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Sample records for astaneh granitoid massif

  1. (222)Rn activity concentration differences in groundwaters of three Variscan granitoid massifs in the Sudetes (NE Bohemian Massif, SW Poland).

    Science.gov (United States)

    Przylibski, Tadeusz A; Gorecka, Joanna

    2014-08-01

    Based on research conducted in three Variscan granitoid massifs located within the crystalline Bohemian Massif, the authors confirmed that the higher the degree of their erosional dissection, the smaller the concentration of (222)Rn in groundwaters circulating in these massifs. This notion implies that radon waters and high-radon waters, from which at least some of the dissolved radon should be removed before feeding them as drinking water to the water-supply system, could be expected in granitoid massifs which have been poorly exposed by erosion. At the same time, such massifs must be taken into account as the areas of possible occurrence of radon medicinal waters, which in some countries can be used for balneotherapy in health resorts. Slightly eroded granitoid massifs should be also regarded as very probable radon prone areas or areas of high radon potential.

  2. Paleoproterozoic anorogenic granitoids of the Zheltav sialic massif (Southern Kazakhstan): Structural position and geochronology

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    Tretyakov, A. A.; Degtyarev, K. E.; Sal'nikova, E. B.; Shatagin, K. N.; Kotov, A. B.; Ryazantsev, A. V.; Pilitsyna, A. V.; Yakovleva, S. Z.; Tolmacheva, E. V.; Plotkina, Yu. V.

    2016-01-01

    The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U-Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural-geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm-Nd isotopic—geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan.

  3. Geochemistry and Sm-Nd isotopic composition of the Imiter Pan-African granitoids (Saghro massif, eastern Anti-Atlas, Morocco): Geotectonic implications

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    Baidada, Bouchra; Cousens, Brian; Alansari, Abdelkhalek; Soulaimani, Abderrahmane; Barbey, Pierre; Ilmen, Said; Ikenne, Moha

    2017-03-01

    The Imiter inlier (eastern part of the Moroccan Anti-Atlas) is located on the northwestern border of the West African Craton (WAC) and exhibits a range of Pan-African granitoids. Three massifs that crosscut the Imiter Saghro Group were targeted in this work: the Igoudrane granodiorite, Bou Teglimt granodiorite and Bou Fliou granite. We present here additional geochemical analyses (major and trace elements) and Sm-Nd isotopic data, which define two distinct groups: (i) the Igoudrane massif (677 Ma) and (ii) the Bou Teglimt granodiorite (576 Ma) and the Bou Fliou granite (550 Ma). Geochemical data confirm the calc-alkaline signature of the studied granitoids. Both groups of granitoids are slightly peraluminous and show strong negative anomalies in Nb, Ta and Ti in multi-element plots normalized to the primitive mantle. The granitoids have low 143Nd/144Nd initial ratios (0.5116-0.5117), with TDM model ages ranging from 1.73 to 1.52Ga. The εNd(t) values are negative, decreasing from the Igoudrane samples (-1.1 to -3.1) to the Bou Teglimt granodiorite (-3.0 to -3.3) and Bou Fliou (-4.2 to -4.8). All these data suggest a mixed magmatic origin involving a juvenile mantle source and an old, at least Paleoproterozoic crust. Given Mesoproterozoic rocks are lacking or very scarce in the Anti-Atlas, these results confirm the existence of an old cratonic basement beneath the eastern Anti-Atlas, and therefore suggest that the northern border of the West African Craton must be placed further to the north, as suggested by previous work in this region.

  4. How is strain localized in a meta-granitoid, mid-crustal basement section? Spatial distribution of deformation in the central Aar massif (Switzerland)

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    Wehrens, P.; Baumberger, R.; Berger, A.; Herwegh, M.

    2017-01-01

    This study investigates strain distribution in granitoid rocks formerly in the middle crust in the Central Aar massif, Switzerland and places the deformation behavior in the tectonic framework of the Alpine orogeny. Strain is heterogeneously distributed in terms of strain partitioning forming several hundreds of closely spaced shear zones (SZ) (>80 SZ/km with SZ thicknesses <10 cm; about 10 SZ/km with SZ thicknesses of 0.5-10 m) separating 3D bodies of low to moderate background strain. Both the degree of background-strain intensity as well as the number of shear zones increases from granitic to granodioritic host rocks and is controlled by primary variations in the mica content between 10 and 15 vol% (granodiorite) and <8 vol% (granite). Shear zones evolved from ductile shearing in granodiorites, whereas they often nucleated from fractures in the stronger granites. The majority of the steep shear zones preferentially accommodated upward motion by the southern block leading to an increase in peak metamorphic conditions from 250 °C in the North to 450 °C in the South of the Aar massif. The shear zones initiated at about 18-20 km depths during a stage of crustal thickening (Handegg phase). Subsequent deformation reactivated some shear zones with a gradual transition from reverse dip-slip over oblique-slip to strike-slip shear zones under local transpressional conditions (Oberaar phase).

  5. Weathering profiles in granitoid rocks of the Sila Massif uplands, Calabria, southern Italy: New insights into their formation processes and rates

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    Scarciglia, Fabio; Critelli, Salvatore; Borrelli, Luigi; Coniglio, Sabrina; Muto, Francesco; Perri, Francesco

    2016-05-01

    In this paper we characterized several weathering profiles developed on granitoid rocks in the Sila Massif upland (Calabria, southern Italy), integrating detailed macro- and micromorphological observations with physico-mechanical field tests and petrographic, mineralogical and geochemical analyses. We focused our attention on the main weathering and pedogenetic processes, trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties, and two common weathering indices, such as the micropetrographic index (Ip) and the chemical index of alteration (CIA). Our results showed that sericite on plagioclase and biotite chloritization, that represent inherited features formed during late-stage hydrothermal alteration of granitoid rocks, may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions, especially in lower weathering grade classes. Moreover, the frequent identification of Fe-Mn oxides and clay coatings of illuvial origin (rather than or in addition to those formed in situ), both at the macro- and microscale, may also explain an overestimation of the weathering degree with respect to field-based classifications. Finally, some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes (cryoclastism and thermoclastism), that lead to rock breakdown even when chemical weathering is not well developed. Hence, our study showed that particular caution is needed for evaluating weathering grades, because traditional field and geochemical-petrographic tools may be biased by inherited hydrothermal alteration, physical weathering and illuvial processes. On the basis of chronological constraints to soil formation obtained from a 42 ka-old volcanic input (mixed to granite parent materials) detected in the soil cover of the Sila Massif upland, a first attempt to estimate

  6. Layered granitoids: Interaction between continental crust recycling processes and mantle-derived magmatism: Examples from the Évora Massif (Ossa-Morena Zone, southwest Iberia, Portugal)

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    Moita, Patrícia; Santos, José F.; Pereira, M. Francisco

    2009-08-01

    In this paper, field, petrographic, mineralogical, geochemical and isotopic (Rb-Sr and Sm-Nd) information from three areas within the Évora Massif (Iberian Variscan Orogen) is presented and discussed aiming at to unravel the relationships between granitoids and units mapped as migmatites and also to evaluate the interplay between mantle and crustal derived magmas. One of the areas - Almansor - displays a well-developed compositional layering (concordant with the regional Variscan structure) which was considered, in previous works, as an alternation of leucosome and melanosome. In this study, the layering is described as intercalation of diatexites, weakly foliated granitoids and trondhjemitic veins. Diatexites have characteristics of crustal melts plus restitic material and, according to geochemical and isotopic evidence, result from anatexis of Ediacaran metasediments. Weakly foliated granitoids and trondhjemitic veins from Almansor have calc-alkaline signatures and may be related to each other by crystal fractionation processes; however, the mixing between mafic (mantle-derived) and felsic (diatexitic melt) magmas revealed by the isotopic data may also explain their genesis. In the Alto de São Bento area, several igneous lithologies (tonalites, granodiorites, porphyritic granites and leucogranites) are present and show typical isotropic igneous textures. Despite structural and textural differences, geochemical data support, for most rocks, an origin from the same calk-alkaline suite, also present at Almansor. The Alto de São Bento leucogranites have an isotopic signature that, although different from that obtained in the Almansor diatexites, is still compatible with an origin involving melting of Ediacaran metasediments; compositions, with very low contents of usually incompatible elements, flat normalized REE patterns and strong negative Eu anomalies, suggest that the anatectic melt has undergone crystal fractionation processes before reaching the composition

  7. Petrogenesis and geochemistry of circa 2.5 Ga granitoids in the Zanhuang Massif: Implications for magmatic source and Neoarchean metamorphism of the North China Craton

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    Wang, Junpeng; Kusky, Timothy; Wang, Lu; Polat, Ali; Wang, Songjie; Deng, Hao; Fu, Jianmin; Fu, Dong

    2017-01-01

    The tectonic framework of the North China Craton (NCC) during late Archean to early Paleoproterozoic (circa 2.5 Ga) is still lacking comprehensive understanding due to subsequent strong deformation and metamorphic overprinting events. Circa 2.5 Ga magmatic and metamorphic activities are widely spread throughout the NCC, which can be used as an efficient target to better understand the tectonic evolution at this period. In this study, based on a detailed field, structural, geochemical, geochronological and Sm-Nd isotopic study, we focus our work on the Haozhuang granitoids in the Zanhuang Massif located at the eastern margin of the Central Orogenic Belt of the NCC. The granitoids mainly include undeformed pegmatite and granodiorite. One pegmatite and two granodiorite samples yield zircon 207Pb/206Pb ages of 2513 ± 29 Ma, 2511 ± 36 Ma and 2528 ± 18 Ma, respectively. The granodiorites show metaluminous and shoshonitic to high-K calc-alkaline series characteristics with A-type granite affinity. The circa 2.5 Ga granodiorites have highly negative εNd(t) values (- 29.22 - 33.12) and TDM model ages between 2671 Ma and 3151 Ma. This work shows clearly, from whole-rock major and trace elements and Sm-Nd isotopic studies, that the Haozhuang granodiorites were derived from partial melting of old and thickened TTG crust rather than mantle sources, and formed in a subduction-related tectonic setting. With geochemical comparison studies to other similar-aged granitic rocks in the Zanhuang Massif, we suggest that these granitic rocks possibly have a certain correlation during the magma evolution. Coupled with our previous geochemical and isotopic studies on circa 2.5 Ga mafic dike swarms, we propose that the similar-aged granitic rocks and mafic dike swarms were produced by an east-dipping subduction polarity reversal event following an arc-continent collision between the Fuping/Wutai island arc and Eastern Block of the NCC above a west-dipping slab. The east

  8. U-Pb (LA-PIMMS) Ages of Inherited Zircons from Early Palaeozoic Granitoids of the W Sudetes, N Bohemian Massif, Central Europe: Implications for Neoproterozoic Continental Reconstructions

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    Crowley, Q. G.; Patocka, F.; Kachlík, V.

    2003-04-01

    A U-Pb laser ablation plasma ionisation multi-collector mass spectrometry (LA-PIMMS) geochronological study of zircons from early Palaeozoic (meta)granitoids of the Czech W Sudetes (E Saxothuringian Zone), NW Bohemian Massif, was carried out in order to determine the range of inherited age spectra preserved in these lithologies. Backscattered SEM images indicate that many zircons have distinct cores and rims. The majority of inherited zircon components yield concordant U-Pb ages that fall into the following age ranges: (1) 520-770 Ma, (2) 1.9-2.2 Ga and (3) ca. 3.0 Ga. These three age populations are typical of the W African Craton and the Armorican Terrane Assemblage of Europe. The age spectra correspond to Cadomian, Birimian / Icartian / Eburnean / Burkinian and Leonian events respectively. Some previous Pb-Pb zircon and whole rock Nd studies of similar lithologies from the W Sudetes (e.g. Hegner &Kröner, 2000) have attributed the presence of Mesoproterozoic 207Pb/206Pb ages to a peri-Amazonian provenance. Although some zircons from this study have yielded apparent Mesoproterozoic ages, they are discordant and can be resolved into early Palaeozoic to Neoproterozoic lower intercept and Palaeoproterozoic to Archaean upper intercept components. This unequivocally proves that an inherited Grenvillian component does not exist in these lithologies. We therefore favour derivation of the Saxothuringian zone and associated members of the Armorican Terrane Assemblage from a W African Craton Gondwanan setting. References: Hegner, E, &Kröner, A. 2000. Review of Nd data and xenocrystic and detrital ages from the pre-Variscan basement in the Eastern Bohemian Massif: speculations on palinspastic reconstructions. In: Franke, W., Altherr, R., Haak, V. &Oncken, O. (eds.), Orogenic Processes: Quantification and Modelling in the Variscan Belt of Central Europe Geological Society of London Special Publication, 179, 113-129.

  9. Did Patagonia collide against Gondwana in the Late Paleozoic? Some Insights From Magnetic Fabrics of Granitoids in the North Patagonian Massif.

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    Rapalini, A. E.; Lopez de Luchi, M. G.; Tomezzoli, R. N.

    2008-05-01

    The Paleozoic tectonic evolution of Patagonia has been a matter of much debate in the last two decades. There is no consensus on whether the North Patagonian Massif (NPM) was accreted by a frontal collision to Gondwana in the Late Paleozoic or if it shared a similar paleotectonic evolution with other Gondwana blocks during the Paleozoic. Different geologic, geochronologic, geophysical and structural data have been interpreted either as supporting or refuting the collisional model. Paleomagnetic data obtained so far is consistent with an authochtonous evolution since the Devonian, but it does not rule out relative displacements of up to 1500 km between Patagonia and Gondwana.Therefore, a Late Paleozoic frontal collision cannot be definitely ruled out on the basis of paleomagnetic data alone. As part of a muldisciplinary research project a magnetic fabric study, by means of the anisotropy of magnetic susceptibility (AMS), was carried out on Late Paleozoic granitoids exposed in northeastern NPM. Two main composite units were studied, the highly to variably foliated Yaminue Complex, poorly dated as Late Carboniferous and ranging in composition from tonalite to leuco-granite, and the much less deformed granodiorites to monzoganites of the Early Permian (283 Ma) Navarrete complex. While the former is composed of both ferro and paramagnetic units, with a dominance of the latter; the Navarrete plutons are basically ferromagnetic. Directional and scalar AMS results joined with meso and microstructural studies permitted the characterization of the deformational and magmatic fabric of the different units. An evolutionary picture of the succesive intrusive events in NPM emerged which confirms an important NNE-SSW contractional event associated with intrusion of the different units that compose the Yaminue Complex. This event ended before the intrusion of the Navarrete Complex, which is governed by a different stress regime. Our results fit the hypothesis of a collisional event

  10. Magnetic fabric and microstructures of Late Paleozoic granitoids from the North Patagonian Massif: Evidence of a collision between Patagonia and Gondwana?

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    López de Luchi, Mónica G.; Rapalini, Augusto E.; Tomezzoli, Renata N.

    2010-10-01

    Widespread Late Paleozoic magmatism in northern Patagonia is a target to test hypotheses on the long standing question over the origin of Patagonia. In recent years, a dispute over whether it is an accreted crustal block that collided with Gondwana in Paleozoic times or an autochthonous part of South America has taken place. As part of a multidisciplinary study, an integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex and the Early Permian Navarrete Plutonic Complex, both exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W). Other investigated units are the Late Carboniferous Tardugno Granodiorite, the newly defined Cabeza de Vaca Granite and the Late Permian San Martin pluton. Over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility (AMS) measurements. A systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units. Microstructures in the Yaminué Complex are indicative of a transition from magmatic to solid-state deformation. Microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex. The Cabeza de Vaca Granite, intrusive in Yaminué Complex, is the most evolved unit and records less intense high-temperature solid-state deformation which suggests that the stress field that controlled the emplacement of the Yaminué Complex outlasted it. According to petrologic and structural considerations, the Navarrete Plutonic Complex has been subdivided into three facies, i.e. Robaina, Guanacos and Aranda, respectively. Microstructures of the Navarrete Plutonic Complex are mostly magmatic to submagmatic, versus the solid-state fabric that characterizes the Robaina facies at the contact with the Yaminué Complex. Combined analyses of AMS and microstructural data lead us to suggest that the Yaminué Complex

  11. Using luminescence dating of coarse matrix material to estimate the slip rate of the Astaneh fault, Iran

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    Rizza, M.; Mahan, S.; Ritz, J.-F.; Nazari, H.; Hollingsworth, J.; Salamati, R.

    2011-01-01

    In this paper, we present optically and infrared stimulated luminescence (OSL and IRSL) ages for four samples from alluvial fan surfaces in the Astaneh Valley. This valley is located in the north-east part of the Alborz range in Iran. Our morphologic interpretations recognize at least three generations of fans in the study area, all of which have been displaced along the left-lateral strike-slip Astaneh fault. Because of the dry, loose, and sometimes complex juxtaposition of the target sediments, we collected the samples in total darkness beneath dark plastic layers placed atop the pit openings. Luminescence ages of the fans are ???55 ka, ???32 ka and ???16 ka. These ages are concurrent with periods of loess deposition and wet climatic conditions previously recorded in the Arabia-Iranian region. They allow estimation of a horizontal slip rate of ???2 mm/yr along the Astaneh fault, which is consistent with additional slip rates determined for the Holocene period along faults further west of the Astaneh fault. ?? 2011 Elsevier B.V.

  12. Ordovician magmatism in the Lévézou massif (French Massif Central): tectonic and geodynamic implications

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    Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Van Den Driessche, Jean

    2017-03-01

    New U-Pb dating on zircon yielded ca. 470 Ma ages for the granitoids from the Lévézou massif in the southern French Massif Central. These new ages do not support the previous interpretation of these granitoids as syn-tectonic intrusions emplaced during the Late Devonian-Early Carboniferous thrusting. The geochemical and isotopic nature of this magmatism is linked to a major magmatic Ordovician event recorded throughout the European Variscan belt and related to extreme thinning of continental margins during a rifting event or a back-arc extension. The comparable isotopic signatures of these granitoids on each side of the eclogite-bearing leptyno-amphibolitic complex in the Lévézou massif, together with the fact that they were emplaced at the same time, strongly suggest that these granitoids were originally part of a single unit, tectonically duplicated by either isoclinal folding or thrusting during the Variscan tectonics.

  13. U-Pb ages and morphology of zircons from different granites within the Saxonian Granulite Massif

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    Sagawe, Anja [Senckenberg Naturhistorische Sammlungen Dresden (Germany). Oeffentlichkeitsarbeit; Gaertner, Andreas; Hofmann, Mandy; Linnemann, Ulf [Senckenberg Naturhistorische Sammlungen Dresden (Germany). Sektion Geochronologie

    2013-07-01

    The Saxonian Granulite Massif comprises various granitoid intrusions with different stages of deformation but of similar ages. However, there is only little knowledge about the magmatic source of these rocks. Combining the external and internal morphology of zircons and taking into consideration their Th-U values allows the differentiation of the granitoids into at least two groups of distinct evolution.

  14. Geochemical study of water-rock interaction processes on geothermal systems of alkaline water in granitic massif; Estudio geoquimico de los procesos de interaccion agua-roca sobre sistemas goetermales de aguas alcalinas en granitoides

    Energy Technology Data Exchange (ETDEWEB)

    Buil gutierrez, B.; Garcia Sanz, S.; Lago San Jose, M.; Arranz Uague, E.; Auque Sanz, L. [Universidad de Zaragoza (Spain)

    2002-07-01

    The study of geothermal systems developed within granitic massifs (with alkaline waters and reducing ORP values) is a topic of increasing scientific interest. These systems are a perfect natural laboratory for studying the water-rock interaction processes as they are defined by three main features: 1) long residence time of water within the system, 2) temperature in the reservoir high enough to favour reaction kinetics and finally, 3) the comparison of the chemistry of the incoming and outgoing waters of the system allows for the evaluation of the processes that have modified the water chemistry and its signature, The four geothermal systems considered in this paper are developed within granitic massifs of the Spanish Central Pyrenes; these systems were studied from a geochemical point of view, defining the major, trace and REE chemistry of both waters and host rocks and then characterizing the composition and geochemical evolution of the different waters. Bicarbonate-chloride-sodic and bicarbonate-sodic compositions are the most representative of the water chemistry in the deep geothermal system, as they are not affected by secondary processes (mixing, conductive cooling, etc). (Author)

  15. U-Th-Pb SHRIMP ages and oxygen isotope composition of zircon from two contrasting late Variscan granitoids, Nisa-Albuquerque batholith, SW Iberian Massif: Petrologic and regional implications

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    Solá, A. Rita; Williams, Ian S.; Neiva, Ana M. R.; Ribeiro, M. Luisa

    2009-08-01

    The late Variscan Nisa-Albuquerque batholith in the SW Iberian Massif, consists of a dominant very coarse-grained porphyritic S-type monzogranite to syenogranite (Nisa monzogranite) surrounding a discontinuous central core that includes contrasting very fine-grained I-type tonalite-granodiorite (Aldeia da Mata tonalite). The batholith is located at the boundary between the Central Iberian and Ossa-Morena Zones, a complex segment of crust that was subject to both Cadomian and Variscan tectonism. Variscan zircons in the Nisa monzogranite can be broadly classified into three texturally and chemically distinct types with mutually indistinguishable SHRIMP 206Pb/ 238U ages: 1) high-U, low-Th/U (< 0.1) outermost overgrowths (307.4 ± 4.0 Ma); 2) moderate U and Th/U zircon with concentric zoning occurring both as inner overgrowths and whole grains (305.4 ± 6.2 Ma)";; and 3) texturally discordant cores (309.0 ± 4.6 Ma). Many other cores have ages in the ranges 2.56-1.85 and 0.66-0.51 Ga. The overgrowths and Variscan cores with low Th/U have uniformly high δ18O (9.5 ± 0.2‰). Variscan cores with moderate Th/U have a wide range of δ18O (6.7-10.9‰). Cores older than 500 Ma have an even wider range of composition (4.4-10.0‰). Zircon from the central Aldeia da Mata tonalite, in contrast, contains no inherited cores, has moderate to high Th/U (0.5-1.8), and is uniform in 206Pb/ 238U age (306.2 ± 3.0 Ma) and δ18O (7.4 ± 0.3‰). The zircon in the Nisa monzogranite records a history of magma genesis involving mixing between 1) a metaluminous magma progressively contaminated by a small sedimentary component, and 2) a more voluminous peraluminous magma originating from a largely metasedimentary source. The inherited zircon age pattern closely matches the age pattern of detrital zircon in early Paleozoic sediments from North Africa. The zircon in the Aldeia da Mata tonalite records nothing of the age of the magma's source rocks, but the moderately high δ18O does preclude

  16. Neoproterozoic granitoids on Wrangel Island

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    Luchitskaya, M. V.; Sergeev, S. A.; Sokolov, S. D.; Tuchkova, M. I.

    2016-07-01

    Based on geochronological U-Pb studies, the age of Wrangel Island granitoids was estimated as Neoproterozoic (Cryogenian). Some granitoids contain zircons with inherited cores with an estimated age of 1010, 1170, 1200, and >2600 Ma, assuming the presence of ancient (Neoarchean-Mesoproterozoic) rocks in the Wrangel Island foundation and their involvement in partial melting under granitoid magma formation.

  17. Granitoid intrusions and related deposits

    Institute of Scientific and Technical Information of China (English)

    孟良义; 李绪俊

    1996-01-01

    Taking the Bainaimiao copper and gold deposits, Inner Mongolia and the Wushan copper deposits, Jiangxi Province as examples, a discussion is devoted to the relationship between the granitoid intrusions and related deposits from different lines of evidence: the spatial distribution, country rocks and alteration of the deposits, trace element contents and vertical zoning of elements in deposits, the metallogenic preference of granitoid intrusions, the metallogenic models and stable isotopic geology. It is concluded that the ore-bearing fluids mainly come from granitoid magmas and granitoid intrusions are closely associated with the related deposits in space.

  18. Exotic crustal components at the northern margin of the Bohemian Massif-Implications from Usbnd Thsbnd Pb and Hf isotopes of zircon from the Saxonian Granulite Massif

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    Sagawe, Anja; Gärtner, Andreas; Linnemann, Ulf; Hofmann, Mandy; Gerdes, Axel

    2016-06-01

    The Saxonian Granulite Massif is located at the northern margin of the Saxo-Thuringian Zone of the peri-Gondwana Bohemian Massif. Eight felsic and mafic granulites were studied with respect to their geochemistry and Usbnd Pb zircon geochronology. The felsic granulites are interpreted to be derived from continental crust of possible granitoid composition. An origin from depleted mantle sources with IAT to MORB composition can be assumed for the mafic granulites. The peak of metamorphism is thought to be timed at about 340 Ma, while several earlier metamorphic events are supposed to have occurred at about 355-360, 370-375, 405, and 450 Ma. They reveal a complex and polyphased geologic evolution of the Saxonian Granulite Massif. Protolith emplacement likely took place at c. 450 and 494 Ma. Hf isotopic data suggest Mesoproterozoic crustal ages at least for parts of the massif. As these crustal ages are exotic for the Bohemian Massif, their origin has to be searched elsewhere. Potential source areas could be Amazonia and Baltica, of which the latter is the one preferred. Furthermore, a composite architecture with at least two components-the felsic granulites with Mesoproterozoic crustal model ages, and the mafic granulites of potential island arc origin-is hypothesised. Their amalgamation to the recent appearance of the Saxonian Granulite Massif is likely bracketed between 375 and 340 Ma.

  19. Petrology of Oligocene Ghaleh Yaghmesh granitoids in the west of Yazd province

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    Bahareh Fazeli

    2017-02-01

    Full Text Available Introduction The generation and evolution of granitic magmas has been a hot debated subject among petrologists. The diversity of their origin has led different authors to propose that these rocks are not simple in their origin and might be generated in more ways than one. In the past several decades, many petrologists used a variety characteristics to subdivide the granitoid rocks. Such proposals have of course been forward by Chappell and White (1974 for the granitoids of Eastern Australia. They divided these granitoids into two distinct types (I-and S-type granitic rocks, which they interpreted as being derived from igneous and sedimentary source rocks, respectively. The Ghaleh Yaghmesh plutonic massif is located in the most western part of Yazd and it forms a part of the Urumieh-Dokhtar magmatic belt. The belt is response to subduction of Neo-Tethyan oceanic crust beneath central Iran (Alavi, 1994. During Cretaceous-Late Tertiary, numerous granitoid bodies were exposed in this belt, many of which have been studied by a number of workers (e.g. Sepahi and Malvandi, 2008; Honarmand et al., 2013; Kananian et al., 2014. The massif composed of diorite, quartzdiorite, tonalite, granodiorite and granite (Oligocene intruded into the Eocene volcanic and pyroclastic rocks including rhyolite, rhyodacite, andesitic, rhyodacitic and rhyolitic tuff. The main purpose of the present paper is to describe the petrography, and whole rock geochemistry of the Ghaleh Yaghmish granitoids as well as discussing their petrogenetic and tectonic significance in the light of the regional geological framework of the study area. Materials and methods After field studies and sampling, fifty thin sections were prepared for petrographic study. Twenty-one fresh samples were selected for XRF chemical analysis performed at the Southern Methodist University (Dallas - USA. Thin polished sections of granodiorite rocks were prepared for composition determining and structure formula

  20. New data on the composition and age of granitoids in the northern part of the Tagil structure (Ural Mountains)

    Science.gov (United States)

    Petrov, G. A.; Ronkin, Yu. L.; Gerdes, A.; Maslov, A. V.

    2016-12-01

    The Tagil structure representing a large fragment of the Paleozoic island arc on the eastern slope of the Urals has been sufficiently well studied in its southern part (Middle Urals). In contrast, reliable data on the age and geochemical properties of various, including granitoid, rock complexes available for its northern part are scarce. The first data on the U-Pb LA-ICP-MS age of zircons from quartz diorites of the Man'ya massif of the Petropavlovsk Complex (436 ± 3 Ma, MSWD = 1.3), tonalites of the same complex (439.4 ± 1.3 Ma, MSWD = 1.3), granites of the Yuzhno-Pomur massif of the Severorudnichnyi Complex (422.4 ± 3 Ma, MSWD = 1.5), and titanite of the same massif (423.4 ± 4.4 Ma, MSWD = 0.84) have been obtained. Based on these data combined with the geochemical properties of the host rocks, the conclusion that they were crystallized at the initial stages of the formation of comagmatic volcanic series is supported; by their composition, granitoids correspond to island arc igneous rocks.

  1. Overview of the geochemistry and Rb/Sr, Sm/Nd isotopes of Middle Jurassic and Tertiary granitoid intrusions: a new insight on tectono-magmatism and mineralization of this period in Iran

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Jazi

    2012-10-01

    Full Text Available One of the most intensive occurrences of magmatism in Iran was in the middle Jurassic period. Among the granitoid intrusions in this period as discrete bodies or complexes can be pointed to Aligoodarz, Alvand, Astaneh, Boroujerd, Malayer, and Chah-Dozdan in the Sanandaj-Sirjan zone; Shir-kuh and Ayrakan in the Central Iran zone; Shah-kuh, Sorkh-kuh and Kalateh-Ahani in the Lut Block. These granitoids are mostly peraluminous and belong to high-K calc-alkaline series. CaO/Na2O ratios (0.12 to 8.37 mostly suggest a clay-free source for formation of the intrusive rocks magma. Chondrite-normalized Rare Earth Elements (REEs diagram do not display high enrichment of Light Rare Earth Elements (LREEs than Heavy Rare Earth Elements (HREEs and general pattern is relatively flat. In addition, diagram shows Eu negative anomaly, which can be attributed to indicate reducing conditions in formation of magma and/or magma derived from plagioclase depth as source. The lower continental crust-normalized spider diagram indicates enrichment in LILE (Rb, Cs, and K and LREE (La and Ce and depletion in Ba, Nb, Ta, Sr, and Ti. Initial 87Sr/86Sr ratios are 0.70609 to 0.71938 and initial εNd values are negative (from -6.51 to -1.1 indicating that magma derived from continental crust. Geochemical and isotopic evidence of the intrusive rocks shows continental crust origin (S-type granitoid and due to continental collision. Geological findings such as stop in sedimentation, regional metamorphism, ophiolite displacement, and continental collision-related mineralization confirm continental collision between Iranian and Arabian plates in the Middle Jurassic period.

  2. New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

    Science.gov (United States)

    Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

    2007-01-01

    The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

  3. Preliminary Results of Three-Dimensional Magnetotelluric Imaging at the Vicinity of Nigde Massif

    Science.gov (United States)

    Bülent Tank, Sabri; Ozaydin, Sinan; Uslular, Göksu; Delph, Jonathan; Abgarmi, Bizhan; Karas, Mustafa; Sandvol, Eric

    2017-04-01

    Magnetotelluric (MT) data were collected to examine the electrical resistivity structure of a metamorphic core complex known as the Niǧde Massif and a northeast - southwest aligned fault zone (Central Anatolian Fault Zone, CAFZ) bounding this massif on the east in Central Anatolia. The Nigde Massif is a crystalline dome close to Inner-Tauride Suture at the southern part of Central Anatolian Crystalline Complex. The sinistral CAFZ (in the south it is called Ecemis fault) is a 700 km long, 2 to 80 km wide zone with an offset of 60 to 80 km. Three-dimensional numerical modeling routines based on data-space modeling (WSINV3DMT and ModEM) were used to invert the MT data collected at forty-seven high quality soundings. The resulting models suggest that (i) there is a large and circular high resistivity, dome-like anomaly that coincides with the Niǧde Massif. This block includes intrusive (Üçkapılı-like) granitoids at the heart of the massif extending to northeast. (ii) Beneath the massif there is a deeper (> 25 km) and relatively higher conductive zone that may have developed as a result of partial melting and is responsible for earlier defined lateral underflow to the northeast. (iii) Clear evidence for low angle normal sense detachment faults bounding the massif were found on several cross sections. (iv) Seismically active Ecemis fault appears as a low to high conductivity interface mostly hidden beneath non-conformable Eocene cover (iv) Ulukısla basin sediments appear as a highly conductive layer. (v) Ophiolitic mélange on the southeast side of Ecemis fault dominate the area with a high conductivity layer.

  4. Geologic Evolution of the Gyala Peri Massif, Southeastern Tibet

    Science.gov (United States)

    Kidd, W.; Zeitler, P.; Meltzer, A.; Lim, C.; Chamberlain, C.; Zheng, L.; Geng, Q.; Tang, Z.

    2002-12-01

    At both the eastern and western terminations of the Himalaya, strong coupling between surface and tectonic processes is manifested in the development of active antiforms in close proximity to large river gorges. In southeastern Tibet the peaks Gyala Peri and Namche Barwa occupy a metamorphic massif that shows remarkable similarities to the Nanga Parbat massif in NW Pakistan, including exposure of high-grade gneisses intruded by Plio-Pleistocene granites. Nanga Parbat has been proposed to constitute a 'tectonic aneurysm' involving erosionally focused strain and related metamorphic reworking. As the Namche Barwa/Gyala Peri massif appears to be quite similar to Nanga Parbat in its geology and geologic setting, we suggest it has a similar origin. Most information to date has been reported from Namche Barwa, with Gyala Peri remaining largely unexplored. Here we report observations from a well-exposed section along the western margin of Gyala Peri. In the west near the Lulang River, a brittle fault zone up to ~1 km wide juxtaposes a metasedimentary/mylonite section on the east against Lhasa/Gandese gneisses and granitoid rocks to the west. The steeply dipping fault zone shows a dominantly east-up (reverse) sense of brittle motion. The lower portion of the Lhasa/Gangdese metamorphic section is cut by dikes of at least two granite phases, a medium-grained Gangdese-like granite, and a leucocratic pegmatite. East of the brittle fault zone, and the metasediments and planar foliated mylonites, there is an ~500 m thick section of S/C mylonites having a dominant reverse and subordinate dextral sense of shear. East of, or possibly in the eastern part of this ductile fault, grey gneisses [presumed basement] are intruded by a syntectonic(?) muscovite granite. Ar-Ar K-feldspar data from Gangdese rocks just west of the brittle fault zone drop to ages of 4 Ma, substantially younger than the pattern seen further to the west at Bayi. Overall, the geology of this section is quite similar

  5. Proterozoic granitoids of the Amazonian craton

    Science.gov (United States)

    dalĺAgnol, R.; Costi, H. T.; Lamarão, C. N.; Teixeira, N. P.; Bettencourt, J. S.; Fraga, L. M.

    2003-04-01

    Proterozoic granitoids are widespread in all provinces of the Amazonian craton. In the Maroni-Itacaiunas Province, granitoids associated with the Trans-Amazonian event include: subduction related, 2.16 to 2.14 Ga, calc-alkaline tonalites and trondhjemites; 2.10 to 2.08 Ga, syncolisional potassic granites; 2.05 Ga, charnockites. In the Tapajós Province, ˜2.01 Ga, tonalites are followed by ˜2.0 Ga volcanic sequences and ˜1.98 to 1.96 Ga calc-alkaline granitoids. A reappraisal of magmatic activity occurred at ˜1.88 Ga when calc-alkaline granitoids, as well as subalkaline, A-type granites, associated with felsic volcanic sequences were formed. A similar picture is observed in the northern Roraima region, where post-collisional 2.0 to 1.96 Ga calc-alkaline granitoids and associated volcanic sequences are followed by 1.92 Ga A-type granites. The remarkable 1.88 Ga magmatic event has a continental scale and is related to an extensional tectonism. It affected also the Archean Carajás Province, where, at this time, within-plate, shallow-level, A-type granites were emplaced. Coeval intermediate to felsic volcanic sequences are widespread in the Central Amazonian Province. In the Pitinga region, these sequences are intruded by ˜1.82 Ga, tin-mineralized granites. In the Central Guiana Belt and in the northwestern domains of the Guiana shield ˜1.55 Ga rapakivi complexes, locally with associated anorthosites and mangerites, are common. In the Rio Negro Province, 1.8 to 1.60 calc-alkaline (?) granitoids and gneisses are dominant. They are followed by 1.55 to 1.52 Ga, oxidized, titanite-bearing A-type granites and S-type, two-mica granites. The evolution of the southwestern part of the Amazonian craton is characterized by the occurrence of successive tectonic events extending from ˜1.75 Ga to ˜1.0 Ga. The oldest granitoids are dominantly calc-alkaline tonalites, trondhjemites and granodiorites. However, the Rondonia region is marked by the occurrence of 1.6 to 1.0 Ga old

  6. Granitoid, upper Cretaceous, contamination, Lut block, Kaje, Iran

    OpenAIRE

    Ali Najafi; Mohammad Hassan Karimpour; Majid Ghaderi; Charles Stern; Lang Farmer, G.

    2013-01-01

    Granitoid rocks of Kaje area, northwest Ferdows, with the composition of diorite, monzodiorite, monzonite, monzogranite, syenogranite and granite, with calk-alkaline and high potassium affinities, have trace and rare earth element geochemical characteristics similar to those from subduction zones, belonging to I-type granitoid rocks. Most of these rocks are oxidized (magnetite series), while one suite is reduced (ilmenite series) showing S-type characteristics. Three samples of granitoid rock...

  7. Miocene metamorphism of pan-African granites in the Edough Massif (NE Algeria); Metamorphisme miocene de granites panafricains dans le massif de l`Edough (Nord-Est de l`Algerie)

    Energy Technology Data Exchange (ETDEWEB)

    Hammor, D. [Universite d`Annaba, El Hadjar Annaba (Algeria). Dept. de Geologie; Lancelot, J. [Montpellier-2 Univ., 34 (France). Laboratoire de Geochimie Isotopique

    1998-09-01

    The Edough Massif is the eastern most crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595{+-} My and 606{+-}55 My and orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18{+-} My U-Pb age that points to a Miocene age of the high-temperature metamorphism. (authors) 18 refs.

  8. Canyons within the slope of the Bohemian Massif created subsequent to the meteorite impact at the end of the Mesozoic

    Energy Technology Data Exchange (ETDEWEB)

    Jiricek, Rudolf [Moravian Oil Co., Hodonin (Czech Republic)

    1996-12-31

    The origin of the deep canyons both in south Moravia and in Lower Austria is attributed to major sea-level changes, possibly caused by the Late Cretaceous-Early Tertiary meteorite impact at Chicxulub (Mexico) and also to the contemporaneous uplift of the Bohemian Massif (Czech Republic). The canyons were eroded by river activity during the Bohemian Massif uplift at the time of the global sea-level fall. The Nesvacilka Canyon was eroded to a depth of 2000 m, which is comparable to the Grand Canyon of the Colorado River. The deep erosion penetrated through the Cretaceous and Jurassic sediments into the Palaeozoic formations and/or the granitoid basement. The canyons have been filled with Palaeogene marine sediments, which are up to 1400 m thick. (author)

  9. Determining the stress of rock massif

    OpenAIRE

    2014-01-01

    Defining the stress rock massif is essential for design of underground facilities and methods of mining in the mines. Assessment the value of stress state of rock massif and rock strength in the various loads allows rational design. This is of particular importance when sizing columns, determining the extent of excavation, the cross-sections of underground rooms in problems with rock bursts and others. This paper briefly gives the basic methods of determining the rock massif stress as part of...

  10. [Analysis of X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry of Pangxidong Composite Granitoid Pluton and Its Implications for Magmatic Differentiation].

    Science.gov (United States)

    Zeng, Chang-yu; Ding, Ru-xin; Li, Hong-zhong; Zhou, Yong-zhang; Niu, Jia; Zhang, Jie-tang

    2015-11-01

    Pangxidong composite granitoid pluton located in the southwestern margin of Yunkai massif. The metamorphic grade of this pluton increases from outside to inside, that is, banded-augen granitic gneisses, gneissoid granites and granites distribute in order from edge to core. X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry are conducted to study the geochemical characteristics of the three types of rocks. The result shows that all the three types of rocks are peraluminous rocks and their contents of main elements and rare earth elements change gradually. From granitic gneisses to granites, the contents of Al₂O₃, CaO, MgO, TiO₂, total rare earth elements and light rare earth elements increase, but the contents of SiO₂ and heavy rare earth elements decrease. It is suggested that the phylogenetic relationship exists between granitic gneisses, gneissoid granites and granites during the multi-stage tectonic evolution process. Furthermore, the remelting of metamorphosed supracrustal rocks in Yunkai massif is probably an important cause of granitoid rocks forming. The evolutionary mechanism is probably that SiO₂ and heavy rare earth elements were melt out from the protolith and gradually enriched upward, but Al₂O₃, CaO, MgO, TiO₂ and light rare earth elements enriched downward.

  11. Suhard Massif. A geomorphological study

    Directory of Open Access Journals (Sweden)

    Liviu CARP

    2013-03-01

    Full Text Available Suhard Mts., part of the Northern Carpathians, stretch over an area of 323 sq km, in the shape of a  northwest-oriented ridge. This massif is composed of crystalline schists  (meso- and epimetamorphic, as well as sedimentary rocks pertaining to the trans-Carpathian flysch deposits (i.e. various types of sandstone, conglomerates and marls in the southwestern sector. Whereas this region is characterized by the occurrence of a wide range of carbonate rocks, we noted the scarcity of karst forms. Geological survey maps of the area indicate the occurrence of few folded structures; moreover, the massif is mostly part of an ample anticline whereby the axis underlies the valley of Bistrita Aurie river, accompanied by a large syncline underlying Cosna river valley (tributary of Dorna river. The prevalence of crystalline rocks within this anticlinorium results in the overall massif shape of these mountains (hence, the name, which is the foundation for the detail structural and lithological relief forms. The array of structural relief forms includes structural plateaus on sedimentary and crystalline carbonate rocks, and steep slopes in the form of both hogbacks and overthrust scarps. The lithological relief occurs primarily as a result of the contrasting chemical composition of various crystalline rocks, whereas sedimentary rocks seldom generate such forms and solely when favored by the structure, as well. Consequently, carbonate rocks are rather discrete and only stand out in the form of clints (lapies and gorges, or hums. As regards the matter of denudation surfaces, which has proved rather difficult to solve, we were able to determine the presence of an erosion surface ranging from 1200-1300 m to 1500-1600 m, wherein neotectonics played a significant role by fragmenting the original surface, particularly in the northwestern sector, where its fragments descend in the shape of consecutive steps towards Rotunda saddle. Periglacial modeling of the relief

  12. Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone, SW Iberia)

    Science.gov (United States)

    Sánchez-García, T.; Pereira, M. F.; Bellido, F.; Chichorro, M.; Silva, J. B.; Valverde-Vaquero, P.; Pin, Ch.; Solá, A. R.

    2014-07-01

    Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm-Nd-Sr isotopes (4 samples) and ID-TIMS U-Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm-Nd isotopic data show moderate negative ɛNdt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.

  13. The Neoproterozoic Granitoids from the Qilian Block, NW China

    Science.gov (United States)

    Tung, K. A.; Yang, H. Y.; Liu, D. Y.; Zhang, J. X.; Yang, H. J.; Shau, Y. H.; Tseng, J. Y.

    2012-04-01

    Field occurrence, petrography, geochemistry, Nd isotopes, and geochronology of the Neoproterozoic granitoids exposed at Tuole, Huangyuan, Duohai, Haiyan, Riyueshan, and Maxianshan in the Qilian block were studied. The Neoproterozoic granitoids are quartz diorite, granodiorite, granite, and leucogranite. They have intruded the schists of the Huangyuan Group, the basement sequence of the Qilian block, and are medium- to coarse-grained. Gneissosities are well developed and are concordant with the schistosities of the country rocks. The Neoproterozoic granitoids plot in the field of diorite, granodiorite, and granite in (K2O+Na2O) vs. SiO2 diagram and are medium- to high-K calc-alkaline. Their REE patterns all show enrichment in LREE's and, with exception of the quartz diorite at Maxianshan, negative Eu anomalies. Their spiderdiagrams also exhibit enrichment in large ion lithophile elements, Rb, Th, U, and K and negative anomalies in Nb, Ta, Sr, P, Ti, and, with exception of the quartz diorite at Maxianshan, Ba. The ages of the Neoproterozoic granitoids are divided into two groups: ca. 800 Ma and ca. 900 Ma. The ɛNd(1 Ga) and TDM are -6.7~-12.7 and 2.2~3.0 Ga for the ca. 800 Ma granitoids and are -4.3~-5.3 and 2.0~2.3 Ga for the ca. 900 Ma granitoids. The granitoids of both age groups were all formed in arc tectonomagmatic environment on active continental margin. The Huangyuan granodiorite, Duohai leucogranite, Haiyan granodiorite, and Maxianshan granite are peraluminous and S-type, and were most probably derived from melting of clay-poor, mature psammitic sources. The Riyueshan granodiorite is metaluminous and I-type, and could have formed by solidification of partial melts of metabasalt or eclogite at pressures of 1-4 GPa. The partial melts may have assimilated MgO-rich crustal rocks before solidification. The Tuole leucogranite and Maxianshan quartz diorite are also I-type, but are weakly peraluminous. They could also have formed from partial melting of metabasalt

  14. Pleistocene glaciation of the Biokovo Massif

    Directory of Open Access Journals (Sweden)

    Manja Žebre

    2013-12-01

    Full Text Available Biokovo massif is situated in the coastal part of the Dinaric Mountains in Croatia. Detailed morphographic and morphometric analysis of the highest parts of the massif were used to determine the extent and characteristics of Late Pleistocene glaciation. The reconstruction of glaciers and calculations of equilibrium line altitude (ELA were carried out. Our research revealed that on the north-eastern side of the highest peak Sveti Jure two cirque glaciers with an overall area of 1 km2 were formed and their ELA was 1515 m a.s.l.

  15. Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

    Science.gov (United States)

    Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

    2016-10-01

    Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

  16. Development of a Comprehensive Plan for Scientific Research, Exploration, and Design: Creation of an Undergroung Radioactive Waste Isloation Facility at the Nizhnekansky Rock Massif

    Energy Technology Data Exchange (ETDEWEB)

    Jardine, L J

    2005-06-15

    ISTC Partner Project No.2377, ''Development of a General Research and Survey Plan to Create an Underground RW Isolation Facility in Nizhnekansky Massif'', funded a group of key Russian experts in geologic disposal, primarily at Federal State Unitary Enterprise All-Russian Design and Research Institute of Engineering Production (VNIPIPT) and Mining Chemical Combine Krasnoyarsk-26 (MCC K-26) (Reference 1). The activities under the ISTC Partner Project were targeted to the creation of an underground research laboratory which was to justify the acceptability of the geologic conditions for ultimate isolation of high-level waste in Russia. In parallel to this project work was also under way with Minatom's financial support to characterize alternative sections of the Nizhnekansky granitoid rock massif near the MCC K-26 site to justify the possibility of creating an underground facility for long-term or ultimate isolation of radioactive waste (RW) and spent nuclear fuel (SNF). (Reference 2) The result was a synergistic, integrated set of activities several years that advanced the geologic repository site characterization and development of a proposed underground research laboratory better than could have been expected with only the limited funds from ISTC Partner Project No.2377 funded by the U.S. DOE-RW. There were four objectives of this ISTC Partner Project 2377 geologic disposal work: (1) Generalize and analyze all research work done previously at the Nizhnekansky granitoid massif by various organizations; (2) Prepare and issue a declaration of intent (DOI) for proceeding with an underground research laboratory in a granite massif near the MCC K-26 site. (The DOI is similar to a Record of Decision in U.S. terminology). (3) Proceeding from the data obtained as a result of scientific research and exploration and design activities, prepare a justification of investment (JOI) for an underground research laboratory in as much detail as the available

  17. The last stages of the Avalonian-Cadomian arc in NW Iberian Massif: isotopic and igneous record for a long-lived peri-Gondwanan magmatic arc

    Science.gov (United States)

    Andonaegui, Pilar; Arenas, Ricardo; Albert, Richard; Sánchez Martínez, Sonia; Díez Fernández, Rubén; Gerdes, Axel

    2016-06-01

    The upper allochthonous units of NW Iberian Massif contain an extensive Cambrian magmatism (c. 500 Ma), covering felsic to mafic compositions. The magmatic activity generated large massifs of granitoids and gabbros, with calc-alkaline and tholeiitic compositions respectively. Petrological and geochemical features of these massifs are characteristic of volcanic arc. The plutons intruded siliciclastic sedimentary series deposited in the periphery of the West Africa Craton. U-Pb/Hf isotopic compositions of detrital zircon in the siliciclastic host series, indicate continental arc activity between c. 750 Ma and c. 500 Ma. It was characterized by a large variety of isotopic sources, including from very old continental input, even Archean, to the addition of a significant amount of juvenile mafic material. These isotopic sources experienced an extensive mixing that explains the composition and isotopic features (εHft from - 50 until + 15) of the represented Cambrian plutons. The Cambrian igneous rocks of the upper units of NW Iberia are related to the latest activity of the Avalonian-Cadomian arc. From the Middle Cambrian arc activity in the periphery of Gondwana was replaced by pronounced extension associated with the development of continental rifting, which finally led to separation of the microcontinent Avalonia. Subsequent drifting of Avalonia to the North caused progressive opening one of the main Paleozoic ocean, the Rheic Ocean.

  18. Petrological and Geochemical Studies on Granitoids in BibinagarBhongir Area, Nalgonda District, Telangana, India.

    OpenAIRE

    Ch. Ramakrishna; Mallesh, G.; Ch. Ravi; M. Narsimha Reddy

    2016-01-01

    The Granitoids of the Bibinagar- Bhongir area in the Nalgonda district are purely high potassic calc alkaline and meta aluminous and A-type belongs to Peninsular Gneissic Complex of the Eastern Dharwar Craton. The petrographic study of granitoids indicates that of pure magmatic origin in the form of different magmatic textures viz. perthitic, porphyritic and poiklitic textures. Geochemically the granitoids are rich in K2O & Na2O suggesting source from calc-alkaline magma. The Gran...

  19. The Montagne Noire migmatitic dome emplacement (French Massif Central): new insights from petrofabric and AMS studies

    Science.gov (United States)

    Charles, Nicolas; Faure, Michel; Chen, Yan

    2009-11-01

    In the southern French Massif Central, the Montagne Noire axial zone is a NE-SW elongated granite-migmatite dome emplaced within Visean south-verging recumbent folds and intruded by syn- to late-migmatization granitoids. The tectonic setting of this dome is still disputed, thus several models have been proposed. In order to better understand the emplacement mechanism of this dome, petrofabric and Anisotropy of Magnetic Susceptibility (AMS) studies have been carried out. In the granites and migmatites that form the dome core, magmatic texture and to a lesser extent weak solid-state texture are dominant. As a paramagnetic mineral, biotite is the main carrier of the magnetic susceptibility. On the basis of 135 AMS sites, the magnetic fabrics appear as independent of the lithology but related to the dome architecture. Coupling our results with previous structural and geochronological studies, allows us to propose a new emplacement model. Between 340-325 Ma, the Palaeozoic series underwent a compressional deformation represented by nappes and recumbent folds involving the thermal event leading to partial melting. Until ˜325-310 Ma, the dome emplacement was assisted by diapiric processes. An extensional event took place at ˜300 Ma, after the emplacement of the late to post-migmatitic granitic plutons. In the northeast side of the dome, a brittle normal-dextral faulting controlled the opening of the Graissessac coal basin.

  20. The mechanics of granitoid systems and maximum entropy production rates.

    Science.gov (United States)

    Hobbs, Bruce E; Ord, Alison

    2010-01-13

    A model for the formation of granitoid systems is developed involving melt production spatially below a rising isotherm that defines melt initiation. Production of the melt volumes necessary to form granitoid complexes within 10(4)-10(7) years demands control of the isotherm velocity by melt advection. This velocity is one control on the melt flux generated spatially just above the melt isotherm, which is the control valve for the behaviour of the complete granitoid system. Melt transport occurs in conduits initiated as sheets or tubes comprising melt inclusions arising from Gurson-Tvergaard constitutive behaviour. Such conduits appear as leucosomes parallel to lineations and foliations, and ductile and brittle dykes. The melt flux generated at the melt isotherm controls the position of the melt solidus isotherm and hence the physical height of the Transport/Emplacement Zone. A conduit width-selection process, driven by changes in melt viscosity and constitutive behaviour, operates within the Transport Zone to progressively increase the width of apertures upwards. Melt can also be driven horizontally by gradients in topography; these horizontal fluxes can be similar in magnitude to vertical fluxes. Fluxes induced by deformation can compete with both buoyancy and topographic-driven flow over all length scales and results locally in transient 'ponds' of melt. Pluton emplacement is controlled by the transition in constitutive behaviour of the melt/magma from elastic-viscous at high temperatures to elastic-plastic-viscous approaching the melt solidus enabling finite thickness plutons to develop. The system involves coupled feedback processes that grow at the expense of heat supplied to the system and compete with melt advection. The result is that limits are placed on the size and time scale of the system. Optimal characteristics of the system coincide with a state of maximum entropy production rate.

  1. Mid-Paleozoic age of granitoids in enclaves within early Cretaceous granulites, Fiordland, southwest New Zealand

    Science.gov (United States)

    Bradshaw, J.Y.; Kimbrough, D.L.

    1991-01-01

    Orthogneisses of granite, quartz monzonite, monzonite, and tonalite, occur locally as isolated enclaves within the Early Cretaceous granulite terrain (Western Fiordland Orthogneiss - WFO). Discordant U-Pb zircon isotopic data (seven fractions) from four granitoid samples from enclaves at George Sound, define an upper intecept age of 341??34 Ma that is interpreted as approximating the time of formation of the granitoid suite. The lower intercept age of 93??37 Ma is interpreted as approximating the time of zircon isotopic disturbance by major episodic Pb loss. The low 87Sr/ 86Sr initial ratio indicates that these mid-Paleozoic granitoids were derived from an isotopically primitive source. The granitoid enclaves within WFO show influences of several different sources. The granitoids provide evidence linking WFO to a mid-Palaeozoic country rock similar to the central Fiordland metasediments. -from Authors

  2. Geochemistry and petrogenesis of Neoproterozoic Mylliem granitoids, Meghalaya Plateau, northeastern India

    Indian Academy of Sciences (India)

    Jyotisankar Ray; Abhishek Saha; Sohini Ganguly; V Balaram; A Keshav Krishna; Sampa Hazra

    2011-06-01

    The Mylliem granitoids of the Meghalaya Plateau, northeastern India, represent one of the disharmonic Neoproterozoic igneous plutons, which are intrusive into low-grade Shillong Group of metasediments. Field studies indicate that the Mylliem granitoids cover an area of about 40 km2 and is characterized by development of variable attitude of primary foliations mostly marked along the margin of the pluton. Xenoliths of both Shillong Group of metasediments and mafic rocks have been found to occur within Mylliem granitoids. Structural study of the primary foliation is suggestive of funnel-shaped intrusion of Mylliem granitoids with no appreciable evidence of shearing. Petrographically, Mylliem granitoids are characterized by pink to white phenocrysts of prismatic microcline/perthite and lath-shaped plagioclase (An20–An29). Groundmass material is characterized by quartz, microcline, plagioclase, muscovite and biotite. Sphene and apatite occur as accessory minerals. Petrographically Mylliem granitoids have been discriminated as granite and granodiorite according to IUGS system of classification. Critical evaluation of geochemical data and variation trends of major oxides/trace elements suggests a significant role of fractional crystallization in the evolution of Mylliem pluton. Th/U ratios (3.22–6.77) indicate a relatively higher abundance of Th over U. Chondrite-normalized REE diagram characteristically shows an enriched LREE pattern and prominent negative Eu anomaly (Eu/Eu* = 0.16–0.42) indicating the significant role of plagioclase fractionation from the parent magma. An overall strong REE fractionation pattern has been envisaged for Mylliem granitoids. The strong REE fractionation of the Mylliem granitoids is depicted by (Ce/Yb) values, which show a range of 1.39 to 1.65. The aluminium saturation index (ASI) (ranging from 1.0 to 1.3), A/CNK ratios (ranging from 1.4 to 2.11) and A/NK ratios (ranging from 1.75 to 2.43) provide evidences for the peraluminous, S

  3. Emplacement ages, geochemical and Sr-Nd-Hf isotopic characterization of Mesozoic to early Cenozoic granitoids of the Sikhote-Alin Orogenic Belt, Russian Far East: Crustal growth and regional tectonic evolution

    Science.gov (United States)

    Jahn, Bor-ming; Valui, Galina; Kruk, Nikolai; Gonevchuk, V.; Usuki, Masako; Wu, Jeremy T. J.

    2015-11-01

    The Sikhote-Alin Range of the Russian Far East is an important accretionary orogen of the Western Pacific Orogenic Belt. In order to study the formation and tectonic evolution of the orogen, we performed zircon U-Pb dating, as well as geochemical and Sr-Nd-Hf isotopic analyses on 24 granitoid samples from various massifs in the Primorye and Khabarovsk regions. The zircon dating revealed that the granitoids were emplaced from 131 to 56 Ma (Cretaceous to Paleogene). In the Primorye Region, granitoids in the coastal Sikhote-Alin intruded the Cretaceous Taukha Accretionary Terrane from ca. 90 to 56 Ma, whereas those along the Central Sikhote-Alin Fault zone intruded the Jurassic Samarka Accretionary Terrane during ca. 110-75 Ma. The "oldest" monzogranite (131 Ma) was emplaced in the Lermontovka area of the NW Primorye Region. Granitoid massifs along the Central Sikhote-Alin Fault zone in the Khabarovsk Region formed from 109 to 58 Ma. Thus, the most important tectonothermal events in the Sikhote-Alin orogen took place in the Cretaceous. Geochemical analysis indicates that most samples are I-type granitoids. They have initial 87Sr/86Sr ratios ranging from 0.7040 to 0.7083, and initial Nd isotopic ratios, expressed as εNd(t) values, from +3.0 to -5.0 (mostly 0 to -5). The data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies, including the subducted accretionary complex ± hidden Paleozoic-Proterozoic basement rocks. Based on whole-rock Nd isotopic data, we estimated variable proportions (36-77%) of juvenile component (=mantle-derived basaltic rocks) in the generation of the granitic magmas. Furthermore, zircon Hf isotopic data (εHf(t) = 0 to +15) indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation. The quasi-continuous magmatism in the Sikhote-Alin orogen suggests that the Paleo-Pacific plate subduction was very active in the

  4. Eburnean and Pan-African granitoids and the Raghane mega-shear zone evolution: Image analysis, U-Pb zircon age and AMS study in the Arokam Ténéré (Tuareg shield, Algeria)

    Science.gov (United States)

    Nouar, O.; Henry, B.; Liégeois, J. P.; Derder, M. E. M.; Bayou, B.; Bruguier, O.; Ouabadi, A.; Amenna, M.; Hemmi, A.; Ayache, M.

    2011-05-01

    In the Arokam Ténéré, the three studied massifs of granitoids are located around the N-S oriented Raghane mega-shear zone, which separates two of the main domains of the Tuareg shield, the Saharan metacraton and the Central Hoggar. The field observations, AMS analyses and U-Pb zircon dating were completed by a study of Landsat images because of the scarcity of outcrops in several parts of the studied area. The image analysis allows to distinguish Arokam-East and Abdou granitoids in the eastern plutonic complex. It has also shown that the western plutonic complex corresponds to two different intrusions: the Yvonne granite and granodiorite. This is confirmed by the magnetic fabric that presents different characteristics in the different granitoids. U-Pb zircon dating and field observations show that the Arokam-West basement granite is much older (1915 Ma) than the Hanane granodiorite (582 Ma) in the central plutonic complex. Arokam-East and -West granites then belong to the Eburnean basement. The magnetic fabric of these granites is mainly associated with a post-magmatic deformation, probably of Pan-African age. Yvonne granodiorite is likely contemporaneous of the main displacement along the Raghane shear zone. The Yvonne granite (594 Ma) and Hanane granodiorite have a fabric similar to that previously obtained in most plutons of the Tiririne area. This fabric is related to the regional stress field, associated with the activity of the Raghane shear zone, during the late-magmatic phase in the plutons. On the contrary, the magnetic fabric of the Abdou pluton is still reflecting only the magma flow.

  5. Dichotomy of The Messada Pluton, Serbo-Macedonian Massif, Greece: From Rifting to Subduction

    Science.gov (United States)

    Vasilatos, Charalampos

    2016-10-01

    The Messada pluton is a mafic intrusion that is located about 12 km SW of Serres town, (Macedonia Greece) that intrudes the two mica, biotite and the augen gneisses of the Vertiskos formation (Serbo-Macedonian massif). The aim of this study is to investigate, define and evaluate the geochemical characteristics of the pluton in order to determine the geotectonic environment in which the parental magma has been formed. The Mesada pluton is a mid to coarse grained intrusion presenting petrographic variety from diorite and quartz diorite to tonalite and granodiorite. The variety in petrography reflects its chemical inhomogeneity in major and trace elements. It is suggested that parts of pluton have been formed by distinctly different types of magmas originated in diverse geotectonic settings. Those parts of quartz diorite and tonalite composition, present similar geochemical characteristics, LILE/HFSE ratios and negative Nb, but no Ti anomalies in their primitive mantle normalized trace elements spider grams. They exhibit higher HFS values than those of granodioritic composition. Moreover, their ORG normalized spider grams not only suggest that they have been evolved by a common parental magma, but also present the typical characteristics of a “crust dominated” within plate pluton that may have been formed in an early stage during rifting, prior to a subsequent subduction episode. This interpretation may be in accordance with the suggestion for the Gondwanian origin of the more silicic Triassic rift related meta-granites (e.g. Arnea plutonic complex) of the Serbo-Macedonian massif. In contrary; the parts of Mesada pluton of granodioritic composition, exhibit a calc-alkaline to high K calc-alkaline magmatic suite and present higher LILE/HFSE and LREE/HREE ratios, related to a higher crustal component contribution for the magma genesis. Furthermore, their primitive mantle normalized spider grams’ present negative anomalies at Nb and Ti. These characteristics

  6. Discovery of the Early Paleozoic post-collisional granites in northern margin of the Erguna massif and its geological significance

    Institute of Scientific and Technical Information of China (English)

    WU Guang; SUN Fengyue; ZHAO Caisheng; LI Zhitong; ZHAO Ailin; PANG Qingbang; LI Guangyuan

    2005-01-01

    The Luoguhe intrusion, located in Mohe County, Heilongjiang Province, is mainly composed of monzogranite, quartz diorite and granodiorite, with minor diorite, tonalite, quartz monzodiorite, quartz monzonite, syenogranite and alkali-feldspar granite. The intrusion can be divided into two lithological units, I.e. Quartz diorite and monzogranite units, with affinities to high-K calc-alkaline series. The quartz diorite unit (SiO2: 54.79%―58.30%, Na2O/CaO: 0.79―1.53 and Shand index: 0.77―0.82) belongs to metaluminous rocks. And the monzogranite unit (SiO2: 65.29%―66.45%, Na2O/CaO:1.73―3.43 and Shand index <1.05) can be considered as weakly peraluminous rocks. The intrusion is characterized by high REE abundance (∑REE = 180.2―344.3 μg/g), medium-strong negative Eu anomalies (δEu = 0.33―0.82), weak REE fractionation [(La/Yb)N = 4.12―10.45], enrichments in Rb, Th, U, K, La, Ce, Nd, Hf, Zr and Sm, but strong depletions of Ba, Nb, Ta, Sr, P and Ti. These characteristics of major, REE and trace elements indicate that the intrusion was formed in a transitional tectonic setting from compressional to extensional regime, which can be classified as post-collisional granitoids. SHRIMP U-Pb zircon analyses yield ages of 517±9 and 504±8 Ma for the quartz diorite and monzogranite units, respectively. The discovery of Early Paleozoic post-collisional granites in the northern margin of the Erguna massif indicates that the northern branch of Paleo-Asian Ocean between Siberian plate and Erguna massif was closed in the Early Paleozoic and the Salair orogeny ended ca. 500 Ma ago.

  7. Enrichment of Mantle-derived Fluids in the Formation Process of Granitoids: Evidence from the Himalayan Granitoids around Kunjirap in the Western Qinghai-Tibet Plateau

    Institute of Scientific and Technical Information of China (English)

    姜耀辉; 凌洪飞; 蒋少涌; 周珣若; 芮行健; 杨万志

    2002-01-01

    Taking the Himalayan granitoids around Kunjirap in the western Qinghai-Tibet plateau as an example, the authors present in this paper the characteristics of the granitoids rich in mantle-derived fluid components and discuss their rock-forming mechanism. The research results indicate that the rock assemblage of the studied granitoids involves diopside syenite-diopside granite-biotite (monzonitic) granite, consisting mainly of K-feldspar, oligoclase, quartz, iron-phlogolite, diopside and edenite. The rocks are rich in mantle-derived fluid components of volatiles including F, alkali metal elements such as K, Na, Rb, Sr and Ba, and radiogenic heat-producing elements such as U and Th. They were generated by the influx of mantle-derived fluids into the lower crust to give rise to partial melting during the lithosphere thinning in the Qinghai-Tibet plateau.

  8. Fluid components in accessory minerals of Pan-African granitoids in the S(o)r Rondane Mountains, East Antarctica

    Institute of Scientific and Technical Information of China (English)

    LI Zi-long; CHEN Han-lin; YANG Shu-feng; TAINOSHO Yoshiaki; SHIRAISHI Kazuyuki; OWADA Masaaki

    2007-01-01

    Fluids (fluorine, chlorine, and OH) in accessory minerals (apatite, titanite and allanite) of Pan-African granitoids(Group-Ⅰ granitoids, Group-Ⅱ granitoids and Mefjell Plutonic Complex) from the Sor Rondane Mountains, East Antarctica were precisely measured by an electronic microprobe analyzer in this study. Apatites in the granites have commonly high fluorine contents. However, fluorine contents from the Group-Ⅰ, Group-Ⅱ granitoids and Mefjell Plutonic Complex (MPC) are of important variation, which F contents (3.21~7.20 wt%) in apatite from the Group-Ⅱ granitoids are much higher than those from the Group-Ⅰ granitoids (1.22~3.60 wt%) and the MPC (3.21~4.11 wt%). Titanite in the MPC has a low fluorine content (0.23~0.50 wt%), being less than those in the Group-Ⅰ granitoids (2.28 wt%) and Group-Ⅱ granitoids (1.85~2.78 wt%). Fluorine in allanite in the Group-Ⅱ granitoids seems to have much lower contents than those from the Group-Ⅰ granitoids and the MPC. Higher fluorine contents in the titanite from the Group-Ⅱ granitoids may be mainly controlled by late-magmatic fluid-rock interaction processes associated with melt, but may not be indicative of original magma contents based on its petrographic feature. Due to very lower chlorine contents from all of accessory minerals, the authors suggest that titanite and apatite with higher fluorine contents in the Group-Ⅱ granitoids have much lower H2O (OH) contents compared with those in the Group-Ⅰ granitoids according to the partition among (F, Cl, OH).Fluorine contents in whole-rock samples show a variation from the higher in the Group-Ⅰ granitoids to the lower in the Group-Ⅱ granitoids and the MPC, which are consistent with the changes of those from the biotite and hornblende as well as fluorite occurred in the Group-Ⅰ granitoids reported previously. Based on the above study of fluorine in accessory minerals and combined with the previous fluorine contents from biotites and

  9. Transition from frictional to viscous deformation in granitoid fault rocks

    Science.gov (United States)

    Peč, M.; Heilbronner, R.; Stünitz, H.

    2009-04-01

    Fracturing of rocks in natural fault zones increases the permeability and produces extremely small grain sizes (jackets. Before deformation, the gouge material needs to be compacted. This is achieved by a set 1 of frictional deformation experiments at different temperatures (T = 24 °C, 300 °C, 500 °C, Pc = 500 MPa, strain rate = 10ˆ-4) to shear strains of approximately gamma = 2.5. In the subsequent experiments (set 2), potential viscous deformation processes are tested in the pre-deformed gouge. After initial frictional deformation (set 1) the samples are left at peak differential stress conditions for one week. Finally, in a third type of experiments (set 3), the peak differential stress was lowered after frictional deformation to a level similar to the confining pressure and held constant for one week. In set 1, the peak shear stresses are temperature independent (given the limited stress resolution of the Griggs apparatus; 300° C = 780 - 870 MPa, 500° C = 760 - 820 MPa). In set 2, the stress relaxation after frictional deformation is clearly temperature dependent (after one week at 300° C, the shear stress is approx. 370 MPa; at 500° C, approx. 230 MPa). In set 3, no creep was observed. Further investigation of this phenomenon is required but probably the differential stress was too low. Microstructural observations show a striking difference between samples of set 1 and set 2. The samples deformed by initial friction only (set 1) show angular clasts and many small grains. The grain size distribution is similar to that observed in natural gouge material from seismic faults and to experimentally cracked granitoid material (Keulen et al. 2007, Heilbronner and Keulen 2006). In the creep-deformed samples (set 2), we observe the disappearance of the grains of < 0.1 μm size, cementation of individual grains into larger ones, and lobate grain boundaries in rounded clasts. Thus, solution - precipitation processes have taken place in creep experiments of

  10. Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China

    Science.gov (United States)

    Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan

    2017-04-01

    Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

  11. PETROLOGY OF S-TYPE BIOTITE GRANITOIDS AND THEIRS MAFIC ENCLAVES, SOUTH OF ELMALI, NİĞDE

    OpenAIRE

    KURT, Hüseyin; Kerim KOÇAK; ASAN, Kürşad; KARAKAŞ, Mustafa

    2006-01-01

    Biotite granitoid contain mainly quartz, biotite, plagioclase, K-feldspar, muscovite as main phases with minor amphiboles, and apatite, zircon, allanite and chlorite and serisite as accessory components. In contrast, enclaves are composed mainly of plagioclase, amphibole, augite, biotite, with accessory sphene, zircon and calcite and epidote. The granitoids including enclaves with metaluminous composition, display chemical and mineralogical characteristics of S-type granitoids, such as peralu...

  12. Comment on "207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the Central Anatolian crust, Turkey" - Boztug, D., Tichomirowa, M. & Bombach, K., 2007, JAES 31, 71-86

    Science.gov (United States)

    Göncüoglu, M. Cemal

    A continent-oceanic island arc collision model was proposed as a new geodynamic scenario for the evolution of the Cretaceous Central Anatolian granitoids in the Central Anatolian crystalline complex (CACC) by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey. Journal of Asian Earth Sciences 31, 71-86]. The key aspects of this model include an intra-oceanic subduction in the Neotethyan Izmir-Ankara Ocean, formation of an island arc and its subsequent collision with the northern margin of the Tauride-Anatolide Platform. The identical scenario was initially proposed by Göncüoglu et al. (1992) [Göncüoglu, M.C., Erler, A., Toprak, V., Yalınız, K., Olgun, E., Rojay, B., 1992. Geology of the western Central Anatolian Massif, Part II: Central Areas. TPAO Report No: 3155, 76 p] . Moreover, the weighted mean values of the reported 207Pb-206Pb single-zircon evaporation ages by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust: Turkey. Journal of Asian Earth Sciences 31, 71-86] from A-type granitoids in the CACC seem to be miscalculated and contrast with the field data.

  13. Origin and geochemistry of Pan-African granitoid rocks in the Gabal Um Shomer area, Southwestern Sinai, Egypt

    Institute of Scientific and Technical Information of China (English)

    E1-Tokhi M.M.; Musallum A.; Amin B.M.

    2009-01-01

    Geological, petrological and geochemical studies indicated that there are two distinct types of granitoid rocks: older quartz diorites to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a meta-aluminous chemistry and a calc-alkaline character, with high MgO, Fe2O3, TiO2, CaO, P2O5, Sr and low SiO2, K2O, and Rb. Their major and trace elements data, together with low 87Sr/ 86Sr ratios (0.7029±0.0008) are indicative of I-type affinities. The second- and third-phase granitoids range from calc-alkaline to alkaline, respectively. The second-phase granitoids have a peraluminous chemistry and high Sr, Ba, CaO, MgO, Al2O3 and Ti2O and low SiO2, K2O, Nb, Y and Rb relative to the third-phase granitoids. The corundum normative nature and field observations suggested that it was formed by partial melting of the lower crust. The third-phase granitoids are alkaline in nature and characterized by higher SiO2, Rb, Y, Nb and lower MgO, Sr and Ba values than the younger granitoids (phase II). They are A-type granitoids which were generated from below or within the existing continental crust.

  14. Emplacement mechanism of Linglong granitoid complex, Shandong Peninsula, China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Linglong granitoid complex (LGC) is composed of four major plutonic units that intruded and cooled in the Middle Jurassic (170-155 Ma). Gravity-anomaly modeling indicates that the LGC is a sheet-like laccolith, less than 10 km thick, that dips shallowly below the surface toward the Tancheng-Lujiang (Tan-Lu) fault, a major lithospheric structure in Eastern China. Measurements of foliation in the field and measurements of planar and linear magnetic fabrics from the study of anisotropy of magnetic susceptibility in the LGC indicate that foliation is dominantly shallowly dipping and magnetic lineation is mainly parallel to the dip direction of the laccolith toward the Tan-Lu fault zone. The trend of lineations is consistent with flow of magma up the thrust to reach shallower levels. The magma of the LGC probably originated by crustal melting within the Tan-Lu fault zone and the emplacement of magma occurred along a shallowly-dipping thrust that drained the Tan-Lu fault zone, the mechanism of which is mainly dike-fed model.

  15. Petrogenesis of shoshonitic granitoids, eastern India:Implications for the late Grenvillian post-collisional magmatism

    Institute of Scientific and Technical Information of China (English)

    B. Goswami; C. Bhattacharyya

    2014-01-01

    Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex (CGC) which belongs to the EW to ENEeWSW tending 1500 km long Proterozoic orogenic belt amalgamating the North and South Indian cratonic blocks. The late Grenvillian (1071 ? 64 Ma) Raghunathpur porphyritic granitoid gneiss (PGG) batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENEeWSW trending North Purulia shear zone. Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features (including major and trace-elements, mineral chemistry and 87Sr/86Sr ratio) suggest these granitoids to be classified as the shosh-onitic type. Raghunathpur batholith was emplaced at around 800 ?C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. The Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridi-zation of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation (w1.0 Ga) of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.

  16. Petrogenesis of shoshonitic granitoids, eastern India: Implications for the late Grenvillian post-collisional magmatism

    Directory of Open Access Journals (Sweden)

    B. Goswami

    2014-11-01

    Full Text Available Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex (CGC which belongs to the EW to ENE–WSW tending 1500 km long Proterozoic orogenic belt amalgamating the North and South Indian cratonic blocks. The late Grenvillian (1071 ± 64 Ma Raghunathpur porphyritic granitoid gneiss (PGG batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE–WSW trending North Purulia shear zone. Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features (including major and trace-elements, mineral chemistry and 87Sr/86Sr ratio suggest these granitoids to be classified as the shoshonitic type. Raghunathpur batholith was emplaced at around 800 °C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. The Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridization of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation (∼1.0 Ga of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.

  17. Geotectonic setting of the Suwałki Anorthosite Massif (NE-Poland) - constraints for 3D geological modelling

    Science.gov (United States)

    Wiszniewska, Janina; Petecki, Zdzislaw; Rosowiecka, Olga; Krzemińska, Ewa

    2017-04-01

    Suwałki Anorthosite Massif (SAM) is located within 200 km long Mesoproterozoic magmatic terrane called Mazury Complex (NE Poland) (Wiszniewska et al. 2002). This is a belt of granitoids and associated mafic and intermediate igneous rocks followed an E-W trending lineament extending from the Baltic Sea through northern Poland and southern Lithuania to western Belarus. Crystalline basement of the Suwałki region is covered by a thick pile (550-1300m) of Phanerozoic sedimentary rocks, which are dipping towards the SW East European Craton`s border. SAM is a complex structure composed primarily of magmatic massif type anorthosites, surrounded by a rim of norite-gabbronorite and diorite rocks. SAM is characterized by magnetic and gravimetric negative anomalies. The gravimetric one is related to anorthosite massif. It is surrounded by a few positive anomalies, which reflect occurrences of denser rocks such as granite, monzodiorite and granodiorite. The large magnetic anomaly is supposed to reflect an effect of an negative inclination of remanent magnetization of anorthosite rocks. This hypothesis was confirmed by magnetic modelling along DSS POLONAISE'97 profile P4 (Petecki, 2006). Existing measurements however do not show prevailing negative inclinations, even though they prove very high remanent magnetization of anorthosites. A pronounced residual magnetic anomalies of Udryń and Krzemianka are related to Fe-Ti-(V) ore deposits recognized by deep boreholes. Based on potential field data it was suggested that anorthosite bottom reaches 2,5-4,5 km depth. Thus it is evident that the geological architecture of SAM and its surrounding area is not fully recognized. The problem is supposed to be resolved using modern methods of geophysical transformations and 3D modelling using GeoModeller software. The final result of the research will be to recognize spatial structure of the SAM and its surrounding. Petrological, mineralogical, geochronological (U-Pb SHRIMP method on

  18. Ordovician chitinozoan biozonation of the Brabant Massif, Belgium.

    Science.gov (United States)

    Samuelsson, J; Verniers, J

    2000-12-01

    Chitinozoans from seven Ordovician units (Abbaye de Villers, Tribotte, Rigenée, Ittre, Bornival, and Brutia formations and a new unnamed unit, here provisionally called the Asquempont unit) belonging to the mainly concealed Brabant Massif, Belgium are described herein. Fifty-six samples were taken from rocks cropping out at the south-eastern rim of the massif in the Orneau, Dyle-Thyle and Senne-Sennette valleys. Microfossil preservation is moderate to poor, and the chitinozoans occur in low numbers. Taxonomically, the recovered chitinozoans are distributed into 29 taxa, some placed under open nomenclature. Together with earlier published graptolite and acritarch data, the analysis of the chitinozoan assemblages resulted in an improved chronostratigraphy of the investigated formations. We propose a local chitinozoan biozonation with 11 zones for the Brabant Massif. The oldest investigated units yielded chitinozoans typical for North Gondwana, and younger units (starting in the middle Caradoc), yielded some taxa also common in Baltica. As the Brabant Massif formed part of the microcontinent Avalonia, the chitinozoan assemblages recovered from the massif support the inferred drifting of Avalonia from high latitudes towards middle latitudes in the Ordovician as was suggested earlier.

  19. Emplacement mechanism of Linglong granitoid complex, Shandong Peninsula, China

    Institute of Scientific and Technical Information of China (English)

    WAN; Tianfeng

    2001-01-01

    [1]Mao Jianren, Petrological characteristics and forming condition of Linglong-Luanjiahe granite pluton, Eastern Shandong (in Chinese with English abstract), Journal of Changchun College of Geology, 1983, 3: 33-45.[2]Sang Longkang, Genesis and evolution of Linglong granites, Journal of China University of Geosciences (Earth Sciences) (in Chinese with English abstract), 1984, 9(1): 101-114.[3]Wen Zhizhong, Discussion on the isotopic age of Linglong granites, Shandong Geology (in Chinese with English abstract), 1985, 1(2): 1-8.[4]Wang Henian, Xu Kejing, Chen Yan, Middle petrozoic Linglong granites and their geological and geochemical evidences transformed by the later stage, Journal of Nanjing University (Earth Sciences) (in Chinese), 1998, (1): 105-118.[5]Hu Shiling, Wang Songshan, Sang Haiqing et al., Isotopic ages of Linglong and Guojialing batholiths in Shandong Province and their geological implication, Acta Petrologica Sinica (in Chinese with English abstract), 1987, (3): 83-89.[6]Xu Jinfang, Shen Buyen, Niu Lianzhu et al., On the granitoids related to gold mineralization in Jiaobei block, Shandong Geology (in Chinese with English abstract), 1989, 5(2): 1-126.[7]Zhang Lianying, Characteristics and geological significance of biotite in the granites situated in Zhaoyuan-Yexian metallogenic belt, Shandong Province, Collection of Geology and Seeking Mineral Deposits (in Chinese with English abstract), 1990, 5(3): 81-92.[8]Sang Longkang, You Zhengdong, Petrogenetic evolution of Linglong granites and their relationship to gold deposits in east Shandong Province, Journal of China University of Geosciences (Earth Sciences) (in Chinese with English abstract), 1992, 17(5): 521-529.[9]Chen Guanyuan, Sun Daisheng, Zhou Xunruo et al., Genetic Mineralogy and Gold Mineralization of Guojialing Granodiorite in Jiaodong Region (in Chinese with English abstract), Wuhan: China University of Geosciences Press, 1993, 230.[10]Chen Zhenshen

  20. La géologie du massif de Gigondas

    NARCIS (Netherlands)

    Fuchter, J.H.G.

    1951-01-01

    A l’E d’Orange-Avignon, au pied du Mt. Ventoux, s’élève un petit massif, qui est limité au N et à l’W par l’Ouvèze (fig. 1), à l'E par la route de Vaison—Malaucène—le Barroux et au S par la route du Barroux à Vacqueras. Dans la littérature géologique ce massif se trouve le plus souvent indiqué sous

  1. Were ancient granitoid compositions influenced by contemporaneous atmospheric and hydrosphere oxidation states?Were ancient granitoid compositions influenced by contemporaneous atmospheric and hydrosphere oxidation states?

    Science.gov (United States)

    Jagoutz, Oliver

    2014-05-01

    A fundamental shift in the nature of granitoids occurs at approximately the Archean-Proterozoic boundary. Archean crust is dominated Na-rich tonalite-trondhjemite-granodiorites (TTGs), whereas post-Archean granitoids are characterized by K-rich granodiorite-granite (GG). Due to the HREE depletion commonly found in TTGs indicating the presence of residual garnet, many researchers have proposed that the difference in Na/K is related to the deeper melting depth of the TTG parental liquids. Here I present a compilation of the relevant experimental data, documenting that no correlation exists between the Na/K of derivative felsic liquids and the pressure of partial melting/fractional crystallization. Instead, the Na/K ratio of the felsic liquid best correlates with the Na/K ratio of the source. This implies that in Archean time the source material of TTG rocks must have been Na/K enriched relative to the modern. Modern granitoids are dominantly formed in a supra subduction zone environment, where a feedback loop exists between subducted materials (oceanic crust and sediments) and arc magmatism. Sea-floor weathering and the Na/K of the altered oceanic crust strongly depends on f(O2) conditions during alteration, which likely changed with earth history. During alteration under oxidized condition K2O is fixated due to the formation of celadonite (K-Mica), wheres during anoxic condition saponite (Na-Smectite) is the stable alteration mineral. I propose that the rise of oxygen at 2600-2400 Ma triggered associated changes in f(O2) seafloor alteration conditions. The change in the dominant seafloor alteration mineral from reduced to oxidized causes a change in the nature of the arc magma source and provides a possible explanation for the observed transition from TTGrocks in the Archean to the GG-granitoids in post-Archean times.

  2. Towards Responsible Massification: Some Pointers for Supporting Lecturers

    Science.gov (United States)

    Albertyn, Ruth M; Machika, Pauline; Troskie-de Bruin, Christel

    2016-01-01

    Teaching large classes poses many challenges to lecturers where massification is a reality in higher education. There are implications for both teaching and effective learning in this context. The need for accountability to learners in education provision served as motivation for a study of large classes in the largest faculty of one university…

  3. Massification in Higher Education: Large Classes and Student Learning

    Science.gov (United States)

    Hornsby, David J.; Osman, Ruksana

    2014-01-01

    In introducing the special issue on "Large Class Pedagogy: Opportunities and Challenges of Massification" the present editorial takes stock of the emerging literature on this subject. We seek to contribute to the massificaiton debate by considering one result of it: large class teaching in higher education. Here we look to large classes…

  4. Attenuation of S wave in the crust of Ordos massif

    Institute of Scientific and Technical Information of China (English)

    LIU Hong-gui; CHUO Yong-qing; CHEN Shu-qing; JIN Chun-hua

    2005-01-01

    We presented attenuation characteristics of S waves in the crust of Ordos massif. Using 487 pieces of digital oscillograms of 19 seismic events recorded by 32 seismologic stations located on Ordos massif and its surroundings, we have calculated the parameter of three-segment geometric attenuation and give the relation of inelastic attenuation Q value with frequency in the crust of Ordos massif, site responses of 32 stations, and source parameters of 19 events by the genetic algorithm. The results indicate that Q value (at 1 Hz) of S-wave in the crust of Ordos massif is much larger than that in the geologically active tectonic region. The site responses of the 32 stations in the high-frequency section do not show clear amplification effect except one or two stations, while in the low-frequency section, there is difference among the stations. The logarithmic value of seismic moment and the magnitude ML of 19 seismic events has a very good linear relationship.

  5. Seismic and magnetic susceptibility anisotropy of middle-lower continental crust: Insights for their potential relationship from a study of intrusive rocks from the Serre Massif (Calabria, southern Italy)

    Science.gov (United States)

    Punturo, Rosalda; Mamtani, Manish A.; Fazio, Eugenio; Occhipinti, Roberta; Renjith, A. R.; Cirrincione, Rosolino

    2017-08-01

    We investigated the relationships between fabric, seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the Serre Massif (Southern Italy). In particular, from five granitoids and one metagabbro, cubes were cut according to the fabric elements and seismic properties up to 400 MPa confining pressure were measured with a triaxial multi-anvil apparatus; we also calculated the elastic properties based on the mineral content and composition. In granitoids, measured average compressional wave velocity (Vp) of the fracture-free aggregate at 400 MPa is 6.2 km/s, whereas average shear wave velocity (Vs) is 3.6 km/s, with Poisson's ratio ranging from 0.240 to 0.257, related to the modal proportions of quartz. In metagabbro, average Vp and Vs at 400 MPa are 6.9 km/s and 3.7 km/s, respectively. Results showed that intrinsic velocity distribution, after microcracks closure, depends on progressive alignment of anisotropic minerals such as biotite, amphibole and pyroxene, with maxima velocities localized within the foliation plane. Mean magnetic susceptibility, Km, of the granitic rocks is units, indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy. Comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties. Moreover, a positive correlation between seismic and magnetic anisotropy has been recognized, indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust. Conversely, in metagabbro, the anisotropy of magnetic susceptibility (AMS) is controlled by magnetite and pyrrhotite although these form < 10% of the rock, which dominantly comprises paramagnetic minerals such as biotite and orthopyroxene. Unlike granitoids, in metagabbro the petrophysical properties are controlled by the paramagnetic minerals, while the magnetic anisotropy is controlled by the

  6. Multiple Feldspar replacement in Hercynian granites of the Montseny-Guilleries Massif (Catalan Coastal Ranges, NE Spain)

    Science.gov (United States)

    Fàbrega, Carles; Parcerisa, David; Gómez-Gras, David

    2013-04-01

    The core of the Montseny-Guilleries Massif (Catalan Coastal Ranges) is mainly composed by late-Hercynian granitoids (leucogranites and granodiorites) intruded within Cambrian to Carnoniferous metasediments. The granites are unconformably covered by Triassic (Buntsandstein) and Paleocene red beds at the western boundary, preserving a continuous outcrop of the Permo-Triassic unconformity for about 20 km. In the southwestern Montseny-Guilleries Massif the granites are covered by the Buntsandstein red sandstones that overlain a peneplain paleorelief called the Permo-Triassic palaeosurface. Beneath the palaeosurface the granite displays a characteristic pink colouration. This pink alteration is characterized by precipitation of minute heamatite crystals and albitization of pristine plagioclases (mostly labradorite). The secondary albite is pseudomorphic (mono- or polycrystalline), optically continuous, non-luminiscent, contains widespread microporosity and displays compositions about Ab98. These features are typical of low temperature replacive feldspars (Kastner and Siever, 1979). Albitization of plagioclases is almost total close to the Permo-Triassic palaeosurface and progressively decreases towards depth, displaying a 150-200 m thick alteration profile. The formation of this profile was controlled by fluid circulation along macro- and microfractures and crystal boundaries. Inside the plagioclase crystals fluid pathways were microfractures, twinning and cleavage planes and crystalline defects. The secondary albite holds widespread unconnected micron-size porosity often filled by Fe-oxides. The reaction front is sharp and displays an abrupt composicional change (Ab65 to Ab98) at micron scale. Porosity only appears to be connected at this reaction front surface. The geometrical arrangement of this alterations suggest that albitization was a shallow process related with Na-rich descending fluids linked to the Permo-Triassic palaeosurface, in a similar way to

  7. Strain partitioning in the Belledonne and Pelvoux massifs. Some clues to understand the Variscan tectono-thermal evolution.

    Science.gov (United States)

    Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jeremie; Blein, Olivier

    2016-04-01

    This contribution presents new structural, petrological, geochemical and geochronological data obtained in the Variscan basement of the Alpine Belledonne and Pelvoux External Crystalline massifs. The Belledonne-Pelvoux area is a stack of four litho-tectonic units. The uppermost unit is the early Ordovician Chamrousse ophiolite. It overthrusts a volcanic-sedimentary unit (VSU) made of an alternation of volcanoclastic rocks, plagiogranites and metapelites. The VSU crops out in the eastern Belledonne and western Pelvoux massifs. It is unconformably overlain by a Visean sandstone-conglomerate series with felsic lava (keratophyres). The lowermost litho-tectonic unit is made of felsic and mafic migmatites and granitoids that form the major part of the Pelvoux massif. The western boundary of this tectonic pile is the "synclinal median" strike-slip fault, on the western side of which crops out the Belledonne micaschist unit made of Cambro-ordovician turbiditic series. The structural analysis revealed four main tectono-thermal events: Dx, D1, D2, and D3. Dx is only recorded in relictual metamorphic assemblage in Ky-Grt-Ab bearing micaschist from the VSU holding an obduction metamorphic gradient (3kbar, 370°C up to 7kbar, 430°C). The age of the Dx event remains unknown. The D1 event, characterized by westward low-angle dipping foliation (S1) and a NE-SW striking stretching lineation (L1), is responsible for the crustal thickening resulting of the Eastward emplacement of the Chamrousse ophiolite upon the VSU. D1 is coeval with a barrovian metamorphism with P-T conditions of 6kbar, 600°C recorded in metapelites, and partial melting developed at the base of the VSU. Monazite LA-ICP-MS U-Pb dating revealed that D1 crustal thickening occurred at 337±7 Ma. D2 is a sinistral transpressional deformation responsible for the folding of S1 and L1, and the development of a NE-SW trending pervasive sub-vertical foliation S2. In the lower structural domain, i.e. the partially molten

  8. Granitoids in the Dalat zone, southern Vietnam: age constraints on magmatism and regional geological implications

    Science.gov (United States)

    Nguyen, Thuy Thi Bich; Satir, Muharrem; Siebel, Wolfgang; Chen, Fukun

    The Dalat zone in southern Vietnam comprises a Cretaceous Andean-type magmatic arc with voluminous granitoids and contemporary volcanic rocks. On the basis of petrographical and mineralogical studies, the granitoids were subdivided into three suites: Dinhquan, Deoca and Cana. Rocks of the Dinhquan suite are hornblende-biotite diorites, granodiorites and minor granites. The Cana suite encompasses mainly leucocratic biotite-bearing granites with scarce hornblende. The Deoca suite is made up of granodiorites, monzogranites and granites. Geochemically, the granitoids are of subalkaline affinity, belong to the high-K, calc-alkaline series, and most of them display typical features of I-type granites. This paper presents the new Rb-Sr mineral and U-Pb zircon and titanite age data for the granitoids, which establish the ages of the plutonic suites as: the Dinhquan at 112-100 Ma, Cana at 96-93 Ma and Deoca at 92-88 Ma. These ages are significantly different from earlier publications, and indicate that the earliest magmatism in the Dalat zone began at 112 Ma ago, that is 30-50 Ma later than previously thought. Our geochronological data are also support the continuation of an Andean-type arc running from SE China via southern Vietnam to SW Borneo.

  9. The geology of uranium in the Saint-Sylvestre granite district (Limousin, Massif Central, France); La geologie de l'uranium dans le massif granitique de Saint-Sylvestre (Limousin - Massif Central Francais)

    Energy Technology Data Exchange (ETDEWEB)

    Marquaire, C.; Moreau, M.; Barbier, J.; Ranchin, G.; Carrat, H.G.; Coppens, R.; Senecal, J.; Koszotolanyi, C.; Dottin, H

    1969-07-01

    This report concerns the geology of uranium in Limousin, more particularly in the St-Sylvestre massif, and the related phenomena: regional geology, petrographic and geochemical zonal distribution observed in various granite massifs, uranium movement in connection with surface alteration, geochronology of uranium ore. The work is made up of six articles covering the various scientific aspects listed above. Each article is headed with an abstract. The paper comprises the following chapters: Foreword by Marcel ROUBAULT. 1. Ch. MARQUAIRE, M. MOREAU Outline of geological conditions in Northern Limousin and distribution of uraniferous occurrences. 2. J. BARBIER, G. RANCHIN, H. G. CARRAT and R. COPPENS Geology of the St-Sylvestre Massif and uranium geochemistry - Introduction to laboratory studies - Problems of methodology. 3. J. BARBIER and G. RANCHIN Petrographical and geochemical zones in the St-Sylvestre granite massif (Limousin - French 'Massif Central'). 4. J. BARBIER and G. RANCHIN Uranium geochemistry in the St-Sylvestre Massif (Limousin - French 'Massif Central') - Occurrences of primary geochemical uranium and replacement processes. 5. J. SENEGAL Monograph of the Brugeaud orebody. 6. R. COPPENS, Ch. KOSZTOLANYI and H. DOTTIN Geochronological study of the Brugeaud mine. 1969. (authors) [French] Ce memoire est consacre a la geologie de l'uranium dans le Limousin, plus specialement dans le massif de St-Sylvestre, et aux phenomenes qui s'y rattachent: geologie regionale, phenomenes de zonalite petrographique et geochimique dans certains massifs granitiques, mouvements de l'uranium lies a l'alteration superficielle, geochronologie du minerai d'uranium. L'ouvrage comprend six articles qui recouvrent les differents aspects scientifiques enumeres. Chacun de ces six articles est precede d'un resume. La composition du memoire st la suivante: Marcel ROUBAULT, Preface. 1. Ch. MARQUAIRE, M. MOREAU Esquisse geologique du

  10. Protracted, coeval crust and mantle melting during Variscan late-orogenic evolution: U-Pb dating in the eastern French Massif Central

    Science.gov (United States)

    Laurent, Oscar; Couzinié, Simon; Zeh, Armin; Vanderhaeghe, Olivier; Moyen, Jean-François; Villaros, Arnaud; Gardien, Véronique; Chelle-Michou, Cyril

    2017-03-01

    The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt, which makes it akin to "hot" orogens. These processes resulted in the development of large granite-migmatite complexes, the largest of which being the 305-300-Ma-old Velay dome in the eastern French Massif Central (FMC). This area also hosts a wide range of late-Variscan plutonic rocks that can be subdivided into four groups: (i) cordierite-bearing peraluminous granites (CPG); (ii) muscovite-bearing peraluminous granites (MPG); (iii) K-feldspar porphyritic, calc-alkaline granitoids (KCG) and (iv) Mg-K-rich (monzo)diorites and lamprophyres ("vaugnerites"). New results of LA-SF-ICP-MS U-Pb zircon and monazite dating on 33 samples from all groups indicate that both granites and mafic rocks emplaced together over a long period of 40 million years throughout the Carboniferous, as shown by intrusion ages between 337.4 ± 1.0 and 298.9 ± 1.8 Ma for the granitoids, and between 335.7 ± 2.1 and 299.1 ± 1.3 Ma for the vaugnerites. Low zircon saturation temperatures and abundant inherited zircons with predominant late Ediacaran to early Cambrian ages indicate that the CPG and MPG formed through muscovite or biotite dehydration melting of ortho- and paragneisses from the Lower Gneiss Unit. The KCG and vaugnerites contain very few inherited zircons, if any, suggesting higher magma temperatures and consistent with a metasomatized lithospheric mantle source for the vaugnerites. The KCG can be explained by interactions between the CPG/MPG and the vaugnerites, or extensive differentiation of the latter. The new dataset provides clear evidence that the eastern FMC was affected by a long-lived magmatic episode characterized by coeval melting of both crustal and mantle sources. This feature is suggested here to result from a lithospheric-scale thermal anomaly, triggered by the removal of the lithospheric mantle root. The spatial

  11. Protracted, coeval crust and mantle melting during Variscan late-orogenic evolution: U-Pb dating in the eastern French Massif Central

    Science.gov (United States)

    Laurent, Oscar; Couzinié, Simon; Zeh, Armin; Vanderhaeghe, Olivier; Moyen, Jean-François; Villaros, Arnaud; Gardien, Véronique; Chelle-Michou, Cyril

    2017-01-01

    The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt, which makes it akin to "hot" orogens. These processes resulted in the development of large granite-migmatite complexes, the largest of which being the 305-300-Ma-old Velay dome in the eastern French Massif Central (FMC). This area also hosts a wide range of late-Variscan plutonic rocks that can be subdivided into four groups: (i) cordierite-bearing peraluminous granites (CPG); (ii) muscovite-bearing peraluminous granites (MPG); (iii) K-feldspar porphyritic, calc-alkaline granitoids (KCG) and (iv) Mg-K-rich (monzo)diorites and lamprophyres ("vaugnerites"). New results of LA-SF-ICP-MS U-Pb zircon and monazite dating on 33 samples from all groups indicate that both granites and mafic rocks emplaced together over a long period of 40 million years throughout the Carboniferous, as shown by intrusion ages between 337.4 ± 1.0 and 298.9 ± 1.8 Ma for the granitoids, and between 335.7 ± 2.1 and 299.1 ± 1.3 Ma for the vaugnerites. Low zircon saturation temperatures and abundant inherited zircons with predominant late Ediacaran to early Cambrian ages indicate that the CPG and MPG formed through muscovite or biotite dehydration melting of ortho- and paragneisses from the Lower Gneiss Unit. The KCG and vaugnerites contain very few inherited zircons, if any, suggesting higher magma temperatures and consistent with a metasomatized lithospheric mantle source for the vaugnerites. The KCG can be explained by interactions between the CPG/MPG and the vaugnerites, or extensive differentiation of the latter. The new dataset provides clear evidence that the eastern FMC was affected by a long-lived magmatic episode characterized by coeval melting of both crustal and mantle sources. This feature is suggested here to result from a lithospheric-scale thermal anomaly, triggered by the removal of the lithospheric mantle root. The spatial

  12. Origin and geodynamic setting of Late Cenozoic granitoids in Sulawesi, Indonesia

    Science.gov (United States)

    Maulana, Adi; Imai, Akira; Van Leeuwen, Theo; Watanabe, Koichiro; Yonezu, Kotaro; Nakano, Takanori; Boyce, Adrian; Page, Laurence; Schersten, Anders

    2016-07-01

    Late Cenozoic granitoids are widespread in a 1600 km long belt forming the Western and Northern Sulawesi tectono-magmatic provinces. They can be divided into three rock series: shoshonitic (HK), high-K felsic calc-alkaline (CAK), and normal calc-alkaline to tholeiitic (CA-TH). Representative samples collected from eleven plutons, which were subjected to petrography, major element, trace element, Sr, Nd, Pb isotope and whole-rock δ18O analyses, are all I-type and metaluminous to weakly peraluminous. The occurrence of the two K-rich series is restricted to Western Sulawesi, where they formed in an extensional, post-subduction tectonic setting with astenospheric upwelling providing thermal perturbation and adiabatic decompression. Two parental magma sources are proposed: enriched mantle or lower crustal equivalent for HK magmas, and Triassic igneous rocks in a Gondwana-derived fragment thrust beneath the cental and northern parts of Western Sulawesi for CAK magmas. The latter interpretation is based on striking similarities in radiogenic isotope and trace element signatures. CA-TH granitoids are found mostly in Northern Sulawesi. Partial melting of lower-middle crust amphibolites in an active subduction environment is the proposed origin of these rocks. Fractional crystallization and crustal contamination have played a significant role in magma petrogenesis, particularly in the case of the HK and CAK series. Contamination by organic carbon-bearing sedimentary rocks of the HK and CAK granitoids in the central part of Western Sulawesi is suggested by their ilmenite-series (reduced) character. The CAK granitoids further to the north and CA-TH granitoids in Northern Sulawesi are typical magnetite-series (oxidized). This may explain differences in mineralization styles in the two regions.

  13. Paleoproterozoic Potassic Granitoids in the Sushui Complex from the Zhongtiao Mountains, Northern China:Geochronology, Geochemistry and Petrogenesis

    Institute of Scientific and Technical Information of China (English)

    TIAN Wei; LIU Shuwen; ZHANG Huafeng

    2006-01-01

    Paleoproterozoic potassic granitoids in the southern Sushui Complex from the Zhongtiao Mountains yielded SHRIMP zircon U-Pb ages of 1968-1944 Ma. Lithologically, the potassic granitoid series consists chiefly of monzodiorite, quartz monzonite and syenogranite. Their trace elements and Sm-Nd isotope characteristics indicate that they were derived from partial melting of Archean TTG rocks in an overthickened continental crust. Petrogenesis of this potassic granitoid series implies a collisional environment within the Trans-North China Orogen in the Paleoproterozoic, which supports a tectonic model of Eastern and Western Continental Blocks being amalgamated in the Paleoproterozoic.

  14. Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust

    Science.gov (United States)

    Wehrens, Philip; Berger, Alfons; Peters, Max; Spillmann, Thomas; Herwegh, Marco

    2016-12-01

    Mid-crustal deformation is classically characterized by the transition from ductile to brittle deformation defining the frictional-to-viscous transition (FVT). Here we investigate an exhumed continental mid-crustal basement section in order to envisage the relationship between ductile and brittle deformation at the FVT. Our detailed study from km- to micro-scale shows that, under greenschist metamorphic conditions, deformation is accommodated by a dense network of highly-localized ductile shear zones. In the investigated case it is not quartz which defines the overall ductile deformation behavior but the viscous granular deformation in shear zones with an ultrafine-grained polymineralic matrix consisting of quartz, feldspar, sheet silicates and epidote. During viscous granular flow mass transfer processes under the presence of fluids promote a chemo-mechanical mixing, resulting in grain size reduction and reaction softening. Coeval with this ductile deformation, fluid-assisted embrittlement occurs, as indicated by biotite-coated fractures, cataclasites and injection of non-cohesive polymineralic gouge material into secondary fractures inside the host rock. The embrittlement during predominant ductile deformation occurs in cycles, i.e. prolonged periods of slow viscous granular flow are interrupted by rapid brittle deformation. We interpret this fluid-assisted cyclic embrittlement evidenced by injection of the fluidized material into off-fault fractures as an alternative equivalent to pseudotachylites and as a microstructural indicator for paleo-seismic activity. With exhumation and associated cooling, localized deformation persists in the ultrafine-grained polymineralic shear zones but progressively transitions to cataclastic flow and finally to pressure-dependent frictional flow; always showing cycles of slow interseismic flow and fast seismic injection events. Overall, in the granitic crust of the Aar-massif, brittle and ductile deformation coexist up to

  15. Hydrogeology of the Olševa massif (Slovenia

    Directory of Open Access Journals (Sweden)

    Jure Krivic

    2002-12-01

    Full Text Available Olševa consists of highly pervious carbonates, forming a relatively big fractured and karstified aquifer. Due to its high-altitude mountainous nature, the aquifer is unpolluted and therefore has to be regarded as a potential source of drinking water for the future.The Olševa aquifer is tectonically divided into three parts. Groundwater from the two smaller aquifers, covering areas of 1,9 and 0,8 km2, located in eastern part of Ol{eva massif, flows toward Northeast into Meža river basin. In spite of several transversal faults, the rest of Olševa massif forms a relatively uniform aquifer that is conveying groundwater in westerly direction towards Rjavica valley. Rjavica valley in Austria represents the discharge area of a majority of groundwater from the main Ol{eva aquifer.

  16. A-type and I-type granitoids and mylonitic granites of Hassan Salaran area of SE Saqqez, Kurdistan, Iran

    Science.gov (United States)

    Abdullah, Fakhraddin Mohammad; Saeed Ahmad, Sheler

    2014-05-01

    The Hassan Salarn area is located 20km to southeast of Saqqez city in Kurdistan Province, western Iran. In this area there are two distinct granitic rock suites consisting A-type and I-type granites and also mylonitic granites. These A-type and I-type granites have various petrological and geochemical characteristics. They also have different origins and petrogenesis. A-type granitoids comprise alkali feldspar granite, syenogranite and quartz alkali feldspar syenite, whereas I-type granitoids are composed of monzogranite, granodiorite and tonalite. Geochemically, A-type granitoids are peralkaline and acmite-normative but I-type granitoids are subalkaline (calc-alkaline), metaluminous and diopside-normative. A-type granitoids are also ferroan alkali and ferroan alkali-calcic whereas I-type granitoids are magnesian and calcic. A-type granitoids resemble to within plate granites and post-orogenic granites whereas I-type granitoids resemble to volcanic arc granites. A-type granitoids contain higher concentrations of alkalies, Zr, Rb, Nb, Y, Th, Ce, high FeO/MgO ratios and lower concentrations of Mg, Ca and Sr, resembling post-orogenic A-type granites. It is possible that heat from a mantle-derived magma which intruded into the lower crust, and/or rapid crustal extension have been essential generation of approriate melts producing A-type granitoids. Thus we can conclude that A-type granitoids were generated from a mixed mantle-crust source. Negative Nb anomalies and low contents of Ti and P probably indicate a subduction-related origin for protolith of I-type granitoids. Negative Nb anomalies and enrichment in Ce relative to its adjacent elements can be related to involvement of continental crust in magmatic processes. I-type granitoids are also enriched in Rb, Ba, K, Th, Ce and depleted in Nb, Zr and Y, indicating that they have had interacted with crust. I-type granitoids may result from contamination of mantle-derived magmas by continental crust during a subduction

  17. U-Pb SHRIMP data and geochemical characterization of granitoids intruded along the Coxixola shear zone, Provincia Borborema, NE Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Guimaraes, Ignez de Pinho; Silva Filho, Adejardo Francisco da; Silva, Francis M.J.V. da, E-mail: ignez@ufpe.br [Universidade Federal de Pernanmbuco (UFPE), Recife, PE (Brazil). Dept. de Geologia; Armstrong, Richard [Australian National University (Australia)

    2011-07-01

    A large volume of granitic magmatism associated with large scale shear zone and metamorphism under high-T amphibolite facies conditions characterize the Brasiliano Orogeny in the Borborema Province, NE Brazil. Granitoids from two plutons and later dykes intruded along the Coxixola shear zone show distinct crystallization ages and geochemical signature. The oldest granitoids (618 ± 5 Ma), Serra de Inacio Pereira Pluton are coeval with the peak of regional metamorphism and they were probably originated by melting of a paleoproterozoic source. The granitoids from the Serra do Marinho Pluton show crystallization age of 563 ± 4 Ma and geochemical signature of post-collisional A-type granites. The later dykes have crystallization age of 526 ± 7 Ma, geochemical signature of A-type granitoids. (author)

  18. Petrographic-geochemical characteristics of granitoids and their epigenetic alteration products in paleovalley fields (Vitim uranium-ore site)

    Science.gov (United States)

    Kuznetsova, E. S.; Domarenko, V. A.; Matveenko, I. A.

    2016-09-01

    The study describes the results of the mineral and element composition of granitoids in basement and weathering crust of Khiagdinsk ore field in Vitim uranium ore site. It has been stated that granitoids in basement consist of leucocratic biotite granite of subalkaline group. The major rock-forming, accessory (apatite, zircon, sphene (titanite), magnetite, monazite, xenotime), and uranium-bearing minerals have been determined. Weathering crust is composed of unlithified or weakly lithified sediments, among which sandy and sandy medium gravel deposits have been distinguished in terms of mineralogical and granulometric texture. High radioactivity of granitoids was revealed in thorium-uranium basement and natural uranium. The combination of the specified factors presupposes that granitoids of Vitim uranium ore site may be a source of uranium in the fields of the paleovalley type.

  19. Miocene mass-transport sediments, Troodos Massif, Cyprus

    Science.gov (United States)

    Lord, A.R.; Harrison, R.W.; BouDagher-Fadel, M.; Stone, B.D.; Varol, O.

    2009-01-01

    Sediment mass-transport layers of submarine origin on the northern and southern flanks of the Troodos ophiolitic massif are dated biostratigraphically as early Miocene and late Miocene, respectively and therefore represent different seismogenic events in the uplift and erosional history of the Troodos terrane. Analysis of such events has potential for documenting Miocene seismic and uplift events regionally in the context of changing stress field directions and plate vectors through time. ?? 2009 The Geologists' Association.

  20. Complete Alpine reworking of the northern Menderes Massif, western Turkey

    Science.gov (United States)

    Cenki-Tok, B.; Expert, M.; Işık, V.; Candan, O.; Monié, P.; Bruguier, O.

    2016-07-01

    This study focuses on the petrology, geochronology and thermochronology of metamorphic rocks within the northern Menderes Massif in western Turkey. Metasediments belonging to the cover series of the Massif record pervasive amphibolite-facies metamorphism culminating at ca. 625-670 °C and 7-9 kbars. U-Th-Pb in situ ages on monazite and allanite from these metapelites record crustal thickening and nappe stacking associated with the internal imbrication of the Anatolide-Taurides platform during the Eocene. In addition, new 39Ar/40Ar single muscovite grain analyses on deformed rocks were performed in three localities within the northern Menderes Massif and ages range from 19.8 to 25.5 Ma. These mylonites may be related to both well-known detachments, Simav to the north and Alaşehir to the south, which accommodate Oligo-Miocene exhumation of the Menderes core complex. U-Th-Pb data on monazite grains (22.2 ± 0.2 Ma) from migmatites emplaced within the Simav detachment confirm these ages.

  1. Petrology, geochronology, geochemistry and petrogenesis of Bajestan granitoids, North of Ferdows, Khorasan Razvi Province

    Directory of Open Access Journals (Sweden)

    Reyhaneh Ahmadirouhani

    2017-02-01

    Full Text Available Introduction The investigated area is situated in the south west of the Khorasan Razavi Province along the North West of the Lut Block. Different types of metal ore bodies along with non-metal deposits have already been documented in the Lut Block (Karimpour et al., 2008. Most of the study area is covered with granitoid rocks. Metamorphic rocks with unknown age are present in the north of the area. Skarns are observed in contact with fault zones and intrusive bodies. Eocene volcanic rocks with andesite and andesibasalt composition are located in the east and north east of the area (Ahmadirouhani et al., 2015. The study area that is a part of the Lut Block has a high potentials for Cu, Fe, Au, and Barite mineralization along the observed alteration zones. In the present study, the petrography, petrogenesis, Sr–Nd isotopes, and U–Pb zircon age of acidic granitoids in the east of Bajestan were investigated. Materials and methods In the current study, 400 rock samples were collected from the field and 170 thin sections were prepared for petrography studies. Thirty samples of volcanic rocks, intrusions, and dykes were analyzed using XRF at the Geological Survey of Iran. Twenty-five samples were selected for the elemental analysis using ICP-MS by the Acme Lab Company (Canada, 16 samples of them were related to acidic intrusive bodies and dykes. In addition, zircon crystals from four samples of the granitoids bodies were collected for U–Pb dating. Approximately 50 zircon grains (i.e. euhedral, clear, uncracked crystals with no visible heritage cores and no inclusions were hand-picked from each sample. Through cathodoluminescence imaging, the internal structure and the origin of zircon grains were examined at the Geological Survey of Vienna, Austria. Moreover, zircons were dated using the (LA-ICP-MS method at the Laboratory of Geochronology, the University of Vienna, Austria using the methodology outlined in Klötzli et al., (2009. Sr and Nd

  2. Deciphering relative timing of fabric development in granitoids with similar absolute ages based on AMS study (Dharwar Craton, South India)

    Science.gov (United States)

    Bhatt, Sandeep; Rana, Virendra; Mamtani, Manish A.

    2017-01-01

    Anisotropy of Magnetic Susceptibility (AMS) data are presented from the Koppal Granitoid (Dharwar Craton, South India) that has U-Pb zircon age of 2528 ± 9 Ma. The magnetic fabric is oriented in NNE-SSW direction. This is parallel to the planar structures that developed during regional D3 deformation, but oblique to the NNW-SSE oriented magnetic foliation as well as field foliation (D1/D2 deformation) recorded in the country rock Peninsular Gneiss. Variation in the intensity of fabric within the granitoid is mapped. It is inferred that the emplacement of Koppal Granitoid took place by ballooning and fabric development within the pluton was syntectonic with regional D3. These results are compared with the time-relationship between emplacement/fabric development and regional deformation reported from the Mulgund Granite (2555 ± 6 Ma; U-Pb zircon), which is also located in the Dharwar Craton and is equivalent to the Koppal Granitoid in age. This granite is known to have emplaced syntectonically with regional D1/D2 deformation, and is thus not related to the same deformation event as the Koppal Granitoid, despite their similar absolute ages. It is argued that in the study area, D3 is ≤2537 Ma, while D1/D2 is ≥2549 Ma in age. Thus, this study highlights the use of AMS in (a) deciphering the relative timing of regional deformation and emplacement of granitoids of equivalent age and (b) constraining the timing of regional superposed deformation events.

  3. Detrital zircon evidence for Hf isotopic evolution of granitoid crust and continental growth

    Science.gov (United States)

    Iizuka, Tsuyoshi; Komiya, Tsuyoshi; Rino, Shuji; Maruyama, Shigenori; Hirata, Takafumi

    2010-04-01

    We have determined U-Pb ages, trace element abundances and Hf isotopic compositions of approximately 1000 detrital zircon grains from the Mississippi, Congo, Yangtze and Amazon Rivers. The U-Pb isotopic data reveal the lack of >3.3 Ga zircons in the river sands, and distinct peaks at 2.7-2.5, 2.2-1.9, 1.7-1.6, 1.2-1.0, 0.9-0.4, and uniformitarian secular change in Hf isotopes of granitoid crusts; Hf isotopic compositions of granitoid crusts deviate from the mantle evolution line from about 3.3 to 2.0 Ga, the deviation declines between 2.0 and 1.3 Ga and again increases afterwards. Consideration of mantle-crust mixing models for granitoid genesis suggests that the noted isotopic trends are best explained if the rate of crust generation globally increased in two stages at around (or before) 3.3 and 1.3 Ga, whereas crustal differentiation was important in the evolution of the continental crust at 2.3-2.2 Ga and after 0.6 Ga. Reconciling the isotopic secular change in granitoid crust with that in sedimentary rocks suggests that sedimentary recycling has essentially taken place in continental settings rather than active margin settings and that the sedimentary mass significantly grew through addition of first-cycle sediments from young igneous basements, until after ˜1.3 Ga when sedimentary recycling became the dominant feature of sedimentary evolution. These findings, coupled with the lack of zircons older than 3.3 Ga in river sands, imply the emergence of large-scale continents at about 3.3 Ga with further rapid growth at around 1.3 Ga. This resulted in the major growth of the sedimentary mass between 3.3 and 1.3 Ga and the predominance of its cannibalistic recycling later.

  4. Were ancient granitoid compositions influenced by contemporaneous atmospheric and hydrosphere oxidation states?

    Science.gov (United States)

    Jagoutz, O. E.

    2013-12-01

    A fundamental shift in the nature of granitoids occurs at approximately the Archean-Proterozoic boundary. Archean crust is dominated Na-rich tonalite-trondhjemite-granodiorites (TTGs), whereas post-Archean granitoids are characterized by K-rich granodiorite-granite (GG). Due to the HREE depletion commonly found in TTGs indicating the presence of residual garnet, many researchers have proposed that the difference in Na/K is related to the deeper melting depth of the TTG parental liquids. Here I present a compilation of the relevant experimental data, documenting that no correlation exists between the Na/K of derivative felsic liquids and the pressure of partial melting/fractional crystallization. Instead, the Na/K ratio of the felsic liquid best correlates with the Na/K ratio of the source. This implies that in Archean time the source material of TTG rocks must have been Na/K enriched relative to the modern. Modern granitoids are dominantly formed in a supra subduction zone environment, where a feedback loop exists between subducted materials (oceanic crust and sediments) and arc magmatism. Sea-floor weathering and the Na/K of the altered oceanic crust strongly depends on f(O2) conditions during alteration, which likely changed with earth history. During alteration under oxidized condition K2O is fixated due to the formation of celadonite (K-Mica), wheres during anoxic condition saponite (Na-Smectite) is the stable alteration mineral. I propose that the rise of oxygen at 2600-2400 Ma triggered associated changes in f(O2) seafloor alteration conditions. The change in the dominant seafloor alteration mineral from reduced to oxidized causes a change in the nature of the arc magma source and provides a possible explanation for the observed transition from TTGrocks in the Archean to the GG-granitoids in post-Archean times.

  5. Mechanisms and Processes Leading to Reverse Zoning in the Andong Granitoid Pluton, Andong Batholith, Korea

    Institute of Scientific and Technical Information of China (English)

    Sang Koo HWANG

    2002-01-01

    The Andong pluton consists of comagmatic granitoid rocks which constitute outstanding examples of reversely zoned granitoids. The pluton has three lithofacies: hornblende biotite tonalite, biotite granodiorite and porphyritic biotite granite. The zoned pattern forms by locating a tonalite core containing high-temperature mafic assemblages in central part,granodiorite rims in marginal part, and a porphyritic granite cap containing more felsic assemblages in topside of the pluton.Mineral abundances as well as bulk compositions of the granitoids indicate that the interior is enriched in mafic minerals and that it shows higher contents of oxides than the margin and topside. The compositional gradients change gradually with continuity between the lithofacies. The regular compositional variations within the pluton support the argument that the pluton behaved as an individual petrochemical system. Model abundances of the granitoids are in agreement with the bulk compositional gradients, suggesting that no significant interaction with country rocks occurred. Remobilization (resurgence) of deeper parts of the system into the more felsic magmas of the chamber explains the reverse zoning. Fractional crystallization was of importance and probably accounts for the selective removal of the settling phases. The Andong pluton is an example of reversely zoned plutons related by remobilization of more mafic but consanguineous magmas. Large-scale upwelling occurred in the pluton leading to the present arrangement of three lithofacies. It is conceivable that remnants of the reverse zoning become more difficult to discern as the plutonic rocks reach the latest stages of their evolution. In this case, the Andong pluton represents an earlier stage in the evolution of a felsic system that is usually represented by the final stages in normally zoned plutons.

  6. Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

    Science.gov (United States)

    Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

    2014-01-01

    Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

  7. Long-term flow-through column experiments and their relevance to natural granitoid weathering rates

    Science.gov (United States)

    White, Art F.; Schulz, Marjorie S.; Lawrence, Corey R.; Vivit, Davison V.; Stonestrom, David A.

    2017-04-01

    Four pairs of fresh and partly-weathered granitoids, obtained from well-characterized watersheds-Merced River, CA, USA; Panola, GA, USA; Loch Vale, CO, USA, and Rio Icacos, Puerto Rico-were reacted in columns under ambient laboratory conditions for 13.8 yrs, the longest running experimental weathering study to date. Low total column mass losses (convergence during the last decade of reaction. NETPATH/PHREEQC code simulations indicated non-stoichiometric dissolution involving Ca release from disseminated calcite and excess K release from interlayer biotite. Effluent 87Sr/85Sr ratios reflected a progressive weathering sequence beginning and ending with 87Sr/85Sr values of plagioclase with an additional calcite input and a radiogenic biotite excursion proportional to the granitoid ages. Effluents became thermodynamically saturated with goethite and gibbsite, slightly under-saturated with kaolinite and strongly under-saturated with plagioclase, consistent with kinetically-limited weathering in which solutes such as Na varied with column flow rates. Effluent Na concentrations showed no clear trend with time during the last decade of reaction (fresh granitoids) or increased slowly with time (weathered granitoids). Analysis of cumulative Na release indicated that plagioclase dissolution achieved steady state in 3 of the 4 fresh granitoids during the last decade of reaction. Surface-area normalized plagioclase dissolution rates exhibited a narrow range (0.95-1.26 10-13 moles m-2 s-1), in spite of significant stoichiometric differences (An0.21 to An0.50). Rates were an order of magnitude slower than previously reported in shorter duration experiments but generally 2-3 orders of magnitude faster than corresponding natural analogs. CrunchFlow simulations indicated that more than a hundredfold decrease in column flow rates would be required to produce near-saturation reaction affinities that would start to slow plagioclase weathering to real-world levels. Extending simulations

  8. Petrogenesis of granitoid rocks at the northern margin of the Eastern Ghats Mobile Belt and evidence of syn-collisional magmatism

    Indian Academy of Sciences (India)

    Samarendra Bhattacharya; Rajib Kar; S Moitra

    2004-12-01

    The northern margin of the Eastern Ghats Mobile belt against the Singhbhum craton exposes granitic rocks with enclaves from both the high-grade and low-grade belts. A shear cleavage developed in the boundary region is also observed in these granitoids. Field features and petrography indicate syn-tectonic emplacement of these granitoids. Petrology-mineralogy and geochemistry indicate that some of the granitoids are derived from the high-grade protoliths by dehydration melting. Others could have been derived from low-grade protoliths. Moreover, microstructural signatures in these granitoids attest to their syn-collisional emplacement.

  9. Long-term flow-through column experiments and their relevance to natural granitoid weathering rates

    Science.gov (United States)

    White, Arthur F.; Schulz, Marjorie S.; Lawrence, Corey R.; Vivit, Davison V.; Stonestrom, David A.

    2017-01-01

    Four pairs of fresh and partly-weathered granitoids, obtained from well-characterized watersheds—Merced River, CA, USA; Panola, GA, USA; Loch Vale, CO, USA, and Rio Icacos, Puerto Rico—were reacted in columns under ambient laboratory conditions for 13.8 yrs, the longest running experimental weathering study to date. Low total column mass losses (Fe-oxyhydroxide precipitation. Surface areas returned to within factors of 2 to 3 of their original values after dithionite extraction. Miscible displacement experiments indicated homogeneous plug flow with negligible immobile water, commonly cited for column experiments. Fresh granitoid effluent solute concentrations initially declined rapidly, followed by much slower decreases over the next decade. Weathered granitoid effluent concentrations increased modestly over the same time period, indicating losses of natural Fe-oxide and/or clay coatings and the increased exposure of primary mineral surfaces. Corresponding (fresh and weathered) elemental effluent concentrations trended toward convergence during the last decade of reaction. NETPATH/PHREEQC code simulations indicated non-stoichiometric dissolution involving Ca release from disseminated calcite and excess K release from interlayer biotite. Effluent 87Sr/85Sr ratios reflected a progressive weathering sequence beginning and ending with 87Sr/85Sr values of plagioclase with an additional calcite input and a radiogenic biotite excursion proportional to the granitoid ages.Effluents became thermodynamically saturated with goethite and gibbsite, slightly under-saturated with kaolinite and strongly under-saturated with plagioclase, consistent with kinetically-limited weathering in which solutes such as Na varied with column flow rates. Effluent Na concentrations showed no clear trend with time during the last decade of reaction (fresh granitoids) or increased slowly with time (weathered granitoids). Analysis of cumulative Na release indicated that plagioclase dissolution

  10. Granitoids of different geodynamic settings of Baikal region (Russia) their geochemical evolution and origin

    Science.gov (United States)

    Antipin, Viktor; Sheptyakova, Natalia

    2016-04-01

    In the southern folded framing of the Siberian craton the granitoid magmatism of different ages involves batholiths, small low-depth intrusions and intrusion-dyke belts with diverse mineral and geochemical characteristics of rocks. Granitoid formation could be related to the Early Paleozoic collision stage and intra-plate magmatism of the Late Paleozoic age of the geologic development of Baikal area. The Early Paleozoic granitoids of Khamar-Daban Ridge and Olkhon region revealed their closeness in age and composition. They were referred to syncollision S-type formations derived from gneiss-schistose substratum of metamorphic sequences. The magmatic rocks were classified into various geochemical types comprising formations of normal Na-alkalinity (migmatites and plagiogranites), calc-alkaline and subalkaline (K-Na granitoids, granosyenites and quartz syenites) series. It is significant, that plagiomigmatites and plagiogranites in all elements repeat the shape of the chart of normalized contents marked for trend of K-Na granitoids, but at considerably lower level of concentrations of all elements. This general pattern of element distribution might indicate similar anatectic origin of both granitoid types, but from crustal substrata distinguished by composition and geochemical features. Comparative geochemical analysis pointed out that the source of melts of the Early Paleozoic granitoids of the Olkhon (505-477 Ma) and Khamar-Daban (516-490 Ma) complexes of the Baikal region could be the crustal substratum, which is obviously the criterion for their formation in the collisional geodynamic setting. Using the Late Paleozoic subalkaline magmatism proceeding at the Khamar-Daban Range (Khonzurtay pluton, 331 Ma) as an example, it was found that the formation of monzodiorite-syenite-leucogranite series was considerably contributed by the processes of hybridism and assimilation through mixing of the upper mantle basaltoid magma derived melts of granitic composition. The

  11. Geochemistry and geochronology of granitoids in the Kibi-Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana

    Science.gov (United States)

    Anum, Solomon; Sakyi, Patrick Asamoah; Su, Ben-Xun; Nude, Prosper M.; Nyame, Frank; Asiedu, Daniel; Kwayisi, Daniel

    2015-02-01

    In Ghana the West African Craton is represented by Birimian and Tarkwaian rocks with extensive granitoid bodies. Granitoids from Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana were analysed for major and trace element contents and found to be characterised by highly-fractionated REE, enrichments, in LILE, and depletion in Nb, Ta and Sr. The LILE enrichment relative to strong Nb-Ta depression, indicates that these granitoids were emplaced in an active margin. Based on field relations, geochemical composition and geochronological data, the granitoids from the Kibi-Asamankese area can be divided into three types, namely; the Eburnean biotite granodiorite (2133-2127 Ma) and hornblende granodiorite (2147 Ma), and the Pre-Eburnean gneissic biotite granite (2193 Ma). The geochemical data of the studied rocks plot in the tholeiitic field, whereas on the A/CNK-A/NK diagram, they generally fall within the metaluminous field, with A/CNK values between 0.69 and 0.88. U-Pb dating of zircons in the granitoids yielded ages ranging from 2193 to 2127 Ma, which are among the oldest ages obtained from the granitoid plutons in Ghana. Such high-precision geochronological data indicate that magmatism occurred over a time-span of about 70 Ma. This provides further evidence that the period 2.1-2.2 Ga was one of the important stages of Birimian magmatism that led to the generation of the granitoids. From the above-mentioned ages, it is possible to link the geological activities to crustal processes and establish the cyclic geotectonic evolution in the West African Craton over time as part of an arc-back-arc basin system.

  12. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    Science.gov (United States)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  13. Geological, petrogical and geochemical characteristics of granitoid rocks in Burma: with special reference to the associated WSn mineralization and their tectonic setting

    Science.gov (United States)

    Zaw, Khin

    The granitoid rocks in Burma extend over a distance of 1450 km from Putao, Kachin State in the north, through Mogok, Kyaukse, Yamethin and Pyinmana in the Mandalay Division, to Tavoy and Mergui areas, Tenasserim Division, in the south. The Burmese granitoids can be subdivided into three N-S trending, major belts viz. western granitoid belt, central graniotoid belt and eastern granitoid belt. The Upper Cretaceous-Lower Eocene western belt granitoids are characterized by high-level intrusions associated with porphyry Cu(Au) related, younger volcanics; these plutonic and volcanic rocks are thought to have been emplaced as a magmatic-volcanic arc (inner magmatic-volcanic arc) above an east-dipping, but westwardly migrating, subduction zone related to the prolonged plate convergence which occurred during Upper Mesozoic and Cenozoic. The central granitoid belt is characterized by mesozonal, Mostly Upper Cretaceous to Lower Eocene plutons associated with abundant pegmalites and aplites, numerous vein-type W-Sn deposits and rare co-magmatic volcanics. The country rocks are structurally deformed, metamorphic rocks of greenschist to upper amphibolite facies ranging in age as early as Upper Precambrian to Upper Paleozoic and locally of fossiliferous, metaclastic rocks (Mid Jurassic to Lower Cretaceous). Available K/Ar radiometric data indicate significant and possibly widespread thermal disturbances in the central granitoid belt during the Tertiary (mostly Miocence). In this study, the distribution, lithological, textural and structural characteristics of the central belt granitoids are reviewed, and their mineralogical, petrological, and geochemical features are presented. A brief description of W-Sn ore veins associated with these granitoid plutons is also reported. Present geological, petrological and geochemical evidences demonstrate that the W-Sn related, central belt granitoids are mostly granodiorite and granite which are commonly transformed into granitoid gneisses

  14. Higher Education, Changing Labour Market and Social Mobility in the Era of Massification in China

    Science.gov (United States)

    Mok, Ka Ho; Wu, Alfred M.

    2016-01-01

    This article attempts to investigate the relationship between the massification of higher education, labour market and social mobility in contemporary China. Though only a short period of time has elapsed from elite to mass education, China's higher education has been characterised as a wide, pervasive massification process. Similar to other East…

  15. Rock massif observation from underground coal gasification point of view

    Directory of Open Access Journals (Sweden)

    T. Sasvári

    2009-04-01

    Full Text Available The Underground coal gasification (UCG of the coal seams is determined by suitable geological structure of the area. The assumption of the qualitative changes of the rock massif can be also enabled by application of geophysical methods (electric resisting methods and geoelectric tomography. This article shows the example of evaluating possibilities of realization of the underground coal gasification in the area of the Upper Nitra Coal Basin in Cíge¾ and Nováky deposits, and recommend the needs of cooperation among geological, geotechnical and geophysical researchers.

  16. Groundwater chemistry of the Oban Massif, South-Eastern Nigeria

    Directory of Open Access Journals (Sweden)

    Solomon John Ekwere

    2012-04-01

    Full Text Available Hydrogeochemical study of the fractured/weathered basement of the Oban Massif, southeastern Nigeria has been carried out. Results indicated that concentrations of major cations and anions exhibited the following order of abundance: Ca>Na>Mg>K and HCO3>SO4>Cl, respectively, with minor variations across sampling seasons. Ca-Na-Cl-SO4 and Ca-Mg-HCO3 water types have been identified as major facies, resultant from congruent influences of weathering (mainly silicates, ion exchange processes, and water mixing.

  17. Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning

    Institute of Scientific and Technical Information of China (English)

    杨树锋; 陈汉林; 姜继双; 竺国强; 谢鸿森; 侯渭; 张月明; 徐惠刚

    1997-01-01

    The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure and high temperature. The laws of velocity changes for them differ with the pressure hoost and temperature rise, and the velocity change of S-type is more violent than that of I-type. The "softening point" of compressional wave velocity ( Vp) is also revealed during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth of "softening", Vp after "softening" and the percentage of Vp’ s drop around the "softening point" for two types of granitoids are obviously different. The depth of "softening" is 15 km approximately and Vp after "softening" is 5. 62 km/s for S-type granitoid. But for I-type granitoid the depth of "softening" is 26 km approximately and Vp after "softening" is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the "softening" of elastic-wave velocity is caused by t

  18. Extensional orogenic collapse captured by strike-slip tectonics: Constraints from structural geology and Usbnd Pb geochronology of the Pinhel shear zone (Variscan orogen, Iberian Massif)

    Science.gov (United States)

    Fernández, Rubén Díez; Pereira, Manuel Francisco

    2016-11-01

    The late Paleozoic collision between Gondwana and Laurussia resulted in the polyphase deformation and magmatism that characterizes the Iberian Massif of the Variscan orogen. In the Central Iberian Zone, initial continental thickening (D1; folding and thrusting) was followed by extensional orogenic collapse (D2) responsible for the exhumation of high-grade rocks coeval to the emplacement of granitoids. This study presents a tectonometamorphic analysis of the Trancoso-Pinhel region (Central Iberian Zone) to explain the processes in place during the transition from an extension-dominated state (D2) to a compression-dominated one (D3). We reveal the existence of low-dipping D2 extensional structures later affected by several pulses of subhorizontal shortening, each of them typified by upright folds and strike-slip shearing (D3, D4 and D5, as identified by superimposition of structures). The D2 Pinhel extensional shear zone separates a low-grade domain from an underlying high-grade domain, and it contributed to the thermal reequilibration of the orogen by facilitating heat advection from lower parts of the crust, crustal thinning, decompression melting, and magma intrusion. Progressive lessening of the gravitational disequilibrium carried out by this D2 shear zone led to a switch from subhorizontal extension to compression and the eventual cessation and capture of the Pinhel shear zone by strike-slip tectonics during renewed crustal shortening. High-grade domains of the Pinhel shear zone were folded together with low-grade domains to define the current upright folded structure of the Trancoso-Pinhel region, the D3 Tamames-Marofa-Sátão synform. New dating of syn-orogenic granitoids (SHRIMP Usbnd Pb zircon dating) intruding the Pinhel shear zone, together with the already published ages of early extensional fabrics constrain the functioning of this shear zone to ca. 331-311 Ma, with maximum tectonomagmatic activity at ca. 321-317 Ma. The capture and apparent cessation

  19. Post-collisional granitoids from the Dabie orogen: New evidence for partial melting of a thickened continental crust

    Science.gov (United States)

    He, Yongsheng; Li, Shuguang; Hoefs, Jochen; Huang, Fang; Liu, Sheng-Ao; Hou, Zhenhui

    2011-07-01

    The geological implications of granitoid magmas with high Sr/Y and La/Yb are debated because these signatures can be produced by multiple processes. This study presents comprehensive major and trace element compositions and zircon SHRIMP U-Pb age data of 81 early Cretaceous granitoids and 4 mafic enclaves from the Dabie orogen to investigate partial melting of the thickened lower continental crust (LCC). On the basis of Sr/Y ratios, granitoids can be grouped into two magma series: (i) high Sr/Y granitoids (HSG) and (ii) normal granitoids with low Sr/Y. Relative to normal granitoids, HSG display the following distinct chemical features: (1) at given SiO 2 and CaO contents, the HSG have significantly higher Sr than normal granitoids, defining two different trends in Sr versus SiO 2, CaO diagrams; (2) highly depleted heavy rare earth element (REE) relative to middle and light REE with (Dy/Yb) N and (La/Yb) N up to 3.2 and 151, respectively; (3) variable and higher Nb/Ta; and (4) positive correlations among Sr/Y, (Dy/Yb) N, (La/Yb) N, and Nb/Ta. High Sr/Y, (La/Yb) N, (Dy/Yb) N, and Sr/CaO of HSG do not correlate with major elements (e.g., SiO 2). Large variations in these ratios at a given SiO 2 content indicate that these features do not reflect magma mixing or fractionation. HSG have higher Sr at a given CaO content and larger variation of (Dy/Yb) N than old crustal rocks (including exposed basement, global mafic LCC xenoliths, high Sr/Y TTG suites, and adakites in modern arcs). This precludes inheritance of the HSG chemical features from these source rocks. Instead, the chemical features of the HSG are best explained by partial melting of the thickened LCC with garnet-dominant, plagioclase-poor, and rutile-present residual lithologies. The coupled chemical features of the HSG are not observed in post-collisional granitoids younger than ca.130 Ma, indicating removal of the eclogitic source and/or residuum of HSG underneath the orogen. These characteristic chemical

  20. Geochronology and geochemistry of late Carboniferous-middle Permian I- and A-type granites and gabbro-diorites in the eastern Jiamusi Massif, NE China: Implications for petrogenesis and tectonic setting

    Science.gov (United States)

    Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Xu, Wen-Liang; Yang, Jin-Hui; Xing, De-He; Chen, Hui-Jun

    2016-12-01

    Late Carboniferous-middle Permian magmatism in the Jiamusi Massif of northeast China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), provides critical evidence regarding the tectonic history and geodynamic processes in the region. The gabbro-diorites of the Longtouqiao pluton and two groups of coeval granite in the study area comprise a bimodal magmatic suite. Precise LA-ICP-MS U-Pb zircon ages indicate that the granitoids and gabbro-diorites were emplaced in the late Carboniferous-middle Permian (302-267 Ma). Group I granites have high SiO2 (70.75-77.04 wt.%) and K2O (3.65-5.89 wt.%) contents, are enriched in LILEs (e.g., Rb, Th, and U) relative to HFSEs and LREEs, and have negative Nb, Ta, P, and Ti anomalies, which collectively indicate affinities with subduction-related magmas. Group II granites are weakly peraluminous (A/CNK = 1.03-1.07) and are characterized by enrichment in alkalis (Na2O + K2O = 8.22-8.90 wt.%), low MgO (0.04-0.09 wt.%) and P2O5 (0.01-0.04 wt.%) contents, high Zr and Nb contents, high 10,000 × Ga/Al ratios, and they are geochemically similar to aluminous A-type granites. All the magmatic zircons in these granitoids have great variations of εHf(t) (+ 7.89 to - 5.60) and two-stage Hf model ages (TDM2) of 0.8-1.7 Ga, which suggest that the precursor magmas originated from a heterogeneous source that involved juvenile components derived from a depleted mantle source during magma generation. The aluminous A-type granite magmas were probably derived by high-temperature partial melting of a felsic crustal source, whereas the other granite magmas probably resulted from partial melting of a mafic lower crust. The gabbro-diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for large positive anomalies in Ba, K, and Pb. These features reflect a limited degree of crustal contamination associated with the subduction-related magmatic processes. These data

  1. 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; 华仁民; 章邦桐; 陆建军; 范春方

    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 orogenic event and the initiation of Pangaea break-up,indicating that a new orogenic Wilson cycle is about to start.Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous.

  2. Abundances of chemical elements of the granitoids in different geotectonic units of China and their characteristics

    Institute of Scientific and Technical Information of China (English)

    SHI Changyi; YAN Mingcai; CHI Qinghua

    2007-01-01

    On the basis of actual analytical data of 767 composited samples collected mainly from about 750 large to middle representative granitoid bodies all over China, the average chemical compositions and element abundances of about 70 chemical elements of SiO2, Al2O3, Fe2O3, FeO, MgO,CaO, Na2O, K2O, H2O+, CO2, TFe2O3, Ag, As, Au, B, Ba, Be,Bi, Cd, Cl, Co, Cr, Cs, Cu, F, Ga, Ge, Hf, Hg, Li, Mn, Mo, Nb,Ni, P, Pb, Rb, S, Sb, Sc, Se, Sn, Sr, Ta, Th, Ti, Tl, U, V, W, Zn,Zr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y in alkalifeldspar granite, syenogranite and adamellite in 7 geotectonic units in China such as Tianshan-Xing'an orogenic series, Sino-Korean metaplatform, Kunlun-Qilian-Qinling orogenic series, Yunnan-Tibet orogenic series,Yangtze metaplatform, South China-Youjiang orogenic zone and Himalayan orogenic belt, are calculated and presented in this paper. In addition, the characteristics of petrochemical parameters, trace element contents and rare earth element dis-tributions of different rock types of the granitoids in different geotectonic units are also sufficiently discussed.

  3. Geochronology of the granitoid hosted Salamangone gold deposit, Lourenco district, Amapa State, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Nogueira, Sonia Aparecida Abissi [Secretaria de Meio Ambiente, Sao Paulo, SP (Brazil). Instituto Geologico]. E-mail: snogueira@igeologico.sp.gov.br; Bettencourt, Jorge Silva [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica]. E-mail: jsbetten@usp.br; Tassinari, Colombo Celso Gaeta [Sao Paulo Univ., SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas]. E-mail: ccgtassi@usp.br

    2000-06-01

    The Salamangone deposit occurs in the Lourenco Gold District, Amapa. It is associated to Paleoproterozoic Metamorphosed supracrustal rocks and a calc-alkaline complex. The deposit lies within a metaluminous weakly peraluminous, calc-alkaline tonalitic-granodioritic pluton. The Au-mineralization consists on an epigenetic quartz-vein system, enriched in Au and As and structurally controlled by a ductile-brittle shear zone. U-Pb zircon analysis of tonalite gave a crystallization age of 2.16 {+-} 0.13 Ga, whereas Sm-Nd T{sub DM} model ages of tonalite and granodiorite range from 2.24 to 2.34 Ga. e{sub Nd} (T) vary from 2.88 to 3.02. Additional whole rock Rb-Sr isochron ages on granitoids yielded values in the range of 2.17 to 2.28 Ga, with {sup 87} Sr/{sup 86} Sr initial ratio of 0.702. The isotopic data and geochemical signature of granitoids suggest that the Lourenco region, as well as the neighboring areas in French Guyana, represents a vast area largely floored by accreted juvenile arc terranes without evidence of Archean crust contamination, being related to the development of a calc-alkaline magmatic arc, which was produced within the Maroni-Itacaiunas Province, during a major Paleoproterozoic orogenic event. (author)

  4. Geology and hydrogeology of the Čemernica mountain massif, Western Serbia

    Directory of Open Access Journals (Sweden)

    Milenić Dejan

    2009-01-01

    Full Text Available The mountain massif of Čemernica, Western Serbia, is an orogenic feature of the Inner Dinarides. Hitherto, hydrogeological prospecting of the Massif was all on a regional scale, not detailed. Only scanty data, previously collected, were mappable on a scale larger than 1:100 000. The 2005 to 2008 research of the Čemernica Mountain Massif included geological and hydrogeological reconnaissance and mapping, the employment of remote sensing, a geophysical survey, the monitoring of quantitative and qualitative groundwater variation parameters, etc. The groundwaters of Čemernica are a large potential resource of water supply to multiple users. This paper is a contribution to the study of the geology and hydrogeology of the Čemernica Mountain Massif.

  5. ECOLOGY-ECONOMICAL ASSESSMENT OF NEW RECLAMATION METHOD FOR CURRENTLY WORKING TECHNOGENIC MASSIFS

    Directory of Open Access Journals (Sweden)

    Alexey Strizhenok

    2017-01-01

    Full Text Available One of the most relevant problems of the mining industry is the need to reduce the negative impact of technogenic massifs formed by wastes of extraction and processing of mineral raw materials. This problem has a significant meaning for currently used massifs, because traditional ways of reclamation are not suitable for them. The article describes the results of a scientific study on the development of the most efficient reclamation method for currently used technogenic massifs. Described in detail the main results of the field observations, methods and equipment of laboratory experiments conducted to determine agro-chemical properties of the soil and optimal composition of binder agent. The article also provides ecological and economic assessment of the proposed method of reclamation. The study was conducted on the example of the real technogenic massif, formed by wastes of phosphorus ore processing.

  6. STRESS-METAMORPHISM AND ISOTOPIC AGE OF SHEAR ZONE GRANITOID TECTONITES OF IRTYSH SHEAR ZONE (ALTAI REGION)

    Institute of Scientific and Technical Information of China (English)

    B.M. Chikov; V.A. Ponomachuk; S.V. Zinoviev; B.N. Lapin; A.T. Titov; A.V. Travin; S.V. Palessky

    2002-01-01

    The Irtysh shear zone (ISZ) of Altai region is the lineament structure of the collision-suture type, where granites of Kalba complex and granodiorites of Zmeinogorsk complex are exposed to regional gneiss-formation and stress-metamorphic alterations. This study is based on detailed structural observations at special grounds using optical and electron microscopy, and on the behavior analysis of isotopic systems from altered granitoids.Within the ISZ area we have established the continuous rows of granitoid stress-metamorphism from initial recrystallization of protolite, its cataclasis and mechanical flaring up to complete recrystallization with alteration of mineral composition and formation of the streaky complexes of granite tectonites of blastomylonite and blastocataclasite types. The directed alteration of rocks has several impulse and is expressed by a change in morphology of mineral grains and their relations, magnification of deformation component in the rock structure, and formation of new mineral phases on the basis of initial ones without surface fluidization. At transformation of isotopic systems from granitoid, their feldspars,biotite and hornblende, we can observe "rejuvenation" of the rock substrate from 270- 290 Ma for Kalba granitoids to 220-235 Ma for their tectonites, and for Rudny Altai granodiorites, their ages changes from 285-317 Ma to 232-257 Ma for their tectonites.

  7. Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia

    DEFF Research Database (Denmark)

    Johansson, Åke; Waight, Tod Earle; Andersen, Tom

    2016-01-01

    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U–Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous...

  8. Tracing long term tectonic evolution of accretionary orogens by U-Pb zircon geochronology: Proterozoic to Jurassic tectonics of the Santander Massif, northern Colombia

    Science.gov (United States)

    Valencia, V. A.; Cardona, A.; Gehrels, G. E.; Ruiz, J.; Ibañez, M.

    2009-12-01

    Accurate orogenic models are nedded to reconstruct complex tectonic histories of long lived convergent margins. Integrated zircon U-Pb geochronology on igneous, sedimentary and metasedimentry rocks within single crustal domains is a powerful tool, as it can be used to trace the timing of rock forming events, magmatic style and episodity, and identify crustal recycling. U-Pb detrital zircon and magmatic geochronology was carried on multiple litostratigraphic units of the Santander Massif in the northeastern Andes, in order to reconstruct its long term Late Proterozoic to Early Mesozoic tectonic evolution. Major zircon forming events includ well defined Grenvillian, Late Neoproterozoic to Ordovician, Silurian, Early Permian and Jurassic events. Major peaks of activity at ca. 197 Ma, 440-410 Ma and 470-490 Ma and 950-1052 Ma, support the existence of continental scale tectonic cycles. Older Mesoproterozoic (1.3-1.5 Ga) crustal input in metasediments and magmatic rocks link these units to crustal recycling on the margins of the Amazon Craton, whereas the older 950-1052 Ma peak indicates the link of this crustal segment with other Andean Grenvillian remnant. Previous interpretations of the Paleozoic Silgara Formation seem incorrect, as acquired dates from this study includ different metamorphic units, deposited and formed after the Silurian and Permian during final stages of Pangea's assemblage, probably as Laurentia migrated to its final Alleghanian position. Finally the presence of the NW South America Jurassic arc is also present in the region by granitoid ages. The limited input of this arc signature within the contemporaneous and overlapping Early Cretaceous sedimentary rocks suggest that this arc was developed in a back arc setting.

  9. Slime mould flora of the Ślęża massif

    Directory of Open Access Journals (Sweden)

    Wanda Stojanowska

    2014-11-01

    Full Text Available In four succeding years 1971-1974 field investigation on the Myxomycetes of Ślęża massif has been carried out. Up to the present only 4 species of slime molds from this region were known. My last investigations give 63 new species and 4 new varieties to slime molds flora of Ślęża massif, and 5 new species to Silesia slime mold flora.

  10. Geochemical constraints on the nature of magma sources for Triassic granitoids from South Qinling in central China

    Science.gov (United States)

    Lu, Ying-Hui; Zhao, Zi-Fu; Zheng, Yong-Fei

    2017-07-01

    A combined study of zircon U-Pb ages and Lu-Hf isotopes, whole-rock major-trace elements and Sr-Nd isotopes as well as mineral chemistry and O isotopes was carried out for Triassic granitoids from the South Qinling orogen in central China. Model calculations were also performed to examine the trace element fractionation during partial melting of crustal rocks. The results provide insights into the nature of magma sources for these granitoids. LA-ICPMS zircon U-Pb dating yields concordant ages of 208 ± 2 to 216 ± 3 Ma for these granitoids from the Shahewan (SHW), Caoping (CP) and Zhashui (ZS) plutons, and no relict zircon cores are identified by the CL imaging and U-Pb dating. The SHW and CP granitoids contain hornblende and are metaluminous with A/CNK ratios of 0.84 to 0.93. They exhibit relatively low SiO2 contents (62.88-69.04 wt.%) but high contents of FeOT, MgO and TiO2, and slightly to negligibly negative Eu anomalies (δEu = 0.79-0.89). Zircons from them show mantle-like δ18O values of 4.71 to 5.72‰. In contrast, the ZS granites contain no hornblende and are metaluminous to weakly peraluminous with A/CNK ratios of 0.99 to 1.03. They show relatively high SiO2 contents (69.32-75.94 wt.%) but low FeOT, MgO and TiO2 contents, and moderate negative Eu anomalies (δEu = 0.63-0.81). They have slightly low zircon δ18O values of 4.60 to 4.83‰. All of these granitoids show arc-like trace element distribution patterns with enrichment in LREE and LILE (e.g., Rb, K and Pb) but depletion in HFSE (e.g., Nb, Ta and Ti). Geochemical comparison and modeling indicate that these granitoids are different from adakitic rocks originating from the thickened lower continental crust. Compared with the composition of felsic melts produced by petrological experiments of various lithologies, it appears that these granitoids are derived from dehydration melting of metabasaltic sources at normal lower crustal depths, and experienced varying degrees of fractional crystallization

  11. Cenozoic rejuvenation events of Massif Central topography (France): Insights from cosmogenic denudation rates and river profiles

    Science.gov (United States)

    Olivetti, Valerio; Godard, Vincent; Bellier, Olivier

    2016-06-01

    The French Massif Central is a part of the Hercynian orogenic belt that currently exhibits anomalously high topography. The Alpine orogenesis, which deeply marked Western European topography, involved only marginally the Massif Central, where Cenozoic faulting and short-wavelength crustal deformation is limited to the Oligocene rifting. For this reason the French Massif Central is a key site to study short- and long-term topographic response in a framework of slow tectonic activity. In particular the origin of the Massif Central topography is a topical issue still debated, where the role of mantle upwelling is invoked by different authors. Here we present a landscape analysis using denudation rates derived from basin-averaged cosmogenic nuclide concentrations coupled with longitudinal river profile analysis. This analysis allows us to recognize that the topography of the French Massif Central is not fully equilibrated with the present base level and in transient state. Our data highlight the coexistence of out-of-equilibrium river profiles, incised valleys, and low cosmogenically derived denudation rates ranging between 40 mm/kyr and 80 mm/kyr. Addressing this apparent inconsistency requires investigating the parameters that may govern erosion processes under conditions of reduced active tectonics. The spatial distribution of denudation rates coupled with topography analysis enabled us to trace the signal of the long-term uplift history and to propose a chronology for the uplift evolution of the French Massif Central.

  12. Geochemistry and petrogenesis of the K-rich 'Bongo-type' granitoids in the Paleoproterozoic Bole-Nangodi greenstone belt of Ghana

    Science.gov (United States)

    Abitty, Emmanuel K.; Dampare, Samuel B.; Nude, Prosper M.; Asiedu, Daniel K.

    2016-10-01

    The 'Bongo-type' granitoids intrude the northern portion (where it cross cuts the Tarkwaian), central and south-central portions of the Bole-Nangodi greenstone belt in Ghana. The non-foliated, porphyritic granitoids are characterised by microcline (5-18 mm), often set in a medium to fine grained matrix of quartz and plagioclase, contains granular quartz and show incipient development of mymerkites under thin section. The major mafic phases are a brownish-green variety of hornblende ± biotite, with sphene, epidote and apatite occurring as accessory minerals. The pink looking 'Bongo-type' granitoids are classified as granites with subordinate granodiorites and quartz monzonites. Whole-rock geochemical analyses show that the granitoids are magnesian and metaluminous to weakly peraluminous. On the basis of their Th-Co-K2O and SiO2 contents, the granitoids classified as high-K calc-alkaline and shoshonite series rocks. They show enriched LILE trends, decoupled LILE-HFSE patterns, negative Ta-Nb anomaly, pronounced negative Ti anomaly and variable positive and negative Sr anomalies. The K-rich granitoids from the middle and south-central portions of the Bole-Nangodi belt show the lowest concentrations of LILE and some HFSE with the most prominent negative Ti and Si anomalies. The 'Bongo-type' granitoids show I-type characteristics. Based on Ba-U-Th concentrations, they are interpreted to have had some interaction with crustal materials or some influence of subducted sediments. The granitoids unequivocally show subduction-related signatures and mimic high silica adakites (HSA). They show evidence of being emplaced in a volcanic arc geotectonic environment. Their geochemical similarities to A-type granitoids, however, suggest an arc-back-arc tectonic setting.

  13. Mineral composition control on inter-mineral iron isotopic fractionation in granitoids

    Science.gov (United States)

    Wu, Hongjie; He, Yongsheng; Bao, Leier; Zhu, Chuanwei; Li, Shuguang

    2017-02-01

    This study reports elemental and iron isotopic compositions of feldspar and its coexisting minerals from four Dabie I-type granitoids to evaluate the factors that control inter-mineral Fe isotopic fractionation in granitoids. The order of heavy iron isotope enrichment is feldspar > pyrite > magnetite > biotite ≈ hornblende. Feldspar has heavier iron isotopic compositions than its co-existing magnetite (Δ56Feplagioclase-magnetite = +0.376‰ to +1.084‰, Δ56Fealkali-feldspar-magnetite = +0.516‰ to +0.846‰), which can be attributed to its high Fe3+/Fetot ratio and low coordination number (tetrahedrally-coordinated) of Fe3+. Δ56Femagnetite-biotite of coexisting magnetite and biotite ranges from 0.090‰ to 0.246‰. Based on homogeneous major and iron isotopic compositions of mineral replicates, the inter-mineral fractionation in this study should reflect equilibrium fractionation. The large variations of inter-mineral fractionation among feldspar, magnetite and biotite cannot be simply explained by temperature variation, but strongly depend on mineral compositions. The Δ56Feplagioclase-magnetite and Δ56Fealkali-feldspar-magnetite are positively correlated with albite mode in plagioclase and orthoclase mode in alkali-feldspar, respectively. This could be explained by different Fe-O bond strength in feldspar due to different Fe3+/∑Fe or different crystal parameters. The Δ56Femagnetite-biotite increases with decreasing Fe3+/∑Febiotite and increasing mole (Na + K)/Mgbiotite, indicating a decrease of β factor in low Fe3+/∑Fe and high (Na + K)/Mg biotite. High-silica leucosomes from Dabie migmatites with a feldspar accumulation petrogenesis have higher δ56Fe values (δ56Fe = 0.42-0.567‰) than leucosome that represents pristine partial melt (δ56Fe = 0.117 ± 0.016‰), indicating that accumulation of feldspar could account for high δ56Fe values of these rocks. High δ56Fe values are also predicted for other igneous rocks that are mainly composed of

  14. Metallogenesis related to Mesozoic Granitoids in the Nanling Range,South China and Their Geodynamic Settings

    Institute of Scientific and Technical Information of China (English)

    HUA Renmin; CHEN Peirong; ZHANG Wenlan; YAO Junming; LIN Jinfu; ZHANG Zhanshi; GU Shengyan; LIU Xiaodong; QI Huawen

    2005-01-01

    Affected by the compressive stress from the South-Central (Indo-China) Peninsula, the Indosinian orogenesis, characterized by collision, thrust and uplifting, took place inside the South China Plate during 250-230 Ma.The ages of the Indosinian granitoids in the Nanling Range and vicinity areas are mostly 240-205 Ma, indicating that they were emplaced in both late collision and post-collision geodynamic environments. No important granite-related metallogenesis occurred in this duration. A post-orogenic setting started at the beginning of the Yanshanian Period, which controlled large-scale granitic magmatism and related metallogenesis. This paper makes the first attempt to divide the Yanshanian Period into three sub-periods, i.e. the early, middle and late Yanshanian Periods, based mainly on the features of magmatism, especially granitoids and related metallogenesis and their geodynamic environments. The magmatic association of the Early Yanshanian (about 185-170 Ma) comprises four categories of magmatism, i.e. basalt, bimodal volcanics, A-type granite and intraplate high-K calc-alkaline (HKCA) magmatism, which indicates an extension-thinning of lithosphere and upwelling of mantle material to a relative small and local extent. Pb-Zn, Cu and Au mineralizations associated with HKCA magmatism represents the first high tide of Mesozoic metallogenesis in the Nanling Range area.During the middle Yanshanian, the lithosphere was subjected to more extensive and intensive extending and thinning, and hence mantle upwelling and basaltic magma underplating caused a great amount of crust remelting granitoids. This period can be further divided into two stages. The first stage (170-150 Ma) is represented by large-scale emplacement of crust remelting granites with local tungsten mineralization at its end. The second stage (150-140 Ma) is the most important time of large-scale mineralizations of non-ferrous and rare metals, e.g. W, Sn, Nb-Ta, Bi, Mo, Be, in the Nanling Range area

  15. On the genetic classification and tectonic implications of the Early Yanshanian granitoids in the Nanling Range, South China

    Institute of Scientific and Technical Information of China (English)

    LI XianHua; LI WuXian; LI Zheng-Xiang

    2007-01-01

    Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range of South China, and are associated with numerous non-ferrous and rare metal mineral deposits. These granitoids consist mainly of slightly peraluminous biotite monzogranites and K-feldspar granites that are closely associated in time and space with subordinate amphibole-bearing granites and muscovite- and garnet-bearing granites. In most previous studies, the biotite-bearing granites were classified as crustal transformation-type (corresponding to the S-type) granites which were interpreted to be derived from the regional Paleoproterozoic meta-sedimentary rocks. In this paper, we re-analyze the geochemical characteristics of a number of representative Early Yanshanian Nanling granitoids. There exists a clear negative correlation between SiO2 and P2O5 for the studied granitoids. The Early Yanshanian Nanling granitoid suites (including amphibole-bearing granodiorites→biotite monzogranites→K-feldspar granites→two-mica (muscovite) granites) are metaluminous to slightly peraluminous I-type or fractionated I-type granites. They were derived predominantly from Proterozoic igneous protoliths. The juvenile crust and/or newly mantle-derived materials might also have been involved in some of these granites. In addition, the I- and fractionated I-type granites are closely associated in time and space with minor amount of A-type felsic and mafic volcanic and intrusive rocks as well as alkaline rocks. All these rocks constitute a typical assemblage of anorogenic, intraplate magmatism, suggesting a dominant lithospheric extensional regime for the Nanling Range and neighboring region during the Early Yanshanian period.

  16. Geodynamic evolution and crustal growth of the central Indian Shield: Evidence from geochemistry of gneisses and granitoids

    Indian Academy of Sciences (India)

    M Faruque Hussain; M E A Mondal; Talat Ahmad

    2004-12-01

    The rare earth element patterns of the gneisses of Bastar and Bundelkhand are marked by LREE enrichment and HREE depletion with or without Eu anomaly. The spidergram patterns for the gneisses are characterized by marked enrichment in LILE with negative anomalies for Ba, P and Ti. The geochemical characteristics exhibited by the gneisses are generally interpreted as melts generated by partial melting of a subducting slab. The style of subduction was flat subduction, which was most common in the Archean. The rare earth patterns and the multi-element diagrams with marked enrichment in LILE and negative anomalies for Ba, P and Ti of the granitoids of both the cratons indicate interaction between slab derived melts and the mantle wedge. The subduction angle was high in the Proterozoic. Considering the age of emplacement of the gneisses and granitoids that differs by ∼ 1 Ga, it can be assumed that these are linked to two independent subduction events: one during Archaean (flat subduction) that generated the precursor melts for the gneisses and the other during the Proterozoic (high angle subduction) that produced the melts for the granitoids. The high values of Mg#, Ni, Cr, Sr and low values of SiO2 in the granitoids of Bastar and Bundelkhand cratons compared to the gneisses of both the cratons indicate melt-mantle interaction in the generation of the granitoids. The low values of Mg#, Ni, Cr, Sr and high values of SiO2 in the gneisses in turn overrules such melt-mantle interaction.

  17. The deformation of the Egersund-Ogna anorthosite massif, south Norway: finite-element modelling of diapirism

    OpenAIRE

    Barnichon, Jean-Dominique; Havenith, Hans-Balder; Hoffer, Benoit; Charlier, Robert; Jongmans, Denis; Duchesne, Jean-Clair

    1999-01-01

    This paper aims at testing the mechanical relevance of the petrological model of anorthosite massif diapiric emplacement. The Egersund-Ogna massif (S. Norway) is of particular interest because recent petrological and geochronological data constrain the initial geometry, emplacement conditions and timing (about 2 m.y.). The formation of this anorthosite massif is in agreement with the classical petrological model, in which accumulation of plagioclase takes place in a deep-seated magma chamber ...

  18. Late-Paleozoic emplacement and Meso-Cenozoic reactivation of the southern Kazakhstan granitoid basement

    Science.gov (United States)

    De Pelsmaeker, Elien; Glorie, Stijn; Buslov, Mikhail M.; Zhimulev, Fedor I.; Poujol, Marc; Korobkin, Valeriy V.; Vanhaecke, Frank; Vetrov, Evgeny V.; De Grave, Johan

    2015-11-01

    The Ili-Balkhash Basin in southeastern Kazakhstan is located at the junction of the actively deforming mountain ranges of western Junggar and the Tien Shan, and is therefore part of the southwestern Central Asian Orogenic Belt. The basement of the Ili-Balkhash area consists of an assemblage of mainly Precambrian microcontinental fragments, magmatic arcs and accretionary complexes. Eight magmatic basement samples (granitoids and tuffs) from the Ili-Balkhash area were dated with zircon U-Pb LA-ICP-MS and yield Carboniferous to late Permian (~ 350-260 Ma) crystallization ages. These ages are interpreted as reflecting the transition from subduction to (post-) collisional magmatism, related to the closure of the Junggar-Balkhash Ocean during the Carboniferous-early Permian and hence, to the final late Paleozoic accretion history of the ancestral Central Asian Orogenic Belt. Apatite fission track (AFT) dating of 14 basement samples (gneiss, granitoids and volcanic tuffs) mainly provides Cretaceous cooling ages. Thermal history modeling based on the AFT data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late Mesozoic and Cenozoic. Late Mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the Cimmerian collisions at the southern Eurasian margin and possibly of the Mongol-Okhotsk Orogeny in SE Siberia during the Jurassic-Cretaceous. Following tectonic stability during the Paleogene, inherited basement structures were reactivated during the Neogene (constrained by Miocene AFT ages of ~ 17-10 Ma). This late Cenozoic reactivation is interpreted as the far-field response of the India-Eurasia collision and reflects the onset of modern mountain building and denudation in southeast Kazakhstan, which seems to be at least partially controlled by the inherited basement architecture.

  19. Deforestation Along the Maya Mountain Massif Belize-Guatemala Border

    Science.gov (United States)

    Chicas, S. D.; Omine, K.; Arevalo, B.; Ford, J. B.; Sugimura, K.

    2016-06-01

    In recent years trans-boundary incursions from Petén, Guatemala into Belize's Maya Mountain Massif (MMM) have increased. The incursions are rapidly degrading cultural and natural resources in Belize's protected areas. Given the local, regional and global importance of the MMM and the scarcity of deforestation data, our research team conducted a time series analysis 81 km by 12 km along the Belize-Guatemalan border adjacent to the protected areas of the MMM. Analysis drew on Landsat imagery from 1991 to 2014 to determine historic deforestation rates. The results indicate that the highest deforestation rates in the study area were -1.04% and -6.78% loss of forested area per year in 2012-2014 and 1995-1999 respectively. From 1991 to 2014, forested area decreased from 96.9 % to 85.72 % in Belize and 83.15 % to 31.52 % in Guatemala. During the study period, it was clear that deforestation rates fluctuated in Belize's MMM from one time-period to the next. This seems linked to either a decline in deforestation rates in Guatemala, the vertical expansion of deforestation in Guatemalan forested areas and monitoring. The results of this study urge action to reduce incursions and secure protected areas and remaining forest along the Belize-Guatemalan border.

  20. Preandean geological configuration of the eastern North Patagonian Massif, Argentina

    Directory of Open Access Journals (Sweden)

    Daniel A. Gregori

    2013-11-01

    Full Text Available The Preandean geological configuration of the eastern North Patagonian Massif is established through the use of geological and geophysical analysis. The positive gravity anomalies located near the Atlantic coast are due to 535 and 540 Ma old rocks belonging to the Pampean Orogeny (Precambrian–middle Cambrian, which are widely recognized in central and northern Argentina. The Famatinian Cycle (Ordovician–Devonian is represented by a Silurian–Devonian marine basin equivalent to those of eastern-central Argentina and South Africa, and which was deformed at the end of the Devonian by an ∼E–W to WNW–ESE compressional event, part of the Famatinian Orogeny. Containing strong gravity gradients, the NW–SE belt is coincident with fault zones which were originated during the Gondwanide Orogeny. This event also produced NW–SE overthrusting of the Silurian–Devonian sequences and strike-slip faults that displaced blocks in the same direction. This deformation event belongs to the Gondwanide Orogeny that includes movements related to a counterclockwise rotation of blocks in northern Patagonia. The strong negative anomalies located in the western part of the area stem from the presence of rocks of the Jurassic Cañadón Asfalto basin interbedded in the Marifil Complex. These volcaniclastic sequences show mild deformation of accommodation zones in a pre-Jurassic paleorelief.

  1. DEFORESTATION ALONG THE MAYA MOUNTAIN MASSIF BELIZE-GUATEMALA BORDER

    Directory of Open Access Journals (Sweden)

    S. D. Chicas

    2016-06-01

    Full Text Available In recent years trans-boundary incursions from Petén, Guatemala into Belize’s Maya Mountain Massif (MMM have increased. The incursions are rapidly degrading cultural and natural resources in Belize’s protected areas. Given the local, regional and global importance of the MMM and the scarcity of deforestation data, our research team conducted a time series analysis 81 km by 12 km along the Belize-Guatemalan border adjacent to the protected areas of the MMM. Analysis drew on Landsat imagery from 1991 to 2014 to determine historic deforestation rates. The results indicate that the highest deforestation rates in the study area were −1.04% and −6.78% loss of forested area per year in 2012-2014 and 1995-1999 respectively. From 1991 to 2014, forested area decreased from 96.9 % to 85.72 % in Belize and 83.15 % to 31.52 % in Guatemala. During the study period, it was clear that deforestation rates fluctuated in Belize's MMM from one time-period to the next. This seems linked to either a decline in deforestation rates in Guatemala, the vertical expansion of deforestation in Guatemalan forested areas and monitoring. The results of this study urge action to reduce incursions and secure protected areas and remaining forest along the Belize-Guatemalan border.

  2. Crustal structure of the northern Menderes Massif, western Turkey, imaged by joint gravity and magnetic inversion

    Science.gov (United States)

    Gessner, Klaus; Gallardo, Luis A.; Wedin, Francis; Sener, Kerim

    2016-10-01

    In western Anatolia, the Anatolide domain of the Tethyan orogen is exposed in one of the Earth's largest metamorphic core complexes, the Menderes Massif. The Menderes Massif experienced a two-stage exhumation: tectonic denudation in the footwall of a north-directed Miocene extensional detachment, followed by fragmentation by E-W and NW-SE-trending graben systems. Along the northern boundary of the core complex, the tectonic units of the Vardar-Izmir-Ankara suture zone overly the stage one footwall of the core complex, the northern Menderes Massif. In this study, we explore the structure of the upper crust in the northern Menderes Massif with cross-gradient joint inversion of gravity and aeromagnetic data along a series of 10-km-deep profiles. Our inversions, which are based on gravity and aeromagnetic measurements and require no geological and petrophysical constraints, reveal the salient features of the Earth's upper crust. We image the northern Menderes Massif as a relatively homogenous domain of low magnetization and medium to high density, with local anomalies related to the effect of interspersed igneous bodies and shallow basins. In contrast, both the northern and western boundaries of the northern Menderes Massif stand out as domains where dense mafic, metasedimentary and ultramafic domains with a weak magnetic signature alternate with low-density igneous complexes with high magnetization. With our technique, we are able to delineate Miocene basins and igneous complexes, and map the boundary between intermediate to mafic-dominated subduction-accretion units of the suture zone and the underlying felsic crust of the Menderes Massif. We demonstrate that joint gravity and magnetic inversion are not only capable of imaging local and regional changes in crustal composition, but can also be used to map discontinuities of geodynamic significance such as the Vardar-Izmir-Ankara suture and the West Anatolia Transfer Zone.

  3. Tephrochronology of the Mont-Dore volcanic Massif (Massif Central, France): new 40Ar/39Ar constraints on the Late Pliocene and Early Pleistocene activity

    Science.gov (United States)

    Nomade, Sébastien; Pastre, Jean-François; Nehlig, Pierre; Guillou, Hervé; Scao, Vincent; Scaillet, Stéphane

    2014-03-01

    The Mont-Dore Massif (500 km2), the youngest stratovolcano of the French Massif Central, consists of two volcanic edifices: the Guéry and the Sancy. To improve our knowledge of the oldest explosive stages of the Mont-Dore Massif, we studied 40Ar/39Ar-dated (through single-grain laser and step-heating experiments) 11 pyroclastic units from the Guéry stratovolcano. We demonstrate that the explosive history of the Guéry can be divided into four cycles of explosive eruption activity between 3.09 and 1.46 Ma (G.I to G.IV). We have also ascertained that deposits associated with the 3.1-3.0-Ma rhyolitic activity, which includes the 5-km3 "Grande Nappe" ignimbrite, are not recorded in the central part of the Mont-Dore Massif. All the pyroclastites found in the left bank of the Dordogne River belong to a later explosive phase (2.86-2.58 Ma, G.II) and were channelled down into valleys or topographic lows where they are currently nested. This later activity also gave rise to most of the volcanic products in the Perrier Plateau (30 km east of the Mont-Dore Massif); three quarters of the volcano-sedimentary sequence (up to 100 m thick) was emplaced within less than 20 ky, associated with several flank collapses in the northeastern part of the Guéry. The age of the "Fournet flora" (2.69 ± 0.01 Ma) found within an ash bed belonging to G.II suggests that temperate forests already existed in the French Massif Central before the Pliocene/Pleistocene boundary. The Guéry's third explosive eruption activity cycle (G.III) lasted between 2.36 and 1.91 Ma. It encompassed the Guéry Lake and Morangie pumice and ash deposits, as well as seven other important events recorded as centimetric ash beds some 60 to 100 km southeast of the Massif in the Velay region. We propose a general tephrochronology for the Mont-Dore stratovolcano covering the last 3.1 My. This chronology is based on 44 40Ar/39Ar-dated events belonging to eight explosive eruption cycles each lasting between 100 and 200

  4. Granitoid magmatism of Alarmaut granite-metamorphic dome, West Chukotka, NE Russia

    Science.gov (United States)

    Luchitskaya, M. V.; Sokolov, S. D.; Bondarenko, G. E.; Katkov, S. M.

    2009-04-01

    Main tectonic elements of West Chukotka are Alazey-Oloy, South-Anyui and Anyui-Chukotka fold systems, formed as a result of collision between structures of North-Asian continent active margin and Chukotka microcontinent [1-3]. South-Anyui fold system, separating Alazey-Oloy and Anyui-Chukotka systems, is considered as suture zon, formed as a result of oceanic basin closing [4-6]. Continent-microcontinent collision resulted in formation of large orogen with of northern and southern vergent structures, complicated by strike-slip deformations [7, 8]. Within Anyui-Chukotka fold system several rises, where most ancient deposits (crystalline basement and Paleozoic cover of Chukotka microcontinent) are exposed, were distinguished [2, 9-11]. Later they were considered as granite-metamorphic domes [12-14]. Alarmaut dome is located at West Chukotka to the north from Bilibino city and is traced from south to north in more than 120 km. General direction of structure is discordant to prevailing NW extensions of tectonic elements of the region. Paleozoic-Triassic deposits are exposed within the Alarmaut dome: 1) D3-C1 - crystalline schists, quartz-feldspar metasandstones, quartzites, marbles (700 m) [11]; 2) C1 - marblized limestones, quartz-feldspar metasandstones, quartzites, amphibole-pyroxene crystalline schists. Limestones contain corals, indicating Visean age of deposits [11]. Metamorphism reaches amphibolite facies, maximum P-T conditions are 660°С and 5 kbar. Migmatites, indicating in situ partial melting, are observed. Intensity of deformations of Paleozoic rocks increases at the boundary with Triassic deposits [11]; in the western part of dome slices of Pz rocks are separated by blastomylonite horizons [14]. Within Alramaut dome granitoids of Lupveem batholith (central part of dome), Bystrinsky pluton (southeastern part), and small Koyvel' and Kelil'vun plutons were studied. New U-Pb SHRIMP zircon data indicate Early Cretaceous (117-112 m.a.) age of granitoids [15

  5. Episodic construction of the Tatra granitoid intrusion (Central Western Carpathians, Poland/Slovakia): consequences for the geodynamics of Variscan collision and Rheic Ocean closure

    Science.gov (United States)

    Gawęda, Aleksandra; Burda, Jolanta; Klötzli, Urs; Golonka, Jan; Szopa, Krzysztof

    2016-06-01

    The Tatra granitoid pluton (Central Western Carpathians, Poland/Slovakia) is an example of composite polygenetic intrusion, comprising many magmatic pulses varying compositionally from diorite to granite. The U-Pb LA-MC-ICP-MS zircon dating of successive magma batches indicates the presence of magmatic episodes at 370-368, 365, 360, 355 and 350-340 Ma, all together covering a time span of 30 Ma of magmatic activity. The partial resorption and recycling of former granitoid material ("petrological cannibalism") was a result of the incremental growth of the pluton and temperature in the range of 750-850 °C. The long-lasting granitoid magmatism was connected to the prolonged subduction of oceanic crust and collision of the Proto-Carpathian Terrane with a volcanic arc and finally with Laurussia, closing the Rheic Ocean. The differences in granitoid composition are the results of different depths of crustal melting. More felsic magmas were generated in the outer zone of the volcanic arc, whilst more mafic magmas were formed in the inner part of the supra-subduction zone. The source rocks of the granitoid magmas covered the compositional range of metapelite-amphibolite and were from both lower and upper crust. The presence of the inherited zircon cores suggests that the collision and granitoid magmatism involved crust of Cadomian consolidation age (c. 530 and 518 Ma) forming the Proto-Carpathian Terrane, crust of Avalonian affinity (462, 426 Ma) and melted metasedimentary rocks of volcanic arc provenance.

  6. Petrotectonic framework of granitoids and associated granulites at Nagavalli Shear Zone (NSZ), Eastern Ghats Belt: Evidence of a late transpression orogeny

    Indian Academy of Sciences (India)

    Tamoghna Saha; Subrata Karmakar

    2015-06-01

    Megacrystic granitoids associated with migmatitic and metasedimentary gneisses occurring around Nagavalli Shear Zone (NSZ) preserve complex metamorphic and deformation history. Thinly laminated discontinuous banding of quartzofeldspathic layer (S1) in the migmatites is the product of first incipient melting during prograde M1–D1 tectonothermal event. Peak M2–D2 event is manifested by the development of S2 gneissic foliation in all rocks, which is axial planar to rootless folds on S1.Porphyroblastic garnet mantled by leucosomal melt fraction in granitoids, suggest that the rock suffered peak granulite facies metamorphism along with host migmatitic gneisses. The subsequent D3 event deforms differently the massive granitoids and the migmatitic granulite gneisses. The D4 deformation acted as transpression with broad northwest–southeast compression that develops strong discontinuous regional-scale anastomosing shear zones transecting the earlier gneissosity (S2) in the granitoids with prominent sinistral shear sense. It deforms the axial plane of regional folds in migmatites and develops superposed non-plane non-cylindrical folds in outcrop to regional scale. Thus we infer megacrystic granitoids were possibly emplaced in pre- to syn-peak metamorphic event within the host granulites. Granitoids and associated migmatitic gneisses of Late Meso- to Neoproterozoic age suffered subsequent petrotectonic events followed by a sinistral transpression acted along NSZ.

  7. Mapping and discriminating the Pan-African granitoids in the Hoggar (southern Algeria) using Landsat 7 ETM+ data and airborne geophysics

    Science.gov (United States)

    Zerrouk, Siham; Bendaoud, Abderrahmane; Hamoudi, Mohamed; Liégeois, Jean Paul; Boubekri, Hichem; El Khaznadji, Riad Ben

    2017-03-01

    This study presents a multidisciplinary approach to discriminate and map different types and generations of Pan-African granitoids in the Hoggar, southern Algeria, using remote sensing and airborne geophysics in close correlation with previous works and established geological maps. RGB (Red, Green, Blue) combinations of band ratios; principal component analysis (PCA) and image classification for Landsat 7 ETM+ (Enhanced Thematic Mapper Plus), allow spatial discrimination and mapping of granitoid rocks of the studied area (200*350 km). This area extend over four contrasted Pan-African terranes (In Tedeini, Iskel, Tefedest and Laouni terranes, the two latter belong to the LATEA (Laouni-Azrou-n-Fad-Tefedest-Egéré-Aleksod-Assodé-Issalane) metacraton. The airborne magnetic intensity provides a wide range of responses from high values (youngest granitoids) to low values (volcano-sedimentary and gneissic country-rocks). Radiometric data, displaying radioelements concentration, discriminate efficiently the late alkaline granitoids (high values), the calk-alkaline granitoids (intermediate values) and the Tonalite-Trondhjemite-Granodiorite series (low values). This study led to the establishment of a more accurate geological map where the geochemical characteristics of the Pan-African granitoids are determined, including plutons not yet studied, especially in the poorly known In Tedeini terrane, and brings new constraints for the geodynamic development of the Tuareg Shield, which includes the Hoggar.

  8. The New England Batholith: constraints on its derivation from Nd and Sr isotopic studies of granitoids and country rocks

    Science.gov (United States)

    Mensel, H. D.; McCulloch, M. T.; Chappell, B. W.

    1985-02-01

    Nd and Sr isotopic compositions are reported for the granitic suites which comprise the late Palaeozoic to earliest Mesozoic New England Batholith of eastern Australia. Some of the granitic suites are typically I-type in their mineralogy, chemistry and isotopic compositions, implying a derivation from igneous (infracrustal) source rocks, whereas other suites have characteristics consistent with a derivation from a protolith which was predominantly sedimentary and relatively felsic (S-types). The I-type granitoids of the Nundle Suite have ɛNd values (+3.3 to +6.1) that are amongst the most primitive yet documented for a relatively felsic (SiO 2 ~ 65%) plutonic suite and these values imply a derivation from either a depleted upper mantle source or, more probably, a complex source region involving both volcanic-arc rocks and detrital material. Their compositions are distinctly more primitive than those of the New England Super-Suite which constitutes the Permian 'core' of the batholith. This extensive Super-Suite (comprising granitoids traditionally designated as I-type) has an overall range in initial Nd and Sr isotopic compositions of -1.7 to +4.6 and 0.70458 to 0.70624 respectively, although the majority of plutons have initial Nd isotopic compositions which fall into a very narrow range (+1.0 ±1.5 ɛunits). This limited range is remarkable considering the extreme lithological diversity and range in chemical composition of the analysed samples (SiO 2 47%-74%) and implies a source region of considerable volume having reasonably uniform isotopic compositions but variation in chemistry. A similarly uniform source isotopically is also indicated for the S-type granitoids of the Carboniferous Hillgrove Suite and Carboniferous-Permian Bundarra Suite with initial ɛNd values of +0.8 to +2.3 and initial 87Sr /86Sr compositions of 0.70474 to 0.70577 showing only limited ranges. Five pelites, three 'felsic' and four 'mafic' greywackes, representing typical country rocks

  9. SHRIMP Zircon U-Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains, Shanxi Province

    Institute of Scientific and Technical Information of China (English)

    YU Shengqiang; LIU Shuwen; TIAN Wei; LI Qiugen; FENG Yonggang

    2006-01-01

    Henglingguan and Beiyu metamorphic granitoids, distributed in the northwest of the Zhongtiaoshan Precambrian complex, comprise trondhjemites and calc-alkaline monzogranites,displaying intrusive contacts with the Archean Zhaizi TTG gneisses. And the Beiyu metamorphic granitoids consist mainly of trondhjemites, distributed at the core of the Hujiayu anticline fold. New SHRIMP zircon U-Pb dating data show that the weighted mean 207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc-alkaline monzogranites and Beiyu metamorphic trondhjemites, respectively, and reveal ~2600 Ma inherited core in magmatic zircons. Whole-rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium- and high-potassium calc-alkaline series.These rocks are characterized by relatively high total alkali contents (Na2O+K2O, up to 9.08%),depleted Nb, Ta, P and Ti, and right-declined REE patterns with moderate to high LREEs/HREEs fractionation (the mean ratio of (La/Yb)n = 25). The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb, Th and K anomalies in the multi-element spider diagrams normalized by primitive mantle. Sm-Nd isotopic data reveal that these granitoids have initial εNd(t)=-1.2 to +2.4 and Nd depleted mantle model ages of TMD = 2622 Ma-2939 Ma. All these geochemical features indicate that these granitoids were formed in an continent-marginal arc, and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and, howbeit, the Henglingguan metamorphic calc-alkaline monzogranites derived from recycling of materials in the ancient crust under a continent-marginal arc. The granitic magma underwent contamination and fractional crystallization during their formation.

  10. Variscan Collisional Magmatism and Deformation In The Viseu Area (northern Central Portugal) - Constraints From U-pb Geochronology of Granitoids

    Science.gov (United States)

    Azevedo, M. R.; Aguado, B. V.; Scaltegger, U.; Nolan, J.; Martins, M. R.; Medina, J.

    The Viseu area is located in the innermost zone of the Iberian Variscan Fold Belt (the Central Iberian Zone). It consists of abundant post-thickening, collision related grani- toids intruded into upper and middle crustal levels. The ascent of granite magmas took place after an extensional tectonic event (D2) and is coeval with D3 dextral and sinis- tral crustal-scale transcurrent shear zones. In the northern part of the area, the presence of a well preserved Upper Carboniferous tectonic basin filled with deformed conti- nental clastic sediments, bounded by contemporaneously exhumed deep crustal rocks and intruded by late-tectonic granites documents an episode of extension involving basin subsidence, uplift and erosion of the basement and granite magmatism in a post- thickening, but syn-convergent scenario. Convergence is manifested by strike-slip tec- tonics and basin inversion. According to structural criteria, the Variscan granitoids can be subdivided into two major groups: (1) syn-D3 granitoids including two dif- ferent petrological associations, highly peraluminous leucogranite and granodiorite- monzogranite intrusions and (2) late-D3 granitoids comprising slightly metaluminous to peraluminous granodiorites and monzogranites. Four plutons representing the syn- D3 leucogranites (Junqueira) and monzogranites (Maceira and Casal Vasco) and the late-D3 biotite granites (Cota) yielded U-Pb zircon + monazite or monazite ages of 310 Ma, 311 Ma, 311 Ma and 306 Ma, respectively. This points to a synchronous emplacement of the different syn-D3 plutons shortly followed by the intrusion of the late-D3 granites and suggests that the Upper Carboniferous plutonism occurred within a short time span of ca. 5 myr. Stratigraphic markers show that the oldest continental sediments in the Carboniferous basin are Westphalian whilst field relationships in- dicate that the deformation occurred prior to the intrusion of the late-D3 granitoids. Precise U-Pb geochronology proves that basin

  11. Potential of thermal emissivity for mapping of greenstone rocks and associated granitoids of Hutti Maski Schist belt, Karnataka

    OpenAIRE

    Guha, A.; K.Vinod Kumar

    2014-01-01

    In the present study, different temperature-emissivity separation algorithms were used to derive emissivity images based on processing of ASTER( Advanced spaceborne thermal emission and reflection radiometer) thermal bands. These emissivity images have been compared with each other in terms of geological information for mapping of major rock types in Hutti Maski schist Belt and its associated granitoids. Thermal emissivity images are analyzed conjugately with thermal radiance image, ...

  12. The rockfall observatory in the Reintal, Wetterstein Massif, German Alps

    Science.gov (United States)

    Schöpa, Anne; Turowski, Jens M.; Hovius, Niels

    2017-04-01

    The Reintal is an Alpine valley in the Wetterstein Massif close to the Zugspitze, Germany's highest mountain. Due to the variety of active geomorphic processes, including rockfalls off the steep limestone cliffs, debris flows, and snow avalanches, and the river Partnach, the Reintal has been the field area of many geomorphological and hydrological research campaigns over the last few decades. In 2014, the Geomorphology Section of the GFZ Potsdam started to install a monitoring network to detect and classify rockfalls in the Reintal. The network includes six seismic stations, optical and infrared cameras, and two weather stations measuring air and rock temperature, air pressure and relative humidity, precipitation, wind speed and direction, and solar radiation. The continuous observations of the network are supplemented by repeated field campaigns including terrestrial laser scans of a prominent rockfall niche at the Hochwanner mountain. The about 1,500 m high north face of the Hochwanner experienced the detachment of a 2.8 Mio m3 rockfall about 500 years ago that created the so-called Steingerümpel (German for rock debris deposit) and dammed the river Partnach. The cliff still shows high rockfall activity, and an 80,000 m3 block can be expected to fall in the near future. In this contribution, the layout of the observatory and details of the seismic network centered around the Hochwanner north face are described. Furthermore, the network data of a severe thunderstorm event in June 2016, that triggered many rockfalls and debris flows in the Reintal, is presented.

  13. New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland

    Directory of Open Access Journals (Sweden)

    A.K. Kotilainen

    2016-09-01

    Full Text Available The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88–1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U–Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870–1863 Ma, and 1855±3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values or 3 to 9 Ma (external errors considered younger than the U–Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith – the closure/saturation temperature of the monazite U–Pb system was probably reached in ~10 m.y. after the crystallization of magmatic zircon in the examined rocks.

  14. Critical Reflection on the Massification of Higher Education in Korea: Consequences for Graduate Employment and Policy Issues

    Science.gov (United States)

    Yeom, Min-ho

    2016-01-01

    The paper critically reviews the results of Korean massification in higher education (HE) and focuses on the consequences related to graduate employment. By analysing statistical data and reviewing related articles, this study explores the process of the massification of HE, investigates major factors influencing the expansion, and analyses and…

  15. A Library Response to the Massification of Higher Education: The Case of the University of Zambia Library

    Science.gov (United States)

    Kanyengo, Christine Wamunyima

    2009-01-01

    This paper looks at the challenges that libraries in Africa face in responding to massification of higher education by discussing the University of Zambia library's response in library and information resources provision. As a result of massification of higher education, libraries have been forced not only to employ new and different strategies to…

  16. Post-Hercynian subvolcanic magmatism in the Serre Massif (Central-Southern Calabria, Italy)

    Science.gov (United States)

    Romano, V.; Cirrincione, R.; Fiannacca, P.; Mazzoleni, P.; Tranchina, A.

    2009-04-01

    In the Serre Massif (Central-Southern Calabria, Italy) dykes and subvolcanic bodies intrude diffusively both Hercynian metamorphic rocks and late-Hercynian granitoids. They range in composition from basaltic andesites to dacite-rhyodacites and can be ascribed to the extensive magmatic activity that affects the entire Hercynian orogenic belt in late Paleozoic - early Mesozoic time. The geodinamic framework of the magmatic activity is still matter of debate, nevertheless most authors agree in correlating magmatism both to the late-orogenic collapse of the Hercynian belt and to the lithosphere thinning responsible for the subsequent continental rifting. In this work, we propose a petrogenetic model for acidic to basic hypabissal bodies from southern Calabria in order to define the nature of sources, discriminate magmatic processes and supply a contribution in the geodynamic reconstruction of the Late Palaeozoic in the Calabria-Peloritani Orogen. In relation to their geochemical affinity, studied dykes have been divided in two groups: a medium- to high-K calc-alkaline and a tholeiitic one. Dykes belonging to the former group, andesitic and dacitic-rhyodacitic in composition, show typical features of subduction-related magmatism, such as LILE and LREE enrichments, depletions in HFSE, peaks in Rb, Th and Ce, accentuated troughs in Ba, Nb-Ta, P and Ti (White and Dupré, 1986; McCulloch and Gamble, 1991), contrasting with the late Hercynian collisional context. On the other side, features typical of intra-plate magmatic activity, such as a moderate enrichment in Ta, Nb, Ce, P, Zr, Hf and Sm relative to MORB composition are also present in studied rocks (Shimizu & Arculus, 1975; Pearce, 1982). REE-patterns are strongly to weakly fractionated for the andesitic rocks (Lan/Ybn = 10.03-13.98) and the dacitic-rhyodacitic ones (Lan/Ybn = 6.00 to 2.82), respectively. The latter rocks exhibit a very slight negative Eu anomaly, whereas no Eu anomaly is recognizable in the andesite

  17. Calibration of the Khibiny Massif velocity model using registration of industrial explosions

    Directory of Open Access Journals (Sweden)

    Asming V.E.

    2015-06-01

    Full Text Available Monitoring of geodynamic activity of the Khibiny Massif assumes an accurate location of seismic events occurring here. This requires on the one hand knowledge of seismic wave velocities in the massif and adjacent territories and on the other hand software tools for seismic location in inhomogeneous media. The Seismic Configurator program developed in the Kola Branch of Geophysical Survey of RAS enables to create velocity models of 3D media, locate events and compute apparent velocities of seismic waves propagating along different paths. As a result of registration of industrial explosions in Khibiny, a set of apparent velocities of Pwaves along paths crossing the massif has been obtained. 2D and 3D velocity models matched the observations have been fitted by these data using the Seismic Configurator program. A method of modification of the existing location system for practical usage of the models has been proposed

  18. Episyenites in meta-granitoids of the Tauern Window (Eastern Alps): unpredictable?

    Science.gov (United States)

    Pennacchioni, Giorgio; Ceccato, Alberto; Fioretti, Anna Maria; Mazzoli, Claudio; Zorzi, Federico; Ferretti, Patrizia

    2016-11-01

    The core of the Tauern tectonic window (Eastern Alps) consists of pre-Alpine granitoids (∼295 Ma) variably deformed during Alpine (∼30 Ma) amphibolite-facies metamorphism. Episyenites occur as local alteration haloes (as wide as a few meters) surrounding steeply dipping, strike-slip faults, with offsets meta-granodiorite) and 13% (meta-aplite), mainly derived from dissolution of quartz. Glacier-polished outcrops allow the detailed investigation of the relationships between the episyenites and the structure of the associated faults. Field mapping indicates that episyenites: (i) are spatially linked to pre-existing faults and statically overprinted these structures; (ii) are discontinuous along faults; (iii) have a thickness (of as much as a few meters) that does not correlate with either the amount of slip along the pre-existing faults or the spatial density of the fracture network; (iv) developed with a similar extent in rocks with conspicuous variations of the original quartz grain size and structure. The studied outcrop includes a relatively large volume of episyenite associated with faults. However, despite the pervasiveness of faulting, episyenites are rare in the Tauern meta-granitoids. This localized occurrence of episyenite is inferred to represent a section of a vertical pipe structure exploiting a portion of the fault network. Our study indicates that the location and the extent of episyenite alteration cannot be simply predicted from the geometry and the fracturing patterns of the pre-existing cataclastic faults. Quartz dissolution during episyenitization was accompanied and/or followed by: (i) pervasive substitution of oligoclase and biotite/chlorite of the meta-granodiorite by albite and vermicular chlorite, respectively; and (ii) precipitation of adularia, albite, anatase, calcite, hematite and zeolites within pores. Isotopic data from the calcite filling of the pores suggest a surficial source of fluids associated with this calcite precipitation

  19. Provenance from zircon U-Pb age distributions in crustally contaminated granitoids

    Science.gov (United States)

    Bahlburg, Heinrich; Berndt, Jasper

    2016-05-01

    The basement of sedimentary basins is often entirely covered by a potentially multi-stage basin fill and therefore removed from direct observation and sampling. Melts intruding through the basin stratigraphy at a subsequent stage in the geological evolution of a region may assimilate significant volumes of country rocks. This component may be preserved in the intrusive body either as xenoliths or it may be reflected only by the age spectrum of incorporated zircons. Here we present the case of an Ordovician calc-alkaline intrusive belt in NW Argentina named the "Faja Eruptiva de la Puna Oriental" (Faja Eruptiva), which in the course of intrusion sampled the unexposed and unknown basement of the Ordovician basin in this region, and parts of the basin stratigraphy. We present new LA-ICP-MS U-Pb ages on zircons from 9 granodiorites and granites of the Faja Eruptiva. The main part of the Faja Eruptiva intruded c. 445 Ma in the Late Ordovician. The zircon ages obtained from the intrusive rocks have a large spread between 2683.5 ± 21.6 and 440.0 ± 4.9 Ma and reflect the underlying crust and may be interpreted in several ways. The inherited zircons may have been derived from the oldest known unit in the region, the thick siliciclastic turbidite successions of the upper Neoproterozoic-lower Cambrian Puncoviscana Formation, which is inferred to represent the basement of the NW Argentina. The basement to the Puncoviscana Formation is not known. Alternatively, the inherited zircons may reflect the geochronological structure of the entire unexposed Early Paleozoic crust underlying this region of which the Puncoviscana Formation was only one component. This crust likely contained rocks pertaining to and detritus derived from earlier orogenic cycles of the southwestern Amazonia craton, including sources of Early Meso- and Paleoproterozoic age. Detritus derived, in turn, from the Faja Eruptiva intrusive belt reflects the origin of the granitoids as well as the inherited

  20. The oxygen isotope composition of granitoid and sedimentary rocks of the southern Snake Range, Nevada

    Science.gov (United States)

    Lee, D.E.; Friedman, I.; Gleason, J.D.

    1982-01-01

    Six diverse intrusive igneous types are exposed as discrete outcrops within an area of 900 km2 in the southern Snake Range, White Pine County, Nevada. The previously recognized variety among these igneous types is reflected in the wide range of ??18O values (-1.1 to 13.4 permil) found in these rocks. This range of ??18O values probably results from differences in source material and post-crystallization history of the different intrusive types. The Jurassic intrusive of the Snake Creek-Williams Canyon area represents the chemical equivalent of a large part of a differentiation sequence, with the entire range of composition (63-76 percent SiO2) exposed over a horizontal distance of about five km. The rather regular increase of ??18O values from the most mafic to the most felsic parts of this pluton, together with ??18O values determined for constituent minerals recovered from five of the samples, supports a fractional crystallization model. The high ??18O values found (10.2-12.2 permil) indicate that the magma likely was derived from or assimilated sedimentary materials. Nine samples of the Cretaceous two-mica granite of the Pole Canyon-Can Young Canyon area have ??18O values in the range 10.6-12.1 permil. These high ??18O values, an initial87Sr/86Sr ratio of 0.7165, and the presence of muscovite along with an accessory mineral suite limited to monazite, apatite, zircon, and an allanite-like mineral, characterize this intrusive mass as an S-type granite. It probably formed through anatexis of late Precambrian pelitic rocks. The granitoid rock exposed in the Young Canyon-Kious Basin area is Tertiary (32 m.y.). Most of this intrusive has been cataclastically deformed as a result of late (18 m.y.) movement on the overlying Snake Range decollement. The undeformed portion of this intrusive has ??18O values of 8.7-10.0 permil. However, the deformed portion of this intrusive has ??18O values as low as -1.1 permil, apparently resulting from isotopic exchange between this

  1. Important Crustal Growth in the Phanerozoic: Isotopic Evidence of Granitoids from East-Central Asia

    Indian Academy of Sciences (India)

    Bor-ming Jahn; Fuyuan Wu; Dawei Hong

    2000-03-01

    The growth of the continental crust is generally believed to have been essentially completed in the Precambrian, and the amount of juvenile crust produced in the Phanerozoic is considered insignificant. Such idea of negligible growth in the Phanerozoic is now challenged by the revelation of very large volume of juvenile crust produced in the period of 500 to 100 Ma in several orogenic belts. While appreciable volumes of juvenile terranes in North America (Canadian Cordillera, Sierra Nevada and Peninsular Range, Appalachians) have been documented based on Nd isotopic data, the mass of new crust formed in the East-Central Asian Orogenic Belt (ECAOB), eastern part of the Altaid Tectonic Collage, appears to be much greater than the above terranes combined. New and published Nd-Sr isotope data indicate that the Phanerozoic granitoids from the southern belt of the ECAOB (Xinjiang-West Mongolia-Inner Mongolia-NE China) as well as from Mongolia and Transbaikalia were generated from sources dominated by a depleted mantle component. These granitoids represent a significant growth of juvenile crust in the Phanerozoic. Although most plutons in this huge orogenic belt belong to the calc-alkaline series, the ECAOB is also characterized by the emplacement of voluminous A-type granites. The origin of these rocks is probably multiple and is still widely debated. However, the isotopic data (Sr-Nd-O) and trace element abundance patterns of A-type granites from the ECAOB clearly indicate their mantle origin. The evolution of the ECAOB and the entire Altaid Collage is most likely related to successive accretion of arc complexes. However, the emplacement of a large volume of post-tectonic A-type granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, partial melting of these basic rocks to produce granitic liquids, followed by extensive fractional crystallization. The proportion of juvenile to recycled, as well as

  2. Dating of the Variscan magnesian plutonism of the external crystalline massifs of the Alps: the Sept Laux granite (Belledone massif, France). Datation du plutonisme magnesien varisque des massifs cristallins externes des Alpes: l'exemple du granite des Sept Laux (massif de Belledonne, France)

    Energy Technology Data Exchange (ETDEWEB)

    Debon, F.; Bartefy, J.C. (BRGM, 38 - Grenoble (France)); Cocherie, A. (Bureau de Recherches Geologiques et Minieres (BRGM), 45 - Orleans (France)); Menot, R.P. (Universite de Saint-Etienne, 42 (France)); Vivier, G. (Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France))

    1994-06-01

    The emplacement of the Sept Laux granite has been dated at 332 [+-] 13 Ma by the single-zircon lead-evaporation technique. This age is placed in the framework of the tectono-metamorphic evolution of the Belledonne massif. Taken with earlier age determinations, it highlights the existence of two major Carboniferous plutonic suites in the external crystalline massifs of the Alps, one early ([approx]330 Ma) and magnesian, the other later ([approx]300 Ma) and more ferriferous. (authors). 29 refs., 2 figs., 2 tabs.

  3. An early Palaeozoic supra-subduction lithosphere in the Variscides: new evidence from the Maures massif

    Science.gov (United States)

    Bellot, Jean-Philippe; Laverne, Christine; Bronner, Georges

    2010-04-01

    Petrographic and geochemical studies of peridotites and melagabbros from the Maures massif (SE France) provide new constraints on the Early Palaeozoic evolution of the continental lithosphere in Western Europe. Peridotites occur as lenses along a unit rooted in the main Variscan suture zone. They are dominantly spinel peridotites and minor garnet-spinel peridotites. Spinel peridotites represent both residual mantle and ultramafic cumulates. Mantle-related dunites and harzburgites display high temperature textures, with olivine (Mg#0.90), orthopyroxene (Mg#0.90) and spinel (TiO2 Morena to the Bohemian massif.

  4. Crust evolution in Southeast China:evidence from Nd model ages of granitoids

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Nd isotopic compositions of 58 granitoids in South China have been reported in this paper.These data together with other published data reveal that granites with Nd model ages (tDM) greater than 1.8 Ga are distributed mainly in three areas:southwestern Zhejiang-northwestern Fujian,two sides of the Wuyi Mountain and Wanyangshan-Zhuguangshan.These granites are believed to be derived from partial melting of old crust in these areas.The Mesozoic granites with tDM<1.6 Ga are distributed in three zones:the Gangang structural zone,Nanling latitudinal structural zone and Fujian-Zhejiang coastal zone.These zones may have been an extensional tectonic setting and mantle-derived components or magmas may have been involved to different extents in the granite formation.Based on Nd model ages of granites and published chronological data of mafic and ultramafic rocks,it is believed that the crust in South China experienced episodic accretions,among which the early-middle Proterozoic is the most important period of crustal accretion.

  5. Crust evolution in Southeast China: evidence from Nd model ages of granitoids

    Institute of Scientific and Technical Information of China (English)

    沈渭洲; 凌洪飞; 李武显; 王德滋

    2000-01-01

    Nd isotopic compositions of 58 granitoids in South China have been reported in this paper; These data together with other published data reveal that granites with Nd model ages (tDM) greater than 1.8 Ga are distributed mainly in three areas: southwestern Zhejiang-northwestern Fujian, two sides of the Wuyi Mountain and Wanyangshan-Zhuguangshan. These granites are believed to be derived from partial melting of old crust in these areas. The Mesozoic granites with (DM < 1.6 Ga are distributed in three zones: the Gangang structural zone, Nanling latitudinal structural zone and Fujian-Zhejiang coastal zone. These zones may have been an extensional tectonic setting and mantle-derived components or magmas may have been involved to different extents in the granite formation. Based on Nd model ages of granites and published chronological data of mafic and ultramafic rocks, it is believed that the crust in South China experienced episodic accretions, among which the early-middle Proterozoic is the most important p

  6. A radiological survey of the Eğrigöz granitoid, Western Anatolia/Turkey.

    Science.gov (United States)

    Canbaz Öztürk, B; Yaprak, G; Çam, N F; Candan, O

    2015-06-01

    A radiological survey of the granitoid areas throughout Western Anatolia was conducted during 2007-14. As a part of this radiological survey, this article presents results obtained from Eğrigöz pluton, which lies in the northeastern region of Western Anatolia. In the investigated area, the activity measurements of the natural gamma-emitting radionuclides ((226)Ra, (232)Th and (40)K) in the granitic rock samples and soils have been carried out by means of the NaI(Tl) gamma-ray spectrometry system. The activity concentrations of the relevant natural radionuclides in the granite samples appeared in the ranges as follows: (226)Ra, 28-95 Bq kg(-1); (232)Th, 50-122 Bq kg(-1) and (40)K, 782-1365 Bq kg(-1), while the typical ranges of the (226)Ra, (232)Th and (40)K activities in the soil samples were found to be 7-184, 11-174 and 149-1622 Bq kg(-1), respectively. Based on the available data, the radiation hazard parameters associated with the surveyed rocks/soils are calculated. The corresponding absorbed dose rates in air from all those radionuclides were always much lower than 200 nGy h(-1) and did not exceed the typical range of worldwide average values noted in the UNSCEAR (2000) report. Furthermore, the data are also used for the mapping of the surface soil activity of natural radionuclides and the corresponding gamma dose rates of the surveyed area.

  7. SHRIMP U-Pb in zircon geochronology of granitoids from Myanmar: temporal constraints on the tectonic evolution of Southeast Asia

    Science.gov (United States)

    Barley, M. E.; Zaw, Khin

    2009-04-01

    The Mesozoic to Tertiary tectonic evolution of Southeast Asia is the result of the convergence and collision of fragments of Gondwanaland with Eurasia culminating in the collision of India. A rapidly growing geochronological database is placing tight constraints on the timing and duration of magmatic episodes, metallogenic and tectonic events in the Himalayas, Tibet and eastern Indochina. However, there is little comparable geochronology for Myanmar. This SHRIMP U-Pb in zircon geochronology focuses on granitoids from the Mogok Metamorphic Belt (MMB, a belt of high grade metamorphic rocks at the edge of the Shan-Thai Terrane), the Myeik Archipelago (Shan-Thai Terrane) and the west Myanmar Terrane. Strongly deformed granitic orthogneisses in the MMB near Mandalay contain Jurassic (~170 Ma) zircons that have partly recrystallised during ~43 Ma high-grade metamorphism. A hornblende syenite from Mandalay also contains Jurassic zircons with evidence of Eocene metamorphism rimmed by thin zones of 30.9 ±0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma). I-type granitoids in the MMB, Myeik Archipelago and west Myanmar confirm that prior to the collision of India, an up to 200km wide magmatic belt extended along the Eurasian margin. The primitive I-type Khanza Chaung granodiorite in the Wuntho batholith in the west Myanmar terrane hosts porphyry-style mineralisation and has a magmatic age of 94  1 Ma. Triassic (~240 Ma), Jurassic (~170 Ma) and Early Cretaceous xenocryst zircons in this granitoid correspond with peaks of granitoid magmatism in the Shan-Thai terrane and establish that west Myanmar was part of the margin of Eurasia during the Mesozoic. A suite of highly fractionated metaluminous to peraluminous I-type granitoids with associated Sn-W-Ta mineralisation emplaced in the Myeik Archipelago of

  8. Estimation of Temperature, Pressure and Oxygen Fugacity of the Cal-Alkaline Basin-Type Granitoids in the Winneba Area, Ghana

    Directory of Open Access Journals (Sweden)

    Nyarko Saah Esther

    2012-01-01

    Full Text Available In Ghana, the granitoids rocks are in two different groups, thus the basin type granitoid and the belt type granitoids. These granitoids have been studied petrographycally mineralogically and geochemically, especially the belt-type granitoids since it is the major host of gold occurrences in Ghana, however there are little studies on the petrogenesis and emplacement conditions of this important rock. In this paper we present the lacking knowledge on the emplacement conditions (temperature, pressure and the oxygen fugacity of the basin-type granitoids in the winneba area of Ghana.The calc-alkaline basin-type granitoids in the Winneba area is composed of quartz+ plagioclase +potash feldspar+ alkali feldspar+ Biotite+ Hornblende +amphibole+ titanite. The plagioclase composition ranges from Ab58 An1.7 Or0.45 to Ab98 An41 Or41 and mainly in the field of albite and oligoclase. The amphiboles however have a compositional range of Mg/(Mg +Fe ranging from 0.52 to 0.62 and a Si content of 7.1 to 7.4 atom per formula unit (afu. Their end-member compositions in the classification diagram are controlled by Magnesio-Hornblend, tschermakitic-Hornblend, and tschemakite substitution types. Scanning Electron Microscope (SEM analyses of coexisting hornblende and plagioclase (hornblende-plagioclase thermometry, Al content in hornblende (aluminum-in-hornblende barometry and the assemblage titanite-magnetite-quartz were used to constrain the P, T and fO2 during the crystallization of the parent magmas. The estimated temperature indicated an average temperature of crystallization of 677ºC reflecting late crystallization from highly oxidized magma (log fO2 -20 bars.The rocks were emplaced at an average pressure of 2.2 kbars corresponding to approximately 8 km depth of below the crust.

  9. Magmatic garnet in the Cordilleran-type Galiléia granitoids of the Araçuaí belt (Brazil): Evidence for crystallization in the lower crust

    Science.gov (United States)

    Narduzzi, F.; Farina, F.; Stevens, G.; Lana, C.; Nalini, H. A.

    2017-06-01

    Magmatic garnet, together with epidote, is a rare mineral association in cordilleran-I-type granitoids and of special petrogenetic significance. The metaluminous to slightly peraluminous (ASI = 0.97-1.07) Galiléia batholith (Brazil) is a large (ca. 30,000 km2), Neoproterozoic (ca. 632-570 Ma) weakly foliated calc-alkaline granitoid body, characterized by the widespread occurrence of garnet (grossular 25-43 mol%) and epidote (pistacite 9.3-22.7 mol%). Field, petrographic and mineral chemical evidence indicates that garnet, epidote, biotite as well as white mica crystals (low-Si phengite), are magmatic. There is no difference in bulk rock major and trace element composition between the Galiléia granitoids and other garnet-free cordilleran-type granitoids worldwide. This evidence strongly suggests that the origin of the uncommon garnet + epidote parageneses is related to the conditions of magma crystallization, such as pressure, temperature and water content. Comparison between the mineral assemblages and mineral compositions from this study and those recorded in crystallization experiments on metaluminous calc-alkaline magmas, as well as within garnet-bearing metaluminous volcanic rocks and granitoids, indicates that the supersolidus coexistence of grossular-rich garnet, epidote and white mica is consistent with magma crystallization at pressures greater than 0.8 GPa (above 25 km depth) and at temperatures below 700 °C, i.e. near the water saturated solidus. Furthermore, resorption textures around garnet (plagioclase ± quartz coronas) and epidote suggest that these minerals have been partially consumed prior to complete crystallization. These findings demonstrate that at 630 Ma the crust underneath the Araçuaí Orogen was already at least 25-30 km thick and relatively cool. However, this contrasts with the marked high heat flow registered from the neighbour Carlos Chagas Batholith located 50 km to the east. In fact such granitoids record granulite

  10. Massification and Diversification as Complementary Strategies for Economic Growth in Developed and Developing Countries

    Science.gov (United States)

    Tyndorf, Darryl; Glass, Chris R.

    2016-01-01

    Numerous microeconomic studies demonstrate the significant individual returns to tertiary education; however, little empirical evidence exists regarding the effects of higher education massification and diversification agendas on long-term macroeconomic growth. The researchers used the Uzawa-Lucas endogenous growth model to tertiary education…

  11. The Massification of Higher Education in the UK: Aspects of Service Quality

    Science.gov (United States)

    Giannakis, Mihalis; Bullivant, Nicola

    2016-01-01

    This article explores several aspects of service quality for the provision of higher education. Alongside the trend of the massification of higher education over the past two decades, higher education institutions are required to review quality across a range of outputs, besides teaching and learning. The study was undertaken within the…

  12. The Massification of Higher Education in the UK: Aspects of Service Quality

    Science.gov (United States)

    Giannakis, Mihalis; Bullivant, Nicola

    2016-01-01

    This article explores several aspects of service quality for the provision of higher education. Alongside the trend of the massification of higher education over the past two decades, higher education institutions are required to review quality across a range of outputs, besides teaching and learning. The study was undertaken within the…

  13. The Pedregal granite (Portugal: petrographic and geochemical characterization of a peculiar granitoid

    Directory of Open Access Journals (Sweden)

    Ferreira, J. A.

    2014-12-01

    Full Text Available The Pedregal granite outcrops in the Central Iberian Zone, northern Portugal, in the eastern border of a synorogenic variscan granite-migmatite complex sub-concordant with the regional metamorphic structures. It is a granitoid (ca. 3 km2 with an elongated NW-SE shape intruded in staurolite-micaschist and banded gneiss-migmatite rocks, with local igneous breccias in the contact. The country rocks belong to a metapelitic and metasammitic sequence of Edicarian-Cambrian age, known as the “Complexo Xisto-Grauváquico” (CXG which shows a main regional foliation with a NW-SE to NNW-SSE direction. The Pedregal granite is peraluminous (its A/CNK parameter ranges from 1.18 to 1.62, with a magnesian and alkali to alkali-calcic signature. The peculiar features of the granite are high contents of Zr (389 to 435 ppm and a LREE flat pattern, which are uncommon characteristics for granitic rocks, as well as the corroded shape of the biotite, and the large amount of secondary muscovite. These peculiar features distinguish it from the adjacent synorogenic granites. The field, petrographical and chemical features of the Pedregal granite are in accordance with a second phase of partial melting of a residuum, depleted by melt segregation during a first melting episode with the involvement of peritectic garnet and abundant residual biotite with LREE- and Zr-bearing accessory minerals. Besides, the intrusive character of the granite, and the presence of metasedimentary xenoliths point out to a secondary diatexite.El granito de Pedregal aflora en la Zona Centro-Ibérica, en el norte de Portugal, en el borde oriental de un complejo granito-migmatítico sinorogénico varisco, subconcordante con las estructuras metamórficas regionales. Es un granitoide (ca. 3 km2 de forma elongada NW-SE, que intruye en micaesquistos estaurolíticos y en rocas gneissico- migmatíticas bandeadas, con brechas ígneas locales en el contacto. Las rocas encajantes pertenecen a una

  14. Effect of sample size on the fluid flow through a single fractured granitoid

    Institute of Scientific and Technical Information of China (English)

    Kunal Kumar Singh; Devendra Narain Singh; Ranjith Pathegama Gamage

    2016-01-01

    Most of deep geological engineered structures, such as rock caverns, nuclear waste disposal repositories, metro rail tunnels, multi-layer underground parking, are constructed within hard crystalline rocks because of their high quality and low matrix permeability. In such rocks, fluid flows mainly through fractures. Quantification of fractures along with the behavior of the fluid flow through them, at different scales, becomes quite important. Earlier studies have revealed the influence of sample size on the confining stressepermeability relationship and it has been demonstrated that permeability of the fractured rock mass decreases with an increase in sample size. However, most of the researchers have employed numerical simulations to model fluid flow through the fracture/fracture network, or laboratory investigations on intact rock samples with diameter ranging between 38 mm and 45 cm and the diameter-to-length ratio of 1:2 using different experimental methods. Also, the confining stress, s3, has been considered to be less than 30 MPa and the effect of fracture roughness has been ignored. In the present study, an extension of the previous studies on “laboratory simulation of flow through single fractured granite” was conducted, in which consistent fluid flow experiments were performed on cy-lindrical samples of granitoids of two different sizes (38 mm and 54 mm in diameters), containing a“rough walled single fracture”. These experiments were performed under varied confining pressure (s3 ¼ 5e40 MPa), fluid pressure (fp ? 25 MPa), and fracture roughness. The results indicate that a nonlinear relationship exists between the discharge, Q, and the effective confining pressure, sef ., and Q decreases with an increase in sef .. Also, the effects of sample size and fracture roughness do not persist when sef . ? 20 MPa. It is expected that such a study will be quite useful in correlating and extrapolating the laboratory scale investigations to in-situ scale and

  15. MASSIF-1: a beamline dedicated to the fully automatic characterization and data collection from crystals of biological macromolecules

    Energy Technology Data Exchange (ETDEWEB)

    Bowler, Matthew W., E-mail: mbowler@embl.fr [European Molecular Biology Laboratory, Grenoble Outstation, 71 avenue des Martyrs, F-38042 Grenoble (France); Université Grenoble Alpes-EMBL-CNRS, 71 avenue des Martyrs, F-38042 Grenoble (France); Nurizzo, Didier, E-mail: mbowler@embl.fr; Barrett, Ray; Beteva, Antonia; Bodin, Marjolaine [European Synchrotron Radiation Facility, 71 avenue des Martyrs, F-38043 Grenoble (France)

    2015-10-03

    MASSIF-1 (ID30A-1) is a new beamline dedicated to the completely automatic characterization and data collection from crystals of biological macromolecules. MASSIF-1 (ID30A-1) is an ESRF undulator beamline operating at a fixed wavelength of 0.969 Å (12.8 keV) that is dedicated to the completely automatic characterization of and data collection from crystals of biological macromolecules. The first of the ESRF Upgrade MASSIF beamlines to be commissioned, it has been open since September 2014, providing a unique automated data collection service to academic and industrial users. Here, the beamline characteristics and details of the new service are outlined.

  16. Cadomian S-type granites as basement rocks of the Variscan belt (Massif Central, France): Implications for the crustal evolution of the north Gondwana margin

    Science.gov (United States)

    Couzinié, Simon; Laurent, Oscar; Poujol, Marc; Mintrone, Michaël; Chelle-Michou, Cyril; Moyen, Jean-François; Bouilhol, Pierre; Vezinet, Adrien; Marko, Linda

    2017-08-01

    From the Neoproterozoic to the early Paleozoic, the northern Gondwana margin was sequentially shaped by the Cadomian accretionary and the Variscan collisional orogens which offers the opportunity to investigate the relative extent of crust production/reworking in both geodynamic settings. In the eastern part of the Variscan French Massif Central (FMC), the Velay Orthogneiss Formation (VOF) represents a consistent lithological unit of the pre-Variscan basement and comprises augen gneisses and leucogneisses. Such rocks constitute a unique record of the pre-Variscan magmatic history and bear critical information on the crustal evolution of the northern Gondwana margin. Here, we present whole-rock major and trace element compositions indicating that: (i) the VOF shows a remarkable geochemical homogeneity; (ii) the protolith of the augen gneisses corresponds to strongly peraluminous, ;S-type; porphyritic granites originating from partial melting of an Ediacaran sedimentary sequence; (iii) the leucogneisses are former leucogranites generated by fractionation of the magma at the origin of the porphyritic granites; and (iv) the whole suite emplaced at shallow crustal levels (< 7 km). U-Pb LA-(MC-)ICP-MS analyses on zircon yielded similar emplacement ages of c. 542 Ma and a narrow range of εHf(t) clustering around 0 for the protoliths of both augen and leucogneisses. This homogeneous Hf isotope signature, notably uncommon for S-type granites, would originate from a sequential process of: (i) inherited zircon dissolution during melting and ascent in the crust due to Zr-undersaturated conditions, (ii) isotopic homogenization of the melt by advection and elemental/isotopic diffusion, followed by (iii) early saturation upon emplacement owing to rapid cooling at shallow crustal levels. We propose that partial melting of Ediacaran sediments occurred during inversion of a Cadomian back-arc basin and was promoted by the high thermal gradient typical of thinned crust domains

  17. Occurrence of springs in massifs of crystalline rocks, northern Portugal

    Science.gov (United States)

    Pacheco, Fernando António Leal; Alencoão, Ana Maria Pires

    2002-02-01

    An inventory of artesian springs emerging from fractures (fracture springs) was conducted in the Pinhão River Basin and Morais Massif, northern Portugal, comprising an area of approximately 650 km2. Over 1,500 springs were identified and associated with geological domains and fracture sets. Using cross-tabulation analysis, spring distributions by fracture sets were compared among geological environments, and the deviations related to differences in rock structure and, presumably, to differences in deformational histories. The relation between spring frequencies and rock structures was further investigated by spectral determination, the model introduced in this study. Input data are the spring frequencies and fracture lengths in each geological domain, in addition to the angles between fracture strikes and present-day stress-field orientation (θ). The model's output includes the so-called intrinsic densities, a parameter indexing spring occurrence to factors such as fracture type and associated deformational regime and age. The highest densities (12.2 springs/km of lineament) were associated with young shear fractures produced by brittle deformation, and the lowest (0.1) with old tensional and ductile fractures. Spectral determination also relates each orientation class to a dominant structural parameter: where spring occurrence is controlled by θ, the class is parallel to the present-day stress-field orientation; where the control is attributed to the length of fractures, the spring occurrence follows the strike of large-scale normal faults crossing the region. Résumé. Un inventaire des sources artésiennes émergeant de fractures (sources de fractures) a été réalisé dans le bassin de la rivière Pinhão et dans le massif de Morais, dans le nord du Portugal, dans une région couvrant environ 650 km2. Plus de 1,500 sources ont été identifiées et associées à des domaines géologiques et à des ensembles de fractures. Grâce à une analyse de tableaux

  18. Petrochemical and Tectonogenesis of Granitoids in the Wuyo-Gubrunde Horst, Northeastern Nigeria: Implication for Uranium Enrichment

    Energy Technology Data Exchange (ETDEWEB)

    Bolarinwa, Anthony Temidayo, E-mail: atbola@yahoo.com; Bute, Saleh Ibrahim [University of Ibadan, Department of Geology (Nigeria)

    2016-06-15

    The Wuyo-Gubrunde Horst in the northeastern Nigeria consists of migmatite gneiss, unaltered, altered, and sheared porphyritic granites, pegmatites, aplites, basalts, and sandstone. Uranium has been reported in rhyolite, sheared rocks, and sandstone within the area. The petrogenesis of the granitoids and associated rocks in the area was evaluated in the light of new geochemical data, which showed that the U content of altered porphyritic granite is highest and hydrothermal-related. The granitoids are metaluminous, sub-alkaline, and S-type granite, and have evolved by partial melting of crustal material emplaced at moderate depth of 20–30 km in a syn-to late-collisional within-plate tectonic setting. The negative Eu/Eu* anomaly and high (La/Yb){sub N} ratio of the granitoids indicate magma fractionation. The low SiO{sub 2} (<53%) and high Fe{sub 2}O{sub 3} (10%) of the altered porphyritic granite compared to other similar rock units suggest pervasive alteration. The associated basalts are tholeiitic, emplaced within continental plate tectonic setting, and enriched in Ni, V, Nb, Sr, and light rare earth elements, and they have SiO{sub 2}, Fe{sub 2}O{sub 3}, V, Th, and Co contents that are similar to those of the altered porphyritic granites. The U occurrence in the Wuyo-Gubrunde Horst is believed to be sourced from the adjoining Bima sandstone in the Benue Trough, which locally contains carbonaceous zones with anomalously high concentrations of U. The Fe{sup 2+}/Fe{sup 3+} redox fronts formed by alteration of the iron-rich basalts provided the requisite geochemical barrier for U-bearing hydrothermal fluid, causing enrichment of U leached and mobilized from the sandstone through fractures in the rocks.

  19. Potential of thermal emissivity for mapping of greenstone rocks and associated granitoids of Hutti Maski Schist belt, Karnataka

    Science.gov (United States)

    Guha, A.; Vinod Kumar, K.

    2014-11-01

    In the present study, different temperature-emissivity separation algorithms were used to derive emissivity images based on processing of ASTER( Advanced spaceborne thermal emission and reflection radiometer) thermal bands. These emissivity images have been compared with each other in terms of geological information for mapping of major rock types in Hutti Maski schist Belt and its associated granitoids. Thermal emissivity images are analyzed conjugately with thermal radiance image, radiant temperature image and albedo image of ASTER bands to understand the potential of thermal emissivity in delineating different rock types of Archaean Greenstone belt. The emissivity images derived using different emissivity extraction algorithms are characterised with poor data dimensionality and signal to noise ratio. Therefore, Inverse MNF false-colour composites(FCC) are derived using bands having better signal to noise(SNR)ratio to enhance the contrast in emissivity. It has been observed that inverse-MNF of emissivity image; which is derived using emissivity-normalisation method is suitable for delineating silica variations in granite and granodioritic gneiss in comparison to other inverse- MNF-emissivity composites derived using other emissivity extraction algorithms(reference channel and alpha residual method). Based on the analysis of ASTER derived emissivity spectra of each rocks, band ratios are derived(band 14/12,band 10/12) and these ratios are used to delineate the rock types based on index based FCC image. This FCC image can be used to delineate granitoids with different silica content. The geological information derived based on processing of ASTER thermal images are further compared with the image analysis products derived using ASTER visible-near-infrared(VNIR) and shortwave infrared(SWIR) bands. It has been observed that delineation of different mafic rocks or greenstone rocks(i.e. separation between chlorite schist and metabasalt) are better in SWIR composites

  20. THE PETROLOGY CHARACTERISTIC OF GRANITOID ROCK BASED ON GEOCHEMICAL ANALYSIS OF BAJAU CAPE COAST AND ITS SURROUNDING, WEST KALIMANTAN

    Directory of Open Access Journals (Sweden)

    Noor C.D. Aryanto

    2017-07-01

    Full Text Available The aim of this study is to identify of petrology characteristic based on geochemical analysis in order to know the granitoid rock type. Administratively, the study area is in the City and District of Singkawang, West Kalimantan Province, at coordinate 108°48'30” - 109°1'30” E and 0°40'30” - 0°54'30” N and, situated ± 145 km to the north of Pontianak City. The outcrop of granitoid along Bajau Cape coast and its surrounding, had been analyzed petrographically and geochemically using AAS method. Based on analysis of five samples show that the ratio mole of Al2O3/(CaO+Na2O +K2O > 1 ranged between 1.12 and 1.7, while the rest of three samples are moderately aluminous, with a ratio value between 0.5 and 1.0. The ratio between K2O and (K2O+Na2O+CaO ranges 0.07 to 0.55 (moderate that forms alkali feldspar normative ranges from 3.8 to 15.89 wt%. This ratio shows that granite alkali feldspar is classified to be calc-alkaline series. Petrographically, this rock is porfiritic texture, hollocrystalline, granular hypodiomorphic and biotite present as phenocryst, yellowish brown, euhedral, thin and platy. The content of oxides element (Na2O and MgO tend to decrease, whereas of other oxides elements, namely Al2O3, TiO2, K2O, FeO and CaO increased, parallel with the raising of SiO2. Therefore, the Singkawang Granitoid can be grouped as alkali feldspar granite, syeno-granite and quartz monzonite.

  1. Petrogenesis of Triassic granitoids in the East Kunlun Orogenic Belt, northern Tibetan Plateau and their tectonic implications

    Science.gov (United States)

    Shao, Fengli; Niu, Yaoling; Liu, Yi; Chen, Shuo; Kong, Juanjuan; Duan, Meng

    2017-06-01

    The East Kunlun Orogenic Belt (EKOB), an important part of the Greater Tibetan Plateau, is an ideal region for understanding the tectonic evolution of the Anyemaqen Ocean. Here, we present zircon U-Pb ages, bulk-rock major and trace element analyses and Sr-Nd-Hf isotope compositions on representative samples of the syn-collisional Dulan batholith at the eastern end of the EKOB. The zircon U-Pb age data indicate that the bulk of the Dulan batholith was emplaced at 240-235 Ma. The granitoids have high- to medium-K and metaluminous characteristics. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in some high field strength elements (HFSEs, e.g., Nb and Ta), while having a flat heavy REE (HREEs) pattern. The mafic magmatic enclaves (MMEs) share the same age, mineralogy and indistinguishable Sr-Nd-Hf isotopes with their granitoid hosts except for the higher HREE abundances. We show that the MMEs represent cumulate formed at earlier stages of the same magmatic system. The trace element data (e.g., Nb/Th, Ta/U) and inherited mantle isotopic characteristics of the Dulan batholith are also consistent with an origin via partial melting of the last fragments of underthrusting ocean crust. Simple mass balance calculations using the Sr-Nd-Hf isotopic data show that 85% Paleo-Tethys MORB and 15% mature crustal material (the Proterozoic gneiss of the study area) contribute to the source of the granitoids. The Dulan batholith shows compositional similarities to the bulk continental curst with inherited mantle isotopic signatures. The syn-collisional felsic magmatism must have contributed to the net continental crust growth in the EKOB. We infer that the Kunlun and Qinling orogens may actually be one single orogen offset later by the Wenquan fault system.

  2. Rock strength measurements on Archaean basement granitoids recovered from scientific drilling in the active Koyna seismogenic zone, western India

    Science.gov (United States)

    Goswami, Deepjyoti; Akkiraju, Vyasulu V.; Misra, Surajit; Roy, Sukanta; Singh, Santosh K.; Sinha, Amalendu; Gupta, Harsh; Bansal, B. K.; Nayak, Shailesh

    2017-08-01

    Reservoir triggered earthquakes have been occurring in the Koyna area, western India for the past five decades. Triaxial tests carried out on 181 core samples of Archaean granitoids underlying the Deccan Traps provide valuable constraints on rock strength properties in the Koyna seismogenic zone for the first time. The data include measurements on granite gneiss, granite, migmatitic gneiss and mylonitised granite gneiss obtained from boreholes KBH-3, KBH-4A, KBH-5 and KBH-7 located in the western and eastern margins of the seismic zone. Salient results are as follows. (i) Increase of rock strength with increasing confining pressure allow determination of the linearized failure envelopes from which the cohesive strength and angle of internal friction are calculated. (ii) Variable differential stresses at different depths are the manifestations of deformation partitioning in close association of fault zone(s) or localized fracture zones. (iii) Fractures controlled by naturally developed weak planes such as cleavage and fabric directly affect the rock strength properties, but the majority of failure planes developed during triaxial tests is not consistent with the orientations of pre-existing weak planes. The failure planes may, therefore, represent other planes of weakness induced by ongoing seismic activity. (iv) Stress-strain curves confirm that axial deformation is controlled by the varying intensity of pre-existing shear in the granitoids, viz., mylonite, granite gneiss and migmatitic gneiss. (v) Frequent occurrences of low magnitude earthquakes may be attributed to low and variable rock strength of the granitoids, which, in turn, is modified by successive seismic events.

  3. Cretaceous and Paleogene granitoid suites of the Sikhote-Alin area (Far East Russia): Geochemistry and tectonic implications

    Science.gov (United States)

    Grebennikov, Andrei V.; Khanchuk, Alexander I.; Gonevchuk, Valeriy G.; Kovalenko, Sergey V.

    2016-09-01

    The Mesozoic and Cenozoic geological history of NE Asia comprises alternating episodes of subduction or transform strike-slip movement of the oceanic plate along the continental margin of Eurasia. This sequence resulted in the regular generation of granitoid suites that are characterized by different ages, compositions, and tectonic settings. The Hauterivian-Aptian orogenic stage of the Sikhote-Alin, associated with the strike-slip displacement of the early Paleozoic continental blocks, the successive deformation of the Jurassic and Early Cretaceous terranes, and the injection of the earliest S-type granitoids. During late Albian, the area underwent syn-strike-slip compression caused by collision with the Aptian island arc and resulted in the injection of voluminous magmas of calc-alkaline magnesian (S- and I-type) and alkali-calcic ferroan (A-type) granitoids into syn-faulting compressional and extensional basins, respectively. Northwestward to westward movement of the Izanagi Plate resulted in the initiation of frontal subduction of the Paleo-Pacific Plate during the Cenomanian-Maastrichtian. In turn, this resulted in the generation of plateau-forming ignimbrites and their intrusive analogs formed from metaluminous I-type felsic magmas. Paleocene-Eocene magmatism in the Sikhote-Alin area commenced after the termination of subduction in a rifting regime related to strike-slip movement of the oceanic plate relative to the continent. The break-off of the subducted plate and the injection of oceanic asthenospheric material into the subcontinental lithosphere resulted in the eruption of lamproites and fayalite rhyolites, and coeval intrusions of gabbro and alkali feldspar granites (B-type). The A-type granitic-rocks and coeval gabbro-monzonites are considered to be reliable indicators of the transform continental margin geodynamic settings.

  4. New insights from U Pb zircon dating of Early Ordovician magmatism on the northern Gondwana margin: The Urra Formation (SW Iberian Massif, Portugal)

    Science.gov (United States)

    Solá, A. R.; Pereira, M. F.; Williams, I. S.; Ribeiro, M. L.; Neiva, A. M. R.; Montero, P.; Bea, F.; Zinger, T.

    2008-12-01

    .85). The geochemical data are compatible with an orogenic geodynamic environment. However, the "orogenic" signature can be considered to represent, in part, an inherited feature caused by melting of the Cadomian basement which also has calc-alkaline affinities. The Early Ordovician crustal growth and associated magmatism, represented by the Urra felsic volcaniclastic rocks and associated calc-alkaline granitoids, diorites and gabbros, can be interpreted in terms of the underplating and temporal storage of mantle-derived magmas as the potential source for the "orogenic melts" that were intruded during Early Paleozoic extension. This record of Early Ordovician magmatism has striking similarities with other correlatives from the Iberian, Bohemian and Armorican massifs that are discussed in this paper. This comparison reinforces the probable existence of a large-scale crustal melting process linked to a significant episode of extension on the northern Gondwana margin that probably resulted in the birth of the Rheic Ocean.

  5. Experimental constraints on the origin of compositional variations in the adakite-TTG-sanukitoid-HMA family of granitoids

    Science.gov (United States)

    Rapp, R. P.

    2003-04-01

    The current debate over whether or not Archean granitoids, including the TTG (tonalite-trondhjemite-granodiorite) and sanukitoid (high-Mg diorite) suites, are compositional analogues of modern day arc magmas related to "hot" subduction (adakites and high-Mg andesites, HMA), is for the most part an issue of semantics, the consequence of a definition for "adakite" that is too loose. That is not to say that the debate doesn't have important implications for the geodynamic setting in which growth of the Archean continental crust took place. Smithies (2000) and Martin (2002) both show that early-mid Archean (3.0--3.8 Ga) granitoids are generally restricted to low-Mg# TTG (with Mg# pressure interval of 1--4 GPa, have shown that low-moderate degrees of melting (˜10--40%) produces granitoid liquids with major- and trace-element characteristics comparable to both Archean TTG and low-Mg# adakite. These liquids are in equilibrium with garnet-bearing (garnet amphibolite or eclogite) crystalline residues; the mineral phases present in these residues (garnet, clinopyroxene, ± amphibole) impart to the melts the distinctive geochemical fingerprint that has come to be associated with both TTG and adakite. Experiments in which these "pristine" melts of garnet-bearing metabasalt are allowed to react with and assimilate mantle peridotite, simulating melt-rock reaction across the slab-wedge interface in modern subduction zones, or at the base of evolving Archean cratons, whatever the tectonic setting, produce hybridized granitoids resembling sanukitoids and HMAs. Assimilation of peridotite causes the Mg# of hybridizedTTG melts to increase, abundances of Cr and Ni to increase, SiO_2 to decrease, and the molar ratio [Al/(Ca+Na+K)] to decrease, but important trace element ratios (e.g., La/Yb, Sr/Y, Th/U) remain relatively unchanged, and primitive-mantle normalized abundance patterns of trace elements parallel those of the initial liquids. In terms of major- and trace-elements, therefore

  6. Architecture of the Sulu crustal suture between the North China Craton and Yangtze Craton: Constraints from Mesozoic granitoids

    Science.gov (United States)

    Zhao, Rui; Wang, Qingfei; Liu, Xuefei; Wang, Wei; Pan, Ruiguang

    2016-12-01

    The Yangtze Craton (YC) and the North China Craton (NCC) collided in the Triassic, producing the prominent NNE-trending Sulu high-ultrahigh pressure metamorphic belt and associated crustal thickening. Late Jurassic-Early Cretaceous granitic plutons in the Sulu orogenic belt and the Jiaobei terrane to the west were used to investigate the crustal architecture across the suture. Our new data show that the granitoids from these two regions have similar chemical and isotope compositions. They are all characterized by very high Sr and low Y-Yb contents, high Sr/Y and (La/Yb)N ratios, similar ƐNd(t) values from - 18.2 to - 21.4, and similar initial 87Sr/86Sr ratios from 0.7076 to 0.7119. The calculated Nd two-stage model ages (TDM2) based on whole rock data vary from 2415 to 2662 Ma. Co-magmatic zircon crystals from the granitoids have variably negative ƐHf(t) values from - 26.8 to - 12.8, with the calculated Hf TDM2 from 2008 to 2892 Ma. The inherited zircon crystals from these rocks are dominated by Neoproterozoic (800-600 Ma) and Triassic-Early Jurassic ( 220 Ma and 180 Ma) ages. The ƐHf(t) values of the inherited zircon crystals with U-Pb ages between 180 Ma and 800 Ma from Sulu and Jiaobei range from - 21.6 to 4.2 and from - 23 to - 1.9, respectively. They all plot within the field of crustal evolution between 1385 and 2583 Ma. The similar whole rock geochemical signatures and similar inherited zircon data indicate a similar source for the granitoids in these two regions. We propose that the source regions across the suture all belong to the YC. The occurrence of the YC crust beneath the NCC at this location is thought to have resulted from the westward subduction of the YC beneath the NCC and subsequent continental collision in the Triassic. In this model, the abundant 800 to 230 Ma inherited zircon crystals in the granitoids are interpreted to have been derived from the source region whereas the rare older inherited zircon crystals are thought to have been

  7. 佳木斯地块花岗质片麻岩的独居石年龄及其地质意义%Monazite Ages and Its Geological Significance of Granitoid Gneiss in the Jiamusi Massif

    Institute of Scientific and Technical Information of China (English)

    温泉波; 刘永江; 李伟民; 韩国卿; 丁凌

    2008-01-01

    依据电子探针独居石Th-U-Pb化学法(CHIME)对分布于佳木斯地块北部花岗质片麻岩进行定年,其中独居石415 Ma年龄值报道了佳木斯地块北部存在志留纪晚期的岩浆热事件,(494.35±23.6)Ma、(506.96±52.20)Ma、(481.04±23.19)Ma的独居石年龄值表明,佳木斯地块北部存在500 Ma(晚泛非期)的高级变质事件,结合南部的锆石SHRIMP年龄数据,认为整个佳木斯地块都存在500 Ma(晚泛非期)的高级变质事件.该时期佳木斯地块和松嫩地块可能已经拼贴到一起,共同遭受了500 Ma(晚泛非期)变质事件的影响.

  8. The Pan-African calc-alkaline granitoids and the associated mafic microgranular enclaves (MME around Wadi Abu Zawal area, North Eastern Desert, Egypt: geology, geochemistry and petrogenesis

    Directory of Open Access Journals (Sweden)

    Asran Mohamed Asran

    2012-01-01

    Full Text Available Introduction: The area around Wadi Abu Zawal is occupied by gneisses-migmatites, island arcs metavolcanics, Dokhan volcanics, Hammamat sediments, intrusive rocks of granitic and gabbroic composition and dyke swarms.Materials and Methods: The present work concerning on the geology, geochemistry and petrogenesis of the MME and the host granitoid rocks of that area. The analytical methods for major and trace elements of some representative samples were carried out by XRF technique at the Institute of BGR in Hannover, Germany.Results: Mineralogically, MME are composed mainly of plagioclase, hornblende, biotite and quartz with accessory of sphene, acicular apatite and opaque oxides, while chlorite and epidote are secondary ones. Whereas Abu Zawal granitoid rocks are subsolvus and consist of variable contents of plagioclase, K-feldspar, quartz, and biotite, with accessory sphene, zircon and opaque oxides, typical of I-type granites. The studied Abu Zawal area represents part of the northeastern Egypt which formed by regional crustal extension and magmatic-arc regimes during Pan-African orogenic event.The MME display major, trace element contents and tectonic setting comparable with the end members of (GDT and (IAG of the Eastern Desert which produced (by fractionation from a mantle-derived tholeiitic magma in an island-arc tectonic environment. Abu Zawal granitoid rocks exhibit trace element characteristics of volcanic-arc granites, and formed in an Andean-type setting.Conclusions: On the variation diagrams, major and trace element contents of the MME and granitoid rocks display conspicuous gap and two distinct trends one for the MME, (IAG and the other for the Abu Zawal granitoid rocks, which indicates that they are not genetically related and suggest the crustal source for the host granitoid rock.

  9. Melting of subducted continental crust: Geochemical evidence from Mesozoic granitoids in the Dabie-Sulu orogenic belt, east-central China

    Science.gov (United States)

    Zhao, Zi-Fu; Liu, Zhi-Bin; Chen, Qi

    2017-09-01

    Syn-collisional and postcollisional granitoids are common in collisional orogens, and they were primarily produced by partial melting of subducted continental crust. This is exemplified by Mesozoic granitoids from the Dabie-Sulu orogenic belt in east-central China. These granitoids were emplaced in small volumes in the Late Triassic (200-206 Ma) and the Late Jurassic (146-167 Ma) but massively in the Early Cretaceous (111-143 Ma). Nevertheless, all of them exhibit arc-like trace element distribution patterns and are enriched in Sr-Nd-Hf isotope compositions, indicating their origination from the ancient continental crust. They commonly contain relict zircons with Neoproterozoic and Triassic U-Pb ages, respectively, consistent with the protolith and metamorphic ages for ultrahigh-pressure (UHP) metaigneous rocks in the Dabie-Sulu orogenic belt. Some granitoids show low zircon δ18O values, and SIMS in-situ O isotope analysis reveals that the relict zircons with Neoproterozoic and Triassic U-Pb ages also commonly exhibit low δ18O values. Neoproterozoic U-Pb ages and low δ18O values are the two diagnostic features that distinguish the subducted South China Block from the obducted North China Block. Thus, the magma source of these Mesozoic granitoids has a genetic link to the subducted continental crust of the South China Block. On the other hand, these granitoids contain relict zircons with Paleoproterozoic and Archean U-Pb ages, which are present in both the South and North China Blocks. Taken together, the Mesozoic granitoids in the Dabie-Sulu orogenic belt and its hanging wall have their magma sources that are predominated by the continental crust of the South China Block with minor contributions from the continental crust of the North China Block. The Triassic continental collision between the South and North China Blocks brought the continental crust into the thickened orogen, where they underwent the three episodes of partial melting in the Late Triassic, Late

  10. Petrogenesis of Granitoids, U-Pb zircon geochronology, Sr-Nd Petrogenesis of granitoids, U-Pb zircon geochronology, Sr-Nd isotopic characteristics, and important occurrence of Tertiary mineralization within the Lut block, eastern Iran

    Directory of Open Access Journals (Sweden)

    M.H. Karimpour

    2012-04-01

    Full Text Available Tertiary intrusive granitoids within the Lut block in the Khorasan Razavi and South Khorasan provinces are mainly sub-volcanic with porphyry texture and their composition varies from granite to diorite but monzonite is dominant. With the exception of Hired, these are classified as belonging to the magnetite-series of I-type granitoids. Chemically, these rocks are meta-aluminous. Those with mineralization are K-rich and those without mineralization such as Najmabad are Na-rich. All intrusive rocks plot in the field of calc-alkaline to adakite except Najmabad that plot in the adakite field. Based on low content of Nb (30, low initial 87Sr/86Sr (17 ppm, low ratio of Zr/Nb (0.707 and low initial εNd value (-3, magmas in the Kaybar-Kuh were more contaminated in the continental crust. Based on depletion in HREE and high ratio of (La/YbN (17-23, magma in Najmabad originated in the deep region in which garnet was present. Based on REE pattern and ration of Eu/Eu* (0.8-1, intrusive rocks within Maherabad, Khoopik, Chah-Shaljami, Kuh Shah and Dehsalm are calc-alkaline and their magma formed in an oxidant condition whereas Kaybar Kuh magma with low ratio of Eu/Eu* (<0.8 was contaminated in the continental crust under reduced conditions. The age of these granitoids is between Middle Eocene and Lower Oligocene. Kaybar-Kuh (43.3 Ma is situated in the north and Chah-Shaljami (33.3 Ma in the south. The initial 87Sr/86Sr ratios decrease from north (0.7077 to south (0.7047 as the age decreases. εNd of Maherabad, Khoopik, Dehsalm, and Chah-Shaljami granitoids is between +0.5 and +2.49 and the initial 87Sr/86Sr ratio is less than 0.7055. The age of the source rock (TDM, which was calculated based on Sm-Nd isotopes indicates that these magma originated from oceanic crust with different ages. Kaybar-Kuh originated from the oldest oceanic crust (840 Ma and was contaminated more in continental crust, but Najmabad originated from a younger oceanic crust (360 Ma with

  11. Petrological and geochemical evolution of the Tolbachik volcanic massif, Kamchatka, Russia

    Science.gov (United States)

    Churikova, Tatiana G.; Gordeychik, Boris N.; Iwamori, Hikaru; Nakamura, Hitomi; Ishizuka, Osamu; Nishizawa, Tatsuji; Haraguchi, Satoru; Miyazaki, Takashi; Vaglarov, Bogdan S.

    2015-12-01

    Data on the geology, petrography, and geochemistry of Middle-Late-Pleistocene rocks from the Tolbachik volcanic massif (Kamchatka, Klyuchevskaya group of volcanoes) are presented and compared with rocks from the neighboring Mount Povorotnaya, Klyuchevskaya group basement, and Holocene-historical Tolbachik monogenetic cones. Two volcanic series of lavas, middle-K and high-K, are found in the Tolbachik massif. The results of our data analysis and computer modeling of crystallization at different P-T-H2O-fO2 conditions allow us to reconstruct the geochemical history of the massif. The Tolbachik volcanic massif started to form earlier than 86 ka based on K-Ar dating. During the formation of the pedestal and the lower parts of the stratovolcanoes, the middle-K melts, depleted relative to NMORB, fractionated in water-rich conditions (about 3% of H2O). At the Late Pleistocene-Holocene boundary, a large fissure zone was initiated and the geodynamical regime changed. Upwelling associated with intra-arc rifting generated melting from the same mantle source that produced magmas more enriched in incompatible trace elements and subduction components; these magmas are high-K, not depleted relative to N-MORB melts with island arc signatures and rift-like characteristics. The fissure opening caused degassing during magma ascent, and the high-K melts fractionated at anhydrous conditions. These high-K rocks contributed to the formation of the upper parts of stratovolcanoes. At the beginning of Holocene, the high-K rocks became prevalent and formed cinder cones and associated lava fields along the fissure zone. However, some features, including 1975-1976 Northern Breakthrough, are represented by middle-K high-Mg rocks, suggesting that both middle-K and high-K melts still exist in the Tolbachik system. Our results show that fractional crystallization at different water conditions and a variably depleted upper mantle source are responsible for all observed variations in rocks within

  12. The ophiolite massif of Kahnuj (western Makran, Southern Iran): new geological and geochronological data; Le massif ophiolitique de Kahnuj (Makran occidental, Iran meridional): nouvelles donnees geologiques et geochronologiques

    Energy Technology Data Exchange (ETDEWEB)

    Kananian, A. [University of Tarbiat Modarress, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Juteau, Th.; Bellon, H. [Universite de Bretagne Occidentale, IUEM, 29 - Brest (France); Darvishzadeh, A. [University of Teheran, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Sabzehi, M. [Geological Survey of Iran, Teheran (Iran, Islamic Republic of); Whitechurch, H. [Universite Louis Pasteur, EOST, Institut de Physique du Globe, 67 - Strasbourg (France); Ricou, L.E. [Institut de Physique du Globe, 75 - Paris (France)

    2001-05-01

    The ophiolite massif of Kahnuj (600 km{sup 2}) consists, from bottom to top, of layered gabbros, isotropic gabbros and ouralite gabbros, agmatites of dioritic to plagio-granitic composition, a sheeted dyke complex and lastly a basaltic pillow lava unit. Amphiboles from gabbros were dated ({sup 40}K-{sup 40}Ar ages) between 156 and 139 Ma and the agmatites are nearly contemporaneous. Potassic granitic veins dated at 93-88 Ma are related to the development of the Ganj arc complex. (authors)

  13. Scorpions from the Mitaraka Massif in French Guiana. II. Description of a new species of Ananteris Thorell, 1891 (Scorpiones: Buthidae).

    Science.gov (United States)

    Lourenço, Wilson R

    2016-01-01

    A new remarkable species belonging to the genus Ananteris Thorell, 1891 (Buthidae) is described from the Mitaraka Massif in French Guiana, a site located near the borders of French Guiana, Brazil, and Suriname. The description of this new species brings further evidence about the biogeographic patterns of distribution presented by most species of the genus Ananteris, which are highly endemic in most biogeographic realms of South America, including the Tepuys and Inselberg Massifs.

  14. 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

  15. Geochemical and Sm–Nd isotopic study of titanite from granitoid rocks of the eastern Dharwar craton, southern India

    Indian Academy of Sciences (India)

    R Anand; S Balakrishnan

    2011-04-01

    Titanite occurs as an accessory phase in a variety of igneous rocks, and is known to concentrate geologically important elements such as U, Th, rare earth element (REE), Y and Nb. The differences in the abundances of the REEs contained in titanite from granitoid rocks could reflect its response to changes in petrogenetic variables such as temperature of crystallization, pressure, composition, etc. Widespread migmatization in the granodiorite gneisses occurring to the east of Kolar and Ramagiri schist belts of the eastern Dharwar craton resulted in the enrichment of the REEs in titanite relative to their respective host rocks. A compositional influence on the partitioning of REEs between titanite and the host rock/magma is also noticed. The relative enrichment of REEs in titanite from quartz monzodiorite is lower than that found in the granodioritic gneiss. Depletion of REE and HFSE (high field-strength elements) abundances in granitic magmas that have equilibrated with titanite during fractional crystallization or partial melting has been modelled. As little as 1% of titanite present in residual phases during partial melting or in residual melts during fractional crystallization can significantly lower the abundances of trace elements such as Nb, Y, Zr and REE which implies the significance of this accessory mineral as a controlling factor in trace element distribution in granitoid rocks. Sm–Nd isotope studies on titanite, hornblende and whole rock yield isochron ages comparable to the precise U–Pb titanite ages, invoking the usefulness of Sm–Nd isochron ages involving minerals like titanite.

  16. Effect of oxidation state on Bi mineral speciation in oxidized and reduced granitoids from the Uetsu region, NE Japan

    Science.gov (United States)

    Izumino, Yuya; Maruoka, Teruyuki; Nakashima, Kazuo

    2016-06-01

    The relationship between bismuth (Bi) mineral speciation and redox state in three types of granitoids from the Uetsu region, northeast Japan is investigated. Electron microprobe analysis of Bi minerals, sphalerite, Mg-Fe-bearing carbonate minerals, and muscovite, as well as sulfur isotope analysis of sulfide minerals and microthermometric study of fluid inclusions reveal that Bi mineral speciation varies according to the redox state of the granitoids. For example, native bismuth and bismuthinite are abundant and Bi sulfosalts are rare in the lowest fS2 and fO2 mineralized zones of the reduced Iwafune granite (S-type, ilmenite-series) while Bi sulfosalts (Bi3+) are abundant and trace amounts of native bismuth (Bi0) and bismuthinite are found in the highest fS2 and fO2 mineralized zones of the oxidized Wasada granodiorite (I-type, magnetite-series). Bismuthinite is a major Bi mineral, and native bismuth and Bi sulfosalts occur in only minor amounts in the mineralized zones of the Nishitagawa granodiorite (I-type, ilmenite-series), which has intermediate fS2 and fO2 to that of the Iwafune and Wasada samples. Our study indicates that Bi mineral speciation related to granitic intrusive activity is controlled by the redox state of the magmatism, such that native bismuth is typical of reducing conditions, whereas Bi sulfosalts are typical of oxidizing conditions.

  17. Effect of sample size on the fluid flow through a single fractured granitoid

    Directory of Open Access Journals (Sweden)

    Kunal Kumar Singh

    2016-06-01

    Full Text Available Most of deep geological engineered structures, such as rock caverns, nuclear waste disposal repositories, metro rail tunnels, multi-layer underground parking, are constructed within hard crystalline rocks because of their high quality and low matrix permeability. In such rocks, fluid flows mainly through fractures. Quantification of fractures along with the behavior of the fluid flow through them, at different scales, becomes quite important. Earlier studies have revealed the influence of sample size on the confining stress–permeability relationship and it has been demonstrated that permeability of the fractured rock mass decreases with an increase in sample size. However, most of the researchers have employed numerical simulations to model fluid flow through the fracture/fracture network, or laboratory investigations on intact rock samples with diameter ranging between 38 mm and 45 cm and the diameter-to-length ratio of 1:2 using different experimental methods. Also, the confining stress, σ3, has been considered to be less than 30 MPa and the effect of fracture roughness has been ignored. In the present study, an extension of the previous studies on “laboratory simulation of flow through single fractured granite” was conducted, in which consistent fluid flow experiments were performed on cylindrical samples of granitoids of two different sizes (38 mm and 54 mm in diameters, containing a “rough walled single fracture”. These experiments were performed under varied confining pressure (σ3 = 5–40 MPa, fluid pressure (fp ≤ 25 MPa, and fracture roughness. The results indicate that a nonlinear relationship exists between the discharge, Q, and the effective confining pressure, σeff., and Q decreases with an increase in σeff.. Also, the effects of sample size and fracture roughness do not persist when σeff. ≥ 20 MPa. It is expected that such a study will be quite useful in correlating and extrapolating the laboratory

  18. Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey

    Science.gov (United States)

    Gücer, Mehmet Ali; Arslan, Mehmet; Sherlock, Sarah; Heaman, Larry M.

    2016-12-01

    In the northern part of the Central Pontides (N Turkey) there are different metamorphic rocks exposed, notably the Devrekani metamorphic rocks. Here, upper amphibolite-lower granulite facies metamorphic rocks contain predominantly paragneiss, orthogneiss and metacarbonate, and to a lesser extent, amphibolite and quartzite, with cross-cutting aplite, pegmatite and granite veins. This is the first report of these rocks and includes new data on the petrochemistry, geochronology and metamorphic evolution of the Devrekani orthogneisses from the Central Pontides. The orthogneisses show five different mineral parageneses with the characteristic mineral assemblage quartz + K-feldspar + plagioclase + biotite ± hornblende ± opaque (± ilmenite and ± magnetite), and accessory minerals (zircon, sphene and apatite). These metamorphic rocks exhibit generally granoblastic, lepidogranoblastic and nematolepidogranoblastic with locally migmatitic and relic micrographic textures. They have well-developed centimeter-spaced gneissic banding and display gneissose structure with symmetric, asymmetric and irregular folds. The petrographic features, mineralogical assemblages and weak migmatization reflect high temperature conditions. Thermometric calculations in the orthogneisses indicate metamorphic temperatures reached 744 ± 33 °C. Field relations, petrography and petrochemistry suggest that the orthogneisses have predominantly granodioritic and some granitic protoliths, that show features of I-type, medium to high-potassic calc-alkaline volcanic arc granitoids. The orthogneisses have high contents of LILEs and low contents of HFSEs with negative Nb and Ti anomalies, which are typical of subduction-related magmas. The orthogneisses also show significant LREE enrichment relative to HREE with negative Eu anomalies (EuN/Eu* = 0.33-1.07) with LaN/LuN = 6.98-20.47 values. Based on U-Pb zircon dating data, the protoliths are related to Permo-Carboniferous (316-252 Ma) magmatism. It is

  19. Granitoides paleozoicos de la Sierra de Narváez, Sistema de Famatina, Argentina: Hibridización de magmas en un margen continental activo

    Directory of Open Access Journals (Sweden)

    Cisterna, C. E.

    1992-12-01

    Full Text Available The granitoids from the Sierra de Narváez were investigated for their geochemical and petrographical characteristics. They are composed of calc-alkaline granites, granodiorites and tonalites, similar to the other paleozoic granitoids of the Famatina System. These rocks are intrusive in the Las Planchadas (volcanic rocks and Suri (sedimentary rocks Formations, which are probably cogenetic with the granitoids within the same magmatic cycle.The study of the granitoids reveals the close relationship between their composition and the abundance of the enclosed magmatic inclusions. The latter represent rocks and granodioritic tonalitic and diorite composition, and have a great number of mineralogical characteristic that suggest the presence of two magmas, mafic and felsic for the origin of such enclaves.The close chemical relationship existing between the inclusions and their host rocks shows that the mafic and felsic components are compositionally modified and that the granitoids are more or less hybridized.Trace elements discrimination diagrams have been used as a tools for fingerprinting the tectonic setting of the Sierra de Narváez granitoids. The geochemistry as well as the geologic relations of the granitoids with the roughly coeval ordovician vulcanism indicate a volcanic arc environment.Las rocas que afloran en el extremo septentrional de la Sierra de Narváez están representadas por una asociación de monzogranitos, granodioritas y tonalitas que definen una serie calcoalcalina, de características similares a las de otros intrusivos del Paleozoico del Sistema de Famatina. Estos granitoides se hallan intruyendo las Formaciones Las Planchadas y Suri, representadas por vulcanitas y metasedimentitas, respectivamente, y corresponderían a un mismo evento magmático del Paleozoico Inferior.Los granitoides estudiados presentan abundantes inclusiones ígneas de composición granodiorítica o tonalítica y diorítica. La estrecha relación que

  20. The Sidi Mohamed peridotites (Edough Massif, NE Algeria): Evidence for an uppe mantle origin

    Indian Academy of Sciences (India)

    Soraya Hadj Zobir; Roland Oberhänsli

    2013-12-01

    The Hercynian Edough massif is the easternmost crystalline massif of the Algerian coast. It consists of two tectonically superposed units composed of micaschists, gneisses, and peridotite. This study concentrates on the small and isolated Sidi Mohamed peridotite outcrop area (0.03 km2). The Sidi Mohamed peridotite is composed mainly of harzburgites (Mg-rich olivine and orthopyroxene as major minerals). The Ni (2051–2920 ppm), Cr (2368–5514 ppm) and MgO (∼28–35 wt.%) whole-rock composition and the relative depletion in Nb make these harzburgites comparable to depleted peridotites related to a subduction zone. We suggest that the Sidi Mohamed ultramafic body was derived directly from the upper mantle and tectonically incorporated into the gneiss units of the Edough metamorphic core complex in a subduction environment.

  1. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics Granitoides estériles del Mioceno en la franja metalogénica de los Andes Centrales, Chile: geoquímica e isotopía de Nd-Hf y U-Pb

    Directory of Open Access Journals (Sweden)

    Katja Deckart

    2010-01-01

    Full Text Available Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were under-taken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32° and 34°S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Mesón Alto massif, 10.3±0.2 Ma (La Gloria pluton, 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith. Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32°S, slightly younger mineralized porphyries at Río Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758-0.512882, plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf i-data variation for the younger age group (10-12 Ma; 7.04-9.54 and show a more scattered range for the older one (14-15 Ma; 8.50-15.34; both sets plot between the DM and CLTUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Río Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening

  2. Petrogenesis of Permian A-type granitoids in the Cihai iron ore district, Eastern Tianshan, NW China: Constraints on the timing of iron mineralization and implications for a non-plume tectonic setting

    Science.gov (United States)

    Zheng, Jiahao; Mao, Jingwen; Chai, Fengmei; Yang, Fuquan

    2016-09-01

    The geochronology and geochemistry of granitoids in the Eastern Tianshan, NW China provide important constraints on the timing of iron mineralization, as well as in understanding evolution history of the southern Central Asian Orogenic Belt (CAOB). Here we present results from a detailed study on granitoid rocks from the Cihai iron ore district in the Beishan region, southern part of the Eastern Tianshan. The granitoid rocks are composed of granodiorite, quartz monzonite, granite, and monzonite. Zircon U-Pb analyses yielded the ages of 294.1 ± 2.2 Ma, 286.5 ± 0.7 Ma, 284.3 ± 3.3 Ma, and 265.6 ± 3.0 Ma, respectively, suggesting they were formed in Early-Middle Permian. Among these granitoid rocks, the ages of quartz monzonite and granite are close to the timing of iron mineralization (~ 282 Ma), indicating they may provide a source of iron in the Cihai ore district. Geochemically, the granodiorite, granite, and quartz monzonite samples are characterized by high FeOt/(FeOt + MgO) and Ga/Al ratios (0.84-0.94 and 2.28-3.27, respectively), as well as high zircon saturation temperatures (781-908 °C), similar to those of typical A-type granitoids. Isotopically, they display consistently depleted Hf isotopic compositions (εHf(t) = + 1.18 to + 15.37). Geological, geochemical, and isotopic data suggest that the Cihai A-type granitoids were derived from melting of juvenile lower crust. Some Early Permian A-type granitoids were recently identified in the Tarim and Eastern Tianshan with the ages between 294 and 269 Ma. The A-type granitoids in the Eastern Tianshan formed earlier between 294-284 Ma and exhibit characteristics of A2 type granitoids, whereas the A-type granitoids in the Tarim formed later between 277-269 Ma and show A1 granitoids affinity. We suggest that the Permian Tarim mantle plume does not account for the formation of the A-type granitoids in the Eastern Tianshan area, and the Eastern Tianshan was in a non-plume tectonic setting during Early Permian

  3. Early Cretaceous subvolcanic calc-alkaline granitoid magmatism in the Nubra-Shyok valley of the Shyok Suture Zone, Ladakh Himalaya, India: Evidence from geochemistry and U-Pb SHRIMP zircon geochronology

    Science.gov (United States)

    Kumar, Santosh; Bora, Sita; Sharma, Umesh K.; Yi, Keewook; Kim, Namhoon

    2017-04-01

    The lithounits constituting the Ladakh Himalaya are exposed along the Indus and Shyok Sutures Zones of northwest Himalaya. The Shyok Suture Zone (SSZ) in northern Ladakh represents a highly tectonized zone of a back-arc basin, which is mainly composed of volcano-sedimentary formations (Shyok and Khardung Formations) intimately, associated with intrusive granitoids. In the Nubra-Shyok valley of the SSZ calc-alkaline granitoids of batholithic dimension are exposed in the Tirit region, referred herein as the Tirit granitoids, which are intrusive evidently into the Shyok volcanic (rhyolite) rocks belonging to the Shyok Formation. In this valley the northern margins of granitoids of the Ladakh batholith can also be found intrusive into the metasediments (shale/slate) and metavolcanics of the Shyok Formation. The compositions and crystallization pressures ( 66 to 91 MPa) of amphiboles in the intrusive Tirit granitoid corroborate a calc-alkaline nature and solidification of Tirit granitoid melt at subvolcanic level equivalent to a minimum of 2.5 km to a maximum of 3.5 km thick overburden of Shyok volcanics. U-Pb SHRIMP zircons from the Tirit granitoids have yielded mean crystallization ages of 109.4 ± 1.1 Ma and 105.30 ± 0.80 Ma, which strengthen the idea of Early Cretaceous subduction beneath the Karakoram terrain. Inherited older zircon cores (278-393 Ma, 476-519-713-952 Ma and 1933 Ma) suggest a contribution from heterogeneous Palaeozoic and Proterozoic sources in the generation of the Tirit granitoids similar to those observed elsewhere in the Karakoram-Kohistan region. A mean crystallization age (105.30 ± 0.80) of zircons in the Tirit granitoid hosting xenoliths of porphyritic volcanics places a minimum eruption age of ca. 105 Ma for the Shyok volcanics. The Ladakh granitoid, Tirit granitoids and porphyritic volcanic xenolith belong to a calc-alkaline series. A mean crystallization age (67.32 ± 0.66 Ma) for zircon in the Ladakh granitoid implies that the Shyok

  4. Timing and Style of Deformation in the Floresta Massif, Axial Eastern Cordillera, Colombia

    Science.gov (United States)

    Saylor, J.; Stockli, D. F.; Mora, A.

    2009-12-01

    The Floresta Massif is one of the largest exposures of Paleozoic and Pre-Cambrian rocks in the Eastern Cordillera. Estimates for the age of onset of shortening-related deformation in the Eastern Cordillera range from late Cretaceous to late Miocene (e.g., Hoorn et al., 1995; Bayona et al., 2008; Parra et al., 2009). The massif is typically interpreted as being exhumed along a high-angle reverse fault (the Soapaga fault) that reactivated Mesozoic extensional structures (e.g., Kammer and Sanchez, 2006). We examined these dual linked issued with new zircon U/Th-He (ZHe) data, new geological mapping and previously published apatite fission track (AFT) data from the Floresta Massif and the associated footwall strata. Previously, an overturned Paleozoic - Cretaceous sequence was mapped emplaced on Tertiary strata along the Soapaga fault. However, new geologic mapping identifies two previously unrecognized thrusts which place, from west to east, Paleozoic strata on Jurassic strata (Fault 3), Jurassic strata on Cretaceous strata (Fault 2) and Cretaceous strata on Tertiary strata (along the previously identified Fault 1). These results are confirmed by AFT and ZHe data. ZHe ages show no resetting in the Tertiary footwall strata, but show partial resetting in the Cretaceous strata and full resetting in the Jurassic and Paleozoic strata. Similarly, AFT data show older ages in the Cretaceous strata than in the Jurassic or Paleozoic strata. Fully reset ZHe ages from Jurassic strata show that exhumation of the Floresta Massif was ongoing by at least the early Oligocene (~ 30 Ma). However, this deformation post-dates an older episode of deformation associated with partially reset ZHe ages in the Cretaceous strata. Based on a decrease in lag time in detrital ZHe data, we infer that the earlier episode of deformation occurred in the mid - late Eocene (45 - 35 Ma).

  5. Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps

    OpenAIRE

    S. Monnier; C. Camerlynck; F. Rejiba; Kinnard, C.; Galibert, P.-Y.

    2011-01-01

    We investigated the Sachette rock glacier, Vanoise Massif, Northern French Alps, using former equilibrium line altitude reconstruction from glacial deposits, aerial photograph analysis, and ground-penetrating radar (GPR). The rock glacier is a young (probably 0.15–0.16 m ns−1) and reflectors having a dipping-syncline structure, typical of true glaciers. Consequently, the rock glacier structure is described as being constituted of ...

  6. Crystal structure of modular sodium-rich and low-iron eudialyte from Lovozero alkaline massif

    Science.gov (United States)

    Rozenberg, K. A.; Rastsvetaeva, R. K.; Aksenov, S. M.

    2016-09-01

    The structure of the sodium-rich representative of the eudialyte group found by A.P. Khomyakov at the Lovozero massif (Kola Peninsula) is studied by X-ray diffraction. The trigonal cell parameters are: a = 14.2032(1) and c = 60.612(1) Å, V = 10589.13 Å3, space group R3m. The structure is refined to the final R = 5.0% in the anisotropic approximation of atomic displacement parameters using 3742|F| > 3σ( F). The idealized formula ( Z = 3) is Na37Ca10Mn2FeZr6Si50(Ti, Nb)2O144(OH)5Cl3 · H2O. Like other 24-layer minerals of the eudialyte group, this mineral has a modular structure. Its structure contains two modules, namely, "alluaivite" (with an admixture of "eudialyte") and "kentbrooksite," called according to the main structural fragments of alluaivite, eudialyte, and kentbrooksite. The mineral found at the Lovozero alkaline massif shows some chemical and symmetry-structural distinctions from the close-in-composition labyrinthite modular mineral from the Khibiny massif. The difference between the minerals stems from different geochemical conditions of mineral formation in the two regions.

  7. The peculiarities of structurizing enclosing rock massif while developing a coal seam

    Science.gov (United States)

    Kozyreva, E. N.; Shinkevich, M. V.

    2017-09-01

    Different concepts of the development of geo-mechanical processes during longwall mining of a seam which are fundamentally different from the conventional ones are introduced in the article. Fundamental principles of the model for structurizing enclosing rock mass while longwall mining along the strike are described. The model was developed on the bases of non-linear geomechanical laws. According to the model, rock mass in the area of mining operation is organized as rock geomechanical layers with shifting arches. And the formation period of shifting arches in disintegrated rock mass is divisible by the length of the stope. Undulate characteristic of a massif as a peculiarity of man-made structurization of a massif is defined. It is shown that structuring the broken massif causes the formation of block-structured system and it can be detected while monitoring the ground pressure in powered support props. The results of the research allow decreasing the negative influence of a ground pressure and can be applied to specify parameters for controlling the roof, defining geometrical dimensions of a mining section and positioning of holing chute (face entry).

  8. Crystallization and emplacement of the Lac St-Jean anorthosite massif (Quebec, Canada)

    Science.gov (United States)

    Woussen, G.; Dimroth, E.; Corriveau, L.; Archer, P.

    1981-05-01

    The Lac St-Jean anorthosite massif underlies an area of over 20,000 km2 and has been emplaced into migmatitic gneisses of the central granulite terrain of the Grenville Province of the Canadian shield. Field data and petrography in an area straddling the anorthosite-gneiss contact, close to Chicoutimi (Quebec) permits an outline of its tecto-magmatic evolution. Depositional magmatic textures in the massif reveals that it crystallized from a magma in a relatively calm tectonic environment. The absence of fusion in pelitic gneisses at the contact proves that the crystallization did not take place at the level presently exposed. The parallelism of subvertical foliation in the enveloping gneisses and the anorthosite indicates that both were deformed together. It is suggested that the deformation results from a diapiric ascent of the anorthosite massif after its consolidation at depth. The depth of consolidation of the anorthosite is estimated at ˜ 25 30 km from subsolidus reaction between plagioclase and olivine. The diapiric ascent is further substantiated by the fact that three sets of mafic dykes of different ages, intrusive into the anorthosite, have a mineralogy which indicates successively decreasing P, T conditions of emplacement from granulite fades to amphibolite facies. An evolution of the basement gneisses and the anorthosite is proposed as a working hypothesis; it relies on the fact that metabasite dyke swarms in the basement gneisses represent a period of major crustal extension and could be used as a stratigraphic subdivision of the Grenville Province.

  9. Significance of Geological Units of the Bohemian Massif, Czech Republic, as Seen by Ambient Noise Interferometry

    Science.gov (United States)

    Růžek, Bohuslav; Valentová, Lubica; Gallovič, František

    2016-05-01

    Broadband recordings of 88 seismic stations distributed in the Bohemian Massif, Czech Republic, and covering the time period of up to 12 years were processed by a cross-correlation technique. All correlograms were analyzed by a novel approach to get both group and phase dispersion of Rayleigh and Love waves. Individual dispersion curves were averaged in five distinct geological units which constitute the Bohemian Massif (Saxothuringian, Teplá-Barrandean, Sudetes, Moravo-Silesian, and Moldanubian). Estimated error of the averaged dispersion curves are by an order smaller than the inherent variability due to the 3D distribution of seismic velocities within the units. The averaged dispersion data were inverted for 1D layered velocity models including their uncertainty, which are characteristic for each of the geological unit. We found that, overall, the differences between the inverted velocity models are of similar order as the variability inside the geological units, suggesting that the geological specification of the units is not fully reflected into the S-wave propagation velocities on a regional scale. Nevertheless, careful treatment of the dispersion data allowed us to identify some robust characteristics of the area. The vp to vs ratio is anomalously low (~1.6) for all the units. The Moldanubian is the most rigid and most homogeneous part of the Bohemian Massif. Middle crust in the depth range of ~3-15 km is relatively homogeneous across the investigated region, while both uppermost horizon (0-3 km) and lower crust (>15 km) exhibit lower degree of homogeneity.

  10. Tourist Activities-Disturbance Factors of Natural Environment in Ciucaș Massif

    Directory of Open Access Journals (Sweden)

    Luminița Costina SĂFTOIU

    2014-10-01

    Full Text Available The study outlines how tourism activities can disturb the natural environment in Ciucaș Massif. Methods used are based on bibliographic research and GIS analysis of morphometric features. Results show that the Ciucaș Massif, as one of the most important mountain in central Romania, is made of conglomerates, which lend specific features to topography. Having several natural sights (The Old Ladies Council, The Sphinx of Bratocea, Zăganului Ridge this massif is declared a protected natural area. The geomorphologic processes: compactions, mudflows, the deepening of tourist paths, rills and gully erosion have a negative impact on the landscape and even on the entire environment, causing erosion and loss of soil and vegetation. Also, the increased number of tourist accommodation facilities and 21 marked tourist trails have resulted in shrinking of forest areas, hayfields and pastures.These numerous changes which occur in this mountain area, lead, in time, to radical, irreversible changes and can affect the local economic development.

  11. Tracing crustal evolution in the NW Iberian Peninsula through the Rb---Sr and U---Pb systematics of Palaeozoic granitoids: a review

    NARCIS (Netherlands)

    Priem, H.N.A.; Tex, E. den

    1984-01-01

    The abundant granitoids in the Palaeozoic basement of the northwestern Iberian Peninsula include 470-440 Ma old suites (Early-Middle Ordovician, now present as orthogneisses) and several Variscan suites. The age data presently available suggest that the latter have been generated in three separate t

  12. Geología y geocronología Rb-Sr de granitoides de Sierra Grande, provincia de Río Negro

    Directory of Open Access Journals (Sweden)

    Ricardo Varela

    2009-04-01

    Full Text Available Al este de Sierra Grande la unidad más antigua es la Ectinita El Jagüelito, metagrauvacas y pizarras, cortadas por granitoides ordovícicos (Rb-Sr en roca total 467 ± 16 Ma; U-Pb en circón 476 ± 4 Ma. Ectinitas y granitoides son cubiertos discordantemente por sedimentitas clásticas fosilíferas silúricas de la Formación Sierra Grande y el total de unidades deformado por pliegues y fallas. Al sur de Sierra Grande, Mina Hiparsa, afloran la Ectinita El Jagüelito, la Formación Sierra Grande y granitoides, en un contexto de fuerte deformación tectónica. Desde mitad de siglo pasado se discute si los granitoides constituyen el basamento de la Formación Sierra Grande o si son intrusivos en la misma. La Formación Sierra Grande está afectada por metamorfismo térmico. Datos radimétricos previos de granitoides son discordantes (Rb-Sr en roca total 252 ± 5 Ma; 363 ± 57 Ma; 318 ± 28 Ma; U-Pb SHRIMP en circón 476 ± 6 Ma. Se efectuaron nuevos análisis Rb-Sr en roca total y minerales y se propone la existencia de dos unidades graníticas. En granitoides del noroeste de la mina, Granito Mina Hiparsa, se obtuvieron dos isocronas (262 ± 6 Ma, 87Sr/86Sr inicial = 0,7162 ± 0,0003 y 263 ± 9 Ma, 87Sr/86Sr inicial = 0,7149 ± 0,0009. En los granitoides al oeste de la Mina Hiparsa, Granodiorita Laguna Medina, se efectuó una isocrona (260 ± 3 Ma, 87Sr/86Sr Inicial = 0,7078 ± 0,0012. Las rocas estudiadas son el producto de plutonismo ordovícico temprano y pérmico tardío-temprano. Las tres isocronas roca total-minerales son pérmicas, pero dos por metamorfismo y reseteo de rocas ordovícicas (87Sr/86Sr inicial ~ 0,7150 y una por cristalización (87Sr/86Sr inicial ~ 0,7080.

  13. Geophysical Constraints on the Nature of Atlantis Massif, 30°N MAR

    Science.gov (United States)

    Blackman, D.

    2005-12-01

    Recent drilling at Atlantis Massif, Mid-Atlantic Ridge 30°N, provides new insights into oceanic core complex (OCC) development. IODP Expeditions 304/305 had high recovery in the footwall of the detachment capping the central dome of the massif: Hole U1309B, 100 m deep; Hole U1309D, 1415 m. Recovery of a dominantly gabbroic sequence challenges prior interpretations that this OCC was mainly ultramafic, geophysical data having suggested much of the uplifted core was mantle peridotite, with Moho less than 1 km deep. Although models based on prior analysis fit the data well and were consistent with outcrops of serpentinized peridotite on the south face of Atlantis Massif, it is now clear that additional complexity needs to be incorporated in the geophysical analysis. The southern ridge is morphologically distinct from the central dome. Does this indicate that the south and central parts of this OCC are fundamentally different? Or, is the serpentinized peridotite exposed on the south wall (and found in a few loose fragments on top of the central dome) a thin veneer of mantle rock that has deformed around a dominantly gabbroic core? The occurrence of many gabbroic samples from the southern ridge could support the latter but models of serpentinization that drives the Lost City hydrothermal system near the peak of the massif might favor the former. New analysis of geophysical data provide further constraints on the scale of possible variability. Prior seismic analysis suggested fresh mantle might shoal by a couple hundred meters 1-2 km north of Site U1309. In contrast, gravity data suggest the highest density rocks occur at and to the south of the site. These observations will be combined in a 3D model of Atlantis Massif and we expect to report initial results. Downhole logging indicates that bulk density increases steadily from 2.8 to 2.9 g/cc downhole. Log and core sample seismic velocity are variable within a 5.5-6.8 km/s range, lower values where degree of alteration

  14. Jurassic hot spring deposits of the Deseado Massif (Patagonia, Argentina): Characteristics and controls on regional distribution

    Science.gov (United States)

    Guido, Diego M.; Campbell, Kathleen A.

    2011-06-01

    The Deseado Massif, Santa Cruz Province, Argentinean Patagonia, hosts numerous Middle to Late Jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs (sinters and travertines, respectively), hydrothermal breccias, quartz veins, and widespread hydrothermal silicification. They indicate pauses in explosive volcanic activity, marking the final stages in the evolution of an extensive Jurassic (ca. 178-151 Ma) volcanic complex set in a diffuse extensional back-arc setting heralding the opening of the Atlantic Ocean. Published paleo-hot spring sites for the Deseado Massif, plus additional sites identified during our recent field studies, reveal a total of 23 locations, five of which were studied in detail to determine their geologic and facies associations. They show structural, lithologic, textural and biotic similarities with Miocene to Recent hot spring systems from the Taupo and Coromandel volcanic zones, New Zealand, as well as with modern examples from Yellowstone National Park, U.S.A. These comparisons aid in the definition of facies assemblages for Deseado Massif deposits - proximal, middle apron and distal siliceous sinter and travertine terraces and mounds, with preservation of many types of stromatolitic fabrics - that likely were controlled by formation temperature, pH, hydrodynamics and fluid compositions. Locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and/or fluvial sediments, silicic to intermediate lava domes, and hydrothermal mineralization, all of which are related to local and regional structural lineaments. Moreover, the numerous geothermal and significant epithermal (those with published minable resources) deposits of the Deseado Massif geological province mostly occur in four regional NNW and WNW hydrothermal-structural belts (Northwestern, Northern, Central, and Southern), defined here by alignment of five or more hot

  15. Garzon Massif basement tectonics: A geopyhysical study, Upper Magdalena Valley, Colombia

    Science.gov (United States)

    Bakioglu, Kadir Baris

    The mechanics and kinematics of basement tectonic uplifts, such as the Laramide Rocky Mountain orogeny, remain poorly understood and controversial. The debate continues in part because of the limited number of well-documented present day analogs. The Garzon Massif rising between the Upper Magdalena Valley and the Llanos Basin of Colombia is an active basement uplift with well, seismic, gravity, and magnetic data available. In the past 10 Ma, PreCambrian age granitic rocks of the Garzon Massif have been uplifted and displaced against Cretaceous and Tertiary sediments of the Upper Magdalena Valley along the Garzon fault. Aerogravimetric data calibrated by well data and 2D seismic data were used to model the geometry of the Garzon fault and the top of basement (Saldana Fm) in 2 dimensions. The density models provide an independent estimate of fault orientation. A high density airborne gravity and magnetic survey were flown over the Garzon fault in 2000, including 2,663 line km along 1 x 5 and 1 x 4 km flight lines at elevations of 2564 and 4589 m above mean sea level. An initial depth model was derived from the well logs, seismic reflection profile, and down-hole velocity surveys. Airborne gravity data was used to produce a Bouguer anomaly gravity map. Average rock densities were estimated from density logs, seismic velocities, and formation rock types. The regional gravity field was estimated and 2-dimensional forward models were constructed with average densities from the wells, seismic velocities, and rock types, and the initial depth model. Since the model fit is dependent on the density assumed for the Garzon Massif rocks, multiple densities and dip angles were tested. The gravity analysis indicates that the Garzon fault is a basement thrust fault dipping at a shallow angle under the Massif. Best-fit models show a true dip of 12 to 17 degrees to the southeast. A regional density and magnetic susceptibility model of the entire Massif is consistent with dense

  16. Neogene Uplift and Exhumation of Plutonic Bodies in the Beni Bou Ifrour Massif (Nador, northeastern Morocco)

    Science.gov (United States)

    Lebret, Noëmie; Jolivet, Laurent; Branquet, Yannick; Bourdier, Jean-Louis; Jolivet, Marc; Marcoux, Eric

    2013-04-01

    In Neogene times, the whole Mediterranean Sea was the center of an intense magmatic activity. This post-collisional magmatism produced a large amount of volcanic edifices through the Alpine belts, together with some intrusives. These plutonic bodies can be associated with skarn-type mineralization, well-known in Elba Island or Serifos Island (Cyclades), where they are generally exhumed by detachment faults. In Morocco, the plutons hosted by the Beni Bou Ifrour massif are connected to the biggest skarn-type iron concentrations of the country (production > 60 Mt, reserves ≈ 25 Mt). The purpose of this work is to explain the late uplift of this massif and subsequent exhumation of the intrusives. As a final product of the Africa-Eurasia plate convergence since ca. 70 Ma, the Rif Mountains constitute the westernmost segment of the Mediterranean Alpine belts. In the oriental part of this range, volcanic summits and Paleozoic to Mesozoic massifs outcrop in the surrounding Mio-Pliocene plains. The Beni Bou Ifrour massif, in the Nador province, consists in a dome-shaped folded Mesozoic series (Domerian to Barremian) affected by a slight epizonal regional metamorphism (ca. 14-12 Ma), dislocated by Neogene NE-SW faults and eventually sealed by upper Miocene transgressive sediments. The hosted intrusives (7.58 ± 0.03 Ma; Duggen et al., 2005) are the plutonic equivalents to the potassic calc-alkaline lavas (andesites mainly) from the surrounding "satellite" volcanic massifs. They turn out to stand in higher topographic position than the younger shoshonitic lavas of the neighboring Gourougou stratovolcano (6.12 ± 0.01 Ma; Duggen et al., 2005). Previous studies have attributed this uplift to the action of normal faults (pull-apart basins; Guillemin & Houzay, 1982), thrusting (Kerchaoui, 1985; 1995) or even of a caldeira resurgence (El Bakkali, 1995). To discriminate against those exhumation mechanisms, field work has been performed, coming along with new cross-sections to

  17. Conditions of crystallization of the Ural platinum-bearing ultrabasic massifs: evidence from melt inclusions

    Science.gov (United States)

    Simonov, Vladimir; Puchkov, Victor; Prikhod'ko, Vladimir; Stupakov, Sergey; Kotlyarov, Alexey

    2013-04-01

    Conditions of the Ural platinum-bearing ultramafic massifs formation attract attention of numerous researchers. A most important peculiarity of such plutons is their dunite cores, to which commercial Pt deposits are related. There are a different opinions about genesis of these massifs and usual methods not always can solve this question. As a result of melt inclusions study in the Cr-spinel the new data on physical and chemical parameters of dunite crystallization of the Nizhnii Tagil platinum-bearing ulrabasic massif (Ural) was obtained. The comparative analysis of Cr-spinels, containing melt inclusions, has shown essential differences of these minerals from chromites of the ultrabasic ophiolite complexes and of modern oceanic crust. Contents of major chemical components in the heated and quenched melt inclusions are close to those in the picrite and this testifies dunite crystallization from ultrabasic (to 24 wt.% MgO) magma. On the variation diagrams for inclusions in Cr-spinel the following changes of chemical compositions are established: during SiO2 growth there is falling of FeO, MgO, and increase of CaO, Na2O contents. Values of TiO2, Al2O3, K2O and P2O5 remain as a whole constant. Comparing to the data on the melt inclusions in Cr-spinel from the Konder massif, we see that values of the most part of chemical components (SiO2, TiO2, K2O, P2O5) are actually overlapped. At the same time, for the Nizhnii Tagil platinum-bearing massif the big maintenances of FeO and CaO in inclusions are marked. Distinct dependence of the majority of components from the MgO content in inclusions is observed: values TiO2, Al2O3 FeO, CaO and Na2O fall at transition to more magnesia melts. On the peculiarities of distribution of petrochemical characteristics melt inclusions in considered Cr-spinels are co-ordinated with the data on evolution of compositions of melts and rocks of model stratified ultramafic plutons during their crystallization in the magmatic chambers. On the

  18. Edad, caracterización petrográfica y Geoquímica del Granitoide del Cerro Falkner, Neuquén Age, petrography and geochemistry of Cerro Falkner's granitoid

    Directory of Open Access Journals (Sweden)

    Sabrina Crosta

    2008-03-01

    Full Text Available El Cerro Falkner se halla constituido por rocas graníticas infrayacentes a las volcanitas de la Formación Ventana de edad paleógena. Dichos intrusivos son de composición granodiorítica, metaluminosos a peraluminosos, subalcalinos, con características de granitos de arco volcánico concordantes con otros granitoides del segmento norte de la Cordillera Patagónica Septentrional. La edad obtenida por el método K-Ar sobre anfíboles de composición tschermakítica (125 ± 20 Ma indica una edad mínima perteneciente al Cretácico inferior para la granodiorita del cerro Falkner, por lo que sería incorrecto utilizar la denominación Formación Los Machis (Cretácico superior para estas rocas. Esta edad, permite vincular las rocas graníticas del área de estudio con el volcanismo representado por el Grupo Divisadero de edad predominantemente cretácica inferior.Cerro Falkner is composed of granitic rocks underlying volcanic rocks of the Ventana Formation of Paleogene age. Those intrusives are granodioritic in composition, metaluminous to peraluminous, subalkaline, with characteristics of volcanic arc granites that are concordant with other granitoids of the Cordillera Patagónica Septentrional's northern segment. The age obtained by the K-Ar method on tschemakitic amphiboles (125 ± 20 Ma points out a minimun age from the lower Cretaceous for the Cerro Falkner's granodiorite. Therefore the use of the term Los Machis Formation (Upper Cretaceous would be incorrect for these rocks. This age, allows us to relate the granitic rocks on the study area to the lower Cretaceous, coeval with the volcanism of the Divisadero Group.

  19. [K+/Na+ in the animal extracellular fluid at weathering of granitoids and problem of the origin of life].

    Science.gov (United States)

    Natochin, Iu V; Felitsyn, S B; Klimova, E V; Shakhmatova, E I

    2012-01-01

    Leaching of granitoids of the paleoproterozoic age was performed from several seconds to 360 days in water solutions (pH water reservoirs with predominance of K+ over Na+. The K+/Na+ ratio exceeding 1 has been shown in prokaryotes, in cells and tissues of the free living and parasitic species of invertebrate and vertebrate animals. At the same time in the extracellular fluid of the fresh water, marine, and terrestrial animals, in which the Na+ concentration varies from 13 to 482 mmol/l, the K+/Na+ ratio is preserved at the level of 0.034 +/- 0.001. These results are discussed in connection with the problem of origin of protocells and of concentration ratios of monovalent cations in water phases of multicellular organisms.

  20. Quantitative estimation of granitoid composition from thermal infrared multispectral scanner (TIMS) data, Desolation Wilderness, northern Sierra Nevada, California

    Science.gov (United States)

    Sabine, Charles; Realmuto, Vincent J.; Taranik, James V.

    1994-01-01

    We have produced images that quantitatively depict modal and chemical parameters of granitoids using an image processing algorithm called MINMAP that fits Gaussian curves to normalized emittance spectra recovered from thermal infrared multispectral scanner (TIMS) radiance data. We applied the algorithm to TIMS data from the Desolation Wilderness, an extensively glaciated area near the northern end of the Sierra Nevada batholith that is underlain by Jurassic and Cretaceous plutons that range from diorite and anorthosite to leucogranite. The wavelength corresponding to the calculated emittance minimum lambda(sub min) varies linearly with quartz content, SiO2, and other modal and chemical parameters. Thematic maps of quartz and silica content derived from lambda(sub min) values distinguish bodies of diorite from surrounding granite, identify outcrops of anorthosite, and separate felsic, intermediate, and mafic rocks.

  1. Biodiversity impact of the aeolian periglacial geomorphologic evolution of the Fontainebleau Massif (France)

    Science.gov (United States)

    Thiry, M.; Liron, M. N.

    2009-04-01

    Landscape features The geomorphology of the Fontainebleau Massif is noteworthy for its spectacular narrow ridges, up to 10 km long and 0.5 km wide, armored by tightly cemented sandstone lenses and which overhang sandy depressions of about 50m. Denudation of the sandstone pans lead to a highly contrasted landscape, with sandstone ridges ("platières") towering sandy depressions ("vallées") and limestone plateaus ("monts"). This forms the geological frame of the spectacular sceneries of the Fontainebleau Massif (Thiry & Liron, 2007). Nevertheless, there is little know about the erosive processes that have built-up these landscapes. Periglacial processes, and among them aeolian ones, appear significant in the development of the Fontainebleau Massif physiography. The periglacial aeolian geomorphology Dunes and dune fields are known since long and cover about 15% to 25% of the Fontainebleau Massif. The aeolian dunes developed as well on the higher parts of the landscape, as well as in the lower parts of the landscape. The dunes are especially well developed in the whole eastern part of the massif, whereas the western part of the massif is almost devoid of dunes. Nevertheless, detailed mapping shows that dunes can locally be found in the western district, they are of limited extension, restricted to the east facing backslope of outliers. Loamy-sand covers the limestone plateaus of the "monts". The loam cover is of variable thickness: schematically thicker in the central part of the plateaus, where it my reach 3 m; elsewhere it may thin down to 0,20-0,30 m, especially at the plateau edges. Blowout hollows are "negative" morphologies from where the sand has been withdrawed. Often these blowouts are decametric sized and well-delimited structures. Others, more complex structures, are made up of several elongated hectometric hollows relaying each other from and which outline deflation corridor more than 1 km long. A characteristic feature of these blowout hollows is the

  2. Age, geochemical affinity and geodynamic setting of granitoids and felsic volcanics in the basement of Wrangel Island

    Science.gov (United States)

    Luchitskaya, Marina; Moiseev, Artem; Sokolov, Sergey; Tuchkova, Marianna; Sergeev, Sergey

    2016-04-01

    Granitoids and basic rocks of Wrangel Island are the components of Precambrian metamorphic basement, exposed in the anticlinorium in the central part of the island and named as Wrangel complex (Kameneva, 1970; Ageev, 1979; Til'man et al., 1964, 1970; Ganelin, 1989; Kos'ko et al., 1993, 2003). The latter is composed of volcanic, volcaniclastic and clastic rocks metamorphosed in greenshist to locally lower amphibolite facies (Kos'ko et al., 2003; Cecile et al., 1991). Obtained earlier datings of granitoids and basic rocks from Wrangel complex display a wide scatter: 609-700 Ma, U-Pb zircon (Cecile et al., 1991; Kos'ko et al., 1993); 590 Ma, Pb-Pb zircon; 574, 575 Ma, K-Ar whole rock; 475 Ma, Rb-Sr muscovite (Kos'ko et al., 2003). Our previous U-Pb SHRIMP datings indicate the episode of granitoid activity in 681-707 Ma (Luchitskaya et al., 2014). Here we present new results from zircon SIMS and LA-ICP-MS U-Pb dating and geochemical data for granites and felsic volcanics of Wrangel complex. Granites of Wrangel complex in the area of Khishchnikov River form small tabular bodies less than 30 meters in thickness. They range from slightly recrystallized muscovite granites to gneissic and mylonitic ones. Felsic and basic volcanics are exposed in the central part of Wrangel Island (rivers Neizvestnaya and Krasnyy Flag). Their interrelations are unknown and earlier they were considered as single bymodal assemblage of C1 sequence (Kos'ko et. al., 1993, 2003). Samples were collected in the area of Pervaya Mountain, visible thickness of volcanics ~100 meters. Basalts are overlain by conglomerates with detrite zircons no younger than 550 Ma (Moiseev et al., 2009, 2015). Wheited mean ages of zircons from muscovite granites and mylonitic ones are 592.9±6.7 Ma (n=10) and 692.9±5.0 Ma (n=30); in two samples we suppose the age of crystallization ~700 Ma. Wheited mean ages of zircons from felsic volcanics are 594.4±7.1 Ma (n=10) and 598.6±7.5 Ma (n=10). Granites and felsic

  3. Genesis of ilmenite-series I-type granitoids at the Baogutu reduced porphyry Cu deposit, western Junggar, NW-China

    Science.gov (United States)

    Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; Hollings, Pete; Jin, LuYing

    2016-03-01

    The Baogutu porphyry Cu deposit is a typical reduced porphyry Cu deposit, likely related to ilmenite-series I-type granitoids. However, the nature of the granitoids (ilmenite-series or magnetite-series) and the genesis of the Baogutu deposit are still under debate. In order to resolve these issues, whole-rock magnetic susceptibility, geochemistry and Sr-Nd-Pb isotopic, zircon U-Pb dating and Hf-O isotopic compositions were carried out. Three different intrusive phases are recognized within the deposit, from oldest to youngest, they are diorite with trace gabbro, diorite-granodiorite porphyry, and hornblende diorite porphyry, all of which were emplaced in the Late Carboniferous (320-306 Ma) and show a metaluminous, calc-alkaline I-type granitoid character with typical supra-subduction zone geochemical affinities. The intrusions are characterized by widespread primary pyrrhotite without anhydrite and hematite, dominant ilmenite over magnetite, low whole rock magnetic susceptibility (< 1 × 10- 4 emu g- 1 oe- 1 or < 3 × 10- 3 SI unit) and low whole rock Fe2O3/FeO ratios (< 0.4), indicating that the granitoids are ilmenite- rather than magnetite-series I-type granitoids. Whole rock Sr-Nd-Pb isotopic compositions show limited variation but slightly enriched characteristics with (87Sr/86Sr)i values of 0.70357-0.70404, εNd (t) of + 6.3 to + 7.8, 206Pb/204Pb of 18.20-19.54 and 208Pb/204Pb of 37.97-39.55. Zircon Hf-O isotopic compositions show εHf (t) values of + 10.7 to + 15.8 and δ18O of 5.3-7.4‰. Zircon and apatite saturation thermometries yield temperatures of 720 to 920 °C with relatively higher temperatures for the porphyries than for the diorite. Limited variations in Sr-Nd-Pb-Hf-O isotopic compositions and extremely young whole rock T2DM (Nd) (430 to 570 Ma) and zircon TDMC (Hf) (310 to 640 Ma) do not indicate significant crustal contamination during magma ascent or emplacement. Rather the Baogutu ilmenite-series I-type granitoids were probably formed by

  4. Jurassic cooling ages in Paleozoic to early Mesozoic granitoids of northeastern Patagonia: 40Ar/39Ar, 40K-40Ar mica and U-Pb zircon evidence

    Science.gov (United States)

    Martínez Dopico, Carmen I.; Tohver, Eric; López de Luchi, Mónica G.; Wemmer, Klaus; Rapalini, Augusto E.; Cawood, Peter A.

    2016-12-01

    U-Pb SHRIMP zircon crystallization ages and Ar-Ar and K-Ar mica cooling ages for basement rocks of the Yaminué and Nahuel Niyeu areas in northeastern Patagonia are presented. Granitoids that cover the time span from Ordovician to Early Triassic constitute the main outcrops of the western sector of the Yaminué block. The southern Yaminué Metaigneous Complex comprises highly deformed Ordovician and Permian granitoids crosscut by undeformed leucogranite dikes (U-Pb SHRIMP zircon age of 254 ± 2 Ma). Mica separates from highly deformed granitoids from the southern sector yielded an Ar-Ar muscovite age of 182 ± 3 Ma and a K-Ar biotite age of 186 ± 2 Ma. Moderately to highly deformed Permian to Early Triassic granitoids made up the northern Yaminué Complex. The Late Permian to Early Triassic (U-Pb SHRIMP zircon age of 252 ± 6 Ma) Cabeza de Vaca Granite of the Yaminué block yielded Jurassic mica K-Ar cooling ages (198 ± 2, 191 ± 1, and 190 ± 2 Ma). At the boundary between the Yaminué and Nahuel Niyeu blocks, K-Ar muscovite ages of 188 ± 3 and 193 ± 5 Ma were calculated for the Flores Granite, whereas the Early Permian Navarrete granodiorite, located in the Nahuel Niyeu block, yielded a K-Ar biotite age of 274 ± 4 Ma. The Jurassic thermal history is not regionally uniform. In the supracrustal exposures of the Nahuel Niyeu block, the Early Permian granitoids of its western sector as well as other Permian plutons and Ordovician leucogranites located further east show no evidence of cooling age reset since mica ages suggest cooling in the wake of crystallization of these intrusive rocks. In contrast, deeper crustal levels are inferred for Permian-Early Triassic granitoids in the Yaminué block since cooling ages for these rocks are of Jurassic age (198-182 Ma). Jurassic resetting is contemporaneous with the massive Lower Jurassic Flores Granite, and the Marifil and Chon Aike volcanic provinces. This intraplate deformational pulse that affected northeastern

  5. A-type granitoid in Hasansalaran complex, northwestern Iran: Evidence for extensional tectonic regime in northern Gondwana in the Late Paleozoic

    Science.gov (United States)

    Azizi, Hossein; Kazemi, Tahmineh; Asahara, Yoshihiro

    2017-07-01

    The Hasansalaran plutonic complex is one of the main intrusive bodies with a wide range of granite, monzonite, diorite and syenite that crop out in northwest Iran. This body includes Paleozoic granitoids that are surrounded and cut by Cretaceous granitoids. Zircon U-Pb age dating shows that the crystallization of this body occurred at 360 Ma ago in the Early Carboniferous. Whole rock compositions of the investigated intrusive body, show high contents of Ga (11.1-76.3 ppm), Zr (73.5-1280 ppm), Zn (43.7-358 ppm), Y(17.9-177 ppm), enrichment of rare earth elements (REEs) together with high Ga/Al ratios and a strong Eu negative anomaly, fairly consistent with typical A-type signature. The low εNd(t = 360 Ma) value (< + 3) and high variation of 87Sr/86Sr(initial) ratios are evidence of the role of the continental component for the evolution of A-type granitoids in the Hasansalaran area. Because of the high contents of Ta, Yb, Nb and Y, all samples are plotted in the within-plate tectonic regime without interfering oceanic released fluids in the subduction zone. These high Nb content rocks (37.2-342 ppm without one sample) are classified as A1-type granitoids. Based on the distribution of A1- and A2-type granitoids in the Late Paleozoic in northwest Iran, the existence of some gabbroic rocks with tholeiitic to alkali composition and a long gap for magmatic activities in the area from 550 to 360 Ma (approximately 180 my.a.) between the Zagros and Tabriz faults, we suggest a new thematic model for evolution of northwest Iran in the Late Paleozoic. Based on our model, the upwelling of a mantle plume, probably due to the proto-Tethys oceanic rollback activity beneath northern Gondwana, had a crucial role in the uplifting of the continental crust and resulted in the crystallization of A-type granitoids with some gabbroic rocks in northwest Iran.

  6. An overview on geochemistry of Proterozoic massif-type anorthosites and associated rocks

    Indian Academy of Sciences (India)

    A K Maji; A Patra; P Ghosh

    2010-12-01

    A critical study of 311 published WR chemical analyses,isotopic and mineral chemistry of anorthosites and associated rocks from eight Proterozoic massif anorthosite complexes of India, North America and Norway indicates marked similarities in mineralogy and chemistry among similar rock types.The anorthosite and mafic-leucomafic rocks (e.g.,leuconorite,leucogabbro, leucotroctolite,anorthositic gabbro,gabbroic anorthosite,etc.)constituting the major part of the massifs are characterized by higher Na2O + K2O, Al2O3, SiO2 Mg#and Sr contents,low in plagioclase incompatible elements and REE with positive Eu anomalies. Their 18O %0 (5.7 –7.5), initial 87Sr/86Sr (0.7034–0.7066)and Nd values (+1.14 to +5.5)suggest a depleted mantle origin. The Fe-rich dioritic rocks occurring at the margin of massifs have isotopic, chemical and mineral composition more close to anorthosite –mafic-leucomafic rocks. However, there is a gradual decrease in plagioclase content, An content of plagioclase and XMg of orthopyroxene, and an increase in mafic silicates, oxide minerals content, plagioclase incompatible elements and REE from anorthosite – mafic-leucomafic rocks to Fe-rich dioritic rocks. The Fe-rich dioritic rocks are interpreted as residual melt from mantle derived high-Al gabbro melt, which produced the anorthosite and mafic-leucomafic rocks. Mineralogically and chemically, the K-rich felsic rocks are distinct from anorthosite –mafic-leucomafic-Fe-rich dioritic suite. They have higher 18O values (6.8 –10.8%) and initial 87Sr/86Sr (0.7067-0.7104). By contrast, the K-rich felsic suites are products of melting of crustal precursors.

  7. Geochemical studies, magmatic evolution, microstructures and replacement mechanisms in Jebale-Barez granitoid Complex (East and Southeast Jiroft

    Directory of Open Access Journals (Sweden)

    Jamal Rasouli

    2017-08-01

    Full Text Available Introduction The Jebale-Barez Plutonic Complex (JBPC is composed of many intrusive bodies and is located in the southeastern province of Kerman on the longitude of the 57◦ 45 ' east to 58◦ 00' and Northern latitudes 28◦ 30' to 29◦ 00'. The petrologic composition is composed of granodiorite, quartzdiorite, granite, alkali-granite, and trace amounts of tonalite with dominant granodiorite composition. Previously, the JBPC was separated into three plutonic phases by Ghorbani (2014. The first plutonic phase is the main body of the complex with composition of quartz-diorite to granodiorite. After differentiation of magma in the magmatic chamber, the porphyritic and not fully consolidated magmas have intruded into the main body. Their compositions were dominantly granodiorite and granite that are defined as the second plutonic phase. Finally, the last phase was started by an intrusion of the holo- leucogranite into the previous bodies. This plutonic activity was pursued by the minor Quaternary basaltic volcanism that shows metamorphic haloes in the contacts. They are dominantly porphyric leucogranites. However, some bodies show dendritic texture that may imply the existence of silicic fluids in the latest crystallization stages. Materials and methods In this article different analysis methods were used. For example, we used a total of two hundred samples of the various granitoids that were selected for common thin section study. Forty four representative samples from the different granitic rocks were selected for whole rock chemical analyses. The analyses of both major and trace elements were performed at the Department of Earth Sciences, the University of Perugia, Italy. The analysis for all major elements was carried out by an X-ray fluorescence spectrometry (XRF using a tube completed with a Rn and W anode under conditions with acceleration voltage of 40-45 kV and electric current ranging from I=30-35 mA. After calcination of powdered

  8. Discovery and implications of the high-pressure pelitic granulite from the Jiaobei massif

    Institute of Scientific and Technical Information of China (English)

    ZHOU Xiwen; WEI Chunjing; GENG Yuansheng; ZHANG Lifei

    2004-01-01

    The high pressure pelitic granulite with peak assemblage of garnet + kyanite + ternary feldspar + muscovite + rutile was discovered in Qixia area in the Precambrian Jiaobei massif, where high pressure basic granulites are widely distributed. The metamorphic peak conditions for the pelitic granulite were calculated as T = 800-840℃ and P =1.0-1.25 GPa on the basis of P-T pseudosection. The post peak P-T path is characterized first by an isothermal decompression (ITD) pattern and then by an isobaric cooling (IBC) pattern, indicating a geodynamic process related to thinning of thickened continental crust.

  9. Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

    Science.gov (United States)

    Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

    2014-05-01

    This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz

  10. Permeability Structure Beneath the Lost City Hydrothermal Field, Atlantis Massif Oceanic Core Complex

    Science.gov (United States)

    McCaig, A. M.; Titarenko, S.

    2012-12-01

    The Lost City Hydrothermal Field (LCHF) has been venting low temperature (50-90 °C) alkaline fluids for at least 120,000 years. It is located close to the crest of the transform wall of the Atlantis Massif (30 °N, MAR), and is underlain by detachment fault schists and serpentinized peridotites with minor gabbro. Only 5km to the north, IODP Hole 1309D sampled 1400 m of gabbroic rocks. An almost linear thermal gradient of ~100 °C/km has recently been measured in the Hole during IODP expedition 340T, a unique piece of data in young ocean crust. The combination of a steep conductive gradient in proximity to a long lived hydrothermal system places severe constraints on the permeability structure of the Massif. We have used Comsol Multiphysics to create the first 2-D topographic model of the LCHF using a N-S profile through the vent site and Hole 1309D. Initial models use a constant basal heat flow (0.2 W/m2) which produces a steady state conductive gradient of about 85 °C/km using temperature-dependent conductivity and heat capacity. We include a low permeability basal layer and in some models a lower permeability zone beneath the IODP Hole with a boundary dipping steeply southwards, corresponding to a boundary between gabbro and serpentinite inferred from seismic tomography. We have used two top boundary conditions; (1) a mixed boundary condition in which dT/dz =0 if flow is upwards, and T=0 if flow is downwards, and (2) T=0. The first boundary condition is normally used in hydrothermal modelling but produces serious vent temperature artifacts at low upward flow rates since heat cannot escape conductively. The second boundary condition produces more stable models and has been shown by Wilcock (1998) to reproduce the form of hydrothermal circulation accurately. However vent temperatures can only be approximated due to the upper thermal boundary layer produced. With a constant permeability in the upper part of the model, transient high temperature vents form near the

  11. Early Ukrainian-Belarusian-Polish traditional melo-massif: Interethnic wedding macro-areas

    Directory of Open Access Journals (Sweden)

    Klymenko Iryna

    2015-01-01

    Full Text Available Through rhythm-typological analysis and cartography the author has detected a similarity in the typological structure of early traditional musical forms belonging to agricultural and wedding genres on the territory which unites Ukraine, Belarus (within its ethnic area at the beginning of the 20th century, Eastern Poland (the Vistula river basin, and Lithuania (Dzūkija and Aukštaitija. This concerns several dozen song types, composed of items from a common grammatical base, forming the Ukrainian- Belarusian-Polish early-traditional melo-massif ‒ UBPEM. These types share interethnic (2-4-lingual areals, which do not correlate with linguistic ones.

  12. Thermochronology and tectonics of the Mérida Andes and the Santander Massif, NW South America

    Science.gov (United States)

    van der Lelij, Roelant; Spikings, Richard; Mora, Andrés

    2016-04-01

    New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature (~ 500 °C-~ 300 °C) thermal histories of igneous and metamorphic rocks exposed in the Mérida Andes of Venezuela, and new apatite and zircon fission track data constrain the ~ 500 °C-~ 60 °C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Mérida Andes suggest that it cooled from > 500 °C to histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Mérida Andes by > 30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Mérida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at ~ 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Mérida Andes in the Late Permian. The coeval onset of exhumation in the Mérida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of Pangaea. Triassic extension is documented in the Central Cordillera of Colombia and Ecuador between ~ 240 Ma and ~ 215 Ma, although extension at this time has not been clearly identified in the Mérida Andes or the Santander Massif. Permian to Triassic cooling is not recorded in the structurally isolated Caparo Block in the southern Mérida Andes, suggesting that it may have constituted a distinct fault block in the Triassic. New fission track data from the Santander Massif suggest that it started exhuming at ~ 40 Ma during a period of accelerated convergence between the Nazca/Farallòn Plate and the western margin of South America. Exhumation in the Santander

  13. MASSIF-1: a beamline dedicated to the fully automatic characterization and data collection from crystals of biological macromolecules

    Science.gov (United States)

    Bowler, Matthew W.; Nurizzo, Didier; Barrett, Ray; Beteva, Antonia; Bodin, Marjolaine; Caserotto, Hugo; Delagenière, Solange; Dobias, Fabian; Flot, David; Giraud, Thierry; Guichard, Nicolas; Guijarro, Mattias; Lentini, Mario; Leonard, Gordon A.; McSweeney, Sean; Oskarsson, Marcus; Schmidt, Werner; Snigirev, Anatoli; von Stetten, David; Surr, John; Svensson, Olof; Theveneau, Pascal; Mueller-Dieckmann, Christoph

    2015-01-01

    MASSIF-1 (ID30A-1) is an ESRF undulator beamline operating at a fixed wavelength of 0.969 Å (12.8 keV) that is dedicated to the completely automatic characterization of and data collection from crystals of biological macromolecules. The first of the ESRF Upgrade MASSIF beamlines to be commissioned, it has been open since September 2014, providing a unique automated data collection service to academic and industrial users. Here, the beamline characteristics and details of the new service are outlined. PMID:26524320

  14. Behaviour of {sup 238}U, {sup 234}U, {sup 228}Ra and {sup 226}Ra in rock alterations: study of Morungaba granitoids, SP-Brazil and ground water in its fractures; Comportamento de {sup 238}U, {sup 234}U, {sup 228}Ra e {sup 226}Ra na alteracao de rochas: estudo dos granitoides de Morungaba (SP) e aguas subterraneas de suas fraturas

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Rosana N. dos [Pontificia Univ. Catolica de Sao Paulo, SP (Brazil). Dept. de Fisica]. E-mail: rosana@pucsp.br; Marques, Leila S. [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas. Dept. de Geofisica]. E-mail: leila@iag.usp.br

    2005-07-01

    This work presents the first results obtained on the investigation of the behavior of uranium and radium radioisotopes in the processes of weathering and rock-water interaction of Morungaba granitoids belonging to Meridional Pluton (Valinhos Town-SP-Brazil). Specific activities of {sup 238}U, {sup 234}U, {sup 228}Ra and {sup 226}Ra were determined in non altered granitoids (Group A), as well as in those affected by different degrees of weathering (Groups B, C and D). The uranium specific activities were determined by alpha spectrometry method, whereas for the determination of radium isotopes high resolution gamma-ray spectrometry technique was employed. The data indicate that {sup 238}U and {sup 234}U are in radioactive equilibrium in the fresh analyzed granitoids, but show a slight depletion of {sup 234}U in relation to {sup 238}U in the weathered rocks. The ({sup 226}Ra/{sup 238}U) and ({sup 226}Ra/{sup 234}U) activity ratios of all investigated rocks are similar, showing a significant {sup 226}Ra depletion, which is probably caused by its preferential leaching. These results indicate that even samples macroscopically classified as fresh rocks, their systems have been opened for some geochemical changes. The high ({sup 234}U/{sup 238}U) activity ratios of groundwaters which are found in the fractures of these granitoids suggest their prolonged residence times in the aquifer and/or their percolation by other rocks presenting different geochemical properties. (author)

  15. Petrogenesis of granitoids in the eastern section of the Central Qilian Block: Evidence from geochemistry and zircon U-Pb geochronology

    Science.gov (United States)

    Li, Jiyong; Niu, Yaoling; Chen, Shuo; Sun, Wenli; Zhang, Yu; Liu, Yi; Ma, Yuxin; Hu, Zhenxing; Zhang, Guorui

    2016-08-01

    The Caledonian-age Qilian Orogenic Belt at the northern margin of the Greater Tibetan Plateau comprises abundant granitoids that record the histories of the orogenesis. We report here our study of these granitoids from two localities. The Qingchengshan (QCS) pluton, which is situated in the eastern section of the Central Qilian Block, is dated at ~430-420 Ma. It has high-K calc-alkaline composition with high SiO2 (> 70 wt%), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and varying degrees of negative Sr and Eu anomalies. The granitoids in the Tongwei (TW) area, 150 km east of the QCS, are complex, the majority of which are dated at ~440 Ma, but there also exist younger, ~230 Ma intrusions genetically associated with the Qinling Orogeny. The Paleozoic TW intrusions also have high SiO2, fractionated REE (rare earth element) patterns, but a negligible Eu anomaly. The whole rock Sr-Nd-Hf isotopic compositions suggest that all these Paleozoic granitoids are consistent with melting-induced mixing of a two-component source, which is best interpreted as the combination of last fragments of subducted/subducting ocean crust with terrigenous sediments. The mantle isotopic signature of these granitoids (87Sr/86Sri: 0.7038 to 0.7100, ɛNd(t): -4.8 to -1.3, ɛHf(t): -0.7 to +4.0) reflects significant (~70 %) contribution of the ocean crust derived in no distant past from the mantle at ocean ridges with an inherited mantle isotopic signature. Partial melting of such ocean crust plus terrigenous sediments in response to the ocean closing and continental collision (between the Qilian and Alashan Blocks) under amphibolite facies conditions is responsible for the magmatism. Varying extents of fractional crystallization (±plagioclase, ±amphibole, ±garnet, ±zircon) of the parental magmas produced the observed QCS and TW granitoids. We note that sample HTC12-01 in the TW area shows an A-type or highly fractionated granite

  16. Petrogenesis of granitoids in the eastern section of the Central Qilian Block: Evidence from geochemistry and zircon U-Pb geochronology

    Science.gov (United States)

    Li, Jiyong; Niu, Yaoling; Chen, Shuo; Sun, Wenli; Zhang, Yu; Liu, Yi; Ma, Yuxin; Hu, Zhenxing; Zhang, Guorui

    2017-02-01

    The Caledonian-age Qilian Orogenic Belt at the northern margin of the Greater Tibetan Plateau comprises abundant granitoids that record the histories of the orogenesis. We report here our study of these granitoids from two localities. The Qingchengshan (QCS) pluton, which is situated in the eastern section of the Central Qilian Block, is dated at 430-420 Ma. It has high-K calc-alkaline composition with high SiO2 (> 70 wt%), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and varying degrees of negative Sr and Eu anomalies. The granitoids in the Tongwei (TW) area, 150 km east of the QCS, are complex, the majority of which are dated at 440 Ma, but there also exist younger, 230 Ma intrusions genetically associated with the Qinling Orogeny. The Paleozoic TW intrusions also have high SiO2, fractionated REE (rare earth element) patterns, but a negligible Eu anomaly. The whole rock Sr-Nd-Hf isotopic compositions suggest that all these Paleozoic granitoids are consistent with melting-induced mixing of a two-component source, which is best interpreted as the combination of last fragments of subducted/subducting ocean crust with terrigenous sediments. The mantle isotopic signature of these granitoids (87Sr/86Sri: 0.7038 to 0.7100, ɛNd(t): -4.8 to -1.3, ɛHf(t): -0.7 to +4.0) reflects significant ( 70 %) contribution of the ocean crust derived in no distant past from the mantle at ocean ridges with an inherited mantle isotopic signature. Partial melting of such ocean crust plus terrigenous sediments in response to the ocean closing and continental collision (between the Qilian and Alashan Blocks) under amphibolite facies conditions is responsible for the magmatism. Varying extents of fractional crystallization (±plagioclase, ±amphibole, ±garnet, ±zircon) of the parental magmas produced the observed QCS and TW granitoids. We note that sample HTC12-01 in the TW area shows an A-type or highly fractionated granite

  17. Zircon U-Pb ages, Hf isotope data, and tectonic implications of Early-Middle Triassic granitoids in the Ailaoshan high-grade metamorphic belt of Southeast Tibet

    Science.gov (United States)

    Wu, Wenbin; Liu, Junlai; Chen, Xiaoyu; Zhang, Lisheng

    2017-04-01

    The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian-Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. An Ailaoshan micro-block within the belt is bounded by the Ailaoshan suture zone to the west and the Red River Fault to the east, and consists of low- and high-grade metamorphic belts. Late Permian-Middle Triassic granitoids that are widely distributed to the west of the Ailaoshan suture zone and within the Ailaoshan micro-block may yield significant information on the Tethyan tectonic evolution of the Ailaoshan tectonic belt. This study reports new LA-ICP-MS zircon U-Pb geochronology and Hf isotope data of four granitoids from the Ailaoshan high-grade metamorphic belt. Zircon grains from the Yinjie granitoid do not have inherited cores and yield a weighted mean U-Pb age of 247.1 ± 2.0 Ma. The zircon ɛ Hf( t) values range from 7.8 to 12.1, and Hf model ages from 775 to 546 Ma, indicating that the granitoid was derived from juvenile crust. The rims of zircons from the Majie and Yuanjiang granitoids yield weighted mean U-Pb ages of 239.5 ± 1.8 and 237.9 ± 2.6 Ma, respectively, whereas the cores yield ages of 1608-352 Ma. The ɛ Hf( t) values of zircon rims range from -20.4 to -5.3, yielding Hf model ages from 2557 to 1606 Ma and suggesting that the source magma of the Majie and Yuanjiang granitoids was derived from ancient crust. An additional granitoid located near the Majie Village yields a zircon U-Pb age of 241.2 ± 1.0 Ma. Based on our geochronological and geochemical data, combined with geological observations, we propose that the Ailaoshan micro-block was derived from the western margin of the Yangtze block, and is comparable to the Zhongzan and Nam Co micro-blocks. The presence of late Permian mafic rocks with rift-related geochemical characteristics within the Ailaoshan micro-block, together with granitoids derived

  18. Zircon U-Pb ages, Hf isotope data, and tectonic implications of Early-Middle Triassic granitoids in the Ailaoshan high-grade metamorphic belt of Southeast Tibet

    Science.gov (United States)

    Wu, Wenbin; Liu, Junlai; Chen, Xiaoyu; Zhang, Lisheng

    2016-05-01

    The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian-Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. An Ailaoshan micro-block within the belt is bounded by the Ailaoshan suture zone to the west and the Red River Fault to the east, and consists of low- and high-grade metamorphic belts. Late Permian-Middle Triassic granitoids that are widely distributed to the west of the Ailaoshan suture zone and within the Ailaoshan micro-block may yield significant information on the Tethyan tectonic evolution of the Ailaoshan tectonic belt. This study reports new LA-ICP-MS zircon U-Pb geochronology and Hf isotope data of four granitoids from the Ailaoshan high-grade metamorphic belt. Zircon grains from the Yinjie granitoid do not have inherited cores and yield a weighted mean U-Pb age of 247.1 ± 2.0 Ma. The zircon ɛ Hf(t) values range from 7.8 to 12.1, and Hf model ages from 775 to 546 Ma, indicating that the granitoid was derived from juvenile crust. The rims of zircons from the Majie and Yuanjiang granitoids yield weighted mean U-Pb ages of 239.5 ± 1.8 and 237.9 ± 2.6 Ma, respectively, whereas the cores yield ages of 1608-352 Ma. The ɛ Hf(t) values of zircon rims range from -20.4 to -5.3, yielding Hf model ages from 2557 to 1606 Ma and suggesting that the source magma of the Majie and Yuanjiang granitoids was derived from ancient crust. An additional granitoid located near the Majie Village yields a zircon U-Pb age of 241.2 ± 1.0 Ma. Based on our geochronological and geochemical data, combined with geological observations, we propose that the Ailaoshan micro-block was derived from the western margin of the Yangtze block, and is comparable to the Zhongzan and Nam Co micro-blocks. The presence of late Permian mafic rocks with rift-related geochemical characteristics within the Ailaoshan micro-block, together with granitoids derived

  19. Geometries of deformed granitoid inclusions in the Sudbury Igneous Complex of the Sudbury Impact Structure, Canada: Evidence for deformation during solidification of the impact melt sheet

    Science.gov (United States)

    Lenauer, Iris; Riller, Ulrich

    2010-05-01

    The Main Mass of the 1.85 Ga Sudbury Igneous Complex (SIC) occupies the central portion of the Sudbury Impact Structure and represents an impact melt sheet that resulted from hypervelocity impact into Archaean and Proterozoic target rocks. During cooling, the ca. 3 km thick melt sheet differentiated into layers of norite, quartz gabbro and granophyre and now hosts one of the world's largest Cu-Ni-PGE deposits. Meteorite impact occurred apparently during an ongoing orogeny, i.e., the ca. 1.89 to 1.80 Ga Penokean orogeny. However, structural evidence for this is still sparse Dike-like, granitoid inclusions are exposed in the norite layer of the southern SIC. Here, sub-planar inclusions are folded and characterized by axial-planar cleavage. More specifically, fold mullions of the granitoid inclusions formed by layer-parallel NNW-SSE shortening. Cuspate-lobate geometries of the inclusion interfaces indicate that the granitoid inclusions were mechanically more competent than the norite host rock during ductile deformation of both lithologies. The contrast in mechanical strength between granitoid inclusions and norite host rock indicates ductile deformation at high temperature and low strain rates in the unconsolidated melt sheet. Shortening directions inferred from the geometry of the inclusions agree with those obtained from inversion of brittle-ductile faults from the same area, geometry of deformation in the metasedimentary strata of the Proterozoic target rocks and l-s mylonitic fabrics developed in the granophyre layer of the SIC and the overlying impact melt breccias. Collectively, these structural characteristics indicate that orogenic deformation in the Sudbury area occurred during cooling and solidification of the impact melt sheet.

  20. Structure and metamorphism of the Gran Paradiso massif, western Alps, Italy

    Science.gov (United States)

    Brouwer, F. M.; Vissers, R. L. M.; Lamb, W. M.

    2002-05-01

    The pressure-temperature-time trajectory and structural history of high-pressure rocks presently exposed in the Gran Paradiso massif provide constraints on the processes that caused their thermal evolution and exhumation. High-pressure metamorphism of the rocks is found to have culminated at temperatures around 525 °C and pressures of 12 to 14 kbar. After high-pressure metamorphism, the rocks cooled during initial decompression, while undergoing top-to-the-west shear on chlorite-bearing shear bands and larger scale shear zones. Biotite-bearing shear bands and larger shear zones related to top-to-the-east deformation affected the Gran Paradiso massif during reheating to temperatures of around 550 °C at 6 to 7 kbar. Further exhumation occurred at relatively high temperatures. A potentially viable explanation of the observed stage of reheating before final cooling and exhumation is breakoff of a subducting slab in the upper mantle, allowing advective heat transfer to the base of the crust. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00410-001-0357-6.

  1. Rapakivi texture in porphyritic dikes within the Karavanke Granitic Massif (Slovenia

    Directory of Open Access Journals (Sweden)

    Giuliano Bellieni

    2002-01-01

    Full Text Available The northern Karavanke Granitic Massif straddles the Slovenian–Austrian border. The investigated area lies in northern Slovenia, and extends from the western Slovenian–Austrian border to the east for about 30 km, with a maximum width of 2 km. The massif exhibits a bimodal magmatic association comprising mainly syenogranite and syenite with contemporaneous gabbroic rocks. Rocks of intermediate composition are less abundant and show field, textural and chemical features suggesting that they have formed as a result of the interaction (mixing and mingling between felsic and mafic magmas. Plagioclasemantled alkali feldspars occur in dikes of porphyritic syenite, which cut larger bodies of gabbroic rocks. Field, mineralogical, petrographic and geochemical evidences suggest that the porphyritic syenite is a hybrid rock, formed by the interaction of mafic and felsic magmas. The formation of plagioclase-mantled alkali feldspar can be explained by the introduction of alkali feldspar from felsic, syenogranitic magma into more mafic magma, causing local undercooling in the portion of mafic magma surrounding the crystals. This resulted in the growth of cellular plagioclase, with quartz infilling, in a thermally and compositionally equilibrating system.

  2. Monazite geochronology, magmatism, and extensional dynamics within the Menderes Massif, western Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Catlos, E J [University of Texas at Austin, Jackson School of Geosciences, Geological Science Department, 1 University Station C1100, Austin, TX 78712-0254 (United States); Baker, C B; Cemen, I [Oklahoma State University, School of Geology, 105 Noble Research Center, Stillwater, OK 74078 (United States); Sorensen, S S [Smithsonian Institution Museum of Natural History, PO Box 37012, MRC 119, Washington, DC, 20013-7012 (United States); Hancer, M [Pamukkale Universitesi, Muhendislik Fakultesi, Jeoloji Muh. Bolmu, Denizli, 20070 Turkey (Turkey)], E-mail: ejcatlos@gmail.com

    2008-07-01

    Geochemical and geochronological data were collected from S-type, peraluminous granites (Salihli and Turgutlu) that intrude a detachment that bounds the northern edge of the central Menderes Massif core complex (Aegean region, western Turkey). The granites may have been generated due to subduction of the Eastern Mediterranean floor along the Hellenic trench. In situ Th-Pb ion microprobe monazite ages from the rocks range from 21.7{+-}4.5 Ma to 9.6{+-}1.6 Ma ({+-}1{sigma}), which could record their exhumation history. Higher uncertainty in the ages is attributed to monazite common Pb, but the range is consistent with cathodoluminescence (CL) images that document complex textures within the granites. Salihli and Turgutlu granites share many similar characteristics, including multiple generations of plagioclase, plagioclase replacing K-feldspar and the development of myrmekite, evidence for fluid interaction, and multiple generations of microcracks. Ages reported here are similar to dates constraining extension reported elsewhere in the Aegean, but indicate additional complexities when linking movement within the Menderes Massif to large-scale geodynamic processes that created other metamorphic core complexes in the region. Difficulties exist in linking the ages obtained from the granites to specific tectonic events due to the presence of secondary alteration textures, generations of mineral growth and multiple episodes of deformation.

  3. New radiocarbon chronology of a late Holocene landslide event in the Mont Blanc massif, Italy

    Science.gov (United States)

    Hajdas, Irka; Sojc, Ursula; Ivy-Ochs, Susan; Akçar, Naki; Deline, Philip

    2016-04-01

    The Ferret valley Arp Nouva peat bog located in the Mont Blanc massif was critically evaluated since previously published radiocarbon dates have led to controversial conclusions on the formation of the swamp. Radiocarbon dating of roots from three pits of up to 1 m depth was applied to discuss the question whether the historical documented rock avalanche occurring in AD 1717 overran the peat bog or formed it at a later stage. Our results indicate that the rock avalanche formed the Arp Nouva peat bog by downstream blockage of the Bellecombe torrent. Furthermore, careful sample preparation with consequent separation of roots from the bulk peat sample provides possible explanation for the too old 14C ages of bulk peat samples dated previously (Deline and Kirkbride, 2009 and references therein). This work demonstrates that a combined geomorphological and geochronological approach is the most reliable way to reconstruct landscape evolution, especially in light of apparent chronological problems. The key to successful 14C dating is a careful sample selection and the identification of material that might be not ideal for chronological reconstructions. References Deline, Philip, and Martin P. Kirkbride. "Rock avalanches on a glacier and morainic complex in Haut Val Ferret (Mont Blanc Massif, Italy)".Geomorphology 103 (2009): 80-92.

  4. Features of change of permanent snow patches in the Mongun-Taiga Massif, 1966–2011

    Directory of Open Access Journals (Sweden)

    D. A. Ganyushkin

    2013-01-01

    Full Text Available The article is dedicated to perennial snow patches of Mongun-Taiga mountain massif (south-western Tuva, their morphology, present state and dynamics over the last 45 years. We created a scheme of snow patch classification with regard to genesis of relief and position on the slopes. Dynamics of snow patches is analyzed for periods between several time points – 1966 (on basis of aerial photos, 2000, 2007–2008 and 2011 (on basis of field measurements and observations. From 1966 to 2008 the number of snow patches decreased by 4 times, the total area – by 15 times, the altitudinal zone of snow patches moved 250–300 m up. In 2008–2011 the altitudinal zone of snow patches partly recovered, its lower limit moved 250 m down, periglacial snow patches recovered, a new type – snow patches of buried ice and debris-covered glaciers appeared. It could be the first face of the process of small glaciers recovery in the massif. Using the changes of the altitudinal position of snow patches in comparison with data of the closest meteorological station we estimated the amount of annual precipitation, critical for the existence of local snow patches.

  5. Methane Seepage at Hyperalkaline Springs in the Ronda Peridotite Massif (Spain)

    Science.gov (United States)

    Etiope, G.; Vadillo, I.; Whiticar, M. J.; Marques, J. M.; Carreira, P. M.; Tiago, I.; Benavente, J.; Jimenez, P.; Urresti, B.

    2014-12-01

    Methane-rich, hyperalkaline spring waters and bubbling pools have been sampled in the Ronda peridotite massif in southern Spain. Water chemistry (T: 17.1-21.5 ºC; pH: 10.7-11.7; DO: migration pathways along faults. Similar 'dry' seepage of abiotic gas was observed in the Philippines, New Zealand, Turkey and Italy. Like other land-based serpentinization systems, the Ronda peridotite massif is characterized by low heat flow (<40 mW/m2), with temperatures <60°C at depths of 1.5 km. At these low T and high pH conditions, CO32- is the only available carbon source dissolved in the water, and unlikely contributes to catalysed Fischer-Tropsch Type reactions. Methane production from CO2 hydrogenation in a gas phase system (unsaturated fractured rocks) cannot be excluded. The presence of ruthenium-enriched chromitites in the Ronda peridotites may support the hypothesis that CH4 is produced by CO2 hydrogenation catalyzed by Ru minerals, even at temperatures below 100°C, as demonstrated in recent laboratory experiments (Etiope and Ionescu, 2014, Geofluids, in press).

  6. The age of Earth's largest volcano: Tamu Massif on Shatsky Rise (northwest Pacific Ocean)

    Science.gov (United States)

    Geldmacher, Jörg; van den Bogaard, Paul; Heydolph, Ken; Hoernle, Kaj

    2014-11-01

    This study presents laser step-heating 40Ar/39Ar age determinations of basaltic lava samples from Tamu Massif, the oldest and largest edifice of the submarine Shatsky Rise in the northwest Pacific and Earth's proposed largest volcano. The rocks were recovered during Integrated Ocean Drilling Program Expedition 324, which cored 160 m into the igneous basement near the summit of Tamu Massif. The analyzed lavas cover all three major stratigraphic groups penetrated at this site and confirm a Late Jurassic/Early Cretaceous age for the onset of Shatsky Rise volcanism. Lavas analyzed from the lower and middle section of the hole yield plateau ages between 144.4 ± 1.0 and 143.1 ± 3.3 Ma with overlapping analytical errors (2σ), whereas a sample from the uppermost lava group produced a significantly younger age of 133.9 ± 2.3 Ma suggesting a late or rejuvenated phase of volcanism. The new geochronological data infer minimum (average) melt production rates of 0.63-0.84 km3/a over a time interval of 3-4 million years consistent with the presence of a mantle plume.

  7. Late Cretaceous evolution of the northern Sistan suture zone, eastern Iran: Implications of magnetic fabrics and microstructures in the Bibi Maryam granitoid

    Science.gov (United States)

    Etemadkhah, Zeinab; Khatib, Mohammad Mahdi; Zarrinkoub, Mohammad Hossein

    2015-04-01

    Anisotropy of magnetic susceptibility (AMS) survey supported by field and microstructural studies have been applied on the Late Cretaceous Bibi Maryam granitoid (BMG) in the northern Sistan suture zone (SSZ), east of Iran. The BMG is composed of quartzdiorite-tonalite with late granodiorite dykes and stocks that are surrounded by steeply SW-dipping Neh shear zone (NSZ). The magmatic fabrics are characterized by transpressional environment dominated by steep dipping foliations (mean strike: N13°W) and sub-horizontal stretching lineations (mean trend: 167°). Based on microstructural studies, it is inferred that these fabrics are related to emplacement and cooling of the pluton and the internal fabrics revealed are evidence of a deformation continuum in the granitoid from magmatic to solid state. Deformation in the region continued even after the BMG had fully crystallized, which led to development of the NW-SE foliations and lineation trend that these fabrics are subparallel with the NSZ. The BMG has emplaced in a transpressional setting that was controlled by a NW-SE stretching direction and supported the model that has proposed the relationship between granitoid emplacement and oblique intra-oceanic subduction of the Neotethys during the Late Cretaceous already recognized in this part of the SSZ.

  8. Late Cretaceous evolution of the northern Sistan suture zone, eastern Iran: Implications of magnetic fabrics and microstructures in the Bibi Maryam granitoid

    Indian Academy of Sciences (India)

    Zeinab Etemadkhah; Mohammad Mahdi Khatib; Mohammad Hossein Zarrinkoub

    2015-04-01

    Anisotropy of magnetic susceptibility (AMS) survey supported by field and microstructural studies have been applied on the Late Cretaceous Bibi Maryam granitoid (BMG) in the northern Sistan suture zone (SSZ), east of Iran. The BMG is composed of quartzdiorite-tonalite with late granodiorite dykes and stocks that are surrounded by steeply SW-dipping Neh shear zone (NSZ). The magmatic fabrics are characterized by transpressional environment dominated by steep dipping foliations (mean strike: N13°W) and sub-horizontal stretching lineations (mean trend: 167°). Based on microstructural studies, it is inferred that these fabrics are related to emplacement and cooling of the pluton and the internal fabrics revealed are evidence of a deformation continuum in the granitoid from magmatic to solid state. Deformation in the region continued even after the BMG had fully crystallized, which led to development of the NW–SE foliations and lineation trend that these fabrics are subparallel with the NSZ. The BMG has emplaced in a transpressional setting that was controlled by a NW–SE stretching direction and supported the model that has proposed the relationship between granitoid emplacement and oblique intra-oceanic subduction of the Neotethys during the Late Cretaceous already recognized in this part of the SSZ.

  9. Stratigraphy of Upper Cretaceous-Palaeogene sequences in the southern and eastern Menderes Massif (western Turkey)

    Science.gov (United States)

    Özer, Sacit; Sözbilir, Hasan; Özkar, İzver; Toker, Vedia; Sari, Bilal

    2001-03-01

    The stratigraphy of the uppermost levels of the Menderes Massif is controversial and within its details lie vital constraints to the tectonic evolution of south-western Turkey. Our primary study was carried out in four reference areas along the southern and eastern Menderes Massif. These areas lie in the upper part of the Menderes metamorphic cover and have a clear stratigraphic relationship and contain datable fossils. The first one, in the Akbük-Milas area, is located south-east of Bafa Lake where the Milas, then Kızılağaç and Kazıklı formations are well exposed. There, the Milas formation grades upwards into the Kızılağaç formation. The contact between the Kızılağaç and the overlying Kazıklı formation is not clearly seen but is interpreted as an unconformity. The Milas and Kızılağaç formations are also found north of Muğla, in the region of Yatağan and Kavaklıdere. In these areas, the Milas formation consists of schists and conformably overlying platform-type, emery and rudist-bearing marbles. Rudists form the main palaeontological data from which a Santonian-Campanian age is indicated. The Kızılağaç formation is characterized by reddish-greyish pelagic marbles with marly-pelitic interlayers and coarsening up debris flow deposits. Pelagic marbles within the formation contain planktonic foraminifera and nanoplankton of late Campanian to late Maastrichtian age. The Kazıklı formation is of flysch type and includes carbonate blocks. Planktonic foraminifera of Middle Palaeocene age are present in carbonate lenses within the formation. In the Serinhisar-Tavas area, Mesozoic platform-type marbles (Yılanlı formation) belonging to the cover series of the Menderes Massif exhibit an imbricated internal structure. Two rudist levels can be distinguished in the uppermost part of the formation: the first indicates a middle-late Cenomanian age and the upper one is Santonian to Campanian in age. These marbles are unconformably covered by the

  10. Enhanced anatexis as a consequence of mantle-derived magma intrusion in the middle crust: a case study from the Eastern French Massif Central

    Science.gov (United States)

    Couzinié, Simon; Moyen, Jean-François; Villaros, Arnaud; Paquette, Jean-Louis; Scarrow, Jane H.; Marignac, Christian

    2014-05-01

    The post-collisional stage of orogens corresponds to a dramatic change in mountain belts dynamics. During this period, large volumes of granitic melts are generated in the crust thus impacting its rheology and overall behavior. Evolving from compression/transpression to extension/transtension enhances exhumation of high-grade metamorphic rocks and subsequent decompression crustal melting. However, other processes can trigger anatexis such as heat or fluid fluxes from the mantle and the crust. The Early Carboniferous nappe stack of the Eastern French Massif Central (EFMC) underwent two successive low-pressure melting events at the end of its evolution, during the Late Carboniferous. They are particularily evident in the southern edge of the Velay Complex, a 100 km-diameter migmatite-granite dome. The M3 'pre-Velay' event corresponds to water-saturated melting in the amphibolite facies at T source and few granite plutons were associated with this event. Contrarily, the M4 'Velay' anatexis occurred under granulite-facies conditions at 760 bearing migmatites are nebulitic to diatexitic as a consequence of biotite breakdown which led to disruption of the solid framework of melanosomes and enhanced melt extraction. This widespread melting event is synchronous with emplacement of the cordierite-bearing restite-rich S-type Velay granite at ca. 305 Ma. Then, the EFMC records an evolution in melting conditions with a clear heat input at the M3-M4 transition. The EFMC anatectic crust is intruded by widespread, Mg-K-rich biotite-rich diorites locally called 'vaugnerites'. These mantle-derived melts emplaced in a partially molten setting, as evidenced by mingling features between vaugnerites and anatectic melts, as well as the presence of hybrid granitoids including a 'vaugnerite' component. In situ (LA-ICP-MS) U-Pb zircon and monazite dating of vaugnerites or coeval granites in the Southern Velay area yielded ages mostly indistinguishable within analytical uncertainties

  11. Petrogenesis and tectonic implications of Permian post-collisional granitoids in the Chinese southwestern Tianshan, NW China

    Science.gov (United States)

    Xia, Bin; Zhang, Lifei; Zhang, Lu

    2016-11-01

    Permian porphyritic granite and leucogranite from the Kekesu and Muzhaerte Valleys in the southwestern (SW) Tianshan orogenic belt, NW China have been studied to decipher their petrogenesis and tectonic implications. For porphyritic granite in the Kekesu Valley, in situ LA-ICPMS zircon U-Pb dating yields crystallization ages of 295-291 Ma. The granite is a high potassic calc-alkaline, slightly peraluminous type, enriched in large ion lithosphere elements (LILE) and light rare earth elements (LREE), but depleted in high field strength elements (HFSE). Zircon Hf isotopic analysis (zircon εHf(t) of -5.8 to -0.2, two-stage Hf model ages of 1323-1680 Ma) and Ti-in-zircon thermometry, which yields crystallization temperatures of 744-749 °C, indicate the parent magma was likely formed by partial melting of a Mesoproterozoic crustal source. By contrast, leucogranite in the Kekesu valley yields crystallization ages of 274-267 Ma. It contains muscovite and garnet, has high silicon and potassium, and is strongly peraluminous. Multiple inherited zircon cores and low zircon crystallization temperatures (687-701 °C), combined with negative zircon εHf(t) values (-7.0 to -4.0), indicate its parent magma was sourced from supracrustal metasedimentary rocks by muscovite-breakdown partial melting. In the Muzhaerte Valley, porphyritic granite has similar major and trace elements characteristics to the Kekesu porphyritic granite. However, its higher zircon εHf(t) values (-0.9 to +3.8) and corresponding lower two-stage Hf model ages (1070-1367 Ma) indicate that the parent magma likely included an input from a more juvenile mantle source. Ti-in-zircon thermometry gives lower crystallization temperature of ∼705 °C. The intrusive relationships between the Permian granitoids and Paleozoic arc plutons, and the LP-HT and (U)HP metamorphic belts, combined with geochronological studies, suggest that these Permian granitoids were generated in a post-collisional environment. It is

  12. Age, petrogenesis and significance of 1 Ga granitoids and related rocks from the Sendra area, Aravalli Craton, NW India

    Science.gov (United States)

    Pandit, M. K.; Carter, L. M.; Ashwal, L. D.; Tucker, R. D.; Torsvik, T. H.; Jamtveit, B.; Bhushan, S. K.

    2003-12-01

    We present new geochronological, petrological, geochemical and isotopic data for granitic and related rocks from the Aravalli Craton, Rajasthan, northwestern India. In the Sendra area, five variably deformed granitoid plutons, ranging in composition from tonalite to granite, cut across carbonate-rich metasedimentary rocks of the Delhi Supergroup. The largest of these bodies, the Chang pluton (˜15 km 2) is dominated by monzogranitic gneisses and aplitic dykes, composed of subequal proportions of quartz, plagioclase (An 7-20) and microcline (Or 92-98), with lesser biotite (Fe ∗=0.8-0.9) and accessory muscovite (Fe ∗=0.7-0.8). U-Pb zircon data (TIMS method) for a biotite granite gneiss yield a weighted mean 207Pb/ 206Pb age of 967.8±1.2 Ma, which we interpret as representing the time of magmatic crystallization. Rb-Sr whole-rock isotopic data for the Chang pluton, including new analyses as well as previously published ones, yield a regression of 906±67 Ma (MSWD=82), which is barely within error of the U-Pb age. There is evidence for open-system behaviour in the Rb-Sr system, particularly for whole-rock samples with low Sr concentrations, and consequently high Rb/Sr. Sm-Nd isotopic data fail to yield meaningful age information. Initial isotopic ratios (at 968 Ma) for Chang pluton granitoids ( ISr=0.7110±14; ɛNd=-3.28±0.47) are compatible with source materials similar to Archaean amphibolitic rocks of the Banded Gneiss Complex. Spatially associated with the Chang pluton is a massive metagabbro, composed of plagioclase (An 45-68) and magnesio-hornblende (Fe ∗=0.3-0.4), with secondary Cl-rich scapolite and ferrian zoisite. The scapolite and zoisite likely crystallized from metamorphic fluids that interacted with nearby calc-silicate schists and gneisses of the Delhi Supergroup. Aside from slight enrichments in Rb, U, Th and Ba, this metagabbro retains a primitive chemical signature similar to N-MORB (LREE depletion, low K), and initial isotopic ratios ( ISr=0

  13. Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

    DEFF Research Database (Denmark)

    Javier Álvaro, J.; Colmenar Lallena, Jorge; Monceret, Eric

    2016-01-01

    Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded...

  14. Massification, Bureaucratization and Questing for "World-Class" Status: Higher Education in China since the Mid-1990s

    Science.gov (United States)

    Ngok, Kinglun

    2008-01-01

    Purpose: This article aims to review the latest developments of the higher education sector in China since the mid-1990s by focusing on the expansion of university education. Design/methodology/approach: It is argued that while massification of higher education is an important indication of the progress in China's higher education system, the…

  15. University Reform in the Post-Massification Era in Japan: Analysis of Government Education Policy for the 21st Century.

    Science.gov (United States)

    Reiko, Yamada

    2001-01-01

    Examines government higher education policy and Japanese higher education reform in the globalization and post-massification eras. Explores the effects of market mechanisms on Japanese higher education policy, the kinds of phenomena that have emerged in this period, and the impact of the government policy shift on Japanese higher education. (EV)

  16. Zircon U-Pb geochronology, geochemistry, and Sr-Nd-Hf isotopes of granitoids in the Yulekenhalasu copper ore district, northern Junggar, China: Petrogenesis and tectonic implications

    Science.gov (United States)

    Yang, Fuquan; Chai, Fengmei; Zhang, Zhixin; Geng, Xinxia; Li, Qiang

    2014-03-01

    The Yulekenhalasu porphyry copper deposit is located in the Kalaxiange'er metallogenic belt in northern Junggar, China. We present the results from zircon U-Pb geochronology, and geochemical and Sr-Nd-Hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting. The granitoids consist of quartz diorite, diorite porphyry, porphyritic monzonite, and quartz porphyry, emplaced at 382, 379, 375-374, and 348 Ma, respectively, which span Late Devonian to early Carboniferous ages. The ore-bearing intrusion is mainly diorite porphyry, with subordinate porphyritic monzonite. The Late Devonian intrusions are characterized by SiO2 contents of 54.5-64.79 wt.%, Na2O contents of 3.82-8.24 wt.%, enrichment in Na, light rare-earth elements (LREEs), and large ion lithophile elements. They also display relative depletion in Y, Ba, P, Nb, Ta, and Ti, and weak negative Eu anomalies (δEu = 0.6-0.87). The early Carboniferous quartz porphyry is characterized by high SiO2 content (72.26-73.35 wt.%), enrichment in LREEs, K, and Sr, and relative depletion in Y (10.82-12.52 ppm) and Yb (1.06-1.15 ppm). The Late Devonian and early Carboniferous granitoids are characterized by positive ɛNd(t) values (5.2-10.1, one sample at - 1.9), positive ɛHf(t) values (7.46-18.45), low (87Sr/86Sr)i values (0.70363-0.70476), and young crustal residence ages. These data indicate that the sources of the granitoids were mainly mantle-derived juvenile rocks. Geochemical and Nd-Sr-Hf isotopic data demonstrate that the Late Devonian granitoids formed in an oceanic island arc, and they were formed from different sources, among which the mineralized diorite porphyry might have originated from a mixed slab-derived and mantle wedge melt source. The early Carboniferous quartz porphyry was likely emplaced in a mature island arc environment, and was probably derived from juvenile crust.

  17. Transformation from Paleo-Asian Ocean closure to Paleo-Pacific subduction: New constraints from granitoids in the eastern Jilin-Heilongjiang Belt, NE China

    Science.gov (United States)

    Ma, Xing-Hua; Zhu, Wen-Ping; Zhou, Zhen-Hua; Qiao, Shi-Lei

    2017-08-01

    The eastern Jilin-Heilongjiang Belt (EJHB) of NE China is a unique orogen that underwent two stages of evolution within the tectonic regimes of the Paleo-Asian and Paleo-Pacific oceans. 158 available zircon U-Pb ages, including 26 ages obtained during the present study and 132 ages from the literature, were compiled and analyzed for the Mesozoic and Cenozoic granitoids from the EJHB and the adjacent Russian Sikhote-Alin Orogenic Belt (SAOB), to examine the temporal-spatial distribution of the granitoids and to constrain the tectonic evolution of the East Asian continental margin. Five stages of granitic magmatism can be identified: Early Triassic (251-240 Ma), Late Triassic (228-215 Ma), latest Triassic to Middle Jurassic (213-158 Ma), Early Cretaceous (131-105 Ma), and Late Cretaceous to Paleocene (95-56 Ma). The Early Triassic granitoids are restricted to the Yanbian region along the Changchun-Yanji Suture, and show geochemical characteristics of magmas from a thickened lower crust source, probably due to the final collision of the combined NE China blocks with the North China Craton. The Late Triassic granitoids, with features of A-type granites, represent post-collisional magmatic activities that were related to post-orogenic extension, marking the end of the tectonic evolution of the Paleo-Asian Ocean. The latest Triassic to Paleocene granitoids with calc-alkaline characteristics were NE-trending emplaced along the EJHB and SAOB and young towards the coastal region, and represent continental marginal arc magmas that were associated with the northwestwards subduction of the Paleo-Pacific Plate. Two periods of magmatic quiescence (158-131 and 105-95 Ma) correspond to changes in the subduction direction of the Paleo-Pacific Plate from oblique relative to the continental margin to subparallel. Taking all this into account, we conclude that: (1) the final closure of the Paleo-Asian Ocean occurred along the Changchun-Yanji Suture during the Early Triassic; (2) the

  18. Tracing magma sources of three different S-type peraluminous granitoid series by in situ U-Pb geochronology and Hf isotope zircon composition: The Variscan Montes de Toledo batholith (central Spain)

    Science.gov (United States)

    Merino Martínez, E.; Villaseca, C.; Orejana, D.; Pérez-Soba, C.; Belousova, E.; Andersen, T.

    2014-07-01

    Three distinct S-type peraluminous granitoid types have been identified within the Variscan Montes de Toledo batholith, located in the Central Iberian Zone (SW European Variscides): type-1, extremely high peraluminous restite-rich granitoids; type-2, highly peraluminous restite-bearing granitoids; and type-3, moderately peraluminous granitoids with mafic microgranular enclaves. Type-1 and type-2 granitoids are restricted to the western part of the batholith, whereas type-3 granites are mostly restricted to the eastern segment. There is a sequential youngering of emplacement age from type-1 (late-tectonic) to type-2 and type-3 granitoids (post-tectonic), extending the timing of the batholith formation for about 19 Ma between 316 and 297 Ma. Although the degree of peraluminousity of the different series could be related to different partial melting conditions or to the variable entrainment of restitic components (including the peritectic mineral assemblage of the melting reactions), whole-rock geochemical signatures and isotope zircon composition of the peraluminous granitoid types suggest contribution of different crustal sources. There is no evidence for the direct mantle-derived material contribution in the genesis of these peraluminous melts. Type-1 and type-2 granitoids contain mostly Archean to Neoproterozoic inherited zircons, whereas type-3 granites show preferentially Neoproterozoic (up to late Cryogenian) and Ordovician inheritance. The wide range of initial Hf isotope composition, ranging to highly radiogenic values (ƐHf up to + 10), of Neoproterozoic zircon inheritances in type-1 and type-2 granitoids suggests derivation from heterogeneous Neoproterozoic metasedimentary sources composed of both juveline and recycled crustal materials, similar in composition to the host Schist-Greywacke Complex metasediments. Trace-element modelling clearly suggests the involvement of metasediments similar to those mentioned from the southern part of the Central Iberian

  19. Natural radioactivity (226Ra, 232Th and 40K) and assessment of radiological hazards in the Kestanbol granitoid, Turkey.

    Science.gov (United States)

    Canbaz, Buket; Cam, N Füsun; Yaprak, Günseli; Candan, Osman

    2010-09-01

    The surveys of natural gamma-emitting radionuclides in rocks and soils from the Ezine plutonic area were conducted during 2007. Direct dose measurement using a survey meter was carried out simultaneously. The present study, which is part of the survey, analysed the activity concentrations of (238)U, (232)Th and (40)K in granitoid samples from all over the region by HPGe gamma spectrometry. The activity concentrations of (226)Ra ranged from 94 to 637 Bq kg(-1), those of (232)Th ranged from 120 to 601 Bq kg(-1)and those of (40)K ranged from 1074 to 1527 Bq kg(-1) in the analysed rock samples from different parts of the pluton. To evaluate the radiological hazard of the natural radioactivity in the samples, the absorbed dose rate (D), the annual effective dose rate, the radium equivalent activity (Ra(eq)) and the external (H(ex)) hazard index were calculated according to the UNSCEAR 2000 report. The thorium-to-uranium concentration ratios were also estimated.

  20. Oxygen and U-Th isotopes and the timescales of hydrothermal exchange and melting in granitoid wall rocks at Mount Mazama, Crater Lake, Oregon

    Science.gov (United States)

    Ankney, Meagan E.; Bacon, Charles R.; Valley, John W.; Beard, Brian L.; Johnson, Clark M.

    2017-09-01

    We report new whole rock U-Th and in-situ oxygen isotope compositions for partially melted (0-50 vol% melt), low-δ18O Pleistocene granitoid blocks ejected during the ∼7.7 ka caldera-forming eruption of Mt. Mazama (Crater Lake, Oregon). The blocks are interpreted to represent wall rocks of the climactic magma chamber that, prior to eruption, experienced variable amounts of exchange with meteoric hydrothermal fluids and subsequent partial melting. U-Th and oxygen isotope results allow us to examine the timescales of hydrothermal circulation and partial melting, and provide an ;outside in; perspective on the buildup to the climactic eruption of Mt. Mazama. Oxygen isotope compositions measured in the cores and rims of individual quartz (n = 126) and plagioclase (n = 91) crystals, and for transects across ten quartz crystals, document zonation in quartz (Δ18OCore-Rim ≤ 0.1-5.5‰), but show homogeneity in plagioclase (Δ18OCore-Rim ≤ ±0.8‰). We propose that oxygen isotope zonation in quartz records hydrothermal exchange followed by high-temperature exchange in response to partial melting caused by injection of basaltic to andesitic recharge magma into the deeper portions of the chamber. Results of modeling of oxygen diffusion in quartz indicates that hydrothermal exchange in quartz occurred over a period of ∼1000-63,000 years. Models also suggest that the onset of melting of the granitoids occurred a minimum of ∼10-200 years prior to the Mazama climactic eruption, an inference which is broadly consistent with results for magnetite homogenization and for Zr diffusion in melt previously reported by others. Uranium-thorium isotope compositions of most granitoid blocks are in 238U excess, and are in agreement with a 238U enriched array previously measured for volcanic rocks at Mt. Mazama. Uranium excess in the granitoids is likely due to enrichment via hydrothermal circulation, given their low δ18O values. The sample with the highest U excess (≥5.8%) also

  1. The Triassic reworking of the Yunkai massif (South China): EMP monazite and U-Pb zircon geochronologic evidence

    Science.gov (United States)

    Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Sano, Yuji; Zhou, Han-Wen; Xiang, Hua; Takahata, Naoto

    2017-01-01

    Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244-236 Ma and 236-233 Ma, respectively. They also yield ages of 233-230 Ma for core domain gneissic granites and 232-229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, 245 Ma and 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0-0.9 Ga) and Early Paleozoic (444-431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP).

  2. Cambrian to Lower Ordovician complexes of the Kokchetav Massif and its fringing (Northern Kazakhstan): Structure, age, and tectonic settings

    Science.gov (United States)

    Degtyarev, K. E.; Tolmacheva, T. Yu.; Tretyakov, A. A.; Kotov, A. B.; Shatagin, K. N.

    2016-01-01

    A comprehensive study of the Lower Palaeozoic complexes of the Kokchetav Massif and its fringing has been carried out. It has allowed for the first time to discover and investigate in detail the stratified and intrusive complexes of the Cambrian-Early Ordovician. Fossil findings and isotope geochronology permitted the determination of their ages. The tectonic position and internal structures of those complexes have also been defined and their chemical features have been analyzed as well. The obtained data allowed us to put forward a model of the geodynamic evolution of Northern Kazakhstan in the Late Ediacaran-Earliest Ordovician. The accumulation of the oldest Ediacaran to Earliest Cambrian siliciclastics and carbonates confined to the Kokchetav Massif and its fringing occurred in a shallow shelf environment prior to its collision with the Neoproterozoic Daut island arc: complexes of the latter have been found in the northeast of the studied area. The Early Cambrian subduction of the Kokchetav Massif under the Daut island arc, their following collision and exhumation of HP complexes led to the formation of rugged ground topography, promoting deposition of siliceous-clastic and coarse clastic units during the Middle to early Late Cambrian. Those sediments were mainly sourced from eroded metamorphic complexes of the Kokchetav Massif basement. At the end of the Late Cambrian to the Early Ordovician within the boundaries of the massif with the Precambrian crust, volcanogenic and volcano-sedimentary units along with gabbros and granites with intraplate affinities were formed. Simultaneously in the surrounding zones, which represent relics of basins with oceanic crust, N-MORB- and E-MORB-type ophiolites were developed. These complexes originated under extensional settings occurred in the majority of the Caledonides of Kazakhstan and Northern Tian Shan. In the Early Floian Stage (Early Ordovician) older heterogeneous complexes were overlain by relatively monotonous

  3. Remains of early Ordovician mantle-derived magmatism in the Santander Massif (Colombian Eastern Cordillera)

    Science.gov (United States)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Cottle, John M.; Hart, Craig J. R.

    2012-10-01

    An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛHft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth's mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure.

  4. Physical-Chemical Factors Affecting the Low Quality of Natural Water in the Khibiny Massif

    Science.gov (United States)

    Mazukhina, Svetlana; Masloboev, Vladimir; Chudnenko, Konstantin; Maksimova, Viktoriia; Belkina, Natalia

    2014-05-01

    One peculiarity of the Khibiny Massif is its spatial location. Rising over 1000 m above the surrounding hilly land and thus obstructing the passage of air masses, it promotes condensation and accumulation of surface and underground water. Annual precipitation here amounts to 600-700 mm in the valleys and up to 1600 mm on mountainous plateaus. Using this water for drinking and household purposes is problematic due to excess Al and F concentrations and high pH values. Now it is known that in its profile, the Massif is represented by three hydrogeological subzones: the upper (aerated), medium and lower ones. The upper subzone spreads throughout the Massif and is affected by the local drainage network and climatic conditions. The medium subzone is permanently saturated with underground water flowing horizontally to sites of discharge at the level of local river valleys and lakes. The fissure-vein water in the lower subzone is confined to tectonic fractures and faults in the so far underexplored, deeper parts of the Massif. Being abundant, this water ascends under high pressure. At places, water has been observed spurting from as deep as 700 m, and even 960 m. In the latter case, the temperature of ascending water was higher than 18 centigrade (Hydrogeology of the USSR, V. 27, 1971). This work was undertaken to reveal the nature of the low quality of water in the Khibiny by using physical-chemical modeling (software package Selector, Chudnenko, 2010). Processes of surface and underground water formation in the Khibiny were examined within a physical-chemical model (PCM) of the "water-rock-atmosphere-hydrogen" system. In a multi-vessel model used, each vessel represented a geochemical level of the process interpreted as spatiotemporal data - ξ (Karpov, 1981). The flow reactor consisted of 4 tanks. In the first tank, water of the Kuniok River (1000 L) interacted with atmosphere and an organic substance. The resulting solution proceeded to tanks 2-4 containing with

  5. Mass-balance modelling of Ak-Shyirak massif Glaciers, Inner Tian Shan

    Science.gov (United States)

    Rets, Ekaterina; Barandun, Martina; Belozerov, Egor; Petrakov, Dmitry; Shpuntova, Alena

    2017-04-01

    Tian Shan is a water tower of Central Asia. Rapid and accelerating glacier downwasting is typical for this region. Study sites - Sary-Tor glacier and Glacier No.354 are located in Ak-Shyirak massif, Naryn headwaters. Sary-Tor was chosen as representative for Ak-Shyirak (Ushnurtsev, 1991; Oledeneniye TianShanya, 1995) for direct mass-balance measurements in 1985-1991. Glacier No.354 was an object of direct mass-balance measurements for 2011-2016. An energy-balance distributed A-Melt model (Rets et al, 2010) was used to reconstruct mass-balance for the glaciers for 2003-2015. Verification of modelingresults showed a good reproduction of direct melting measurements data on ablation stakes and mass loss according to geodetic method. Modeling results for Glacier No. 354 were compared to different modeling approach: distributed accumulation and temperature-index melt (Kronenberg et al, 2016)

  6. Application of GIS technologies to monitor secondary radioactive contamination in the Delegen mountain massif

    Science.gov (United States)

    Alipbeki, O.; Kabzhanova, G.; Kurmanova, G.; Alipbekova, Ch.

    2016-06-01

    The territory of the Degelen mountain massif is located within territory of the former Semipalatinsk nuclear test site and it is an area of ecological disaster. Currently there is a process of secondary radioactive contamination that is caused by geodynamic processes activated at the Degelen array, violation of underground hydrological cycles and as a consequence, water seepage into the tunnels. One of the methods of monitoring of geodynamic processes is the modern technology of geographic information systems (GIS), methods of satellite radar interferometry and high accuracy satellite navigation system in conjunction with radioecological methods. This paper discusses on the creation of a GIS-project for the Degelen array, facilitated by quality geospatial analysis of the situation and simulation of the phenomena, in order to maximize an objective assessment of the radiation situation in this protected area.

  7. Spatial coincidence of rapid inferred erosion with young metamorphic massifs in the Himalayas

    Science.gov (United States)

    Finlayson, David P.; Montgomery, David R.; Hallet, Bernard

    2002-03-01

    A spatially distributed rate-of-erosion index (EI) based on models of bedrock river incision documents a strong spatial correspondence between areas of high erosion potential and young metamorphic massifs as well as structural highs throughout the Himalayas. The EI is derived from slopes and drainage areas calculated from a hydrologically corrected digital elevation model (GTOPO30) combined with precipitation data (IIASA) to generate synthetic annual stream discharges. These variables drive three generalized process models to produce EI maps that, while differing in detail, provide an internally consistent, spatially continuous index of large-scale erosion rates. The large spatial variation in potential erosion rates in the Himalayas suggested by the EI patterns contrasts with the uniform convergence of the Indian subcontinent. If these EI gradients persist through time, they support the emerging view of a positive feedback between localized, rapid erosion and upward advection of lower crust.

  8. Acidification des eaux de source et saturnisme dans le Massif vosgien.

    OpenAIRE

    1999-01-01

    Les recherches menées à  l'occasion du programme DEFORPA ont montré que les dépôts acides et la sylviculture avaient directement contribué à une acidification des sols et des eaux de surface du Massif vosgien. L'étude de la variation de l'acidité des eaux de source depuis 30 ans a confirmé une acidification progressive de l'eau captée sur les roches les plus pauvres, comme le grès vosgien. Nous avons expérimentalement vérifié que cette acidification a considérablement augmenté la teneur en pl...

  9. The topographic signature of Quaternary tectonic uplift in the Ardennes massif (Western Europe

    Directory of Open Access Journals (Sweden)

    N. Sougnez

    2011-04-01

    Full Text Available Geomorphic processes that produce and transport sediment, and incise river valleys are complex; and often difficult to quantify over longer timescales of 103 to 105 y. Morphometric indices that describe the topography of hill slopes, valleys and river channels have commonly been used to compare morphological characteristics between catchments and to relate them to hydrological and erosion processes. This study aims to analyze the link between tectonic uplift rates and landscape morphology based on slope and channel morphometric indexes. To achieve this objective, we selected 10 catchments of about 150 to 250 km2 across the Ardennes Massif (a Palaeozoic massif of NW Europe, principally located in Belgium that cover various tectonic domains with uplift rates ranging from about 0.06 to 0.20 mm yr−1 since mid-Pleistocene times. The morphometric analysis indicates that the slope and channel morphology of third-order catchments is not yet in topographic steady-state, and exhibits clear convexities in slope and river profiles. Our analysis indicates that the fluvial system is the main driver of topographic evolution and that the spatial pattern of uplift rates is reflected in the distribution of channel steepness and convexity. The spatial variation that we observe in slope and channel morphology between the 10 third-order catchments suggests that the response of the fluvial system was strongly diachronic, and that a transient signal of adjustment is migrating from the Meuse valley towards the Ardennian headwaters.

  10. Cancrinite from nepheline syenite (mariupolite) of the Oktiabrski massif, SE Ukraine, and its growth history

    Science.gov (United States)

    Dumańska-Słowik, Magdalena; Pieczka, Adam; Heflik, Wiesław; Sikorska, Magdalena

    2016-03-01

    Secondary cancrinite, (Na5.88K< 0.01)∑ 5.88(Ca0.62 Fe0.01Mn0.01Zn< 0.01 Mg< 0.01)∑ 0.64[Si6.44Al 5.56O24](CO3)0.67(OH)0.26(F< 0.01,Cl< 0.01)·2.04H2O), was found as accessory component of mariupolite (albite-aegirine nepheline syenite) from the Oktiabrski massif in the Donbass (SE Ukraine). It probably crystallized from a subsolidus reaction involving nepheline (and sodalite?) and calcite dissolved in the aqueous-carbonic fluid at the maximum temperature of 930 °C, decreasing to hydrothermal conditions. It is depleted in sodium, calcium and carbon, what results in the occurrence of vacant positions at both cationic and anionic sites. Ca-deficient cancrinite crystallized from the same hydrothermal Si-undersaturated fluids enriched in the ions such as Na+, Ca2 +, Cl-, F-, HCO3-, which formed calcite, sodalite, natrolite and fluorite. It has dark-red CL colours with patchy zoning, what indicates the variable/diverse fluid composition during its formation. In the CL spectrum of cancrinite only one broad emission band at 410 nm is observed, which can be attributed to O* center (the recombination of a free electron with an O- hole center). The formation of secondary CO3-rich species, i.e. cancrinite and calcite in mariupolite suggests that redox conditions in the Oktiabrski massif were oxidizing at the postmagmatic stage.

  11. The Gondwana Orogeny in northern North Patagonian Massif: Evidences from the Caita Có granite, La Seña and Pangaré mylonites, Argentina

    Directory of Open Access Journals (Sweden)

    Daniel A. Gregori

    2016-07-01

    Full Text Available Structural analyses in the northern part of the North Patagonia Massif, in the foliated Caita Có granite and in La Seña and Pangaré mylonites, indicate that the pluton was intruded as a sheet-like body into an opening pull-apart structure during the Gondwana Orogeny. Geochronological studies in the massif indicate a first, lower to middle Permian stage of regional deformation, related to movements during indentation tectonics, with emplacement of foliated granites in the western and central areas of the North Patagonian Massif. Between the upper Permian and lower Triassic, evidence indicates emplacement of undeformed granitic bodies in the central part of the North Patagonian Massif. A second pulse of deformation between the middle and upper Triassic is related to the emplacement of the Caita Có granite, the development of mylonitic belts, and the opening of the Los Menucos Basin. During this pulse of deformation, compression direction was from the eastern quadrant.

  12. U-Pb zircon geochronology, Sr-Nd isotope geochemistry, and petrogenesis of oxidant granitoids at Keybarkuh, southwest of Khaf

    Directory of Open Access Journals (Sweden)

    Ehsan Salati

    2012-10-01

    Full Text Available Keybarkuh area is located 70 km southwest of Khaf, Khorasan Razavi province. The study area is situated in northeastern Lut block. The rock units in the area are Paleozoic metamorphic rocks and Cretaceous to Tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. Based on magnetic susceptibility, the intrusive rocks are divided into oxidant and reduced series. In this study, the oxidant intrusions are discussed. These intrusions are mostly high-K to shoshonitic and also meta-aluminous type. Their magma formed in subduction magmatic arc and they belong to I-type granitoid series. Enrichment of Large Ion Lithophile Elements (LILE such as Rb, Cs, K, Ba, and Th relative to High Field Stength Elements (HFSE such as Nb, Zr, and Ti supported the idea. Enrichment of Light Rare Earth Elements (LREE and depletion of Heavy Rare Earth Elements (HREE are also typical of subduction magmatism. Negative anomalies of Eu/Eu* can be attributed to the presence of residual plagioclase in a mantle source and contamination of magma by reduced continental crust. The amount of Nb > 11 ppm, lower ratio of Zr/Nb 0.706, initial 143Nd/144Nd (> 0.512 and εNd (< -3.5 indicate that magma contaminated by reduced continental crust. Hornblende biotite granodiorite porphyry dated using U-Pb zircon geochronology at 43.44 Ma (Middle Eocene. Based on calculated TDM, magma derived from ancient slab with 820 Ma age in the Keybarkuh area, was affected by the highest continental crust contamination during its ascent.

  13. Petrogenesis of post-collisional A-type granitoids from the Urumieh-Dokhtar magmatic assemblage, Southwestern Kerman, Iran: Constraints on the Arabian-Eurasian continental collision

    Science.gov (United States)

    Dargahi, Sara; Arvin, Mohsen; Pan, Yuanming; Babaei, Abbed

    2010-03-01

    Three plutons (Deh-Siahan, Bande-Bagh and Baghe-Khoshk Sharghi, collectively referred to as the DBB hereafter) in southwestern Kerman, in the southeastern part of the Urumieh-Dokhtar magmatic assemblage (UDMA) of the Zagros orogenic belt differ from the typical calc-alkaline metaluminous, I-type intrusions of the region. The DBB intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite. The DBB granitoids are metaluminous to slightly peraluminous, alkaline to shoshonitic in composition and have high total alkali contents with K 2O > Na 2O, high FeO T/MgO values, and low CaO and MgO contents. They are enriched in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y and REEs except Eu) and depleted in Sr and Ba relative to primordial mantle, and have low concentrations of transitional metals. These features along with various geochemical discriminant diagrams suggest that the DBB granitoids are post-collisional A-type granitoids, which had not been recognized previously in the UDMA. The chondrite-normalized REE patterns of the DBB granitoids show slightly enriched light REEs [(La/Sm) N = 2.26-4.13], negative Eu anomalies [(Eu/Eu*) N = 0.19-0.74] and flat heavy REE patterns [(Gd/Yb) N = 0.80-1.87]. The negative Eu anomaly indicates an important role for plagioclase and/or K-feldspar during fractional crystallization. Whole-rock Rb-Sr isotope analysis yields an isochron age of 33 ± 1 Ma with an initial 87Sr/ 86Sr value of 0.7049 ± 0.0001. Whole-rock Sm-Nd isotope analysis gives ɛNdt values from + 2.56 to + 3.62 at 33 Ma. The positive ɛNdt and low ISr values of the DBB granitoids together with their TDM of 0.6-0.7 Ga suggest their formation from partial melting of a lithospheric mantle source, modified by fluids or melts from earlier subduction processes. Melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability

  14. 关于花岗岩类形成作用概念的讨论%A discussion on the conception of the forming process of granitoid

    Institute of Scientific and Technical Information of China (English)

    刘家远

    2001-01-01

    On the basis of a large number of actual data of a series of characteristics of the forming process of granitoids of different ages associated with endogenic metallogenesis in Jiangxi and the Nanling region,the forming process of granitoid and the perfect course of its ore-forming continuous evolution have been expounded and proved.On this basis,the perfect conception of the forming process of modern granitoids including magmatic genration, magmatism and petrogenesis, and magmatic hydrothermalism and metallogenesis has been suggested.Above-mentioned three parts belong to different stages of development and evolution of the same process.The process of magmatic generation (namely migmatization and granitization)is the first step of undergoing formation of all granitoids.However only,some granites formed in the early period of geological history or the specified tectonic environment(synorogenesis and syncollision) can preserve characte-ristics of migmatization and granitization in some degree.Magmatic hydrothermalism and metallogenesis are the highest stage of the development of the formation of granitoids,but the developmental stage is not of all granitoids.Gegerally,some granites formed in the late stage of geological history or the specified tectonic environment(mainly late-orogenesis and post-orogenesis) should develop magmatic hydrothemalism and metallogenesis in some degree. The ore-forming granites of the specified ages occur within different rigions and different orogenic belts.%以江西及南岭地区不同时代花岗岩类形成过程的一系列特征及其与内生金属成矿作用的关系等方面大量的实际资料为依据,论证了花岗岩类形成作用及其成矿连续演化的完整过程;进而提出现代花岗岩类形成作用的完整概念包括岩浆的发生,岩浆的作用与成岩,以及岩浆热液的活动与成矿三个部分。三者属同一作用过程发展演化的不同阶段。岩浆的发生过

  15. Typologie des aquifères du cristallin: exemple des massifs des Aiguilles rouges et du Mont-blanc (France, Italie et Suisse)

    OpenAIRE

    Dubois, Jean-Daniel; Gabus, Jacques-Henri

    2008-01-01

    This hydrogeological study of the crystalline aquifers of the Mont-Blanc and the Aiguilles Rouges massifs is part of the AQUITYP project, which has been carried out at the Geology Laboratory of the Swiss Federal Institute of Technology, Lausanne (GEOLEP). This study has encompassed the observation, sampling and systematic chemical analysis of more than 160 surface and groundwaters. Many of the springs are located within the numerous galleries and tunnels which cut the crystalline massifs of t...

  16. Petrological mineralogical and geochemical characterization of the granitoids and fracture fillings developed in Ratones Mines (Spain); Caracterizacion petrologica, mineralogica, geoquimica y evaluacion del comportamiento geoquimico de las REE en la fase solida (granitoides y rellenos fisurales) del sistema de interaccion agua-roca delentorno de la Mina Ratones

    Energy Technology Data Exchange (ETDEWEB)

    Buil Gutierrez, B. [Ciemat. Madrid (Spain)

    2002-07-01

    The petrological, mineralogical and geochemical characterisation of the granitoids and fracture fillings developed in the Ratones Mine (Caceres, Spain) has been done in order to understand rock-water interaction processes which control water geochemical parameters. Special interest has been devoted to the analysis and interpretation of REE patterns in the solid phase (granitoids and fracture fillings) because they constitute geochemical tracers in water-rock interaction process. Moreover, REE are considered as actinide analogues. In order to characterise the solid phase (granitoids and fracture fillings) several investigation scales (system, outcrop, whole rock, mineral and geochemical components) have been considered and different types of samples have been analysed. These factors control the methodological approach used in this investigation. The analytical methods we have used in this investigation are microscope, qualitative and semi-quantitative methods (XRD, SEM,EDAX) and quantitative methods (ICP-MS, XRF, EM, LAM-IC-MS). The bulk of the granitoids located around the Ratones Mine Belongs to the alkaline feldspar granite-sienogranite lihotype and they show a peraluminous and subalkaline pattern. From the mineralogical point of view, they are composed by quartz, K-feldspar (Or>90%), showing sericitation, moscovitization and turmolinization altherations, alkaline plagioclase (An-=-3%), usually altered to sericite, saussirite and less frequently affected by moscovitization processes, Fe-Al biotite, frequently affected by chloritization processes and sometimes replaced by muscovite, and finally muscovite (>2% celadonite and <4% paragonite) both of primary and secondary origin. The differences observed between the different lithotypes are related with the modal proportion of the principal minerals,with the presence or absence of certain accessory minerals ( turmaline, cordierite), with specific textural patterns, grain size and also with the richness in specific

  17. U-Pb zircon geochronology, petrochemical and Sr-Nd isotopic characteristic of Late Neoproterozoic granitoid of the Bornaward Complex (Bardaskan-NE Iran)

    Science.gov (United States)

    Bagherzadeh, R. Monazzami; Karimpour, M. H.; Farmer, G. Lang; Stern, C. R.; Santos, J. F.; Rahimi, B.; Heidarian Shahri, M. R.

    2015-11-01

    The Bornaward Granitoid Complex (BGC) in the Taknar Zone is located in the northeast of Central Iranian Block. The BGC consists of granite, alkaligranite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite and diorite that have intruded into the center of Taknar Zone. These intrusive rocks affected by low grade metamorphism. Because of there are no reliable isotope dating data, for the Bornaward Granitoid Complex rocks have been proposed discordant ages (Jurassic, Cretaceous or even younger ages) by many studies. In the present study, new isotopic information based on zircon U-Pb dating has revealed the origin and time of the formation of the BGC. These new results do not confirm previously proposed ages. The results obtained from zircon U-Pb dating of the BGC rocks suggest late-Neoproterozoic (Precambrian) age (540-550 Ma). The Bornaward Granitoid Complex is middle-high metaluminous to lower-middle peraluminous and belongs to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichment in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REE) plots indicate minor enrichment of LREE compared to HREE, and strong negative anomaly of Eu compared to other Rare Earth Elements. Furthermore, initial 87Sr/86Sr and 143Nd/144Nd range from 0.70351 to 0.71689 and 0.511585 to 0.512061, respectively, and initial εNd isotope values for granite, granodiorite and diorite range from -6.73 to 2.52. These all indicate that the BGC has derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr and undergoing extensive crustal contamination (S-type granite).

  18. A linear Hf isotope-age array despite different granitoid sources and complex Archean geodynamics: Example from the Pietersburg block (South Africa)

    Science.gov (United States)

    Laurent, Oscar; Zeh, Armin

    2015-11-01

    Combined U-Pb and Lu-Hf isotope data from zircon populations are widely used to constrain Hadean-Archean crustal evolution. Linear Hf isotope-age arrays are interpreted to reflect the protracted, internal reworking of crust derived from the (depleted) mantle during a short-lived magmatic event, and related 176Lu/177Hf ratios are used to constrain the composition of the reworked crustal reservoir. Results of this study, however, indicate that Hf isotope-age arrays can also result from complex geodynamic processes and crust-mantle interactions, as shown by U-Pb and Lu-Hf isotope analyses of zircons from well characterized granitoids of the Pietersburg Block (PB), northern Kaapvaal Craton (South Africa). Apart from scarce remnants of Paleoarchean crust, most granitoids of the PB with ages between 2.94 and 2.05 Ga (n = 32) define a straight Hf isotope-age array with low 176Lu/177Hf of 0.0022, although they show a wide compositional range, were derived from various sources and emplaced successively in different geodynamic settings. The crustal evolution occurred in five stages: (I) predominately mafic crust formation in an intra-oceanic environment (3.4-3.0 Ga); (II) voluminous TTG crust formation in an early accretionary orogen (3.0-2.92 Ga); (III) internal TTG crust reworking and subduction of TTG-derived sediments in an Andean-type setting (2.89-2.75 Ga); (IV) (post-)collisional high-K magmatism from both mantle and crustal sources (2.71-2.67 Ga); and (V) alkaline magmatism in an intra-cratonic environment (2.05-2.03 Ga). The inferred array results from voluminous TTG crust formation during stage II, and involvement of this crust during all subsequent stages by two different processes: (i) internal crust reworking through both partial melting and assimilation at 2.89-2.75 Ga, leading to the formation of biotite granites coeval with minor TTGs, and (ii) subduction of TTG-derived sediments underneath the PB, causing enrichment of the mantle that subsequently became

  19. The Borodinskii Massif of potassium porphyric granite: Results of U-Pb dating and its tectonic position (Fennoscandian Shield)

    Science.gov (United States)

    Baltybaev, Sh. K.; Rizvanova, N. G.; Glebovitsky, V. A.

    2016-09-01

    It has been demonstrated for the first time that the Svecofennian crustal porphyric granites in the southeastern part of the Fennoscandian Shield are clearly subdivided into two age groups of 1.87 and 1.80 Ga. The representative of the first group is the Kuznechenskii Massif of porphyric granites with a U-Pb age of 1874 ± 4 Ma belongs to the group of plutons formed during the orogenic stage of Svecofennide evolution. The Borodinskii Massif with an age of 1797 ± 2 Ma is a member of the second group: these plutons were formed under tectonically stable (epiplatform) conditions. Therefore, the formation of porphyric granites occurred as the result of repeated generation of crustal magmas during multistage accretional growth of the Svecofennian crust.

  20. Solid Inclusions in Au-nuggets, genesis and derivation from alkaline rocks of the Guli Massif, Northern Siberia

    Directory of Open Access Journals (Sweden)

    Dvorani Sami N.

    2016-04-01

    Full Text Available A total of 112 Au-nuggets, collected from alluvial placer deposits of the Ingarinda River from the Guli massif, located in northem Siberia, Russia, were investigated. The Guli massif consists of a huge dunite-clinopyroxenite complex (the largest complex in the world, an alkaline to highly alkaline rock suite (melilite, nephelinite, ijolite enveloping the dunite and carbonatite intrusions, associated with disseminated schlieren type chromitite and Au-Ag, Pt placer deposits. The nuggets are characterized by various sizes and shapes and show chemical compositions Au, Au-Ag and AuCu, typical for a derivate of carbon-atites and/or ultramafic complexes. A great variety of oxide, silicate, REE-minerals, carbonate and sulphide inclusions have been detected in the nuggets, which are identical in mineralogy and chemical composition to mineral constituents of the alkaline to highly alkaline rock suite surrounding the Guli dunite core complex thus, considered as the source for Au-nuggets.

  1. A MASSIF Effort To Determine The Mass-Luminosity Relation for Stars of Various Ages, Metallicities, and Evolution States

    Science.gov (United States)

    Henry, Todd J.; Beedict, G. Fritz; Gies, Douglas R.; Golimowski, David A.; Ianna, Philip A.; Mason, Brian; McArthur, Barbara; Nelan, Edmund; Torres, Guillermo

    2004-01-01

    The MASSIF (Masses and Stellar Systems with Interferometry) Team will use SIM to investigate the mass content of the Galaxy - from huge stars to barely glimmering brown dwarfs, and from hot white dwarfs to exotic black holes. We will target various samples of the Galactic population to determine and relate the fundamental characteristics of mass, luminosity, age, composition, and multiplicity - attributes that together yield an extensive understanding of the stars. Our samples will include distant clusters that span a factor of 5000 in age, and commonplace stars and substellar objects that lurk near the Sun. The principal goals of the MASSIF Key Project are to (1) define the mass-luminosity relation for main sequence stars in five fundamental clusters so that effects of age and metallicity can be mapped (Trapezium, TW Hydrae, Pleiades, Hyades, and M67), and (2) determine accurate masses for representative examples of nearly every type of star, stellar descendant or brown dwarf in the Galaxy.

  2. Theoretical relation between water flow rate in a vertical fracture and rock temperature in the surrounding massif

    CERN Document Server

    Maréchal, Jean-Christophe

    2010-01-01

    A steady-state analytical solution is given describing the temperature distribution in a homogeneous massif perturbed by cold water flow through a discrete vertical fracture. A relation is derived to express the flow rate in the fracture as a function of the temperature measured in the surrounding rock. These mathematical results can be useful for tunnel drilling as it approaches a vertical cold water bearing structure that induces a thermal anomaly in the surrounding massif. During the tunnel drilling, by monitoring this anomaly along the tunnel axis one can quantify the flow rate in the discontinuity ahead before intersecting the fracture. The cases of the Simplon, Mont Blanc and Gotthard tunnels (Alps) are handled with this approach which shows very good agreement between observed temperatures and the theoretical trend. The flow rates before drilling of the tunnel predicted with the theoretical solution are similar in the Mont Blanc and Simplon cases, as well as the flow rates observed during the drilling....

  3. Initial subduction of the Paleo-Pacific Oceanic plate in NE China: Constraints from whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes of the Khanka Lake granitoids

    Science.gov (United States)

    Liu, Kai; Zhang, Jinjiang; Wilde, Simon A.; Zhou, Jianbo; Wang, Meng; Ge, Maohui; Wang, Jiamin; Ling, Yiyun

    2017-03-01

    Northeast China is located in the eastern part of the Central Asian Orogenic Belt (CAOB) and was influenced by Paleo-Pacific subduction during the Mesozoic. Abundant granitoids from the late Paleozoic to early Mesozoic in NE China record this process, including the Khanka Lake granitoids, which resulted in extensive growth of continental crust in the area. However, the question of how and when the Paleo-Pacific tectonic system began to affect NE China is still highly controversial. The Khanka Lake granitoids can be subdivided into two main components based on their geochemical characteristics, namely granodiorite and syenogranite. The granodiorite has a U-Pb age of 249 Ma and is adakite-like (enriched in LREE and LILEs with high Mg#, Sr, La/Yb, Sr/Y and Na2O/K2O), with zircon εHf(t) values of - 0.65 to 1.61, produced by the magma mixing between melting of the lower continental crust and juvenile basaltic magma. The syenogranite has zircon U-Pb ages of 209 to 199 Ma and geochemical features of highly fractionated I-type granites, with high SiO2, total alkalis and low Mg (and Mg#), Fe, Cr and Ni, and positive zircon εHf(t) of 1.72 to 5.12, indicating an origin from remelting of juvenile crust. The granitoids were intruded by felsic veins between 195 and 184 Ma with positive zircon εHf(t) from 0.57 to 5.32. The εHf(t) values of the granitoids become more positive as the zircon U-Pb ages become younger, suggesting continuous melting of juvenile crust during subduction. It is concluded that the Khanka Lake granitoids record the early stage of subduction of the Paleo-Pacific Oceanic plate, which commenced at least ca. 250 Ma ago.

  4. The Galicia-Ossa-Morena Zone: Proposal for a new zone of the Iberian Massif. Variscan implications

    Science.gov (United States)

    Arenas, Ricardo; Díez Fernández, Rubén; Rubio Pascual, Francisco J.; Sánchez Martínez, Sonia; Martín Parra, Luis Miguel; Matas, Jerónimo; González del Tánago, José; Jiménez-Díaz, Alberto; Fuenlabrada, Jose M.; Andonaegui, Pilar; Garcia-Casco, Antonio

    2016-06-01

    Correlation of a group of allochthonous terranes (referred to as basal, ophiolitic and upper units) exposed in the NW and SW of the Iberian Massif, is used to propose a new geotectonic zone in the southern branch of the Variscan Orogen: the Galicia-Ossa-Morena Zone. Recent advances in SW Iberia identify most of the former Ossa-Morena Zone as another allochthonous complex of the Iberian Massif, the Ossa-Morena Complex, equivalent to the Cabo Ortegal, Órdenes, Malpica-Tui, Bragança and Morais complexes described in NW Iberia. The new geotectonic zone and its counterparts along the rest of the Variscan Orogen constitute an Internal Variscan Zone with ophiolites and units affected by high-P metamorphism. The Galicia-Ossa-Morena Zone includes a Variscan suture and pieces of continental crust bearing the imprint of Ediacaran-Cambrian events related to the activity of peri-Gondwanan magmatic arcs (Cadomian orogenesis). In the Iberian Massif, the general structure of this geotectonic zone represents a duplication of the Gondwanan platform, the outboard sections being juxtaposed on top of domains located closer to the mainland before amalgamation. This interpretation offers an explanation that overcomes some issues regarding the differences between the stratigraphic and paleontological record of the central and southern sections of the Iberian Massif. Also, equivalent structural relationships between other major geotectonic domains of the rest of the Variscan Orogen are consistent with our interpretation and allow suspecting similar configurations along strike of the orogen. A number of issues may be put forward in this respect that potentially open new lines of thinking about the architecture of the Variscan Orogen.

  5. Discovery of Ordovician–Silurian metamorphic monazite in garnet metapelites of the Alpine External Aiguilles Rouges Massif

    OpenAIRE

    Schulz, Bernhard; Raumer, Jürgen F. von

    2011-01-01

    The pre-Mesozoic, mainly Variscan metamorphic basement of the Col de Bérard area (Aiguilles Rouges Massif, External domain) consists of paragneisses and micaschists together with various orthogneisses and metabasites. Monazite in metapelites was analysed by the electron microprobe (EMPA-CHIME) age dating method. The monazites in garnet micaschists are dominantly of Variscan age (330–300 Ma). Garnet in these rocks displays well developed growth zonations in Fe–Mg–Ca–Mn and crystallized at maxi...

  6. A new interpretation for the garnet zoning in metapelitic rocks of the silgará formation, southwestern santander massif, colombia

    OpenAIRE

    Ríos Reyes Carlos Alberto; Castellanos Alarcón Oscar Mauricio; Takasu Akira

    2011-01-01

    A Barrovian sequence of the Silgará Formation at the southwestern Santander Massif, Colombian Andes, contains zoned garnets in which major and trace element zoning correlates with distribution of mineral inclusions, which may indicate that garnet growth rate varied through time and affected both composition and texture ofgarnets, although different garnet producing reactions have also played an important role in the chemical zoning of garent. However, a local metasomatism process associated t...

  7. Scorpions from the Mitaraka Massif in French Guiana: Description of one new genus and species (Scorpiones: Chactidae).

    Science.gov (United States)

    Lourenço, Wilson R

    2016-01-01

    A new genus and species, Spinochactas mitaraka gen. n., sp. n. (Chactidae) are described from the Mitaraka Massif in French Guiana, a site located near the borders of French Guiana, Brazil, and Suriname. The description of the new genus and species brings further evidence of the biogeographic pattern of distribution presented by some elements of the family Chactidae endemic to the Tepuys or to the Inselberg formations of South America.

  8. The first dating results for gabbro of the dunite-clinopyroxenite-gabbro complex of the Chistop massif (North Urals)

    Science.gov (United States)

    Petrova, G. A.; Ronkin, Yu. L.; Lvov, P. A.; Maslov, A. V.

    2017-08-01

    The first data on the Late Riphean age by U-Pb and Sm-Nd analysis (≥922 ± 14 and 686 ± 19 Ma, respectively) were obtained for rocks of the dunite-clinopyroxenite-gabbro complex of the Chistop massif in the Patinum-bearing Belt of the Urals. These data allow one to assume that the formation of the Ural paleoocean probably started immediately after the break-up of Rodinia.

  9. The Arequipa Massif of Peru: New SHRIMP and isotope constraints on a Paleoproterozoic inlier in the Grenvillian orogen

    Science.gov (United States)

    Casquet, C.; Fanning, C. M.; Galindo, C.; Pankhurst, R. J.; Rapela, C. W.; Torres, P.

    2010-01-01

    The enigmatic Arequipa Massif of southwestern Peru is an outcrop of Andean basement that underwent Grenville-age metamorphism, and as such it is important for the better constraint of Laurentia-Amazonia ties in Rodinia reconstruction models. U-Pb SHRIMP zircon dating has yielded new evidence on the evolution of the Massif between Middle Paleoproterozoic and Early Paleozoic. The oldest rock-forming events occurred in major orogenic events between ca. 1.79 and 2.1 Ga (Orosirian to Rhyacian), involving early magmatism (1.89-2.1 Ga, presumably emplaced through partly Archaean continental crust), sedimentation of a thick sequence of terrigenous sediments, UHT metamorphism at ca. 1.87 Ga, and late felsic magmatism at ca. 1.79 Ga. The Atico sedimentary basin developed in the Late-Mesoproterozoic and detrital zircons were fed from a source area similar to the high-grade Paleoproterozoic basement, but also from an unknown source that provided Mesoproterozoic zircons of 1200-1600 Ma. The Grenville-age metamorphism was of low- P type; it both reworked the Paleoproterozoic rocks and also affected the Atico sedimentary rocks. Metamorphism was diachronous: ca. 1040 Ma in the Quilca and Camaná areas and in the San Juán Marcona domain, 940 ± 6 Ma in the Mollendo area, and between 1000 and 850 Ma in the Atico domain. These metamorphic domains are probably tectonically juxtaposed. Comparison with coeval Grenvillian processes in Laurentia and in southern Amazonia raises the possibility that Grenvillian metamorphism in the Arequipa Massif resulted from extension and not from collision. The Arequipa Massif experienced Ordovician-Silurian magmatism at ca. 465 Ma, including anorthosites formerly considered to be Grenvillian, and high-T metamorphism deep within the magmatic arc. Focused retrogression along shear zones or unconformities took place between 430 and 440 Ma.

  10. The investigation of molybdenum migration in aqueous media landscape of the Khibiny massif to develop environmental activities

    Directory of Open Access Journals (Sweden)

    Sulimenko L.P.

    2015-06-01

    Full Text Available Relations of natural and technogenic factors at forming of molybdenum making streams in superficial and underground waters in the Khibiny massif have been studied. The priority sources of receipt of molybdenum in water objects have been considered. Taking into account hydrogeochemistrical properties of molybdenum the terms of strategy of decline of its negative influence on superficial currents in the conditions of productive mining complex activity have been defined

  11. The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

    Science.gov (United States)

    Martínez Catalán, José R.

    2012-07-01

    An arcuate structure, comparable in size with the Ibero-Armorican arc, is delineated by Variscan folds and magnetic anomalies in the Central Iberian Zone of the Iberian Massif. Called the Central Iberian arc, its sense of curvature is opposite to that of the Ibero-Armorican arc, and its core is occupied by the Galicia-Trás-os-Montes Zone of NW Iberia, which includes the Rheic suture. Other zones of the Iberian Massif are bent by the arc, but the Ossa-Morena and South Portuguese zones are not involved. The arc formed during the Late Carboniferous, at final stages of thermal relaxation and collapse, and an origin related with right-lateral ductile transpression at the scale of the Variscan belt is proposed. The Central Iberian arc explains the width of the Central Iberian Zone, clarifies the position of the allochthonous terranes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central zone represents the continuation of the southwest branch of the arc detached by strike-slip tectonics.

  12. Platinum group element mineralization of the Svetly Bor and Veresovy Bor clinopyroxenite-dunite massifs, Middle Urals, Russia

    Science.gov (United States)

    Stepanov, S. Yu.; Malitch, K. N.; Kozlov, A. V.; Badanina, I. Yu; Antonov, A. V.

    2017-05-01

    The new data for the geology and mineralogy of the platinum group element (PGE) mineralization related to the chromite-platinum ore zones within the dunite of the Svetly Bor and Veresovy Bor massifs in the Middle Urals are discussed. The geological setting of the chromite-platinum ore zones, their platinum content, compositional and morphological features of the platinum group minerals (PGM) are compared to those within the Nizhny Tagil massif, the world standard of the zonal complexes in the Platinum Ural belt. The chromite-platinum orebodies are spatially related to the contacts between differently granular dunites. Majority of PGM are formed by Pt-Fe alloys that are close in terms of stoichiometry to isoferroplatinum (Pt3Fe), and associated with Os-Ir alloys, Ru-Os and Ir-Rh sulfides, and Ir-Rh thiospinels of the cuproiridsite-cuprorhodsite-ferrorhodsite solid solution. The tetraferroplatinum (PtFe)-tulameenite (PtFe0.5Cu0.5) solid solution and Pt-Cu alloys belong to the later PGM assemblage. The established features of the chromite-platinum ore zones testify to the highly probable identification of the PGE mineralization within the dunite of the Svetly Bor and Vesesovy Bor massifs and could be used in prospecting and exploration for platinum.

  13. Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

    Science.gov (United States)

    Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.

    2014-12-01

    In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.

  14. Geology and Tectonic Evolution of the Kazdaǧ Massif (NW Anatolia)

    Science.gov (United States)

    Erdoğan, B.; Akay, E.; Hasözbek, A.; Satır, M.; Siebel, W.

    2009-04-01

    In the northwestern part of Anatolia along the Izmir-Ankara Suture Zone, the Kazdağ and Uludağ metamorphic massifs form an E-W trending belt between the Sakarya Continent in the north and the Menderes Massif in the south. Internal succession of these two massifs have been described as metamorphic complexes consisting of various kinds of micaschists, quartz mica schist, gneisses, amphibolites and marbles. In the Kazdağ metamorphics, metaophiolites have been described additionally (Okay et al., 1991; Yaltırak and Okay, 1994; Okay et al., 1996; Duru et al., 2004). These metamorphic complexes were considered to form the basement of the Sakarya Continent tectonically overlain by the Early Permian (Topuz et al., 2004) to Late Triassic (Okay and Monie, 1997; Okay et al., 2002) Karakaya Complex. This old basement and the Karakaya Complex were suggested to be unconformably overlain by Liassic and younger platform limestones and detritals (Altıner et al., 1991). In the literature, it has also been suggested that the Kazdağ Massif had experienced polyphase metamorphism, first during Carboniferous time, second during Early Triassic and third during Tertiary (Bingöl, 1971; Okay et al., 1996; Okay and Satır, 2000). In this study we mapped the Kazdağ Massif on 1/25000 scale, studied its internal stratigraphy and structures and performed some petrologic analyses and radiogenic age determinations. Stratigraphically in the lower part of the Kazdağ metamorphic sequence, there is a part of an oceanic crust represented by metaultramafic rocks and gabbroic metacumulates. Geochemistry of these banded metagabbros show a mid-oceanic affinity. This oceanic crust is overlain, along an unconformity, by a platform type marble succession. At the base of the marbles, there is a basal conglomerate, clasts of which derived from the underlying ultramafic sequence. Thick white marble sequence is overlain along a gradational boundary with a metadetrital succession consisting of quartz mica

  15. Late Carboniferous remagnetisation of Palaeozoic rocks in the NE Rhenish Massif, Germany

    Science.gov (United States)

    Zwing, A.; Bachtadse, V.; Soffel, H. C.

    During stepwise thermal and alternating field demagnetisation experiments on Devonian and Lower Carboniferous carbonate and clastic rocks from the north-eastern part of the Rhenish Massif, Germany, three components of magnetisation (A, B, C) are identified. Component A is a recent viscous overprint that parallels the local present day geomagnetic field. Component B is mainly observed from 260 up to 550 °C during thermal demagnetisation and is carried by magnetite. In two localities, where red siltstones and red carbonate rocks were sampled, component B is stable up to 670 °C, indicating the presence of hematite. Three clusters of in situ B directions can be identified, which are controlled by the tectonic position of the sampling areas. These are from NW to SE: the Remscheid anticline (RA), the Lüdenscheid syncline (LS) and the Attendorn and Wittgenstein synclines (AS/WS). Standard and inclination-only fold tests, using parametric resampling, yield optimal statistical parameters at increasing amounts of untilting ranging from 0% in the South up to 57% in the North of the NE Rhenish Massif. Despite the variations in optimal untilting, the resulting site mean directions of component B do not differ significantly in inclination. These results are interpreted to reflect the acquisition of magnetisation during progressive northward migration of the deformation front in Late Carboniferous times. The resulting palaeolatitudes (RA: 1°S +2°-3°; LS: 2°S +3°-2°; AS/WS: 1°S +3°-4°) are in good agreement with the predicted position of the sampling area in the Late Carboniferous, as derived from a published Apparent Polar Wander Path for Baltica and Laurentia. The unblocking temperature spectra and the synfolding nature of B yield strong evidence that chemical processes, possibly driven by fluid migration during orogenesis, caused this remagnetisation. A third component C was observed in zones of tight folding with steeply dipping to overturned bedding planes and is

  16. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

    Science.gov (United States)

    Bonin, Bernard; Tatu, Mihai

    2016-08-01

    The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

  17. Ductile deformation of garnet in mylonitic gneisses from the Münchberg Massif (Germany)

    Science.gov (United States)

    Vollbrecht, Axel; Pawlowski, Jan; Leiss, Bernd; Heinrichs, Till; Seidel, Madlen; Kronz, Andreas

    2006-12-01

    Mylonitic gneisses from the Münchberg Massif contain single grains (type I) and polycrystalline aggregates (type II) of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation. Lattice-preferred orientations of quartz (textures) symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments. Garnet textures measured by EBSD together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation: (1) For the single grains stretching can be attributed to diffusion creep along grain boundary zones (Coble creep). The related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning. Pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing. (2) For the polycrystalline garnet aggregates consisting of cores grading into fine-grained mantles, dislocation creep and associated rotation recrystallization can be assumed. Continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are {100} and equivalent systems according to the cubic lattice symmetry. The same holds for garnets which appear to be completely recrystallized. For this type of fine-grained aggregates an alternative nucleation model is discussed. Due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation, primary growth zones are strongly disturbed. Since for the considered rock unit of the Münchberg Massif peak metamorphic temperatures

  18. Differential denudations of the Argentera Alpine external crystalline massif (SE France) revealed by fission track thermo-chronology (zircons, apatites); Denudations differentielles du massif cristallin externe alpin de l'Argentera (Sud-Est de la France) revelees par thermochronologie traces de fission (apatites, zircons)

    Energy Technology Data Exchange (ETDEWEB)

    Bigot-Cormier, F.; Sosson, M. [Centre National de la Recherche Scientifique (CNRS-UMR 6526), Geosciences Azur, 06 - Valbonne (France); Poupeau, G. [Maison des Geosciences, 38 - Grenoble (France)

    2000-03-01

    A fission track thermo-chronological study of the Argentera external crystalline massif (western Alps) reveals tectonic blocks with differential vertical motions. The northwest area cooled down about 300 deg. C from the Upper Cretaceous and the remaining of the massif crossed the 250 deg. C isotherm in the 29-20 Ma time interval, after the internal nappe over-thrust. Moreover the massif cooled below 120 deg. C more than 12.5 Ma ago and its denudation rate increased locally 6 Ma ago and more generally since 3.5 Ma in relation with the reverse motion along the Bersezio fault. (authors)

  19. Silurian A-type granitoids in the southern margin of the Tongbai-Dabieshan: Evidence from SHRIMP zircon geochronology and geochemistry

    Institute of Scientific and Technical Information of China (English)

    MA; Changqian; SHE; Zhenbing; XU; Pin; WANG; Lingyan

    2005-01-01

    SHRIMP U-Pb dating on magmatic zircons extracted from a riebeckite quartz syenite in the Huangyangshan pluton in Suizhou, the southern margin of Tongbai-Dabieshan yielded an age of 439±6Ma. According to the morphology and high Th/U ratios of the zircons, the age is interpreted as crystallization timing of the pluton. The Huangyangshan pluton is composed of peralkaline quartz syenite, alkaline granite and syenite. All of the rocks are characterized by high agpaitic index (A.I.=(Na+K)/Al, molar ratio) and Fe-number [FeOT/(FeOT+MgO)], low CaO and MgO contents, enrichment of high field strength elements (i.e. Nb, Zr, Ga, Y, Hf) and light REEs, evidently negative Eu anomalies and high Ga/Al ratios, which are consistent with anorogenic A-type granitoids. Being part of the South Qinling-South Dabieshan Paleozoic alkaline rock belt, the Huangyangshan A-type granitoid pluton results from the Paleozoic extension-initial rifting in the northern margin of the Yangtze Craton related to the opening of the eastern Paleo-Tethyan Ocean.

  20. Petrology of Teofilândia granitoids: An example of 2.1 Ga crustal accretion in the São Francisco Craton (Bahia, Brazil)

    Science.gov (United States)

    Nascimento, H. S.; Nédélec, Anne; Bouchez, Jean-Luc

    2017-07-01

    Teofilândia granitoids are representative of the Paleoproterozoic plutonic rocks, which intruded the Serrinha block, an Archean crustal fragment of the Sao Francisco Craton (Bahia, Brazil). Three plutons were emplaced, the Teofilândia granodiorite, the Barrocas trondhjemite and the Santa Rosa granite, respectively dated at 2130, 2127 and 2073 Ma. The two first plutons are calc-alkaline rocks following a trondhjemitic trend. They resemble Archean TTGs (tonalites-trondhjemites-granodiorites) by their major and trace element compositions and especially by their fractionated REE patterns, with very low HREE contents. These juvenile magmas resulted from partial melting of a young mafic protolith, likely represented by the nearby Rio Itapicuru greenstone belt. Barrocas trondhjemite and Teofilândia granodiorite derive from similar sources, possibly at different depths and with a different degree of melting. The rocks were deformed at high temperature during the Trans-Amazonian collision and are therefore pre-collisional and ascribed to a subduction stage. The younger Santa Rosa pluton is a small, syn-to post-collisional granite that derived from anatexis of the Archean crust. It is representative of a second, volumetrically minor, plutonic episode of potassic, shoshonitic or alkaline affinities. The large amount of 2.1 Ga granitoids emplaced in Brazil as well as in the West African craton, suggests that, at that time, a global event of possible mantle origin was responsible for the intense magmatic activity that involved both crustal accretion and crustal reworking in many places of the world.

  1. Mineralogy and geochemistry of microgranular enclaves in Palaeoproterozoic Malanjkhand granitoids, central India: evidence of magma mixing, mingling, and chemical equilibration

    Science.gov (United States)

    Kumar, Santosh; Rino, Vikoleno

    2006-11-01

    Palaeoproterozoic ( ca 2,480 Ma) felsic magmatism of Malanjkhand region of central Indian Precambrian shield, referred to as Malanjkhand granitoids (MG), contain xenoliths of country rocks and mesocratic to melanocratic, fine-grained porphyritic microgranular enclaves (ME). The shape of ME is spheroidal, ellipsoidal, discoidal, elongated, and lenticular, varying in size from a few centimeters to about 2 m across. The contact of ME with the host MG is commonly sharp, crenulate, and occasionally diffuse, which we attribute to the undercooling and disaggregation of ME globules within the cooler host MG. The ME as well as MG show hypidiomorphic texture with common mineral Hbl-Bt-Kfs-Pl-Qtz assemblage, but differ in modal proportions. The variation in minerals' composition, presence of apatite needles, elongated biotites, resorbed plagiclase, ocellar quartz, and other mafic-felsic xenocrysts strongly oppose the restite and cognate origins of ME. Compositions of plagioclases (An3-An29), amphiboles (Mg/Mg+Fe2+=0.55-0.69), and biotites (Mg/Mg+Fe2+=0.46-0.60) of ME are slightly distinct or similar to those of MG, which suggest partial to complete equilibration during mafic-felsic magma interactions. Al-in-amphibole estimates the MG pluton emplacement at ca 3.4 ± 0.5 kbar, and therefore, magma mixing and mingling must have occurred at or below this level. The FerightleftharpoonsMg substitution in biotites of ME and MG largely suggests subduction-related, calc-alkaline metaluminous (I-type) nature of felsic melts. Most major and trace elements against SiO2 produce near linear variation trends for ME and MG, probably generated by the mixing of mafic and felsic magmas in various proportions. Trace including rare earth elements patterns of ME-MG pairs, however, show partial to complete equilibration, most likely governed by different degrees of elemental diffusion. The available evidence supports the model of ME origin that coeval mafic (enclave) and felsic (MG) magmas produced

  2. Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton

    Science.gov (United States)

    Fan, Wenbo; Jiang, Neng; Xu, Xiyang; Hu, Jun; Zong, Keqing

    2017-05-01

    An integrated study of zircon U-Pb ages and Hf-O isotopic compositions, whole rock elemental and Sr-Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U-Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO2 (43.7-52.6%), high Ca, Mg, Fe and H2O contents. It possesses subduction-related trace element patterns, enriched Nd-Hf isotopic signatures as well as elevated zircon δ18O values (6.2-7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO2 = 75.4-75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd-Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable εNd (t) and εHf(t) values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the

  3. Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India

    Science.gov (United States)

    Sarkar, S. C.; Kabiraj, S.; Bhattacharya, S.; Pal, A. B.

    1996-07-01

    At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate alteration assemblages, defined by alkali feldspar (K-feldspar≫albite)+dusty hematite in feldspar±biotite±muscovite, are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite+biotite+epidote/zoisite, surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness of 200 m and dips 65° 75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied by limited copper enrichment, is observed down to a depth of 100 m or more from the surface. Primary ores consist essentially of chalcopyrite and pyrite with minor magnetite and molybdenite. δ34S (‰) values in pyrite and chalcopyrite (-0.38 to +2.90) fall within the range characteristic of granitoid-hosted copper deposits. δ18O (‰) values for vein quartz (+6.99 to +8.80) suggest exclusive involvement of juvenile water. Annealed fabrics are common in the ore. The sequence of events that led to the present state of hypogene mineralization is suggested to be as follows: fracturing of the host rock, emplacement of barren vein quartz, pronounced wall-rock alteration accompanied by disseminated mineralization and the ultimate stage of intense silicification accompanied by copper mineralization. Fragments of vein quartz and altered wall rocks and striae in the ore suggest post-mineralization deformation. The recrystallization fabric, particularly in chalcopyrite and sphalerite, is a product of dynamic recrystallization associated with the post-mineralization shearing. The petrology of the host

  4. Eocene Granitoids of the Okhotsk Complex in Sakhalin Island, Russian Far East: Petrogenesis and tectonic implications from zircon U-Pb ages, geochemical and Sr-Nd isotopic characteristics

    Science.gov (United States)

    Liao, Jia Ping; Alexandrov, Igor; Jahn, Bor-ming

    2016-04-01

    Sakhalin Island represents an important part of the Western Pacific Orogenic Belt (or "Nipponides"). The island comprises several accreted terrains that have recorded strike-slip displacements and block rotations from Cretaceous to Tertiary. These terrains include fore-arc basins, accretionary complexes and island arc assemblages. The stratigraphic features of most terrains can be correlated to those of Hokkaido Island of Japan. However, little research has been undertaken on the magmatic activities on Sakhalin, so a direct comparison of crustal development and tectonic activities with Hokkaido has not been fulfilled. We intend to study the petrogenesis of granitic complexes of Sakhalin to resolve this problem. In this work, we present new results of age determination and geochemical analyses of the Okhotsk Complex and discuss the tectonic implications. The Okhotsk complex is one of the three main granitoid complexes in Sakhalin Island. It intruded into the Ozersk accretionary terrain that is composed of island arc assemblages and marine sediments and has traveled northward and accreted to Sakhalin Island in Eocene. Eleven samples from the Okhotsk Complex, including 7 granitoids, 1 enclave, 2 rhyolites, and 1 dacite, were subject to zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic analyses. The results show that the entire complex was emplaced within 42 to 44 Ma. The 7 granitoids are slightly peraluminous, ferroan, and alkali-calcic. The REE abundances of granitoids show consistent patterns with weak LREE enrichment and negative Eu anomaly. The spidergrams show negative Ta-Nb-Ti anomaly as expected in most granitoids. They possess transitional characteristics between I- and A-type granites. For isotopic signatures, the granitoids have ɛNd(t) values of +2.8 to +3.7, initial 87Sr/86Sr ratios of 0.7047 to 0.7050, and Sm-Nd model ages (TDM-1) of 700-1100 Ma. The middle Eocene magmatic episode (42-44 Ma) of the Okhotsk Complex can find its counterpart in

  5. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Science.gov (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

    2016-09-01

    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  6. Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran

    Science.gov (United States)

    Mirnejad, H.; Lalonde, A. E.; Obeid, M.; Hassanzadeh, J.

    2013-06-01

    Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300 km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217-200 Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite-tonalite-granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite-tonalite-granodiorite stock from Dehnow-Vakilabad (217 ± 4-215 ± 4 Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212 ± 5.2 Ma and 199.8 ± 3.7 Ma, respectively. The high initial 87Sr/86Sr ratios (0.708042-0.708368), low initial 143Nd/144Nd ratios (0.512044-0.51078) and low ɛNd(t) values (- 5.5 to - 6.1) of quartz diorite-tonalite-granodiorite stock along with its metaluminous to mildly peraluminous character (Al2O3/(CaO + Na2O + K2O) Mol. = 0.94-1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤ 18 ppm) and heavy REE (HREE) (Yb 594 ppm) and high ratio of Sr/Y (> 35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87Sr/86Sr ratios (0.705469-0.706356), initial 143Nd/144Nd ratios (0.512204-0.512225) and ɛNd(t) values (- 2.7 to - 3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then

  7. The Thermal Regime of Air in the Rarău Massif

    Directory of Open Access Journals (Sweden)

    Mihailescu Catalin Mihai

    2016-06-01

    Full Text Available The air temperature variability and locally global warming impact, in the North Eastern Carpathians, have analyzed, namely in the high area of the Massif Rarău, as the environmental implications of these changes. Also taking into account the touristic potential of this area, some aspects of thermal regime change have been highlighted, with implications for tourism. For this study the string climate data have been used from the meteorological station Rarău, currently belonging to the Faculty of Geography and Geology, University Alexandru Ioan Cuza. The yearly average of air temperature at the meteorological station Rarău was 2.5°C over the period 1958-2015. The annual variations were from -1.3°C in comparition with the annual average in 1980 to +1.7°C in 2015. The lowest monthly average was in January, 6.7°C, the highest in July, 11.8°C and annual average amplitude was 18.5°C.

  8. Palaeostress perturbations near the El Castillo de las Guardas fault (SW Iberian Massif)

    Science.gov (United States)

    García-Navarro, Encarnación; Fernández, Carlos

    2010-05-01

    Use of stress inversion methods on faults measured at 33 sites located at the northwestern part of the South Portuguese Zone (Variscan Iberian Massif), and analysis of the basic dyke attitude at this same region, has revealed a prominent perturbation of the stress trajectories around some large, crustal-scale faults, like the El Castillo de las Guardas fault. The results are compared with the predictions of theoretical models of palaeostress deviations near master faults. According to this comparison, the El Castillo de las Guardas fault, an old structure that probably reversed several times its slip sense, can be considered as a sinistral strike-slip fault during the Moscovian. These results also point out the main shortcomings that still hinder a rigorous quantitative use of the theoretical models of stress perturbations around major faults: the spatial variation in the parameters governing the brittle behaviour of the continental crust, and the possibility of oblique slip along outcrop-scale faults in regions subjected to general, non-plane strain.

  9. Spatial variability in channel and slope morphology within the Ardennes Massif, and its link with tectonics

    Directory of Open Access Journals (Sweden)

    N. Sougnez

    2010-09-01

    Full Text Available Geomorphic processes that produce and transport sediment, and incise river valleys are complex; and often difficult to quantify over longer timescales of 103 to 105 years. Morphometric indices that describe the topography of hill slopes, valleys and river channels have commonly been used to compare morphological characteristics between catchments and to relate them to hydrological and erosion processes. This work focuses on a wide range of slope and river channel morphometric indices to study their behavior and strength in regions affected by low to moderate tectonic activity. We selected 10 catchments of about 150 to 250 km2 across the Ardennes Massif that cover various tectonic domains with uplift rates ranging from about 0.06 to 0.20 mm year−1 since mid-Pleistocene times. The morphometric analysis indicates that the slope and channel morphology of third-order catchments is not yet in topographic steady-state, and exhibits clear convexities in slope and river profiles. Our data indicate that the fluvial system is the main driver of topographic evolution and that the spatial pattern of uplift rates is reflected in the distribution of channel steepness and convexity. The spatial variation that we observe in slope and channel morphology between the 10 third-order catchments suggests that the response of the fluvial system was strongly diachronous, and that a transient signal of adjustment is migrating from the Meuse valley towards the Ardennian headwaters.

  10. Raman imaging of fluid inclusions in garnet from UHPM rocks (Kokchetav massif, Northern Kazakhstan).

    Science.gov (United States)

    Korsakov, Andrey V; Dieing, Thomas; Golovin, Aleksandr V; Toporski, Jan

    2011-10-01

    Confocal Raman imaging of fluid inclusions in garnet porphyroblasts from diamond-grade metamorphic calc-silicate rocks from the Kumdy-Kol microdiamond deposit (Kokchetav Massif, Northern Kazakhstan) reveals that these fluid inclusions consist of almost pure water with different step-daughter phases (e.g., calcite, mica and rare quartz). These fluid inclusions are characterized by negative crystal shape of the host-garnet and they exclusively occur within the core of garnet porphyroblasts. These observations are consistent with their primary origin, most likely at ultrahigh-pressure (UHP) metamorphic conditions. The euhedral newly formed garnet, different in color and composition, was found to be associated with these fluid inclusions. It is proposed that newly formed garnet and water fluid inclusions appear by reaction between the hydrous fluid and the garnet-host. These fluid inclusions provide an unequivocal record of almost pure H(2)O fluids, indicating water-saturated conditions within subducted continental crust during prograde stage and/or ultrahigh-P metamorphism.

  11. IODP Expedition 340T: Borehole Logging at Atlantis Massif Oceanic Core Complex

    Directory of Open Access Journals (Sweden)

    Donna Blackman

    2013-03-01

    Full Text Available Integrated Ocean Drilling Program (IODP Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP. Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800–1400 meters below seafloor (mbsf portionof the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offsetnow extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution.

  12. Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps

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    S. Monnier

    2011-12-01

    Full Text Available We investigated the Sachette rock glacier, Vanoise Massif, Northern French Alps, using former equilibrium line altitude reconstruction from glacial deposits, aerial photograph analysis, and ground-penetrating radar (GPR. The rock glacier is a young (probably <6000 yr and active landform. The GPR survey consisted of two CMP measurements and four constant-offset profiles. From CMP measurements, the radar wave velocity in exposed shallow massive ice is 0.165–0.17 m ns−1. The constant-offset GPR data was processed and analysed in order to reconstruct the stratigraphy and model the radar wave velocity in two dimensions. The integration of the morphology, the velocity models, and the stratigraphy emphasized, in the upper half of the rock glacier, the good correspondence between high radar wave velocities (>0.15–0.16 m ns−1 and reflectors having a dipping-syncline structure, typical of true glaciers. Consequently, the rock glacier structure is described as being constituted of a glacial massive ice core embedded into diamictons. Our study of the Sachette rock glacier highlights possible significance of rock glaciers and interactions between glacier and permafrost in alpine environments.

  13. Time scales of regional circulation of saline fluids in continental aquifers (Armorican massif, Western France

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    A. Armandine Les Landes

    2014-06-01

    Full Text Available In recent decades, saline fluids have been sampled worldwide at great depths in continental basements. Although some of them have been attributed to marine transgressions the mechanisms allowing their circulation is not understood. In this paper, we describe the horizontal and vertical distribution of moderately saline fluids (60 to 1400 mg L−1 sampled at depths ranging from 41 to 200 m in aquifers at the regional scale of the Armorican Massif (northwestern France. The horizontal and vertical distributions of high chloride concentrations are in good agreement with both the altitudinal and vertical limits and succession of the three major transgressions between the Mio-Pliocene and Pleistocene ages. The mean chloride concentration for each transgression area is exponentially related to the time spanned until present. It defines the potential laws of leaching of marine waters by fresh meteoric waters. The results of the Armorican aquifers provide the first observed constraints for the time scales of seawater circulation in the continental basement and the subsequent leaching by fresh meteoric waters. The general trend of increasing chloride concentration with depth and the time frame for the flushing process provide useful information to develop conceptual models of the paleo-functionning of Armorican aquifers.

  14. Re-evaluation of lead isotopic data, southern Massif Central, France

    Science.gov (United States)

    Sinclair, A. J.; Macquar, J. C.; Rouvier, H.

    1993-04-01

    Three independent Pb isotope homogenizing processes operating on large volumes of rock material during limited intervals in the Phanerozoic have been used to define a unique evolutionary curve for rock and ore lead isotopic compositions of the southern Massif Central, France. The model is 126_2004_Article_BF00196336_TeX2GIFE1.gif begin{gathered}{text{ x}}_{text{t}} = 18.641{text{ }} - {text{ 9}}{text{.56(e}}^{{text{L1*t}}} - 1{text{)}} {text{y}}_{text{t}} = 15.678{text{ }} - {text{ 0}}{text{.06934(e}}^{{text{L2*t}}} - 1{text{)}} {text{ z}}_{text{t}} = 38.701{text{ }} - {text{ 30}}{text{.8(e}}^{{text{L3*t}}} - 1{text{)}} where xt, yt and zt are the calculated isotopic ratios (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb respectively) at time t years ago and L1, L2 and L3 are the decay constants of 238U, 235U and 232Th respectively. The model gives the following ages for averages of the three sets of data used in its generation: age of mineralization for carbonate-hosted lead-zinc ore of Les Malines, ca. 150 Ma; emplacement of the Saint-Guiral-Liron granite, ca. 290 Ma; and an estimated average age of a group of Cambrian syngenetic deposits, ca. 520 Ma. These ages are in close agreement with ages determined by independent methods.

  15. Nature of radioactive contamination of components of ecosystems of streamflows from tunnels of Degelen massif.

    Science.gov (United States)

    Panitskiy, A V; Lukashenko, S N

    2015-06-01

    The paper provides data on environmental contamination due to radionuclides' migration with water. As a result of investigations there was obtained data on character of contamination of soil cover, surface water and underflow from tunnels of Degelen massif. Character of radionuclides' spatial distribution in environment was also shown. Mobility ranges of radionuclides' vertical and horizontal movements have been established in soils both across and along the stream flow. There was also shown a possibility to forecast radionuclides' concentration in soil by specific activity of these radionuclides in water. Different concentrations of radionuclides in associated components of the ecosystem (surface waters - ground waters - soils) have shown disequilibrium of their condition in this system. Generalization of investigation results for tunnel water streams' with water inflows, chosen as investigation objects in this work, allows to forecast radionuclides' behavior in meadow soils and other ecosystems of water streams from tunnels of Degelen test site. Based on analysis of curves, describing radionuclides' behavior in horizontal direction, we can forecast, that at this stage (137)Cs and (239+240)Pu would not be distributed more than 1.5 km from the access to the daylight surface, (90)Sr - not more than 2 km. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Raman mapping of coesite inclusions in garnet from the Kokchetav Massif (Northern Kazakhstan).

    Science.gov (United States)

    Korsakov, Andrey V; Hutsebaut, Didier; Theunissen, Karel; Vandenabeele, Peter; Stepanov, Alexander S

    2007-12-15

    Coesite inclusions occur in a wide range of lithologies and coesite is therefore a powerful ultrahigh-pressure (UHP) indicator. The transformation of coesite to quartz is evidenced by three optically well identifiable characteristics (e.g. palisade textures, radial crack patterns, polycrystalline quartz pseudomorphs). Under overpressure monomineralic coesite (on an optical basis), lacking the above transformation characteristics may survive. Raman micro-spectroscopy was applied on monomineralic coesite inclusions in garnet porphyroblasts from diamond-bearing garnet-clinozoisite-biotite gneisses of the Barchi-Kol area (Kokchetav Massif, Northern Kazakhstan). These coesite inclusions are euhedral and display a characteristic anisotropic hallo. However, Raman maps and separate spectra of these inclusions display shifted bands for coesite and quartz. Microscopically undetectable, quartz shows on the Raman map as a thin shell around coesite inclusion. Shift of the main coesite band allows to estimate their overpressure: coesite inclusions record 0-2.4 GPa in garnet and zircon. The quartz shell remains under lower pressure 0-1.6 GPa. The possible application of coesite and quartz Raman geobarometers for UHP metamorphic rocks is discussed.

  17. A large and complete Jurassic geothermal field at Claudia, Deseado Massif, Santa Cruz, Argentina

    Science.gov (United States)

    Guido, Diego M.; Campbell, Kathleen A.

    2014-04-01

    Late Jurassic geothermal deposits at Claudia, Argentinean Patagonia, are among the largest (40 km2) and most varied in the Deseado Massif, a 60,000 km2 volcanic province hosting precious metals (Au, Ag) mineralization generated during diffuse back arc spreading and opening of the South Atlantic Ocean. Both siliceous sinter and travertine occur in the same stratigraphic sequence. Deposits range from those interpreted as fluvially reworked hydrothermal silica gels, to extensive apron terraces, to a clustering of high-temperature subaerial vent mounds. Paleoenvironmentally diagnostic textures of sinters include wavy laminated, bubble mat and nodular fabrics, and for travertines comprise fossil terracette rims, wavy laminated, bubble mat, spherulitic, oncoidal, and peloidal fabrics. Of special note is the presence of relatively large (to 25 cm high), inferred subaqueous "Conophyton" structures in travertines, which serve as analogs for some Precambrian stromatolites and imply the presence of relatively deep pools maintained by voluminous spring discharges. The Claudia geothermal field is geographically and geologically linked to the Cerro Vanguardia epithermal project (total resource of ~ 7.8 million ounces Au equivalent) via proximity, similar veins, and structural linkages, making it an especially large and relevant prospect for the region. The combined Claudia-Cerro Vanguardia hydrothermal system likely represents a fortuitous alignment of focused fluid flow and structure conducive to forming a giant epithermal ore deposit, with respect to size, ore concentration and potentially duration, in the Late Jurassic of Patagonia.

  18. First insights on the molybdenum-copper Bled M'Dena complex (Eglab massif, Algeria)

    Science.gov (United States)

    Lagraa, Karima; Salvi, Stefano; Béziat, Didier; Debat, Pierre; Kolli, Omar

    2017-03-01

    Molybdenum-Copper showings in the Eglab massif (eastern part of the Reguibat rise of Algeria), are found in quartz-monzodiorite and granodiorite of the Bled M'Dena complex, a Paleoproterozoic circular structure of ∼5 km in diameter, comprising volcanic and intrusive suites. The latter consist of quartz-diorite, quartz-monzodiorite and granodiorite with a metaluminous normative composition. They display an "adakitic character" with moderate light rare-earth element (LREE) enrichment, minor Eu anomalies, high Sr/Y ratio and low Yb concentration, suggestive of a hydrous, arc magma of volcanic-arc affinity. The mineralization occurs mostly in quartz + molybdenite + chalcopyrite stockwork veins marked by widespread propylitic alteration along the selvages. Molybdenite and chalcopyrite are commonly associated with calcite, which precipitated at relatively late stages of the hydrothermal alteration. Fluid inclusions related to the mineralization stage, range from aqueous to aqueous-carbonic to solid bearing. The latter inclusions have the highest homogenization temperature (up to ∼400 °C), are salt saturated, and commonly contain molybdenite and/or chalcopyrite crystals. The petrology and geochemistry of the host rocks, the style of the hydrothermal alteration, the ore mineral associations, and the characteristics of the fluid inclusions, are all coherent in indicating that the Bled M'Dena represents a Paleoproterozoic porphyry style Mo mineralization, which is far unreported in the African continent.

  19. Use of a garbage dump by some mammal species in the Majella massif (Abruzzo, Italy

    Directory of Open Access Journals (Sweden)

    Aldo Martina

    1997-12-01

    Full Text Available Abstract In several previous works the presence of urban solid wastes in the feeding habits of some animal species has been documented. This study was carried out to discover which species visit a rubbish dump located in an area of the Majella massif. Monthly nightime direct observations, from September 1990 to May 1992, revealed the presence of dogs Canis [lupus] familiaris, domestic cats Felis [silvestris] catus, wolves Canis lupus and red foxes Vulpes vulpes. The fox was the most frequently observed species. Fox visits to the dump were distributed more continuously during the entire period of the study then the other species. An "asymmetry analysis" was carried out to find out the animals' favourite time to use the dump. The analysis produced time lag values of 02:00 A.M. to 05:00 A.M. The wolf was observed the least. During the monthly observations a similar trend between the cat and wolf came to light. The two species also visited the dump at similar times (wolf: 07:00-11:00 P.M.; cat: 05:00-10:00 P.M.. Dog visits to the dump were less continuous in comparison with other species: no preferred time was revealed. Some environmental factors, related to the geographical area and management of the dump limited waste availability. This probably had an effect on the presence of the animals.

  20. Variaciones texturales y movilidad geoquímica asociadas a milonitización: la zona de cizalla del granitoide El Tigre, Sierra de Pie de Palo, Sierras Pampeanas Occidentales, San Juan Textural variations and chemical mobility during mylonitization: The El Tigre granitoid shear zone, Sierra de Pie de Palo, western sierras pampeanas, San Juan

    Directory of Open Access Journals (Sweden)

    Brígida Castro De Machuca

    2010-03-01

    Full Text Available Una faja de cizalla dúctil con foliación milonítica de dirección NEE y buzamiento al sudeste, afecta a un granitoide mesoproterozoico (Granitoide El Tigre: 31º31'30''S-68º15'12''O que forma parte del basamento cristalino de la Sierra de Pie de Palo, Sierras Pampeanas Occidentales. El análisis cinemático de la faja indica una componente principal de desplazamiento de rumbo con sentido de movimiento dextral. En el granitoide no deformado (protolito se preservan asociaciones minerales y texturas relícticas, ígneas y metamórficas, que son obliteradas por la deformación. La milonitización operó en un sistema abierto provocando la movilización (ganancia o pérdida de casi todos los elementos mayores y traza, incluyendo las tierras raras e isótopos de Rb/Sr y Sm/Nd. Los cambios químicos fueron controlados mayormente por transporte sintectónico de fluidos y por transformaciones mineralógicas producidas durante la milonitización (disminución del contenido de granate, biotita y minerales accesorios y neoformación de mica blanca en la matriz de las milonitas. Las variaciones isotópicas entre el protolito y las milonitas también serían resultado de la intervención de fluidos durante la deformación, con interacción variable entre fluido y rocas de caja. Los cambios texturales, mineralógicos y químicos experimentados por el granitoide durante la milonitización, permiten reconstruir su evolución tectono-metamórfica y las condiciones metamórficas imperantes. Las asociaciones minerales y microestructuras de deformación de las milonitas sugieren para la faja de cizalla del granitoide El Tigre condiciones propias de la facies de esquistos verdes, con temperaturas inferiores a los 400 °C. Este evento deformante tuvo lugar a los 473 ± 10 Ma durante la orogenia Famatiniana.A high-strain ductile shear zone trending NEE with southeasterly dipping mylonitic foliation, has been recognized affecting a Mesoproterozoic (ca. 1105 Ma

  1. A Preliminary Study on the Evolutionary Characteristics of Rare Earth Elements (REE)in Granitoid Rocks and Their Formation Mechanisms in Xianghualing Region,Hunan Province,China

    Institute of Scientific and Technical Information of China (English)

    杜绍华; 邱瑞照

    1991-01-01

    Recognized in the Xianghualing region,South Hunan are three major types of granitoids,i.e.,biotite granite,zinnwaldite-albite granite and xianghuagite,which evolved form the same granitic magma,but were formed at different stages.These granitoid rocks constitute a complete magmatic evolutionary series.With the evolution of magma,REE contents and negative Eu anomalies tend to decrease progressively,and LREE become more and more enriched relative to HREE .The facts mentioned above show that the tendency of REE evolution in granitoid rocks in the region studied is different from that in other regions.Evidence indicates that the granitic magma system became more and more depleted in Si(K+Na),but richer and richer in Al,Li,F and H2O+ during the process of its evolution,re-sulting in relatively weak acidity and strong alkalinity .It may be the most important factor leading to a specific REE evolutionary trend for the granitoid rocks in this region.In addition,the changing oxidation-reduction environments at different evolutionary stages of this magma system may be anoth-er important factor which should be taken into consideration.

  2. Geochemistry and 207Pb/ 206Pb zircon ages of granitoids from the southern portion of the Tamboril-Santa Quitéria granitic-migmatitic complex, Ceará Central Domain, Borborema Province (NE Brazil)

    Science.gov (United States)

    de Araujo, Carlos E. G.; Costa, Felipe G.; Pinéo, Tercyo R. G.; Cavalcante, José C.; Moura, Candido A. V.

    2012-02-01

    The Tamboril-Santa Quitéria Complex is an important Neoproterozoic granitic-migmatitic unit from the Ceará Central Domain that developed from ca. 650 to 610 Ma. In general the granitoids range in composition from diorite to granite with predominance (up to 85%) of granitic to monzogranitic composition with biotite as the main mafic AFM phase. Geochemical and 207Pb/ 206Pb evaporation zircon geochronology studies were applied in a group of these abundant monzogranitic rocks from the region of Novo Oriente in the southern portion of the Ceará Central Domain. In this area the granitoids are weakly peraluminous biotite granitoids and deformed biotite granitoids of high-K calc-alkaline and ferroan composition, which we interpreted as primary magmas (segregated diatexites) derived from the partial melting of crustal material. The close temporal relation of this magmatism with local eclogitic and regional high temperature metamorphism in Ceará Central Domain point out to an orogenic setting, arguably emplaced during the collisional stage. Subordinate coeval juvenile mantle incursions are also present. This crustally derived magmatism is the primary product of the continental thickening that resulted from the collision between the rocks represented by the Amazonian-West African craton (São Luiz cratonic fragment) to the northwest and the Paleoproterozoic-Archean basement of the Borborema Province to the southeast along the Transbrasiliano tectonic corridor.

  3. Lithologic Distribution and Geologic History of the Apollo 17 Site: The Record in Soils and Small Rock Particles from the Highland Massifs

    Science.gov (United States)

    Jolliff, Bradley L.; Rockow, Kaylynn M.; Korotev, Randy L.; Haskin, Larry A.

    1996-01-01

    Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm-4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm-4 mm fragments provide a bridge between compositions of less than 1 mm fines and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm-4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% Incompatible-Trace-Element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm - 4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31 % agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass- weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their

  4. New paleomagnetic data from Bornholm granitoids testing whether the East-European Craton rotated during the 1.50-1.45 Ga Danopolonian orogeny

    Science.gov (United States)

    Lubnina, N.; Bogdanova, S.; Cecys, A.

    2009-04-01

    According to the palaeogeographic reconstructions, the East-European Craton (EEC) was part of the Palaeo- to Mesoproterozoic supercontinent Nuna / Columbia (Hoffman, 1997; Rogers and Santosh, 2002). Particularly important was the period between 1.5 and 1.3 Ga, when incipient break-up of this supercontinent occurred (Condie, 2002) but the EEC ("Baltica") still remained in close connection with other continental blocks. During the entire Mesoproterozoic, however, the EEC featured different geodynamic regimes in its presently western and eastern parts. In the west, these were convergent, while rifting prevailed in the east (Bogdanova et al., 2008). Previously, paleomagnetic studies of the Mesoproterozoic Ladoga Lake mafic rocks in NE Russia and the Dalarna mafic dykes in Sweden have disclosed a regular trend from the older Dalarna dykes to the younger dolerites of Lake Ladoga, suggesting an anticlockwise rotation of about 20 degrees. That rotation could either have affected the entire EEC as a result of the Danopolonian orogeny at ca. 1.50-1.45 Ga or have been associated with local block-displacement events in the Pasha-Ladoga graben (Lubnina et al., 2005, 2007). In the present study, we have tested these alternative possibilities by carrying out new paleomagnetic studies of Mesoproterozoic granitoids from the Danish island of Bornholm in the South Baltic Sea, which is a key area of the Danopolonian orogeny. On SW Bornholm, the 1.46 Ga Ronne granodiorites, which are cut by NNW trending thin dolerite dykes have been sampled in the Klippelokke quarry. Remanence measurements were performed using a 2G cryogenic magnetometer at the Palaeomagnetic Laboratory of the Department of Geology, Lund University, Sweden. Conventional progressive thermal or alternating field (AF) demagnetizations were applied to all specimens. During the stepwise thermal and AF demagnetization experiments, two components of NRM were isolated in the majority of the granitoid specimens. The low

  5. Geochronology and geochemistry of Late Cretaceous-Paleocene granitoids in the Sikhote-Alin Orogenic Belt: Petrogenesis and implications for the oblique subduction of the paleo-Pacific plate

    Science.gov (United States)

    Tang, Jie; Xu, Wenliang; Niu, Yaoling; Wang, Feng; Ge, Wenchun; Sorokin, A. A.; Chekryzhov, I. Y.

    2016-12-01

    We present zircon U-Pb ages, major and trace element analyses, and zircon Hf isotope data on the Late Cretaceous-Paleocene granitoids at the southern end of the Sikhote-Alin Orogenic Belt of the Russian Far East. These data are used to discuss the petrogenesis of the granitoids in the context of the paleo-Pacific subduction beneath the eastern Eurasia. Zircons from four granitoid samples give emplacement ages of 56, 83, 91, and 92 Ma. These granitoids with high SiO2 (73.43-76.76 wt%) are metaluminous to weakly peraluminous (A/CNK = 0.97-1.03) and belong to the high-K calc-alkaline series (K2O = 3.75-4.95 wt%). They are all enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and relatively depleted in high field strength elements (HFSEs) with striking depletion also in Ba, Sr, P and Eu. They are petrographically and geochemically consistent with being of I-type granitoids. The zircons have εHf (t) values (- 0.8 to + 7.6) higher than whole-rock εHf (t) values predicted from whole-rock εNd (t) (- 4.1 to + 0.5) in the literature. All these observations suggest that primary magmas parental to these granitoids were likely to have derived from partial melting of a juvenile lower crust accompanied by assimilation with ancient mature crust during magma ascent and evolution. A recent study illustrates that the collision of an exotic terrane carried by the paleo-Pacific plate with the continental China at 100 Ma accreted the basement of the Chinese continental shelf (beneath East and South China Seas), and resulted in a new plate boundary of transform nature between the NNW moving paleo-Pacific plate and the eastern margin of the shelf. Our new data and analysis of existing data support this hypothesis, but we hypothesize that this transform becomes transpressional in its northern segment with oblique subduction of the paleo-Pacific plate beneath northeastern Asia as manifested by the Late Cretaceous-Paleocene granitoids in the Russian

  6. Petrogenesis of Late Mesozoic granitoids and coeval mafic rocks from the Jiurui district in the Middle-Lower Yangtze metallogenic belt of Eastern China: Geochemical and Sr-Nd-Pb-Hf isotopic evidence

    Science.gov (United States)

    Xu, Yao-Ming; Jiang, Shao-Yong; Zhu, Zhi-Yong; Yang, Shui-Yuan; Zhou, Wei

    2014-03-01

    Large-scale Cu-Au mineralization is associated with the Late Mesozoic granitoids in the Jiurui district of the Middle-Lower Yangtze Mineralization Belt in Eastern China. To constrain the petrogenesis of these granitoids and coeval mafic rocks, a detailed geochemical and Sr-Nd-Pb-Hf isotopic study was performed. The Jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry. These granitoids are characterized by SiO2 and K2O contents of 58.8 wt.% to 68.6 wt.% and 1.9 wt.% to 5.7 wt.%, respectively. These granitoids show relatively high MgO contents (1.0 wt.% to 3.1 wt.%, average 2.1 wt.%) and high Mg# values (39 to 70, average 54). The Jiurui granitoids are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE), and compatible trace elements (Cr, Ni and V) but are relatively depleted in Nb, Ta, Y and Yb. These rocks show a negligible negative Eu anomaly (Eu/Eu* = 0.76-1.13, average 0.91) and nearly no negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7060 to 0.7092, and the ɛNd(t) values vary from - 5.4 to - 2.0. The granitoids show radiogenic Pb isotopic ratios with values of 206Pb/204Pb (17.93-18.21), 207Pb/204Pb (15.55-15.58), and 208Pb/204Pb (38.16-38.56) for the plagioclases. The zircon Hf isotopic compositions show ɛHf(t) values from - 11.8 to 2.4. The coeval mafic rocks consist of lamprophyre, diabase and fine-grained mafic dyke. These rocks are characterized by SiO2 contents ranging from 47.6 wt.% to 54.8 wt.%, with a negative Eu anomaly and a positive to negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7059 to 0.7071, and the ɛNd(t) values vary from - 3.8 to - 1.4. By comparing the geochemical and isotopic compositions of the Jiurui granitoids and the coeval mafic rocks, we conclude that the granitoids are similar to adakites that were likely related to the delamination processes, and the coeval mafic rocks may have originated directly from

  7. Post-collisional high-Mg granitoids from the Paleoproterozoic East Sarmatian Orogen (East European Craton): Evidence for crust-mantle interaction

    Science.gov (United States)

    Terentiev, R. A.; Santosh, M.

    2017-03-01

    The East Sarmatian Orogen (ESO) is located along the southwestern domain of the East European Craton and occupies a key tectonic link between the Sarmatian and Volgo-Uralian domains. Here we investigate the Paleoproterozoic Novaya Melovatka pluton and its mafic-ultramafic xenoliths to gain insights into the role of interaction between intermediate-felsic crustal melt with mantle rocks as a mechanism for the generation of high-Mg granitoids at crustal pressures. The pluton is composed of biotite-orthopyroxene quartz dioritic and monzodioritic porphyrites (Phase 1) and medium-grained biotite-amphibole quartz diorite, tonalite and granodiorite and commingled Phase 1 mafic magmatic enclaves (MME) (Phase 2). The general geochemical characteristics of these rocks are similar to those of Late-Archean high-Mg sanukitoids. The TDM (model) ages for intermediate Phase 1 and granitoid Phase 2 are similar and show a range of 2324-2439 and 2284-2519 M, respectively. The εNd(t) values are grouped around subchondritic values (=+1.4-+1.9 and + 1.1-+2.2) and the initial 87Sr/86Sr ratios are in the range of 0.70202-0.70390. The complex compositional zoning of minerals suggests that the rocks crystallized as synchronous but discrete magma pulses, with limited to significant mixing. Based on the geochemical features we infer that the Phase 1 rocks formed from partial melting of a mantle wedge metasomatized to different degrees by fluids/melts. The presence of MMEs, compositional zoning of minerals including reversely zoned amphiboles, plagioclases with thin calcic overgrowths, and acicular apatite, as well as the whole-rock geochemical features are consistent with a hybrid origin of the high-Mg granitoids belonging to Phase 2. Geobarometry indicates crystallization at upper-crustal depths (i.e. 1.7-2.4 kbar). The igneous suite evolved by fractional crystallization of orthopyroxene, hornblende, plagioclase and biotite. Here we propose a tectonic model involving partial melting of the

  8. Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

    Science.gov (United States)

    Zeng, Renyu; Lai, Jianqing; Mao, Xiancheng; Li, Bin; Ju, Peijiao; Tao, Shilong

    2016-05-01

    Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and LaN/YbN from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (TZr) from 947 to 1072 °C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, LaN/YbN ratios from 27 to 32. These I-type intrusions have no Eu anomalies and TZr ranges from 818 to 845 °C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 ± 3.7 Ma and 361.7 ± 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative εHf(t) values (-11 ± 0.5 to -9 ± 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have εHf(t) values that range from -8 ± 1.0 to +10 ± 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at ∼444 Ma. Geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence

  9. Guandishan Granitoids of the Paleoproterozoic Lüliang Metamorphic Complex in the Trans-North China Orogen:SHRIMP Zircon Ages,Petrogenesis and Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    LIU Shuwen; LI Qiugen; LIU Chaohui; LU Yongjun; ZHANG Fan

    2009-01-01

    The Paleoproterozoic Liiliang Metamorphic Complex(PLMC)is situated in the middle segment of the western margin of the Trans-North China Orogen(TNCO),North China Craton(NCC). As the most important Iithological assemblages in the southern part of the PLMC,Guandishan granitoids consist of early gneissic tonalities,granodiorites and gneissic monzogranites,and younger gneissic to massive monzogranites.Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series;the early gneissic monzogranites are transitional from high-K caic-alkaline to the shoshonite series;the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series,and all rocks are characterized by right-declined REE patterns and negative Nb,Ta,Sr,P,and Ti anomalies in the primitive mantle normalized spidergrams.SHRIMP zircon U-Pb isotopic dating reveal that the early gneissic tonalities and granodiorites formed at ~2.17 Ga,the early gneissic monzogranites at ~2.06 Ga,and the younger gneissic to massive monzogranites at ~1.84 Ga.Sm-Nd isotopic data show that the early gneissic tonalities and granodiorites have εNd(t) values of +0.48 to -3.19 with Nd-depleted mantle model ages (TDM)of 2.76-2.47 Ga,and early gneissic monzogranites have εNd(t) values of -0.53 to -2.51 with TDM of 2.61-2.43 Ga,and the younger gneissic monzogranites have εNd(t) values of -6.41 to -2.78 with a TDM of 2.69-2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities,granodiorites,and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks,respectively,in a continental arc setting.The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust.Combined with previously regional data,we suggest that the PaleOproterOzOic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best

  10. Rb-Sr middle Devonian age of cordierite bearing migmatites from Lyonnais area (French Massif Central). Age Rb-Sr, Devonien moyen des migmatites a cordierite du Lyonnais (Massif central Francais)

    Energy Technology Data Exchange (ETDEWEB)

    Duthou, J.L. (Clermont-Ferrand-2 Univ., 63 - Aubiere (France)); Chenevoy, M.; Gay, M. (Lyon-1 Univ., 69 - Villeurbanne (France))

    1994-10-01

    On the basis of Rb-Sr whole rock data, a middle Devonian age (384[+-]16 Ma) is ascribed to the cordierite bearing migmatites (gneiss d'Aubusson) in the Lyonnais area. In the barrovian domain, this anatexis is therefore synchronous throughout the northern part of the french ''Massif Central''. Rb and Sr concentrations were determined by X-ray fluorescence analysis, and isotopic compositions by mass spectrometry. (A.B.). 28 refs., 2 figs. 1 tab.

  11. Dirty or Tidy ? Contrasting peraluminous granites in a collapsing Orogen: Examples from the French Massif Central

    Science.gov (United States)

    Villaros, Arnaud; Pichavant, Michel; Moyen, Jean-François; Cuney, Michel; Deveaud, Sarah; Gloaguen, Eric; Melleton, Jérémie

    2013-04-01

    Post collisional collapse commonly enhances crustal melting. Such melting typically produces peraluminous granitic magmas. In the French Massif Central, a mid-crustal segment of the western Variscan belt, two large granitic bodies were produced during the collapse of the Variscan Belt. The St Sylvestre Leucogranitic Complex (SSyL) in the western part of the Massif Central and the Velay Migmatitic Complex (VMC) in the Eastern part. Although these two complexes are formed in similar geodynamic context they present meaningful petrological and geochemical differences. The VMC (~305 Ma) is clearly intrusive in migmatitic terranes. The migmatitic host recorded two successive melting events M3 (720 °C and 5kb) dated between 335 and 315 Ma and M4 (850°C and 4 kb) dated at 305 Ma. The compositions of the VMC are strictly H2O-undersaturated and ranges from leucogranitic to granodioritic. Three main successive granite types have been distinguished (1) A heterogeneous banded biotite granite, (2) A main biotite-cordierite granite, where cordierite can be prismatic, as cockade or pseudomorphic (3) a late magmatic with large K-feldspar phenocryst and prismatic cordierite. The compositions of the VMC granites are quite similar to typical Australian S-type granites in the sense that they also show a positive correlation between ferromagnesian abundance and aluminosity. The SSyL (~320 Ma) is intrusive in upper greenschist facies to upper amphibolite migmatitic metasediment and orthogneiss (~3kb). The compositional variety observed in the SSyL suggests a continuous trend from a moderately mafic, peraluminous magma (cd- and sill- granite) to a H2O saturated granite ("two-mica" granite) facies and finally to an extremely felsic, H2O-saturated magma. Three granitic units have been recognized in the SSyL: (1) the western "Brame Unit" composed of the less evolved cd- and sill- granite facies (2) the central "St Sylvestre Unit", composed mainly by U-rich two-mica granite, intruded by two

  12. The magmatic history of the Vetas-California mining district, Santander Massif, Eastern Cordillera, Colombia

    Science.gov (United States)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Valencia, Víctor; Hart, Craig J. R.

    2013-08-01

    The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U-Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ˜1240 and 957 Ma; (2) early Ordovician calc-alkalic magmatism, which was synchronous with the Caparonensis-Famatinian Orogeny (˜477 Ma); (3) middle to late Ordovician post-collisional calc-alkalic magmatism (˜466-436 Ma); (4) late Triassic to early Jurassic magmatism between ˜204 and 196 Ma, characterized by both S- and I-type calc-alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc-alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic-hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic-early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204-199 Ma), Intermediate rocks (199-198 Ma), and late leucogranites, herein referred to as Alaskites-II (198-196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins.

  13. High-pressure metamorphism in the Early Variscan subduction complex of the SW Iberian Massif

    Science.gov (United States)

    Rubio Pascual, Francisco J.; Matas, Jerónimo; Martín Parra, Luis M.

    2013-04-01

    Several units exposed in the boundary area of the Ossa Morena Zone (OMZ) and the South Portuguese Zone (SPZ) preserve petrographic and thermobarometric evidence for an early metamorphic episode (M1), developed under a high-P, low to intermediate-T gradient, related to Early Variscan subduction in the SW Iberian Massif. In the OMZ, these are the Cubito-Moura Unit (Pmin ~ 9.2 kbar and T = 395 ± 45 °C), blueschists from its basal mélange (Pmin ~ 12.4 kbar and T = 310 ± 11 °C), and the underlying Fuenteheridos Group (P = 10.9 ± 0.4 kbar and T = 449 ± 31 °C). The equivalent units in the SPZ are the La Minilla Formation (P = 8.7 ± 0.4 kbar and T = 388 ± 16 °C) and the lawsonite pseudomorphs-bearing Pulo do Lobo Formation. All these units formed part of an approximately NE verging orogenic wedge (present coordinates) developed by the accretion of subducted slabs of the outermost margin of Gondwana and other elements of the Rheic Ocean realm, from at least the Middle Devonian to the lowermost Tournaisian. High-pressure rocks were subsequently emplaced on more internal zones of the OMZ that only experienced a younger high-T, low to intermediate-P metamorphism (M2). This high-T event was coeval with magmatic activity from the uppermost Devonian to the Middle Mississippian, probably as a consequence of transtensional lithospheric thinning and/or delamination of the lower crust and mantle lithosphere of the Gondwana margin. Pre-Late Devonian synorogenic sedimentation in forearc and back-arc basins of the subduction complex evolved to a Late Devonian-Middle Mississippian foreland basin system in early collisional stages. Finally, a new Middle-Late Mississippian fold-and-thrust belt with opposite (SW) vergence and new foreland basins developed during late collisional stages.

  14. Alpine thermal events in the central Serbo-Macedonian Massif (southeastern Serbia)

    Science.gov (United States)

    Antić, Milorad D.; Kounov, Alexandre; Trivić, Branislav; Wetzel, Andreas; Peytcheva, Irena; von Quadt, Albrecht

    2016-07-01

    The Serbo-Macedonian Massif (SMM) represents a crystalline belt situated between the two diverging branches of the Eastern Mediterranean Alpine orogenic system, the northeast-vergent Carpatho-Balkanides and the southwest-vergent Dinarides and the Hellenides. We have applied fission-track analysis on apatites and zircons, coupled with structural field observations in order to reveal the low-temperature evolution of the SMM. Additionally, the age and geochemistry of the Palaeogene igneous rocks (i.e. Surdulica granodiorite and dacitic volcanic rocks) were determined by the LA-ICPMS U-Pb geochronology of zircons and geochemical analysis of main and trace elements in whole-rock samples. Three major cooling stages have been distinguished from the late Early Cretaceous to the Oligocene. The first stage represents rapid cooling through the partial annealing zones of zircon and apatite (300-60 °C) during the late Early to early Late Cretaceous (ca. 110-ca. 90 Ma). It is related to a post-orogenic extension following the regional nappe-stacking event in the Early Cretaceous. Middle to late Eocene (ca. 48-ca. 39 Ma) cooling is related to the formation of the Crnook-Osogovo-Lisets extensional dome and its exhumation along low-angle normal faults. The third event is related to regional cooling following the late Eocene magmatic pulse. During this pulse, the areas surrounding the Surdulica granodiorite (36 ± 1 Ma) and the slightly younger volcanic bodies (ca. 35 Ma) have reached temperatures higher than the apatite closure temperature (120 °C) but lower than ca. 250 °C. The geochemistry of the igneous samples reveals late- to post-orogenic tectonic setting during magma generation.

  15. Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry

    Directory of Open Access Journals (Sweden)

    Skála Roman

    2015-06-01

    Full Text Available Upper Cretaceous to Pleistocene volcanic rocks of the Bohemian Massif represent the easternmost part of the Central European Volcanic Province. These alkaline volcanic series include rare melilitic rocks occurring as dykes, sills, scoria cones and flows. They occur in three volcanic periods: (i the Late Cretaceous to Paleocene period (80–59 Ma in northern Bohemia including adjacent territories of Saxony and Lusatia, (ii the Mid Eocene to Late Miocene (32.3–5.9 Ma period disseminated in the Ohře Rift, the Cheb–Domažlice Graben, Vogtland, and Silesia and (iii the Early to Late Pleistocene period (1.0–0.26 Ma in western Bohemia. Melilitic magmas of the Eocene to Miocene and Pleistocene periods show a primitive mantle source [(143Nd/144Ndt=0.51280–0.51287; (87Sr/86Srt=0.7034–0.7038] while those of the Upper Cretaceous to Paleocene period display a broad scatter of Sr–Nd ratios. The (143Nd/144Ndt ratios (0.51272–0.51282 of the Upper Cretaceous to Paleocene rocks suggest a partly heterogeneous mantle source, and their (87Sr/86Srt ratios (0.7033–0.7049 point to an additional late- to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr- and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~1 to 2 GPa and between 1000 to 1200 °C, respectively. Nepheline crystallized at about 500 to 770 °C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source.

  16. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    Science.gov (United States)

    Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

    2002-01-01

    The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

  17. Rockfall hazard assessment by means of the magnitude-frequency curves in the Montserrat Massif (central Catalonia, Spain): first insights

    Science.gov (United States)

    Janeras, Marc; Domènech, Guillem; Pons, Judit; Prat, Elisabet; Buxó, Pere

    2016-04-01

    Montserrat Massif is located about 50 km North-West of Barcelona (Catalonia, North-Eastern Spain). The rock massif is constituted by an intercalation of conglomerate and fine layers of siltstones due to the Montserrat fan-delta sedimentation within the Eocene age. The current relief is consequence of the several depositional episodes and the later tectonic uplift, leading to stepped slopes up to 250 m high, and a total height difference close to 1000 m. Montserrat Mountain has been a pilgrimage place since the settlement of the monastery, around the year 1025, and a spot of touristic interest, mostly within the last 150 years, when the first rack railway was inaugurated to reach the sanctuary. The amount of 2.4 M visitors in 2014 reveals the potential risk derived from rockfalls. To assess and mitigate this risk, a plan funded by the Catalan government is currently under development. Three rockfall mechanisms and magnitude ranges have been identified (Janeras et al. 2011): 1) physicochemical weathering causing the detachment of pebbles and aggregates (0.0001 - 0.1 m3); 2) thermic-induced tensions responsible for the generation of slabs and plates (0.1 - 10 m3); and 3) intersection of structural joints within the rock mass resulting in blocks of 10 - 10,000 m3. In order to quantify the rockfall hazard, a magnitude-frequency analysis has been performed starting from an event-based inventory gathered from field surveillance and historical research. A methodology has been applied to take the maximum profit of only 30 registers with information on volume and date. The massif has been split into several domains with sampling homogeneity. For each one, there have been defined several periods of time during which, all the rockfall events of a given volume have been recorded. Thus, the magnitude-frequency relationship, for each domain, has been calculated. Results show that the curves are well fitted by a power law with exponents ranging from -0.59 to -0.68 for magnitudes

  18. Geometry and thermal structure of the Menderes Massif Core Complex (Western Turkey), implications for thermal evolution of Hellenic subduction zone

    Science.gov (United States)

    Roche, Vincent; Jolivet, Laurent; Guillou-Frottier, Laurent; Tuduri, Johann; Bouchot, Vincent; Beccaletto, Laurent; Lahfid, Abdeltif

    2016-04-01

    The eastern Mediterranean region is one of the most promising geothermal areas, with more than 250 geothermal fields discovered in Turkey (Parlaktuna, 2013), in a region of active tectonics and volcanism. Although the potential of these deep geothermal resources has not been systematically investigated yet, the geothermal activity of the western Turkey area is the most recent signature of the high heat flow (120-140 mW/m²; Aydin, 2005, from Teczan, 1995). Based on Turkish data, 2084 MWt are being utilized for direct applications and most of the energy originates from the Menderes Massif (Baba et al., 2015). This large-scale thermal anomaly at the surface is correlated to a long wavelength east-west increase of surface heat flow that could reflect the thermal state of Aegean subduction zone at depth. In order to better understand and characterize the possible connections between large-scale mantle dynamics and surface processes in space and time, we study the structure and thermal evolution of the Menderes Massif. Both the acceleration of the Aegean extension in the Middle Miocene and the recent escape of Anatolia have been proposed to result from several slab tearing events, the first one being located below western Turkey and the Eastern Aegean Sea. These events have triggered the formation of metamorphic complexes with contrasted exhumation P-T paths. While the extension in the Aegean domain is well-characterized with high-temperature domes in the center and east, the succession of several metamorphic events in the Menderes Massif and their significance in terms of geodynamics is still debated. Hence, the exhumation history is key to understanding the temporal and spatial distribution of the thermal signature of the Hellenic slab and its tearing/detachment. The Menderes Massif displays a large variety of metamorphic facies, from the Barrovian type metamorphism in the Eocene (the Main Menderes Metamorphism) to the coeval (?) HP-LT metamorphism on the southernmost

  19. Geochronology Intermediary Laboratory implantation at the Rio Grande do Norte Federal University: the dating of the Serrinha Granitoid (RN) and the correlate Brasiliana extensional deformation; Implantacao do Laboratorio Intermediario de Geocronologia na UFRN: a datacao do granitoide de Serrinha (RN) e da deformacao extensional brasiliana correlata

    Energy Technology Data Exchange (ETDEWEB)

    Macedo, Maria Helena F.; Sa, Emanuel F. Jardim de; Souza, Zorano S. [Pernambuco Univ., Recife, PE (Brazil). Nucleo de Pesquisa em Geodinamica e Geofisica; Mendes, Franklin S. [Pernambuco Univ., Recife, PE (Brazil). Curso de Quimica; Ramalho, Karlos A.C. [Pernambuco Univ., Recife, PE (Brazil). Curso de Geologia

    1997-12-31

    The article describes the activities developed by the Geochronology Intermediary Laboratory at the Federal University of the Rio Grande do Norte, a Brazilian university, where there were the preoccupation of establishing strategies for a geochronological development. It relates the Rubidium-Strontium (Rb/Sr) and Samarium-Neodymium (Sm/Nd) methods, describing the analysis realized in these methodologies. Afterward, it presents the geological and petrographic situation of the Granitoide de Serrinha, located at Rio Grande do Norte State, Brazil and its geochronological data 8 refs., 2 figs.

  20. Geological and geochemical reconnaissance in the central Santander Massif, Departments of Santander and Norte de Santander, Colombia

    Science.gov (United States)

    Evans, James George

    1976-01-01

    The central Santander Massif is composed of Precambrian Bucaramanga Gneiss and pre-Devonian Silgara Formation intruded by Mesozoic quartz diorite, quartz monzonite, and alaskite and Cretaceous or younger porphyry. Triassic (Bocas Formation), Jurassic (Jordan and Giron Formations).and Cretaceous (Tambor, Rosa Blanca, Paja, Tablazo, Simiti, La Luna, and Umir Formations) sedimentary rocks overlie the metamorphic rocks and are younger than most of the intrusions. A geological and geochemical reconnaissance of part of the central Santander Massif included the Vetas and California gold districts. At Vetas the gold is generally in brecciated aphanitic quartz and phyllonite. Dark-gray material in the ore may be graphite. The ore veins follow steep west-northwest- and north-northeast-striking fracture zones. No new gold deposits were found. Additional geochemical studies should concentrate on western Loma Pozo del Rey and on improvement of the gold extraction process. At California the gold is in pyritiferous quartz veins and quartz breccia. Ore containing black sooty material (graphite?) is highly radioactive. Some of the mineralization is post-Lower Cretaceous. Soil samples indicate that gold deposits lie under the thick blanket of soil on the ridges above the zone of mining. Three principal gold targets are outlined by gold and associated minerals in pan concentrates. The close relation of gold and copper anomalies suggests that copper may be useful as a pathfinder for gold elsewhere in the region. Based on occurrences of gold or high concentrations of pyrite or chalcopyrite in pan concentrates and on analytical data, eight potential gold targets are outlined in the central massif. Reconnaissance of the surrounding region is warranted.

  1. Geochemistry, geochronology, and cathodoluminescence imagery of the Salihli and Turgutlu granites (central Menderes Massif, Western Turkey): Implications for Aegean tectonics

    Science.gov (United States)

    Catlos, E. J.; Baker, C.; Sorensen, S. S.; Çemen, I.; Hançer, M.

    2009-04-01

    The Menderes Massif (western Turkey) is an important metamorphic core complex located in the Aegean region; geochemical and geochronological data from this extensional domain facilitates our understanding of large-scale extension of the Earth's lithosphere. S-type, peraluminous granites (Salihli and Turgutlu) that intrude the Alasehir detachment which bounds the northern edge of the central Menderes Massif may have been generated due to subduction of the Eastern Mediterranean floor along the Hellenic trench. In situ Th-Pb ion microprobe monazite ages from the granites range from 21.7±4.5 Ma to 9.6±1.6 Ma (±1s). The range is consistent with cathodoluminescence (CL) imagery that document complex textures within the samples. Salihli and Turgutlu granites share many similar characteristics, including multiple generations of plagioclase (some with shocked cores consistent with magma mixing), plagioclase replacing K-feldspar and the development of myrmekite, clear evidence for fluid infiltration, and multiple generations of microcracks and microfaults. The granites may have evolved from compositionally distinct magma sources, as Salihli samples in general contain allanite as the major accessory mineral, whereas Turgutlu granites contain monazite. However, the CL imagery document similar alteration textures. Ages reported here are similar to dates constraining extension reported elsewhere in the Aegean, but indicate a level of complexity when linking movement within the Menderes Massif to the large-scale geodynamic processes that created other metamorphic core complexes in the region. Difficulties exist in linking the ages obtained from the granites to specific tectonic events due to the presence of secondary alteration textures, generations of mineral growth, and multiple episodes of deformation.

  2. Relationship between Bajo Pobre and Chon Aike formations (Deseado Massif, Patagonia, Argentina):a melt inclusions study

    Science.gov (United States)

    Busà, T.; Bellieni, G.; Fernandez, R.; Hecheveste, H.; Piccirillo, E. M.

    2003-04-01

    The Deseado Massif covers the centre-east of the Santa Cruz Province, in the extra-Andean Patagonia. Although the Deseado Massif is mainly composed of silicic volcanic rocks (Chon Aike Formation, CA; 151.5 ±0.5 - 177.8 ±0.4 Ma), mafic and intermediate volcanites (Bajo Pobre Formation, BP; 152.7 ±0.5 and 164 ±0.3 Ma) outcrop largely in the central part of the Massif. In this paper quarz-trapped melt inclusions (rhyolitic in composition) from selected samples of the BP and the CA are analysed. On the basis of major elements content, for BP the sequence from andesite (BP whole rock) to ryholite (trapped as inclusions in quartz) can be modelled by simple fractional crystallisation of ortho- and clinopyroxene, plagioclase, quartz and apatite. As regards trace elements, a good calculated/measured ratio (around 1 ±0.2) is obtained assuming only a relatively high apatite fractionation. Since the apatite fractionation amount is not acceptable for major elements, the evolution of BP Formation cannot be modelled by a simple process of fractional crystallisation, and a contamination process probably occurred. The sequence from BP to CA cannot be modelled by fractional crystallisation. 30% batch melting of BP andesite (BP whole rock) produces a magma from which the CA ryholites (trapped as inclusions in quartz) can be obtained by Rayleigh fractional crystallisation of ortho- and clinopyroxene, plagioclase, magnetite, quartz, apatite and small amounts of zircon and minor allanite. Since the latter one was not observed in the analysed sample, a contamination process during magma evolution cannot be completely excluded. Finally, on the basis of the different trace elements concentration (Nb anomaly, different content in LILE, B/Be and B/Nb), it is possible to suppose that, at the time of the BP and CA emplacement, a changing in the tectonic setting, from subduction to a lithospheric extension, was active.

  3. Using remote sensing imagery and GIS to identify land cover and land use within Ceahlau Massif (Romania

    Directory of Open Access Journals (Sweden)

    GEORGE CRACU

    2014-11-01

    Full Text Available Using remote sensing imagery and GIS to identify land cover and land use within Ceahlău Massif (Romania. In this study we considerer land cover and land use asessment within Ceahlău Massif (Romania using satellite imagery and GIS . To achieve this goal, we used a Landsat 7 ETM + satellite image, which was processed using specialized software in analyzing satellite images and GIS software in several stages:  Downloading, importing and layer stack of all spectral bands composing satellite image;  Establishment of areas of interest for each category of land cover and land use, which were digitized on - screen and for which spectral signatures characteristics were established;  Supervised image classification using Maximum Likelihood Method;  Importing the resulting m ap (raster in GIS environment and creating the final land cover/land use map for Ceahlău Massif. In the study area we identified nine land cover/land use classes: deciduous forests, mixed forests, coniferous forests, secondary grasslands, subalpine vegeta tion, alpine meadows, agricultural land, lakes and built area. By analizing the spatial distribution of these classes, it was found that forests are the best represented class, occupying an area of 188.4 km² (56.4% of total, followed by secondary grassl and, which occupies an area of 68.2 km² (20.4% of total, lakes (26.6 km² or 7.98% of total and agricultural land (16.1 km² or 4.86%

  4. La simulation stochastique des fractures pour évaluer l'incertitude géotechnique dans le cas d'un tunnel en massif rocheux

    OpenAIRE

    2005-01-01

    Les massifs rocheux sont hétérogènes, discontinus et anisotropes. Le comportement mécanique d'un massif dépend fortement de la fracturation naturelle et de ses propriétés, qui doivent donc être prises en compte en particulier dans les travaux de creusement des ouvrages souterrains. On présente ici une application d'une méthodologie complète qui part de la géologie structurale d'un massif et arrive à la simulation géomécanique au voisinage d'un tunnel, en passant par l'analyse des données sur ...

  5. Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: An integrated geodynamic and petrological modelling approach

    Science.gov (United States)

    Palin, Richard M.; Reuber, Georg S.; White, Richard W.; Kaus, Boris J. P.; Weller, Owen M.

    2017-06-01

    The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India-Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure-temperature-time (P-T-t) path has been derived from thermomechanical simulations tailored for Eocene subduction in the northwestern Himalaya. Phase equilibrium modelling performed along this P-T path has described the petrological evolution of felsic and mafic components of the massif crust, and shows that differences in their fluid contents would have controlled the degree of metamorphic phase transformation in each during subduction. Our model predicts that peak P-T conditions of ∼2.6-2.8 GPa and ∼600-620 ∘C, representative of 90-100 km depth (assuming lithostatic pressure), could have been reached just ∼3 Myr after the onset of subduction of continental crust. This P-T path and subduction duration correlate well with constraints reported for similar UHP eclogite in the Kaghan Valley, Pakistan Himalaya, suggesting that the northwest Himalaya contains dismembered remnants of what may have been a ∼400-km-long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. A maximum overpressure of ∼0.5 GPa was calculated in our simulations for a homogeneous crust, although small-scale mechanical heterogeneities may produce overpressures that are larger in magnitude. Nonetheless, the extremely high pressures for peak metamorphism reported by some workers (up to 4.8 GPa) are unreliable owing to conventional thermobarometry

  6. Research the dynamical characteristics of slow deformation waves as a rock massif response to explosions during its outworking

    Science.gov (United States)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2015-04-01

    As a result of long-term natural geomechanics and geophysical observation data on mines of complex ore rocks, generalization of the non-linear reaction of rock massif to heavy dynamic influences have been established. In addition, pendulum type waves have been observed and the sources of them have been located inside geoblocks of different hierarchic levels (Oparin et al., 2010). At the same time, these waves propagate with wide low (compared with seismic waves) velocity values (Kurlenja et al., 1993; Oparin et al., 2006). Research into the massif state with the use of the dynamic systems theory approach (Naimark et al., 2009; Chulichkov, 2003; Hachay et al., 2010) has been developed to ascertain the criteria of dissipative regimes changing for real rock massifs, which are under heavy man-caused influence. To realize such research we used the data from the seismic record of the Tashtagol mine for the two-year period from June 2006 up to June 2008. We used the space-time coordinates for all dynamic massif event responses, which occurred during that period inside the mine space and for the explosions - values fixed by seismic station energy (Hachay et al., 2010). The phase diagrams of the massif state for the northern and southern parts of the mine space were plotted in coordinates Ev(t) and d(Ev(t))/dt, t - time - in parts of 24 hours, Ev - the dissipated massive seismic energy - in joules. Hachay et al., (2010) analysed the morphology of seismic response phase trajectories on the explosion influences during different serial intervals in the southern part of the mine. In that period, according to data for different explosions in the mine, the majority of the total energy had been injected into the southern part of the mine. Moreover, at the end of 2007, just in the southern part, the strongest rock burst during the whole history of the working mine happened. We developed a new processing method of seismological information in real, which we can use directly in the

  7. Les roches basiques et ultrabasiques des Lacs Robert et le Trias de Chamrousse (Massif de Belledonne) Etude petrologique et geologique

    NARCIS (Netherlands)

    Tex, den E.

    1950-01-01

    La région que j’ai étudiée et relevée est située dans les Alpes françaises, à environ 4° longitude est et 50°15’ latitude nord, et à environ 2000 mètres d’altitude. Elle fait partie de la chaîne dite „chaîne de Belledonne” qui s’étend des massifs de Beaufort et du Grand Mont dans le N N E jusqu’à ce

  8. Geochemical features of gold-quartz veins in granitoid intrusives and terrigenous masses of the Yana-Kolyma folded belt in the northeast of Russia

    Science.gov (United States)

    Volkov, A. V.; Sidorov, A. A.; Savva, N. E.; Kolova, E. E.; Murashov, K. Yu.; Sidorova, N. V.

    2016-09-01

    The main task of this study was to reveal geochemical and distinctive features of gold-quartz vein ores of deposits in granitoid intrusive bodies and in terrigenous black-schist masses of the Yana-Kolyma folded belt. The results obtained point to the significant role of metamorphism of the enclosing terrigenous carbonaceous masses in ore formation of both types of deposits. The established facts are not contradictory to the metamorphic-magmagene model of the formation of gold deposits in the Yana-Kolyma belt. The geochemical similarity of both types of deposits shows that these are products of the same orogenic system, which confirms the validity of combining these deposits to form a unified gold-quartz formation.

  9. Typomorphic characteristic features of accessory ilmenite in granitoids of the polyphase Aleisk-Zmeinogorsk complex (N-W Rudny Altai area

    Directory of Open Access Journals (Sweden)

    Novoselov K.L.

    2016-01-01

    Full Text Available The paper material is devoted to the research of crystallomorphology, accessory ilmenite expansion, characteristic features of its chemical composition, paragenetic association and conditions for mineral formation in Devonian granitoids of the polyphase Aleisk-Zmeinogorsk complex. Two ilmenite generations formed at various crystallization stages of the magmatic melt have been identified by the morphological features of the ilmenite crystals, chemical composition and paragenesis. Early-magmatic Ilmenite1 singled out at the protocrystallization stage during reduction and weakly-oxidizing environment conditions. It is characterized by the crystalline-faced shapes, low content of the pyrophanite minal and V admixture. Ilmenite 2 singled out at the major crystallization stage of the melt in the conditions of higher oxygen fugacity as the forms of the flattened, xenomorphic grains with the enhanced pyrophanite concentration and Nb admixture.

  10. Origins of Early Mesozoic granitoids and their enclaves from West Kunlun, NW China: implications for evolving magmatism related to closure of the Paleo-Tethys ocean

    Science.gov (United States)

    Wang, Chao; Liu, Liang; Korhonen, Fawna; Yang, Wen-Qiang; Cao, Yu-Ting; He, Shi-Ping; Zhu, Xiao-Hui; Liang, Wen-Tian

    2016-04-01

    Early Mesozoic granitoids and microgranular enclaves (MEs) are widespread in the West Kunkun, northwestern Tibetan plateau, and record the tectonic evolution of Eurasia-Tethys in this area. This study reports geochemistry, zircon U-Pb and Hf isotopic data for a suite of granitoids and their MEs from the Middle Triassic Bulunkou pluton (BP) and the Late Triassic Akazishan pluton (AP) from the West Kunlun. LA-ICP-MS U-Pb zircon dating of a sample from the BP host monzogranite and an enclave, as well as a AP monzogranite, yielded ages of 236 ± 2, 230 ± 7 and 208 ± 1 Ma, respectively. The BP monzogranite and its enclaves from the northwestern part of the West Kunlun are mainly weakly peraluminous granites characterised by relatively high Rb, Th, Rb/Sr (2.64-9.03) and HREE contents, and low Mg#, Sr/Y and negative Eu anomalies. Zircons from the BP monzogranite have ɛHf(t) values from -5.7 to -1.6. Zircons from enclaves of the BP show more variable ɛHf(t) values from -4.1 to 3.8. We consider that the BP granites are likely to have been formed by partial melting of metasedimentary rocks at shallow crustal depth, and their enclaves, composed of quartz + biotite + plagioclase + garnet + K-feldspar, are relics from the melting of a source at middle crustal depths. The AP host and its enclaves from the southeastern part of the West Kunlun have low Rb, Rb/Sr (0.15-1.90) and weakly negative Eu anomalies but high HREE contents indicating limited fractionation of plagioclase without residual garnet in their source. The inferred protolith is an intermediate igneous rock in the middle or lower crust. MEs hosted in the AP have high Mg# (39.7-45.0) and Nb and weakly negative Eu anomalies, as well as high Sr, P and Ti, corresponding to a medium-K basaltic rock, which may have originated from mixing of partial melting of metasomatised mantle wedge that has been modified by upwelling asthenospheric mantle and crustal melting in the deep source. Post-collisional southeasternward

  11. Sedimentary geology as a key to understanding the tectonic evolution of the Mesozoic-Early Tertiary Paikon Massif, Vardar suture zone, N Greece

    Science.gov (United States)

    Brown, Sally A. M.; Robertson, Alastair H. F.

    2003-08-01

    This paper demonstrates how sedimentary evidence can provide a key to elucidating the regional tectonic and palaeoceanographic significance of a complex partly metamorphic terrane, in this case the Paikon Massif. The Paikon Massif is located centrally within the Vardar-Axios zone of N Greece and is critical to the reconstruction of Neotethys in the E Mediterranean region. The massif is here restored as a single tectono-stratigraphic unit of Jurassic to Early Tertiary age that originated along the margin of a continental unit known as the Serbo-Macedonian Zone. In this area, a Mesozoic oceanic basin, the Almopias Ocean, opened in the Triassic between the Serbo-Macedonian continent to the NE and another continental unit, the Pelagonian Zone, to the SW. Initial deep-water deposition along the northwesterly passive margin of the Almopias Ocean is represented within the Paikon Massif by metamorphosed redeposited carbonates and hemipelagic sediments (Gandatch Formation). Above, this the Jurassic Paikon Volcanic Group comprises two volcanogenic units of island arc-type (Livadia and Kastaneri Formations). The arc developed along the SW margin of the Serbo-Macedonian continent in response to NE subduction of the Almopias Ocean. The subduction also resulted in the opening of a related back-arc basin in Mid-Late Jurassic, represented by the Guevgueli ophiolite, now to the NE of the Paikon Massif. The massif underwent ductile deformation and inferred HP/LT metamorphism during Late Jurassic time, related to subduction beneath the Serbo-Macedonian active margin. Exhumation took place rapidly by Kimmeridgian time, followed by a shallow-water transgression (Khromni Limestones). Subsequent emergence and fluvial deposition (Ghrammos Formation) reflect a regional extensional or transtensional event. Following a marine transgression, influenced by eustatic sea-level rise and tectonic subsidence (Aptian-Albian), a carbonate platform developed throughout the Paikon Massif (Cretaceous

  12. Two-stage fluid flow and element transfers in shear zones during collision burial-exhumation cycle: Insights from the Mont Blanc Crystalline Massif (Western Alps)

    Science.gov (United States)

    Rolland, Y.; Rossi, M.

    2016-11-01

    The Mont-Blanc Massif was intensely deformed during the Alpine orogenesis: in a first stage of prograde underthrusting at c. 30 Ma and in a second stage of uplift and exhumation at 22-11 Ma. Mid-crustal shear zones of 1 mm-50 m size, neighbouring episyenites (quartz-dissolved altered granite) and alpine veins, have localised intense fluid flow, which produced substantial changes in mineralogy and whole-rock geochemistry. Four main metamorphic zones are oriented parallel to the strike of the massif: (i) epidote, (ii) chlorite, (iii) actinolite-muscovite ± biotite and (iv) muscovite ± biotite. In addition, phlogopite-bearing shear zones occur in the chlorite zone, and calcite-bearing shear zones are locally found in the muscovite zone. The initial chemical composition of the granitic protolith is relatively constant at massif scale, which allows investigating compositional changes related to shear zone activity, and subsequent volume change and elements mobility. The variations of whole-rock composition and mineral chemistry in shear zones reflect variations in fluid/rock ratios and fluid's chemistry, which have produced specific mineral reactions. Estimated time-integrated fluid fluxes are of the order of 106 m3/m2. The mineral assemblages that crystallised upon these fluid-P-T conditions are responsible for specific major and trace element enrichments. The XFe (Fe/Fe + Mg) pattern of shear zone phyllosilicates and the δ13C pattern of vein calcite both show a bell-type pattern across the massif with high values on the massif rims and low values in the centre of the massif. These low XFe and δ13C values are explained by down temperature up-flow of a Fe-Mg-CO2-rich and silica-depleted fluid during stage 1, while the massif was underthrusting. These produced phlogopite, chlorite and actinolite precipitation and quartz hydrolysis, resulting in strong volume losses. In contrast, during stage 2 (uplift), substantial volume gains occurred on the massif rims due to the

  13. Geology and uranium occurrences in the Forez tertiary plain (in the French 'Massif Central'); Geologie et mineralisations uraniferes de la plaine tertiaire du Forez (Massif Central francais)

    Energy Technology Data Exchange (ETDEWEB)

    Duclos, P. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses - 92 (France). Centre d' Etudes Nucleaires

    1967-01-01

    In the first part, the observations made during the geological survey of the Forez Tertiary plain (in the French 'Massif Central') are recalled. Then, using various methods, the author lists the formations according to chronology. Finally, a reconstitution of the geological history of this subsidence basin is attempted. In the second part, the occurrence of 17 uranium bearing geochemical anomalies is commented upon. Each of these various anomalies is given a place on the stratigraphic scale. This enables the author to put the successive phases of uranium deposition into their proper perspective in the history of the plain. In conclusion, the author points out the usefulness of these uraniferous geochemical anomalies. (author) [French] Dans la premiere partie, l'auteur rappelle les observations faites au cours de l'etude geologique de la plaine tertiaire du Forez (Massif Central francais). Puis se servant de differentes methodes, il etablit une chronologie des formations. Enfin, il termine par un essai de reconstitution de l'histoire geologique de ce bassin de subsidence. Dans la deuxieme partie, il commente la decouverte de 17 anomalies geochimiques uraniferes. Il situe ces differentes anomalies dans la serie stratigraphique. Ceci lui permet de replacer les depots successifs de l'uranium dans l'histoire de la plaine. Enfin, il indique l'interet de ces anomalies geochimiques uraniferes. (auteur)

  14. Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

    Science.gov (United States)

    Javier Álvaro, J.; Colmenar, Jorge; Monceret, Eric; Pouclet, André; Vizcaïno, Daniel

    2016-06-01

    Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing. The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances.

  15. Research on isotope geology: Isotopes ages of volcanic rocks from Ryeongnam Massif, Korea

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Seong Cheon; Chi, Se Jung; Kim, Yoo Sook [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)

    1997-12-01

    Chronostratigraphy of most volcanic rocks in the Ryeongnam Massif have been undefined or mis-classified in different geological maps due to total absence of reported isotope ages. Twenty-four new isotope ages are given for age-undefined volcanic units and some related igneous bodies. Most of volcanic rocks show high [La/Yb]n ratios and LREE enrichments which are characteristics of subduction-related high-K calc-alkali volcanic rocks occurred in the active continental margin. Preliminary results on carbon and oxygen stable isotope ratios({delta}{sup 13}C=-1.7{approx}-6.2 per mil; {delta}{sup 18} O=-21.6{approx}-24.7 per mil) of druse- or phenocryst-calcite from andesitic and basaltic rocks in the southern coastal region indicate a magmatic origin. Based on new K-Ar whole-rock ages, chronological guidelines are established as follows: 1) Gayasan andesite (78{+-}4Ma) - Gurye andesitic tuff (81{+-}4Ma); 2) Gurye andesite (68{+-}4Ma) - Suncheon andesitic tuff (67{+-}3Ma) - Yeosu basaltic andesite (67{+-}3Ma) - Narodo andesite (70{+-}3Ma); 3) Taebaeg Baegbyeongsan basaltic andesite (62{+-}3Ma) - Gurye Obongsan andesite (64{+-}3Ma) - Yeosu dacite (63{+-}3Ma) - Dolsando andesite (62{+-}3Ma) - Jangheung Buyongsan andesite (65{+-}3Ma); 4) Suncheon Joryedong andesite (55{+-}2Ma) - Goheung andesite (56{+-}3Ma); 5) Taebaeg Baegbyeonsan basaltic andesite (48{+-}2Ma) - Yeosu basalt (51{+-}3Ma). Resetted age (49{+-}2Ma) of an intrusive rhyolite implies the timing of thermal alteration in the Wondong Fe-Mine of the Taebaegsan Mineralized Belt. K-Ar hornblende ages of two hornblendite stocks in the southern Jangsu suggests apparent emplacement-ages of late Triassic (210{+-}9Ma) and early Permian (274{+-}10Ma), independently. K-Ar hornblende age (1023{+-}37Ma) of the Ogbang amphibolite implies a reduction of original age due to later thermal effect probably attributed to either later intrusion or regional metamorphism. (author). 56 refs., 19 tabs., 14 figs.

  16. Nanogranitoids in garnet clinopyroxenites of the Granulitgebirge (Bohemian Massif): evidence for metasomatism and partial melting?

    Science.gov (United States)

    Borghini, Alessia; Ferrero, Silvio; Wunder, Bernd; O'Brien, Patrick J.; Ziemann, Martin A.

    2017-04-01

    Primary nanogranitoids occur in garnet from the garnet clinopyroxenites of the Granulitgebirge, Bohemian Massif. They form clusters in the inner part of the garnet, and may occur both as polycrystalline and glassy inclusions with size from 5 to 20 µm. Because of their random distribution in garnet these inclusions are interpreted as primary inclusions, thus formed during the growth of the garnet. Garnet does not show any major element zoning. Nanogranitoids were identified in garnet clinopyroxenites from two different locations and show slightly different mineral assemblages. Kumdykolite or albite, phlogopite, osumilite, kokchetavite and a variable amount of quartz occur in both locations. However, osumilite is more abundant in one locality and kokchetavite in the other. All these phases are identified using Raman Spectroscopy. Both assemblages are consistent with the origin of these inclusions as former droplets of melt. Nanogranitoids from one locality have been re-homogenized at 1000°C and 22 kbar to a hydrous glass of granodioritic/quartz-monzonitic composition in a piston cylinder apparatus. The chosen experimental conditions correspond to the formation of the host garnet (O'Brien & Rötzler, 2003) and thus of melt entrapment. Nanogranitoid-bearing garnet clinopyroxenites occur in bodies of serpentinized peridotites, hosted in turn in felsic granulites. The garnet clinopyroxenites show granoblastic texture dominated by garnet and clinopyroxene porphyroblasts with a variable amount of interstitial plagioclase, biotite, two generations of amphiboles (brown and green) and rutile and opaque minerals as accessories. The bulk rock composition is basic to intermediate, and the garnet chemistry varies from 24% Alm, 65% Prp and 11% Grs to 38% Alm, 36% Prp and 26 % Grs between one outcrop and the other. The origin of the investigated inclusions could be due to different processes: localized melting of metasomatized mafic rocks with simultaneous production of garnet or

  17. Microfracturing and fluid mixing in granites: W (Sn) ore deposition at Vaulry (NW French Massif Central)

    Science.gov (United States)

    Vallance, Jean; Cathelineau, Michel; Marignac, Christian; Boiron, Marie-Christine; Fourcade, Serge; Martineau, François; Fabre, Cécile

    2001-07-01

    The Vaulry W-(Sn) mineralisation, located at the eastern boundary of the Blond rare metal leucogranite, is contained in a set of subvertical quartz veins, locally with muscovite and minor quartz selvages. The sequence of deposition was: (1) milky quartz, predominantly as fracture filling, generally affected by subsequent ductile deformation; (2) hyaline quartz-wolframite-cassiterite; (3) minor sulphides. Other sets of quartz veinlets, although generally barren are observed in the Blond massif. Fluid migration at the microscopic scale within the granite and in the vicinity of quartz fractures was constrained by studying the geometry of fluid-inclusion planes and fluid-inclusion chemistry in and outside the mineralised area. Three major sets of subvertical fluid-inclusion planes are recognised: a N050°-060°E set, mostly developed in the veins and in the immediate vicinity, a N110°-130°E set, regionally developed in the granite and a N140-160°E set of local extent. As a whole, the density of FIP decreases from the mineralised zones toward the barren part of the pluton, except for the N140°-160°E set. These are locally abundant around quartz veinlets with similar orientations that form a broad "N-S" band near the Blond locality. Mineralising fluids observed as primary inclusions in cassiterite and in undeformed hyaline quartz are mostly aqueous, with moderate salinity and a minor volatile component, at variance with many other W-(Sn) deposits in the Variscan belt. Ore deposition occurred around 315°C, at an estimated depth of 5.5 km, under hydrostatic to slightly suprahydrostatic pressures. It resulted from fluid mixing, in the central part of a large hydrothermal system, between two end-members: (i) a hot (425-430°C) moderately saline fluid, that contained a diluted volatile component and, although Na-dominated, minor amounts of Li and Ca. The estimated δ18O indicates that this fluid was completely equilibrated with the tectono-magmatic pile (pseudo

  18. Generation and evolution processes of Paleoproterozoic massive-type Sancheong anorthosite complex, Yeongnam massif, Korea

    Science.gov (United States)

    Kang, Ji-Hoon; Lee, Deok-Seon

    2016-04-01

    The Paleoproterozoic (˜1.87-1.79 Ga) Sancheong anorthosite complex in the Jirisan province of the Yeongnam massif, Korea, consists of massive-type and foliation-type Sancheong anorthosite (SA), Fe-Ti ore body (FTO), and mafic granulite (MG). We report their characteristics and interrelation on foliations, occurrences, lithofacies, composition minerals, suggesting the generation and evolution processes of the Sancheong anorthosite complex with the origin of their foliations. The main characteristics and interrelation are as follows: multilayer structures of FTO, straight-, anastomosing-, uneven-types FTO and MG veins derived from blocking associate with size reduction of SA, gradual or irregular boundaries of SA blocks, FTO and MG showing bulbous lobate margins and comb structures between SA blocks, flow foliations and linear arrangements of FTO and MG, discontinuous shear zone of SA, orientation of FTO and MG foliations parallel to the boundaries of SA blocks, predominance of FTO and MG foliations toward the boundaries of SA blocks, flow folding structures of FTO and MG foliation, lithfacies change of MG into FTO by the injection of MG into SA, and very similar assemblage of mafic minerals and chemical composition of ilmenite and almost equal occurrence and foliation features between FTO and MG. Such evidences indicate that the SA, FTO, MG foliations are magmatic foliations which were formed in a not fully congealed state of SA from the results of the fracturing of partly congealed SA, the injection and flow of FTO and MG melts into the fractured SA, the dynamic intercompaction between them. It also implies that the SA, FTO, MG were not formed from the intrusion and differentiation of magmas which were different from each other in genesis and age but from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma. Our new model suggests that the Sancheong anorthosite complex was generated and evolved as following sequence: the

  19. Transient thrust events recorded in the Aare Massif, Bernese Alps (Grimsel Test Site, Switzerland)

    Science.gov (United States)

    Hartvich, F.; Stemberk, J.

    2016-12-01

    The Grimsel Test Site (GTS) is located at an altitude of 1730 m a.s.l. in the granitic formations of the Aare Massif 300 - 500 m under the surface. In November 2012, documented faults within the GTS were instrumented for 3-D monitoring of fault slips in the scope of the LArge Scale MOnitoring project (LASMO). In total 7 devices were installed across faults crossing a 350 m long section of the GTS. The instrumented faults have various strike: W-E, SW-NE, WNW-ESE and WSW-ENE. The faults are instrumented with optical-mechanical extensometers TM71 which allow to measure 3D micro-displacements as well as rotations on the basis of the moiré effect of optical interference. The devices installed in GTS reach the accuracy better than 0.007 mm and the angular deviation between two blocks separated by a discontinuity - i.e. their relative rotation - can be measured with a resolution better than 0.00016 rad. Regular monitoring has started on Dec. 5,2012 and the reading is performed regularly once per day. The first results of 3-D fault displacement monitoring show transient slips recorded during 2 short periods along all monitored faults, alternating with long periods of tectonic quiescence without any fault activity. The measured directions of fault slips enable us to estimate two approximately N - S oriented compression events, causing northwards thrust movements. First period lasted from Dec. 27, 2012 to Feb. 13, 2013. However, major phase of the displacement occurred between Jan. 26 and 29, 2013. Recorded fault slips represent northwards oriented thrusts and strike-slips. A value of individual slips ranges from 0.004 to 0.04 mm. Moreover, the strike-slip movements were recorded during days when two local micro-earthquakes were observed close to GTS: on Jan. 29, 2013 (M = 1.29) and on Feb. 13, 2013 (M = 1.15). The second period of activity lasted from Sept. 7, 2013 to Oct. 28, 2013, and occurred after more than 7 months of no recorded fault slips. The main phase of the

  20. Geomorphological map of glaciated gorges in a granitic massif (Gredos range, Central Spain).

    Science.gov (United States)

    Campos, Néstor; Tanarro, Luis Miguel; Palacios, David

    2017-04-01

    A detailed geomorphological map on a 1:10,000 scale is presented for a high mountain area in Gredos range (Iberian Central System), this area is located in a granitic massif 160 km West of Madrid and comprises three gorges : La Vega, Taheña-Honda and La Nava. Only few detailed geomorphological maps of the Gredos range are available despite the wide diversity of landforms, in order to improve the understanding of this zone, this geomorphological map of the area has been produced, showing in detail the geomorphologic diversity of these gorges. The map was created with the aid of 25 cm resolution aerial photographs, 25 cm resolution satellite images, Iberpix 3D images provided by the Spanish National Geographic Institute and verified with field work. The landforms were delimitated with a stereoscope and satellite image pairs and digitized using GIS and CAD software, in some areas 3D glasses has been used with 3D images and the software Esri ArcScene. The landforms resulting from interpretation of aerial photographs and satellite images were classified using the IGUL (Institute of Geography, University of Lausanne) legend system (developed at the end of the 1980s) combined with the legend proposed by Peña et al. (1997) and some personal adaptations. The map legend includes 45 landforms divided into seven sections: structural, hydrography, fluvial, gravitative, glacial, nival and anthropic landforms. The use of both legend systems allows us to represent the landform types distributed over an area of 40 km2 and to identify the geomorphic processes involved in their morphogenesis, this variety of processes and landforms identified demonstrated that geomorphological cartography obtained by combining traditional image interpretation and GIS technology facilitates the production of geomorphological maps and the obtaining of valuable data for identify and understand surface processes and landforms. References: Maillard, B., Lambiel, C., Martin, S., Pellitero, R., Reynard, E

  1. Ssismic Methodologies Applied To The Characterization Of Fractured Rock Massifs: Case Studies

    Science.gov (United States)

    Marti, D.; Carbonell, R.; Flecha, I.; Palomeras, I.; Font-Capo, J.; Vazquez-Sune, E.; Perez-Estaun, A.

    2007-05-01

    The detailed characterization of fractured media in the shallow subsurface is becoming important. The detailed knowledge of the fracture network is mandatory in any hydrogeological model to constrain the potential pathways for water circulation. The geophysical methodolgies can provide a detailed image of the fractured rock and also the 3D distribution of physical properties. Two case studies are discussed in this work. The characterization of fractures in a waste disposal site and, the design and construction of a subway tunnel. In the first case, a multiseismic experiment was carried out in an old abandoned uranium mine. 2D and 3D seismic experiments including VSP, surface seismic reflection and travel time seismic tomography provided a 3D image of the internal structure of a granitic massif for hydrogeological studies of the preferred paths for the migration of contaminants. The tectonic stability of the site was also addressed by means of seismic measurements. The joint interpretation of all the available data enabled the interpretation of the low velocity anomalies in the 3D seismic tomography image as the fragile fractures and the alteration associated to them. A 3D image of the geometry of the heterogeneous weathered surface layer was also obtained. This surface is controlled by the complex network of faults and dykes observed in the area. The second case study involves 2D and 3D seismic experiments to aid the horizontal drilling of tunnels for a new subway line in Barcelona (Spain). Seismic data acquisition in a densely populated city is very difficult. The street layout determines the geometry of the acquisition experiments. The instrumentation can not always be located on the surface projection of the tunnel trace, therefore, pseudo 3D acquisition is required, deploying the instrumentation were it is possible. Furthermore, the shallow subsurface features extremely heterogeneous "weathered" layer of variable thickness (building fundations, sewage system

  2. TRANSITION FROM CARBONATE PLATFORM TO PELAGIC DEPOSITION (MID JURASSIC- LATE CRETACEOUS, VOURINOS MASSIF, NORTHERN GREECE

    Directory of Open Access Journals (Sweden)

    NICOLAOS CARRAS

    2004-03-01

    Full Text Available A Jurassic- Cretaceous carbonate succession crops out along the Zyghosti Rema, Kozani (Northern Greece. The substratum consists of the ophiolitic succession of the Vourinos Massif (Pelagonian Domain: serpentinites tectonically overlain by basalts, with thin lenses of radiolarian cherts of middle Bathonian age. The contact with the overlying Jurassic limestones is tectonic. Eight informal units have been distinguished within the Mesozoic limestones, from the base upwards. (A bioclastic, intraclastic and oolitic packstone (Callovian- Oxfordian. (B bioclastic packstone and coral boundstone (Oxfordian . (C bioclastic and oncoidal wackestone with Clypeina jurassica (Oxfordian- Upper Kimmeridgian. (D (Upper Kimmeridgian- Portlandian: oncoidal packstone and rudstone (facies D1; intraclastic and bioclastic grainstone and packstone (facies D2; neptunian dykes with intraclastic and bioclastic wackestone and packstone filling (facies D3; neptunian dykes with Fe-Mn rich laterite filling and with pink silty filling of early Late Cretaceous age. An unconformity surface, due to emersion and erosion of the platform during the latest Jurassic- Early Cretaceous, is overlain by (E intraclastic, bioclastic packstone and grainstone (Cenomanian. (F massive body of debrites with coral, echinoderm, algae and rudist large clasts (facies F1 (Cenomanian; turbiditic beds of bioclastic, intraclastic and lithoclastic rudstone and grainstone (facies F2. (G thin bedded bioclastic mudstone and wackestone with planktonic foraminifers and radiolarians, alternating with turbiditic beds of bioclastic, intraclastic packstone and rudstone and with conglomeratic levels and slumped beds of the previous turbidites (upper Santonian- lower Campanian. (H: bioclastic packstone with planktonic foraminifers (facies H1 (lower Campanian - ?Maastrichtian; amalgamated turbiditic beds of bioclastic wackestone and packstone with planktonic foraminifers (facies H2; turbiditic beds of bioclastic

  3. 桂北新元古代两类过铝花岗岩的地球化学研究%Geochemical studies on two types of Neoproterozoic peraluminous granitoids in northern Guangxi

    Institute of Scientific and Technical Information of China (English)

    葛文春; 李献华; 李正祥; 周汉文; 李寄嵎

    2001-01-01

    The Neoproterozoic granitoids in northern Guangxi consist ofbiotite granodiorite and biotite granitoids. The geochemical characteristics indicate that biotite granodiorite is equivalent to cordierite-bearing peraluminous granitoids (CPG), while biotite granitoids are similar to muscovite-monzonitic granite (MPG). Biotite granitoids are the result of partial melting of mature crust, and the formation of biotite granodiorites are related to the mixing of mantle plume-derived mafic magma and crustal-derived peraluminous biotite granitic magma. The formation of these two types of Neoproterozoic peraluminous granitoids is irrelevant to the compressional structures caused by collisional orogney which led to crustal thickening, but relevant to extensional structures caused by the ascent of mantle plume which led to the breakup of Rodinia supercontinent.%广西北部新元古代花岗岩类岩石包括黑云母花岗闪长岩和黑云母花岗岩。地球化学特征表明,黑云母花岗闪长岩与含堇青石的过铝花岗岩(CPG)相当,而黑云母花岗岩则类似于白云母二长花岗岩(MPG)。黑云母花岗岩类是成熟地壳岩石部分熔融作用的产物,而黑云母花岗闪长岩类的形成与地幔柱起源的镁铁质岩浆和地壳起源的过铝质黑云母花岗岩浆之间的混合作用有关。这两类新元古代过铝花岗岩的形成与碰撞造山导致地壳加厚的挤压性构造无关,而与导致Rodinia超大陆裂解的地幔柱上升诱发岩石圈伸展的张性构造相联系。

  4. Petrology of an aegirine-riebeckite gneiss-bearing part of the Hesperian massif: The Galiñeiro and surrounding areas, Vigo, Spain

    NARCIS (Netherlands)

    Floor, P.

    1967-01-01

    The investigated area forms part of the crystalline basement of the southwestern half of the Iberian peninsula (Hesperian Massif). In it, Precambrian paragneisses of predominantly greywacke composition surround granite-gneisses with whole-rock Rb-Sr ages of 486-500 m.y. Hercynian granites are intrus

  5. Determination of Granite Rock Massif Weathering and Cracking of Surface Layers in the Oldest Parts of Medieval Mine Depending on Used Mining Method

    Science.gov (United States)

    Lednická, Markéta; Kaláb, Zdeněk

    2016-06-01

    The paper presents the use of selected non-destructive testing methods for the purpose of specifying information on weathering and cracking of surface layers of granite rock massif in the medieval Jeroným Mine (the Czech Republic). This mine has been declared the National Heritage Site of the Czech Republic and its opening as a mining museum to the public is gradually prepared. Geological and geomechanical evaluation documents the possibility to find all kinds of weathering grades of rock massif in this mine. Two non-destructive methods have been tested, namely the measurement of ultrasonic pulse velocity and the measurement of Schmidt hammer rebound value. Field measurements were performed in two selected galleries to verify the application of such methods in specific conditions of underground spaces. Used mining method is one of the parameters later influencing cracking of rock massif. In selected galleries, two different mining methods were used which means that a part of a gallery profile was mined out by hand tools in the Middle Ages and another part of the profile was later mined out by blasting. Measurements in these galleries have enabled to analyse the influence of used mining methods on cracking of rock massif in the impaired zone, and, consequently, on ongoing weathering processes in those zones.

  6. Use of Digital Elevation Models to understand map landforms and history of the magmatism Khibiny Massif (Kola Peninsula, Russia)

    Science.gov (United States)

    Chesalova, Elena; Asavin, Alex

    2016-04-01

    This work presents an improved geomorphological methodology that uses 3D model of relief, remotely-sensed data, geological, geophysical maps and tools of Geographical Information Systems. On the basis of maps of 1: 50,000 and 1: 200,000 the Digital Elevation model (DEM) of Khibiny massif was developed. We used software ARC / INFO v10.2 ESRI. A DEM was used for analyzing landform by extracting the slope gradient, curvature, valley pro?les, slope, aspect and so on. The results were gradually re?ned from the interpretation of satellite imagery and geological map Geomorphological analysis will allow us to determine spatial regularities in inner massive construction. We try to found areas where gas emissions (CH4/H2) enrich, according to morphometry, geology, tectonic and other environments. The main regional blocks were de?ned by different morphological evidences: impression zone, similar to subsidence caldera; uplift zone, domed area (located in the highest part of massif and zone of intersection of main faults) and others. It says that there are the few stages in the development of the Khibiny massif. There is no common concept of the consequence of intrudes magmatic phases now. And we hope that our geomorphical analysis take a new evidences about this problems. Locations of the blocks' borders (tectonic zones) were recognized by lineament analysis of valleys and tectonic faults presented in relief. Erosion system is represented by valleys of 4 ranks. It inherits the zone of tectonic disturbances 3 groups of faults were recognized: 1) Global lineament system cross whole peninsula - existing before Khibiny massif intrusion; 2) Faults associated with the formation of the intrusive phases sequence and magma differentiation and with later collision history during magma cooling; 3) Crack system related to neotectonic process. We believed that if different magmatic phases intrude in similar tectonic environment, the common spatial system of faults will be formed. Really we

  7. The conservation status of mammals and avifauna in the Montagne des Français massif, Madagascar

    Directory of Open Access Journals (Sweden)

    Georgina Starkie

    2009-06-01

    Full Text Available The Montagne des Français is a limestone massif in northern Madagascar, which is characterised by a wide range of biotopes including xerophytic karst, gallery forest, dry western forest, grassland and caves. It is situated only 12 km from the regional capital, Antsiranana, and few, if any areas of primary forest remain. In the first comprehensive study to have been carried out at this location we report the presence of 12 mammal species. We also report the presence of 63 bird species. We use data derived from both structured and semi - structured interviews to assess the conservation status of the mammals and birds within the massif. Our study shows that local beliefs are dominated by taboos or fady and that these vary within families and communities. Current anthropogenic pressures on biodiversity include zebu grazing, charcoal production, hunting and rice cultivation. The massif was afforded Temporary Protected Area Status in 2006 and our results suggest that this protection should be made permanent. We propose opportunities for further research and sustainable development initiatives that could contribute to the conservation of the biological resources within the massif. Success in conserving this area will only be achieved if the local communities are fully engaged. RÉSUMÉ: La Montagne des Français est un massif calcaire au nord de Madagascar, caractérisé par une vaste gamme de biotopes, y compris une formation calcaire connue localement sous le nom de ‘tsingy’ avec une végétation xérophyte, une forêt riveraine, une forêt sèche de l’ouest, des zones herbeuses et des grottes. Elle se trouve à 12 km seulement de la plus grande ville du nord, Antsiranana, et présente une couverture de forêts intactes extrêmement réduite. Le travail sur le terrain a été réalisé par des bénévoles de Frontier et des chercheurs de Frontier et de l’Université d’Antsiranana. Des inventaires on été effectués pendant une année, au

  8. Geoquímica isotópica de los granitoides de la sierra de Chepes: un modelo geotectónico y termal, implicancias para el orógeno famatiniano Isotopic geochemistry of granitoids in the Sierra de Chepe: a geotectonic and thermal model, implications for the Famatinian Orogeny

    Directory of Open Access Journals (Sweden)

    Juan A. Dahlquist

    2004-03-01

    Full Text Available Los datos isotópicos obtenidos a partir de las sierras de Chepes y Los Llanos (orogenia famatiniana, Ordovícico inferior, demuestran que el magma primordial de composición intermedia y metaluminosa (SiO2= 60-62% fue esencialmente derivado por fusión de una antigua litósfera continental, con probable contribución parcial de la litosfera mantélica subcontinental, pero sin contribución directa de la astenósfera. Al mismo tiempo, otro magma primordial fue generado por fusión de una secuencia metasedimentaria, debido al calor proveniente del magma metaluminoso durante su emplazamiento. Aunque el proceso petrogenéticoque explica el origen de los granitoides de la orogenia famatiniana ha sido considerado previamente, no existe un consenso general con relación al modelo geotectónico y termal asociado con la producción de estos magmas. La combinación de los datos isotópicos, petrológicos y geoquímicos de las sierras de Chepes y Los Llanos, sugieren que la demanda térmica requerida para la génesis de los magmas es compatible con un modelo de régimen extensional. El complejo granítico Papudo-Quintero, batolito de la Costa de Chile Central, es representativo del magmatismo comúnmente conocido como andino-tipo. Estudios sobre este complejo granítico indican que el magma primordial fue esencialmente de origen mantélico (manto astenosférico. La generación del magma sigue el clásico escenario para la generación de granitoides producidos en ambientes convergentes de placas, con subducción de una placa oceánica bajo un margen continental y fusión parcial de una cuña astenosférica. Este proceso, contrasta con el modelo extensional propuesto para los granitoides de las sierras de Chepes - Los Llanos, el cual sugiere que el modelo andino-tipo no es aplicable a estos granitoides famatinianos. Los datos geocronológicos y petrológicos sugieren que el magmatismo famatiniano tuvo corta duración y que el régimen extensional inicial

  9. Phlogopite compositions as an indicator of both the geodynamic context of granitoids and the metallogeny aspect in Memve'ele Archean area, northwestern Congo craton

    Science.gov (United States)

    Ntomba, Sylvestre M.; Bidzang, François Ndong; Ottou, José Eric Messi; Goussi Ngalamo, François Jeannot; Bisso, Dieudonné; Magnekou Takamte, Christelle Rufine; Ondoa, Joseph Mvondo

    2016-06-01

    and high temperatures, low and high fugacity and high water fugacity generated Ba-bearing phlogopite grains both in trondhjemite samples (S13W6) and remaining granitoids during partial melting of the mantle. The phlogopite grains with low Mg# in S13W6 sample have more Ba than all remain phlogopites. The presence of high Ba contents in these phlogopite grains can be explained by (1) the admixture of residual and new Ba rich melts or (2) the presence of both low Mg and Mn contents in the octahedral site that generate a large interlayer site which accommodate more Ba or (3) both mechanisms are displayed to crystallize these phlogopite grains. Thus Ba rich phlogopites occur in the fresh granitoids depending only on early magmatic processes or hydrothermal alteration at high temperature. Contents of titanium are only controlled by temperature during phlogopite crystallizations. Moreover, igneous phlogopites are used as metallogenic indicator. The study is useful to the exploration efforts for barium ore and shows that the Ba-rich parent granitoids can produce Ba-rich soils which can be potential economic interest for Cameroon.

  10. Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

    Science.gov (United States)

    Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

    2017-07-01

    The orbicular granitoid of Caldera, located at the northern part of the Chilean Coastal Range, is a spectacular example of radial textures in orbicular structures. The orbicular body crops out as a 375 m2 tabular to lensoidal intrusive sheet emplaced in the Lower Jurassic Relincho pluton. The orbicular structures are 3-7 cm in diameter ellipsoids hosted in a porphyritic matrix. The orbicules are comprised by a Qtz-dioritic core (3-5 cm in diameter) composed by Pl + Hbl + Qtz + Bt ± Kfs with equiaxial textures and a gabbroic shell (2-3 cm in diameter) characterized by feathery and radiate textures with a plagioclase + hornblende paragenesis. The radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core. The radial shell, called here inner shell, is in contact with the granodioritic equiaxial interorbicular matrix through a 2-3 mm wide poikilitic band around the orbicule (outer shell). The outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine-grained rounded plagioclase and magnetite. The oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule, i.e. orthogonal to the radial inner shell. The coarse-grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and K-feldspar megacrysts. This work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole-rock geochemical study of the different parts of the orbicular granitoid, together with thermobarometric and crystallographic data, and theoretical modeling of the crystallization and element partitioning processes. We propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively: superheating, volatile exsolution, undercooling, geochemical fractionation and

  11. Zircon typology combined with SmNd whole-rock isotope analysis to study Brioverian sediments from the Armorican Massif

    Science.gov (United States)

    Dabard, M. P.; Loi, A.; Peucat, J. J.

    1996-02-01

    The identification of source materials contributing to mature terrigenous clastic deposits is made difficult due to a lack of useful discriminant criteria. SmNd isotope analysis can provide some indication of the present of mantle-derived constituents in clastic rocks. However, since this method is based on whole-rock samples, it is only possible to obtain the averaged composition of the different source materials involved. Moreover, SmNd isotope systematics can be strongly influenced by the presence of heavy minerals rich in rare earth elements and/or displaying isotopic ratios very different to the sedimentary host. In this manner, 0.1% of zircon or 0.01% of monazite from an extraneous source is sufficient to modify significatively the SmNd signature of the whole-rock. The typological study of zircon populations is an extremely valuable tool, especially since this mineral is highly resistant and exhibits a morphology controlled by the physical and chemical conditions under which it crystallized. Zircons that have been reworked in a sedimentary deposit display typologies that make it possible to identify the different igneous rock-types present in the source region. Moreover the typological study can be associated with a single-grain PbPb dating. This twofold approach was applied to Brioverian sedimentary rocks (Neoproterozoic III to Early Palaeozoic in age) from the Central Brittany Domain (Armorican Massif, NW France). It is proposed that these deposits inherited a major component from juvenile crustal materials ( ɛND(540) = - 1.4 to - 6.3), reflecting the presence of igneous precursors with a dominantly mantle-derived origin (zircon sub-types S19, S20, S24, S25 etc.), to which was added another component of crustal anatectic affinity (zircon sub-types S2, S6, S7 etc.). Two igneous source regions are identified on the basis of the present study: the anatectic granitic massifs of the Mancellian Batholith (540 Ma), along with a coeval ignimbritic

  12. Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history?

    Science.gov (United States)

    Jedlicka, Radim; Faryad, Shah Wali

    2017-08-01

    High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite

  13. Geochemistry and mineralogy of Pd in the magnetitite layer within the upper gabbro of the Mesoarchean Nuasahi Massif (Orissa, India)

    Science.gov (United States)

    Prichard, Hazel M.; Mondal, Sisir K.; Mukherjee, Ria; Fisher, Peter C.; Giles, Nicolas

    2017-07-01

    Palladium concentrations of 1-3 ppm with an average Pt/Pd ratio of 0.15 have been located for the first time in a magnetitite layer in the Nuasahi Massif in Orissa India. This layer occurs at a high stratigraphic level in the complex and is nearly 4-km long and 5-12-m thick. The sections of the Pd-rich zone identified to date extend over a distance of 1 km at the southern end of the layer. Several phases of mineralization are evident. The first, primary assemblage of platinum-group minerals (PGM) contains Pd-sulfides (vysotskite), Pd-Pb alloys (zvyagintsevite), and a Pd-In alloy, a mineral probably new to mineralogy. These PGM are confined to central magnetite grains in the magnetitites. The magnetite grains with exsolved fine laths of ilmenite at centers are referred to as central magnetite grains. These central magnetite grains are commonly surrounded by blebs of ilmenite and magnetite that contain the majority of the PGM. These are dominated by Pd-antimonides, variably altered to Pd-oxides, and other PGM including PtAs2 (sperrylite), RuS2 (laurite), and IrRhAsS (irarsite/hollingwothite). Many of these PGM also occur in the interstitial silicates, with rare occurrences in the central magnetite grains. We propose that the platinum-group elements (PGE) crystallized during a minor sulfide saturation event that occurred as the magnetitites crystallized. This event produced the minor Cu-sulfides in these magnetitites. Later introduction of antimony and arsenic, during the alteration event that produced the blebby ilmenite and magnetite, led to the more primary PGM being succeeded by the main PGM assemblage, dominated by Pd-antimonides. These are associated with secondary Cu minerals and sperrylite. Subsequent oxidation during weathering in the hot wet Indian climate produced the Pd-oxides. The Nuasahi Massif is a sill-like Archean layered ultramafic-mafic intrusion genetically linked to high-Mg siliceous basalt or boninites and is characterized by unusually thick

  14. Apatite fission track thermochronology of Khibina Massif (Kola Peninsula, Russia): Implications for post-Devonian Tectonics of the NE Fennoscandia

    Science.gov (United States)

    Veselovskiy, Roman V.; Thomson, Stuart N.; Arzamastsev, Andrey A.; Zakharov, Vladimir S.

    2015-12-01

    The thermal history of the Kola Peninsula area of NE Fennoscandia remains almost fully unknown because of the absence of any thermochronological data such as apatite and/or zircon fission track or (Usbnd Th)/He ages. In order to fill this gap and to constrain the post-Devonian erosion and exhumation history of this region, we present the results of apatite fission track (AFT) dating of eleven samples selected from the cores taken from different depths of the northern part of the Khibina intrusive massif. The Rbsbnd Sr isochron age of this alkaline magmatic complex which is located at the center of Kola Peninsula is 368 + 6 Ma (Kramm and Kogarko, 1994). Samples were analyzed from depths between + 520 and - 950 m and yielded AFT ages between 290 and 268 Ma with an age uncertainty (1σ) of between ± 19 Ma (7%) and ± 42 Ma (15%). Mean track lengths (MTL) lie between 12.5 and 14.4 μm. Inverse time-temperature modeling was conducted on the age and track length data from seven samples of the Khibina massif. Thermal histories that best predict the measured data from three samples with the most reliable data show three stages: (1) 290-250 Ma-rapid cooling from > 110 °C to 70 °C/50 °C for lower/upper sample correspondingly; (2) 250-50 Ma-a stable temperature stage; (3) 50-0 Ma-slightly increased cooling rates down to modern temperatures. We propose that the first cooling stage is related to late-Hercynian orogenesis; the second cooling stage may be associated with tectonics accompanying with opening of Arctic oceanic basin. The obtained data show that geothermal gradient at the center of Kola Peninsula has remained close to the modern value of 20 °C/km for at least the last 250 Myr. AFT data show that the Khibina massif has been exhumed not more then 5-6 km in the last 290 Myr.

  15. Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain

    Science.gov (United States)

    Marchesi, Claudio; Garrido, Carlos J.; Bosch, Delphine; Bodinier, Jean-Louis; Gervilla, Fernando; Hidas, Károly

    2013-01-01

    Geochemical studies of primitive basalts have documented the presence of crustal-derived garnet pyroxenite in their mantle sources. The processes whereby melts with the signature of garnet pyroxenite are produced in the mantle are, however, poorly understood and somewhat controversial. Here we investigate a natural example of the interaction between melts of garnet pyroxenite derived from recycled plagioclase-rich crust and surrounding mantle in the Ronda peridotite massif. Melting of garnet pyroxenite at ˜1.5 GPa generated spinel websterite residues with MREE/HREE fractionation and preserved the positive Eu anomaly of their garnet pyroxenite precursor in whole-rock and clinopyroxene. Reaction of melts from garnet pyroxenite with depleted surrounding peridotite generated secondary fertile spinel lherzolite. These secondary lherzolites differ from common spinel lherzolite from Ronda and elsewhere by their lower-Mg# in clinopyroxene, orthopyroxene and olivine, lower-Cr# in spinel and higher whole-rock Al2O3, CaO, Sm/Yb and FeO* at a given SiO2. Remarkably, secondary spinel lherzolite shows the geochemical signature of ghost plagioclase in the form of positive Eu and Sr anomalies in whole-rock and clinopyroxene, reflecting the transfer of a low-pressure crustal imprint from recycled pyroxenite to hybridized peridotite. Garnet pyroxenite melting and melt-peridotite interaction, as shown in the Ronda massif, may explain how the signature of subducted or delaminated crust is transferred to the mantle and how a garnet pyroxenite component is introduced into the source region of basalts. The efficiency of these processes in conveying the geochemical imprint of crustal-derived garnet pyroxenite to extruded lavas depends on the reactivity of pyroxenite melt with peridotite and the mantle permeability, which may be controlled by prior refertilization reactions similar to those documented in the Ronda massif. Highly fertile heterogeneities produced by pyroxenite

  16. Soil thermal regime and geomorphogenesis at Fuentes Carrionas massif (Cantabrian Range, NW Iberian Peninsula).

    Science.gov (United States)

    Pellitero, Ramon; Serrano Cañadas, Enrique

    2015-04-01

    Fuentes Carrionas is a massif within the Cantabrian Range, in NW Iberian Peninsula. Its altitude ranges between 1400 and 2500 meters and its climate is an oceanic/Mediterranean transition one, with cold temperatures and heavy snowfall in the winter/early spring season, and a warm and dry summer season. Due to its outstanding altitude and lithological variety in the Cantabrian Range context, Fuentes Carrionas holds some periglacial activity (gelifluction, frost shattering) which is absent elsewhere in NW Iberian Peninsula. This work is relates the soil thermal regime across the mountain gradient to landforms formation. 14 thermometers (11 i-button, protected in a plastic can, and three UTL data loggers) were buried at a shallow depth (10 cm.) between autumn 2009 and summer 2012. 12 thermometers were placed between 1900 and 2400 m.a.s.l. at 250 meters altitude interval at the four main aspects. Two additional thermometers were place in the Curavacas N face for permafrost identification. Thermometers were calibrated to yield a measurement every 6 hours starting from 8 AM during one year's time. Data was collected annually in the summer season. Some additional soil temperature data was obtained from an external project in the same area for the 2007-2009 interval. In this case thermometers were "Hobbo" model, and they were also buried to a shallow depth. Results show a permafrost free mountain range. Annual average soil temperatures range between 1 and 8 degrees Celsius. Snow pack appears as a decisive factor in winter temperatures, as the zero curtain effect can be tracked in many cases. Snow cover patterns show a distinctive behavior between S and N aspects, with a 3 months snow cover on the southern faces and between 6 and 9 at the northern analogues. This cover has a relevant impact on geomorphological processes. There is a clear relation between spring snow melt and solifluction or channelized erosion. Also, snow cover prevents the occurrence of freeze/thaw cycles

  17. Mineralogy and ore fluid chemistry of the Roc Blanc Ag deposit, Jebilet Hercynian massif, Morocco

    Science.gov (United States)

    Essarraj, Samira; Boiron, Marie-Christine; Cathelineau, Michel; Tarantola, Alexandre; Leisen, Mathieu; Hibti, Mohamed

    2017-03-01

    The Roc Blanc Ag deposit is located about 20 km north of Marrakesh city (Morocco) in the Jebilet Hercynian massif. The ore bodies consist of N-S to NE-SW quartz (±carbonates) veins hosted by the Sarhlef marine sediments. These series, deposited in a Devonian-Carboniferous rift basin context, were deformed during the Hercynian orogeny, and submitted to low-grade regional metamorphism. Two major stages of fluid circulation and metal deposition are distinguished on the basis of mineralogical and paleo-fluid studies carried out on quartz and dolomite (microthermometry, Raman spectroscopy, LA-ICP-MS on individual inclusions, and O, H stable isotope data): (i) an early Fe-As stage, characterized by the circulation of metamorphic aqueous-carbonic fluids, under P-T conditions lower than 200 MPa ± 20 MPa and 400 °C respectively, along N-S structures; (ii) the ore stage, characterized by the circulation of a Na-Mg-K ± Ca high salinity brine, poor in gas but rich in metals such as Fe, Sr, Ba, Zn, Pb, ± Cu (salinity ranging from 19.6 wt% to likely more than 30 wt% NaCl equiv.) and the deposition of a sphalerite/dolomite-calcite assemblage; such a fluid likely evolved to a Na-K-(Ca-Mg)-Ag brine, with significant Pb and Sb concentrations and lower Sr, Ba and Zn concentrations than in the preceding fluid (salinity up to 19.4 wt% NaCl equiv.). The Ag content of the second mineralizing brine ranges from 0.9 mmol/kg to 9.4 mmol/kg solution (100 ppm-1000 ppm), whereas the base metal brine is generally Ag poor (up to 1.3 mmol/kg solution: 140 ppm). Dilution of the Ag brine by low salinity fluids (<6 wt% NaCl equiv., and Th from 130° to 230 °C) seems to be the main driving mechanism for the Ag ore deposition at Roc Blanc, with a possible involvement of cooling and reduction reactions in black schists. Base metal and Ag fluids may have circulated at average temperatures around 200 ± 30 °C or slightly higher and under hydrostatic pressures, along dominant E-W structures. The ore

  18. Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France)

    Science.gov (United States)

    Cosmidis, Julie; Benzerara, Karim; Morin, Guillaume; Busigny, Vincent; Lebeau, Oanez; Jézéquel, Didier; Noël, Vincent; Dublet, Gabrielle; Othmane, Guillaume

    2014-02-01

    The availabilities of iron and phosphorus have considerably impacted biological productivity in past and present natural aquatic environments, and therefore have been key regulators of climate changes over geological time scales. Microbial organisms are known to play important roles in reactions that drive Fe and P cycling at redox interfaces in Earth's surface environments. Here we study the depth variations of Fe and P speciation in Lake Pavin (Massif Central, France), a deep (bottom depth ˜92 m) and permanently stratified lake with anoxic and ferruginous conditions in the water column below ˜60 m depth. We particularly focus on the potential roles of microbes on Fe and P transformations and traces left by these processes in the sedimenting particular matter. Bulk chemical analyses, powder X-ray diffraction and X-ray absorption spectroscopy (XAS) at the Fe K-edge were performed to characterize the mineralogy and Fe oxidation state of solid particles at different depths in the water column and in sediments deposited at the bottom of the lake. Fe is mainly hosted by Fe(III)-(oxyhydr)oxides and phyllosilicates in the shallower oxygenated water column of the lake (25 m). The amount of Fe in suspended matter increases with depth, and an additional amorphous Fe(II)-Fe(III)-phosphate phase is detected close to the chemocline (at 56 m depth), while vivianite (an Fe(II)-phosphate with a formula of Fe(II)3(PO4)2·8(H2O)) becomes dominant in the deeper anoxic water (67 m and 86 m depths). Fe-(oxyhydr)oxides are preserved down to these depths in the water column suggesting that Fe-reduction has little impact on the particulate Fe budget over the monimolimnion. These Fe-(oxyhydr)oxides undergo reductive dissolution at the surface of the sediments, where vivianite is the main Fe-bearing phase. These results are confirmed by imaging at the micrometer and nano-scales using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and synchrotron-based scanning

  19. The tectonic evolution of the Irtysh tectonic belt: New zircon U-Pb ages of arc-related and collisional granitoids in the Kalaxiangar tectonic belt, NW China

    Science.gov (United States)

    Hong, Tao; Klemd, Reiner; Gao, Jun; Xiang, Peng; Xu, Xing-Wang; You, Jun; Wang, Xin-Shui; Wu, Chu; Li, Hao; Ke, Qiang

    2017-02-01

    Precise geochronological constraints of the Irtysh tectonic belt situated between the Saur Island Arc and the Altay Terrane are crucial to a better understanding of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Recently, we discovered repeatedly deformed arc-related and collisional granitoids in the Kalaxiangar tectonic belt (KTB), which is located in the eastern part of the Irtysh tectonic belt. In this study, we report new whole-rock geochemical, zircon U-Pb and Hf isotopic data of the arc-related and collisional granitoids. Our data reveal that 1) arc-related granodioritic porphyries formed at ca. 382-374 Ma. Recrystallized zircon grains from a (ultra-)mylonitic granodiorite of the Laoshankou zone in the southern KTB display a U-Pb age of ca. 360 Ma; 2) syn-collisional granodioritic porphyries, which distribute along faults and parallel to the cleavage, were emplaced at ca. 367-356 Ma, with εHf(t) values varying from + 7.8 to + 14.2 and Hf model ages from 873 to 459 Ma; 3) a post-collisional A-type granodioritic porphyry, which crosscuts the NW-NNW trending schistosity of the metasedimentary country rocks at a low angle, has an age of ca. 324-320 Ma, while the εHf(t) values range from + 7.6 to + 14.4 with Hf model ages from 850 to 416 Ma; 4) post-collisional strike-slip A-type granite dykes, exposed along strike-slip faults, gave ages between 287 and 279 Ma, whereas the εHf(t) values range from + 4.9 to + 12.7 and the Hf model ages from 995 to 500 Ma; and 5) A-type biotite granite dykes, which intruded along conjugate tension joints, have ages of 274-271 Ma, and εHf(t) values from + 1.5 to + 13.2 with Hf model ages from 1196 to 454 Ma. Consequently, we propose that the collision between the Saur Island Arc and the Altay Terrane occurred in the Early Carboniferous (ca. 367-356 Ma) and the subsequent post-collisional tectonic process continued to the Late Carboniferous (ca. 324-320 Ma). It is further suggested that the Irtysh tectonic belt

  20. Comparison of the behaviour of rare earth elements in surface waters, overburden groundwaters and bedrock groundwaters in two granitoidic settings, Eastern Sweden

    Energy Technology Data Exchange (ETDEWEB)

    Roennback, Pernilla [School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar (Sweden)], E-mail: pernilla.ronnback@hik.se; Astroem, Mats [School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar (Sweden); Gustafsson, Jon-Petter [Department of Land and Water Resources Engineering, KTH, Royal Institute of Technology, SE-100 44 Stockholm (Sweden)

    2008-07-15

    This work, which was done within the Swedish nuclear waste management program, was carried out in order to increase the understanding of the mobility and fate of rare earth elements (REEs) in natural boreal waters in granitoidic terrain. Two areas were studied, Forsmark and Simpevarp, one of which will be selected as a site for spent nuclear fuel. The highest REE concentrations were found in the overburden groundwaters, in Simpevarp in particular (median {sigma}REE 52 {mu}g/L), but also in Forsmark (median {sigma}REE 6.7 {mu}g/L). The fractionation patterns in these waters were characterised by light REE (LREE) enrichment and negative Ce and Eu anomalies. In contrast, the surface waters had relatively low REE concentrations. They were characterised either by an increase in relative concentrations throughout the lanthanide series (Forsmark which has a carbonate-rich till) or flat patterns (Simpevarp with carbonate-poor till), and had negative Ce and Eu anomalies. In the bedrock groundwaters, the concentrations and fractionation patterns of REEs were entirely different from those in the overburden groundwaters. The median La concentrations were low (just above 0.1 {mu}g/L in both areas), only in a few samples were the concentrations of several REEs (and in a couple of rare cases all REEs) above the detection limit, and there was an increase in the relative concentrations throughout the lanthanide series. In contrast to these large spatial variations, the temporal trends were characterised by small (or non existent) variations in REE-fractionation patterns but rather large variations in concentrations. The Visual MINTEQ speciation calculations predicted that all REEs in all waters were closely associated with dissolved organic matter, and not with carbonate. In the hydrochemical data for the overburden groundwater in particular, there was however a strong indication of association with inorganic colloids, which were not included in the speciation model. Overall the

  1. Repeated granitoid intrusions during the Neoproterozoic along the western boundary of the Saharan metacraton, Eastern Hoggar, Tuareg shield, Algeria: An AMS and U-Pb zircon age study

    Science.gov (United States)

    Henry, B.; Liégeois, J. P.; Nouar, O.; Derder, M. E. M.; Bayou, B.; Bruguier, O.; Ouabadi, A.; Belhai, D.; Amenna, M.; Hemmi, A.; Ayache, M.

    2009-09-01

    The N-S oriented Raghane shear zone (8°30') delineates the western boundary of the Saharan metacraton and is, with the 4°50' shear zone, the most important shear zone in the Tuareg shield. It can be followed on 1000 km in the basement from southern Aïr, Niger to NE Hoggar, Algeria. Large subhorizontal movements have occurred during the Pan-African orogeny and several groups of granitoids intruded during the Neoproterozoic. We report U-Pb zircon datings (laser ICP-MS) showing that three magmatic suites of granitoids emplaced close to the Raghane shear zone at c. 790 Ma, c. 590 and c. 550 Ma. A comprehensive and detailed (158 sites, more than 1000 cores) magnetic fabric study was performed on 8 plutons belonging to the three magmatic suites and distributed on 200 km along the Raghane shear zone. The main minerals in all the target plutons do not show visible preferential magmatic orientation except in narrow shear zones. The AMS study shows that all plutons have a magnetic lineation and foliation compatible with the deformed zones that are zones deformed lately in post-solidus conditions. These structures are related to the nearby mega-shear zones, the Raghane shear zone for most of them. The old c. 793 Ma Touffok granite preserved locally its original structures. The magnetic structures of the c. 593 Ma Ohergehem pluton, intruded in the Aouzegueur terrane, are related to thrust structures generated by the Raghane shear zone while it is not the case of the contemporaneous plutons in the Assodé-Issalane terrane whose structures are only related to the subvertical shear zones. Finally, the c. 550 Ma granite group has magnetic structure related to the N-S oriented Raghane shear zone and its associated NNE-SSW structures when close to them, but NW-SE oriented when further. These NW-SE oriented structures appear to be characteristic of the late Neoproterozoic evolution of the Saharan metacraton and are in relation to the convergence with the Murzuq craton. This

  2. Mineralogy and geochemistry of granitoids from Kinnaur region, Himachal Higher Himalaya, India: Implication on the nature of felsic magmatism in the collision tectonics

    Indian Academy of Sciences (India)

    Brajesh Singh; Santosh Kumar; Masao Ban; Kazuo Nakashima

    2016-10-01

    Felsic magmatism in the southern part of Himachal Higher Himalaya is constituted by Neoproterozoic granite gneiss (GGn), Early Palaeozoic granitoids (EPG) and Tertiary tourmaline-bearing leucogranite (TLg). Magnetic susceptibility values ($\\lt$3 ×10$^{−3}$ SI), molar Al$_2$O$^3$/(CaO+Na$_2$O+K$_2$O) ($\\geq$1.1), mineral assemblage (bt–ms–pl–kf–qtz ± tur ± ap), and the presence of normative corundum relate these granitoids to peraluminous S-type, ilmenite series (reduced type) granites formed in a syncollisional tectonic setting. Plagioclase from GGn (An$_{10}$–An$_{31}$) and EPG (An$_{15}$–An$_{33}$) represents oligoclase to andesine and TLg (An$_2$–An$_{15}$) represents albite to oligoclase, whereas compositional ranges of K-feldspar are more or less similar (Or$_{88}$ to Or$_{95}$ in GGn, Or$_{86}$ to Or$_{97}$ in EPG and Or$_{87}$ to Or$_{94}$ in TLg). Biotites in GGn (Mg/Mg+Fe$^t$ = 0.34–0.45), EPG (Mg/Mg+Fe$^t$ = 0.27–0.47), and TLg (Mg/Mg+Fe$^t$ = 0.25–0.30) are ferribiotites enriched in siderophyllite, which stabilised between FMQ and HM buffers and are characterised by dominant 3Fe$\\rightleftarrows$2Al, 3Mg$\\rightleftarrows$2Al substitutions typical of peraluminous (S-type), reducing felsic melts. Muscovite in GGn (Mg/Mg+Fe$^t$ = 0.58–0.66), EPG (Mg/Mg+Fe$^t$ = 0.31−0.59), and TLg (Mg/Mg+Fet = 0.29–0.42) represent celadonite and paragonite solid solutions, and the tourmaline fromEPG and TLg belongs to the schorl-elbaite series, which are characteristics of peraluminous, Li-poor, biotite-tourmaline granites. Geochemical features reveal that the GGn and EPG precursor melts were most likely derived from melting of biotite-rich metapelite and metagraywacke sources, whereas TLg melt appears to have formed from biotite-muscovite rich metapelite and metagraywacke sources. Major and trace elements modelling suggest that the GGn, EPG and TLg parental melts have experienced low degrees (∼13, ∼17 and ∼13%, respectively) of kf

  3. New petrographic, geochemical and geochronological data for the Reguengos de Monsaraz pluton (Ossa Morena Zone, SW Iberian Massif, Portugal)

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, A.; Santos, J. F.; Azevedo, M. R.; Mendez, M. H.; Ribeiro, S.

    2010-07-01

    The Reguengos de Monsaraz pluton is a late to post-tectonic Variscan intrusion occurring in the Ossa Morena Zone (Iberian Variscan Chain). The dominant lithological types are tonalites and granodiorites, but the internal area of the massif is composed of gabbro-dioritic rocks. Field evidence shows that the intrusion is heterogeneous at mesoscopic scale suggesting that the emplacement of mafic and felsic magmas was contemporaneous. Petrographic and geochemical studies reveal that the different lithologic types define a continuous sequence with compositions varying from metaluminous to slightly peraluminous and a typical calc-alkaline signature. In Harker variation diagrams, it is possible to observe systematic rectilinear correlations pointing to the involvement of magma mingling/mixing processes in the petrogenesis of this sequence. Rb-Sr isotopic data, using a mineral-mineral pair from a granodiorite sample, yielded an age of 298 Ma, interpreted as a cooling age after igneous crystallization. (Author) 13 refs.

  4. The promotion of geotourism in protected areas: a proposal of itinerary through the Matese Massif (Campania and Molise regions, Italy).

    Science.gov (United States)

    Rosskopf, Carmen Maria; Filocamo, Francesca; Amato, Vincenzo; Cesarano, Massimo

    2016-04-01

    The Matese Massif is a ca. 1000 km2 wide and NW-SE elongated carbonate relief, located in the inner sector of the Southern Apennine chain. It has a tabular setting with steep structural slopes bordering the central high mountain sector including its major peaks and is crossed from approximately west to east by the border between Campania and Molise regions. The Matese Mountains represent a key area for the comprehension of the geological and tectonic evolution of the Southern Apennines since Mesozoic times. Its long-term geomorphological evolution has been controlled by Quaternary tectonics and climate variations that have allowed the temporary or permanent establishment of various environments and morphodynamics. Deposits and landforms originated by glacial, periglacial, karst and fluvial processes, along with a rich assemblage of tectonic-structural features and landforms of complex origin have given origin to a geological heritage of exceptional value. The geosites actually censured within the Campanian sector of Matese are reported in the Geosites Map of Campania, available at the website of Campania Region and partly included in the Italian Geosites Inventory of ISPRA. The geosites of the Molise sector have been recently assessed within the geosite inventory carried out by Molise University. They are reported in the Geosites Map of Molise, available at the website of Molise Region, and partly included in the ISPRA's National Inventory of Geosites. The Matese area is largely included in protected areas: the Campania portion falls within the Matese Regional Park, established in 2002, while most of the Molise sector falls in the extensive ZPS/SIC IT72222287. To better protect and exploit the unique natural and geological heritage of the Matese Massif, numerous initiatives aimed at the establishment of the National Park of Matese have continued for several years and very recent attempts to promote the Matese Geopark have been made, but unfortunately without any

  5. High grade metamorphism in the Bundelkhand massif and its implications on Mesoarchean crustal evolution in central India

    Indian Academy of Sciences (India)

    S P Singh; S B Dwivedi

    2015-02-01

    The Bundelkhand Gneissic Complex (BnGC) in the central part of the Bundelkhand massif preserves a supracrustal unit which includes pelitic (garnet–cordierite–sillimanite gneiss, garnet–sillimanite gneiss, biotite gneiss and garnet–biotite gneiss) and mafic (hornblende–biotite gneiss and garnetiferous amphibolite) rocks. Granulite facies metamorphism of the complex initiated with breaking down of biotite to produce garnet and cordierite in the pelitic gneisses. Geothermobarometric calculations indicate metamorphic conditions of 720°C/6.2 kbar, followed by a retrograde (687°C/4.9 kbar) to very late retro-grade stages of metamorphism (579°C/4.4 kbar) which is supported by the formation of late cordierite around garnet. The P–T conditions and textural relations of the garnet–cordierite-bearing gneiss suggest a retrograde cooling path of metamorphism.

  6. CLASTS OF UPPERMOST ALBIAN (VRACONIAN LIMESTONE IN THE EOCENE CUCCURU 'E FLORES CONGLOMERATE OF THE M. ALBO MASSIF (EASTERN SARDINIA

    Directory of Open Access Journals (Sweden)

    IGINIO DIENI

    2012-03-01

    Full Text Available Rare clasts of richly fossiliferous uppermost Albian (Vraconian auctt. glauconitic and phosphatic, ammonite-bearing limestone have been found in the Eocene Cuccuru ’e Flores Conglomerate in the area of M. Albo massif (eastern Sardinia. The limestone is wholly comparable in facies and fossil assemblage to the classical outcrop known in the Orosei area. The fossil content includes also brachiopods and abundant planktonic foraminifers of the Thalmanninella (formerly Rotalipora appenninica Zone. In the palaeontological part the brachiopods Orbirhynchia parkinsoni and Capillithyris capillata are described and discussed. Vraconian highly condensed deposits, characterized by basal erosional gaps of variable importance, have particular relevance, being known to be widely distributed in the northern Tethyan margin with common characteristics, such as authigenic glauconite, phosphatic nodules and a rich outer-shelf fauna. 

  7. Multistage evolution of UHT granulites from the southernmost part of the Gföhl Nappe, Bohemian Massif, Lower Austria

    Science.gov (United States)

    Schantl, Philip; Hauzenberger, Christoph; Linner, Manfred

    2016-04-01

    A detailed petrological investigation has been undertaken in leucocratic kyanite-garnet bearing and mesocratic orthopyroxene bearing granulites from the Dunkelsteiner Wald, Pöchlarn-Wieselburg and Zöbing granulite bodies from the Moldanubian Zone in the Bohemian Massif (Austria). A combination of textural observations, conventional geothermobarometry, phase equilibrium modelling as well as major and trace element analyses in garnet enables us to confirm a multistage Variscan metamorphic history. Chemically homogenous garnet cores with near constant grossular-rich plateaus are considered to reflect garnet growth during an early HP/UHP metamorphic evolution. Crystallographically oriented rutile exsolutions restricted to those grossular-rich garnet cores point to a subsequent isothermal decompression of the HP/UHP rocks. Overgrowing garnet rims show a pronounced zonation and are interpreted as the result of dehydration melting reactions during an isobaric heating phase which could have taken place near the base of an overthickened continental crust, where the previously deeply subducted rocks were exhumed to. For this HP granulite facies event maximum PT conditions of ~1050 °C and 1.6 GPa have been estimated from leucocratic granulites comprising the peak mineral assemblage quartz, ternary feldspar, garnet, kyanite and rutile. The pronounced zoning of garnet rims indicates that the HP granulite facies event must have been short lived since diffusion in this temperature region is usually sufficient fast to homogenize a zoning pattern in garnet. A retrogressive metamorphic stage is documented in these rocks by the replacement of kyanite to sillimanite and the growth of biotite. This retrograde event took place within the granulite facies but at significantly lower pressures and temperatures with ~0.8 GPa and ~760 °C. This final stage of re-equilibration is thought to be linked with a second exhumation phase into middle crustal levels accompanied by intensive

  8. Statistical adaptation of ALADIN RCM outputs over the French alpine massifs - application to future climate and snow cover

    Science.gov (United States)

    Rousselot, M.; Durand, Y.; Giraud, G.; Mérindol, L.; Dombrowski-Etchevers, I.; Déqué, M.

    2012-01-01

    In this study, snowpack scenarios are modelled across the French Alps using dynamically downscaled variables from the ALADIN Regional Climate Model (RCM) for the control period (1961-1990) and three emission scenarios (SRES B1, A1B and A2) by the mid- and late of the 21st century (2021-2050 and 2071-2100). These variables are statistically adapted to the different elevations, aspects and slopes of the alpine massifs. For this purpose, we use a simple analogue criterion with ERA40 series as well as an existing detailed climatology of the French Alps (Durand et al., 2009a) that provides complete meteorological fields from the SAFRAN analysis model. The resulting scenarios of precipitation, temperature, wind, cloudiness, longwave and shortwave radiation, and humidity are used to run the physical snow model CROCUS and simulate snowpack evolution over the massifs studied. The seasonal and regional characteristics of the simulated climate and snow cover changes are explored, as is the influence of the scenarios on these changes. Preliminary results suggest that the Snow Water Equivalent (SWE) of the snowpack will decrease dramatically in the next century, especially in the Southern and Extreme Southern part of the Alps. This decrease seems to result primarily from a general warming throughout the year, and possibly a deficit of precipitation in the autumn. The magnitude of the snow cover decline follows a marked altitudinal gradient, with the highest altitudes being less exposed to climate change. Scenario A2, with its high concentrations of greenhouse gases, results in a SWE reduction roughly twice as large as in the low-emission scenario B1 by the end of the century. This study needs to be completed using simulations from other RCMs, since a multi-model approach is essential for uncertainty analysis.

  9. Statistical adaptation of ALADIN RCM outputs over the French alpine massifs – application to future climate and snow cover

    Directory of Open Access Journals (Sweden)

    I. Dombrowski-Etchevers

    2012-01-01

    Full Text Available In this study, snowpack scenarios are modelled across the French Alps using dynamically downscaled variables from the ALADIN Regional Climate Model (RCM for the control period (1961–1990 and three emission scenarios (SRES B1, A1B and A2 by the mid- and late of the 21st century (2021–2050 and 2071–2100. These variables are statistically adapted to the different elevations, aspects and slopes of the alpine massifs. For this purpose, we use a simple analogue criterion with ERA40 series as well as an existing detailed climatology of the French Alps (Durand et al., 2009a that provides complete meteorological fields from the SAFRAN analysis model. The resulting scenarios of precipitation, temperature, wind, cloudiness, longwave and shortwave radiation, and humidity are used to run the physical snow model CROCUS and simulate snowpack evolution over the massifs studied. The seasonal and regional characteristics of the simulated climate and snow cover changes are explored, as is the influence of the scenarios on these changes. Preliminary results suggest that the Snow Water Equivalent (SWE of the snowpack will decrease dramatically in the next century, especially in the Southern and Extreme Southern part of the Alps. This decrease seems to result primarily from a general warming throughout the year, and possibly a deficit of precipitation in the autumn. The magnitude of the snow cover decline follows a marked altitudinal gradient, with the highest altitudes being less exposed to climate change. Scenario A2, with its high concentrations of greenhouse gases, results in a SWE reduction roughly twice as large as in the low-emission scenario B1 by the end of the century. This study needs to be completed using simulations from other RCMs, since a multi-model approach is essential for uncertainty analysis.

  10. The 226Ra isotope activities in ground water samples drawn of two wells from the Meridional Pluton, Morungaba Granitoids, eastern Sao Paulo State; Atividades do 226Ra em aguas subterraneas extraidas de dois pocos localizados no pluton meridional, granitoides de Morungaba, SP

    Energy Technology Data Exchange (ETDEWEB)

    Lucas, Fabio de Oliveira; Silva Junior, Mario Goncalves da; Bertolla, Luciana; Ribeiro, Fernando Brenha [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas. Dept. de Geofisica]. E-mail: brenha@iag.usp.br

    2005-07-01

    The 226Ra activities, both in solution and associated with suspended solids, were measured in ground water samples drawn from two wells drilled in a fractured granitic aquifer from the Meridional Pluton, Morungaba Granitoids, eastern Sao Paulo State. The 226Ra isotope activities were measured in a sequence of samples collected about one month apart between March, 2003 and April 2004. The 226Ra activities were measured by radon gas emanometry. The mean dissolved 226Ra activity concentration activities observed in the two wells were (44.9 {+-} 7.1) mBq/L and (51.6 {+-} 8.8) mBq/L. The 226Ra activity of the suspend solids in a liter of these waters varied between (0,6 {+-} 0,1) mBq and (13 {+-} 1) mBq, respectively. (author)

  11. Variaciones texturales y movilidad geoquímica asociadas a milonitización: la zona de cizalla del granitoide El Tigre, Sierra de Pie de Palo, Sierras Pampeanas Occidentales, San Juan

    Directory of Open Access Journals (Sweden)

    Brígida Castro De Machuca

    2010-03-01

    Full Text Available Una faja de cizalla dúctil con foliación milonítica de dirección NEE y buzamiento al sudeste, afecta a un granitoide mesoproterozoico (Granitoide El Tigre: 31º31'30''S-68º15'12''O que forma parte del basamento cristalino de la Sierra de Pie de Palo, Sierras Pampeanas Occidentales. El análisis cinemático de la faja indica una componente principal de desplazamiento de rumbo con sentido de movimiento dextral. En el granitoide no deformado (protolito se preservan asociaciones minerales y texturas relícticas, ígneas y metamórficas, que son obliteradas por la deformación. La milonitización operó en un sistema abierto provocando la movilización (ganancia o pérdida de casi todos los elementos mayores y traza, incluyendo las tierras raras e isótopos de Rb/Sr y Sm/Nd. Los cambios químicos fueron controlados mayormente por transporte sintectónico de fluidos y por transformaciones mineralógicas producidas durante la milonitización (disminución del contenido de granate, biotita y minerales accesorios y neoformación de mica blanca en la matriz de las milonitas. Las variaciones isotópicas entre el protolito y las milonitas también serían resultado de la intervención de fluidos durante la deformación, con interacción variable entre fluido y rocas de caja. Los cambios texturales, mineralógicos y químicos experimentados por el granitoide durante la milonitización, permiten reconstruir su evolución tectono-metamórfica y las condiciones metamórficas imperantes. Las asociaciones minerales y microestructuras de deformación de las milonitas sugieren para la faja de cizalla del granitoide El Tigre condiciones propias de la facies de esquistos verdes, con temperaturas inferiores a los 400 °C. Este evento deformante tuvo lugar a los 473 ± 10 Ma durante la orogenia Famatiniana.

  12. Evolution process of the Late Silurian–Late Devonian tectonic environment in Qimantagh in the western portion of east Kunlun, China: Evidence from the geochronology and geochemistry of granitoids

    Indian Academy of Sciences (India)

    Nana Hao; Wanming Yuan; Aikui Zhang; Yunlei Feng; Jianhui Cao; Xiaoning Chen; Xueqin Cheng; Xuanxue Mo

    2015-02-01

    The East Kunlun Orogenic Belt has undergone a composite orogenic process consisting of multiple orogenic cycles and involving many types of magmatic rocks spread over the whole district. However, due to bad natural geographical conditions and complex superimposed orogenic processes, most of the Caledonian orogenic traces were modified by the late tectonic uplift and denudation, so these rocks are poorly studied. Multiperiodic magmatic activity during the Late Silurian (approximately 420 Ma)–Late Devonian (approximately 380 Ma) exists in the Qimantagh area. We obtained 5 zircon U–Pb ages from the Late Silurian–Late Devonian granitoids in the Qimantagh area. Those ages are 420.6 ± 2.6 Ma(Nalingguole biotite monzogranite), 421.2 ± 1.9 Ma (Wulanwuzhuer potassium granite), 403.7 ± 2.9 Ma (Yemaquan granodiorite), 391.3 ± 3.2 Ma (Qunli granite porphyry), and 380.52 ± 0.92 Ma (Kayakedengtage granodiorite). These granitoids belong to the sub-alkaline, high-K calc-alkaline, metaluminous or weakly or strongly peraluminous series. The rocks are right oblique types, having overall relative LREE enrichment and HREE depletion, though rocks from different times may exhibit different degrees of Eu anomalies or overall moderate Eu depletion. The rocks are rich in large ion lithophile elements (LILE), such as Rb, Th, and K, and high field strength elements (HFSE), such as Zr and Hf, and are depleted in Ba, Nb, Ta, Sr, P, Eu, and Ti. The rocks have complex composition sources. The Late Silurian granitoids are mainly crust-derived. Most of the Devonian granitoids are crust-mantle mixed-source and only some parts of them are crust-derived, especially the Middle Devonian granitoids. Those mid-acidic and acidic intrusive rocks are formed in a post-collision tectonic setting, lithosphere delamination may have occurred in the Early Devonian (407 Ma), and the study area subsequently experienced an underplating of the mantle-derived magma at least until the Late Devonian (380 Ma).

  13. Edad, caracterización petrográfica y Geoquímica del Granitoide del Cerro Falkner, Neuquén

    Directory of Open Access Journals (Sweden)

    Sabrina Crosta

    2008-03-01

    Full Text Available El Cerro Falkner se halla constituido por rocas graníticas infrayacentes a las volcanitas de la Formación Ventana de edad paleógena. Dichos intrusivos son de composición granodiorítica, metaluminosos a peraluminosos, subalcalinos, con características de granitos de arco volcánico concordantes con otros granitoides del segmento norte de la Cordillera Patagónica Septentrional. La edad obtenida por el método K-Ar sobre anfíboles de composición tschermakítica (125 ± 20 Ma indica una edad mínima perteneciente al Cretácico inferior para la granodiorita del cerro Falkner, por lo que sería incorrecto utilizar la denominación Formación Los Machis (Cretácico superior para estas rocas. Esta edad, permite vincular las rocas graníticas del área de estudio con el volcanismo representado por el Grupo Divisadero de edad predominantemente cretácica inferior.

  14. Zircon Senstive High Resolution Ion Microprobe (SHRIMP) study of granitoid intrusions in Zhaoye Gold Belt of Shandong Province and its implication

    Institute of Scientific and Technical Information of China (English)

    苗来成; 罗镇宽; 黄佳展; 关康; N.J. McNaughton; D. I. Groves

    1997-01-01

    The zircon Sensitive High Resolution Ion Microprobe (SHRIMP) results show that granitoid intrusions in Zhaoyc Gold Belt were emplaced at two periods of Mesozoic: Linglong and Luanjiahe types of granitic intrusions were emplaced between 160 Ma and 150 Ma (late Jurassic); Guojialing type of granodioritic intrusions, 130 Ma and 126 Ma (early Cretaceous). All the three types contain at least two major generations of inherited zircons with Precambrian ( >650 Ma) and early Mesozoic ages (200-250 Ma), respectively. The former suggests that these plu-tonic rocks are of crustal origin and that Precambrian basement with component of sialic crust up to 3.4 Ga old ( Middle Archean) exists in the region. The presence of abundant inherited zircons with early Mesozoic age indicates that the Precambrian basement was affected by a major tectono-thermal event, that is the collision of the North and South China blocks, at 250 Ma to 200 Ma. SHRIMP results also indicate that the gold mineralization in the region took place

  15. Geological evolution of the center-southern portion of the Guyana shield based on the geochemical, geochronological and isotopic studies of paleoproterozoic granitoids from southeastern Roraima, Brazil; Evolucao geologica da porcao centro-sul do escudo das Guianas com base no estudo geoquimico, geocronologico e isotopico dos granitoides paleoproterozoicos do sudeste de Roraima, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, Marcelo Esteves

    2006-07-01

    This study focuses the granitoids of center-southern portion of Guyana Shield, southeastern Roraima, Brazil. The region is characterized by two tectonic-stratigraphic domains, named as Central Guyana (GCD) and Uatuma-Anaua (UAD) and located probably in the limits of geochronological provinces (e.g. Ventuari-Tapajos or Tapajos-Parima, Central Amazonian and Maroni-Itacaiunas or Transamazon). The aim this doctoral thesis is to provide new petrological and lithostratigraphic constraints on the granitoid rocks and contribute to a better understanding of the origin and geo dynamic evolution of Guyana Shield. The GCD is only locally studied near to the UAD boundary, and new geological data and two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the lithostratigraphic picture in the other areas of Cd (1.96-1.93 Ga). Regional mapping, petrography, geochemistry and zircon geochronology carried out in the Urad have showed widespread Paleoproterozoic calc-alkaline granitic magmatism. These granitoid rocks are distributed into several magmatic associations with different Paleoproterozoic (1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and geochronological studies have distinguished two main sub domains in the UAD. In the northern UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites (1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement (2.03 Ga) crop out northeast of this area, and are formed by meta volcano-sedimentary sequence (Cauarane Group) and TTG-like calc-alkaline association (Anaua Complex). Xenoliths of meta diorites (Anaua Complex) and para gneisses (Cauarane Group) reinforce the intrusive character of Martins Pereira

  16. Geological evolution of the center-southern portion of the Guyana shield based on the geochemical, geochronological and isotopic studies of paleoproterozoic granitoids from southeastern Roraima, Brazil; Evolucao geologica da porcao centro-sul do escudo das Guianas com base no estudo geoquimico, geocronologico e isotopico dos granitoides paleoproterozoicos do sudeste de Roraima, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, Marcelo Esteves

    2006-07-01

    This study focuses the granitoids of center-southern portion of Guyana Shield, southeastern Roraima, Brazil. The region is characterized by two tectonic-stratigraphic domains, named as Central Guyana (GCD) and Uatuma-Anaua (UAD) and located probably in the limits of geochronological provinces (e.g. Ventuari-Tapajos or Tapajos-Parima, Central Amazonian and Maroni-Itacaiunas or Transamazon). The aim this doctoral thesis is to provide new petrological and lithostratigraphic constraints on the granitoid rocks and contribute to a better understanding of the origin and geo dynamic evolution of Guyana Shield. The GCD is only locally studied near to the UAD boundary, and new geological data and two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the lithostratigraphic picture in the other areas of Cd (1.96-1.93 Ga). Regional mapping, petrography, geochemistry and zircon geochronology carried out in the Urad have showed widespread Paleoproterozoic calc-alkaline granitic magmatism. These granitoid rocks are distributed into several magmatic associations with different Paleoproterozoic (1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and geochronological studies have distinguished two main sub domains in the UAD. In the northern UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites (1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement (2.03 Ga) crop out northeast of this area, and are formed by meta volcano-sedimentary sequence (Cauarane Group) and TTG-like calc-alkaline association (Anaua Complex). Xenoliths of meta diorites (Anaua Complex) and para gneisses (Cauarane Group) reinforce the intrusive character of Martins Pereira

  17. U-Pb geochronology by La-CIP-MS and petrography of Sao Carlos massif - stanniferous province of Rondonia; Geocronologia U-Pb por La-ICP-MS e petrografia do macico Sao Carlos - Provincia Estanifera de Rondonia

    Energy Technology Data Exchange (ETDEWEB)

    Debowski, Beatriz P.; Geraldes, Mauro Cesar; Nogueira, Camila; Almeida, Bruna Saar de [Universidade do Estado do Rio de Janeiro, (UERJ), RJ (Brazil)

    2015-07-01

    U-Pb dating by ICP-MS-LA were performed in four samples of the Massif Sao Carlos massif, representative of the younger Granites of Rondonia belonging to the stanniferous province of the same State. Dated samples are granites of pink in colour and coarse-grained to porphyry with main mineralogy consisting of feldspar pertitic to mesopertitic, quartz, plagioclase in lower proportion, biotite and amphibole in some cases. Ages obtained were 986 ± 14 Ma, 974 ± 10 Ma, ± 8 Ma 992.7 and 996 ± 8 Ma and represent the age of crystallization of the Massif. Such ages are concordant with others reported on the bibliography ratifying the inclusion of the massif in the younger Granites of Rondonia, which are directly associated with the most significant mineralization of cassiterite in the State.

  18. New fission-track age constraints on the exhumation of the central Santander Massif: Implications for the tectonic evolution of the Northern Andes, Colombia

    Science.gov (United States)

    Amaya, Sergio; Zuluaga, Carlos Augusto; Bernet, Matthias

    2017-06-01

    The Late Cretaceous to late Neogene exhumation history of the central Santander Massif in the Northern Andes of Colombia is controlled by the geodynamic interactions between the Caribbean, South American and Nazca plates, as well as the Neogene collision and accretion of the Panama arc. Slab-breakoff of the Caribbean plate, with the tip of the slab tear presently being located beneath Bucaramanga, and the east-west oriented Caldas tear are the main structures relating seismic activity and Late Miocene to Pleistocene magmatic/hydrothermal activity and associated gold mineralization in the central Santander Massif. Here we present new apatite (AFT) and zircon fission-track (ZFT) data from 18 samples collected along two profiles in the California-Vetas block (including the Rio Charta), to the south of the Rio Charta fault, and from Bucaramanga to Picacho on the western flank of the central Santander Massif. The fission-track data are used for time-temperature history modelling and for estimating long-term average exhumation rates. The California-Vetas block in the central Santander Massif to the north of the Rio Charta fault cooled rapidly at a rate of about 24 °C/Myr between 10 and 5 Ma. Fast cooling was not related to post-magmatic cooling or hydrothermal activity, but rather to exhumation, with rates based on apatite fission-track cooling ages on the order of 0.3-0.4 km/Myr. However, long-term average exhumation rates since the Late Cretaceous, based on zircon fission-track data, were only on the order of 0.1-0.2 km/Myr. Our data indicate that next to the Rio Charta fault also the Surata fault contributed to the exhumation of the California-Vetas block. The western flank of the central Santander Massif, shows a more complete thermal history along the Bucaramanga-Picacho profile, with the exposure of an exhumed zircon fission-track partial annealing zone. Thermal history modelling of zircon fission-track data of this profile shows that after burial and heating from

  19. Martian alkaline basites chemically resemble basic rocks of the Lovozero alkaline massif, Kola peninsula

    Science.gov (United States)

    Kochemasov, G.

    " (syenite, granite) for Mars [5]. Actually the martian missions successively discovered andesite, dacite, low-Fe highlands. Now "Spirit" has found on a small outlier of highlands -Columbia Hills -a batch of thinly layered gently dipping light rocks that surely are not impact melts as at very short distance there is a sharp transition from light Fe-poor to ultrabasic rocks (on opposite slopes of this small hill) [6]. This layered sequence of more or less altered and weathered rocks resembles differentiated sequences of Lovozero and other alkaline and UB-alkaline massifs of Kola Peninsula (though fresh and much richer in alkalis). Here we compare compositions of alkaline basic rocks of Columbia Hills (dyke or sill [4]) with that of basic volcanics and a later dyke at Lovozero. 5 analyses in wt.%: 1-Backstay (tra1 chybasalt) & 2-Irvine (basalt) of CH, 3-augiteporphyrite, 4-essexite-porphyrite, 5- alkali- lamprophyre dyke of Lovozero. SiO2 -49.9, 47.7, 45.78, 48.09, 41.57; TiO2 - 0.93, 1.07, 7.80, 2.35, 2.92; Al2 O3 -13.2; 10.8, 8.08; 13.74; 11.77; Fe2 O3 -3.40, 7.79 (4.99), 5.90, 6.00, 4.53; FeO -10.6, 12.5 (15.0), 8.65, 7.60, 8.28; MnO -0.25, 0.37, 0.12, 0.17, 0.28; MgO -8.36, 10.8, 7.61, 7.19, 10.59; CaO -6.09, 6.12, 10.73, 8.77, 11.24; Na2 O -4.02, 2.72, 2.80, 2.84, 3.63; K2 O -1.02, 0.69, 1.97, 2.09, 1.38. Compositional similarities between basites occurring in alkaline conditions on both planets can be found. References: [1] Kochemasov G.G. (1999) Theorems of wave planetary tectonics // Geophys. Res. Abstr., v. 1, # 3, 700; [2] Gellert R. et al. (2006) JGR Planets, v. 111, #E2, EO2505; [3] Squyres S.W. et al. (2006) JGR Planets, v.111, #E2, EO2511; [4] McSween H.Y. et al. (2006) JGR Planets, submitted ; [5] Kochemasov G. G. (1995) Golombek M.P., Edgett K.S., Rice J.W. Jr. (Eds). Mars Pathfinder Landing Site Workshop II: Characteristics of the Ares Vallis Region and Field trips to the Channeled Scabland, Washington. LPI Tech. Rpt. 95-01. Pt.1.LPI, Houston, 1995, 63 pp.; [6

  20. Palaeomagnetic studies in the Permian Basin of Largentière and implications for the Late Variscan rotations in the French Massif Central

    Science.gov (United States)

    Henry, B.; Becq-Giraudon, J. F.; Rouvier, H.

    1999-07-01

    Detailed geological observations and palaeomagnetic analyses were carried out in the Largentière Stephano-Autunian basin and on the Stephanian deposits of the Alès coalfield, both located at the southeastern margin of the French Massif Central. Because of unfavourable rock types, the Alès Stephanian deposits did not yield any results. The palaeomagnetic pole (164.9 degE, 45.4 degN, K=89, A_95=4.1 deg) deduced from a study of the Autunian sediments of the Largentière Basin agrees very well with the reference pole for stable Europe. The Lodève-Largentière area, that is the southeastern border of the Massif Central, has been stable since Early Permian time with respect to stable Europe, whereas the western part (the Saint-Affrique Rodez Basin and, probably, the Brive Basin) has been rotated counterclockwise.

  1. Magnesite-bearing fracture zones of the Zlatibor ultrabasic massif (Serbia as a discrete structural-morphological type of magnesite deposits in ultrabasites

    Directory of Open Access Journals (Sweden)

    Ilić Miloje

    2011-01-01

    Full Text Available In this paper, a discrete structural-morphological type of magnesite deposits in ultrabasites, i.e., in magnesite-bearing fracture zones, is presented. The most prominent occurrences of such zones in Serbia are in the Zlatibor ultrabasic massif and they are economically very significant because they contain large reserves of high-quality magnesite, as well as of the accompanying sepiolite.

  2. Reassignment to the Middle Devonian of some rugose corals investigated by LE MAÎTRE (1934) in the Chalonnes Formation from the Southeastern Armorican Massif (France)

    OpenAIRE

    2011-01-01

    Nine taxa of rugose corals collected by LEMAÎTRE (1934) and coming from the Chalonnes Formation of the Southeastern Armorican Massif in France have been revised. They belong to the genera Stringophyllum WEDEKIND, 1922, Sociophyllum BIRENHEIDE, 1962, Acanthophyllum DYBOWSKI, 1873, Beugniesastraea COEN-AUBERT, 1989 and Fasciphyllum SCHLÜTER, 1885. Among this material, Stringophyllum acanthicum (FRECH, 1885), Sociophyllum elongatum (SCHLÜTER, 1881), Acanthophyllum vermiculare (GOLDFUSS, 1826) an...

  3. Observations sur le contact ouest du granite des Sept-Laux près du Rivier d’Allemont (Massif de Belledonne S.L.)

    NARCIS (Netherlands)

    Veen, van der A.H.

    1952-01-01

    La stratification des roches cristallines (d'âge antéstéphanien) des massifs centraux des Alpes est en général à peu près parallèle à la schistosité. Également les intrusions granitiques y sont plus ou moins concordantes. Cependant les recherches sous la direction du Professeur E. Niggli de Leiden

  4. Mass flux into the Nanga Parbat-Haramosh massif: Orogen-parallel transport, lower crustal flow, or both?

    Science.gov (United States)

    Whipp, D. M.; Beaumont, C.; Braun, J.

    2011-12-01

    Relative to most of the Himalaya, the Nanga Parbat-Haramosh massif requires an additional mass flux into its base to balance extreme rates of surface denudation (>10 mm/a) over the last ~2-3 Ma. One proposed source is middle to lower crustal flow into the massif (e.g., Zeitler et al., 2001), which while likely inactive elsewhere along strike, may be sustainable by very rapid surface denudation, a high geothermal gradient, and thermal weakening of rocks beneath the syntaxes. An alternative source is orogen-parallel (OP) transport due to oblique convergence and strain partitioning along the Himalayan arc (e.g., Seeber and Pêcher, 1998). Several observations including (1) predominantly orogen-normal slip on the frontal thrusts deduced from seismic events, (2) OP extension accommodated on orogen-normal structures, and (3) distributed and segmented strike-slip faulting trending parallel to the arc are consistent with strain partitioning and OP mass transport. A key question is can this mechanism supply sufficient mass to the Nanga Parbat syntaxis, or is local channel flow required? We explore mass transport into the western Himalayan syntaxis region using lithospheric-scale 3D mechanical and coupled thermo-mechanical models of an arcuate orogen. The crust is either frictional plastic or power-law viscous, with a constant low viscosity lower crust present in some experiments. Applied velocity boundary conditions are transmitted to the base of the crust by a strong frictional plastic mantle lithosphere, and mantle detachment/subduction drives formation of a bivergent, arcuate orogen. To assess the magnitude of mass transport from strain partitioning, we first explore purely mechanical experiments featuring a 5-km-high Tibet-like plateau above a weak lower crust and with a frictional plastic decollement that dips at 10° beneath the incipient orogen, similar to the Himalayan basal detachment. Preliminary results show gravitational feedback from the plateau drives

  5. Quantitatively structural control of the karst based on speleological cave survey data: Cabeza Llerosos massif (Picos de Europa, Spain)

    Science.gov (United States)

    Ballesteros, D.; Jiménez-Sánchez, M.; García-Sansegundo, J.; Borreguero, M.; Sendra, G.

    2012-04-01

    Speleological cave survey characterizes each cave passage by a 3D line (called shot survey) defined by its length, direction and dipping. This line represents the three-dimensional geometry of the karst system and cave passage scale and can be statistically analyzed and compared with the geometry of the massif discontinuities. The aim of this work is to establish the quantitative influence of the structural geology in caves based on the comparison between cave survey data, joint and bedding measurements with stereographic projection. 15 km of cave surveys from Cabeza Llerosos massif (Picos de Europa, Northern Spain) were chosen to illustrate the method. The length of the cavities range between 50 to 4,438 m and their depth is up to 738 m. The methodology of work includes: 1) cave survey collection from caving reports; 2) geological mapping and cross-sections with cavities projection;3) data collection of bedding and joints in caves and near outcrops;4) definition of families of joints and bedding planes by stereographic projection; 5) definition of groups of cave passages from stereographic projection (based on their directions and dipping) and 6) comparison between bedding, families of joints and cave survey data by stereographic projection. Seven families of joints have been defined in all the area of study. The joint families are: J1) sub-vertical, J2) N63/68SE, J3) N29E/46NW, J4) N52E/72NW, J5) N129E/17NE, J6) N167E/57NE and J7) N180E/26E; the bedding is N30-55/60-80NE. Five groups of cave passages have been defined. "A" group of cave passage is formed by sub-vertical series; it is represented by the 61 % of all the cave passages and is conditioned by the joint families J1, J3, J4 and J6, as well as their intersections. "B" group is formed by N10W-N10E/3-20N galleries; it corresponds with the 13 % of the series and is controlled by the intersection between families J5 and J6. "C" group is defined by N20-70E/0-50NE passages; it is represented by the 13 % of the

  6. Incidence of mass movement processes after an historical episode of heavy snowfall in the Asturian Massif (Northern Spain)

    Science.gov (United States)

    Garcia-Hernandez, Cristina; Ruiz-Fernández, Jesús; Gallinar, David

    2015-04-01

    This research examines a mass movement event caused in the context of the Great Blizzard of 1888, one of the most severe recorded blizzards in the history of Europe, whose implications go far beyond. In the Asturian Massif the episode consisted in four linked and consecutive snowstorms that took place between the 14th of February 1888 and the 8th of April 1888, creating snow covers with a depth ranging between 5 and 7 m, snow avalanches and flooding, causing dozens of deaths and large material damage. The Asturian Massif belongs to the Atlantic-climate area and is composed mainly by sedimentary and metamorphic paleozoic rocks. Many sectors of the Massif are between 1.000 and 2.000 m a.s.l., and its topography is characterized by a great height difference and steep slopes. Because of the lack of deep soils suitable for farming, the main traditional activity has been livestock keeping, and goods traffic. We have devised a method that enables the reconstruction of this event on the basis of nivo-meteorogical conditions, geographical location and socio-economic impact. The mass movement episode has been studied through the issues of 6 newspapers published in Asturias between the 20th of January and 30th of May 1888, the ancient meteorological station data of the University of Oviedo, and field work. A logical database structure has been designed with the aim to store and cross the information for statistical analysis. Thirty six mass movement worthy of consideration were documented, 28 of them causing material damage (six homes destroyed and at least 22 interruptions with the traffic flow on roads, highways and railways). Ten high- and mid-elevation mountain municipalities were affected by mass movement. We must consider that only the most important events, or those that happened in crowded places, have been considered by the newspapers, so the total number of mass movements should be considered as a minimum figure. We have got to identify and classify 27 of them; 16

  7. U-Pb dating of granodiorite and granite units of the Los Pedroches batholith. Implications for geodynamic models of the southern Central Iberian Zone (Iberian Massif)

    Science.gov (United States)

    Carracedo, M.; Paquette, J. L.; Alonso Olazabal, A.; Santos Zalduegui, J. F.; García de Madinabeitia, S.; Tiepolo, M.; Gil Ibarguchi, J. I.

    2009-10-01

    The first U-Pb geochronological results on the magmatic alignment of the Los Pedroches batholith are presented. The batholith is composed of a main granodioritic unit, several granite plutons and an important acid to basic dyke complex, all of them intrusive after the main Variscan regional deformation phase, D1, along the boundary between the Ossa-Morena and Central Iberian zones (SW Iberian Massif). Zircons from samples on both extremes of the granodiorite massif record nearly simultaneous magmatic crystallization at ca. 308 Ma, while the emplacement of granite plutons was diachronic between 314 and 304 Ma. The U-Pb results combined with new field and textural observations allow to better constrain the age of Variscan deformations D2 and D3 across the region, while the age of D1 remains imprecise. Transcurrent D2 shearing-tightening of D1 folds occurred around 314 Ma (lower Westphalian) in relation to the emplacement of the first granitic magmas. D3 faults and shear bands bearing a strong extensional component developed at ca. 308 Ma (upper Westphalian), associated to the intrusion of the main granodiorite pluton (granodiorite) of the batholith. Together with available geochemical and geophysical information, these results point to the Variscan reactivation of lithospheric fractures at the origin and subsequent emplacement of hybrid magmas within this sector of the Massif.

  8. Zircon geochronology of the Klyuchevskoi gabbro-ultramafic massif and the problem of the age of the Mohorovicic paleoboundary in the Central Urals

    Science.gov (United States)

    Ivanov, K. S.; Krasnobaev, A. A.; Smirnov, V. N.

    2012-02-01

    The Klyuveskoi gabbro-ultramafic massif is the most representative ophiolite complex on the eastern portion of the Uralian paleoisland arc part. The massif is composed of dunite-harzburgite (tectonized mantle peridotites) and dunite-wehrlite-clinopyroxenite-gabbro (layered part of the ophiolite section) rock associations. The U-Pb age was obtained for the accessory zircons from the latter association using a SHRIMP-II ion microprobe at the Center for Isotopic Research at the Karpinskii Russian Geological Research Institute. The euhedral zircon crystals with thin rhythmic zoning from dunites are 441.4 ± 5.0 Ma in age. Zircons from olivine clinopyroxenite show three age clusters with sharply prevalent grains 449.0 ± 6.8 Ma in age. Two points give 1.7 Ga, which is probably related to the age of the mantle generating the layered complex. One value corresponds to 280 Ma, which possibly reflects exhumation of ultramafic rocks in the upper crust during the collision of the Uralian foldbelt. Thus, dunites and olivine pyroxenites from the Klyuchevskoi massif are similar in age at 441-449 Ma. The bottom of the layered part of the ophiolite section corresponds to the M paleoboundary and, consequently, the age of the Mohorovicic discontinuity conforms with the Ordovician-Silurian boundary in this part of the Urals.

  9. The systematics and paleobiogeographic significance of Sub-Boreal and Boreal ammonites (Aulacostephanidae and Cardioceratidae from the Upper Jurassic of the Bohemian Massif

    Directory of Open Access Journals (Sweden)

    Hrbek Jan

    2014-10-01

    Full Text Available Upper Jurassic marine deposits are either rarely preserved due to erosion or buried under younger sediments in the Bohemian Massif. However, fossil assemblages from a few successions exposed in northern Bohemia and Saxony and preserved in museum collections document the regional composition of macro-invertebrate assemblages and thus provide unique insights into broad-scale distribution and migration pathways of ammonites during the Late Jurassic. In this paper, we focus on the systematic revision of ammonites from the Upper Oxfordian and Lower Kimmeridgian deposits of northern Bohemia and Saxony. The ammonites belong to two families (Aulacostephanidae and Cardioceratidae of high paleobiogeographic and stratigraphic significance. Six genera belong to the family Aulacostephanidae (Prorasenia, Rasenia, Eurasenia, Rasenioides, Aulacostephanus, Aulacostephanoides and one genus belongs to the family Cardioceratidae (Amoeboceras. They show that the Upper Jurassic deposits of the northern Bohemian Massif belong to the Upper Oxfordian and Lower Kimmeridgian and paleobiogeographically correspond to the German-Polish ammonite branch with the geographical extent from the Polish Jura Chain to the Swabian and Franconian Alb. Therefore, the occurrences of ammonites described here imply that migration pathway connecting the Polish Jura Chain with habitats in southern Germany was located during the Late Oxfordian and Early Kimmeridgian in the Bohemian Massif.

  10. THE MIOCENE AND DEVONIAN MAGMATISM AT THE JUNCTION BETWEEN THE TUVA-MONGOLIAN MASSIF AND SIBERIAN CRATON: COMMON COMPONENT OF MANTLE SOURCES AND ITS ORIGIN

    Directory of Open Access Journals (Sweden)

    Sergey V. Rasskazov

    2015-09-01

    Full Text Available Devonian dikes of the Urik-Belaya and Shagayte-Gol-Urik zones and Miocene lavas of the Urik volcanic field are spatially associated with each other at the structural junction between the Neoproterozoic Tuva-Mongolian massif and Siberian craton. The former dike belt is represented by basalts and basaltic andesites of tholeiitic series and the latter one by trachybasalts, trachyandesitic basalts of moderately alkaline series and trachybasalts, phonotephrites of highly alkaline one. The Urik volcanic field is composed of trachybasalts and trachyandesitic basalts of moderately alkaline series. A partial similarity between magmatic series of different age is found in terms of major oxides, trace elements, and Sr, Pb isotopes. The common component corrected for age was defined through its converging mixing trends with those of the lithospheric mantle and crust. The component identification was a basis for deciphering the nature of isotopic and geochemical heterogeneity of evolved magmatic sources. It was inferred that the common component characterizes either a modified (depleted reservoir of the lower mantle or, more likely, a local region of the convecting asthenospheric mantle that underlies the Tuva-Mongolian massif. The latter interpretation assumes the formation of a locally convecting asthenosphere in the middle Neoproterozoic, along with the development of the Oka zone at the massif, and puts constrains on later sufficient processing of the asthenosphere due to rising plumes or subducting slabs.

  11. Tectonic evolution of the Irtysh collision belt: New zircon U-Pb ages of deformed and collisional granitoids in the Kalaxiangar area, NW China

    Science.gov (United States)

    Tao, Hong; Jun, Gao; Xingwang, Xu; Klemd, Reiner

    2016-04-01

    The CAOB is thought to have formed by multiple accretion and collision of various microcontinents, island arcs, oceanic plateaus and accretionary wedges due to the closure of the Paleo-Asia Ocean [1, 2, 3]. The Irtysh collision belt is located at the middle-western part of the CAOB and generally thought to be the result of the collision of the Sawuer Island arc and the Altay Terrane, subsequent to the consumption of the Early Paleozoic Junggar Ocean, a branch of Paleo-Asia Ocean. Therefore, the exact timing of the Irtysh collision belt is crucial for a better understanding of the tectonic evolution of this collision belt and will provide constraints on the evolution of the CAOB. Recently, we discovered various collisional granitoids in the Kalaxiangar tectonic belt (KTB), which is located in the eastern part of the Irtysh collision belt. In this contribution, we report new geochemical whole-rock, zircon U-Pb and Hf isotopic data of the arc-related and collisional granitoids. Our new results reveal that 1) the arc-related granodioritic porphyries formed at ca. 374 Ma. Furthermore, recrystallized zircons from the granodioritic mylonite and ultramylonite of the Laoshankou ductile deformation zone have a similar U-Pb age of ca. 360 Ma; 2) the syn-collisional granodioritic porphyries, which distribute along cleavege, were emplaced at ca. 355 Ma; 3) the post-collisional A-type granodioritic porphyry, which cuts the NW-NNW trending schistosity at a low angle, has an age of ca. 323 Ma, ɛHf(t) values from + 7.5 to + 14.4, and young Hf model ages between 387 and 658 Ma; 4) the post-collisional A-type granite dykes, which are exposed along strike-slip faults, have ages between 282.5 and 279.2Ma, ɛHf(t) values from + 4.8 to + 12.6, and Hf model ages between 436 and 729 Ma; 5) the A-type biotite granite dykes that intruded along conjugate tension joints have ages between 273.9 and 271.4 Ma, ɛHf(t) values from + 1.1 to + 12.8, and Hf model ages between 393 and 979 Ma. In

  12. Heat and mass transfers in the Late variscan: evidence from gold depôsits in the French Massif Central

    Science.gov (United States)

    Cathelineau, M.; Boiron, M. C.; Fourcade, S.; Marignac, C.

    2003-04-01

    In many medium- to high-grade metamorphic terranes of the West European Variscan belt, there are few, if any, reliable mineral records of the retrograde path. The S Limousin area (W French Massif Central) is a good example: there, the lithotectonic pile (including numerous granite intrusions) was "freezed" below ca. 350°C (Ar dating of white micas) since ca. 340 Ma. Yet, there is evidence for subsequent, sometimes pervasive, fluid and heat pulses although the latter were not accompanied by widespread retrograde metamorphism (insufficient duration/amount). A major episode of heat and mass transfer corresponds to the formation of gold deposits, thought to have occurred at ca. 305 Ma. The study of fluid inclusions from these deposits and surrounding rocks demonstrates the persistence of heat and fluid production at depth, although the pattern of fluid circulation changed with time. (i) In a first, protracted stage (340-305 Ma), fluid circulation in the Limousin top-middle crust (300-350 Mpa, 11-13 km depth) was restricted to a set of structural drains (shear-zones hosting early quartz veins) and involved volatile-bearing (CO2-dominated) fluids that, from O-isotope evidence, were focused from deep reservoirs where used heat advection resulted in a long-lived ductile behaviour of the shear-zones contrasting with the brittle regime prevailing in the surrounding crust. (ii) Around 305 Ma, when the Limousin pile was in the upper crust (above ca. 5 km), a change occurred in the pattern of fluid circulation, simultaneously with the inception of post-thickening extension. Pervasive fluid flow occurred through a network of interconnected microcraks while the nature of the fluids was changing. A hot eas, at the scale of the "upper crust reservoir" diffuse deposition of arsenopyrite resulted in a huge regional As anomaly in the Limousin gneisses. The source of the hot saline fluid is speculative. By comparison with the SE French Massif Central, the existence of a large magmatic

  13. Age, petrogenesis, and tectonic setting of the Permian bimodal volcanic rocks in the eastern Jiamusi Massif, NE China

    Science.gov (United States)

    Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Dong, Yu; Liu, Xi-Wen; Ji, Zheng

    2017-02-01

    We present new in situ zircon U-Pb and Hf isotope, whole-rock geochemical, and Sr-Nd isotopic data for volcanic rocks from the Jiejinkou and Baoqing areas in the eastern Jiamusi Massif. These volcanic rocks are bimodal and consist of basalts, basaltic andesites, rhyolites, and rhyolitic tuffs that can be subdivided into mafic and silicic groups. Zircon U-Pb dating by LA-ICP-MS indicates that these volcanic rocks were erupted between the Early and Middle Permian (290-267 Ma). The mafic rocks in this area have positive εNd(t) (+0.07 to +6.43) values, and are enriched in light rare earth elements (LREEs) and depleted in heavy REE, Nb, and Ta. From these rocks, the meta-basalt of Jinlu and basaltic andesite of Taipinggou and Haojiatun were derived from parental magmas generated by the partial melting of depleted mantle wedge material that was metasomatized by subduction-related melts. These magmas then underwent variable degrees of fractional crystallization and assimilated insignificant amounts of crustal material. The meta-basalt of Liming likely originated from the metasomatized mantle-derived melts hybridized by the convective asthenosphere during the evolution of the magmas. In comparison, the silicic rocks have negative εNd(t) and variable zircon εHf(t) values, are enriched in the large-ion lithophile elements (LILEs) and LREE, and are depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), yielding arc-like geochemical signatures. The geochemical and zircon εHf(t) characteristics of Jiangfeng and Longtouqiao rhyolites are indicative of formation from magmas generated by the partial melting of mafic lower crustal material, whereas the Liming meta-rhyolite was probably produced from a source involving some depleted mantle components. The bimodal volcanic rocks provide convincing evidence that the Early-Middle Permian volcanism in the Jiamusi Massif occurred in an extensional environment probably associated with slab break-off during the westward

  14. Sylvicultural procedures in catchment areas of the mountain streams as exemplified by the Skrzyczne massif in Poland

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    Małek Stanisław

    2014-03-01

    Full Text Available Extensive disintegration of spruce forests in the Beskidy Mts. in South Poland generates a need to regenerate sizeable areas as well as to rebuild forest stands which have defended themselves against breakdown. In practice, the magnitude of relevant management tasks does not allow for keeping up with the progressive destruction of forest, especially at higher altitudes, where natural regeneration does not occur as much as necessary. In addition, the species composition is limited to spruce, sometimes accompanied by beech and fir, whereas other species have a negligible share. What may be helpful in solving this problem is the method of regeneration of such areas and of establishment of under-canopy cultures, consisting of patchwork, multi-stage regeneration task performance, starting from the areas with the best chance of reforestation success and using the existing self-sown trees. Such areas undoubtedly include habitats with better water balance, i.e. humid habitats (in the case of larger areas, distinguished in the forest management plan as humid forest site types. The aim of the present study was to propose management of watercourses and headwater areas in the region of the Skrzyczne massif where the selected catchments are situated on the southern (the Malinowski Stream and the northern (the Roztoka Czyrna stream slopes of this massif. The research was carried out in August 2012 and included juxtaposition of available hydrological maps with actual field conditions along with identification of springs and streams and the course of their beds in order to update the existing data. The updating of the forest numerical maps in the existing databases of the State Forests IT System (SILP included verification of the course of streams and determination of their nature (permanent or periodic with a division into the existing ones and the added ones. The data was recorded against the background of the division of the forest surface, contour lines

  15. Geochemical and Sr-Nd-Pb-O isotope composition of granitoids of the Early Cretaceous Copiapó plutonic complex (27°30'S), Chile

    Science.gov (United States)

    Marschik, Robert; Fontignie, Denis; Chiaradia, Massimo; Voldet, Pia

    2003-10-01

    Early Cretaceous plutonic rocks exposed south of Copiapó form part of the Coastal Batholith of northern Chile. These rocks intrude arc-derived volcanic and volcaniclastic rocks and marine limestones that were deposited in the Early Cretaceous Atacama backarc basin. The Copiapó plutonic complex consists mainly of calc-alkaline, medium- to coarse-grained diorite, granodiorite, tonalite, monzodiorite, and quartz monzonite. The plutonic rocks are subalkaline to alkaline, metaluminous, magnetite-series, volcanic arc, I-type granitoids. Batholithic magmas are a heat, potential fluid, metal, and sulphur source for the hydrothermal iron oxide-rich Cu-Au mineralization in the Candelaria-Punta del Cobre district. Ore-related hydrothermal alteration affected large portions of the Copiapó complex. The least altered batholithic rocks have initial 87Sr/ 86Sr of 0.703070-0.703231; initial 143Nd/ 144Nd of 0.512733-0.512781; and 206Pb/ 204Pb, 207Pb/ 204Pb, and 208Pb/ 204Pb of 18.428-18.772, 15.550-15.603, and 38.127-38.401, respectively. The δ18O values for these rocks range from +6.9 to +8.6‰. Isotope signatures and trace element distributions suggest that the magmas are mantle derived. A subduction fluid-modified mantle source may explain the geochemical characteristics of the Copiapó complex. The ascent of magmas occurred along deep-rooted structures without significant crustal contamination, though minor contamination by relatively young (e.g. Jurassic) igneous rocks during ascent is possible. Intrusive rocks with high-K to shoshonitic characteristics probably represent residual liquids of less evolved magmas. The regional geologic context suggests that the plutons of the Copiapó complex were emplaced at a relatively shallow crustal level of 2-3 km.

  16. Timing of granitic magmatism in the northern Borborema Province, Brazil: a U Pb study of granitoids from the Alto Pajeú Terrain

    Science.gov (United States)

    Bastos Leite, P. R.; Bertrand, J.-M.; de Lima, E. S.; Leterrier, J.

    2000-11-01

    The Alto Pajeú Terrain (APT) is a SW-NE trending fold belt in the Neoproterozoic Borborema Province (NE Brazil), formed by metasedimentary sequences interlayered with metavolcanosedimentary units, both intruded by granitic rocks of different compositions and ages. The tectonic evolution of the APT involves Mesoproterozoic and Neoproterozoic transtensional and contractional tectonic events. In this study, we present U-Pb zircon ages of five granitoids selected according to a generally accepted relative chronology: (a) the Tuparetama granite and Tuparetama migmatitic granite with low angle gneissic foliation represent syn-tangential rocks presumably related to a Transamazonian event; (b) the Amparo granite with high angle gneissic foliation related to the Brazilian/Pan-African event; and (c) the Tabira and Jabitacá post-strike-slip granites. The results obtained do not confirm the generally accepted chronology of events. Granites previously classified in different groups (Tuparetama, Amparo, and Jabitacá) belong to the same orogenic cycle (Brazilian). Large batholiths, previously suspected to have been emplaced after the strike-slip deformation, represent older crustal remnants within them. In each case they consist of particular rock types — an alkaline high-temperature granite (Tabira) and a 'granulite' (Tuparetama migmatitic granite). These older ages imply that pre-Brazilian crust-forming events such as the Transamazonian Orogeny (Tuparetama migmatitic granite estimated at ca. 2050 Ma) and Cariris Velhos event (Tabira granite at ca. 972 Ma) occurred in the APT, and their records survived the intense recycling which characterizes the Brazilian/Pan-African orogeny.

  17. The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

    Science.gov (United States)

    Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei

    2017-01-01

    Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early

  18. Magma associations in Ediacaran granitoids of the Cachoeirinha‒Salgueiro and Alto Pajeú terranes, northeastern Brazil: Forty years of studies

    Science.gov (United States)

    Sial, Alcides N.; Ferreira, Valderez P.

    2016-07-01

    Granitic magmatism in the Cachoeirinha‒Salgueiro and Alto Pajeú terranes in the Transversal Zone Domain of the Borborema Province, northeastern Brazil, occurred in three main time intervals: 650-620 Ma, 590-560 Ma and 545-520 Ma. The oldest one is characterized by intrusions of magmatic-epidote (mEp) bearing calc-alkalic (some with trondhjemitic affinities) and high-K calc-alkalic plutons, synkinematic to the main regional foliation, under contractional tectonic regime, and exhibits TDM plutons is compatible with partial fusion of subducted oceanic basaltic crust (mEp-bearing calc-alkalic tonalites/granodiorites, equivalent to adakites). Voluminous intrusions in the 590-560 Ma interval are represented by abundant mEp-free high-K calc-alkalic, peralkalic, ultrapotassic, mEp-bearing high-K calc-alkalic, and less abundant shoshonitic magmas. Nd-model ages for this group of plutons vary from 1.5 to 2.5 Ga and ƐNd (0.6 Ga) ranges from -8 to -20; δ18O (zircon) varies from 6.4 to 7.9‰VSMOW. Values of δ18O (zircon) for the 590‒560 Ma old group of plutons coupled with Nd isotope data are compatible with remelting of crustal (negative ƐNd, 1.6 to 2.0 Ga old) source rocks. O- and Nd-isotope data for this group of plutons are compatible with underplating of basaltic magma in the base of the lower crust for the high-K calc-alkalic granitoids, coeval to transcurrent movements along sigmoidal shear zones. Intrusion of one shoshonitic (Serrote do Arapuá), one calc-alkalic (Riacho do Icó) plutons besides the peralkalic Manaíra-Princeza Isabel dike set have witnessed this transition from contractional to transcurrent movements along shear zones, around 610‒600 Ma.

  19. Molybdenite Re/Os dating, zircon U-Pb age and geochemistry of granitoids in the Yangchuling porphyry W-Mo deposit (Jiangnan tungsten ore belt), China: Implications for petrogenesis, mineralization and geodynamic setting

    Science.gov (United States)

    Mao, Jingwen; Xiong, Bikang; Liu, Jun; Pirajno, Franco; Cheng, Yanbo; Ye, Huishou; Song, Shiwei; Dai, Pan

    2017-08-01

    The Yangchuling W-Mo deposit, located in the Jiangnan porphyry-skarn (JNB) tungsten ore belt, is the first recognized typical porphyry W-Mo deposit in China in the 1980's. Stockworks and disseminated W-Mo mineralization occur in the roof pendant of a 0.3 km2 monzogranitic porphyry stock that intruded into a granodiorite stock, hosted by Neoproterozoic phyllite and slate. LA-ICPMS zircon U-Pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143.8 ± 0.5 Ma and 149.8 ± 0.6 Ma, respectively. Six molybdenite samples yielded a Re-Os weighted mean age of 146.4 ± 1.0 Ma. Geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements (LILE) relative to high field strength elements (HFSE), indicating a peraluminous nature (A/CNK = 1.01-1.08). Two granitoids are characterized by a negative slope with significant light REE/heavy REE fractionation [(La/Yb)N = 8.38-23.20] and negative Eu anomalies (Eu/Eu* = 0.69-0.76). The P2O5 contents of the Yangchuling granitoids range from 0.12% to 0.17% and exhibit a negative correlation with SiO2, reflecting that they are highly fractionated I-type. They have high initial 87Sr/86Sr ratios (0.7104-0.7116), low negative εNd(t) (- 5.05 to - 5.67), and homogeneous εHf(t) between - 1.39 and - 2.17, indicating similar sources. Additionally, two-stage Nd model ages (TDM2) of 1.3-1.4 Ga and two-stage Hf model ages (TDM2) of 1.2-1.3 Ga are consistent, indicating that Neoproterozoic crustal rocks of the Shuangqiaoshan Group could have contributed to form the Yangchuling magmas. Considering the two groups of parallel Late Mesozoic ore belts, namely the Jiangnan porphyry-skarn tungsten belt (JNB) in the south and the Middle-Lower Yangtze River porphyry-skarn Cu-Au-Mo-Fe ore belt (YRB) in the north, the Nanling granite-related W-Sn ore belt (NLB) in the south, the neighboring Qin-Hang porphyry-skarn Cu-Mo-hydrothermal Pb-Zn-Ag ore belt (QHB

  20. Petrogenesis and tectonic implications of the high-K Alamas calc-alkaline granitoids at the northwestern margin of the Tibetan Plateau: Geochemical and Sr-Nd-Hf-O isotope constraints

    Science.gov (United States)

    Zhang, Qichao; Liu, Yan; Huang, He; Wu, Zhenhan; Zhou, Qing

    2016-09-01

    The Alamas granitoid pluton in the eastern part of the Western Kunlun Orogen, the northwestern margin of the Tibetan Plateau, is composed of quartz diorite. Zircon separates from the pluton has SIMS U-Pb age of ∼446 Ma. Rocks from the pluton have a narrow range of SiO2 (56.84-62.57 wt%), MgO (1.76-2.94 wt%), and total alkalis (Na2O + K2O = 5.14-9.59 wt%), and are metaluminous and high-K calc-alkaline to shoshonitic in composition. They are enriched in light rare earth elements (LREEs), with (La/Yb)N = 14-25, and show weakly negative Eu anomalies. These rocks are relatively enriched in Sr (472-676 ppm) and Ba (435-2388 ppm), and depleted in Nb, Ta, Th, and Ti. Their εNd(t) values range from -6.4 to -8.4, and (87Sr/86Sr)i = 0.7184-0.7200. Zircons from the pluton show εHf(t) values of -1.4 to -8.8, and δ18O = 6.4-9.0‰. Geochemical data indicate that the granitoids were likely derived from the reworking of an ancient, deep crustal source, influenced by a minor mantle-derived component. Magmatic differentiation was dominated by the fractional crystallization of hornblende, biotite, and accessory minerals such as apatite, allanite, and Fe-Ti oxides. In summary, the Late Ordovician Alamas pluton is an I-type granitoid that was emplaced in a post-collisional environment, suggesting that this tectonic stage had already initiated prior to ∼445 Ma.

  1. Crustal melting and recycling: geochronology and sources of Variscan syn-kinematic anatectic granitoids of the Tormes Dome (Central Iberian Zone). A U-Pb LA-ICP-MS study

    Science.gov (United States)

    López-Moro, F. J.; López-Plaza, M.; Gutiérrez-Alonso, G.; Fernández-Suárez, J.; López-Carmona, A.; Hofmann, M.; Romer, R. L.

    2017-04-01

    In this study, we report U-Pb Laser Ablation ICP-MS zircon and ID-TIMS monazite ages for peraluminous granitoid plutons (biotite ± muscovite ± cordierite ± sillimanite) in the Tormes Dome, one of the gneiss-cored domes located in the Central Iberian Zone of the Variscan belt of northern Spain. Textural domains in zircon, interpreted to represent the magmatic crystallization of the granitoids (and one monazite fraction in the Ledesma pluton) yielded ages around 320 Ma, in agreement with other geochronological studies in the region. This age is interpreted to date the timing of decompression crustal melting driven by the extensional collapse of the orogenic belt in this domain of the Variscan chain of western Europe. In addition, there are several populations of inherited (xenocrystic) zircon: (1) Carboniferous zircon crystals (ca. 345 Ma) as well as one of the monazite fractions in the coarse-grained facies of the Ledesma pluton that also yielded an age of ca. 343 Ma. (2) Devonian-Silurian zircon xenocrysts with scattered ages between ca. 390 and 432 Ma. (3) Middle Cambrian-Ordovician (ca. 450-511 Ma). (4) Ediacaran-Cryogenian zircon ages (ca. 540-840 Ma). (5) Mesoproterozoic to Archaean zircon (900-2700 Ma). The abundance of Carboniferous-inherited zircon shows that crustal recycling/cannibalization may often happen at a fast pace in orogenic scenarios with only short lapses of quiescence. In our case study, it seems plausible that a "crustal layer" of ca. 340 Ma granitoids/migmatites was recycled, partially or totally, only 15-20 My after its emplacement.

  2. Evolution of hut access facing glacier shrinkage in the Mer de Glace basin (Mont Blanc massif, France)

    Science.gov (United States)

    Mourey, Jacques; Ravanel, Ludovic

    2016-04-01

    Given the evolution of high mountain environment due to global warming, mountaineering routes and huts accesses are more and more strongly affected by glacial shrinkage and concomitant gravity processes, but almost no studies have been conducted on this relationship. The aim of this research is to describe and explain the evolution over the last century of the access to the five alpine huts around the Mer de Glace glacier (Mont Blanc massif), the larger French glacier (length = 11.5 km, area = 30 km²), a major place for Alpine tourism since 1741 and the birthplace of mountaineering, by using several methods (comparing photographs, surveying, collecting historical documents). While most of the 20th century shows no marked changes, loss of ice thickness and associated erosion of lateral moraines generate numerous and significant changes since the 1990s. Boulder falls, rockfalls and landslides are the main geomorphological processes that affect the access, while the glacier surface lowering makes access much longer and more unstable. The danger is then greatly increased and the access must be relocated and/or equipped more and more frequently (e.g. a total of 520 m of ladders has been added). This questions the future accessibility to the huts, jeopardizing an important part of mountaineering and its linked economy in the Mer de Glace area.

  3. High-yielding aquifers in crystalline basement: insights about the role of fault zones, exemplified by Armorican Massif, France

    Science.gov (United States)

    Roques, Clément; Bour, Olivier; Aquilina, Luc; Dewandel, Benoît

    2016-12-01

    While groundwater constitutes a crucial resource in many crystalline-rock regions worldwide, well-yield conditions are highly variable and barely understood. Nevertheless, it is well known that fault zones may have the capacity to ensure sustainable yield in crystalline media, but there are only a few and disparate examples in the literature that describe high-yield conditions related to fault zones in crystalline rock basements. By investigating structural and hydraulic properties of remarkable yielding sites identified in the Armorican Massif, western France, this study discusses the main factors that may explain such exceptional hydrogeological properties. Twenty-three sites, identified through analysis of databases available for the region, are investigated. Results show that: (1) the highly transmissive fractures are related to fault zones which ensure the main water inflow in the pumped wells; (2) the probability of intersecting such transmissive fault zones does not vary significantly with depth, at least within the range investigated in this study (0-200 m); and (3) high yield is mainly controlled by the structural features of the fault zones, in particular the fault dip and the presence of a connected storage reservoir. Conceptual models that summarize the hydrological properties of high-yield groundwater resources related to fault zones in crystalline basement are shown and discussed.

  4. PETROGRAPHIC AND GEOCHEMICAL CHARACTERISTICS OF GABBROIC ROCKS: CENTRAL ANATOLIAN MASSIF, YEŞİLHİSAR-KAYSERİ (TURKEY

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    Fuat IŞIK

    2002-02-01

    Full Text Available The study area is located within the Central Anatolian Massif around Yeşilhisar (Kayseri. The oldest rock units in the area are ophiolitic rocks which are mainly found as gabbro and dunites. The gabbros are dark green,blackish green coloured and hard, thin-medium granular hipidiomorf textured. Main Composition of gabbroic rocks are hornblende, clinopyroxen, plagioclase, quartz and opaque minerals, sphene and spinel are accessory minerals. The dunites are yellowish, greenish yellow coloured and fragile and stockwork textured. The main components of the dunites are olivine, pyroxen and chromite. The gabbroic rocks are mainly toleitic and can be classified as metaaluminious rocks. Main and trace element variations indicate that the fractionation of hornblende and Fe-Ti oxide minerals. Ratio of Condridite normalized Light REE to Heavy REE displays no enrichment La/LuN = 0.26. Trace and REE contents of the gabbroic rocks indicate that these rocks were a product of MORB like source.

  5. The evolution of a late-Variscan high-T/low-P region: the southeastern margin of the Bohemian massif

    Science.gov (United States)

    Büttner, S.; Kruhl, J. H.

    A characteristic feature of the Moldanubian part of the central European Variscides is late-orogenic high-T/low-P metamorphism. Its past history and the possible reasons for this metamorphism are highlighted by the tectonometamorphic development at the south- eastern margin of the Bohemian massif. During the Variscan orogeny, at ca. 340 Ma, two different crustal segments were juxtaposed by thrusting (the Drosendorf unit on top of the Monotonous unit). This probably marks a collisional event that is widespread in the southeastern Moldanubian zone. The collision was followed by crustal uplift accompanied by strong heating in the lowermost structural unit (Monotonous unit). During the subsequent orogenic collapse, the Moldanubian nappe pile was thrust over parts of the Moravo-Silesian terrane. A late stage of crustal extension under greenschist-facies conditions is linked with pluton emplacement. In general, magmatic underplating as well as delamination of the lithospheric mantle explains the high-T/low-P metamorphism and the large-scale plutonism in the southeastern Moldanubian zone.

  6. Characteristics of Polycrystalline Garnets in Micaschists From the Southern Menderes Massif (Turkey) and the Solitude Range (BC, Canada)

    Science.gov (United States)

    Anderson, C.; Whitney, D. L.; Seaton, N.

    2008-12-01

    Electron backscatter diffraction (EBSD) analysis of garnets in metamorphic rocks has revealed the presence of grain boundaries within what appear, based on morphology, to be single crystals. There have only been a few previous studies that have described these types of polycrystals in nature. In this study we analyzed garnets from two suites of metamorphic rocks: kyanite-staurolite schist from the Solitude Range, SW Rocky Mountains (BC, Canada), and mica schist from the southern Menderes Massif (western Turkey). Garnets from both sites are growth zoned and formed during a single metamorphic event, although the Solitude Range garnets record in their zoning and inclusion textures a change from chloritoid-present to staurolite- present (chloritoid-out) reaction history. The garnet-bearing rocks from these sites formed at P-T conditions of 430-550 C, 7-8 kbar (Menderes) and 550-600 C, 6-7 kbar (BC). Less than 10% of the garnets analyzed are polycrystals, but all polycrystals detected have similar characteristics: high-angle misorientation boundaries that crosscut inclusions and inclusion trails. Most polycrystals have 2-3 domains (crystals), but one complex polycrystal was comprised of 16 distinct lattice domains. In most cases, misorientation boundaries crosscut growth zoning, but one Menderes polycrystal exhibited distinct zoning in each domain. Most polycrystals likely formed early in the garnet growth history as closely-spaced nuclei coalesced, but clustering (coalescence) continued throughout the history of garnet crystallization in these rocks.

  7. A new species of the genus Pristimantis (Amphibia, Craugastoridae) associated with the moderately elevated massifs of French Guiana.

    Science.gov (United States)

    Fouquet, Antoine; Martinez, Quentin; Courtois, Elodie A; Dewynter, Maël; Pineau, Kévin; Gaucher, Philippe; Blanc, Michel; Marty, Christian; Kok, Philippe J R

    2013-12-23

    We describe a new Pristimantis from French Guiana, northern South America, which is mainly distinguished from known phenotypically related congeners (i.e. species from the polyphyletic unistrigatus species group) occurring at low and middle elevations in the Guiana Shield by the combination of a distinct tympanum, a lower ratio of tibia vs. hand length, a reddish groin region, and a distinct advertisement call consisting of clusters of generally four short notes. The new species inhabits pristine primary forests on the slopes of isolated massifs reaching more than 400 m elevation, and seems not to occur below ca. 200 m above sea level. Such a sharp altitudinal limit suggests a strong influence of thermal variation on the distribution of the species, and therefore a potential sensitivity to climate change. With only nine isolated populations documented so far, the new species should be prioritized for conservation. Historical climate fluctuations during the Quaternary are likely responsible for the distribution pattern of the new species. 

  8. Multidisciplinary characterisation of sedimentary processes in a recent maar lake (Lake Pavin, French Massif Central and implication for natural hazards

    Directory of Open Access Journals (Sweden)

    E. Chapron

    2010-09-01

    Full Text Available Sedimentation processes occurring in the most recent maar lake of the French Massif Central (Lake Pavin are documented for the first time based on high resolution seismic reflection and multibeam bathymetric surveys and by piston coring and radiocarbon dating on a sediment depocentre developed on a narrow sub aquatic plateau. This new data set confirms the mid Holocene age of maar lake Pavin formation at 6970±60 yrs cal BP and highlights a wide range of gravity reworking phenomena affecting the basin. In particular, a slump deposit dated between AD 580–640 remoulded both mid-Holocene lacustrine sediments, terrestrial plant debris and some volcanic material from the northern crater inner walls. Between AD 1200 and AD 1300, a large slide scar mapped at 50 m depth also affected the southern edge of the sub aquatic plateau, suggesting that these gas-rich biogenic sediments (laminated diatomite are poorly stable. Although several triggering mechanisms can be proposed for these prehistoric sub-aquatic mass wasting deposits in Lake Pavin, we argue that such large remobilisation of gas-rich sediments may affect the gas stability in deep waters of meromictic maar lakes. This study highlights the need to further document mass wasting processes in maar lakes and their impacts on the generation of waves, favouring the development of dangerous (and potentially deadly limnic eruptions.

  9. U-Th-Pb dating of the Brossasco ultrahigh-pressure metagranite, Dora-Maira massif, western Alps

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, J.L.; Montel, J.M. [Centre National de la Recherche Scientifique, 63 - Clermont-Ferrand (France); Chopin, C. [Ecole Normale Superieure, 75 - Paris (France). Lab. de Geologie

    1999-01-01

    The Brossasco metagranite is part of the coherent ultrahigh-pressure metamorphic terrane in the Dora-Maira massif and, although it has reached Alpine peak metamorphic conditions of about 725 C/30 kbar, still locally preserves an undeformed magmatic texture. In order to obtain new chronological constraints on this key area of the western Alps, we studied the behaviour of the U-Th-Pb system in zircons and monazites from such an undeformed facies. Only zircon fractions containing very small needle-shaped inclusions are concordant at 304{+-}3 Ma. This result is interpreted as the emplacement age of the granite. All other zircons show an old inherited memory and the more U-rich of these crystals were affected by an episodic Pb loss with a poorly defined lower intercept at 60{+-}45 Ma. Both TIMS (thermo-ionisation mass spectrometry) and electron-microprobe analysis of monazites show that this last event has also disturbed their U-Pb and Th-Pb isotopic systems, without resetting them completely. Comparison with cofacial rock-types which have been completely reworked under these extreme P-T conditions shows that deformation and mass transfer as well as the nature of the protoliths and the characteristics of their zircons have a much more pronounced influence on the behaviour of isotopic systems than the temperature and/or pressure parameters. This evidence is an obvious limitation to the use of the blocking-temperature concept. (orig.)

  10. Mantle lithosphere transition from the East European Craton to the Variscan Bohemian Massif imaged by shear-wave splitting

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    L. Vecsey

    2014-01-01

    Full Text Available We analyse splitting of teleseismic shear-wave recorded during the PASSEQ passive experiment (2006–2008 focussed on the upper mantle structure across the Trans-European Suture Zone (TESZ. 1009 pairs of the delay times of the slow split-shear waves and orientations of the polarized fast-shear waves exhibit lateral variations across the array, as well as backazimuth dependences of measurements at individual stations. While a distinct regionalization of the splitting parameters exists in the Phanerozoic part of Europe, a correlation with the large-scale tectonics around the TESZ and in the East European Craton (EEC is less evident. No general and abrupt change in the splitting parameters (anisotropic structure can be related to the Teisseyre–Tornquist Zone (TTZ, marking the edge of the Precambrian province on the surface. Instead, regional variations of anisotropic structure were found along the TESZ/TTZ. We suggest a south-westward continuation of the Precambrian mantle lithosphere beneath the TESZ and the adjacent Phanerozoic part of Europe, probably as far as towards the Bohemian Massif.

  11. Present state and dynamics of glacio-nival systems of Mongun-Taiga and Tavan-Bogdo-Ola mountain massifs

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    K. V. Chistyakov

    2015-01-01

    Full Text Available Climate-induced variations of glacio-nival systems (snow patches, glaciers, stone-ice formations of the high-mountain massifs Mongun-Taiga and Tavan-Bogdo-Ola (north slope were investigated for 1966-2013 period using results of field observations and analysis of aerial photos. Regional 25-year climatic cycles of the variations have been determined. Characteristics of response of glacio-nival objects to the climate changes were obtained. Results of preliminary mass balance calculations made for the 2012/13 glaciological year and values of the mass balance index calculated for the period 1966-2013 for the Seliverstov Glacier together with recorded climate cooling, increase of snow accumulation, and slowing down of glacier snout retreats give evidence to beginning of new 25-year cycle that is expected to be more favorable phase for existence of the above glacio-nival systems. Five-phase scheme of retreats of the valley glaciers happened after the LIA maximum was constructed on the basis of results of field observations performed for many years. Each phase is characterized by different retreat mechanisms as well as by different response to the same climate change that can be used as a basis for forecasting of future glacial dynamics. Rates of the thermokarst processes determined from observations and general mechanisms of dynamics of stone-ice formations are also discussed in the paper.

  12. Soil Heterogeneity Reflected in Biogeography of Beech Forests in the Borderland Between the Bohemian Massif and the Outer Western Carpathians

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    Samec Pavel

    2014-12-01

    Full Text Available Soil environment characteristics naturally affect the biogeographical classification of forests in central Europe. However, even on the same localities, different systems of vegetation classification de-scribe the forest types according to the naturally dominant tree species with different accuracy. A set of 20 representative natural beech stands in the borderland between the Bohemian Massif (Hercyni-an biogeographical subprovince and the Outer Western Carpathians (Westcarpathian subprovince was selected in order to compare textural, hydrostatic, physico-chemical and chemical properties of soils between the included geomorphological regions, bioregions and biotopes. Differences in the soils of the surveyed beech stands were mainly due to volume weight and specific weight, maximum capillary capacity (MCC, porosity, base saturation (BS, total soil nitrogen (Nt and fulvic acids. Specifics in the relations between these soil characteristics indicated that transient trans-Hercynian beech forests developed in the borderland between the two compared subprovinces. Soils of the investigated Hercynian beech forests were generally characterized by lower BS and lower Nt. Soils of the trans-Hercynian beech forests were more similar to the Carpathian beech forest soils than soils in the other Hercynian beech forests. Soils of the trans-Hercynian and Carpathian beech forests showed similarly higher BS, deeper occurrence of humic substances, lower specific weight and also higher MCC. Higher content of humic substances as well as MCC indicated an equal effect on forest ecology, which may contribute to more accurate classification of forests.

  13. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil; Petrologia e geocronologia (U/Pb-Sm/Nd) do Granito Passagem, Complexo Granitoide Pensamiento, SW do Craton Amazonico (MT)

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, Gisely Carmo de, E-mail: giselycarmo@hotmail.co [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Programa de Pos-Graduacao em Geociencias; Sousa, Maria Zelia Aguiar de, E-mail: mzaguiar@terra.com.b [Universidade Federal de Mato Grosso(ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Recursos Minerais; Ruiz, Amarildo Salina; Matos, Joao Batista de, E-mail: asruiz@gmail.co, E-mail: jmatos@cpd.ufmt.b [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Geologia Geral

    2010-09-15

    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  14. Neoproterozoic granitoids associated with the Bou-Azzer ophiolitic melange (Anti-Atlas, Morocco): evidence of adakitic magmatism in an arc segment at the NW edge of the West-African craton

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    Beraaouz, E. H.; Ikenne, M.; Mortaji, A.; Madi, A.; Lahmam, M.; Gasquet, D.

    2004-06-01

    The Neoproterozoic intrusions of the Bou-Azzer El Graara inlier consist of metaluminous, medium to high-K, I-type granitoids. Two groups of granitoids can be distinguished based on chemistry and isotopic signature: (1) the early (≈670 Ma) medium-K calc-alkaline, pre-collisional diorites of Ousdrat, Bou-Azzer, Bou-Izbane, and Ait-Hmane, with less fractionated REE patterns (2.6 Bleida characterized by relatively more fractionated REE patterns (8.9 15%, 3 < %Na 2O < 6.4, Yb < 1.8 ppm, Y < 20 ppm and isotopic ratios of Sr and Nd similar to the ophiolitic rocks). However their La/Yb and Sr/Y are relatively low in most of the samples. The origin of these arc magmas is not completely understood. In this paper we argue that some of these rocks probably contain components of adakitic melts. The early group was produced by partial melting of subducted oceanic crust followed by interaction of the melt with the overlying mantle wedge, and the late group by dehydration melting of underplated basalts in the lower crust in the garnet stability field.

  15. SHRIMP U-Pb zircon geochronology of Mesozoic granitoids from the Bariloche region (Argentina): Implications for the Middle-Late Jurassic evolution of the North Patagonian batholith.

    Science.gov (United States)

    Castro, Antonio; Vujovich, Graciela; Fernández, Carlos; Moreno-Ventas, Iñaki; Martino, Roberto; Corretgé, Guillermo; Díaz-Alvarado, Juan; Heredia, Nemesio; Gallastegui, Gloria

    2010-05-01

    A detailed U-Pb geochronological study has been carried out on granitoids of the North Patagonian batholith in the region of Bariloche (Argentina), between 40°30' S and 41°45' S. In this region, the calc-alkaline, subduction-related, granitic bodies of the North Patagonian batholith intruded an Early Jurassic volcano-sedimentary sequence contemporary with the intrusion of the Subcordilleran Patagonian batholith (J1 magmatism), and unconformably overlying a metamorphic Gondwanan basement. All these rocks were affected by the Andean compressional phases during the Cenozoic. U-Pb SHRIMP dating of zircon crystals from 11 samples (109 spots) of diorites, tonalites, granodiorites and granites yielded dates ranging from 173 ± 3 Ma to 150 ± 2 Ma (Aalenian to Tithonian). No significant age differences have been identified among the distinct lithological types. Also no spatial trend emerges from these results, although ages tend to be younger westward in the traverse of the Manso River (≈ 41° 35' S). Two peaks appear in the probability density plot of zircon ages. Most of the dated zircons are Bajocian-Bathonian (Middle Jurassic, ≈169 Ma, J2 magmatism), while a secondary peak is observed at the boundary Oxfordian-Kimmeridgian (Late Jurassic, ≈ 156 Ma, J3 magmatism). The J2 magmatic period is coeval to the main stage of effusive activity (V2) in the huge volcanic Chon Aike Province, while J3 coincides with the lesser V3 period of volcanism in Chon Aike. These new geochronological data strongly contribute to the knowledge of the first stages of tectonic evolution of the Andean subduction margin in southern South America. Contrary to previous models, it can be proposed that the subduction-related Mesozoic magmatism started well before the Late Jurassic, and that a continuous supply of calc-alkaline magmas dominated the active margin of South America during at least 190 Ma, from the Early Jurassic to nowadays. Therefore, no dramatic time gap can be observed between

  16. Melt source and evolution of I-type granitoids in the SE Tibetan Plateau: Late Cretaceous magmatism and mineralization driven by collision-induced transtensional tectonics

    Science.gov (United States)

    Yang, Li-Qiang; Deng, Jun; Dilek, Yildirim; Meng, Jian-Yin; Gao, Xue; Santosh, M.; Wang, Da; Yan, Han

    2016-02-01

    -type granitoids within the Yidun Arc.

  17. Nd isotopic variation of Paleozoic-Mesozoic granitoids from the Da Hinggan Mountains and adjacent areas, NE Asia: Implications for the architecture and growth of continental crust

    Science.gov (United States)

    Yang, Qidi; Wang, Tao; Guo, Lei; Tong, Ying; Zhang, Lei; Zhang, Jianjun; Hou, Zengqian

    2017-02-01

    There is a long-standing controversy regarding the tectonic division, composition and structure of the continental crust in the Da Hinggan Mountains and adjacent areas, which are mainly part of the southeastern Central Asian Orogenic Belt (CAOB). This paper approaches these issues via neodymium isotopic mapping of Paleozoic-Mesozoic (480 to 100 Ma) granitoids. On the basis of 943 published and 8 new whole-rock Nd isotopic data, the study area can be divided into four Nd isotopic provinces (I, II, III and IV). Province I (the youngest crust, Nd model ages (TDM) = 0.8-0.2 Ga) is a remarkable region of Phanerozoic crustal growth, which may reflect a major zone for closures of the Paleo-Asian Ocean. Province II (slightly juvenile crust, TDM = 1.0-0.8 Ga), the largest Nd isotopic province in the southeastern CAOB, is considered to reflect the recycling of the initial crustal material produced during the early stage (Early Neoproterozoic) evolution of the Paleo-Asian Ocean. Province III (slightly old crust, TDM = 1.6-1.1 Ga) is characterized by ancient crustal blocks, such as the central Mongolian, Erguna, Dariganga and Hutag Uul-Xilinhot blocks, which represent micro-continents and Precambrian basements in the southeastern CAOB. Several parts of Province III are located along the northern margin of the North China Craton (NCC), which is interpreted as a destroyed cratonic margin during the Paleozoic and Mesozoic. Province IV (the oldest crust, TDM = 2.9-1.6 Ga) mainly occurs within the NCC and reflects its typical Precambrian nature. These mapping results indicate that the boundary between Provinces II and III (the northern margin of the NCC) along the Solonker-Xar Moron Fault can be regarded as the lithospheric boundary between the CAOB and NCC. Provinces I and II account for 20% and 44% of the area of the southeastern CAOB, respectively, and therefore the ratio of continental growth is 64% from the Neoproterozoic to the Mesozoic, which is typical for this part of the

  18. Preliminary palynological analysis of a Holocene peat bog from Apakará-tepui (Chimantá Massif, Venezuelan Guayana

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    Rull, V.

    2011-12-01

    Full Text Available Preliminary palynological analysis of a Holocene peat bog from Apakará-tepui (Chimantá Massif, Venezuelan Guayana.- This paper reports the preliminary palynological results, at a millennial scale, of a Holocene peat bog sequence, since around 8.0 cal kyr BP to the present, obtained in the summit of the Apakará-tepui (2170 m elevation, in the Chimantá massif, located in the neotropical Venezuelan Guayana. The early Holocene was characterized by a vegetation different to the present, in which trees and shrubs dominated and Myrica (Myricaceae was the main element of the gallery forests around a permanent water body, as indicated by the continuous presence of Isoëtes (Isoëtaceae in high percentages. Around the middle Holocene (5.3 cal kyr BP, a shift towards more herbaceous and non-flooded communities occurred, and the present day vegetation established. This has been interpreted as a shift from warmer and wetter climates to cooler and drier conditions. The first phase, from 8.0 to 5.3 cal kyr BP, falls within a warming phase widely documented worldwide, known as the Holocene Thermal Maximum. The millennial trends shown here will be refined with further studies at centennial to decadal time scales. These results support the hypothesis that the best sites to detect paleoenvironmental changes in the summits of the tabular Guayana mountains are close to altitudinal ecotones.

    Análisis palinológico preliminar de una turbera holocena del Apakará-tepui (Macizo de Chimantá, Guayana venezolana.- Este artículo presenta los resultados palinológicos preliminares, a escala de milenios, de una secuencia holocena, desde 8.0 cal kyr BP hasta la actualidad, obtenida en la cima del Apakará-tepui (2170 m de altitud, en el Macizo del Chimantá, situado en la región neotropical de la Guayana venezolana. El Holoceno temprano se caracterizó por una vegetación diferente a la actual, dominada por árboles y arbustos, en la que

  19. Geological setting and petrogenesis of symmetrically zoned, miarolitic granitic pegmatites at Stak Nala, Nanga Parbat - Haramosh Massif, northern Pakistan

    Science.gov (United States)

    Laurs, B.M.; Dilles, J.H.; Wairrach, Y.; Kausar, A.B.; Snee, L.W.

    1998-01-01

    Miarolitic granitic pegmatites in the Stak valley in the northeast part of the Nanga Parbat - Haramosh Massif, in northern Pakistan, locally contain economic quantities of bi- and tricolored tourmaline. The pegmatites form flat-lying sills that range from less than 1 m to more than 3 m thick and show symmetrical internal zonation. A narrow outer or border zone of medium-to coarse-grained oligoclase - K-feldspar - quartz grades inward to a very coarse-grained wall zone characterized by K-feldspar - oligoclase - quartz - schorl tourmaline. Radiating sprays of schorl and flaring megacrysts of K-feldspar (intermediate microcline) point inward, indicating progressive crystallization toward the core. The core zone consists of variable mixtures of blocky K-feldspar (intermediate microcline), oligoclase, quartz, and sparse schorl or elbaite, with local bodies of sodic aplite and miarolitic cavities or "pockets". Minor spessartine-almandine garnet and lo??llingite are disseminated throughout the pegmatite, but were not observed in the pockets. The pockets contain well-formed crystals of albite, quartz, K-feldspar (maximum microcline ?? orthoclase overgrowths), schorl-elbaite tourmaline, muscovite or lepidolite, topaz, and small amounts of other minerals. Elbaite is color-zoned from core to rim: green (Fe2+- and Mn2+-bearing), colorless (Mn2+-bearing), and light pink (trace Mn3+). Within ???10 cm of the pegmatites, the granitic gneiss wallrock is bleached owing to conversion of biotite to muscovite, with local quartz and albite added. Schorl is disseminated through the altered gneiss, and veins of schorl with bleached selvages locally traverse the wallrock up to 1 m from the pegmatite contact. The schorl veins can be traced into the outer part of the wall zone, which suggests that they formed from aqueous fluids derived during early saturation of the pegmatite-forming leucogranitic magma rich in H2O, F, B, and Li. Progressive crystallization resulted in a late-stage sodic

  20. Latest Cambrian-Early Ordovician rift-related magmatic activity in the Kouřim Unit, Bohemian Massif

    Science.gov (United States)

    Soejono, Igor; Machek, Matej; Sláma, Jiří; Janoušek, Vojtěch

    2017-04-01

    Pre-collisional history of high-grade Variscan complexes is mostly difficult to reveal, due to intense reworking during the development of the orogenic belt. An ancient magmatism could provide a unique possibility to study it. The Kouřim Unit represents an extensive pre-Variscan plutonic body involved into the tectonic collage of the Kutná Hora Crystalline Complex, at the northern margin of the Moldanubian Domain in the Bohemian Massif. The LA-ICP-MS zircon ages and geochemical characteristics of (meta-)igneous rocks from the Kouřim Unit allow us to determine the timing and nature of magmatic activity within this part of the Bohemian Massif and thus to decipher its pre-Variscan evolution. The Kouřim Unit is composed of strongly metamorphosed and deformed sequence of magmatic rocks, dominated mainly by various types of migmatites, coarse-grained orthogneisses and minor metadiorites. The newly obtained LA-ICP-MS U-Pb zircon ages of four orthogneisses ranging between 486 ± 2 Ma and 484 ± 2 Ma are interpreted as timing the magma crystallization. The single metadiorite gave concordia age of 337 ± 2 Ma interpreted as the age of migmatitization. Few discordant older ages from metadiorite are considered as older xenocrysts more or less reset during the Variscan metamorphism. The orthogneisses are acid (SiO2 = 68.6-76.4 wt. %), exclusively subaluminous and seem to form a single calc-alkaline trend, whereas the metadiorite is intermediate (SiO2 = 54.3 wt. %; mg# = 61), distinctly metaluminous and displays tholeiitic character. The chondrite-normalized REE patterns for the orthogneisses show LREE enrichment (LaN/YbN = 1.5-8.9) and deep negative Eu anomalies (Eu/Eu* = 0.42-0.32); the NMORB-normalized spiderplots feature LILE/HFSE enrichment with deep negative Nb- Ta-Ti anomalies. In contrast, both patterns of metadiorite resemble those of NMORB (LaN/YbN = 0.5, Eu/Eu* = 0.96). The apparent magmatic arc-like geochemical signature of the orthogneisses is interpreted as

  1. Microstructural evolution of the Yugu peridotites in the Gyeonggi Massif, Korea: Implications for olivine fabric transition in mantle shear zones

    Science.gov (United States)

    Park, Munjae; Jung, Haemyeong

    2017-07-01

    Large-scale emplaced peridotite bodies may provide insights into plastic deformation process and tectonic evolution in the mantle shear zone. Due to the complexity of deformation microstructures and processes in natural mantle rocks, the evolution of pre-existing olivine fabrics is still not well understood. In this study, we examine well-preserved transitional characteristics of microstructures and olivine fabrics developed in a mantle shear zone from the Yugu peridotite body, the Gyeonggi Massif, Korean Peninsula. The Yugu peridotite body predominantly comprises spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We classified highly deformed peridotites into four textural types based on their microstructural characteristics: proto-mylonite; proto-mylonite to mylonite transition; mylonite; and ultra-mylonite. Olivine fabrics changed from A-type (proto-mylonite) via D-type (mylonite) to E-type (ultra-mylonite). Olivine fabric transition is interpreted as occurring under hydrous conditions at low temperature and high strain, because of characteristics such as Ti-clinohumite defects (and serpentine) and fluid inclusion trails in olivine, and a hydrous mineral (pargasite) in the matrix, especially in the ultra-mylonitic peridotites. Even though the ultra-mylonitic peridotites contained extremely small (24-30 μm) olivine neoblasts, the olivine fabrics showed a distinct (E-type) pattern rather than a random one. Analysis of the lattice preferred orientation strength, dislocation microstructures, recrystallized grain-size, and deformation mechanism maps of olivine suggest that the proto-mylonitic, mylonitic, and ultra-mylonitic peridotites were deformed by dislocation creep (A-type), dislocation-accommodated grain-boundary sliding (D-type), and combination of dislocation and diffusion creep (E-type), respectively.

  2. Paleomagnetism of Jurassic and Cretaceous rocks bounding the Santa Marta massif - NW corner of Colombia, South America

    Science.gov (United States)

    Bayona, G.; Jimenez, G.; Silva, C.

    2008-12-01

    The Santa Marta massif (SMM) is a complex terrain located in the NW margin of South America, bounded by the left-lateral Santa Marta fault to the west and the right-lateral Oca fault to the north. The SMM is cored by Precambrian metamorphic and Jurassic intrusive rocks, whereas along the SE flank crop out Jurassic volcanic rocks overlying unconformably by Limestones of Cretaceous age. Paleomagnetic analysis of 30 sites in the Jurassic and Cretaceous units in the SE region uncovered two principal magnetic components. The component "a", isolated in low coercivity and temperatures, has declinations to the north and moderate positive inclinations representing the actual field direction (n=11, D=347.6 I=23 K=30.77, a95=8.4). The component "c", with high coercivity and temperatures, has two orientations. After two-step tilt corrections, the first has northward declination and positive, low inclination (n=9, D=12, I=3, K=18.99, a95=12.1); this direction was uncovered in Cretaceous and some Jurassic rocks near to the Santa Marta fault, and we consider it as a Cretaceous component. The second direction was uncovered only in Jurassic rocks and has NNE declinations with negative-low inclinations (n=9, D=11.3 I=-14.3 K=12.36, a95=15.2); this direction represents a Jurassic component. Jurassic and Cretaceous directions isolated in areas faraway of the Santa Marta Fault suggest slight clockwise vertical-axes rotation. The Jurassic component suggests northward translation of the SMM from Paleolatitude -7.3, to near the magnetic equador in the Cretaceous, and to northern latitudes in the Cenozoic.

  3. Catastrophic rock slope failures and late Quaternary developments in the Nanga Parbat-Haramosh Massif, Upper Indus basin, northern Pakistan

    Science.gov (United States)

    Hewitt, Kenneth

    2009-06-01

    The Nanga Parbat-Haramosh Massif has some of the greatest relief on Earth and highest measured rates of uplift, denudation, and river incision in bedrock. Many studies have sought to understand how its morphology relates to geotectonic evolution and glaciations. However, few catastrophic rock slope failures had been recognised and many of their impacts had been attributed to other processes. Recently more than 150 of these landslides have been found within a 100-km radius of Nanga Parbat (8125 m). New discoveries are reported east, north and west of Nanga Parbat along the Indus streams. Most generated long-run-out rock avalanches that dammed the Indus or its tributaries, some impounding large lakes. They initiated episodes of intermontane sedimentation followed by trenching and removal of sediment. Valley-floor features record a complex interplay of impoundment and sedimentation episodes, superimposition of streams in pre-landslide valley floors, and exhumation of buried features. These findings depart from existing reconstructions of Quaternary events. A number of the rock-avalanche deposits were previously misinterpreted as tills or moraine and their associated lacustrine deposits attributed to glacial lakes. Features up to 1000 m above the Indus, formerly seen as tectonically raised terraces, are depositional features emplaced by landslides, or erosion terraces recording the trenching of valley fill in landslide-interrupted river reaches. Unquestionably, tectonics and glaciation have been important but decisive and misread formative events of the Holocene involve a post-glacial, landslide-fragmented fluvial system. The latter has kept valley developments in a chronic state of disequilibrium with respect to climatic and geotectonic controls. Accepted glacial chronologies are put in doubt, particularly the extent and timing of the last major glaciation. The pace and role processes in the Holocene have been seriously underestimated.

  4. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    Science.gov (United States)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2017-04-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  5. A NEW INTERPRETATION FOR THE GARNET ZONING IN METAPELITIC ROCKS OF THE SILGARÁ FORMATION, SOUTHWESTERN SANTANDER MASSIF, COLOMBIA

    Directory of Open Access Journals (Sweden)

    Ríos Reyes Carlos Alberto

    2008-06-01

    Full Text Available A Barrovian sequence of the Silgará Formation at the southwestern Santander Massif, Colombian Andes, contains zoned garnets in which major and trace element zoning correlates with distribution of mineral inclusions, which may indicate that garnet growth rate varied through time and affected both composition and texture ofgarnets, although different garnet producing reactions have also played an important role in the chemical zoning of garent. However, a local metasomatism process associated to the action of late magmatic fluids associated to the emplacement of the Pescadero Pluton (external forcing mechanism would be also considered. In particular, Ca, Mn and Y zoning patterns in some garnets correspond with inclusion-rich vs. inclusion-free zones, althoughthe distribution of inclusions does not correlate with chemical zoning (i.e., the same inclusions are found in Ca-rich and Ca-poor zones of the garnet. There is a similar lack of correlation with accessory phases (apatite, monazite, xenotime, ilmenite or rutile. In a garnet from the garnet-staurolite zone, a high Mn core containsabundant and randomly oriented apatite, monazite and ilmenite inclusions, while a euhedral low Ca mantle zone is inclusion-free and the high Ca / low Mn rim zone contains apatite, monazite and ilmenite aligned parallel to the margins of the garnet. Inclusions in garnet can also represent mineral phases were not completely consumed during garnet growth. Association of garnet zoning trends and patterns with inclusion distribution may help differentiatebetween processes that identically affect major-element zoning but that produced variable textures in the garnet.

  6. Glacial history of a mid-altitude mountain massif: cartography and dating in the Chablais area (France, Switzerland)

    Science.gov (United States)

    Perret, A.; Reynard, E.; Delannoy, J.-J.

    2012-04-01

    The Chablais area, considered as one of the cradles of glaciology (de Charpentier, 1841; Morlot, 1859), has been studied for a long time but several questions still remain unresolved. This study aims to reconstruct the glacial history of the massif, in order to explain the glacial landforms, which constitute an important part of the local geomorphology. The study focuses on the last glacial cycle (OIS 5 - OIS 2). The area is primarily associated with the the Valais glacier, by several local glacial flows and, to a lesser extent, by the Giffre glacier. Its position at the interface of the important Valais glacial flow and less powerful local flows is a specificity of the study area, which implies several bifurcations, penetration of the main glacier into laterals valleys, damming situations, and different responses of the various ice bodies to climatic changes. The study is divided in four steps. (1) The first step was to carry out a wide bibliographic survey to identify the state of knowledge, especially in relation to areas previously poorly studied and areas that needed to be reconsidered given developments in dating methods. (2) Field surveys allowed us to complete observations and prepare local geomorphological maps (of glacial landforms and associated phenomena). (3) The third step was to assemble heterogeneous data (old and new maps, Digital Terrain Models, aerial photographies) in a GIS to establish maps of glacial stages. (4) Finally, the absolute and relative chronology of deglaciation (Guitter, 2003) was completed by cosmogenic nuclide dating. Results have allowed us to address the conditions of glacial landform deposition and evolution in a mid-altitude mountain range, and show the need to be prudent in comparing results of different dating methods. Our results suggest that the ages obtained are overall too young in regard to 10Be ages on the northern alpine foreland (Ivy-Ochs et al., 2004) and are in conflict with 14C dates obtained in the area

  7. A Search for Amino Acids and Nucleobases in the Martian Meteorite Roberts Massif 04262 Using Liquid Chromatography-Mass Spectrometry

    Science.gov (United States)

    Callahan, Michael P.; Burton, Aaron S.; Elsila, Jamie E.; Baker, Eleni M.; Smith, Karen E.; Glavin, Daniel P.; Dworkin, Jason P.

    2013-01-01

    The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of beta-alanine and gamma-amino-eta-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal eta-omega-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites. A carbon isotope ratio of -24(0/00) +/- 6(0/00) for beta-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of eta-omega-amino acids may be due to a high temperature Fischer-Tropschtype synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.

  8. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    Science.gov (United States)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2016-09-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  9. Monazite and zircon as major carriers of Th, U, and Y in peraluminous granites: examples from the Bohemian Massif

    Science.gov (United States)

    Breiter, Karel

    2016-12-01

    The chemical compositions of zircon and monazite and the relationships between the contents of Th, U, Y, and REE in both minerals and in the bulk samples of their parental rocks were studied in three Variscan composite peraluminous granite plutons in the Bohemian Massif. It was established that granites of similar bulk composition contain zircon and monazite of significantly different chemistry. Monazite typically contains 5-13 wt% (rarely up to 28 wt%) ThO2, 0.4-2 wt% (up to 8.2 wt%) UO2, and 0.5-2 wt% (up to 5 wt%) Y2O3, whereas zircon typically contains less than 0.1 wt% (rarely up to 1.7 wt%) ThO2, less than 1 wt% UO2 (in the Plechý/Plockenstein granite, commonly, 1-2 wt% and scarcely up to 4.8 wt% UO2), and less than 1 wt% Y2O3 (in the Nejdek pluton often 2-5, maximally 7 wt% Y2O3). Monazite is an essential carrier of thorium, hosting more than 80 % of Th in all studied granites. Monazite also appears to be an important carrier of Y (typically 14-16 %, and in the Melechov pluton, up to 81 % of the total rock content) and U (typically 18-35 % and occasionally 6-60 % of the total rock budget). The importance of zircon for the rock budget of all the investigated elements in granites is lower: 4-26 % U, 5-17 % Y, and less than 5 % Th.

  10. 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

  11. Two episodes of subduction and collision events at the northern foot of Dabie Mountains: Evidence from petrology and structural geology of granitoid rocks

    Institute of Scientific and Technical Information of China (English)

    YANG; Kunguang; (

    2001-01-01

    [1]Liu Yican, Xu Shutong, Jiang Laili, The meta-flysch nappe in the northern part of the Dabie mountains, Regional Geology of China (in Chinese), 1998, 17(2): 156.[2]Zhang Erpeng (ed.), Geological map of Qinling-Dabie mountains and adjacent region of the People’s Republic of China (1:1 000 000), Beijing: Geological Publishing House, 1992.[3]Liu Zhigang, Niu Baogui, Ren Jishun, Disintegration of the Xinyang group and its tectonicimplications, Geological Review (in Chinese), 1992, 38 (4): 293.[4]Yang Kunguang, Ma Changqian, Yang Weiran, Significanse of study of Mafan Caledonian intrusion in Beihuaiyang depression, Earth Science (in Chinese), 1998, 23(3): 236.[5]Taylor, S. R., Mclenan, S. M., The Continental Crust, Its Composition and Evolution, Oxford: Blackwell, 1990, 312.[6]Hafmann, A. W., Chemical differentiation of the Earth, the relationship between mantle, continental crust and oceanic crust, Amer. Reviews in Mineralogy, 1988, 13: 201.[7]Bathchelor, R. A., ,Bowden, P., Petrogenetic interpretation of granitoid rocks series using multiation parameters, Chem. Geol., 1985, 4: 45.[8]Briqueu, L., Bougault, H., Joron, J. L., Quantification of Nb, Ta, Ti and anomalies in magma associated with subduction zones: petrogenetic implication, Earth Planet. Sci. Lett., 1984, 85: 386.[9]Ma Changqian, Li Zhichang, Ehlers, C. et al., A post-collisional magmatic plumbing system: Mesozoic granitoid plutons from the Dabieshan high-pressure and ultrahigh-pressure metamorphic zones, east-central China, Lithos, 1988, 45: 431.[10]Yang Kunguang, Ma Changqian, Xu Changhai et al., Differential uplift between Beihuaiyang and Dabie orogenic belt, Science in China, Ser. D, 2000, 43(2): 193.[11]Gower, T. J. W., Simpson, C., Phase boundary mobility in naturally deformed high-grade quartzo-feldstathic rocks: evidence for diffusional creep, J. Struct. Geol., 1992, 14: 301.[12]Tullis, J. A., Christis, J. M., Griggs, D. T., Microstructures and

  12. Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance

    Science.gov (United States)

    Bettencourt, Jorge Silva; Juliani, Caetano; Xavier, Roberto P.; Monteiro, Lena V. S.; Bastos Neto, Artur C.; Klein, Evandro L.; Assis, Rafael R.; Leite, Washington Barbosa, Jr.; Moreto, Carolina P. N.; Fernandes, Carlos Marcello Dias; Pereira, Vitor Paulo

    2016-07-01

    The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Carajás Mineral Province comprises greenstone belts (3.04-2.97 Ga), metavolcanic-sedimentary units (2.76-2.74 Ga), granitoids (3.07-2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74-2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with Nb-Y-Sn-Be-U. The latter, as well as Sn-W and Au-EGP deposits are coeval with ca. 1.88 Ga A2-type granites. The Tapajós Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0-1.87 Ga), two calc-alkaline volcanic sequences (2.0-1.95 Ga to 1.89-1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas Cu-Au and Cu-Mo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98-1.75 Ga), generated in ocean-ocean orogenies. Disseminated and vein-type Au ± Cu and Au + base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Col

  13. Geochemistry and tectonostratigraphy of the basal allochthonous units of SW Iberia (Évora Massif, Portugal): Keys to the reconstruction of pre-Pangean paleogeography in southern Europe

    Science.gov (United States)

    Fernández, Rubén Díez; Fuenlabrada, José Manuel; Chichorro, Martim; Pereira, M. Francisco; Sánchez-Martínez, Sonia; Silva, José B.; Arenas, Ricardo

    2017-01-01

    The basal allochthonous units of NW and SW Iberia are members of an intra-Gondwana suture zone that spreads across the I