desarrollo de clivaje localmente, consisten en lavas basálticas, andesíticas, dacíticas y riolíticas, facies hialoclásticas, depósitos resedimentados sin-eruptivos y volcanogénicos. Si bien ambas asociaciones son subalcalinas y peraluminosas, se concluye, para los representantes tremadocianos, que sus características son consistentes con un ambiente donde fueron producidos fundidos de un manto empobrecido (MORB y enriquecidos durante eventos de subducción, asociados con la evolución de una cuenca marginal. Las volcanitas arenigianas muestran filiación geoquímica de arco magmático continental. Ambas asociaciones exhiben características similares a las observadas en la Puna occidental, lo que plantearía la posible continuación en la Puna del arco magmático ordovícico reconocido en el Sistema de Famatina.Volcano-sedimentary Ordovician sections from the north of the Sistema de Famatina are analyzed, contributing with new petrological data to the understanding of the nature of magmas and associated volcanic processes related to the evolution of the magmatic arc in the region. Previous paleontological information, supported by structural studies and contact relationships with a granodiorite dated in 485 ± 7 Ma, assigned to these sedimentary rocks of Las Angosturas an early Tremadoc age, as well as an early to middle Arenig age to those of the Vuelta de Las Tolas - Chaschuil and Quebrada Larga - Punta Pétrea sections. The lithotypes that integrate the Tremadoc successions are basaltic, andesitic, dacitic and rhyodacitic lavas, interfingered with massive and laminated siltstones and fine psammites, with superimposed deformation and important hydrothermal alteration, as well as low grade and contact metamorphism. The Arenig deposits, folded and affected by well developed cleavage in some sectors, consist on basaltic, andesitic, dacitic and rhyolitic lavas, associated to hyaloclastic facies, syn-eruptive re-sedimented deposits and volcanogenic sedimentary facies. Despite both associations are subalkaline and peraluminous, for the early Tremadoc terms it is concluded that geochemical characteristics are compatible with an environment where melts from a depleted mantle (MORB were produced, and enriched during subduction events. All these characteristics can be related to a marginal basin evolution. The Arenig volcanic rocks instead display a clear continental magmatic arc filiation. Both associations have similar characteristics to those observed in the western Puna region, which makes it probable to extend the magmatic arc recognized in the Sistema de Famatina within the Puna during Ordovician times.

  1. The Pan-African Prydz Belt in East Antarctica: a Collisional Orogen or an Intraplate Orogen%东南极泛非普里兹带:碰撞造山带还是板内造山带

    Institute of Scientific and Technical Information of China (English)

    李淼; 刘晓春

    2006-01-01

    东南极普里兹带是近几年在南极大陆上识别出的一条重要的泛非期构造带,因其成因涉及到冈瓦纳超大陆在寒武纪时的形成与演化问题,因此一直是国际地学界关注的焦点.但到目前为止,对于该造山带的构造属性还存在着不同的认识,有些人认为它是板内造山带,而另一些人认为它是两个大陆板块之间的碰撞带.其基本特征是:普里兹带两侧为前泛非期不同性质的岩石圈单元,整个区域经历了早期中-下地壳挤压逆冲和晚期中-上地壳伸展垮塌的构造演化历史,区域麻粒岩相变质作用表现为近等热减压的顺时针p-t轨迹.此外,东南极克拉通与冈瓦纳其他块体在500 Ma前的古地磁极移曲线并不一致.所以,尽管目前尚未发现蛇绿岩套、岛弧增生杂岩或高压变质岩等直接指相标志,但这些特征均反映了普里兹带是板间碰撞拼合的缝合带,而不是板内造山带,东南极地盾本身则是由不同块体在泛非期拼合而成的.

  2. The noble gas systematics of late-orogenic H 2O-CO 2 fluids, Mt Isa, Australia

    Science.gov (United States)

    Kendrick, M. A.; Honda, M.; Oliver, N. H. S.; Phillips, D.

    2011-03-01

    The noble gases (He, Ne, Ar, Kr and Xe) are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere, crust and mantle. This study illustrates how noble gases can be used to trace fluid origins in high-temperature metamorphic and mineralising environments; and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously. We report data for H 2O and CO 2 fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the Proterozoic Mt Isa Inlier of Australia. Sulphide fluid inclusions are dominated by crustal 4He. However, co-variations in fluid inclusion 20Ne/ 22Ne, 21Ne/ 22Ne, 40Ar/ 36Ar and 136Xe/ 130Xe indicate noble gases were derived from three or more reservoirs. In most cases, the fluid inclusions elemental noble gas ratios (e.g. Ne/Xe) are close to the ranges expected in sedimentary and crystalline rocks. However, the elemental ratios have been modified in some of the samples providing evidence for independent pulses of CO 2, and interaction of CO 2 with high-salinity aqueous fluids. Compositional variation is attributed to mixing of: (i) magmatic fluids (or deeply sourced metamorphic fluids) characterised by basement-derived noble gases with 20Ne/ 22Ne ˜ 8.4, 21Ne/ 22Ne ˜ 0.4, 40Ar/ 36Ar ˜ 40,000 and 136Xe/ 130Xe ˜ 8; (ii) basinal-metamorphic fluids with a narrow range of compositions including near-atmospheric values and (iii) noble gases derived from the meta-sedimentary host-rocks with 20Ne/ 22Ne ˜ 8-9.8, 21Ne/ 22Ne < 0.1, 40Ar/ 36Ar < 2500 and 136Xe/ 130Xe ˜ 2.2. These data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in Mt Isa's largest ore deposits. In addition the data show how noble gases in fluid inclusions can provide information on fluid origins, the composition of the crust's major lithologies, fluid-rock interactions and fluid-fluid mixing or immiscibility processes.

  3. The origin and hydrothermal mobilization of carbonaceous matter associated with Paleoproterozoic orogenic-type gold deposits of West Africa

    Czech Academy of Sciences Publication Activity Database

    Kříbek, B.; Sýkorová, Ivana; Machovič, V.; Knésl, I.; Laufek, F.; Zachariáš, J.

    2015-01-01

    Roč. 270, November 01 (2015), s. 300-317. ISSN 0301-9268 Institutional support: RVO:67985891 Keywords : carbonaceous matter * gold deposits * graphite Subject RIV: DB - Geology ; Mineralogy Impact factor: 5.664, year: 2014

  4. The crustal structure of Ellesmere Island, Arctic Canada—teleseismic mapping across a remote intraplate orogenic belt

    DEFF Research Database (Denmark)

    Schiffer, Christian; Stephenson, Randell Alexander; Oakey, Gordon;

    2016-01-01

    Bay and the consequent convergence of the Greenland plate. The details of this complex evolution and the present-day deep structure are poorly constrained in this remote area and deep geophysical data are sparse. Receiver function analysis of seven temporary broad-band seismometers of the Ellesmere...... Island Lithosphere Experiment complemented by two permanent stations provides important data on the crustal velocity structure of Ellesmere Island. The crustal expression of the northernmost tectonic block of Ellesmere Island (∼82°–83°N), Pearya, which was accreted during the Ellesmerian orogeny, is...

  5. Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste : Constraints on deformation processes in young orogens

    OpenAIRE

    Tate, Garrett W.; McQuarrie, Nadine; D. J. J. van Hinsbergen; Bakker, Richard R.; Harris, Ron; Willett, Sean; Reiners, Peter W.; Fellin, Maria Giuditta; Ganerød, Morgan; Zachariasse, Willem Jan

    2014-01-01

    Although exhumation and surface uplift are important parameters in understanding orogenesis, the opportunity to measure both in close proximity is rare. In Timor-Leste (East Timor), deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart, permitting direct relation of uplift and exhumation by comparing micropaleontology to thermochronology interpreted through one-dimensional thermal modeling. Foraminifera in two deepwater synorogenic basin...

  6. Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste : Constraints on deformation processes in young orogens

    NARCIS (Netherlands)

    Tate, Garrett W.; McQuarrie, Nadine; van Hinsbergen, D.J.J.; Bakker, Richard R.; Harris, Ron; Willett, Sean; Reiners, Peter W.; Fellin, Maria Giuditta; Ganerød, Morgan; Zachariasse, Willem Jan

    2014-01-01

    Although exhumation and surface uplift are important parameters in understanding orogenesis, the opportunity to measure both in close proximity is rare. In Timor-Leste (East Timor), deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart, permitt

  7. Accessory priderite and burbankite in multiphase solid inclusions in the orogenic garnet peridotite from the Bohemian Massif, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Naemura, K.; Shimizu, I.; Svojtka, Martin; Hirajima, T.

    2015-01-01

    Roč. 110, č. 1 (2015), s. 20-28. ISSN 1345-6296 Grant ostatní: Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100131203 Institutional support: RVO:67985831 Keywords : garnet peridotite * Variscan orogeny * multiphase solid inclusion * priderite * burbankite Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.742, year: 2014

  8. Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review

    Science.gov (United States)

    Küster, Dirk; Harms, Ulrich

    1998-12-01

    Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite-granite, biotite-hornblende-granite, quartz-monzonite and quartz-syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sr i-ratios between 0.7060 and 0.7236 and ɛNd( t) values between -15.8 and -5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sr i-ratios (0.7036-0.7075) and positive ɛNd( t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities, except the incompatible element enrichments. The resemblance indicates a strongly related petrogenesis of both granite associations.

  9. Long-term exhumation of a Palaeoproterozoic orogen and the role of pre-existing heterogeneous thermal crustal properties

    DEFF Research Database (Denmark)

    McGregor, E.D.; Nielsen, S.B.; Stephenson, R.A.;

    2013-01-01

    Ma. Modelling the 3D exhumation of a heterogeneous crust with flat topography demonstrates that some of the variability in observed fission-track ages could be attributed to heterogeneity in crustal heat production and thermal conductivity. The remaining variability in the observed dataset...

  10. Geologic and geochemical insights into the formation of the Taiyangshan porphyry copper–molybdenum deposit, Western Qinling Orogenic Belt, China

    Science.gov (United States)

    Kun-Feng Qiu; Taylor, Ryan D.; Yao-Hui Song; Hao-Cheng Yu; Kai-Rui Song; Nan Li

    2016-01-01

    Taiyangshan is a poorly studied copper–molybdenum deposit located in the Triassic Western Qinling collisional belt of northwest China. The intrusions exposed in the vicinity of the Taiyangshan deposit record episodic magmatism over 20–30 million years. Pre-mineralization quartz diorite porphyries, which host some of the deposit, were emplaced at 226.6 ± 6.2 Ma. Syn-collisional monzonite and quartz monzonite porphyries, which also host mineralization, were emplaced at 218.0 ± 6.1 Ma and 215.0 ± 5.8 Ma, respectively. Mineralization occurred during the transition from a syn-collisional to a post-collisional setting at ca. 208 Ma. A barren post-mineralization granite porphyry marked the end of post-collisional magmatism at 200.7 ± 5.1 Ma. The ore-bearing monzonite and quartz monzonite porphyries have a εHf(t) range from − 2.0 to + 12.5, which is much more variable than that of the slightly older quartz diorite porphyries, with TDM2 of 1.15–1.23 Ga corresponding to the positive εHf(t) values and TDM1 of 0.62–0.90 Ga corresponding to the negative εHf(t) values. Molybdenite in the Taiyangshan deposit with 27.70 to 38.43 ppm Re suggests metal sourced from a mantle–crust mixture or from mafic and ultramafic rocks in the lower crust. The δ34S values obtained for pyrite, chalcopyrite, and molybdenite from the deposit range from + 1.3‰ to + 4.0‰, + 0.2‰ to + 1.1‰, and + 5.3‰ to + 5.9‰, respectively, suggesting a magmatic source for the sulfur. Calculated δ18Ofluid values for magmatic K-feldspar from porphyries (+ 13.3‰), hydrothermal K-feldspar from stockwork veins related to potassic alteration (+ 11.6‰), and hydrothermal sericite from quartz–pyrite veins (+ 8.6 to + 10.6‰) indicate the Taiyangshan deposit formed dominantly from magmatic water. Hydrogen isotope values for hydrothermal sericite ranging from − 85 to − 50‰ may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic–hydrothermal system. Alternatively, δD variability may have been caused by a minor amount of mixing with meteoric waters. We propose that the ore-related magma was derived from partial melting of the ancient Mesoproterozoic to Neoproterozoic middle to lower continental crust. This crust was likely metasomatized during earlier subduction, and the crustal magmas may have been contaminated with lithospheric mantle derived magma triggered by MASH (e.g., melting, assimilation, storage, and homogenization) processes during collisional orogeny. In addition, a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas.

  11. Granitic magma emplacement and deformation during early-orogenic syn-convergent transtension: The Stare Sedlo complex, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Tomek, Filip; Žák, J.; Chadima, Martin

    2015-01-01

    Roč. 87, JUL (2015), s. 50-66. ISSN 0264-3707 Institutional support: RVO:67985831 Keywords : anisotropy of magnetic susceptibility (AMS) * Bohemian Massif * pluton emplacement * granite * transtension * Variscan orogeny Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.217, year: 2014

  12. Is there any Eburnean orogen in the western Anti-Atlas (Morocco). A case history in the Kerdous massif

    International Nuclear Information System (INIS)

    New geological investigations of the Kerdous show that: 1) schists and quartzites belong to one lithostratigraphic sequence derived from sediments of a passive continental margin; 2) the deformation history is dominated by a moderate phase of large, open folds trending WNW-ESE, associated with recrystallization under low-grade metamorphic conditions and 3) syn- to late-tectonic plutonism is responsible for thermal aureoles that have reshaped the surrounding metasediments. The Kerdous appears as monocyclic and most probably Pan-African in age. (authors). 10 refs., 1 fig., 5 photos

  13. The constraints of strain partitioning and geochronology in Luonan-Luanchuan tectonic belts on Qinling orogenic belt

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The Luonan-Luanchuan tectonic belt lies between the North China Block and Qinling Mountains, in- cluding the Luonan-Luanchuan fault zone and the strong deformation zone to the north of the fault. The ductile shear zone, imbricate brittle fault and duplex structure in the fault zone now are the expression of the same tectonic event in different depth. Such lineation structure exists in the tectonic belts as mineral lineation, elongation lineation, crenulation lineation, sheath folds and so on, indicating NE-directed plate motion. Fold axes and thrusts in the strong deformation zone are inclined to the Luonan-Luanchuan fault zone at small angles. The structures with different natures show a regular pattern, produced during oblique convergence of plates. The convergence factors are as follows:The direction of plate convergence is 22°, 31° and the angle between the plate convergence direction and plate boundary is 73°, 82° respectively in the west and east segment. The Luonan-Luanchuan tectonic belt was deformed strongly in 372 Ma, resulted from Erlangping back-arc ocean basin subduction sin- istrally and obliquely to North China Block during the collision of North China Block and South China Block.

  14. The Precambrian of Transangaria, Yenisei Ridge (Siberia): Neoproterozoic microcontinent, Grenville-age orogen, or reworked margin of the Siberian craton?

    Science.gov (United States)

    Kuzmichev, Alexander B.; Sklyarov, Eugene V.

    2016-01-01

    The Yenisei Ridge was traditionally perceived as an uplifted segment of the western Siberian craton affected by Neoproterozoic collision events. However, the suggestions for Archaean or Palaeoproterozoic ('Siberian') basement in Transangaria have not been confirmed by reliable geochronological data. A new view regards most of the Ridge, namely, its Transangarian segment, to be an exotic Neoproterozoic terrane that collided with Siberia in the late Neoproterozoic. This paper presents new U-Pb SHRIMP zircon ages demonstrating that Archaean rocks (2611 ± 12 Ma) actually exist in this territory. We also provide a review of published U-Pb zircon ages for igneous and metamorphic rocks of Transangaria together with our new age data. This geochronological dataset clarifies the geology of the Yenisei Ridge and leads to new conclusions, as follows. (1) It is likely that Transangaria was originally underlain by an Archaean-Palaeoproterozoic basement, similar to that of the Siberian craton. (2) Geochronological data do not confirm the idea of widespread "Greenvillian age" granitoides in Transangaria. (3) The Neoproterozoic evolution of the Yenisei Ridge segment of the Siberian craton margin includes the following events. (i) Collision of an unidentified terrane with the western margin (in recent coordinates) of the Siberian craton during 900-855 Ma. The colliding terrane is no longer present in the current structure. (ii) Dextral shearing during 830-800 Ma may have been caused by counter-clockwise rotation of the Siberian craton. (iii) Extensional conditions prevailed during 800-700 Ma. The Isakovka oceanic basin formed at this time interval. (iv) Thrusting of the Isakovka island arc and accretionary prism onto the Siberian margin occurred during the late Neoproterozoic (650-630 Ma) and caused high-pressure metamorphism.

  15. Geological and structural setting, age, and geochemistry of the orogenic gold deposits at the Pataz Province, Eastern Andean Cordillera, Peru

    OpenAIRE

    Haeberlin, Yves; Fontboté, Lluis; Moritz, Robert

    2004-01-01

    La province de Pataz au Nord-Pérou est la plus septentrionale des ceintures paléozoïques d'or, antimoine et tungstène orogéniques (mésothermales) de la Cordillère Orientale des Andes Centrales. Longue de plus de 160 km, elle est connue pour ses veines épigénétiques de quartz aurifères riches en sulfures (ressource: 40 millions d'onces d'or). Les minéralisations, datées à ~314 Ma, sont localisées dans des fractures inverse-décrochantes dextres et d'extension le long des marges et à l'intérieur...

  16. The Wassa deposit : a poly-deformed orogenic gold system in southwest Ghana. Implications for regional exploration

    OpenAIRE

    Perrouty, S.; Jessell, Mark; Bourassa, Y.; Miller, J.; Apau, D.; Siebenaller, Luc; Velasquez, G.; Baratoux, Lenka; Ailleres, L.; Beziat, D.; Salvi, S.

    2015-01-01

    The Ashanti greenstone belt in southwest Ghana hosts many gold deposits distinguished by different timing and structural contexts. This study investigates the evolution of the Wassa system by integrating field and geophysical observations. This 4 million ounces (past production and current resources) gold deposit is interpreted to represent the oldest gold mineralization event in West Africa with gold-bearing pyrites aligned and stretched within the Si ductile fabric. Mineralized quartz-carbo...

  17. Geological and structural setting, age, and geochemistry of the orogenic gold deposits at the Pataz Province, Eastern Andean Cordillera, Peru

    OpenAIRE

    Haeberlin, Yves

    2001-01-01

    La province de Pataz au Nord-Pérou est la plus septentrionale des ceintures paléozoïques d'or, antimoine et tungstène orogéniques (mésothermales) de la Cordillère Orientale des Andes Centrales. Longue de plus de 160 km, elle est connue pour ses veines épigénétiques de quartz aurifères riches en sulfures (ressource: 40 millions d'onces d'or). Les minéralisations, datées à ~314 Ma, sont localisées dans des fractures inverse-décrochantes dextres et d'extension le long des marges et à l'intérieur...

  18. Remote sensing as a preliminary analysis for the detection of active tectonic structures: an application to the Albanian orogenic system

    Directory of Open Access Journals (Sweden)

    Andrea Favretto

    2013-12-01

    Full Text Available As is well known, both the traditional direct geological and geophysical survey methods used to identify geologic features are very expensive and time-consuming procedures. In this regard, remote sensing methods applied to multispectral and medium spatial resolution satellite images allow a more focused approach with respect to the more specific geologic methods. This is achieved by a preliminary land inspection carried out by the semi-automated analysis of satellite imagery. This avoids wasting resources as the geological/geophysical survey methods can be later applied only to those zones suspected of having certain tectonic activity (derived by the remotely sensed imagery. This paper will evaluate an ASTER sensor satellite image (and its derived Digital Elevation Model or DEM, in order to point out the suspected presence of active geologic structures (faults. The area in question is west – central Albania. The results of the remote sensing procedures are later compared with the established data for the same area taken by satellite images, in order to verify the reliability of the adopted method. The source of the established data has been from the bibliography.

  19. The post-orogenic evolution of the Northeast Greenland Caledonides constrained from apatite fission track analysis and inverse geodynamic modelling

    DEFF Research Database (Denmark)

    Pedersen, Vivi Kathrine; Nielsen, S.B.; Gallagher, Kerry

    2012-01-01

    than 350 Ma, and the length distributions are predominantly narrow unimodal, with c-axis projected mean track lengths between 13.3 and 15.0 μm. The passive margin of Northeast Greenland differs from other studied passive margins in terms of AFT age trends, as we observe no correlation with elevation or...... deposition, and thermal histories are found by solving the one-dimensional transient conduction–advection heat equation. These thermal histories are used with the observed fission track data to constrain acceptable strain rate histories and exhumation paths. The results suggest that rifting has been focused...... flexural isostatic response to erosional unloading, we find no need for introducing post-rift related uplift mechanisms....

  20. Uplifting of the Jiamusi Block in the eastern Central Asian Orogenic Belt, NE China: evidence from basin provenance and geochronology

    Science.gov (United States)

    Liu, Yongjiang; Wen, Quanbo; Han, Guoqing; Li, Wei

    2010-05-01

    The main part of Jiamusi Block, named as Huanan-Uplift, is located in the northeastern Heilongjiang, China. The Huanan-Uplift is surrounded by many relatively small Mesozoic-Cenozoic basins, e.g. Sanjiang Basin, Hulin Basin, Boli Basin, Jixi Basin, Shuangyashan Basin and Shuanghua Basin. However previous research works were mainly focused on stratigraphy and palaeontology of the basins, therefore, the coupling relation between the uplift and the surrounding basins have not been clear. Based on the field investigations, conglomerate provenance studies of the Houshigou Formation in Boli Basin, geochronology of the Huanan-Uplift basement, we have been studied the relationships between Huanan-Uplift and the surrounding basins. The regional stratigraphic correlations indicates that the isolated basins in the area experienced the same evolution during the period of the Chengzihe and the Muling Formations (the Early Cretaceous). The paleogeography reconstructions suggest that the area had been a large-scale basin as a whole during the Early Cretaceous. The Huanan-Uplift did not exist. The paleocurrent directions, sandstone and conglomerate provenance analyses show that the Huanan-Uplift started to be the source area of the surrounding basins during the period of Houshigou Formation (early Late Cretaceous), therefore, it suggests that the Jiamusi Block commenced uplift in the early Late Cretaceous. The granitic gneisses in Huanan-Uplift give 494-415 Ma monazite U-Th-total Pb ages, 262-259 Ma biotite and 246-241 Ma K-feldspar 40Ar/39Ar ages. The cooling rates of 1-2 ℃/Ma from 500-260 Ma and 10-11 ℃/Ma from 260-240 Ma have been calculated based on the ages. This suggests that the Jiamusi Block had a rapid exhumation during late Permian, which should be related to the closure of the Paleo-Asian Ocean between the Siberian and North China continents. It is concluded that during the late Paleozoic the Jiamusi Block was stable with a very slow uplifting. With the closure of the Paleo-Asian Ocean the Jiamusi Block underwent a very rapid exhumation in the late Permian. In the early Mesozoic the area went into a basin developing stage and formed a large basin as a whole during the Early Cretaceous. In the Late Cretaceous the Jiamusi Block started uplifting and the basin was broken into isolate small basins. References: Bureau of Geology and Mineral Resources of Heilongjiang Province. Regional geology of Heilongjiang Province. Beijing: Geological Publishing House, 1993.578-581. Cao Chengrun, Zheng Qingdao. Structural evolution feature and its significance of hydrocarbon exploration in relict basin formation, Eastern Heilongjiang province. Journal of Jilin university (Earth Science Edition), 2003, 33(2):167-172. Lang Xiansheng. Biologic Assemblage features of Coal-bearing Strata in Shuangyashan-Jixian coal-field. Coal geology of China, 2002, 14(2):7-12. Piao Taiyuan , Cai Huawei , Jiang Baoyu. On the Cretaceous coal-bearing Strata in Eastern Heilongjiang. Journal Of Stratigraphy, 2005, 29:489-496. Wang Jie , He Zhonghua , Liu Zhaojun , Du Jiangfeng , Wang Weitao. Geochemical characteristics of Cretaceous detrital rocks and their constraint on provenance in Jixi Basin. Global Geology,2006, 25(4):341-348. DickinsonW R and Christopher A. Suczek. Plate Tectonics and Sandstone Composition. AAPG B. 1979,63(12 ):2164-2182. DickinsonW R, Beard L S, Brakenridge G R, et al. Provenance of North American Phanerozoic sandstones in relation to tectonic setting. Bull Geo-Soc Amer, 1983, 94: 222-235. Maruyama S, Seno T. Orogeny and relative plate motions: Example of the Japanese Islands. Tectonophysics, 1986,127(3-4):305-329. Maruyama S, Isozaki Y, Kimura Gand Terabayashi M C.Paleogeographic maps of the Japanese Islands: plate tectonic systhesis from 750 Ma to the present. Island Arc, 1997,6:121-142.

  1. Geomorphic response of an active metamorphic core-complex in a collisional orogen: Example from the Lunggar Shan, Southern Tibet

    International Nuclear Information System (INIS)

    We present structural and neotectonic mapping from the Lunggar Shan rift in southern Tibet. The Lunggar Shan is a N-trending mountain range ∼70 km long N-S and up to 40 km wide E-W. The Lunggar Shan is bounded on its east side by a low-angle (0) east-dipping detachment fault that juxtaposes mylonitic gneiss and variably deformed granites in its footwall against alluvial fans and Neogene gravels in its hangingwall. Foliations in the mylonitic footwall dip 40 m of throw on individual scarps. An intriguing observation is that an intrabasinal topographic high is actively developing near areas of inferred maximum extension, with lacustrine sediments being uplifted and eroded. This observation indicates that the rift basin initially developed as a typical half-graben system that underwent a transition from deposition, to uplift and erosion perhaps as a result of isostatic rebound of the footwall at depth, warping the overlying hangingwall basin. If correct, the Lunggar Shan may represent a modern analogue to the supradetachment basin model

  2. Structural evolution of the La Trocha fault zone: Oblique collision and strike-slip basins in the Cuban Orogen

    Science.gov (United States)

    Cruz-Orosa, Israel; Sã Bat, Francesc; Ramos, Emilio; Rivero, LluíS.; VáZquez-Taset, Yaniel M.

    2012-10-01

    The La Trocha fault zone acted as a major left-lateral transfer zone and is bounded by the La Trocha (LTF), Zaza-Tuinicú (ZTF), Cristales (CTF) and Taguasco (TGF) faults. These faults were consistent with the clockwise rotation of convergence and shortening in central Cuba. From the Paleocene to the Early Eocene (65-48 Ma), a SSW-NNE shortening produced transtension in the LTF and transpression in the ZTF. Subsequently, during the Middle Eocene (48-37 Ma), shortening shifted to a SW-NE direction, resulting in the normal component of the LTF and transpression in the ZTF and CTF. Since the Late Eocene (37 Ma), central Cuba has been welded to the North American Plate. The post-welding deformation gave rise to transtension of the LTF and TGF. This deformation is consistent with a WSW-ENE shortening and reflects activity in the transform boundary of the Cayman Trough. Both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left-lateral displacement is deduced from the concordance between oblique collision and structural features. Plate-kinematics and the structural evolution of the La Trocha fault zone indicate that the related Central Basin is a strike-slip polygenetic basin and that the formation of this system (i.e., fault zone - strike-slip basin) was a consequence of the Paleogene oblique collision between the Caribbean Volcanic Arc and the Bahamas Borderland (North American plate).

  3. Interpretation of ages of arc magmatism, metamorphism, and collisional tectonics in the taconian orogen of western New England

    Science.gov (United States)

    Ratcliffe, N.M.; Hames, W.E.; Stanley, R.S.

    1998-01-01

    Available geochronologic ages of volcanic and intrusive rocks of the Taconian arc complex of western New England suggest that the Shelburne Falls and Bronson Hill arcs are not temporally or spatially discrete. Arc activity ranges from earliest Ordovician to Silurian. Activity in the Early and Middle Ordovician coincided with outboard accretionary tectonics and metamorphism that was contemporaneous with the older igneous activity in the Shelburne Falls arc and Bronson Hill arcs. Activity at about 455 to 445 Ma coincides with the collisional stage of the Taconian orogeny that affected Caradocian and older rocks of the Laurentian margin. The 455 to 445 Ma range for the collisional stage of Taconian orogeny in western New England is bracketed by biostratigraphic ages of sedimentary rocks formed on the Laurentian margin and 40Ar/39Ar ages of prograde hornblende formed during Taconian metamorphism. The previous 40Ar/39Ar age estimate of 465 Ma for this collisional and metamorphic event is now known to be too old because this age violates the age of metasedimentary rocks involved in the collisional tectonics. Acceptance of the newer 40Ar/39Ar age estimates of 445 to 450 Ma for Taconian metamorphism during collision establishes the contemporaneity with arc activity in the Bronson Hill arc. Taken together these data support the concept of a long-lived volcanic arc terrane(s) that prograded oceanward. Collision with this time-composite arc terrane(s) in the Caradocian produced the Taconian orogeny rather than the collision of a separate and smaller arc called the "Shelburne Falls arc" by Karabinos and others (1998).

  4. Volcanosedimentary Basins in the Arabian-Nubian Shield: Markers of Repeated Exhumation and Denudation in a Neoproterozoic Accretionary Orogen

    Directory of Open Access Journals (Sweden)

    Victoria Pease

    2013-07-01

    Full Text Available The Arabian-Nubian Shield (ANS includes Middle Cryogenian-Ediacaran (790–560 Ma sedimentary and volcanic terrestrial and shallow-marine successions unconformable on juvenile Cryogenian crust. The oldest were deposited after 780–760 Ma shearing and suturing in the central ANS. Middle Cryogenian basins are associated with ~700 Ma suturing in the northern ANS. Late Cryogenian basins overlapped with and followed 680–640 Ma Nabitah orogenesis in the eastern ANS. Ediacaran successions are found in pull-apart and other types of basins formed in a transpressive setting associated with E-W shortening, NW-trending shearing, and northerly extension during final amalgamation of the ANS. Erosion surfaces truncating metamorphosed arc rocks at the base of these successions are evidence of periodic exhumation and erosion of the evolving ANS crust. The basins are evidence of subsequent subsidence to the base level of alluvial systems or below sea level. Mountains were dissected by valley systems, yet relief was locally low enough to allow for seaways connected to the surrounding Mozambique Ocean. The volcanosedimentary basins of the ANS are excellently exposed and preserved, and form a world-class natural laboratory for testing concepts about crustal growth during the Neoproterozoic and for the acquisition of data to calibrate chemical and isotopic changes, at a time in geologic history that included some of the most important, rapid, and enigmatic changes to Earth’s environment and biota.

  5. High elevation of low-relief surfaces in mountain belts: does it equate to post-orogenic surface uplift?

    OpenAIRE

    BABAULT, Julien; Bonnet, Stéphane; Van Den Driessche, Jean; Crave, Alain

    2007-01-01

    We present experiments of upraising and relaxing topographies showing that peneplanation can occur above the ultimate base level (sea level). After active uplift, the erosion of a topography bounded by a piedmont generates a final smooth and highly elevated topography. Smoothing at high elevation is even possible during active uplift if the evolution of topography is disrupted by the deposition of the products of erosion on its piedmont which is the case at the transition from underfilled to ...

  6. SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Early Paleozoic volcanic rocks in Nuomuhong area occurred as basalt slice and meta-volcanic slice. SHRIMP zircon U-Pb dating of the basalt slice and the meta-volcanic slice show that the age of the basalt slice is 419±5 Ma, and that of the meta-volcanic slice is 401± 6 Ma. These ages directly testify that there existed Early Paleozoic ocean-continent transform in East Kunlun, the basalt slice was formed in an extensional mid-ocean ridge setting and the meta-volcanic rock slice was formed in an extrusion subduction and collision setting. The inherited zircon age of 1734 Ma in volcanic rocks reflects that the base of East Kunlun may be Middle Proterozoic.

  7. Electron microprobe chemical ages of monazite from Qinling Group in the Qinling Orogen:Evidence for Late Pan-African metamorphism?

    Institute of Scientific and Technical Information of China (English)

    CHEN Qiang; CHEN Nengsong; WANG Qinyan; SUN Min; WANG Xinyu; LI Xiaoyan; SHU Guiming

    2006-01-01

    Electron microprobe chemical dating was carried out on monazites enclosed in two generations of mineral paragenesis of St + Ky + Grt and Sil + And + Grt + St, respectively, from the Qinling Group. Two different ages, 520±23 Ma and 435±9 Ma,were obtained from these monazites. This indicates that the Qinling Group experienced a metamorphism during the Early Cambrian, which is probably in response to the Late Pan-African subduction-accretion tectonothermal event.

  8. Plate Margin Deformation and Active Tectonics Along the Northern Edge of the Yakutat Terrane in the Saint Elias Orogen, Alaska and Yukon, Canada

    Science.gov (United States)

    Bruhn, Ronald L.; Sauber, Jeanne; Cotton, Michele M.; Pavlis, Terry L.; Burgess, Evan; Ruppert, Natalia; Forster, Richard R.

    2012-01-01

    The northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane into the cusp of southern Alaska. The nature and magnitude of accretion and translation on upper crustal faults and folds is poorly constrained, however, due to pervasive glaciation. In this study we used high-resolution topography, geodetic imaging, seismic, and geologic data to advance understanding of the transition from strike-slip motion on the Fairweather fault to plate margin deformation on the Bagley fault, which cuts through the upper plate of the collisional suture above the subduction megathrust. The Fairweather fault terminates by oblique-extensional splay faulting within a structural syntaxis, allowing rapid tectonic upwelling of rocks driven by thrust faulting and crustal contraction. Plate motion is partly transferred from the Fairweather to the Bagley fault, which extends 125 km farther west as a dextral shear zone that is partly reactivated by reverse faulting. The Bagley fault dips steeply through the upper plate to intersect the subduction megathrust at depth, forming a narrow fault-bounded crustal sliver in the obliquely convergent plate margin. Since . 20 Ma the Bagley fault has accommodated more than 50 km of dextral shearing and several kilometers of reverse motion along its southern flank during terrane accretion. The fault is considered capable of generating earthquakes because it is linked to faults that generated large historic earthquakes, suitably oriented for reactivation in the contemporary stress field, and locally marked by seismicity. The fault may generate earthquakes of Mw <= 7.5.

  9. Origin of eclogite and garnet pyroxenite from the Moldanubian Zone of the Bohemian Massif, Czech Republic and its implication to other mafic layers embedded in orogenic peridotites

    Czech Academy of Sciences Publication Activity Database

    Obata, M.; Hirajima, T.; Svojtka, Martin

    2006-01-01

    Roč. 88, 1-2 (2006), s. 321-340. ISSN 0930-0708 R&D Projects: GA AV ČR IAA3013006 Institutional research plan: CEZ:AV0Z30130516 Keywords : eclogite * pyroxenite * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.038, year: 2006

  10. Cave levels as proxies for measuring post-orogenic uplift: Evidence from cosmogenic dating of alluvium-filled caves in the French Pyrenees

    Science.gov (United States)

    Calvet, M.; Gunnell, Y.; Braucher, R.; Hez, G.; Bourlès, D.; Guillou, V.; Delmas, M.

    2015-10-01

    The rates and chronology of valley incision in mountain ranges have been studied in various parts of the globe, but the causes of river incision are often blurred because tectonic, climatic, and sea level-related forcing signals are difficult to distinguish from one another. The Têt River limestone gorge in the Eastern Pyrenees, which displays multiple cave levels containing datable alluvial deposits, provides an opportunity for clarifying this debate. Horizontal epiphreatic passages in limestone can be used as substitutes for fluvial terraces because they correspond to former valley floors and, therefore, also record the position of former local base levels. In the Têt canyon, the passages are filled with quartz-rich sand and gravel sequences that can be dated by 26Al/10Be burial dating. The canyon has cut into a Middle Miocene pediment system-now forming a raised plateau at 1250-1500 m-and displays nine cave levels over a vertical height of 1 km. One alluvial fill sequence in a cave at + 270 m above datum (i.e., the local river bed) yielded a weighted mean age of 5.14 ± 0.41 Ma; another, situated at + 110 m above datum, yielded weighted mean ages of 2.23 ± 0.230 Ma and 1.20 ± 0.286 Ma. The data convert to a mean incision rate of ~ 52 m·Ma- 1 since the beginning of the Pliocene, and involved an acceleration to 92 m·Ma- 1 during the Quaternary. Pre-burial catchment denudation rates range from 35 to 7 m·Ma- 1, and these also doubled during the early Quaternary. It is concluded that: (i) valley incision into the Miocene pediment has been occurring since 5, probably 10 Ma; (ii) there is no evidence of a Messinian canyon in the Villefranche gorge, strongly suggesting through various additional indicators that interference of the Messinian Salinity Crisis with the canyon incision history was minimal; (iii) valley deepening was not a steady process, and recorded periods of stability around 1-2 Ma and perhaps 6-5 Ma; and (iv) the terraced network of epiphreatic cave levels is primarily explained by tectonic uplift. It follows that the elevated erosion surfaces of the Pyrenees, such as the Miocene pediment directly situated above the canyon edge, were not shaped at high elevations, e.g., by 'altiplanation'; they formed, instead, close to base level and were uplifted in successive stages by tectonic processes. The study emphasizes the more general proposition that tectonic signals (as opposed to climatic or eustatic) in valley-incision chronologies are best singled out at locations situated among the outer ranges of mountain belts, i.e., in canyons such as the Têt, that respond immediately to base level changes relative to the adjacent foreland. In the inner ranges, fluvial incision is more likely to be affected by the interference of climatic factors (e.g., glaciers), or to be delayed by bedrock impediments to upstream-propagating knickpoints.

  11. Paleomagnetism of the Gran Sasso range salient (central Apennines, Italy): Pattern of orogenic rotations due to translation of a massive carbonate indenter

    OpenAIRE

    Satolli, S.; Dipartimento di Scienze della Terra, Università di Chieti, Chieti, Italy; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Calamita, F.; Dipartimento di Scienze della Terra, Università di Chieti, Chieti, Italy

    2005-01-01

    We report on the paleomagnetism (39 new sites) of Gran Sasso, an indenter-controlled salient of the external central Apennines formed by two orthogonal limbs. We find that Gran Sasso is a complex salient, paleomagnetically corresponding to neither a nonrotating nor an oroclinal end-member. Data from the core of the arc show that the indenter itself did not undergo any rotation. Conversely, rotations of variable magnitude and sign are observed along the curveshaped thrust fronts. Rotatio...

  12. Tracing metamorphism, exhumation and topographic evolution in orogenic belts by multiple thermochronology: a case study from the Nízke Tatry Mts., Western Carpathians

    Czech Academy of Sciences Publication Activity Database

    Danišík, M.; Kadlec, Jaroslav; Glotzbach, Ch.; Weisheit, A.; Dunkl, I.; Kohút, M.; Evans, N. J.; Orvošová, M.; McDonald, B. J.

    2011-01-01

    Roč. 104, č. 2 (2011), s. 285-298. ISSN 1661-8726 R&D Projects: GA AV ČR IAA3013201 Institutional research plan: CEZ:AV0Z30130516 Keywords : (U–Th–[Sm])/He dating * fission track dating * thermal modelling * exhumation * zircon * apatite * Nízké Tatry Mts. * Western Carpathians Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.879, year: 2011

  13. Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand

    International Nuclear Information System (INIS)

    Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing veins in the Alpine Schist and from Miocene gold-bearing veins and vein breccias from the Shotover-Macetown area in the northwest Otago Schist belt. The lead isotopic signatures are consistent with derivation of Pb in the vein minerals predominantly from metasedimentary rocks that underlie the region. Differences in Pb isotopic signatures between deposits are interpreted to result from lateral and vertical lithological variability within the source rock mass. The host rocks also contain metabasic rocks with N-MORB, E-MORB or within-plate basalt chemistry. However, the observed Pb isotopic signatures in the gold-bearing veins preclude incorporation of significant amounts of Pb from the metabasites. The Pb isotopic signatures of lamprophyre dikes that were intruded into the Otago Schist coeval with Miocene gold mineralisation are distinctly more radiogenic than those of the hydrothermal veins. Thus, although the lamprophyre dikes were emplaced into similar extensional structural sites to the gold-bearing veins, there was no genetic relationship between lamprophyre dikes and gold mineralisation. (author). 67 refs., 5 figs., 2 tabs.

  14. Magnetic fabrics of the syn to post orogenic granite suites of the Brusque metamorphic complex (Dom Feliciano Belt, Santa Catarina, Brasil

    International Nuclear Information System (INIS)

    The Dom Feliciano belt in southern Brazil and Uruguay has accommodated the collision between the cratons of Kalahari and Congo versus the Luis Alves microplate as a fragment of the Rio de La Plata craton during the Rio Doce orogeny in the late Neoproterozoic. The Sierra Ballena - Major Gercino shear zone was interpreted as the suture between the cratons. In the state of Santa Catarina three suites of highly evolved granites intruded the Brusque metamorphic complex in the northwest of the Major Gercino shear zone. Magmatic contacts between the different suites denote to their close temporal intrusion sequence. Shear zone activity is documented by local low temperature brittle deformation of the intrusive suites. Fabrics of the granites were obtained by the measurement of the anisotropy of the magnetic susceptibility (AMS). Low bulk susceptibilities (Kvol -6 SI) and a low degree of the total anisotropy (P' < 1.07) suggest a paramagnetic origin of the magnetic fabrics that may be directly correlated with the macroscopic rock fabric. Planar fabrics form a dome-like foliation pattern for the main Valsungana intrusion occupying the southwestern part of the NE-SW elongated intrusion. Linear fabrics show a weakly defined ENE-WSW trend parallel to the late stage transcurrent extension of the basement. It is suggested that a number of dome-like intrusions that follow the trend of the Major Gercino shear zone in the northwest were emplaced and subsequently amalgamated in the course of magma ascent leading to present outcrop shape of the intrusive complex

  15. Sequence Stratigraphy, Correlations Between Wopmay Orogen and Kilohigok Basin, and Further Investigations of the Bear Creek Group (Goulburn Supergroup), District of Mackenzie, N.W.T.

    OpenAIRE

    Grotzinger, J. P.; Adams, R D; McCormick, D. S.; Myrow, P.

    1989-01-01

    Results indicate that the Rifle, Beechey, Link, and basal Burnside Formations are correlative with the lower member of the Odjick Formation (Coronation Supergroup). The lower Burnside Formation is also correlative with the middle member of the Odjick Formation. Correlatives of the Hackett Formation and Kimerot Group are not present in the Coronation Supergroup. In the Tinney Hills area the Rifle Formation is divided into four sequences. The marine to alluvial transition in the north Tin...

  16. Besshi-type mineral systems in the Palaeoproterozoic Bryah Rift-Basin, Capricorn Orogen, Western Australia:Implications for tectonic setting and geodynamic evolution

    Institute of Scientific and Technical Information of China (English)

    Franco Pirajno; Yanjing Chen; Nuo Li; Chao Li; Limin Zhou

    2016-01-01

    In this contribution we use VMS mineral systems in the Bryah rift-basin to constrain the tectonic setting of the widespread mafic and ultramafic magmatism that characterises the rift-basin in question. Two distinct, but temporally closely associated, lithostratigraphic sequences, Narracoota and Karalundi For-mations, are discussed. The Karalundi Formation is the main host of VMS mineral systems in the region. The Karalundi Formation consists of turbiditic and immature clastic sediments, which are locally intercalated with basaltic hyaloclastites, dolerites and banded jaspilites. We propose that the basaltic hyaloclastites, dolerites and clastics and jaspilites rocks, form a distinct unit of the Karalundi Formation, named Noonyereena Member. The VMS mineral systems occur near the north-east trending Jenkin Fault and comprise the giant and world-class DeGrussa and the Red Bore deposits. The nature of these deposits and their intimate association with terrigenous clastic rocks and dominantly marine mafic volcanic and subvolcanic rocks, as well as the common development of peperitic margins, are considered indicative of a Besshi-type environment, similar to that of present-day Gulf of California. Our Re-Os age data from a primary pyrite yielded a mean model age of 2012 ? 48 Ma, which coincides (within error) with recent published Re-Os data (Hawke et al., 2015) and confirms the timing of the proposed geodynamic evo-lution. We propose a geodynamic model that attempts to explain the presence of the Narracoota and Karalundi Formations as the result of mantle plume activity, which began with early uplift of continental crust with intraplate volcanism, followed by early stages of rifting with the deposition of the Karalundi Formation (and Noonyereena Member), which led to the formation of Besshi-type VMS deposits. With on-going mantle plume activity and early stages of continental separation, an oceanic plateau was formed and is now represented by mafic-ultramafic rocks of the Narracoota Formation.

  17. Tectono-metamorphic evolution of a hot orogen during Gondwanaland assembly: a case study from Palni hills metapelite granulite, south India

    Science.gov (United States)

    Bhadra, S.; Nasipuri, P.

    2012-04-01

    This study deals with the tectono-metamorphic evolution of Sapphirine-cordierite-bearing metapelite granulite at Perumalmalai, south India, that occurs as enclave within deformed migmatitic enderbite gneiss of Kodaikanal massif, Madurai granulite block (MB), south India. Pre-peak mineral paragenesis is represented by an inclusion assemblage of sillimanite + plagioclase + Ti-rich biotite ±quartz in Al-rich orthopyroxene. Dehydration melting of biotite marked the onset of ultra-high temperature metamorphism (M1A, ~1000 °C, 10 Kbar). Early stage of retrograde metamorphism (M1B) is characterized by the development of type1-symplectite and corona textures. In type1-symplectite an innermost vermicular sapphirine (Spr - XMg: 0.90, Al/Si: 6.17) - cordierite (Crd) symplectite on sillimanite is followed by cordierite (XMg: 0.94) moat. A meso-perthitic layer laced the interface between cordierite moat and orthopyroxene porphyroblast, the latter showing prominent rim-ward decrease in Al2O3 (up to 3 wt%). The cordierite rim at the interface between sillimanite and orthopyroxene characterizes corona texture. Type1-symplectite and corona domains are circumnavigated by Ti-poor biotite (TiO2: ~3.2 wt%) showing shape preferred alignment, and set in a feldspar matrix showing wide compositional range. By implication, leucosome crystallization was possibly prolonged and enhanced by deformation. Type1-symplectite and corona textures were resulted from melt-solid interaction or silica-metasomatism during early stage of retrogression, Opx+Sil = Spr+Crd → Opx+Sil+melt = Crd. The retrograde metamorphism is constrained at 9 kbar and 950°C, implying an early stage of near-isothermal decompression. Late stage retrograde metamorphism (M2) is also characterized by symplectite textures, type2-symplectite, with innermost sapphirine-cordierite symplectite followed by cordierite corona. Sapphirine in type2-symplectite domain (XMg: 0.89; Al/Si: 5.92), which occurs as inclusion in Opx, is chemically distinct than sapphirine occurring in texturally similar type1 symplectite domain. Orthopyroxene porphyroblast records largest rim-ward decrease in Al2O3 (core: ~ 8 wt%; rim: 4.4 wt%). Also this domain lacks any veneer of meso-perthitic feldspar. P, T condition of M2 metamorphism is constrained at 7.5 kbar, 900 °C indicating a second stage of near-isothermal decompression (Opx+Sil = Spr + Crd). Monazites though occur as small inclusion (40 μm) in orthopyroxene porphyroblast, are predominant and larger (>100μm) in the biotite-feldspar defining leucosome domain suggesting melt-crystallization-assisted growth of monazite. Consequently, 560 Ma ages, which is recorded either uniformly from Opx-included monazite or from the core of matrix monazite, qualify to peak M1A and M1B metamorphism. The age relation further re-affirms that MB is a part of the transcontinental Pan-African granulite block that formed during Gondwanaland assembly and extends across Madagascar-India-Antarctica. As documented recently, final juxtaposition of MB with Archean Dharwar craton to the north was during Cambrian and marked by the closure of paleo-Mozambique Ocean along the Palghat Cauvery Shear Zone. Importantly, younger ages of 496 Ma were recorded from the rim of matrix monazite grains. Without proper textural relation, significance of this age remains uncertain. However, we tend to believe that 500 Ma age corresponds to M2 retrograde metamorphism and final exhumation of the UHT granulite at Perumalmalai. If proven, this possibly coincides with the tectonic extrusion related domal uplift of the MB during the final stage of Gondwanaland assembly.

  18. Kinematically - controlled deep contact of the East European Platform and the Carpathian Orogen in the Vrancea Bending Zone and contact with the Neogene Volcanic Zone

    Science.gov (United States)

    Dragut, Dorina-Alina

    2016-04-01

    The complex zone between the Moesian and East European platforms to the south and east and the Southern Europe continental units were amalgamated in the last 20 million years in an intricate dynamics of what was thought to be the eastern component of the Alpine Tethys. By seismic tomography and attenuation studies, a high velocity body extended from the near surface to deeper levels than 300 km was pointed out as having a very complex geometry which suggests a very active three dimensional evolution. Most of the frequent, persistent and clustered seismic events from this contact area known as Vrancea Seismogenic Zone are located into this high velocity body. The origin of this seismicity is highly controversial. Among most of the accepted assumptions on its origins, two look like most robust: (a) the recent studies consider the subduction of the Tehys oceanic lithosphere, and (b) delamination of a portion of the East European / Moesian continental mantle after the oceanic lithosphere subduction ended sometimes in the mid-Miocene. The delamination zone was probably a near-horizontal mid-lithospheric interface dripping down into the mantle. Towards the internal part of the Bend Zone, the volcanic activity, dominant in the Neogene time, ceased some 400,000 years ago but there are evidences that the last stages of the alkali-basaltic volcanic activity has post-volcanic effects even at present. We integrate satellite geodesy results with various seismological studies in order to explain the very small values of the present-day horizontal component of the velocity field, almost at the edge of technological detectability. The vectors have a very peculiar distribution which we interpret as supporting the idea of the mantle flow around the high seismic velocity body detected via seismological investigations. We estimate an anti-clockwise deep rotation flow around the lithospheric "slab" which is seated adjacent to the astensosphere advancing towards the surface, having surface expressions. We postulate this as a result of deep, mantle flow, accompanied by penetration of the melting processes at the contact between the astenosphere and the high velocity body.

  19. Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault; implications for the northern margin of the Central Anatolian Plateau, Turkey

    OpenAIRE

    Yildirim, C.; Schildgen, T.F.; Helmut Echtler; H. Melnick; Strecker, M. R.

    2011-01-01

    Surface uplift at the northern margin of the Central Anatolian Plateau (CAP) is integrally tied to the evolution of the Central Pontides (CP), between the North Anatolian Fault (NAF) and the Black Sea. Our regional morphometric and plate kinematic analyses reveal topographic anomalies, steep channel gradients, and local high relief areas as indicators of ongoing differential surface uplift, which is higher in the western CP compared to the eastern CP and fault-normal components of geodetic sl...

  20. Stable isotope and fluid inclusion signatures of hydrothermal fluids in transcrustal fault zones: significance for orogenic, Archean lode-gold mineralization

    International Nuclear Information System (INIS)

    Full text: Large to giant (>1t) gold deposits are typically hosted in second- and third-order structures adjacent to largely barren, transcrustal fault zones. Gold-bearing hydrothermal fluids have been channelled within the transcrustal fault zones from mantle and deep crustal sources into the second- and third-order structures, where gold has been deposited. Transcrustal fault zones are long-lived structures with specific deformation events relating to gold deposition in the second- and third-order structures. For example the Archaean Perseverance Fault in the Yilgarn Craton of Western Australia evolved from a wide (5km) ductile shear zone during D2 to a narrow (2-CH4-dominated compositions with minor H2O and H2S components, whereas there are H2O-dominated H2O-CO2+CH4 fluids with a significant H2S component in the second- and third-order shear zones at the Sigma gold deposit, a major gold deposit 5km to the north of the CTZ. These differences can be explained by continuous phase separation, with CO2-vapour escape into the upper portions of the ductile uncapped CTZ, contrasting with in-situ phase separation of the gold-bearing fluids in crack-seal veins in the second-order shear zones at Sigma, with trapping of both the episodic vapour and liquid components in individual sealed veins. Gold mineralization in the second- and third-order structures appears to be controlled by the high H2S activity of the aqueous hydrothermal fluids. because gold was likely carried in a bisulphide complex and was deposited during sulfidation reactions in the wallrock and phase separation in the quartz vein. In contrast, the carbonic fluids in the CTZ lacked the ability to carry significant metal ligands due to their low H2S activity. Oxygen isotopes from hydrothermal quartz within the CTZ (13.3 to 15.6 per mil, av. 14.0 per mil; VSMOW) are heavier than those from mineralized quartz veins in second- and third-order shear zones (11.8 to 19.6 per mil, av. 12.2 per mil). Calculated d18O fluid compositions for quartz in the CTZ range from 8.0 to 10.3 per mil at 350 deg C (based on arsenopyrite and chlorite thermometry). Hydrogen isotopes from fluid inclusion waters trapped in quartz have a large variation from -62.5 per mil to -7.2 per mil in the CTZ fluids, whereas hydrogen in fluid inclusions in quartz in the second- and third-order shear zones shows a restricted range from -67.6 to -39.8 per mil. The oxygen isotope shift of about 2 per mil from the CTZ to the second- and third-order fault zones may be explained by two competing processes: 1) the hydrothermal fluids in the CTZ equilibrated, at least partially, with metasedimentary rocks in the footwall, and or 2) there was fractionation of oxygen isotopes during phase immiscibility of a combined H2O-CO2 fluid. The preferential trapping of CO2-rich fluids in the CTZ, and H2O-rich fluids in the second- and third-order fault zones, therefore, could account for the shift in d18O. At present, the first process is preferred, because of the ubiquitous presence of the metasedimentary rocks in the footwall and the consistent d18O composition of the CTZ, even in hydrothermal quartz veins which contain significant H2O. The large variation in the hydrogen isotopes in fluid inclusions in quartz in the CTZ may be explained by late Archean and post-Archean reactivation of the CTZ and the introduction of fluids related to late-fractures fills, whereas apparently minor reactivation of the second- and third-order structures resulted in a restricted range of dD. Copyright (1999) Geological Society of Australia

  1. Reinterpretacion estratigráfica y petrología de la Formacion Chuscho, Precordillera de La Rioja Stratigraphical reinterpretation and petrology of the Cerro Chuscho Formation. Precordillera of La Rioja

    Directory of Open Access Journals (Sweden)

    L.E. Fauqué

    2003-06-01

    Full Text Available En la Precordillera de Jagüé (provincia de la Rioja, fueron agrupados bajo la denominación de Andesita Cerro Chuscho los afloramientos de volcanitas de: Punta del Agua, Cerro Chuscho y Las Casitas. Se consideraba a estas rocas comagmáticas, constituyendo el cerro Chuscho un cono subvolcánico heterogéneo compuesto por una autobrecha de flujo, integrada por rocas calcoalcalinas correspondientes al ciclo precordillerano. En este trabajo se asigna a los afloramientos del cerro Chuscho (Formación Chuscho como un complejo de volcanitas máficas intraordovícicas, representado por diques y filones de diabasas y por basaltos de estructura almohadillada. Conforman una facies ofiolítica asociada con las sedimentitas ordovícicas y, por lo tanto, quedarían incluidas en la Faja Ofiolítica Famatiniana, asociada a la apertura de un rift oceánico de cuenca marginal formado durante la acreción de Chilenia en el Cambro-Ordovícico. Sus características parecen cambiar a lo largo del rift, pasando de N-Morb en la Cordillera Frontal a E-Morb (P-MORB en la Precordillera de San Juan y La Rioja; estas diferentes características se deben muchas veces al cambio de elevación del rift respecto del manto. Por su parte, las Andesitas Punta del Agua (Formación Punta del Agua, son andesitas orogénicas de arco volcánico, de acuerdo a sus características geoquímicas, con edades que irían desde el Carbonífero superior al Pérmico inferior.In the region of Precordillera of Jagüe, in La Rioja province, the Palaeozoic volcanic rocks, known as the Punta del Agua, Cerro Chuscho and Las Casitas formations, have been grouped into one unit, the "Andesita Cerro Chuscho". These rocks have been considered to be comagmatic and to form a subvolcanic complex of autoclastic breccias and calc-alkaline lava flows of the precordilleran orogenic cycle. In our study, the Cerro Chuscho Formation is reinterpreted as a mafic volcanic complex. Of Ordovician, it includes dykes

  2. Anomalous values of gravity and magnetism in the western margin of Gondwana

    Science.gov (United States)

    Weidmann, Cecilia; Gimenez, Mario; Klinger, Federico Lince; Alvarez, Orlando

    2016-01-01

    This research is based on a joint geological and geophysical study performed in the South Central Andes region. We acquired and processed terrestrial and satellite gravity data, as well as terrestrial and aeromagnetic data. Balanced geological cross-sections were constrained by physical properties of rocks (densities and magnetic susceptibilities obtained from field samples and well log). This study was performed in order to interpret a complex region that is still under debate: the location of Famatinian magmatic arc and its boundary with the Cuyania terrain. By means of gravity anomaly we developed direct and inverse models constrained by field data. The existence of a major high-density geological structure was evidenced from these models, located below the Vinchina basin and to the east of Cerro Rajado respectively. The existence of such gravity high could be linked to the boundary between the Famatinian magmatic arc and the accreted Cuyania wedge.

  3. La formación Chango Real (NW de Sierras Pampeanas, República Argentina), ejemplo del magmatismo paleozoico (Cambrico?). Diferencias geoquímicas con batolitos ordovicicos

    OpenAIRE

    Lazarte, J. E.

    1992-01-01

    Chango Real Formation is part of Lower Paleozoic magmatism in Sierras Pampeanas Range, Northwestern Argentina. It is a biotitic, granitic ortogneiss, peraluminous, calcalkaline from Cambrian(?), different from others Ordovician batholiths. The origin of the magma was in a convergent active margin of plate, generated in the middle crust. It evolved by fractional crystallization (the last stage ended at 4 kb and 680º C) and was deformed during Famatinian Cycle (Ordovician-Silurian).L...

  4. The tectonic history of the Niğde-Kırşehir Massif and the Taurides since the Late Mesozoic: Paleomagnetic evidence for two-phase orogenic curvature in Central Anatolia

    Science.gov (United States)

    Ćinku, Mualla Cengiz; Hisarli, Z. Mümtaz; Yılmaz, Yücel; Ülker, Beyza; Kaya, Nurcan; Öksüm, Erdinç; Orbay, Naci; Özbey, Zeynep Üçtaş

    2016-03-01

    The Niğde-Kırşehir Massif, known also as the Central Anatolian Block, is bordered by the sutures of the Neotethys Ocean. The massif suffered several deformation phases during and after the consumption of the surrounding oceans and the postcollisional events of the continental pieces of Anatolia in latest Cretaceous to Miocene. Previous paleomagnetic studies on the Niğde-Kırşehir Massif and its surroundings displayed either insufficient data or have claimed large rotations and/or remagnetization. In order to understand the tectonic history of the Niğde-Kırşehir Massif and its adjacent blocks we have sampled 147 different sites in the age range of Upper Jurassic to Miocene from the Niğde-Kırşehir Massif throughout its W/SW and E/SE boundaries and the central-southeastern Taurides. The results display that except the limestones in central Taurides, all rocks examined carry a primary magnetization. Among these an important finding is that rotations between the massif and the central-eastern Taurides indicate an oroclinal bending with counterclockwise rotation of R = 41.1° ± 7.6° in the SE and clockwise rotation of R = 45.9° ± 9.3° in the central Taurides from Upper Cretaceous rocks with respect to the African reference direction. Paleomagnetic rotations in the SE Taurides are compatible with the vergent direction of the thrusts generated from consumption of the Intra-Tauride Ocean prior to postcollisional convergence between Taurides and the massif. In the central Taurides it has been shown that the clockwise rotation of 45.9 ± 9.3 started in Middle Eocene, because of a remagnetization in Upper Cretaceous limestones. The deformation was linked to the final closure of the southern Neotethys and the collision between the African and Eurasian plates. In the Niğde-Kırşehir Massif counterclockwise rotation up to 25.5° ± 7.3° is recognized during Middle Eocene and interpreted in terms of block rotation together with the Taurides. After the Miocene a counterclockwise rotation of 16.8° ± 3.9° along the Eastern Taurides shows that this area was mostly affected by the westward movement of Anatolia despite the Niğde-Kırşehir Massif and its SW/W area—the central Taurides—which is recognized as stable with counterclockwise rotation less than 10°.

  5. Origin and Tectonic Evolution of the Orogenic Nappe Structure Belt and Relative Basins of the Cuba Islands%古巴推覆构造带周边盆地充填序列及其构造演化

    Institute of Scientific and Technical Information of China (English)

    陈榕; 吴朝东; 申延平; 张晨晨; 房亚男

    2014-01-01

    根据古巴群岛地层特征,将古巴推覆构造带及其周边划分为尤卡坦、巴哈马、中部