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Sample records for metamorphic rocks

  1. Fluids in metamorphic rocks

    NARCIS (Netherlands)

    Touret, J.L.R.

    2001-01-01

    Basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated. A major problem relates to the number of inclusions, possibly formed on a wide range of P-T conditions, having also suffered, in most cases, extensive changes after initial trapping. The

  2. Uranium deposits in magmatic and metamorphic rocks

    International Nuclear Information System (INIS)

    1989-01-01

    The association of uranium with certain types of magmatic and metamorphic rocks is well known. They have consequently been explored and studied quite extensively. In recent years interest in them has been eclipsed by the discovery of larger, lower cost deposits in other geological environments. Nonetheless, magmatic and metamorphic rocks continue to be important sources of uranium and large areas of the Earth's crust with such rocks are prospective locations for additional discoveries. As future exploration and development could be more difficult the full importance of individual deposits may not be recognized until after many years of investigation and experience. In addition to being important host rocks, magmatic and metamorphic rocks have been of considerable interest to uranium geologists as they are considered to be important source rocks for uranium and thus can lead to deposits nearby in other environments. Furthermore, these rocks provide important information on the geochemical cycle of uranium in the Earth's crust and mantle. Such information can lead to identification of uranium provinces and districts and to a basic understanding of processes of formation of uranium deposits. The International Atomic Energy Agency convened a Technical Committee Meeting on Uranium Deposits in Magmatic and Metamorphic Rocks. The meeting was held in Salamanca, Spain, from 29 September to 3 October 1986. It was followed by a two day field trip to uranium deposits in the Ciudad Rodrigo and Don Benito areas. The meeting was attended by 48 participants from 22 countries. Two panels were organized for discussion of the following topics: (1) ore deposit genesis and characterization and (2) exploration and resource assessment. The technical papers together with the panel reports form this publication. The scope and variety of the papers included and the panel reports provide a good coverage of current knowledge and thinking on uranium in magmatic and metamorphic rocks

  3. Well log responses in metamorphic rocks near Maribor

    Directory of Open Access Journals (Sweden)

    1995-12-01

    Full Text Available In the Stražun forest at Pobrežje near Maribor, (Eastern Slovenia six boreholes have been drilled from 860 to 1600m deep. The paper describes geological conditions in mentioned boreholes, as well as in wider surroundings of Maribor with stress on metamorphic rocks. Based on pétrographie analysis of the rocks cuttings and well logs the upper phyllitic part ant the lower Pohorje series of themetamorphic complex could be separated. The first one includes phyllites with phyllitic quartzites and silicate marmorized limestones. The Pohorje series is represented by two-mica gneiss and schist, mainly with inclusions of amphibolite and eclogite, and subordinately retrograde chlorite-amphibole schist. The welllog responses for particular lithological sequences of metamorphic complex have been distinguished on the basis of conventional electrologs and gamma ray measurements.The problem of lithological interpretation of well logs in these rocks is described. Two fields of well log responses are distinguishable, as separated by the degree of natural radioactivity. Apart from veined quartzite, all rocks fromthe phyllitic part of the metamorphic complex are highly radioactive. In the Pohorje series gneiss, schist and diaphtorite-phyllonite are highly radioactive, while amphibolite, eclogite and retrograde chlorite-amphibole schist have low radioactivity.Finally, typical well log responses in lithological sequences of the discussed metamorphic rocks are presented.

  4. Analysis of lineament swarms in a Precambrian metamorphic rocks ...

    Indian Academy of Sciences (India)

    Analysis of lineament swarms in a Precambrian metamorphic rocks in India ... Lineament; fracture; remote sensing; hydrology; data analysis. ... The unfiltered analysis technique shows that the major lineament and fracture trends are oriented along EW and NS directions respectively, thus failing to provide any correlation ...

  5. Petrology of blueschist facies metamorphic rocks of the Meliata Unit

    Directory of Open Access Journals (Sweden)

    Faryad Shah Wali

    1997-06-01

    Full Text Available Meliata blueschists originated from basalts, limestones, pelites, psammitic and amphibolite facies basement rocks. Compositionally, the metabasalts have a geochemical signature mostly indicative of a transitional arc-MORB origin, but some mafic rocks having affinity with within plate basalts also present. The mafic blueschists consist of blue amphibole, epidote and albite, rarely also garnet, Na-pyroxene and chloritoid. Apart from phengite and quartz the metapelites and metapsammites contain one or more of the minerals: chloritoid, paragonite, glaucophane, albite, chlorite, occasionally also Na-pyroxene and garnet. Amphibolite facies rocks contain relic garnet, plagioclase and hornblende, the latter two replaced by albite and blue amphibole, respectively. The zoning patterns of blue amphibole, garnet and chloritoid suggest their formation during prograde stage of metamorphism. P-T conditions of meta-morphism are estimated to be about 350-460 oC and 10-12 kbar.

  6. Chafalote metamorphic suite metapelitic rocks (southheastern Uruguayan shield)

    International Nuclear Information System (INIS)

    Masquelin, H.; Nessi, A.; Paris, A.

    2005-01-01

    Chafalote Metamorphic Suite is characterized by politic, psamitic, calc-silicate and mafic gneisses, which are affected by a Neoproterozoic granulite facies metamorphism. The rocks derived from semipelite and pelite protoliths show mineral assemblages and textures typical for temperature over 8000 0 C. The metapelite fabrics are described to interpret these protoliths and to better understand the relationships between metamorphism and deformation. The main reference surface is interpreted as a S composite banding (Sb=So/S1/S2). Some layers record graded and crossed bedding preserved in fine-grained quartz-rich semipelites. They contain orthopyroxene. A correlation is presented between thermal peak fabrics and retrograde path derived fabrics, both for meapelites.

  7. Microdeformation in Vredefort rocks; evidence for shock metamorphism

    Science.gov (United States)

    Reimold, W. U.; Andreoli, M. A. G.; Hart, R. J.

    Planar microdeformations in quartz from basement or collar rocks of the Vredefort Dome have been cited for years as the main microtextural evidence for shock metamorphism in this structure. In addition, Schreyer describes feldspar recrystallization in rocks from the center of the Dome as the result of transformation of diaplectic glass, and Lilly reported the sighting of mosaicism in quartz. These textural observations are widely believed to indicate either an impact or an internally produced shock origin for the Vredefort Dome. Two types of (mostly sub) planar microdeformations are displayed in quartz grains from Vredefort rocks: (1) fluid inclusion trails, and (2) straight optical discontinuities that sometimes resemble lamellae. Both types occur as single features or as single or multiple sets in quartz grains. Besides qualitative descriptions of cleavage and recrystallization in feldspar and kinkbands in mica, no further microtextural evidence for shock metamorphism at Vredefort has been reported to date. Some 150 thin sections of Vredefort basement rocks were re-examined for potential shock and other deformation effects in all rock-forming minerals. This included petrographic study of two drill cores from the immediate vicinity of the center of the Dome. Observations recorded throughout the granitic core are given along with conclusions.

  8. Thermal evolution of high-pressure metamorphic rocks in the Alps

    NARCIS (Netherlands)

    Brouwer, F.M.

    2000-01-01

    There are two major and currently unresolved issues in Alpine geology concerning the metamorphic evolution of the rocks in the internal zones of the Alps. First, rocks showing evidence for geologically young, high-pressure to very high-pressure metamorphism are now exposed at the Earth's surface,

  9. Metamorphers

    KAUST Repository

    Sorger, Johannes

    2018-01-18

    In molecular biology, illustrative animations are used to convey complex biological phenomena to broad audiences. However, such animations have to be manually authored in 3D modeling software, a time consuming task that has to be repeated from scratch for every new data set, and requires a high level of expertise in illustration, animation, and biology. We therefore propose metamorphers: a set of operations for defining animation states as well as the transitions to them in the form of re-usable storytelling templates. The re-usability is two-fold. Firstly, due to their modular nature, metamorphers can be re-used in different combinations to create a wide range of animations. Secondly, due to their abstract nature, metamorphers can be re-used to re-create an intended animation for a wide range of compatible data sets. Metamorphers thereby mask the low-level complexity of explicit animation specifications by exploiting the inherent properties of the molecular data, such as the position, size, and hierarchy level of a semantic data subset. We demonstrate the re-usability of our technique based on the authoring and application of two animation use-cases to three molecular data sets.

  10. Heat production rate from radioactive elements in igneous and metamorphic rocks in eastern desert, Egypt

    International Nuclear Information System (INIS)

    Abbady, A G.E.; Arabi, A.M.; Abbay, A.

    2005-01-01

    Radioactive heat - production data of igneous and metamorphic rocks cropping out from the eastern desert are presented. Samples were analysed using low level gamma-ray spectrometer (HPGe) in the laboratory. A total of 205 rock samples were investigated, covering all major rock types of the area. The heat-production rate of igneous rocks ranges from 0.11 (basalt) to 9.53 Μ Wm-3 (granite). In metamorphic rocks it varies from 0.28 (serpentinite) to 0.91 (metagabroo) Μ W.m-3. The contribution due to U is about (51%), whereas that of Th (31%) and (18%) by K. The corresponding values in igneous rocks are 76%: 19%: 5%, respectively. The calculated values showed good agreement with global values expect in some areas contained granite rocks

  11. Metamorphic history of Early Archean rocks of Anabaric shield

    International Nuclear Information System (INIS)

    Bibikova, E.V.; Belov, A.N.; Gracheva, T.V.; Makarov, V.A.; Rozen, O.M.; Sumin, L.V.

    1987-01-01

    U-Pb isotopic and thermoisochronous investigation into accessory zircons referring to two generations including relict magmatogenic and newly formed metamorphogenic ones, is conducted to ascertain the metamorphism time and substrate age evaluation. The results of the investigation conducted state two metamorphism stages within the limits of Anabaric shield: 1.97±0.02 billions of years ago and 2.6±0.1 billions of years ago, characterized by various geochemical parameters. Premetamorphic age of Daodynsk series roks is no younger than 3±2.0 billions of years

  12. Analysis of lineament swarms in a Precambrian metamorphic rocks

    Indian Academy of Sciences (India)

    Addressing the geologic significance of lineaments and their correlation with joints/fractures is still unclear. The present study attempts to analyse the lineament swarms developed in a Precambrian metamorphic terrain in India using both unfiltered and filtered techniques. The unfiltered analysis technique shows that the ...

  13. Radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico with annotated bibliography

    International Nuclear Information System (INIS)

    McLemore, V.T.

    1982-02-01

    The primary objectives of this report are to list known radioactive occurrences in veins and igneous and metamorphic rocks in New Mexico, and to provide an annotated bibliography of geologic reports concerning these regions. Only plutonic, metamorphic, vein, and Precambrian quartz-pebble conglomerate uranium deposits are considered in this report; other nonsandstone uranium deposits (such as shale, limestone, phosphorite, coal, evaporative precipitates, and fossil placer deposits) will be considered at a later time. These objectives were achieved through a literature search. Some field examinations of some of the radioactive occurrences have been completed. A table of known radioactive occurrences in veins and igneous and metamorphic rocks was compiled from the literature (Appendix I)

  14. Contact Metamorphism in the Supracrustal Rocks of the ...

    African Journals Online (AJOL)

    granite intrusion in metabasites at Mawemeru area produced heat that baked the respective country rocks through epidote-amphibolite- to amphibolite-facies. Critical and informative mineral assemblages in the metairostones of Geita Hills are ...

  15. Radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico with annotated bibliography

    International Nuclear Information System (INIS)

    McLemore, V.T.

    1982-01-01

    From an extensive literature search and field examination of 96 nonsandstone radioactive occurrences, the author compiled an annotated bibliography of over 600 citations and a list of 327 radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico. The citations are indexed by individual radioactive occurrence, geographic area, county, fluorspar deposits and occurrences, geochemical analyses, and geologic maps. In addition, the geology, mineralization, and uranium and thorium potential of 41 geographic areas in New Mexico containing known radioactive occurrences in veins and igneous and metamorphic rocks or that contain host rocks considered favorable for uranium or thorium mineralization are summarized. A list of aerial-radiometric, magnetic, hydrogeochemical, and stream-sediment survey reports is included

  16. contact metamorphism in the supracrustal rocks of the sukumaland ...

    African Journals Online (AJOL)

    Mgina

    intrusion in metabasites at Mawemeru area produced heat that baked the respective country rocks through ... felsic pyroclastic and lava flows and .... grains in the matrix have the chemical composition of ferrotschermakite similar to rims of the coarse laths. M4 site in these amphiboles has intermediate values of Na ranging ...

  17. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high temperature-high pressure metamorphic rocks

    Science.gov (United States)

    Guoqing, Zhou

    The NEJXO with a N.E.-S.W. elongation occurs in the mid-Lower Qigong Group, under which lies the Jiuling Group (1401 Ma) and above which lies the Shangshu Group (817 ± 87 Ma), so that the age of NEJXO is defined to be Proterozoic between 1401 Ma and 817 ± 87 Ma. The sediments of the Jiuling Group show evidence of continental derivation, but the Qigong Group and Shangshu Group are characterised by CA volcanic rocks and probably represent a gradually growing island-arc. Thus, we regard the NEJXO as occurring in a back-island-arc basin between the ancient continent and the island-arc. On the whole, the main members of dismembered ophiolite are all present. The metamorphic periodotite present in them, is considered to be especially important, because it may be the sole representative of the older mantle present and it differs from those younger. The high-T metamorphic rocks associated with the NEJXO are various hornstones and melilite marble, whereas the high-P metamorphic rocks are aragonite-jadeite-glaucophane schist and schistose lawsonite marble. From the fact that high-P metamorphism was superimposed on the high-T metamorphic rocks, it may be suggested that early tension (at opening stage) and late compression (at closing stage) occurred during the development of the basin.

  18. Subsolidus segregation of quartz in metamorphic differentiation of metasedimentary rocks

    Science.gov (United States)

    Artimenko, M. V.

    2017-08-01

    Thermodynamic modeling of the SiO2-TiO2-Al2O3-Fe2O3-MnO-MgO-CaO-Na2O-K2O-P2O5-H2O (STAFMMCNKPOH) system at 600°C, 5 kbar has been applied to investigate dissolution and re-precipitation of quartz. Comparing silica molality in the STAFMMCNKPOH and SiO2-H2O systems, there is seen to be no effect of mineral assemblage on quartz solubility. From quantitatively estimated water/rock ratio required to dissolve quartz completely, one can deduce that the segregation of quartz appears to be due to diffusive transport of silica in inner pore fluid rather than to advective transport (in fluid flow).

  19. Morphological preservation of carbonaceous plant fossils in blueschist metamorphic rocks from New Zealand.

    Science.gov (United States)

    Galvez, M E; Beyssac, O; Benzerara, K; Bernard, S; Menguy, N; Cox, S C; Martinez, I; Johnston, M R; Brown, G E

    2012-03-01

    Morphological and chemical evidence of ancient life is widespread in sedimentary rocks retrieved from shallow depths in the Earth's crust. Metamorphism is highly detrimental to the preservation of biological information in rocks, thus limiting the geological record in which traces of life might be found. Deformation and increasing pressure/temperature during deep burial may alter the morphology as well as the composition and structure of both the organic and mineral constituents of fossils. However, microspore fossils have been previously observed in intensely metamorphosed rocks. It has been suggested that their small size, and/or the nature of the polymer composing their wall, and/or the mineralogy of their surrounding matrix were key parameters explaining their exceptional preservation. Here, we describe the remarkable morphological preservation of plant macrofossils in blueschist metamorphic rocks from New Zealand containing lawsonite. Leaves and stems can be easily identified at the macroscale. At the microscale, polygonal structures with walls mineralized by micas within the leaf midribs and blades may derive from the original cellular ultrastructure or, alternatively, from the shrinkage during burial of the gelified remnants of the leaves in an abiotic process. Processes and important parameters involved in the remarkable preservation of these fossils during metamorphism are discussed. Despite the excellent morphological preservation, the initial biological polymers have been completely transformed to graphitic carbonaceous matter down to the nanometer scale. This occurrence demonstrates that plant macrofossils may experience major geodynamic processes such as metamorphism and exhumation involving deep changes and homogenization of their carbon chemistry and structure but still retain their morphology with remarkable integrity even if they are not shielded by any hard-mineralized concretion. © 2012 Blackwell Publishing Ltd.

  20. Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

    OpenAIRE

    Ogilvie, Paula; Gibson, Roger L.

    2017-01-01

    Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or seque...

  1. Microstructure of selected metamorphic rock types - application of petrographic image analysis

    Czech Academy of Sciences Publication Activity Database

    Šachlová, Š.; Schenk, Vladimír; Schenková, Zdeňka

    2010-01-01

    Roč. 7, č. 4 (2010), s. 431-443 ISSN 1214-9705 R&D Projects: GA MŠk(CZ) LC506 Institutional research plan: CEZ:AV0Z30460519 Keywords : metamorphic rock * texture * structure Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.452, year: 2010 www.irsm.cas.cz/abstracts/AGG/04_10/4_Sachlova.pdf

  2. Dating by fission tracers of some metamorphic rocks within the city of Rio de Janeiro

    International Nuclear Information System (INIS)

    Fonseca, A.C.; Poupeau, G.

    1984-01-01

    Fission-Track (FT) ages were measured in apatites from metamorphic rocks outcropping within the city of Rio de Janeiro. One apatite presented a 'substraction age' of 124 + - 10 my (2σ) and a second one a 'plateau age' of 117 + - 5 my. These ages are supposed to be related to the isostatic uplift related to the opening of the South-Atlantic Ocean. A younger plateau age of 85 + - 5 my might possibly be related to a later readjustment phase. Based on these and Fonseca et al. (1984) results, a cooling history for the rocks in Rio de Janeiro city is proposed. (Author) [pt

  3. The age of the rocks and the metamorphic episodes from the Southeastern of Sao Paulo state

    International Nuclear Information System (INIS)

    Tassinari, C.C.G.; Kawashita, K.; Schmuss, R. van; Taylor, P.N.

    1988-01-01

    Rb-Sr, Pb-Pb and U-Pb geochronologic studies carried out on precambrian rocks from the southeastern Sao Paulo state suggest a Complex geologic evolution during the Archean and Proterozoic times. This region is divided in five differents allochthonous terranes named Itapira-Amparo, Piracaiba-Jundiai, Sao Roque, Embu and Costeiro, separated by thrust and strike-slip faults. The Itapira-Amparo domain has a original history dating back to 3.4 Ga. and since 2.6 to 2.5 Ga. and 2.2 to 1.9 Ga. metamorphic rockformation episode occurred involving both mantle-derived magmas and recycled material. Supracrustal sequences developed around 1.4 Ga. The domain was locally reworked in 0.8 - 0.65 Ga. In the Piracaia-Jundiai the main rock-formation event occurred at 1.4 Ga., but this domian was affected by strong granization and migmatization episodes during the period 1.1 - 0.6 Ga. The third terrain is characterized by the Sao Roque metavolcanossedimentary sequence developed during the time period 1.8 - 0.7 Ga., and comprising two metamorphic superimposed events (1.4 and 0.8 - 0.7 Ga.). the post-tectonics granites ranging in ages from 0.7 to 0.55 Ga. Within the Embu terrain ages of 2.5, 1.4 and 0,75 Ga. were obtained for the metamorphic terrain, with post-tectonic activities around 650 Ma. In the Costeiro domain all the metamorphic rocks developed in late-Proterozoic time, with syntectonic phase around 650 Ma [pt

  4. Geology of uranium vein deposits (including Schwartzwalder Mine) in Proterozoic metamorphic rocks, Front Range, Colorado

    International Nuclear Information System (INIS)

    Voto, R.H. de; Paschis, J.A.

    1980-01-01

    The Schwartzwalder uranium deposit is one of many uranium vein occurrences in the Lower Proterozoic metamorphic rocks of the Front Range, Colorado. The principal veins of significant uranium content occur marginal to the Colorado Mineral Belt; are localized by structural dilation zones, vein junctions, fault deflections or branching; and occur dominantly within or at the contact of certain preferred metamorphic-stratigraphic units, particularly the siliceous, garnetiferous gneisses, where these rock units are broken by faults and fractures associated with the north-northwest-trending throughgoing faults. Uranium at the Schwartzwalder mine occurs primarily as open-space brecciated vein filling along the steeply west-dipping Illinois vein and numerous east-dipping subsidiary veins where they cut preferred metamorphic host rocks that are tightly folded. Uraninite occurs with molybdenite, adularia, jordisite, ankerite, pyrite, base-metal sulphides, and calcite in vein-filling paragenetic sequence. Minor wall-rock alteration is mainly hematite alteration and bleaching. Vertical relief on the developed ore deposit is 900 metres and still open-ended at depth. No vertical zonation of alteration, vein mineralogy, density of the subsidiary veins, or ore grade has been detected. The Schwartzwalder uranium deposit is of substantial tonnage (greater than 10,000 metric tons of U 3 O 8 ) and grade (averaging 0.57% U 3 O 8 ). Structural mapping shows that the Illinois vein-fault is a Proterozoic structure. Discordant Proterozoic (suggested) and Laramide dates have been obtained from Schwartzwalder ore. The data suggest, therefore, a Proterozoic ancestry of this heretofore presumed Laramide (Late Cretaceous-Early Tertiary) hydrothermal uranium deposit. The authors suggest a polygenetic model for the origin of the Schwartzwalder uranium deposit

  5. Gneiss Macuira: tectonic evolution of Paleozoic metamorphic rocks of the Alta Guajira, Colombia

    International Nuclear Information System (INIS)

    Lopez I; A Julian; Zuluaga C; A, Carlos

    2012-01-01

    The Macuira Gneiss is a Paleozoic metamorphic unit that outcrops in the Simarua, Jarara and Macuira ranges, Alta Guajira. It is composed by a lithologies metamorphosed under amphibolite facies P-T conditions and consist of amphibolitic and quartz feldspathic gneisses, amphibolites, schists, pegmatites, calc-silicated rocks and marbles, with migmatization evidences in gneisses and amphibolites. Five foliations (S1-5) and three folding events (F1-3) were identified and interpreted as product of two metamorphic events, developed in a progressive barrovian metamorphic gradient of intermediate pressure with intermediate P-T ratio, interpreted as product of continental collision tectonics. This unit is important in understanding of the tectonic evolution of the Alta Guajira and Caribbean because it records different deformational phases pre-, syn- and post-migmatitic, that could be related with different tectonic episodes: the first associated with the collision between Laurasia and Gondwana (Alleghanian Orogeny - Late Paleozoic), and the second related with the Caribbean Plate evolution (Andean Orogeny - Meso-Cenozoic).

  6. Short-Wavelength Infrared (SWIR) spectroscopy of low-grade metamorphic volcanic rocks of the Pilbara Craton

    Science.gov (United States)

    Abweny, Mohammad S.; van Ruitenbeek, Frank J. A.; de Smeth, Boudewijn; Woldai, Tsehaie; van der Meer, Freek D.; Cudahy, Thomas; Zegers, Tanja; Blom, Jan-Kees; Thuss, Barbara

    2016-05-01

    This paper shows the results of Short-Wavelength Infrared (SWIR) spectroscopy investigations of volcanic rocks sampled from low-grade metamorphic greenstone belts of the Archean Pilbara Craton in Western Australia. From the reflectance spectra a range of spectrally active minerals were identified, including chlorites, hornblende, actinolite, epidote and white micas. The rock samples were grouped into mineral assemblages based on their spectrally identified minerals and stratigraphic positions. The metamorphic amphibolite and greenschist facies could be identified from the SWIR spectroscopic data as well as three sub zones of the greenschist facies: 1) a zone containing Fe-chlorite; 2) a zone containing intermediate chlorite and epidote; and 3) a zone containing intermediate chlorite, actinolite and hornblende. Spectral parameters were calculated from the reflectance spectra to assess the metamorphic grade and zones. Plots of the depth parameters of the Fe-OH feature near 2250 nm versus the Mg-OH feature near 2390 nm differentiate the metamorphic amphibolite and greenschist facies and a transition zone between the two. The wavelength position parameter of the Mg-OH absorption feature near 2340 nm also serves to discriminate between the various metamorphic sub zones. The identification of the metamorphic grades of the volcanic sequences in greenstone belts with SWIR spectroscopy is useful for regional geological field studies, exploration for metamorphic mineral deposits hosted in the greenstone belts and the interpretation of hyperspectral remote sensing data sets covering similar types of terranes.

  7. Pressure Variations in Metamorphic Rocks: Implications for the Interpretation of Petrographic Observations

    Science.gov (United States)

    Tajčmanová, Lucie

    2014-05-01

    Metamorphic petrologists and structural geologists, using direct measurements, bring the only direct observational constrains for validating geodynamic models. Therefore, petrological and structural geological observations are essential for the quality and reproducibility of geodynamic reconstructions and models. One of the important assumptions for geodynamic reconstructions arises from the pressure and temperature estimates in the petrology analysis. Pressure is commonly converted to depth through the equation for lithostatic pressure and so the original position of the rock sample within the Earth's interior can be constrained. The current assumption that the studied sample corresponds to uniform pressure may not be correct, and if so, it has serious implications. Increasing evidence from analytical data shows that pressure is not constant even on a grain scale, posing new challenges because, if ignored, it leads to an incorrect use of petrology data in constraining geodynamic models. Well known examples of the preservation of coesite and diamond in a host mineral like garnet show that high pressure inclusions are preserved during decompression. Tajčmanová et al. (2014) has shown that grain-scale pressure variations can develop and that these pressure variations allow compositional zoning in minerals preserved over geological time scales. A new unconventional barometric method based on equilibrium under pressure variations has been developed . Such pressure variations are also connected with differences in fluid pressure in open systems and can be thus observed at all scales. Tajčmanová L., Podladchikov Y., Powell R., Moulas E., Vrijmoed J. and Connolly J. (2014). Grain scale pressure variations and chemical equilibrium in high-grade metamorphic rocks.Journal of Metamorphic Geology, doi:10.1111/jmg.12066 This work was supported by ERC starting grant 335577 to Lucie Tajcmanova

  8. Ultra-high temperature granulite-facies metamorphic rocks from the Mozambique belt of SW Tanzania

    Science.gov (United States)

    Sommer, H.; Kröner, A.

    2013-06-01

    The metamorphic rocks in the Neoproterozoic (Pan-African) Mozambique belt of southwestern Tanzania, around the town of Songea, can be subdivided into one- and two pyroxene bearing charnockitic gneisses, migmatitic granitoid gneisses and amphibolite-facies metapelites. Lower-grade amphibolite-facies rocks are rare and can be classified as sillimanite- and/or garnet-bearing metapelites. Most of the studied charnockitic gneisses show excellent corona textures with large orthopyroxene grains rimmed by clinopyroxene, followed by quartz and well developed garnet rims due to the reaction Opx + Pl = Grt + Cpx + Qtz that formed during isobaric cooling. These and other charnockitic gneisses show symplectites of orthopyroxene and An-rich plagioclase that resulted from the breakdown of garnet during isothermal decompression due to the reaction Grt + Cpx + Qtz = Opx + Pl. Geothermobarometric calculations yield up to ~ 1050 °C and up to ~ 12 kbar for peak metamorphic conditions. These are higher temperature and slightly lower pressure conditions than reported for other granulite-facies terrains in the Mozambique belt of Tanzania. Single zircon Pb-Pb evaporation and U-Pb SHRIMP ages for magmatic zircons extracted from two charnockitic and two granitic gneisses cluster in two groups, one at ~ 750 Ma and one at ~ 1150 Ma with the older reflecting the time of emplacement of the igneous precursors, and the younger approximating the time of charnockitization. These protolith ages are similar to those farther east in the Masasi area of southern Tanzania, as well as in northern Mozambique and in southern Malawi, and suggest that the Mozambique belt consists of chronologically heterogeneous assemblages whose pre-metamorphic tectonic setting remains obscure.

  9. Partial melting of ultrahigh-pressure metamorphic rocks during continental collision: Evidence, time, mechanism, and effect

    Science.gov (United States)

    Chen, Yi-Xiang; Zhou, Kun; Gao, Xiao-Ying

    2017-09-01

    Partial melting of ultrahigh-pressure (UHP) metamorphic rocks during continental collision has been increasingly found in nature. More and more studies have devoted to the evidence, time, mechanism and effect of crustal anataxis at mantle to lower crust depths. This is particularly so for UHP rocks from the Dabie-Sulu orogenic belt, whereas similar studies on these issues are relatively minor for other UHP terranes. The petrological evidence, especially microstructural observations and multiphase solid inclusion analyses, have been accumulated for the partial melting of UHP metamorphic rocks in collisional orogens. The results indicate that this is a kind of low-degree crustal anataxis at convergent plate margins due to decompressional dehydration of the UHP rocks themselves. Thus it has great bearing on intracrustal differentiation and crust-mantle interaction in continental subduction channels. Zircon may grow through peritectic reactions due to the breakdown of hydrous minerals. By dating of the peritectic zircons that contain coesite or diamond inclusions, the time of crustal anatexis under UHP conditions can be directly determined. In general, the partial melting of UHP rocks mainly took place at the stage of their early exhumation, partly still in the UHP regime and partly in the subsequent high-pressure (HP) regime. The crustal anatexis still at mantle depths is common in many UHP terranes, possibly facilitating exhumation of deeply subducted continental slices toward shallower levels. Petrological and geochemical studies indicate that phengite dehydration-driven melting during exhumation is the common mechanism for the anatexis of UHP rocks, though the other hydrous minerals were also involved in this process. The resulted HP to UHP melts may occur at different spatial scales and show significant fractionation in melt-mobile incompatible trace elements such as LILE and LREE. These melts are enriched in LILE to large extent and LREE and Th to small extent

  10. Study on Kalimantan uranium province: The assessment on uranium mineralization of metamorphic and granitic rocks at Schwaner mountains

    International Nuclear Information System (INIS)

    Tjokrokardono, Soeprapto

    2002-01-01

    Uranium exploration activities done by CEA-BATAN had discovered uranium occurrences as the radiometric and uranium content anomalies at metamorphic and granite rocks of Schwaner Mountains, Kalimantan. A part of the occurrences on metamorphic rocks at Kalan basin has been evaluated and be developed onto follow-up step of prospecting by construction of some drilling holes and an exploration adit. In order to increase the national uranium resources, it is necessarily to extent the exploration activity to out side or nearby of Kalan basin. The goal of this assessment is to understand the uranium accumulation mechanism at Pinoh metamorphic rocks of Kalan Kalimantan and to delineate areas that uranium may exist. The assessment was based on the aspect of geology, anomaly of radioactivity and uranium contents, tectonics and alterations. Pinoh metamorphic rocks which is influenced by Sukadana granite intrusion are the high potential rocks for the uranium accumulation, because the intrusion contains a relatively high of U, Th, Cu, Zn, Nb, Mn, and W. The potential rock distributions are in between G. Ransa granite intrusion at the east and Kotabaru granite intrusions at the west. The mineralizations are categorized as vein type deposits of granitic association

  11. Short-Wavelength Infrared (SWIR) spectroscopy of low-grade metamorphic volcanic rocks of the Pilbara Craton

    NARCIS (Netherlands)

    Abweny, Mohammad S.; van Ruitenbeek, Frank J A; de Smeth, Boudewijn; Woldai, Tsehaie; van der Meer, Freek D.; Cudahy, Thomas; Zegers, Tanja; Blom, Jan Kees; Thuss, Barbara

    This paper shows the results of Short-Wavelength Infrared (SWIR) spectroscopy investigations of volcanic rocks sampled from low-grade metamorphic greenstone belts of the Archean Pilbara Craton in Western Australia. From the reflectance spectra a range of spectrally active minerals were identified,

  12. Geothermal brine well: Mile-deep drill hole may tap ore-bearing magmatic water and rocks Undergoing Metamorphism

    Science.gov (United States)

    White, D.E.; Anderson, E.T.; Grubbs, D.K.

    1963-01-01

    A deep geothermal well in California has tapped a very saline brine extraordinarily high in heavy metals and other rare elements; copper and silver are precipitated during brine production. Preliminary evidence suggests that the brine may be pure magmatic water and an active ore-forming solution. Metamorphism of relatively young rocks may also be occurring within accessible depths.

  13. First report of garnet corundum rocks from southern India: Implications for prograde high-pressure (eclogite-facies?) metamorphism

    Science.gov (United States)

    Shimpo, Makoto; Tsunogae, Toshiaki; Santosh, M.

    2006-02-01

    We report here for the first time the occurrence of garnet and corundum in Mg-Al-rich rocks at Sevitturangampatti (Namakkal district) in the Palghat-Cauvery Shear Zone System (PCSS), southern India. The rocks contain several rare mineral assemblages such as garnet-corundum-sillimanite-cordierite-sapphirine-spinel-Mg-rich staurolite, garnet-corundum-sodic gedrite-cordierite-sillimanite/kyanite, garnet-Mg-rich staurolite-sillimanite/kyanite, sodic gedrite-Mg-rich staurolite-corundum-sapphirine, biotite-corundum-sapphirine and sodic gedrite-sapphirine-spinel-cordierite. Both garnet and corundum in these rocks occur as coarse-grained (1 mm to 10 cm) porphyroblasts in the matrix of sillimanite, cordierite and gedrite. Kyanite is common as inclusions in garnet, but matrix aluminosilicates are mainly sillimanite. The presence of rare garnet + corundum, which has so far been reported from kimberlite xenoliths, aluminous eclogites and ultrahigh-pressure metamorphic rocks as well as in high-pressure experiments, suggests that the assemblage is an indicator of an unusually high-pressure event, which has not been recorded in previous studies from southern India. Phase analysis of quartz-absent MAS system also suggests high-pressure stability of the assemblage. The inference of high pressure metamorphism is also supported by the presence of Mg-rich [Mg/(Fe + Mg) = 0.51] staurolite, which has been reported from high-pressure rocks, included from cores of coarse-grained garnet and gedrite. Porphyroblastic occurrence of garnet + corundum as well as staurolite and kyanite inclusions suggests that the area underwent prograde high-pressure metamorphism, probably in the eclogite field. The rocks subsequently underwent continuous heating at 940 to 990 °C, suggesting ultrahigh-temperature (UHT) metamorphism along a clockwise trajectory. Sapphirine + cordierite and spinel + cordierite symplectites between garnet and sillimanite suggest near isothermal decompression after the peak event

  14. Radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico with annotated bibliography. [Over 600 citations

    Energy Technology Data Exchange (ETDEWEB)

    McLemore, V. T.

    1982-01-01

    From an extensive literature search and field examination of 96 nonsandstone radioactive occurrences, the author compiled an annotated bibliography of over 600 citations and a list of 327 radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico. The citations are indexed by individual radioactive occurrence, geographic area, county, fluorspar deposits and occurrences, geochemical analyses, and geologic maps. In addition, the geology, mineralization, and uranium and thorium potential of 41 geographic areas in New Mexico containing known radioactive occurrences in veins and igneous and metamorphic rocks or that contain host rocks considered favorable for uranium or thorium mineralization are summarized. A list of aerial-radiometric, magnetic, hydrogeochemical, and stream-sediment survey reports is included.

  15. Arrested development - a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

    Science.gov (United States)

    Ogilvie, Paula; Gibson, Roger L.

    2017-02-01

    Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P-T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P-T conditions during successive layer growth along the P-T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P-T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate

  16. X-ray color maps of the zoned garnets from Silgará Formation metamorphic rocks,SantanderMassif, Eastern Cordillera (Colombia

    Directory of Open Access Journals (Sweden)

    Takasu Akira

    2010-12-01

    Full Text Available

    The metamorphic rocks of the Lower Paleozoic Silgará Formation of the Santander Massif, Eastern Cordillera (Colombia, were affected by a Barrovian-type metamorphism under low to high temperature and medium pressure conditions. These rocks contain garnet porphyroblasts, which show several kinds of chemical zoning patterns. The garnet grains behave as closed systems with respect to the rock matrix. Most of the observed zoning patterns are due to gradual changes in physicochemical conditions during growth. However, some garnet grains show complex zoning patterns during multiple deformation and metamorphic events.

  17. The Metamorphic Rocks-Hosted Gold Mineralization At Rumbia Mountains Prospect Area In The Southeastern Arm of Sulawesi Island, Indonesia

    Directory of Open Access Journals (Sweden)

    Hasria Hasria

    2017-09-01

    Full Text Available Recently, in Indonesia gold exploration activities  are not only focused along volcanic-magmatic belts, but also starting to shift along metamorphic and sedimentary terrains. The study area is located in Rumbia mountains, Bombana Regency, Southeast Sulawesi Province. This paper is aimed to describe characteristics of alteration and ore mineralization associated  with metamorphic rock-related gold deposits.  The study area is found the placer and  primary gold hosted by metamorphic rocks. The gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC. These quartz veins are currently recognized in metamorphic rocks at Rumbia Mountains. The quartz veins are mostly sheared/deformed, brecciated, irregular vein, segmented and  relatively massive and crystalline texture with thickness from 1 cm to 15.7 cm. The wallrock are generally weakly altered. Hydrothermal alteration types include sericitization, argillic, inner propylitic, propylitic, carbonization and carbonatization. There some precious metal identified consist of native gold and ore mineralization including pyrite (FeS2, chalcopyrite (CuFeS2, hematite (Fe2O3, cinnabar (HgS, stibnite (Sb2S3 and goethite (FeHO2. The veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18.4 ppm. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type. The orogenic gold deposit is one of the new targets for exploration in Indonesia

  18. Characteristics of ophiolite-related metamorphic rocks in the Beysehir ophiolitic mélange (Central Taurides, Turkey), deduced from whole rock and mineral chemistry

    Science.gov (United States)

    Çelik, Ömer Faruk; Delaloye, Michel F.

    2006-04-01

    Small outcrops of the metamorphic rocks of the Beysehir ophiolite appear to the west of Gencek and to the south of Durak (South of Beysehir Lake) in the Central Tauride Belt in Turkey. Amphibolitic rocks in the ophiolitic mélange have an igneous origin. Protoliths of these rocks were probably alkali basalts, gabbros or some ultramafic cumulates, such as pyroxenite. The amphibolites of the Beysehir Ophiolite can be divided into four groups: (1) amphibole+garnet+plagioclase±epidote (as secondary minerals)±opaque such as ilmenite±accessory minerals such as sphene and apatite; (2) amphibole+pyroxene+plagioclase±epidote±accessory minerals such as sphene, apatite±chlorite, calcite (as secondary mineral); (3) amphibole±plagioclase±opaque±accessory minerals; (4) amphibole+plagioclase±epidote±biotite and muscovite±opaque±accessory minerals. These metamorphic rocks show mainly granoblastic, grano-nematoblastic, porphyroblastic and/or poikiloblastic textures. All amphiboles in the amphibolites are calcic and cluster in the range from magnesio-hastingsite, pargasite to actinolite. Amphibole compositions are characterized by SiO 2=(38.02-54.3%), Al 2O 3=(1.5-12.8), FeO=(10.03-14.67%), K 2O=(0.2-1.8%), MgO=(5.5-15.7), Mg*=(0.3-0.8). The amphibolites show an alkaline to subalkaline character. However, the primitive mantle normalized incompatible trace element diagram shows close similarity with the typical ocean island basalt (OIB) pattern. The Rock/Chondrite normalized REE diagram of the amphibolites also confirms their OIB signature. Tectonomagmatic discrimination diagrams based on the immobile trace elements suggest a mostly within-plate alkali basalt (WPB) environment. Beysehir ophiolitic mélange contains amphibolites from ophiolite-related metamorphic rocks, but the matrix of the Beysehir ophiolitic mélange is not metamorphosed. Blocks of metamorphic rocks and the ophiolitic rocks may have been incorporated into the ophiolitic mélange in an oceanic

  19. Tectonic Stacking of HP/LT Metamorphic Rocks in Accretionary Wedges and the Role of Shallowing Slab-Mantle Decoupling

    Science.gov (United States)

    Aygül, Mesut; Oberhänsli, Roland

    2017-11-01

    High-pressure/low-temperature (HP/LT) chloritoid-bearing micaschists crop out widely in the central part of northern Turkey and represent deep-seated subduction-accretionary complexes. Three peak metamorphic assemblages are identified in the area studied: (1) garnet-chloritoid-glaucophane with pseudomorphs after lawsonite; (2) chloritoid with pseudomorphs after glaucophane; and (3) chloritoid with pseudomorphs after jadeite in addition to phengite, paragonite, quartz, chlorite, rutile, and apatite. The latter is interpreted as transformation of a chloritoid + glaucophane assemblage to chloritoid + jadeite with increasing pressure; PT modeling indicates 17 and 22-25 kbars for the two peak parageneses. The diversity of peak metamorphic assemblages and the PT estimates suggest that basal accretion occurred at different depths within the wedge. The depth of the basal accretion is possibly controlled by the slab-mantle decoupling depth. Stretching and thinning of the lithospheric fore arc induced by the slab rollback possibly caused shallowing of the slab-mantle decoupling depth which limited depth of the basal accretion from 70-80 km to 55 km within the subduction channel. A slab-mantle coupling depth-controlled basal accretion may also explain the scarcity of eclogite and high-grade blueschist facies metamorphic rocks in active intraoceanic subduction zones. Because the overriding plate is young and hot in intraoceanic subductions, the slab and mantle are coupled at a relatively shallow depth before eclogitization of the oceanic crust. This prevents accretion and exhumation of eclogite along the subduction channel.

  20. The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

    Science.gov (United States)

    Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

    2016-04-01

    The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

  1. Oxygen fugacity and chemical potentials as determinant factors in constraining the metamorphic evolution of subducted rodingites and enclosing ultramafic rocks.

    Science.gov (United States)

    Laborda López, Casto; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Gómez-Pugnaire, María Teresa; Garrido, Carlos J.; Jabaloy-Sánchez, Antonio; Padrón-Navarta, José Alberto

    2017-04-01

    Rodingites are Ca-, Al-enriched and Si-undersaturated rocks formed from mafic precursors enclosed in peridotites. Formation of both rodingites and serpentinites occurs simultaneously during serpentinization. Therefore, rodingites are common rocks associated with serpentinites in exhumed terrains, which experienced subduction and HP metamorphism. However, uncertainties remain about the factors that constrain the diverse mineral associations occurring in meta-rodingites as well as their response to devolatilization and redox reactions during subduction. In the Cerro del Almirez ultramafic massif (S-Spain) meta-rodingite bodies are enclosed both in Atg-serpentinite and Chl-harzburgite, which are separated by a transitional zone that represents the front of prograde serpentinite dehydration during subduction. Different types of meta-rodingites are found associated with these two ultramafic lithologies: Grandite-meta-rodingite (type 1) within Atg-serpentinite, Epidote-meta-rodingite (type 2) within both of them, especially in the vicinity of the dehydration front, and Pyralspite-meta-rodingite (type 3) within Chl-harzburgite. Type 1 consists of garnet, chlorite and clinopyroxene with minor titanite, magnetite and ilmenite. Several garnet generations are found within this meta-rodingite type: Grt1 (Ti-rich hydrogrossular, 78-90 wt% grossular), Grt2 (6-20 wt% pyralspite, 80-93 wt% grandite), and Grt3 (Ti-rich grandite, 38-40 wt% andradite). Type 2 meta-rodingite consists of epidote and clinopyroxene with minor titanite, garnet and chlorite. It appears partially transforming type 1 rocks within Atg-serpentinite and its amount increases gradually towards the dehydration front. Just across this front, in the Chl-harzburgite domain, all meta-rodingites are type 2. Type 3 meta-rodingite overgrew type 2 assemblages and consists of garnet (Grt4, 38-50 wt% almandine, 12-31% pyrope, 17-35% grossular), epidote, clinopyroxene, amphibole, chlorite, titanite and rutile. All meta

  2. The geology of the surrounding metamorphic rock of Zaer granite (Morocco): contribution to the search for uranium

    International Nuclear Information System (INIS)

    Mathias, Laurent

    1984-01-01

    This research thesis reports a study which aimed at reconstituting the geological history of the Zaer region in Morocco with objectives of mining exploration and of assessment of its uranium metallogenic potential. The author examined the whole geological context by studying stratigraphy, sedimentology, tectonic, and petrography of rocks belonging to the concerned area. The main objective was to determine the origin of uranium between a granitic one and a sedimentary one. This meant a reconstitution of the geological history, and therefore the study of the metamorphized sedimentary surrounding rock, of the intrusive granite and of their different possible relationships. On a first part, the author analysed outcropping formations and tried to assign them with a stratigraphic position. He also tried to define the deposition modalities of these formations which could have conditioned sedimentary sites. In a second part, the author reports the study of geological structures and tectonic in order to try to recognise possible structures which could have promoted uranium deposition and trapping in the surrounding rock as well as in granite. The last part addresses the petrography of the different rocks met in the area, and mineralization, notably that of uranium [fr

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

    Directory of Open Access Journals (Sweden)

    Arifudin Idrus

    2014-06-01

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

  4. Evaluation of hydrologic isolation from evidence in mine openings in igneous and metamorphic rocks in the Maritime Provinces of Canada

    International Nuclear Information System (INIS)

    Martinez, J.D.

    1975-09-01

    Conditions in the mines inspected ranged from very wet to very dry. The Heath Steele Mine certainly provided an example of severe leakage through either the country rock, the ore, or both. By way of contrast, the Brunswick Mine is very dry, particularly at the 2800 foot level. A note of caution is raised by this dissimilarity, inasmuch as the local geologic setting for both mines is very much alike. The Buchans Mine also provided evidence of dry conditions at the depth inspected (3215 ft). The Ming Mine at Baie Verte is also nearly dry with a decrease in water leakage with depth. It seems reasonable to tentatively conclude that mined openings in the rock types investigated (volcanics and sediments metamorphosed to a low or subgreen schist facies and intensely deformed) would provide hydraulic isolation at depths on the order of 2800-3200 feet below the surface or greater. It is disturbing to have found one mine that is very wet at shallow depths and to have received reports of some water problems in shaft construction. This report in conjunction with other more comprehensive studies should provide a point of departure for more detailed studies of the nature and causes of hydraulic isolation provided by igneous and metamorphic rocks. 27 figs

  5. Calculation of stability of sodic phases in high-pressure metapelites and observation of Sambagawa metamorphic rocks

    Science.gov (United States)

    Kouketsu, Y.; Enami, M.

    2010-12-01

    P-T pseudosection analyses of high-pressure metapelites from several subduction related regions were carried out by using the computer program Perple_X 07 in order to determine the mineral equilibrium, particularly the stability of sodic phases, in the model system MnO-Na2O-K2O-CaO-FeO-MgO-Al2O3-SiO2-H2O. Metapelites from Sambagawa, Western Alps, New Caledonia, Greece, and South Tianshan were selected for these analyses. Although the occurrence of sodic pyroxene in these metapelite samples is free or very rare, all the samples are considered to have undergone high-pressure metamorphism under blueschist-eclogite facies conditions. The bulk rock compositions of these metapelites have relatively low XNa [=Na/(Al + Na)] values. Therefore, the rare occurrences of sodic pyroxene in these samples are possibly due to their characteristic bulk rock compositions, although this has not been proved yet. The calculation results for the stability of sodic phases under the blueschist and eclogite facies conditions indicate the following. (1) Sodic pyroxene in the studied metapelites is stable only under higher-pressure conditions of P > 2.5 GPa, although its stable P-T range increases toward the lower-pressure side with increasing XNa value of the bulk-rock composition. (2) Paragonite and glaucophane are stable throughout the wide XNa range of bulk-rock compositions of host rocks under the blueschist and quartz-eclogite facies conditions. (3) The stability field of paragonite enlarges with the presence of CO2 in the metamorphic fluid. Thus, the high stability of paragonite and glaucophane in metapelites and the close relationship between the stability of sodic pyroxene and the bulk-rock composition explain why omphacite-bearing metapelites are rarely found. Observations of Sambagawa metapelites were carried out on the basis of these results. In the Besshi region of the Sambagawa belt, quartz grains with a high residual pressure of up to 0.8 GPa extensively occur as inclusions in

  6. P-T evolution of metasedimentary rocks of the Santa Filomena Complex, Riacho do Pontal Orogen, Borborema Province (NE Brazil): Geothermobarometry and metamorphic modelling

    Science.gov (United States)

    Santos, Felipe H.; Amaral, Wagner S.; Luvizotto, George L.; Martins de Sousa, Daniel F.

    2018-03-01

    We present in this paper petrologic data and discuss the pressure-temperature (P-T) metamorphic history of the neoproterozoic metasedimentary rocks of the Santa Filomena Complex, Riacho do Pontal Orogen, which is inserted in the southern portion of the Borborema Province (Northeast Brazil). Therefore, the data provide constraints on metamorphic evolution during Neoproterozoic Brasiliano Orogeny in Northeast Brazil. The rocks studied are aluminous schists and paragneisses. Silver-gray and red pelitic schists are intensely deformed, biotite-muscovite rich, contain centimeter-sized garnet, staurolite and kyanite porphyroblasts, and subordinately plagioclase and quartz. Paragneisses are from light gray to dark gray colored, medium to coarse-grained and display a well-spaced foliated matrix of biotite, and kyanite and garnet porphyroblasts. Locally, the schists and paragneisses are migmatized. Pressure-temperature modelling based on thermobarometric calculations indicate that metamorphism reached 643 °C with pressures estimated in 12 kbar. Pre-peak and post-peak metamorphic conditions are constrained by mineralogical and textural relationships: garnet inclusion-rich and inclusion-free (possible of higher T) are documented and the inclusion-rich core probably indicates a Sn-1 foliation that was transposed by Sn. The pre-peak stage most probably occurred close to 500 °C and 8 kbar, in upper greenschist to lower amphibolite facies metamorphism along kyanite stability field. We also propose that post-peak stage was associated with isothermal decompression along a possible path of tectonic exhumation in conditions of 600 °C and 7 kbar. To further evaluate the equilibrium condition, pressure-temperature pseudosections were calculated for the metasedimentary rocks. Thus, the estimated metamorphic peak took place in the upper amphibolite facies. A suggested clockwise pressure-temperature path is compatible with the regional tectonic setting of continent-continent collision

  7. Seismicity in an active rift exposing ultra-high pressure metamorphic rocks: D'Entrecasteaux Islands, Papua New Guinea

    Science.gov (United States)

    Dieck, C. C.; Abers, G. A.; Eilon, Z.; Gaherty, J. B.; Verave, R.

    2013-12-01

    Continental crust has rifted in the Woodlark Rift, Papua New Guinea for the last 6Ma, with sea floor spreading where extension is largest and farthest from the Euler pole. The D'Entrecasteaux Islands (DIs) lie immediately west of the present-day seafloor spreading centers. Metamorphic core complexes (MCCs) dominate these islands, some of which contain the youngest known ultra-high pressure (UHP) metamorphic rocks. These have been exhumed at 90 km depth, coeval with continental rifting. Sea floor magnetic anomalies and GPS data indicate 20-30 mm/yr extension should be accommodated across the rift near the DIs; however, it has been debated whether that takes place along the MCC-bounding faults, or parallel structures bounding the Papua Peninsula. To address these questions, we report on regional seismicity from the 2010-2011 CDPapua passive seismic experiment, which comprised an array of 31 on-land and 8 ocean-bottom seismographs over a 200km x 300km region centered on the DIs. We have used P- and S- wave arrivals to detect and locate local earthquakes. Most detected earthquakes lie outside the array, at very active subduction zones 300-600 km distant, but still an average of 3.3 local earthquakes within the array are observed to occur each day. Unexpectedly, we located a cluster of intermediate depth earthquakes, ranging from 70-110 km depth. This deep activity represents the first evidence of sub-crustal seismicity in this region and comes from the depths at which UHP rocks originate, ~100 km along strike from where they are exposed. The seismicity lies toward the Euler pole from the DIs, where extension is less, so potentially represents a not-yet-exhumed source region of UHP rocks in a less-extended region. Most crustal seismicity lies proximate to the D'Entrecasteaux Islands and is concentrated on the dome-bounding faults, revealing that these structures are actively accommodating extension and that MCC exhumation persists. Just SW of the westernmost DI, a dense

  8. Geochemical Characteristics of Metamorphic Rock-Hosted Gold Deposit At Onzon-Kanbani Area, Central Myanmar

    Directory of Open Access Journals (Sweden)

    Aung Tay Zar

    2017-09-01

    Full Text Available Gold and associated base metal mineralization of Onzon-Kabani area located in the western border of generally N-S trending Mogoke Metamorphic Belt where well-known Sagaing fault is served as a western boundary of this area. In this research area, many artisanal and small-scale gold mines were noted in last three decades. Gold mineralization is hosted in marble and gneiss unit of research area but most common in marble unit. Variety of igneous intrusions are also observed in research area. Mineralizations are observed as fissure filling veins as well as lesser amount of disseminated nature in marble unit. Mineralogically, gold are associated with other base metal such as pyrite, galena, sphalerite, chalcopyrite, marcasite and arsenopyrite. Hydrothermal alteration halos are developed in peripheral of hydrothermal conduits or mineralization veins from proximal to distal such as 1 silicic, 2 sericite-illite, and 3 propylitic alteration.  Most of hydrothermal minerals from each altered zones showed that near neutral condition of pH (e.g. adularia, calcite, illite, sericite and chlorite. Alternatively, hydrothermal alteration zones that show with ore minerals such as native gold, electrum, sphalerite, galena, chalcopyrite, arsenopyrite and marcasite which mostly observed in silicic alteration zone. Typical boiling characters of vein textures and fluid inclusion petrography are observed in hydrothermal system of research area. Boiling, cooling and mixing are possiblily responsible for gold deposition in hydrothermal system. In this paper, authors are documented to clarify the type of mineralization based on hydrothermal alterations, ore and gangue mineral assemblages and fluid inclusion study. All of these data can describe and play an important role for both with respect to understanding deposit genesis and in mineral exploration.

  9. Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu

    Science.gov (United States)

    Narayana, B. L.; Natarajan, R.; Govil, P. K.

    1988-01-01

    Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

  10. Weathering of Igneous, Metamorphic, and Sedimentary Rocks in a Semi-arid Climate - An Engineering Application of Petrology

    Science.gov (United States)

    Harrison, W. J.; Wendlandt, R. F.

    2003-12-01

    Over the last 10 years, analytical methods have been introduced to students in CSM's undergraduate geological engineering program through a multi-year and multi-course approach. Beginning with principles and simple applications of XRD and SEM in sophomore Mineralogy and building on these skills in subsequent junior and senior year courses, geological engineers acquire proficiency in analytical methods. Essential workplace skills are thus acquired without adding an extra course in the undergraduate program. The following exercise is completed by juniors in an integrated Ig.-Met.-Sed. petrology course. The identification of clay mineral assemblages in soils provides a unique opportunity to demonstrate how basic principles of petrology and geochemistry are applied to engineering design criteria in construction site preparation. Specifically, the problem investigates the conditions leading to the formation of smectite in soils and the resulting construction risk due to soil expansion. Students examine soils developed on igneous, metamorphic, and sedimentary rocks near Denver, Colorado. The field locations are areas of suburban growth and several have expansive soil problems. The 2-week exercise includes sample collection, description, and preparation, determining clay mineralogy by XRD, and measurement of Atterberg Plasticity Indices. Teaching materials may be found at: http://serc.carleton.edu/NAGTWorkshops/petrology03/. This exercise accomplishes three objectives: First, skills in XRD analysis are developed by introducing students to concepts of particle size separation, particle orientation, and sequential analysis steps which are standard practices in clay characterization. Second, lecture material on the geochemistry of weathering of different rock types is reinforced. Students interpret the origin of clay mineral assemblages developed in soils derived from Precambrian gneisses, lower Paleozoic feldspathic sandstones, upper Paleozoic marine shales, and Tertiary

  11. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil)

    Science.gov (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2017-04-01

    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  12. Variable mineral composition of metamorphic rocks from a single quarry compared to their ASR potential (Bohemian Massif, Czech Republic)

    Science.gov (United States)

    Stastna, Aneta; Sachlova, Sarka; Pertold, Zdenek; Nekvasilova, Zuzana; Prikryl, Richard

    2013-04-01

    The alkali-silica reaction (ASR) is one of the most damaging factors for concrete structures. ASR originates due to the presence of reactive silica (SiO2) that reacts with alkaline ions under wet conditions. The reaction mechanism consists of four different steps: initial attack of OH- compounds on SiO2 at aggregate-cement paste boundary; formation of silanol groups at SiO2 surface; formation of siloxane groups and their polymerization; adsorption of alkaline and Ca2+ ions and formation of alkali-silica gels. Alkali-silica gels tend to absorb water molecules and swell causing increasing internal pressures in concrete and microcracking. The most reactive aggregates are mainly composed of amorphous and/or fine-grained SiO2-rich phases. In the Czech Republic, ASR was observed in deteriorating concrete structures containing very fine-grained quartz (quartz in tuffaceous sandstones and greywackes), as well as quartz indicating variable degree of deformation (quartz in quartzite, granodiorite and various metamorphic rock types). In this study, mineralogical-petrographic methods (polarizing, electron and cathodoluminescence microscopy) were combined with the accelerated mortar bar test (following the standard ASTM C1260), with the aim to quantify the ASR potential, as well as to distinguish reactive mineral phases. Different aggregate varieties from the Těchobuz quarry (Moldanubian Zone, Czech Republic) have been compared. Mineralogical-petrographic characteristics permit a distinction between 1) medium-grained plagioclase quartzite and 2) fine-grained biotite-plagioclase-quartz paragneiss and 3) fine-grained calc-silicate rock. Mineralogical composition of the first type is quartz + Ca-plagioclase + K-feldspar + biotite + chlorite + diopside + pyrite + apatite + titanite ± calcite. The second type has mineral assemblage including quartz + Ca-plagioclase + K-feldspar + biotite + chlorite + pyrite + tourmaline + apatite + titanite ± calcite. The third type contains

  13. Microtectonic-assisted P-T determination on low-grade Alpine metamorphic rocks from the "Tisia Mega-Unit" of the Slavonian Mountains in Croatia

    Science.gov (United States)

    Balen, Dražen; Lihter, Iva; Massonne, Hans-Joachim

    2016-04-01

    The internal structure of the Tisia (Tisza) Mega-Unit in the Alpine-Carpathian-Dinaridic orogenic system encompasses large Alpine nappe systems brought to its present-day position by complex regional-scale movements. The Slavonian Mountains are part of the Bihor nappe system which is below the Codru and above the Mecsek nappe systems. The low-grade metamorphic schist unit of the Slavonian Mountains includes numerous rocks which were previously related to Precambrian and/or Lower Paleozoic orogeneses. However, recent studies (e.g. Balen, 2014, European Geosciences Union General Assembly, EGU 2014-6122) show that the metapelites of this unit should be attributed to the Alpine orogeny and the poorly known P-T conditions, which they experienced, should be refined. Although metapelites can be sensitive to changes of metamorphic conditions and, therefore, be suitable for the P-T estimation of metamorphic event(s), the extraction of mineral assemblages, being in equilibrium, and associated microtectonic data for particular low-grade metamorphic rocks is not straightforward. On the contrary, due to lack of suitable minerals and complex mictotectonic features, one can be faced with a severe problem concerning (dis)equilibrium. To avoid this, the observation scale in the research was set to the sub-mm level taking into account microtectonic positions of minerals. The investigated samples from the Slavonian Mountains are fine-grained schists consisting of chlorite (15-30 vol. %), white mica (15-25 vol. %), quartz (10-25 vol. %), feldspars (albite 10-15 vol. %; some K-feldspar), biotite (Financial support by the Croatian Science Foundation (IP-2014-09-9541) and T. Theye's help during microprobe work is greatly acknowledged.

  14. Titanite-bearing calc-silicate rocks constrain timing, duration and magnitude of metamorphic CO2 degassing in the Himalayan belt

    Science.gov (United States)

    Rapa, Giulia; Groppo, Chiara; Rolfo, Franco; Petrelli, Maurizio; Mosca, Pietro; Perugini, Diego

    2017-11-01

    The pressure, temperature, and timing (P-T-t) conditions at which CO2 was produced during the Himalayan prograde metamorphism have been constrained, focusing on the most abundant calc-silicate rock type in the Himalaya. A detailed petrological modeling of a clinopyroxene + scapolite + K-feldspar + plagioclase + quartz ± calcite calc-silicate rock allowed the identification and full characterization - for the first time - of different metamorphic reactions leading to the simultaneous growth of titanite and CO2 production. The results of thermometric determinations (Zr-in-Ttn thermometry) and U-Pb geochronological analyses suggest that, in the studied lithology, most titanite grains grew during two nearly consecutive episodes of titanite formation: a near-peak event at 730-740 °C, 10 kbar, 30-26 Ma, and a peak event at 740-765 °C, 10.5 kbar, 25-20 Ma. Both episodes of titanite growth are correlated with specific CO2-producing reactions and constrain the timing, duration and P-T conditions of the main CO2-producing events, as well as the amounts of CO2 produced (1.4-1.8 wt% of CO2). A first-order extrapolation of such CO2 amounts to the orogen scale provides metamorphic CO2 fluxes ranging between 1.4 and 19.4 Mt/yr; these values are of the same order of magnitude as the present-day CO2 fluxes degassed from spring waters located along the Main Central Thrust. We suggest that these metamorphic CO2 fluxes should be considered in any future attempts of estimating the global budget of non-volcanic carbon fluxes from the lithosphere.

  15. Variability in Rock Thermal Properties in the Late Archean Crust of the Kapuskasing Structural Zone and Implications for its Thermal Structure and Metamorphic History.

    Science.gov (United States)

    Merriman, J. D.; Whittington, A. G.; Hofmeister, A. M.

    2017-12-01

    The thermal properties of rocks such as internal heat production and thermal diffusivity (α) play a key role in determining the thermal structure of the lithosphere, and consequently, the rates and styles of metamorphism within the crust. Over the last decade, measurements of α using the method laser flash analysis have shown the ability of a rock to conduct heat can vary by as much as a factor of 5 between common rock types, and decrease by up to a factor of 10 for the same rock between 25-1000°C. Here we present a preliminary model for the variability in rock throughout the crust based on measurements of the α of a suite of 100 samples from late Archean crust exposed in and around the Kapuskasing Structural Zone in Ontario, Canada. Preliminary results suggest that α is controlled primarily by mineralogy, and can vary not only between different rock types as described above, but also within the same rock by a factor of 1.5 (or more). Thermal diffusivity results were combined with heat producing element concentrations measured with ICP-MS to create a thermal model of the Kapuskasing Structural Zone prior its uplift and exposure. To provide additional constraints for P-T conditions within the pre-uplift KSZ crust, a combination of trace-element and pseudosection thermobarometry was used to estimate metamorphic temperatures during an extended period of crustal stability at the end of the Archean. Preliminary results were compared to finite-difference numerical models of the steady-state geothermal gradient using heat production back-calculated to 2.6 Ga. Results suggest a minimum thickness of the continental lithosphere during the late Archean of at least 150 km. To test the response of the crust to the effects of large thermal events such as pluton emplacement, we also performed time-dependent models of the thermal structure of the pre-uplift KSZ crust. These models suggest that heat from thermal events in the upper and middle crust result in a more insulating

  16. Geochronology, geochemistry, and petrogenesis of late Permian to early Triassic mafic rocks from Darongshan, South China: Implications for ultrahigh-temperature metamorphism and S-type granite generation

    Science.gov (United States)

    Xu, Wang-Chun; Luo, Bi-Ji; Xu, Ya-Jun; Wang, Lei; Chen, Qi

    2018-05-01

    The role of the mantle in generating ultrahigh-temperature metamorphism and peraluminous S-type granites, and the extent of crust-mantle interaction are topics fundamental to our understanding of the Earth's evolution. In this study we present geochronological, geochemical, and Sr-Nd-Hf isotopic data for dolerites and mafic volcanic rocks from the Darongshan granite complex belt in western Cathaysia, South China. LA-ICP-MS U-Pb zircon analyses yielded magma crystallization ages of ca. 250-248 Ma for the dolerites, which are coeval with eruption of the mafic volcanic rocks, ultrahigh-temperature metamorphism, and emplacement of S-type granites in the Darongshan granite complex belt. The mafic volcanic rocks are high-K calc-alkaline or shoshonitic, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta and Ti. The dolerites are characterized by high Fe2O3tot (11.61-20.39 wt%) and TiO2 (1.62-3.17 wt%), and low MgO (1.73-4.38 wt%), Cr (2.8-10.8 ppm) and Ni (2.5-11.4 ppm). Isotopically, the mafic volcanic rocks have negative whole-rock εNd(t) values (-6.7 to -9.0) and high ISr values (0.71232 to 0.71767), which are slightly depleted compared with the dolerite samples (εNd(t) = -10.3 to -10.4 and ISr = 0.71796 to 0.71923). Zircons in the dolerites have εHf(t) values of -7.6 to -10.9. The mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent, whereas the dolerites formed by late-stage crystallization of enriched lithospheric mantle-derived magmas after fractionation of olivine and pyroxene. The formation of these mantle-derived mafic rocks may be attributed to transtension along a NE-trending strike-slip fault zone that was related to oblique subduction of the Paleo-Pacific plate beneath South China. Such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh-temperature metamorphism and S-type granites, and

  17. SHRIMP U–Pb and REE data pertaining to the origins of xenotime in Belt Supergroup rocks: evidence for ages of deposition, hydrothermal alteration, and metamorphism

    Science.gov (United States)

    Aleinikoff, John N.; Lund, Karen; Fanning, C. Mark

    2015-01-01

    The Belt–Purcell Supergroup, northern Idaho, western Montana, and southern British Columbia, is a thick succession of Mesoproterozoic sedimentary rocks with an age range of about 1470–1400 Ma. Stratigraphic layers within several sedimentary units were sampled to apply the new technique of U–Pb dating of xenotime that sometimes forms as rims on detrital zircon during burial diagenesis; xenotime also can form epitaxial overgrowths on zircon during hydrothermal and metamorphic events. Belt Supergroup units sampled are the Prichard and Revett Formations in the lower Belt, and the McNamara and Garnet Range Formations and Pilcher Quartzite in the upper Belt. Additionally, all samples that yielded xenotime were also processed for detrital zircon to provide maximum age constraints for the time of deposition and information about provenances; the sample of Prichard Formation yielded monazite that was also analyzed. Ten xenotime overgrowths from the Prichard Formation yielded a U–Pb age of 1458 ± 4 Ma. However, because scanning electron microscope – backscattered electrons (SEM–BSE) imagery suggests complications due to possible analysis of multiple age zones, we prefer a slightly older age of 1462 ± 6 Ma derived from the three oldest samples, within error of a previous U–Pb zircon age on the syn-sedimentary Plains sill. We interpret the Prichard xenotime as diagenetic in origin. Monazite from the Prichard Formation, originally thought to be detrital, yielded Cretaceous metamorphic ages. Xenotime from the McNamara and Garnet Range Formations and Pilcher Quartzite formed at about 1160– 1050 Ma, several hundred million years after deposition, and probably also experienced Early Cretaceous growth. These xenotime overgrowths are interpreted as metamorphic–diagenetic in origin (i.e., derived during greenschist facies metamorphism elsewhere in the basin, but deposited in sub-greenschist facies rocks). Several xenotime grains are older detrital grains of igneous

  18. Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration.

    Science.gov (United States)

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-16

    Since water is only composed of oxygen and hydrogen, δ 18 O and δ 2 H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (-65 ± 1 o vs. -20 ± 2°); the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ 18 O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss.

  19. Comparative geothermometry based on major-element and oxygen isotope distributions in Precambrian metamorphic rocks from southwestern Montana

    International Nuclear Information System (INIS)

    Dahl, P.S.

    1979-01-01

    Mineral assemblages in the Kelly and Carter Creek areas of the Ruby Range, southwestern Montana, indicate orthopyroxene-zone and sillimanite-K felspar-zone metamorphism, respectively. Because the two areas are small and contain diverse lithologies, they are ideal for a comparative study of mineral-pair geothermometers and grade indicators. For the Kelly area, various major-element methods (clinopyroxene-orthopyroxene, garnet-orthopyroxene, garnet-hornblende, garnet-biotite, and K feldspar-plagioclase) yield a consensus peak temperature estimate of 745 +- 50 0 C. For the Carter Creek area, garnet-clinopyroxene, garnet-hornblende, garnet-biotite, and K fledspar-plagioclase methods plus assemblage data yield 675 +- 45 0 c. Coexisting quartz and magnetite in metamorphic iron-formations from the two areas yield anomalously low temperature estimates of 530 +- 15 0 C and 475 +- 25 0 C, respectively, based on oxygen isotopic fractionations of 8.41 +- 0.30 per mil and 9.92 +- 0.20 per mil. Similarly, Mg distributions between calcite and dolomite in metadolomites from the Kelly area yield estimates of ca. 545 0 C. These lower temperatures are probably the result of (1) solid-state diffusion of chemical species between minerals; or (2) recrystallization of quartz, magnetite, and carbonates (i.e., the non-refractory minerals) during retrograde or subsequent low-grade metamorphism. Another low estimate (545 0 C) is obtained from rim compositions of coexisting garnet and cordierite in one magnesian meta-pelite sample from the Kelly area. This estimate is consistent with the observation of cordierite coronas on garnet, a texture that suggests retrograde origin for the cordierite. These data show it cannot be assumed a priori that a given geothermometer will record peak metamorphic temperature. Instead, the bimodal discordance of estimates presented here reflects the varied response of different mineral pairs to a given metamorphic and tectonic history

  20. Measurement of activity concentration of 222Rn in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks, municipio de Amparo, SP

    International Nuclear Information System (INIS)

    Oliveira, Igor Jose Chaves de

    2008-01-01

    A sampling system was assembled for field 222 Rn activity concentration measurements in ground waters. The system consists of a sampling flask that prevents the contact between the water sample and the atmosphere and a closed line for radon extraction from water. The system, its operation and calibration, are described in full detail, as well as, the conversion of the measured alpha counting rates in activity concentrations. The assembled system was used in 222 Rn activity concentrations measurements in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks. The wells are located at the urban area of the city of Amparo and are exploited for public use water. One well, named Vale Verde, is 56 meters deep and crosses 18 meters of soil, 26 meters of quartz rich gneiss and 12 meters of biotite-gneiss. The other well, named Seabra, is 117 meters deep, crosses 28 meters of soil and weathered rocks and ends in granite-gneiss. The mean activity concentrations for the year long observation were (377 +- 25) Bq/dm 3 , for Seabra well, and (1282 +- 57) Bq/dm3, for the Vale Verde well. The 222 Rn activity concentrations fall in the activity concentration range reported in the literature for similar geology areas and are larger than the concentrations found neighboring areas of the same metamorphic Complex. The seasonal activity concentration variations seem to correlate with rain fall variations in the study area. (author)

  1. Rocks age and metamorphic occurrence from the southeastern part of Sao Paulo State and their crustal evaluation

    International Nuclear Information System (INIS)

    Tassinari, C.C.G.

    1988-01-01

    Pb-Pb and Rb-Sr whole rock isotope systematics and U-Pb on zircons method analyses are reported for rocks from the southeastern part of Sao Paulo state Brazil. The isotopic studies on granitic intrusions, orthogneissic rocks and migmatitic terranes, in this area, provides an important indication of the age and nature of the continental crust. (author) [pt

  2. Behaviour of zircon in high-grade metamorphic rocks: evidence from Hf isotopes, trace elements and textural studies

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Košler, J.; Pedersen, R. B.

    2007-01-01

    Roč. 154, č. 3 (2007), s. 335-356 ISSN 0010-7999 Grant - others:Grant Agency of the Charles University(CZ) 264/2005/B-GEO Institutional research plan: CEZ:AV0Z30130516 Keywords : Hf isotopes * zircon * granulite * U-Pb dating * laser ablation * ICP-MS * garnet * decompression * metamorphic reaction Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.216, year: 2007

  3. Application of graphite as a geothermometer in hydrothermally altered metamorphic rocks of the Merelani-Lelatema area, Mozambique Belt, northeastern Tanzania

    Science.gov (United States)

    Malisa, Elias Pausen

    1998-02-01

    Upper Precambrian pelitic and psammitic gneisses in the Mozambique Belt are usually graphite rich. The determination of crystallisation temperatures around and in the hydrothermally altered rocks of the Merelani-Lelatema mining areas, northeastern Tanzania, were made by studying the lattice parameter C of graphite. In this way, the migration of the chromophore elements giving colour to the gemstones, e.g. tanzanite, green garnet and green tourmaline in the area, can be studied. Within the hydrothermally altered zone graphite gives temperatures that range from 523°C to 880°C. These temperatures are much higher than the 390-440°C obtained through fluid inclusion studies of tanzanite, which indicates that the graphite was not hydrothermally introduced. Furthermore the hydrothermal solutions are post-metamorphic.

  4. The role of amphiboles in the metamorphic evolution of the UHP rocks: a case study from the Tso Morari Complex, northwest Himalayas

    Science.gov (United States)

    Singh, Preeti; Pant, Naresch C.; Saikia, Ashima; Kundu, Amitava

    2013-11-01

    Amphiboles represent a crucial phase of the ultra-high-pressure (UHP) metamorphic rocks as their solid solution behavior reflects both bulk compositional and P- T changes. Three different types of amphibole have been reported from the UHP metamafic rocks of the Tso Morari Crystalline Complex, NW Himalayas: Na-rich (glaucophane); Na-Ca-rich (barroisite, taramite, winchite) and Ca-rich (tremolite, magnesio-hornblende, pargasite). The Na-amphibole is presented as a core of the zoned amphibole with Na-Ca-rich rim; Na-Ca-amphibole is presented as inclusion in garnets as well as in matrix, and Ca-amphibole is generally found in the matrix. The Na-Ca-amphibole is observed at two different stages of metamorphism. The first is pre-UHP, and the second is post-garnet-omphacite assemblage though with a significant difference in composition. The pressure-temperature estimations of the formation of these two sets of Na-Ca-amphiboles corroborate their textural associations. Ca-rich amphiboles are generally present in the matrix either as symplectite with plagioclase or as a pseudomorph after garnet along with other secondary minerals like chlorite and biotite. Two different types of zoning have been observed in the amphibole grains: (1) core is Na-rich followed by Na-Ca rim and (2) core of Na-Ca-amphibole is followed by Ca-rich rim. The pre-UHP (or the prograde P- T path) and post-UHP stages (or the retrograde P- T path) of Tso Morari eclogites are defined by characteristic amphibole compositions, viz. Na/Na-Ca-amphibole, Na-Ca-amphibole and Ca-amphibole and thus indicate their utility in inferring crustal evolution of this UHP terrain.

  5. Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China

    Science.gov (United States)

    Xiao, Yuanyuan; Niu, Yaoling; Wang, Kuo-Lung; Iizuka, Yoshiyuki; Lin, Jinyan; Wang, Dong; Tan, Yulong; Wang, Guodong

    2017-09-01

    To understand the geochemistry of subduction zone metamorphism, especially the large-scale mass transfer at forearc to subarc depths, we carried out a detailed study of a ∼1.5 m size metabasaltic block with well-preserved pillow structures from the Chinese Western Tianshan high- to ultrahigh-pressure metamorphic belt. This metabasaltic block is characterized by omphacite-rich interiors gradually surrounded by abundant channelized (veins) glaucophane-rich patches toward the rims. The glaucophane-rich rims share the same peak metamorphic conditions with omphacite-rich interiors, but have experienced stronger blueschist-facies overprinting during exhumation. Representative samples from the glaucophane-rich rims and omphacite-rich interiors yield a well-defined Rb-Sr isochron age of 307 ± 23 Ma, likely representing this overprinting event. Both glaucophane-rich rims and omphacite-rich interiors show elevated K-Rb-Cs-Ba-Pb-Sr contents relative to their protolith, reflecting a large-scale enrichment of these elements and formation of abundant phengite during subduction. Compared with the omphacite-rich interiors, the glaucophane-rich rims have gained rare earth elements (REEs, >25%), U-Th (∼75%), Pb-Sr (>100%) and some transition metals like Co and Ni (25-50%), but lost P (∼75%), Na (>25%), Li and Be (∼50%); K-Rb-Cs-Ba show only 10% loss. These chemical changes would be caused by serpentinite-derived fluids during the exhumation in the subduction channel. Therefore, there are two stages of fluid action in the subduction channel. As the formation of phengite stabilizes K-Rb-Cs-Ba at the first stage, the residual fluids released from the phengite-rich metabasaltic rocks would be depleted in these elements, which are unlikely to contribute to elevated contents of these elements in arc magmas if phengite remains stable at subarc depths. In addition, the decrease of U/Pb ratios as the preferred enrichment of Pb over U in the eclogitic rocks during the first stage

  6. Formation And Exhumation Of High Pressure Metamorphic Rocks From Oman: New Constraints From U-Pb Dating Of Zircon And Rutile

    Science.gov (United States)

    El-Shazly, A. K.; Walker, J. D.

    2003-12-01

    Basement and continental shelf units structurally underlying the Semail ophiolite in Saih Hatat, NE Oman were metamorphosed under high pressure, low temperature (high P/T) conditions, and occur in two plates. The lower plate consists of eclogite facies rocks that grade westward into garnet blueschists and crossite epidote schists. The upper plate consists of thrust sheets of lower grade metasedimentary and metavolcanic rocks formed under pumpellyite - actinolite to lawsonite albite facies conditions. The eclogite facies rocks had a clockwise P-T path, with peak conditions of 12 12 kbar to ˜ 4 kbar, and a stage of near isobaric cooling followed by cooling and decompression. High P/T rocks from the upper plate are also characterized by clockwise P-T paths with a segment of near isothermal decompression, and reached peak conditions that ranged from ˜ 310° C, P pile. A distinct pressure gap of > 3 kbar results from the juxtaposition of the lower and upper plates. U-Pb dating of zircon and rutile grains from two lower plate blueschists yield ages ranging from Proterozoic to Late Cretaceous: data cluster near a Late Creatceous age on the younger end of the array and spread to Mesoproterozoic values at the older end. A weighted mean of the 238U/206Pb ages from the youngest and most concordant fractions (one zircon and 2 rutile crystals) yields 80.1 +/- 5 Ma. These results are consistent with Rb/Sr isochron ages of 78 +/- 2 Ma obtained using phengite, clinopyroxene, and epidote from seven eclogite facies samples, and suggest that high P/T metamorphism in Saih Hatat was almost coeval with the emplacement of the Semail ophiolite. We conclude that the lower plate blueschists and eclogites formed by intracontinental thrusting and subduction of the thinned leading edge of the Oman continental margin in an east dipping subduction zone. The upper plate rocks which were part of the hanging wall of this subduction zone, were metamorphosed by tectonic loading by the ophiolite

  7. Ultrasonic polarization measurements of elastic-anisotropic properties of metamorphized rocks on the slit of the German KTB superdeep well in the 4100-7100 m depth range

    Science.gov (United States)

    Kovalevskiy, Mikhail

    2013-04-01

    garnet amphibolites samples. There was observed a tendency to persistence in propagation rate of compression and shear wave velocities. The pattern of change in anisotropy factors for compression and shear waves in depth shows itself in a similar way. There is an inverse correlation between density and anisotropy. R E F E R E N C E S 1. Emmermann R., Althaus E., Giese P., Stockhert B.. KTB Hauptbohrung. Results of Geoscientific Investigation in the KTB Field Laboratory. Final Report: 0-9101m. KTB Report 95-2. Hannover. 1995. 2. Gorbatsevich F.F. Acoustopolariscopy of rock forming minerals and crystalline rocks. Apatity, Kola Science Centre RAS, 2002, p. 140. (In Russian) 3. Kovalevskiy M.V. Automated hardware-software complex Acoustpol: Tutorial: Apatity, «K & M» Publ., 2009. 54p. (In Russian). 4. Kovalevsky M.V., Gorbatsevich F.F., Harms U., Dahlheim H.-A. Ultrasonic polarization measurements of elastic-anisotropic properties of metamorphized rocks on the slit of German KTB Superdeep Well // Geophysical magazine.- Geophysics Institute of NAS of Ukraine. -2012.- Issue 34.-#2.-P. 36-48. (In Russian)

  8. Preliminary Assessment of the Hydrogeology and Groundwater Availability in the Metamorphic and Siliciclastic Fractured-Rock Aquifer Systems of Warren County, Virginia

    Science.gov (United States)

    Nelms, David L.; Moberg, Roger M.

    2010-01-01

    Expanding development and the prolonged drought from 1999 to 2002 drew attention to the quantity and sustainability of the groundwater resources in Warren County, Virginia. The groundwater flow systems of the county are complex and are controlled by the extremely folded and faulted geology that underlies the county. A study was conducted between May 2002 and October 2008 by the U.S. Geological Survey, in cooperation with Warren County, Virginia, to describe the hydrogeology of the metamorphic and siliciclastic fractured-rock aquifers and groundwater availability in the county and to establish a long-term water monitoring network. The study area encompasses approximately 170 square miles and includes the metamorphic rocks of the Blue Ridge Physiographic Province and siliciclastic rocks of the Great Valley section of the Valley and Ridge Physiographic Province. Well depths tend to be shallowest in the siliciclastic rock unit (predominantly in the Martinsburg Formation) where 75 percent of the wells are less than 200 feet deep. Median depths to bedrock are generally less than 40 feet across the county and vary in response to the presence of surficial deposits, faults, siliciclastic rock type, and topographic setting. Water-bearing zones are generally within 200 feet of land surface; median depths, however, are slightly deeper for the hydrogeologic units of the Blue Ridge Province than for those of the Great Valley section of the county. Median well yields for the different rock units generally range from 10 to 20 gallons per minute. High-yielding wells tend to cluster along faults, along the eastern contact of the Martinsburg Formation, and within potential lineament zones. Specific capacity is relatively low and ranges from 0.003 to 1.43 gallons per minute per foot with median values from 0.12 to 0.24 gallon per minute per foot. Transmissivity values derived from specific capacity data range over four orders of magnitude from 0.6 to 380 feet squared per day

  9. K-Ar ages of some metamorphic rocks of Oban massif and their implications for the tectonothermal evolution of Southeastern Nigeria

    International Nuclear Information System (INIS)

    Ekwueme, B.N.; Itaya, Tetsumaru; Yabe, Hisatomo

    2000-01-01

    The following K-Ar ages have been obtained on mineral separates from some metamorphic rocks in the Oban massif: amphibolites (592-930 Ma), banded gneisses (492-538 Ma), granodioritic gneiss (502 Ma), schists (514-519 Ma) and charnockite (481 Ma). Comparison of these ages with previous dates obtained by the Rb-Sr whole rock method and the Pb-Pb evaporation technique on single zircon throws light on the cooling history and orogenic events in the Oban massif. The banded gneiss in the Oban massif yields a zircon age of 1932±5 Ma, indicating that it was emplaced during the early Proterozoic (Eburnean orogeny). The K-Ar age of 492-538 Ma suggests that these rocks were metamorphosed during the Pan-African orogeny. This age is similar to the Rb-Sr isochron age of 510±10 Ma earlier suggested to be the age of migmatization in the Oban massif. The amphibolite yielded Rb-Sr isochron ages of 784±31 Ma and 1313±37 Ma. The age of 1313±37 Ma fits into the Kibaran event. The K-Ar hornblende age of 930±37 Ma on the same amphibolite strongly suggests that this amphibolite belongs to an event older than Pan-African (600±150 Ma) and has not been reset perfectly by the Pan-African event. The migmatitic schists in the Oban massif yielded a Rb-Sr isochron age of 527±16 Ma which has been interpreted as the age of its migmatization. One sample of this schist, however, gave a model age of 676±24 Ma. The K-Ar ages for the Oban massif schists (514-519 Ma) are close to the Rb-Sr isochron age of ca. 527 Ma and confirm that a metamorphic event occurred in the area at this time. This was followed by final cooling at 515±10 Ma. Charnockite in the Oban area has yielded a zircon age of 584±20 Ma, which is Pan-African. The age possibly dates the time of formation of the charnockites. The K-Ar age (481 Ma) obtained in this study is approximately 100 Ma younger than the zircon age and possibly dates the subsequent cooling of the charnockite through hornblende blocking temperature. (author)

  10. SEM observation of grain boundary structures in quartz-iron oxide rocks deformed at intermediate metamorphic conditions

    Directory of Open Access Journals (Sweden)

    Leonardo Lagoeiro

    2011-09-01

    Full Text Available Several studies have demonstrated the effect of a second phase on the distribution of fluid phase and dissolution of quartz grains. However, as most observations came from aggregates deformed under hydrostatic stress conditions and mica-bearing quartz rocks, 3-D distribution of pores on quartz-quartz (QQB and quartz-hematite boundaries (QHB has been studied. Several fracture surfaces oriented according to finite strain ellipsoid were analyzed. The pore distribution characterizes the porosity and grain shape as highly anisotropic, which results from the nature and orientation of boundaries. QHB have physical/chemical properties very different from QQB, once the hematite plates have strong effect on wetting behavior of fluid, likewise micas in quartzites. They are pore-free flat surfaces, normal to compression direction, suggesting that they were once wetted with a continuous fluid film acting as faster diffusion pathway. At QQB, the pores are faceted, isolated, close to its edges reflecting the crystallographic control and an interconnected network of fluid along grain junctions. The QQB facing the extension direction are sites of fluid concentration. As consequence, the anisotropic dissolution and grain growth were responsible for the formation of hematite plates and tabular quartz grains significantly contributing for the generation of the foliation observed in the studied rocks.Muitos estudos têm demonstrado o efeito de uma segunda fase sobre a distribuição de fase fluida e dissolução de grãos de quartzo. Entretanto, como a maioria das observações vêm de agregados deformados sob condições de tensão hidrostática e em rochas quartzosas ricas em mica, a distribuição 3D de poros e bordas quartzo-quartzo (BQQ e quartzo-hematita (BQH tem sido estudada. Várias superfícies de fraturas orientadas segundo o elipsóide de deformação finita foram analisadas. A distribuição dos poros caracteriza a porosidade e a forma dos grãos como

  11. Interplay between water infiltration, metamorphic reactions and strain localization during subduction of gabbro from the basement rocks of the Lofoten anorthosite complex

    Science.gov (United States)

    Nasipuri, P.; Stunitz, H.; Menegon, L.; Berger, A.

    2012-04-01

    Eclogitization of lower crustal rocks occurs during subduction processes. During the prograde segment of subduction cycle and subsequent exhumation, ranges of mineral assemblages are produced under different P-T conditions. In this contribution, we describe the role of water and formation of syn-kinematic mineral assemblages in the ductile shear zone within leucogabbro and in the retrograde equivalent (characterized by alternate bands of mafic and felsic layers) that are separated by a distance of 100-150 meter. In the undeformed gabbro, Plagioclase (Pl0), olivine (Ol0) and orthopyroxene (Opx0) form the igneous texture. The onset of metamorphism (M1, 700 0C, 1GPa) during subduction processes is indicated by growth of metamorphic Opx1 and Grt1 corona around Pl0 and Ol0. Cm- wide alternating bands of a mixture of Pl-amphibole (Amph) ± Spl and GrtI(M1) - Opx -Omph - Grt II (M2A, 650-750 0C, > 1.8 GPa) phase mixtures characterize shear zones. Omph overgrow deformed Opx grains (D1). Clinopyroxene (Cpx) -Pl symplectite (M2B, 600-650 0C, 1 GPa) occur at the outer rim the Omph. Breakdown of Grt I/IIto Amph ± Pl (An rich) ± Spl with increased water activity form during M3 metamorphism. In the retrograde eclogite, the mafic layer is composed of Cpx, sodic Pl and Qtz (grain size 50 μm). Coarse-grained calcic Pl (grain size 50-75 μm) forms the felsic layer. Grt porphyrolcast (eq. Grt I/II) with inclusions of Pl and Qtz occur within the mafic layer. A thin layer of amphibole and clinozoisite layer overgrows at the contact between the mafic and felsic layer (6000C, 0.6-0.8 GPa). In the ductile shear zone, crystallographic data of recrystallized Opx0 (grain size 20-30 μm) and the relict Opx0, chemical similarity and the grain size reduction indicate that Opx deformed by at the onset of subduction. The deformed Opx grains show sinistral sense of shear. Although, the fine-grained Pl is expected to show random CPO characteristics of diffusion creep, the strong CPO of Pl is

  12. Natural Radioactivity of Intrusive-Metamorphic and Sedimentary Rocks of the Balkan Mountain Range (Serbia, Stara Planina

    Directory of Open Access Journals (Sweden)

    Sanna Masod Abdulqader

    2017-12-01

    Full Text Available Stara Planina (also known as the Balkan mountain range is known for numerous occurrences and deposits of uranium and associated radionuclides. It is also famous for its geodiversity. The geologic framework is highly complex. The mountain is situated between the latitudes of 43° and 44° N and the longitudes from 22°16′ to 23°00′ E. Uranium exploration and radioactivity testing on Stara Planina began back in 1948. Uranium has also been mined in the zone of Kalna, within the Janja granite intrusive. The naturally radioactive geologic units of Stara Planina are presented in detail in this paper. The main sources of radioactivity on Stara Planina can be classified as: 1. Granitic endogenous—syngenetic–epigenetic deposits and occurrences; 2. Metamorphogenic—syngenetic; and 3. Sedimentary, including occurrences of uranium deposition and fluctuation caused by water in different types of sedimentary rocks formed in a continental setting, which could be classified under epigenetic types. The area of Stara Planina with increased radioactivity (higher than 200 cps, measured by airborne gamma spectrometry, is about 380 square kilometers. The highest values of measured radioactivity and uranium grade were obtained from a sample taken from the Mezdreja uranium mine tailing dump, where 226Ra measures 2600 ± 100 Bq/kg and the uranium grade is from 76.54 to 77.65 ppm U. The highest uranium (and lead concentration, among all samples, is measured in graphitic schist with high concentrations of organic (graphitic material from the Inovska Series—99.47 ppm U and 107.69 ppm Pb. Thorium related radioactivity is the highest in granite samples from the Janja granite in the vicinity of the Mezdreja granite mine and the Gabrovnica granite mine tailing dump, and it is the same—250 ± 10 Bq/kg for 232Th, while the thorium grade varies from 30.82 to 60.27 ppm Th. In gray siltstones with a small amount of organic material, the highest radioactivity is

  13. The transition zone between the Pernambuco-Alagoas Domain and the Sergipano Belt (Borborema Province, NE Brazil): Geochronological constraints on the ages of deposition, tectonic setting and metamorphism of metasedimentary rocks

    Science.gov (United States)

    Neves, Sérgio P.; Rangel da Silva, José Maurício; Bruguier, Olivier

    2016-12-01

    Metasedimentary rocks in the transition zone between the Pernambuco-Alagoas Domain and the Sergipano Belt (southern Borborema Province, NE Brazil) were studied in order to place constraints on the geological evolution of this portion of West Gondwana. High-grade metamorphic conditions are recorded by the garnet-sillimanite assemblage and common anatexis in pelitic paragneisses. Two samples dated by LA-ICP-MS in the north yielded a predominance of early Neoproterozoic detrital zircons, with age peaks between 990 Ma and 827 Ma, with the youngest grain suggesting deposition after 670 Ma. Low Th/U zircons (Th/U < 0.1) in these samples display a significant spread in ages, from 691 to 568 Ma. One sample in the south is dominated by a homogenous population of Paleoproterozoic grains, with a 2200 Ma peak. The southernmost sample also contains Paleoproterozoic zircons but the most abundant population is Neoproterozoic, and characterized by age peaks at c. 670, 647 and 623 Ma. These results show that deposition of sediments in the southern PEAL Domain and in the northern Sergipano Belt occurred in the Late Neoproterozoic. The differing age spectra between samples are correlated with potential source rocks in the study area or in its proximity, reflecting variable input from local sources. The data are interpreted to indicate that during the course of an extensional event at c. 673-647 Ma, Tonian granitic intrusions and synextensional metamorphic rocks were unroofed and eroded to provide zircons for sediments deposited in the north, whereas Paleoproterozoic and synextensional magmatic rocks were the main sources for sediments in the south. Peak metamorphic conditions and contractional deformation are constrained to c. 630-600 Ma.

  14. The parentage of low-grade metasediments in the Sanbagawa Metamorphic Belt, Shikoku, southwest Japan, based on whole-rock geochemistry

    Science.gov (United States)

    Kiminami, Kazuo; Ishihama, Shigetaka

    2003-07-01

    In order to identify the parentage of low-grade metasediments in the Besshi unit of the Sanbagawa Metamorphic Belt in Shikoku, southwest Japan, we have studied the bulk chemistry of psammitic and pelitic rocks in the Sanbagawa Belt and in related nonmetamorphosed Middle/Late Jurassic-Cretaceous accretionary complexes (Southern Chichibu and Northern Shimanto Belts). Tectonostratigraphic relationships and paleontological evidence suggest a post-Middle Jurassic depositional age for the protoliths of the Sanbagawa psammitic/pelitic schists. Zr/TiO 2 ratios of metasandstones in the Besshi unit differ from those of the Middle/Late Jurassic sandstones in the Southern Chichibu Belt. Besshi metasandstones from the Iya-Inouchidani area have chemical affinities with sandstones from the KSII unit (Coniacian-Campanian) of the Northern Shimanto Belt. The Besshi unit in the Asemi-Tachikawa area can be subdivided into northern and southern parts based on the geochemistry of the metasandstones and metapelites. The geochemistry of the metasediments suggests that the parents of the northern and southern parts are the KSII unit and KSIc unit (Late Albian-Early Coniacian), respectively. The depositional ages of the protoliths of the Besshi metasandstones and metapelites are thus inferred to be Late Albian-Early Coniacian (southern part of the Asemi-Tachikawa area), and Coniacian-Campanian (Iya-Inouchidani area and the northern part of the Asemi-Tachikawa area). These conclusions are consistent with the radiometric ages of metasediments from Asemi-Tachikawa, and imply that most of the low-grade metasediments in the Sanbagawa Belt are an underplated, deeper facies of the Cretaceous Shimanto accretionary complex. Protoliths of the Besshi unit represent muddy facies with greenstones, whereas the KSIc and KSII units in the Shimanto Belt mainly consist of sandy facies of probable trench-fan and trench-wedge origin. The lithologic contrast between the KSIc/KSII and Besshi units may be

  15. Development and application of laser microprobe techniques for oxygen isotope analysis of silicates, and, fluid/rock interaction during and after granulite-facies metamorphism, highland southwestern complex, Sri Lanka

    Energy Technology Data Exchange (ETDEWEB)

    Elsenheimer, D.W.

    1992-01-01

    The extent of fluid/rock interaction within the crust is a function of crustal depth, with large hydrothermal systems common in the brittle, hydrostatically pressured upper crust, but restricted fluid flow in the lithostatically pressured lower crust. To quantify this fluid/rock interaction, a Nd-YAG/CO[sub 2] laser microprobe system was constructed to analyze oxygen isotope ratios in silicates. Developed protocols produce high precision in [sigma][sup 18]O ([+-]0.2, 1[sigma]) and accuracy comparable to conventional extraction techniques on samples of feldspar and quartz as small as 0.3mg. Analysis of sub-millimeter domains in quartz and feldspar in granite from the Isle of Skye, Scotland, reveals complex intragranular zonation. Contrasting heterogeneous and homogeneous [sigma][sup 18]O zonation patterns are revealed in samples <10m apart. These differences suggest fluid flow and isotopic exchange was highly heterogeneous. It has been proposed that granulite-facies metamorphism in the Highland Southwestern Complex (HSWC), Sri Lanka, resulted from the pervasive influx of CO[sub 2], with the marbles and calc-silicates within the HSWC a proposed fluid source. The petrologic and stable isotopic characteristic of HSWC marbles are inconsistent with extensive decarbonation. Wollastonite calc-silicates occur as deformed bands and as post-metamorphis veins with isotopic compositions that suggest vein fluids that are at least in part magmatic. Post-metamorphic magmatic activity is responsible for the formation of secondary disseminated graphite growth in the HSWC. This graphite has magmatic isotopic compositions and is associated with vein graphite and amphibolite-granulite facies transitions zones. Similar features in Kerela Khondalite Belt, South India, may suggest a common metamorphic history for the two terranes.

  16. Rubidium-strontium whole-rock ages of Kataragama and Pottuvil charnockites and East Vijayan gneiss: Indication of a 2 Ga metamorphism in the highlands of southeast Sri Lanka

    Energy Technology Data Exchange (ETDEWEB)

    De Maesschalck, A.A.; Oen, I.S. (Vrije Universiteit, Amsterdam (Netherlands)); Hebeda, E.H.; Verschure, R.H. (NWO Laboratorium voor Isotopen Geologie, Amsterdam (Netherlands)); Arps, C.E.S. (RGM, Leiden (Netherlands))

    1990-09-01

    Highland Group granulite-facies rocks of the Kataragama klippe in southeast Sri Lanka yield a Rb-Sr whole-rock apparent age of 1,930 {plus minus} 130 Ma, MSWD = 39, and a {sup 87}Sr/{sup 86}Sr intercept of 0.715 {plus minus} 0.005, indicating a Highlandian metamorphism about 2.0 Ga ago. A charnockitic gneiss at Komari near Pottuvil, east Sri Lanka, gives a Rb-Sr whole-rock isochron age of 820 {plus minus} 70 Ma, MSWD = 0.78, initial {sup 87}Sr/{sup 86}Sr = 0.725 {plus minus} 0.007, suggesting a metamorphic resetting at about 0.8 Ga. The Rb-Sr whole-rock data of an East Vijayan biotite-hornblende gneiss fit a reference isochron of 800 Ma with a {sup 87}Sr/{sup 86}Sr intercept of 0.705; the low {sup 87}Sr/{sup 86}Sr intercept may be explained by a juvenile addition to the older crust. A review of available data from various isotopic dating methods suggests that the Highland Group supracrustals were deposited 2.5-2.0 Ga ago, metamorphosed in the granulite-facies about 2.0 Ga (M1) ago, and disturbed by resetting events about 1.1 Ga (M2), 0.8 Ga (M3), and 0.55 Ga (M4) ago. The East Vijayan supracrustals were deposited 2.0-1.1 Ga ago, invaded by granites and metamorphosed in the amphibolite-facies about 1.1 Ga (M2) ago, and disturbed by resetting events about 0.8 (M3) and 0.55 Ga (M4) ago. Overthrusting of the Kataragama granulites over the East Vijayan gneisses occurred post-M3.

  17. Paleomagnetism of the Upper Proterozoic and Devonian rocks from the Kłodzko Metamorphic Complex in the West Sudetes (SW Poland): tectonic implications for the Variscan belt of Central Europe

    Science.gov (United States)

    Kądziałko-Hofmokl, Magdalena; Kruczyk, Jadwiga; Mazur, Stanisław; Siemiątkowski, Jacek

    2003-12-01

    The Kłodzko Metamorphic Complex (KMC) consists of Upper Proterozoic metaigneous and metasedimentary rocks forming a stack pile thrusted over the Givetian and overlain by Frasnian-Fammenian sediments. Magnetomineralogical experiments show that the magnetic minerals are secondary. The paleomagnetic experiments identified three components of the Natural Remanent Magnetization; labeled A1, A2 and M. The mean pole positions calculated in situ correspond with the Baltica Upper Devonian (A1: PlatS=-18°, PlongE=317°), Permo-Carboniferous (A2: PlatS=-39°, PlongE=2°) and Triassic-Jurassic (M: PlatS=-60°C, PlongE=308°) segments of the Apparent Polar Wander Path (APWP) for Baltica. This indicates that the region studied was situated close to the Baltica plate at least since the Upper Devonian and was not folded after this period.

  18. Retrograde corona texture in pre-Himalayan metamorphic mafic xenoliths, Sutlej valley, NW Himalaya: Implication on rare occurrence of high-grade rocks in the Himalaya

    Science.gov (United States)

    Thakur, S. S.

    2014-07-01

    The present study documents extensive retrogression in mafic xenoliths embedded in the Kinnaur Kailash Granite (∼500 Ma), Sutlej valley, NW Himalaya. Most of the mafic xenoliths are hornblende-rich and are characterized by numerous retrograde corona textures such as garnet coronae around clinopyroxene and plagioclase, titanite coronae around ilmenite, and hornblende coronae around clinopyroxene. This implies that the mafic xenoliths had undergone granulite-facies metamorphism in the early stage of metamorphic evolution, and have been extensively retrograded at a later stage to the present day amphibole-rich mafic xenoliths. The retrogression path traced by these mafic xenoliths can be constrained through P-T estimates using hbl-grt and hbl-pl geothermometry, hbl-grt-pl geobarometry, and Thermocalc3.21 calculations. The estimated results suggest temperatures in the range of 536-662 °C and pressures in the range of 4.5-6.7 kbar for the formation of the corona textures. P-T calculation of garnet forming reaction rim around clinopyroxene further shows that retrogression had started at ∼650 °C and ∼7.3 kbar. These observations suggest that retrogression played a major role in the obliteration of most of the high-grade pre-Himalayan xenoliths from the Himalaya.

  19. The nature of the Ailao Shan-Red River (ASRR) shear zone: Constraints from structural, microstructural and fabric analyses of metamorphic rocks from the Diancang Shan, Ailao Shan and Day Nui Con Voi massifs

    Science.gov (United States)

    Liu, Junlai; Tang, Yuan; Tran, My-Dung; Cao, Shuyun; Zhao, Li; Zhang, Zhaochong; Zhao, Zhidan; Chen, Wen

    2012-03-01

    The structural geology, timing of shearing, and tectonic implications of the ASRR shear zone, one of the most striking lineaments in Southeast Asia, have been the topics of extensive studies over the past few decades. The Xuelong Shan (XLS), Diancang Shan (DCS), Ailao Shan (ALS) and Day Nui Con Voi (DNCV) metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution. Our field structural analysis, detailed microstructural and fabric analysis, as well as the quartz, sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during Cenozoic tectonic evolution in the shear zone. Among the contrasting structural and microstructural associations in the shear zone, D2 structures, which were formed at the brittle to ductile transition during large-scale left-lateral shearing in the second deformation episode, predominate over the structural styles of the other two deformation episodes. Discrete micro-shear zones with intensive grain size reduction compose the characteristic structural style of D2 deformation. In addition, several types of folds (early shearing folds, F21, and late-shearing folds, F22) were formed in the sheared rocks, including discrete to distributed mylonitic foliation, stretching lineation and shear fabrics (e.g., mica fish, domino structures, as well as sigma and delta fabrics). A sequence of microstructures from syn-kinematic magmatic flow, high-temperature solid-state deformation, to brittle-ductile shearing is well-preserved in the syn-kinematic leucocratic intrusions. Deformation structures from the first episode (D1) are characterized by F1 folds and distributed foliations (S1) in rocks due to pure shearing at high temperatures. They are preserved in weakly sheared (D2) rocks along the eastern margin of the ALS belt or in certain low-strain tectonic enclaves within the shear zone. Furthermore, semi

  20. Measured versus calculated thermal conductivity of high-grade metamorphic rocks – inferences on the thermal properties of the lower crust at ambient and in-situ conditions

    DEFF Research Database (Denmark)

    Ray, Labani; Förster, Hans-Jürgen; Förster, Andrea

    The bulk thermal conductivity (TC) of 26 rock samples representing felsic, intermediate and mafic granulites, from the Southern Granulite Province, India, is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity is also calculated from modal mineralogy...... (determined by XRD and EPMA), applying mixing models commonly used in thermal studies. Most rocks are fine- to medium -grained equigranular in texture. All samples are isotropic to weakly anisotropic and possess low porosities (

  1. Measured versus calculated thermal conductivity of high-grade metamorphic rocks – inferences on the thermal properties of the lower crust at ambient and in-situ conditions

    DEFF Research Database (Denmark)

    Ray, Labani; Förster, Hans-Jürgen; Förster, Andrea

    The bulk thermal conductivity (TC) of 26 rock samples representing felsic, intermediate and mafic granulites, from the Southern Granulite Province, India, is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity is also calculated from modal mineralogy...... (determined by XRD and EPMA), applying mixing models commonly used in thermal studies. Most rocks are fine- to medium -grained equigranular in texture. All samples are isotropic to weakly anisotropic and possess low porosities (..., between 2.5 and 3.5 W/(mK) for intermediate granulites and between 2.4 and 2.7 W/(mK) for mafic granulites. Considering this data and literature compilations, rocks representative for the lower continental crust typically display values between 2 and 3 W/(mK) at ambient temperature and pressure conditions...

  2. U–Pb zircon and biostratigraphic data of high‐pressure/ low‐temperature metamorphic rocks of the Talea Ori : tracking the Paleotethys suture in central Crete, Greece

    NARCIS (Netherlands)

    Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

    2016-01-01

    Inherited deformation microfabrics of detrital quartz grains and U–Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite–Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds

  3. Geochemical character of serpentinites associated with high- to ultrahigh-pressure metamorphic rocks in the Alps, Cuba, and the Himalayas: Recycling of elements in subduction zones

    Science.gov (United States)

    Hattori, KéIko H.; Guillot, StéPhane

    2007-09-01

    Serpentinites associated with eclogitic rocks were examined from three areas: the Alps, Cuba, and the Himalayas. Most serpentinites have low Al/Si and high concentrations of Ir-type platinum group elements (PGE) in bulk rock compositions, indicating that they are hydrated mantle peridotites. A few samples contain high Al/Si and low concentrations of Ir-type PGE, suggesting that they are ultramafic cumulates. Among the hydrated mantle peridotites, we identified two groups, primarily on the basis of Al/Si and Mg/Si ratios: forearc mantle serpentinites and hydrated abyssal peridotites. Forearc serpentinites occur in the Himalayas and along a major deformation zone in Cuba. All serpentinites in the Alps and most serpentinites in Cuba are hydrated abyssal peridotites. Himalayan serpentinites have low Al/Si and high Mg/Si ratios in bulk rock compositions, and high Cr in spinel; they were serpentinized by fluids released from the subducted Indian continent and enriched in fluid-mobile elements, and show high 87Sr/86Sr, up to 0.730, similar to the values of rocks of the subducted margin of the Indian continent. Although Himalayan serpentinites have a similar refractory geochemical signature as the Mariana forearc serpentinites, the former contain markedly high concentrations of fluid-mobile elements and high 87Sr/86Sr compared to the latter that were hydrated by subducted Pacific Ocean crust. The data indicate that the enrichment of fluid-mobile elements in forearc serpentinites depends on the composition of subducted slabs. Alpine serpentinites and most Cuban serpentinites show moderate Al/Si similar to abyssal peridotites. Hydration of peridotites near the seafloor is supported by micro-Raman spectra of earlier formed lizardite, high δ34S (+11 to +17‰) of sulphides, and elevated 87Sr/86Sr, ranging from 0.7037 to 0.7095. The data support the contribution of S and Sr from seawater and sediments. These serpentinites are not highly enriched in fluid-mobile elements

  4. Stratigraphic and structural implications of conodont and detrital zircon U—Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska

    Science.gov (United States)

    Moore, Thomas E.; Aleinikoff, John N.; Harris, Anita G.

    1997-01-01

    New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between about 408 and 396 Ma) and Silurian to Devonian at two other locations. Spherical to oblong detrital zircons from quartz-mica schist of the overlying Marion Creek schist yield mostly discordant U—Pb data suggestive of provenance ages of 3.0, 2.0-1.8, and 1.5-1.4 Ga; however, several euhedral grains of zircon from Marion Creek quartz-mica schist have concordant U—Pb ages from 370 to 360 Ma. The Marion Creek schist in our study area therefore is at least 26 m.y. younger than the Emma Creek schist. The age data imply that the protolith of the Emma Creek schist is age correlative with Devonian carbonate rocks in the Hammond and North Slope terranes, whereas the Marion Creek schist is age correlative with Upper Devonian and Lower Mississippian clastic sedimentary rocks of the Endicott Group in the Endicott Mountains terrane and shale and carbonate units in the De Long Mountains and Sheenjek River terranes. Consequently, tectonic models restoring the entire Coldfoot terrane beneath partly or wholly coeval rocks of the Hammond, Endicott Mountains, De Long Mountains, and Sheenjek River terranes of the Arctic Alaska superterrane require revision. Alternative reconstructions, including restoration of the Coldfoot terrane inboard of the Endicott Mountains terrane or outboard of the De Long Mountains and Sheenjek River terranes are plausible but require either larger amounts of shortening than previously suggested or indicate problematic facies relations.

  5. Seawater-like trace element signatures (REE + Y) of Eoarchaean chemical sedimentary rocks from southern West Greenland, and their corruption during high-grade metamorphism

    Science.gov (United States)

    Friend, C. R. L.; Nutman, A. P.; Bennett, V. C.; Norman, M. D.

    2008-02-01

    Modern chemical sediments display a distinctive rare earth element + yttrium (REE + Y) pattern involving depleted LREE, positive La/La*SN, Eu/Eu*SN, and YSN anomalies (SN = shale normalised) that is related to precipitation from circumneutral to high pH waters with solution complexation of the REEs dominated by carbonate ions. This is often interpreted as reflecting precipitation from surface waters (usually marine). The oldest broadly accepted chemical sediments are c. 3,700 Ma amphibolite facies banded iron-formation (BIF) units in the Isua supracrustal belt, Greenland. Isua BIFs, including the BIF international reference material IF-G are generally considered to be seawater precipitates, and display these REE + Y patterns (Bolhar et al. in Earth Planet Sci Lett 222:43 60, 2004). Greenland Eoarchaean BIF metamorphosed up to granulite facies from several localities in the vicinity of Akilia (island), display REE + Y patterns identical to Isua BIF, consistent with an origin by chemical sedimentation from seawater and a paucity of clastic input. Furthermore, the much-debated magnetite-bearing siliceous unit of “earliest life” rocks (sample G91/26) from Akilia has the same REE + Y pattern. This suggests that sample G91/26 is also a chemical sediment, contrary to previous assertions (Bolhar et al. in Earth Planet Sci Lett 222:43 60, 2004), and including suggestions that the Akilia unit containing G91/26 consists entirely of silica-penetrated, metasomatised, mafic rock (Fedo and Whitehouse 2002a). Integration of our trace element data with those of Bolhar et al. (Earth Planet Sci Lett 222:43 60, 2004) demonstrates that Eoarchaean siliceous rocks in Greenland, with ages from 3.6 to 3.85 Ga, have diverse trace element signatures. There are now geographically-dispersed, widespread examples with Isua BIF-like REE + Y signatures, that are interpreted as chemically unaltered, albeit metamorphosed, chemical sediments. Other samples retain remnants of LREE depletion but

  6. Metamorphism in mesosiderites

    Science.gov (United States)

    Delaney, J. S.; Nehru, C. E.; Prinz, M.; Harlow, G. E.

    Previous studies of mesosiderites have identified a metamorphic overprint in these meteorites. However, the effects and implications of this overprint have not yet been explored in detail. The present study documents several important textural and chemical features of the mesosiderites. The components of mesosiderites are examined, taking into account orthopyroxenites, olivine in clasts, mesosiderite mafic clasts, and metal. The characteristics of the silicate matrix of the mesosiderites is explored, and textural and chemical evidence of metamorphism is discussed, giving attention to coronas on olivine clasts, overgrowths on Mg-pyroxene clasts, rims on iron rich pyroxene grains, poikiloblasts of plagioclase, and resorption of clasts. Aspects of redox formation of merrillite are considered along with the causes and the implications of metamorphism. It is found that metamorphism has radically changed the texture of the silicate fraction of the mesosiderites.

  7. Peak metamorphic temperatures from cation diffusion zoning in garnet

    DEFF Research Database (Denmark)

    Smit, Matthijs Arjen; Scherer, Erik; Mezger, Klaus

    2013-01-01

    is robust and provides a reliable means of estimating peak temperatures for different types of high-grade metamorphic rock. The tool could be of particular advantage in rocks where critical assemblages for conventional thermometry do not occur or have been replaced during retrogression.......) to develop a tool that uses the diffusion zoning of these cations in garnet to constrain peak temperature conditions for garnet-bearing rocks. The thermometric approach was externally tested by applying it to garnet crystals from various metamorphic terranes worldwide and comparing the results to published...

  8. Gold in Metamorphic rocks: Facts and Fancy

    Directory of Open Access Journals (Sweden)

    Gheorghe Udubas̡a

    2002-04-01

    Full Text Available The characterization of shear zone related ores (SZRO is still a matter of debate. In an attempt to attenuate the existing controversial points of view some classifications of the SZRO are here proposed, taking into account both their mineralogy and geochemistry (protore nature, ore minerals assemblages etc. and their size. The small scale SZRO seem to depend on the existence of a protore, as a source of metals, whereas the large scale SZRO may have an epigenetic overprint and the source of metals can be multiple, juvenile included. Finally, a fractal-like classification of ore deposits is proposed, in which the SZRO have their natural place.

  9. Gold in Metamorphic rocks: Facts and Fancy

    OpenAIRE

    Gheorghe Udubas̡a; Sorin Silviu Udubas̡a

    2002-01-01

    The characterization of shear zone related ores (SZRO) is still a matter of debate. In an attempt to attenuate the existing controversial points of view some classifications of the SZRO are here proposed, taking into account both their mineralogy and geochemistry (protore nature, ore minerals assemblages etc.) and their size. The small scale SZRO seem to depend on the existence of a protore, as a source of metals, whereas the large scale SZRO may have an epigenetic overprint and the source of...

  10. Using quantitative phase petrology to understand metamorphism

    Science.gov (United States)

    White, Richard

    2015-04-01

    Quantitative phase petrology has become one of the mainstay methods for interpreting metamorphic rocks and processes. Its increased utility has been driven by improvements to end-member thermodynamics, activity-composition relationships and computer programs to undertake calculations. Such improvements now allow us to undertake calculations in increasingly complex chemical systems that more closely reflect those of rocks. Recent progress in activity-composition (a-x) relationships is aimed at developing suites of a-x relationships in large chemical systems that are calibrated together, which will allow a more direct application of the method to metamorphic rocks. In addition, considerable progress has been made in how quantitative phase diagrams can be used to understand features, including chemical potential diagrams for reaction textures, methods for fractionating bulk compositions and methods for modelling open system processes. One feature of calculated phase diagrams is that they present us with a great amount of information, such as mineral assemblages, mineral proportions, phase compositions, volume or density etc. An important aspect to using this information is to understand the potential uncertainties associated with these, which are significant. These uncertainties require that calculated phase diagrams be used with caution to interpret observed features in rocks. Features such as mineral zoning and reaction textures should still be interpreted in a semi-quantitative way, even if based on a fully quantitative diagram. Exercises such as the interpretation of reaction overstepping based on relating phase diagrams to observed mineral core compositions are likely to give spurious results given the infelicities in existing a-x models. Despite these limitations, quantitative phase petrology remains the most useful approach to interpreting the metamorphic history of rocks in that it provides a theoretical framework in which to interpret observed features rather

  11. Metamorphic P-T-t-d evolution of (U)HP metabasites from the South Tianshan accretionary complex (NW China) - Implications for rock deformation during exhumation in a subduction channel

    Czech Academy of Sciences Publication Activity Database

    Soldner, J.; Oliot, E.; Schulmann, K.; Štípská, P.; Kusbach, Vladimír; Anczkiewicz, R.

    2017-01-01

    Roč. 47, July (2017), s. 161-187 ISSN 1342-937X Institutional support: RVO:67985530 Keywords : eclogite * Tianshan massif * (U)HP metamorphic belt Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 6.959, year: 2016

  12. Measurement of activity concentration of {sup 222}Rn in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks, municipio de Amparo, SP; Medida da atividade do {sup 222}Rn em aguas subterraneas extraidas de dois pocos perfurados em rochas metamorficas do Complexo Amparo, municipio de Amparo, SP

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Igor Jose Chaves de

    2008-07-01

    A sampling system was assembled for field {sup 222}Rn activity concentration measurements in ground waters. The system consists of a sampling flask that prevents the contact between the water sample and the atmosphere and a closed line for radon extraction from water. The system, its operation and calibration, are described in full detail, as well as, the conversion of the measured alpha counting rates in activity concentrations. The assembled system was used in {sup 222}Rn activity concentrations measurements in ground waters drawn from two wells drilled in the Amparo Complex metamorphic rocks. The wells are located at the urban area of the city of Amparo and are exploited for public use water. One well, named Vale Verde, is 56 meters deep and crosses 18 meters of soil, 26 meters of quartz rich gneiss and 12 meters of biotite-gneiss. The other well, named Seabra, is 117 meters deep, crosses 28 meters of soil and weathered rocks and ends in granite-gneiss. The mean activity concentrations for the year long observation were (377 +- 25) Bq/dm{sup 3}, for Seabra well, and (1282 +- 57) Bq/dm3, for the Vale Verde well. The {sup 222}Rn activity concentrations fall in the activity concentration range reported in the literature for similar geology areas and are larger than the concentrations found neighboring areas of the same metamorphic Complex. The seasonal activity concentration variations seem to correlate with rain fall variations in the study area. (author)

  13. Diffusion models in metamorphic thermo chronology: philosophy and methods

    International Nuclear Information System (INIS)

    Munha, Jose Manuel; Tassinari, Colombo Celso Gaeta

    1999-01-01

    Understanding kinetics of diffusion is of major importance to the interpretation of isotopic ages in metamorphic rocks. This paper provides a review of concepts and methodologies involved on the various diffusion models that can be applied to radiogenic systems in cooling rocks. The central concept of closure temperature is critically discussed and quantitative estimates for the various diffusion models are evaluated, in order to illustrate the controlling factors and the limits of their practical application. (author)

  14. Metamorphic Testing for Cybersecurity.

    Science.gov (United States)

    Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey; Zhou, Zhi Quan

    2016-06-01

    Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity.

  15. Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

    Directory of Open Access Journals (Sweden)

    Mirijam Vrabec

    2010-06-01

    Full Text Available Ultrahigh-pressure (UHP metamorphism has been recorded in Eo-Alpine garnet peridotites from the PohorjeMts., Slovenia, belonging to the Eastern Alps. The garnet peridotite bodies are found within serpentinized metaultrabasitesin the SE edge of Pohorje and are closely associated with UHP kyanite eclogites. These rocks belongto the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriaticfault system.Garnet peridotites show signs of a complex four-stage metamorphic history. The protolith stage is represented bya low-P high-T assemblage of olivine + Al-rich orthopyroxene + Al-rich clinopyroxene + Cr-spinel. Due to metamorphism,primary clinopyroxene shows exsolutions of garnet, orthopyroxene, amphibole, Cr-spinel and ilmenite. TheUHP metamorphic stage is defined by the assemblage garnet + olivine + Al-poor orthopyroxene + clinopyroxene +Cr-spinel. Subsequent decompression and final retrogression stage resulted in formation of kelyphitic rims aroundgarnet and crystallization of tremolite, chlorite, serpentine and talc.Pressure and temperature estimates indicate that garnet peridotites reached the peak of metamorphism at 4 GPaand 900 °C, that is well within the UHP stability field. Garnet peridotites in the Pohorje Mountains experiencedUHP metamorphism during the Cretaceous orogeny and thus record the highest-pressure conditions of all Eo-Alpinemetamorphism in the Alps.

  16. SHRIMP-RG U-Pb ages of provenance and metamorphism from detrital zircon populations and Pb-Sr-Nd signatures of prebatholithic metasedimentary rocks at Searl Ridge, northern Peninsular Ranges batholith, southern California: Implications for their age, origin, and tectonic setting

    Science.gov (United States)

    Premo, Wayne R.; Morton, Douglas M.

    2014-01-01

    Twenty-four samples were collected from prebatholithic metasedimentary rocks along Searl Ridge, the north rim of the Diamond Valley Reservoir, Domenigoni Valley, centrally located in the northern Peninsular Ranges of southern California. These rocks exhibit progressive metamorphism from west to east across fundamental structural discontinuities now referred to as a “transition zone.” Documented structural and mineralogical changes occur across this metamorphic gradient. Sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) U-Pb ages were obtained from detrital zircons from metasedimentary rocks through the transition zone. To the west, metapelitic and minor metasandstone units yielded numerous concordant 206Pb/238U ages between 210 and 240 Ma, and concordant 207Pb/206Pb ages at 1075–1125 Ma, 1375–1430 Ma, and 1615–1735 Ma, although distinct differences in provenance were noted between units. A few older 207Pb/206Pb ages obtained were ca. 2250 Ma and ca. 2800 Ma. Rocks of the eastern part of the transition zone include high-grade paragneisses that yielded numerous concordant 206Pb/238U ages between 103 and 123 Ma and between 200 and 255 Ma, and concordant 207Pb/206Pb ages at 1060–1150 Ma, 1375–1435 Ma, and 1595–1710 Ma. Some zircon results from these high-grade gneisses are marked by distinct Pb-loss discordia with lower-intercept ages of ca. 215 Ma and Paleoproterozoic upper-intercept ages. Younger ages between 100 and 105 Ma are mainly obtained from rims of some zircon grains that are characterized by low Th/U values (1000 ppm), indicating the likelihood of metamorphic zircon growth at that time. The similarity of zircon age populations between western and eastern units through the transition zone indicates that this fundamental structure probably dissects sediments of the same basin. This supposition is further supported by initial whole-rock Pb-Sr-Nd isotopic data that show similar average initial 206Pb/204Pb (18.65 to 18

  17. Interpreting metamorphic and metasomatic reactions from mineral textures

    Science.gov (United States)

    Austrheim, Hâkon; Putnis, Andrew

    2010-05-01

    Metamorphism and metasomatism both involve the reequilibration of mineral assemblages due to changes in pressure, temperature and/or chemical environment. The distinction between metasomatism (which is a metamorphic reaction involving a significant change in chemical composition) and metamorphism (essentially isochemical) may appear to be well defined, but since no reaction can occur without transport these definitions require that we specify an arbitrary length scale to distinguish the two processes. It is generally accepted that material transport, even on a local scale, involves a fluid phase, and that dissolution and reprecipitation reactions are involved in converting one assemblage to another (Carmichael, 1969; Philpotts and Ague, 2009). Given that the fluid phase is not just pure water, a key question is the thermodynamic as well as the kinetic role of the fluid phase in the reaction. In a metamorphic event P-T paths are inferred from sequences of discontinuous reactions assumed to take place as a rock crosses univariant reaction lines in P-T space and continuous reactions involving chemical reequilibration in coexisting minerals. Any fluid is assumed to merely play a catalytic role and not affect the thermodynamics of the reaction. The criteria for a ‘metamorphic event' are primarily based on mineral textures in a rock, but this is subject to misinterpretation, as pointed out by Vernon et al. (2008). Microstructural criteria which have been considered reliable as indicating a sequence of metamorphic reactions in P,T space include corona structures and partial replacement textures, both suggesting arrested metamorphic reactions (Vernon and Clarke, 2008). As a typical example of a corona structure we describe the textural and chemical characteristics of a reaction between kyanite and garnet to form sapphirine and plagioclase. Based on Na mobility. we argue that the availability and chemistry of the fluid is the primary driver for the reaction (Straume and

  18. Geochronological constraints on the metamorphic sole of the Semail ophiolite in the United Arab Emirates

    Directory of Open Access Journals (Sweden)

    Nick M.W. Roberts

    2016-07-01

    Full Text Available The Semail ophiolite of Oman and the United Arab Emirates (UAE provides the best preserved large slice of oceanic lithosphere exposed on the continental crust, and offers unique opportunities to study processes of ocean crust formation, subduction initiation and obduction. Metamorphic rocks exposed in the eastern UAE have traditionally been interpreted as a metamorphic sole to the Semail ophiolite. However, there has been some debate over the possibility that the exposures contain components of older Arabian continental crust. To help answer this question, presented here are new zircon and rutile U-Pb geochronological data from various units of the metamorphic rocks. Zircon was absent in most samples. Those that yielded zircon and rutile provide dominant single age populations that are 95–93 Ma, partially overlapping with the known age of oceanic crust formation (96.5–94.5 Ma, and partially overlapping with cooling ages of the metamorphic rocks (95–90 Ma. The data are interpreted as dating high-grade metamorphism during subduction burial of the sediments into hot mantle lithosphere, and rapid cooling during their subsequent exhumation. A few discordant zircon ages, interpreted as late Neoproterozoic and younger, represent minor detrital input from the continent. No evidence is found in favour of the existence of older Arabian continental crust within the metamorphic rocks of the UAE.

  19. Gold, uranium and thorium in zones of greenschist displacement metamorphism

    International Nuclear Information System (INIS)

    Gavrilenko, B.V.; Savitskij, A.V.; Titov, V.V.

    1987-01-01

    Distribution of gold, uranium (bar and mobile) and thorium in 15 zones of greenschist dislocated metamorphism in different structures of the Karelo-Kola region carried out by geologic formations of the Early-Archean-Late-Proterozoic age has been studied. More than 200 samples of well core from 0-200 m depths have been analyzed. The results obtained testify to the increase of gold, uranium and less thorium content in zones of green-schist dislocated metamorphism in comparison with the enclosing rocks 1.4-3.1 times. The variation coefficient of gold, uranium and thorium content in green-schist dislocated tectonites increases 1.5-2.9 times. The correlation coefficient of Au/U mob. pair is +0.69, and Au/U bar pair -+0.87. Essential correlation between concentrations of all three elements in enclosing rocks is absent

  20. Repeated shock and thermal metamorphism of the Abernathy meteorite

    Science.gov (United States)

    Lambert, P.; Lewis, C.; Moore, C. B.

    1984-01-01

    Based on the example of Abernathy (L6 chondrite), it is shown how petrographic investigation can be used to unravel the nature, chronology and conditions of superposed metamorphic events in chondrites. Features considered include the texture of the rock, optical characteristics of olivine, pyroxene and plagioclase, refractive index of plagioclase, metallographical characteristics and microhardness of Fe-Ni alloys. It is deduced that Abernathy has been involved in at least six metamorphic events since the formation of the chondrite. Four distinct shock events and two separate reheating events have been identified. The chronology of these events is established. The conditions for the last four events are reasonably well constrained. These include severe reheating (T greater than 1200 C); severe shock causing complete melting of plagioclase and local melting of the rock (P between 90 and 110 GPa, T between 1250 and 1350 C); mild shock (P between 10 and 25 GPa, T less than 500 C); and reheating below 800 C.

  1. Nanoscale transient porosity controls large-scale metamorphic fluid flow

    Science.gov (United States)

    Plümper, Oliver; Botan, Alexandru; Los, Catharina; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2016-04-01

    The reaction of fluids with rocks is fundamental for Earth's dynamics as they facilitate heat/mass transfer and induce volume changes, weaknesses and instabilities in rock masses that localize deformation enabling tectonic responses to plate motion. During these fluid-rock interactions it is the ability of a rock to transmit fluid, its permeability, that controls the rates of metamorphic reactions. However, although some geological environments (e.g., sediments) are open to fluids, the majority of solid rocks (e.g., granites, elcogites, peridotites, etc.) are nearly impermeable. Surprisingly though, even in rocks that are nominally impermeable widespread fluid-rock interactions are observed leading to the question: How can fluids migrate through vast amounts of nominally impermeable rocks? Here we investigate one of the most wide-spread fluid-mediated metamorphic processes in the Earth's crust, the albitization of feldspatic rocks. We show that fluid flow and element mobilization during albitization is controlled by an interaction between grain boundary diffusion and reaction front migration through an interface-coupled dissolution-precipitation process. Using a combination of focused ion beam scanning electron microscopy (FIB-SEM)-assisted nanotomography combined with transmission electron microscopy (TEM) reveals that the porosity is dictated by pore channels with a pore diameter ranging between 10 to 100 nm. Three-dimensional visualization of the feldspar pore network reveals that the pore channels must have been connected during the replacement reaction. Analysis of the pore aspect ratios suggests that a Rayleigh-Taylor-type instability associated to surface energy minimization caused the disconnection of the pore channels. Fluid transport in nanometer-sized objects with at least one characteristic dimension below 100 nm enables the occurrence of physical phenomena that are impossible at bigger length scales. Thus, on the basis of our microstructural

  2. Self-induced nanofluidic transport enables crustal-scale metamorphism

    Science.gov (United States)

    Plümper, Oliver; Botan, Alexandru; Los, Catharina; Liu, Yang; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2017-04-01

    The reaction of fluids with rocks is fundamental for Earth's dynamics as they facilitate heat/mass transfer and induce volume changes, weaknesses and instabilities in rock masses that localize deformation enabling tectonic responses to plate motion. During these fluid-rock interactions it is the ability of a rock to transmit fluid, its permeability, that controls the rates of metamorphic reactions. However, although some geological environments (e.g., sediments) are open to fluids, the majority of solid rocks (e.g., granites, elcogites, peridotites, etc.) are nearly impermeable. Surprisingly though, even in rocks that are nominally impermeable widespread fluid-rock interactions are observed leading to the question: How can fluids migrate through vast amounts of nominally impermeable rocks? Here we investigate one of the most wide-spread fluid-mediated metamorphic processes in the Earth's crust, the albitization of feldspatic rocks. We show that fluid flow and element mobilization during albitization is controlled by an interaction between grain boundary diffusion and reaction front migration through an interface-coupled dissolution-precipitation process. Using a combination of focused ion beam scanning electron microscopy (FIB-SEM)-assisted nanotomography combined with transmission electron microscopy (TEM) we show that the porosity is dictated by pore channels with a pore diameter ranging between 10 to 100 nm. Three-dimensional visualization of the feldspar pore network reveals that the pore channels must have been connected during the replacement reaction. Analysis of the pore aspect ratios suggests that a Rayleigh-Taylor-type instability associated to surface energy minimization caused the disconnection of the pore channels. Fluid transport in nanometer-sized objects with at least one characteristic dimension below 100 nm enables the occurrence of physical phenomena that are impossible at bigger length scales. Thus, on the basis of our microstructural

  3. Assessment of role of metamorphic remobilization in genesis of uranium ores from Ralston Buttes area, Colorado

    International Nuclear Information System (INIS)

    Chatterjee, S.K.

    1984-01-01

    The Ralston Buttes mining district, the principal source of commercial uranium in the Front Range since the late 1940s, is located northeast of Golden and southeast of the Front Range mineral belt. Uranium ore occurs in veins emplaced in fault breccia in Precambrian metamorphic rocks. The progenitors of the metamorphic rocks are a possible source for the uranium. Hornblende gneisses of the Idaho Springs Formation is the major rock type in the area, thus its origin is a major consideration in assessing the quantity of uranium that might have been contributed by metamorphic processes. To evaluate this, 41 rock samples (19 hornblende gneisses, 7 biotite gneisses, 5 chlorite gneisses, and 10 metapelites) were analyzed for major elements, and 3 rock samples (16 hornblende gneisses, 8 biotite gneisses, 4 chlorite gneisses, and 5 mica schists) were analyzed for trace metals (Rb, Sc, Zr, V, Ni, Co, Cr, Ba, U, and Th). Four samples of hornblende gneiss and 1 sample of mica schists were also analyzed for rare earth elements. Major elements are rare earth data indicate that the hornblende gneiss was derived from sediments and tholeiitic basalts. Trace element data suggest a volcanic provenance for these sediments. Rare earth patterns and uranium and thorium abundances of metapelites are similar to average North American shales. Low uranium and thorium values and low thorium-uranium ratios in hornblende gneisses and mica schists preclude large-scale uranium remobilization during metamorphism of these source rocks

  4. Structural evolution of the Semail Ophiolite metamorphic sole, Wadi Hawasina and Northern Jebel Nakhl Culmination, Oman

    Science.gov (United States)

    Hurtado, C.; Bailey, C.; Visokay, L.; Scharf, A.

    2017-12-01

    The Semail ophiolite is the world's largest and best-exposed ophiolite sequence, however the processes associated with both oceanic detachment and later emplacement onto the Arabian continental margin remain enigmatic. This study examines the upper mantle section of the ophiolite, its associated metamorphic sole, and the autochthonous strata beneath the ophiolite at two locations in northern Oman. Our purpose is to understand the structural history of ophiolite emplacement and evaluate the deformation kinematics of faulted and sheared rocks in the metamorphic sole. At Wadi Hawasina, the base of the ophiolite is defined by a 5- to 15-m thick zone of penetratively-serpentinized mylonitic peridotite. Kinematic indicators record top-to-the SW (reverse) sense-of-shear with a triclinic deformation asymmetry. An inverted metamorphic grade is preserved in the 300- to 500-m thick metamorphic sole that is thrust over deep-water sedimentary rocks of the Hawasina Group. The study site near Buwah, in the northern Jebel Nakhl culmination, contains a N-to-S progression of mantle peridotite, metamorphic sole, and underlying Jurassic carbonates. Liswanite crops out in NW-SE trending linear ridges in the peridotite. The metamorphic sole includes well-foliated quartzite, metachert, and amphibolite. Kinematic evidence indicates that the liswanite and a serpentinized mélange experienced top to-the north (normal) sense-of-shear. Two generations of E-W striking, N-dipping normal faults separate the autochthonous sequence from the metamorphic sole, and also cut out significant sections of the metamorphic sole. Fabric analysis reveals that the metamorphic sole experienced flattening strain (K<0.2) that accumulated during pure shear-dominated general shear (Wk<0.4). Normal faulting and extension at the Buwah site indicates that post-ophiolite deformation is significant in the Jebel Akhdar and Jebel Nakhl culminations.

  5. Structure, metamorphism, and geochronology of the Cosmos Hills and Ruby Ridge, Brooks Range schist belt, Alaska

    Science.gov (United States)

    Christiansen, Peter B.; Snee, Lawrence W.

    1994-01-01

    The boundary of the internal zones of the Brooks Range orogenic belt (the schist belt) is a fault contact that dips toward the hinterland (the Yukon-Koyukuk province). This fault, here referred to as the Cosmos Hills fault zone, juxtaposes oceanic rocks and unmetamorphosed sedimentary rocks structurally above blueschist-to-greenschist facies metamorphic rocks of the schist belt. Near the fault contact, schist belt rocks are increasingly affected by a prominent, subhorizontal transposition foliation that is locally mylonitic in the fault zone. Structural and petrologic observations combined with 40Ar/39Ar incremental-release geochronology give evidence for a polyphase metamorphic and deformational history beginning in the Middle Jurassic and continuing until the Late Cretaceous. Our 40Ar/39Ar cooling age for Jurassic metamorphism is consistent with stratigraphic and other evidence for the onset of Brooks Range orogenesis. Jurassic metamorphism is nearly everywhere overprinted by a regional greenschist-facies event dated at 130–125 Ma. Near the contact with the Cosmos Hills fault zone, the schist belt is increasingly affected by a younger greenschist metamorphism that is texturally related to a prominent foliation that folds and transposes an older fabric. The 40Ar/39Ar results on phengite and fuchsite that define this younger fabric give recrystallization ages ranging from 103 to less than 90 Ma. We conclude that metamorphism that formed the transposition fabric peaked around 100 Ma and may have continued until well after 90 Ma. This age for greenschist metamorphism is broadly synchronous with the depositional age of locally derived, shallow-marine clastic sedimentary strata in the hanging wall of the fault zone and thus substantiates the interpretation that the fault zone accommodated extension in the Late Cretaceous. This extension unroofed and exhumed the schist belt during relative subsidence of the Yukon-Koyukuk province.

  6. Thermal modeling of pluton emplacement and associated contact metamorphism:Parashi stock emplacement in the Serranía de Jarara (Alta Guajira, Colombia

    Directory of Open Access Journals (Sweden)

    Zuluaga C. Carlos A.

    2010-12-01

    Full Text Available

    In the northernmost portion of the Serrania de Jarara (Alta Guajira, Colombia, low - medium grade metamorphic rocks from the Etpana Metamorphic Suite were thermally affected by emplacement of a small calc-alkaline intrusion (Parashi Stock. Detailed petrographic analysis in collected rock samples across the NE and NW plutonic contacts show occurrences of textural and mineralogical changes in the country rock fabric that evidence contact metamorphism overprinting regional metamorphism of the Etpana Suite. These changes include growth of andalusite (chiastolite, calcic clinopyroxeneand amphibole porphyroblast crosscutting Sn+1 metamorphicfoliation. Hornblende-plagioclase barometry (ca. 3.1 kbar and cooling models for the stock show maximum time temperature evolution in the country rock at the interpreted depth of intrusion (ca. 11 km and help to evaluate the behavior of the country rock with the changing local geotherm.

  7. Cretaceous metamorphic core complexes in the Otago Schist, New Zealand

    International Nuclear Information System (INIS)

    Forster, M.A.; Lister, G.S.

    2003-01-01

    The median antiformal axis of the Otago Schist, New Zealand, is marked by a zone of relatively high-grade (up to garnet-biotite-albite) greenschist facies rocks 40 Ar/ 39 Ar geochronology has been earned out in conjunction with structural analysis in regions distant from the effects of the Alpine Fault to determine the origin of this metamorphic welt. We have determined that the metamorphic welt is bounded on its northern and southern sides by multistage ductile shear zone(s) marked by intensely developed fabrics, and/or low-angle normal faults. These structures extend over a strike length of > ∼ 200 km and on the southern side of the metamorphic welt they mark the boundary between the Caples and the Torlesse terranes. The oldest such shear zone formed between 122 and 118 Ma. The metamorphic welt was exhumed beneath low-angle normal faults and ductile shear zones that formed from 112 to 109 Ma. The shear zones form the carapace to elongate domal culminations in the central Otago Schist. These geomorphological features are Cretaceous metamorphic core complexes dissected by younger Quaternary faults. Exhumation of the shear zones occurred shortly before volcanogenic sediments began to deposit on a Cretaceous unconformity. We propose that both the Cretaceous unconformity and the underlying ductile shear zones and low-angle faults are a direct result of extensional tectonism. The ductile shear zones display both 'cross-belt' and 'belt-parallel' stretching lineations. Cross-belt stretching may have been caused by rollback of the subducting Pacific slab. Belt parallel extension is interpreted to have taken place during extension associated with rifting between Australia and Antarctica, prior to breakup. Copyright (2003) Geological Society of Australia

  8. Isotopic evidence for two neoproterozoic high-grade metamorphic events in the Brazilia belt

    International Nuclear Information System (INIS)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Piuzanna, Danielle; Moraes, Renato de; Gioia, Simone Maria C.L

    2001-01-01

    The Brasilia Belt is part of a Brasiliano/Pan African orogen developed between the Amazon and Sao Francisco cratons. The stabilization of the belt occurred after the last metamorphic event at ca. 620 Ma. There has been increasing geochronological evidence, however, for an older Neoproterozoic metamorphic event at ca. 780 Ma, observed mainly in high grade rocks of three large mafic-ultramafic complexes in the northern part of the belt. In this study we present: (i) new U-Pb and Sm-Nd geochronological data, (ii) a review of the existing metamorphic ages in the Brasilia Belt, and (iii) a discussion on the tectonic model to explain the two Neoproterozoic metamorphic ages (au)

  9. Geochemistry and paleotectonomagmatic setting of metabasites protolith from Asalem metamorphic complex (northwest Rasht

    Directory of Open Access Journals (Sweden)

    Mohsen Nasrabady

    2016-12-01

    Full Text Available Asalem metamorphic complex consists mostly of metabasite, metapelite and serpentinite. Metabasites display metamorphic features of greenschist and blueschist facies. Greenschist facies rocks that found as both foliated and massive types contain mineralogical assemblage of actinolite, chlorite, albite and epidote. Blueschists contain mineralogical assemblage of sodic amphibole, epidote and phengite. Whole rock analyses of the metabasites indicate basaltic to andesitic composition with mainly calcalkaline nature of their protolith. According to the discrimination diagrams of tectonomagmatic setting, the protolith of investigated metabasites has been islands arc and somewhat mid ocean ridge. The patterns of rare earth elements and spider diagrams of the Asalem metabasites resemble to the basic and intermediate magmatism of islands arc or suprasubduction setting as well. Greenschists and blueschists facies rocks of the Asalem metamorphic complex have been probably equivalent to islands arc or young and hot oceanic crust of suprasubduction zone setting. This portion of oceanic basin unlike the subducted even and thick oceanic lithosphere of Paleotethys during accretion in the shallower levels of accretionary prisms, have underwent metamorphic conditions of blueschist and greenschist facies and finally gave rise to the formation of the metabasites of the Asalem metamorphic complex.

  10. Metamorphic zircon formation at the transition from gabbro to eclogite in Trollheimen-Surnadalen, Norwegian Caledonides

    Science.gov (United States)

    Beckman, Victoria; Möller, Charlotte; Söderlund, Ulf; Corfu, Fernando; Chamberlain, Kevin

    2013-04-01

    A transition zone from gabbro to eclogite via coronitic stages has been investigated at Vindøldalen in south central Norway, with the aim of linking reaction textures to metamorphic zircon growth and obtaining a direct U-Pb zircon age of the metamorphic process. Different rocks from the transition zone contain various types of zircon: I) as igneous prismatic grains; II) metamorphic polycrystalline rims and pseudomorphs after baddeleyite, and III) tiny (> 10µm) bead-like zircon grains associated with a) oxidation and b) resorption of Ti-Fe oxides. During progressive transformation from gabbro to eclogite, titanomagnetite (magnetite with ilmenite lamellae) was oxidised to titanohematite (hematite + ilmenite); at advanced stages of recrystallization to eclogite, rutile was produced at the expense of Fe-Ti oxide. Textural relations suggests that the FeTi-oxides were the main source of Zr. Subsolidus liberation of Zr and formation of zircon beads took place by oxidation of titanomagnetite during fluid-assisted metamorphism in undeformed corona gabbro, and by resorption of FeTi-oxide in undeformed and strongly deformed rock domains that were recrystallized to eclogite. Secondary ionization mass spectrometry (SIMS) and Thermal ionization mass spectrometry (TIMS) were used to obtain U-Pb ages of zircon and baddeleyite. Magmatic baddeleyite yields a TIMS age of 1.46 Ga dating igneous crystallisation, whereas the SIMS age for baddeleyite and magmatic zircon from the same gabbro is slightly younger. Bead-type metamorphic zircon from eclogite gives an age of 425±10 Ma (TIMS), and dates directly the metamorphic transition from gabbro to eclogite in the upper basement of the Lower Allochthon in the south-central Scandinavian Caledonides. The metamorphic zircon age does not necessarily date the peak metamorphic temperature, but reflects fluid-induced reactions and oxidation of primary phases.

  11. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes

    Science.gov (United States)

    Bustamante, Andres; Juliani, Caetano

    2011-10-01

    In the surroundings of Caldas and El Retiro cities (Colombia) metamorphic rocks derived from basic and pelitic protoliths comprise the Caldas amphibole schist and the Ancón schist respectively. Subordinated metamorphosed granite bodies (La Miel gneiss) are associated to these units, and The El Retiro amphibolites, migmatites and granulites crops out eastwards of these units, separated by shear zones. The Caldas amphibole schist and the Ancón schist protoliths could have been formed in a distal marine reduced environment and amalgamated to the South American continent in an apparent Triassic subduction event. The El Retiro rocks are akin to a continental basement and possible include impure metasediments of continental margin, whose metamorphism originated granulite facies rocks and migmatites as a result of the anatexis of quartz-feldspathic rocks. The metamorphism was accompanied by intense deformation, which has juxtaposed both migmatites and granulite blocks. Afterward, heat and fluid circulation associated with the emplacement of minor igneous intrusions resulted in intense fluid-rock interaction, variations in the grain size of the minerals and, especially, intense retrograde metamorphic re-equilibrium. Thermobarometric estimations for the Caldas amphibole schist indicate metamorphism in the Barrovian amphibolite facies. The metamorphic path is counter-clockwise, but retrograde evolution could not be precisely defined. The pressures of the metamorphism in these rocks range from 6.3 to 13.5 kbar, with narrow temperature ranging from 550 to 630 °C. For the Ancón schist metapelites the P- T path is also counter-clockwise, with a temperature increase evidenced by the occurrence of sillimanite and the cooling by later kyanite. The progressive metamorphism event occurred at pressures of 7.6-7.2 kbar and temperatures of 645-635 °C for one sample and temperature between 500 and 600 °C under constant pressure of 6 kbar. The temperature estimated for these rocks

  12. Accessories after the facts: Constraining the timing, duration and conditions of high-temperature metamorphic processes

    Science.gov (United States)

    Taylor, Richard J. M.; Kirkland, Christopher L.; Clark, Chris

    2016-11-01

    High-temperature metamorphic rocks are the result of numerous chemical and physical processes that occur during a potentially long-lived thermal evolution. These rocks chart the sequence of events during an orogenic episode including heating, cooling, exhumation and melt interaction, all of which may be interpreted through the elemental and isotopic characteristics of accessory minerals such as zircon, monazite and rutile. Developments in imaging and in situ chemical analysis have resulted in an increasing amount of information being extracted from these accessory phases. The refractory nature of these minerals, combined with both their use as geochronometers and tracers of metamorphic mineral reactions, has made them the focus of many studies of granulite-facies terrains. In such studies the primary aim is often to determine the timing and conditions of the peak of metamorphism, and high-temperature metasedimentary rocks may seem ideal for this purpose. For example pelites typically contain an abundance of accessory minerals in a variety of bulk compositions, are melt-bearing, and may have endured extreme conditions that facilitate diffusion and chemical equilibrium. However complexities arise due to the heterogeneous nature of these rocks on all scales, driven by both the composition of the protolith and metamorphic differentiation. In additional to lithological heterogeneity, the closure temperatures for both radiogenic isotopes and chemical thermometers vary between different accessory minerals. This apparent complexity can be useful as it permits a wide range of temperature and time (T-t) information to be recovered from a single rock sample. In this review we cover: 1) characteristic internal textures of accessory minerals in high temperature rocks; 2) the interpretation of zircon and monazite age data in relation to high temperature processes; 3) rare earth element partitioning; 4) trace element thermometry; 5) the incorporation of accessory mineral growth

  13. Assessment of fire-damaged concrete. Combining metamorphic petrology and concrete petrography

    NARCIS (Netherlands)

    Larbi, J.A.; Nijland, T.G.

    2001-01-01

    Metamorphic petrology is a branch of geology that deals with the study of changes in rocks due changing physio-chemical conditions. As conditions shift in or out of the thermodynamic stability field of phases, new phases may appear whereas others disappear. A basic approach is mapping of so-called

  14. New 207 Pb/ 206 Pb-Zr minimum evaporation, metamorphic 87 Rb ...

    African Journals Online (AJOL)

    New ages were obtained from charnockites and tonalites collected in the So'o Group in the Ntem Complex. The rocks were analyzed for their petrography, tectonics and 207Pb/206Pb zircon minimum ages of their zircons as well as metamorphic 87Rb/86Sr isochron ages. The charnockites yielded zircon ages with a mean ...

  15. Review of the intrusive, structural and metamorphic history of the Namaqualand geotraverse and environs

    International Nuclear Information System (INIS)

    Blignault, H.J.; Van Aswegen, G.; Van der Merwe, S.W.

    1981-01-01

    The Namaqualand excursion is concerned with the geologic strata, stratigraphy and metamorhic history of the Namaqualand geotraverse and its environs. The general aim of the project was to decipher the history and interactions of tectonic, metamorphic and magmatic processes. Isotope dating were used to determine the ages of various rock formations

  16. Spatial and temporal relations of the ophiolites and the metamorphic soles along the Tauride belt, Turkey

    Science.gov (United States)

    Parlak, Osman; Simsek, Emrah; Ezgi Ozturk, Selena; Simsek, Gokce; Simsek, Tugce; Robertson, Alastair; von Quadt, Albrecht; Köpke, Jürgen; Karaoglan, Fatih

    2016-04-01

    The Tauride belt ophiolites were generated above an intra-oceanic subduction zone and emplaced in the Late Cretaceous over the Tauride carbonate platform. The Tauride ophiolites are underlain by well-preserved metamorphic soles that have a constant structural position between the ophiolitic mélange, below and harzburgitic mantle tec- tonites, above. The dynamothermal metamorphic soles display a typical inverted metamorphic sequence, grading from amphibolite facies directly beneath the highly sheared harzburgitic tectonite to greenschist facies close to the melange contact. They display variable structural thickness (up to 500 m). The metamorphic soles beneath the Tauride ophiolites are interpreted to relate to the initiation of subduction and emplacement processes. The metamorphic soles are intruded by isolated post-metamorphic diabase dikes, derived from island arc tholeiitic magmas. In some places along the Tauride belt (Koycegiz and Pozanti-Karsanti regions), the contact between the metamorphic sole and the overlying serpentinized harzburgites is characterized by a 1.5-2 m thick zone of sheared serpentinized harzburgitic mantle tectonites, intercalated with amphibolites. These lithologies are cut by thick mafic dikes (7-8 m thick, individually) which postdate intraoceanic metamorphism and high-temperature ductile deformation. This contact is interpreted as an intra-oceanic decoupling surface along which volcanics in the upper levels of the down-going plate were metamorphosed to amphibolite facies and accreted to the base of the hanging wall plate. The geochemistry of the metamorphic sole amphibolites suggests their derivation from different geochemical environments; i.e. seamount-type alkaline basalts, mid-ocean ridge basalt (MORB) and island arc basalts. Zircon and rutile separates from the crustal rocks (gabbro and diabase) and from the metamorphic soles of the Tauride ophiolites have been dated by U-Pb SIMS (Edinburgh University) and LA-MC-ICP-MS (ETH Zurich

  17. Alkali control of high-grade metamorphism and granitization

    Directory of Open Access Journals (Sweden)

    Oleg G. Safonov

    2014-09-01

    Full Text Available We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is implemented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes: rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s.

  18. Uranium, thorium and potassium in Indian rocks and ores

    Indian Academy of Sciences (India)

    Abstract. Usinglsodiurn iodide gamma-ray spectrometer, the radioactivity content of the crustal material from various places in India has been estimated. “Sedi- mentary and metamorphic rocks contain more uranium and. thorium than igneous rocks. PhoSphate rocks and ores from Kerala region contain higher nranir m and.

  19. Monazite behaviours during high-temperature metamorphism: a case study from Dinggye region, Tibetan Himalaya

    Science.gov (United States)

    Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang

    2017-04-01

    Monazite is a key accessory mineral for metamorphic geochronology, but its growth mechanisms during melt-bearing high-temperature metamorphism is not well understood. Therefore, the petrology, pressure-temperature and timing of metamorphism have been investigated in pelitic and psammitic granulites from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent an isothermal decompression process from pressure conditions of >10 kbar to armour effect of matrix crystals (biotite and quartz). Most monazite grains formed at the M3-stage (21-19 Ma) through either dissolution-reprecipitation or recrystallization that was related to biotite dehydration melting reaction. These monazite grains record HREE and Y signatures in local equilibrium with different reactions involving either garnet breakdown or peritectic garnet growth. Another peak of monazite growth occurs during melt crystallization ( 15 Ma), and these monazites are unzoned and have homogeneous compositions. Our results documented the widespread recrystallization to account for monazite growth during high-temperature metamorphism and related melting reactions that trigger monazite recrystallization. In a regional sense, our P-T-t data along with published data indicate that the pre-M1 eclogite-facies metamorphism occurred at 39-30 Ma in the Dinggye Himalaya. Our results are in favour of a steady exhumation of the GHC rocks since Oligocene that was contributed by partial melting. Key words: U-Th-Pb geochronology, Monazite, Recrystallization, Pelitic granulite, Himalaya

  20. Comparative chronology of Archean HT/UHT crustal metamorphism

    Science.gov (United States)

    Caddick, Mark; Dragovic, Besim; Guevara, Victor

    2017-04-01

    Attainment of high crustal heat fluxes and consequent partial melting is critical to the stabilization of continental roots. Understanding the processes and timescales behind partial melting of continental crust in the Archean is thus paramount for understanding Archean tectonic modes and how stable cratons formed. High-temperature (HT) to ultrahigh-temperature (UHT) metamorphic rocks can record evidence for dynamic processes that result in advective heat fluxes and a substantial deviation from normal crustal geothermal gradients. Examination of the pressure-temperature conditions and timescales of HT/UHT metamorphism is thus essential to understanding the tectonic processes behind extreme crust heat fluxes and the formation of stable cratonic crust. Here, utilizing both traditional and nontraditional petrologic and geochronologic techniques, we compare the pressure-temperature-time paths of two Neoarchean terranes: the eastern Beartooth Mountains of the Wyoming Craton and the Pikwitonei Granulite Domain of the Superior Province. The Beartooth Mountains of Montana, USA, expose Archean rocks of the Wyoming Craton that are dominated by an ˜2.8 Ga calc-alkaline granitoid batholith known as the Long Lake Magmatic Complex (LLMC). The LLMC contains widespread, up to km-scale metasedimentary roof pendants, with ID-TIMS Sm-Nd garnet geochronology and laser ablation split stream (LASS) monazite geochronology suggesting that metamorphism occurred almost 100 Ma after entrainment by the LLMC [1]. Phase equilibria modeling and Zr-in-rutile thermometry constrain peak pressures and temperatures of ˜6-7 kbar and ˜780-800˚ C. Major element diffusion modeling of garnet suggest that granulite-facies temperatures were only maintained for a short duration, 150,000 km2 of high-grade metamorphic rocks situated in the NW Superior Province. Phase equilibria modeling and trace element thermometry constrain peak temperatures in the southernmost part of the PGD to ˜760˚ C, while across

  1. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    Science.gov (United States)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  2. Metamorphic complexes in accretionary orogens: Insights from the Beishan collage, southern Central Asian Orogenic Belt

    Science.gov (United States)

    Song, Dongfang; Xiao, Wenjiao; Windley, Brian F.; Han, Chunming; Yang, Lei

    2016-10-01

    The sources of ancient zircons and the tectonic attributions and origins of metamorphic complexes in Phanerozoic accretionary orogens have long been difficult issues. Situated between the Tianshan and Inner Mongolia orogens, the Beishan orogenic collage (BOC) plays a pivotal role in understanding the accretionary processes of the southern Central Asian Orogenic Belt (CAOB), particularly the extensive metamorphic and high-strained complexes on the southern margin. Despite their importance in understanding the basic architecture of the southern CAOB, little consensus has been reached on their ages and origins. Our new structural, LA-ICP-MS zircon U-Pb and Hf isotopic data from the Baidunzi, Shibandun, Qiaowan and Wutongjing metamorphic complexes resolve current controversial relations. The metamorphic complexes have varied lithologies and structures. Detrital zircons from five para-metamorphic rocks yield predominantly Phanerozoic ages with single major peaks at ca. 276 Ma, 286 Ma, 427 Ma, 428 Ma and 461 Ma. Two orthogneisses have weighted mean ages of 294 ± 2 Ma and 304 ± 2 Ma with no Precambrian inherited zircons. Most Phanerozoic zircons show positive εHf(t) values indicating significant crustal growth in the Ordovician, Silurian and Permian. The imbricated fold-thrust deformation style combined with diagnostic zircon U-Pb-Hf isotopic data demonstrate that the metamorphic rocks developed in a subduction-accretion setting on an arc or active continental margin. This setting and conclusion are supported by the nearby occurrence of Ordovician-Silurian adakites, Nb-rich basalts, Carboniferous-Permian ophiolitic mélanges, and trench-type turbidites. Current data do not support the presence of a widespread Precambrian basement in the evolution of the BOC; the accretionary processes may have continued to the early Permian in this part of the CAOB. These relationships have meaningful implications for the interpretation of the tectonic attributions and origins of other

  3. Origin of pseudotachylite in the lower Witwatersrand Supergroup, Vredefort Dome (South Africa): constraints from metamorphic studies

    Science.gov (United States)

    Gibson, R. L.; Reimold, W. U.; Wallmach, T.

    1997-12-01

    Small, sub-millimetre to centimetre thick, pseudotachylite veins in metapelitic rocks of the lower Witwatersrand Supergroup in the collar of the Vredefort Dome are recrystallized to a biotite±cordierite paragenesis, indicating the attainment of lower amphibolite facies metamorphic conditions ( T ≥ 500°C) following their formation. The veins occur along ubiquitous anastomosing fracture networks displaying millimetre- to centimetre-scale displacements and truncate, and incorporate fragments of, an older, ca. 2.05 Ga, mid-amphibolite facies, peak metamorphic assemblage. The post-pseudotachylite metamorphism is attributed to the same event that caused highly variable annealing of ca. 2.02 Ga shock microdeformation features in rocks across the dome. Together with the disproportionately large volume of pseudotachylite in the rocks relative to that found in tectonic provinces, and the absence of evidence of genetically related large-scale shear or fault zones, this metamorphic evidence suggests an origin for the pseudotachylite related to the 2.02 Ga Vredefort bolide impact event that produced the dome. Possible origins for the pseudotachylite include shock brecciation and melting, post-shock decompression melting, and friction melting associated with the post-impact high-velocity excavation and modification phases of crater formation. The post-pseudotachylite metamorphism is attributed to the combined effects of an elevated pre-impact crustal geotherm (˜25°C/km) related to the waning stages of the 2.05 Ga peak metamorphism, release of elastic strain energy from the impact shock event and contact effects beneath the impact melt body.

  4. Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment

    Science.gov (United States)

    Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.

    2017-01-01

    Clumped isotope compositions of slowly-cooled calcite and dolomite marbles record apparent equilibrium temperatures of roughly 150-200 °C and 300-350 °C, respectively. Because clumped isotope compositions are sensitive to the details of T-t path within these intervals, measurements of the Δ47 values of coexisting calcite and dolomite can place new constraints on thermal history of low-grade metamorphic rocks over a large portion of the upper crust (from ∼5 to ∼15 km depth). We studied the clumped isotope geochemistry of coexisting calcite and dolomite in marbles from the Notch Peak contact metamorphic aureole, Utah. Here, flat-lying limestones were intruded by a pluton, producing a regular, zoned metamorphic aureole. Calcite Δ47 temperatures are uniform, 156 ± 12 °C (2σ s.e.), across rocks varying from high-grade marbles that exceeded 500 °C to nominally unmetamorphosed limestones >5 km from the intrusion. This result appears to require that the temperature far from the pluton was close to this value; an ambient temperature just 20 °C lower would not have permitted substantial re-equilibration, and should have preserved depositional or early diagenetic Δ47 values several km from the pluton. Combining this result with depth constraints from overlying strata suggests the country rock here had an average regional geotherm of 22.3-27.4 °C/km from the late Jurassic Period until at least the middle Paleogene Period. Dolomite Δ47 in all samples above the talc + tremolite-in isograd record apparent equilibrium temperatures of 328-12+13 °C (1σ s.e.), consistent with the apparent equilibrium blocking temperature we expect for cooling from peak metamorphic conditions. At greater distances, dolomite Δ47 records temperatures of peak (anchi)metamorphism or pre-metamorphic diagenetic conditions. The interface between these domains is the location of the 330 °C isotherm associated with intrusion. Multiple-phase clumped isotope measurements are complemented by

  5. Deciphering metamorphic evolution of rocks by means of Hf isotopes

    Czech Academy of Sciences Publication Activity Database

    Sláma, Jiří; Košler, J.; Pedersen, R. B.

    2006-01-01

    Roč. 70, 18 /S1/ (2006), A596-A596 ISSN 0046-564X. [Goldschmidt Conference /16./. 27.08.2006-01.09.2006, Melbourne] Institutional research plan: CEZ:AV0Z30130516 Keywords : Hafnium * Hf isotopes * granulite Subject RIV: DD - Geochemistry

  6. Analysis of lineament swarms in a Precambrian metamorphic rocks ...

    Indian Academy of Sciences (India)

    Addressing the geologic significance of lineaments and their correlation with joints/fractures is still unclear. The present study ... shows that the major lineament and fracture trends are oriented along EW and NS directions respec- tively, thus failing to ... literally as straight lines in the horizontal plane in 1:50,000 scale.

  7. Analysis of lineament swarms in a Precambrian metamorphic rocks ...

    Indian Academy of Sciences (India)

    Addressing the geologic significance of lineaments and their correlation with joints/fractures is still unclear. The present study attempts to analyse the lineament swarms developed in a Precambrian meta- morphic terrain in India using both unfiltered and filtered techniques. The unfiltered analysis technique shows that the ...

  8. Metamorphism of bauxites on Naxos, Greece

    NARCIS (Netherlands)

    Feenstra, A.

    1985-01-01

    This thesis presents the results of a petrological-mineralogical and geochemical study of the metamorphosed karstbauxites on the island of Naxos, Greece. The bauxites have been subject to an Eocene highpressure metamorphism (M1), followed by a Late Oligocene-Miocene medium-pressure metamorphism

  9. Amphibolite to granulite progressive metamorphism in the Niquelândia Complex, Central Brazil: regional tectonic implications

    Science.gov (United States)

    Filho, C. F. Ferreira; De Moraes, R.; Fawcett, J. J.; Naldrett, A. J.

    1998-01-01

    The Niquelândia Complex is a major Proterozoic mafic and ultramafic layered intrusion in central Brazil. Ductile deformation and associated metamorphic recrystallization are widespread along ductile shear zones. Bands of alumina and silica-rich rocks (less than few meters thick) occur in the central parts of these ductile shear zones. Metamorphic grade, ranging from amphibolite to granulite facies, increases progressively downward in the layered intrusion stratigraphy. The three mapped metamorphic zones: amphibolite zone, amphibolite-granulite transition zone and granulite zone, are parallel to the intrusion stratigraphy. Metabasites show progressive changes in mineral assemblages, texture, and Ca-amphibole composition in a traverse covering the three metamorphic zones. With increasing metamorphic grade, amphibolites (hbl+pl ± cpx ± grt ± ep) give way to hornblende granulites (hbl+pl+cpx+opx) and anhydrous mafic granulites (pl+cpx+opx). The Ti, A1 IV and Na+K content of amphiboles increase progressively with metamorphic grade. Quartz-rich rocks have kyanite as the Al 2SiO 5 polymorph in the amphibolite zone, whereas sillimanite occurs in the granulite zone. Geothermobarometry and mineral stability data indicate P-T conditions of peak metamorphism at about 700 °C and 6-8 kbars in the amphibolite zone and temperatures higher than 800 °C in the granulite zone. In quartz-rich rocks of the granulite zone, retrogressive processes are indicated by reaction coronas of sil+grt between peak metamorphic assemblages of hc+qtz and replacement of sillimanite by kyanite. These reactions have an appreciable temperature dependence and together they indicate a retrogressive path characterized by an initial period of nearly isobaric cooling. Previously reported U-Pb zircon dating demonstrates the coeval nature of the amphibolite and granulite facies metamorphism and supports the notion that the entire terrain represents a single continuous crustal section. The metamorphic age

  10. Metamorphic Evolution of Garnet-bearing Epidote-Barroisite Schist from the Meratus Complex in South Kalimantan, Indonesia

    Directory of Open Access Journals (Sweden)

    Nugroho Imam Setiawan

    2015-09-01

    Full Text Available DOI:10.17014/ijog.2.3.139-156This paper presents metamorphic evolution of metamorphic rocks from the Meratus Complex in South Kalimantan, Indonesia. Eight varieties of metamorphic rocks samples from this location, which are garnet-bearing epidote-barroisite schist, epidote-barroisite schist, glaucophane-quartz schist, garnet-muscovite schist, actinolite-talc schist, epidote schist, muscovite schist, and serpentinite, were investigated in detail its petrological and mineralogical characteristics by using polarization microscope and electron probe micro analyzer (EPMA. Furthermore, the pressure-temperature path of garnet-bearing epidote-barroisite schist was estimated by using mineral parageneses, reaction textures, and mineral chemistries to assess the metamorphic history. The primary stage of this rock might be represented by the assemblage of glaucophane + epidote + titanite ± paragonite. The assemblage yields 1.7 - 1.0 GPa in assumed temperature of 300 - 550 °C, which is interpreted as maximum pressure limit of prograde stage. The peak P-T condition estimated on the basis of the equilibrium of garnet rim, barroisite, phengite, epidote, and quartz, yields 547 - 690 °C and 1.1 - 1.5 GPa on the albite epidote amphibolite-facies that correspond to the depth of 38 - 50 km. The retrograde stage was presented by changing mineral compositions of amphiboles from the Si-rich barroisite to the actinolite, which lies near 0.5 GPa at 350 °C. It could be concluded that metamorphic rocks from the Meratus Complex experienced low-temperature and high-pressure conditions (blueschist-facies prior to the peak metamorphism of the epidote amphibolite-facies. The subduction environments in Meratus Complex during Cretaceous should be responsible for this metamorphic condition.

  11. The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

    Directory of Open Access Journals (Sweden)

    Yuri de Melo Portella

    2016-09-01

    Full Text Available The Cedrolina chromitite body (Goiás-Brazil is concordantly emplaced within talc-chlorite schists that correspond to the poly-metamorphic product of ultramafic rocks inserted in the Pilar de Goiás Greenstone Belt (Central Brazil. The chromite ore displays a nodular structure consisting of rounded and ellipsoidal orbs (up to 1.5 cm in size, often strongly deformed and fractured, immersed in a matrix of silicates (mainly chlorite and talc. Chromite is characterized by high Cr# (0.80–0.86, high Fe2+# (0.70–0.94, and low TiO2 (av. = 0.18 wt % consistent with variation trends of spinels from metamorphic rocks. The chromitite contains a large suite of accessory phases, but only irarsite and laurite are believed to be relicts of the original igneous assemblage, whereas most accessory minerals are thought to be related to hydrothermal fluids that emanated from a nearby felsic intrusion, metamorphism and weathering. Rutile is one of the most abundant accessory minerals described, showing an unusually high Cr2O3 content (up to 39,200 ppm of Cr and commonly forming large anhedral grains (>100 µm that fill fractures (within chromite nodules and in the matrix or contain micro-inclusions of chromite. Using a trace element geothermometer, the rutile crystallization temperature is estimated at 550–600 °C (at 0.4–0.6 GPa, which is in agreement with P and T conditions proposed for the regional greenschist to low amphibolite facies metamorphic peak of the area. Textural, morphological, and compositional evidence confirm that rutile did not crystallize at high temperatures simultaneously with the host chromitite, but as a secondary metamorphic mineral. Rutile may have been formed as a metamorphic overgrowth product following deformation and regional metamorphic events, filling fractures and incorporating chromite fragments. High Cr contents in rutile very likely are due to Cr remobilization from Cr-spinel during metamorphism and suggest that Ti was

  12. Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

    Science.gov (United States)

    Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.

    1999-01-01

    The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

  13. Evolution of Migmatitic Granulite Complexes: implications from Lapland Granulite Belt, Part I: metamorphic geology

    Directory of Open Access Journals (Sweden)

    Pekka Tuisku

    2006-01-01

    Full Text Available The Palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Proterozoic terrains in the NE part of the Fennoscandian Shield concurrently with the accretion of Svecofennian arc complexes at ~1.9 Ga. The belt consists mainly of aluminous migmatiticmetagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly into the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas. This is supported by structural and contact relations of metasediments and igneous rocks, and by the lack progressive metamorphic reaction textures in the igneous rock series. The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quartz assemblageat 750−850°C and 5−8.5 kbar which lead to formation of a restitic palaeosome and peraluminous granitic melt in metapelites. Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pelitic rocks (650°C under the stability field of andalusite coexisting with potassium feldspar (2−3 kbar. Cooling was accompanied by the crystallization of the neosomes, often carrying aluminium-rich phases. Postmetamorphic duplexing of the LGB is clearly seen in the distribution of calculated PT conditions.

  14. Permian high-temperature metamorphism in the Western Alps (NW Italy)

    Science.gov (United States)

    Kunz, Barbara E.; Manzotti, Paola; von Niederhäusern, Brigitte; Engi, Martin; Darling, James R.; Giuntoli, Francesco; Lanari, Pierre

    2018-01-01

    During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused high-temperature low-to-medium pressure metamorphism and partial melting in the lower crust. Permian metamorphism and magmatism has extensively been recorded and dated in the Central, Eastern, and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields temperatures of 580-890 °C from Ti-in-zircon and 630-850 °C from Zr-in-rutile for Permian metamorphic rims. These temperature estimates, together with preserved mineral assemblages (garnet-prismatic sillimanite-biotite-plagioclase-quartz-K-feldspar-rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian metamorphism. U/Pb ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups ( 330 and 300 Ma) are followed seamlessly by a broad range of Permian ages (300-250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly, dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin.

  15. Search for underground openings for in situ test facilities in crystalline rock

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, H.A.; Strisower, B.; Corrigan, D.J.; Graf, A.N.; O' Brien, M.T.; Pratt, H.; Board, M.; Hustrulid, W.

    1980-01-01

    With a few exceptions, crystalline rocks in this study were limited to plutonic rocks and medium to high-grade metamorphic rocks. Nearly 1700 underground mines, possibly occurring in crystalline rock, were initially identified. Application of criteria resulted in the identification of 60 potential sites. Within this number, 26 mines and 4 civil works were identified as having potential in that they fulfilled the criteria. Thirty other mines may have similar potential. Most of the mines identified are near the contact between a pluton and older sedimentary, volcanic and metamorphic rocks. However, some mines and the civil works are well within plutonic or metamorphic rock masses. Civil works, notably underground galleries associated with pumped storage hydroelectric facilities, are generally located in tectonically stable regions, in relatively homogeneous crystalline rock bodies. A program is recommended which would identify one or more sites where a concordance exists between geologic setting, company amenability, accessibility and facilities to conduct in situ tests in crystalline rock.

  16. Search for underground openings for in situ test facilities in crystalline rock

    International Nuclear Information System (INIS)

    Wollenberg, H.A.; Strisower, B.; Corrigan, D.J.; Graf, A.N.; O'Brien, M.T.; Pratt, H.; Board, M.; Hustrulid, W.

    1980-01-01

    With a few exceptions, crystalline rocks in this study were limited to plutonic rocks and medium to high-grade metamorphic rocks. Nearly 1700 underground mines, possibly occurring in crystalline rock, were initially identified. Application of criteria resulted in the identification of 60 potential sites. Within this number, 26 mines and 4 civil works were identified as having potential in that they fulfilled the criteria. Thirty other mines may have similar potential. Most of the mines identified are near the contact between a pluton and older sedimentary, volcanic and metamorphic rocks. However, some mines and the civil works are well within plutonic or metamorphic rock masses. Civil works, notably underground galleries associated with pumped storage hydroelectric facilities, are generally located in tectonically stable regions, in relatively homogeneous crystalline rock bodies. A program is recommended which would identify one or more sites where a concordance exists between geologic setting, company amenability, accessibility and facilities to conduct in situ tests in crystalline rock

  17. Post-peak metamorphic evolution of the Sumdo eclogite from the Lhasa terrane of southeast Tibet

    Science.gov (United States)

    Cao, Dadi; Cheng, Hao; Zhang, Lingmin; Wang, Ke

    2017-08-01

    A reconstruction of the pressure-temperature-time (P-T-t) path of high-pressure eclogite-facies rocks in subduction zones may reveal important information about the tectono-metamorphic processes that occur at great depths along the plate interface. The majority of studies have focused on prograde to peak metamorphism of these rocks, whereas after-peak metamorphism has received less attention. Herein, we present a detailed petrological, pseudosection modeling and radiometric dating study of a retrograded eclogite sample from the Sumdo ultrahigh pressure belt of the Lhasa terrane, Tibet. Mineral chemical variations, textural discontinuities and thermodynamic modeling suggest that the eclogite underwent an exhumation-heating period. Petrographic observations and phase equilibria modeling suggest that the garnet cores formed at the pressure peak (∼2.5 GPa and ∼520 °C) within the lawsonite eclogite-facies and garnet rims (∼1.5 GPa and spans an interval of ∼7 million years, which is a minimum estimate of the duration of the eclogite-facies metamorphism of the Sumdo eclogite.

  18. Investigation into the metamorphic Nappes of the Central Scandinavian Caledonides on the basis of Rb-Sr and K-Ar age determination

    International Nuclear Information System (INIS)

    Reymer, A.P.S.

    1979-01-01

    This study concerns age determinations on several rock units of metamorphic nappes in the central Scandinavian Caledonides. Rb-Sr analyses on whole-rocks and minerals (biotite, muscovite/phengite, feldspars, garnet) were made as well as K-Ar determinations on biotite, muscovite/phengite, amphibole and feldspar. (Auth.)

  19. Dating of retrograde metamorphism in Western Carpathians by K-Ar analysis of muscovites

    International Nuclear Information System (INIS)

    Cambel, B.; Korikovskij, S.P.; Krasivskaya, I.S.; Arakelyants, M.M.

    1986-01-01

    Using the K-Ar isotope dating method of muscovites it was found that many retrogradely metamorphosed rocks are the results of Variscan retrograde metamorphism and are not pre-Cambrian or Alpine metamorphites (diaphthorites). Samples for dating were taken from the Western Carpathian crystalline formation. The content of radiogenic argon was determined by mass spectrometry using the method of isotope dilution. (M.D.)

  20. Rock magnetic properties

    International Nuclear Information System (INIS)

    Hearst, R.B.; Morris, W.A.

    1991-01-01

    In 1978 the Nuclear Fuel Waste Management Program began the long task of site selection and evaluation for nuclear waste disposal. The Canadian Nuclear Fuel Waste Management Program, administered by Atomic Energy of Canada Limited, Research Company has provided the geophysicist with the unique opportunity to evaluate many modes of geophysical investigation in conjunction with detailed geologic mapping at a number of research areas. Of particular interest is research area RA-7, East Bull Lake, Algoma District, Ontario. Geophysical survey methods applied to the study of this included detailed gravity, ground magnetics, VLF, an airborne magnetic gradiometer survey and an airborne helicopter magnetic and EM survey. A comprehensive suite of rock property studies was also undertaken providing information on rock densities and magnetic rock properties. Preliminary modeling of the magnetic data sets assuming only induced magnetization illustrated the difficulty of arriving at a magnetic source geometry consistent with the mapped surficial and borehole geology. Integration of the magnetic rock properties observations and industry standard magnetic modelling techniques provides a source model geometry that is consistent with other geophysical/geological data sets, e.g. gravity and observed geology. The genesis of individual magnetic signatures in the East Bull Lake gabbro-anorthosite record the intrusion, metamorphism and fracture alteration of the pluton. As shown by this paper, only by understanding the rock magnetic signatures associated with each of these events is it possible to obtain geologically meaningful interpretative models

  1. On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

    Directory of Open Access Journals (Sweden)

    David E. Kelsey

    2015-05-01

    Full Text Available Ultrahigh temperature (UHT metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 °C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as ‘normal’ in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine + quartz, orthopyroxene + sillimanite ± quartz and osumilite in Mg–Al-rich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar thermobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1 development of a ferric iron activity–composition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions; (2 quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3 more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4 recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions; (5 more strongly linking U–Pb geochronological data from zircon and monazite to P–T points or path segments through using Y + REE partitioning between accessory and major phases, as well as phase

  2. 40Ar/ 39Ar mineral age constraints for the tectonothermal evolution of the Sambagawa metamorphic belt, central Shikoku, Japan: a Cretaceous accretionary prism

    Science.gov (United States)

    Takasu, A.; Dallmeyer, R. D.

    1990-12-01

    The Sambagawa metamorphic belt exposed in central Shikoku, Japan, is tectonostratigraphically represented by the Oboke and structurally overlying Besshi nappe complexes. Oboke units consist of metamorphic rocks largely derived from clastic protoliths (sandstone and conglomerate) whereas Besshi units are dominated by rocks with oceanic protolith affinities (shale, chert, and greenstone). Whole-rock schist samples from low-grade Oboke units record intermediate temperature. {40Ar }/{39Ar } plateau ages of 70-77 Ma, which are interpreted to closely date attainment of maximum metamorphic conditions. Whole-rock schist samples from Besshi units (chlorite zone) record plateau ages of 85-94 Ma suggesting an earlier metamorphic climax within this structural level. Amphibole within the albite-biotite zone in Besshi records {36Ar }/{40Ar } vs. {39Ar }/{40Ar } plateau isotope correlation ages of 84-87 Ma, which are interpreted as dating the post-metamorphic cooling through temperatures required for intracrystalline retention of argon. A slightly older isotope correlation age (94 Ma) is recorded by amphibole from the higher grade oligioclase-biotite zone. Contrasts in amphibole cooling ages are interpreted as reflecting thrust-related metamorphic inversion and resultant earlier cooling of higher grade structural units. Muscovite from all structural levels of the Besshi nappe complex records {40Ar }/{39Ar } plateau ages of 76-89 Ma. These are interpreted to date post-metamorphic cooling through appropriate closure temperatures following structural assembly of the Besshi nappe complex. Protoliths of the Besshi units originated at approx. 130 Ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx. 90-100 Ma. Higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex. During subsequent structural uplift to shallower crustal levels the Besshi nappe complex was tectonically emplaced over Oboke

  3. Distribution, facies, ages, and proposed tectonic associations of regionally metamorphosed rocks in Southwestern Alaska and the Alaska Peninsula

    Science.gov (United States)

    Dusel-Bacon, Cynthia; Doyle, Elizabeth O.; Box, Stephen E.

    1996-01-01

    The oldest dated metamorphic sequence in Alaska, the fault-bounded Kilbuck Terrane, consists of continental rocks that were metamorphosed under amphibolite-facies conditions during early Proterozoic (1.77 Ga) time. Proterozoic or early Paleozoic metamorphic ages are also possible for greenschist- and amphibolite-facies continental rocks in interior Alaska (Ruby and Nixon Fork terranes). Medium-grade metamorphism on the Alaska Peninsula accompanied intrusion of a Jurassic arc. North of Bristol Bay, low-grade, locally high-pressure Mesozoic metamorphism is attributed to the progressive underthrusting of a subduction complex beneath an oceanic arc followed by underthrusting of the Kilbuck Terrane beneath the subduction complex.

  4. Metamorphic evolution of the Lesser Himalayan Crystalline Sequence, Siyom Valley, NE Himalaya, India

    Science.gov (United States)

    Nandini, P.; Thakur, S. S.

    2011-03-01

    The paper reports classical Barrovian inverted metamorphism in the Lesser Himalayan Crystalline Sequence, Siyom Valley, NE Himalaya. The sequence is thrust-bounded and constitutes a part of the western limb of the Siang antiform. Six metamorphic zones are delineated with increasing grade from biotite zone through garnet-, staurolite-, kyanite-, sillimanite- to sillimanite-K-feldspar zone with increasing structural level. Granulite-facies pelitic assemblages, marked by the occurrence of garnet + cordierite occur in the sillimanite-K-feldspar zone. Three phases of folding, F 1, F 2 and F 3 and two generations of planar structures, S 1 and S 2 are recognised. Peak metamorphic mineral growths are dominantly syn-F 2. Metamorphic isograds and boundary thrusts of the sequence are co-folded around the Siang antiform by F 3 deformation. Garnet shows prograde growth zoning in lower grade rocks and retrograde diffusion zoning in higher grade rocks. Pelites of the sillimanite-K-feldspar zone show textural evidence of decompression such as corona of cordierite around kyanite. Breakdown reactions of muscovite and biotite in this zone are attributed to decompression. Geothermobarometric calculations show gradual increase of temperature from garnet zone to sillimanite-K-feldspar zone, whereas pressure increases sharply from garnet zone to staurolite zone and remains nearly constant thereafter. Peak metamorphism reached temperature of >750 °C and pressure of ˜10 kbar in the sillimanite-K-feldspar zone. P-T estimates, decompression reactions and pseudosection topologies suggest a clockwise path with steep decompression for the evolution of the sillimanite-K-feldspar zone in the Siyom Valley.

  5. First evidence of high-pressure metamorphism in the ''Cover Series'' of the southern Menderes Massif. Tectonic and metamorphic implications for the evolution of SW Turkey

    Science.gov (United States)

    Rimmelé, Gaëtan; Oberhänsli, Roland; Goffé, Bruno; Jolivet, Laurent; Candan, Osman; Çetinkaplan, Mete

    2003-11-01

    The Menderes Massif occupies a large part of western Turkey. It is tectonically overlain by nappes of the Izmir-Ankara Suture Zone (including the Bornova Flysch Zone) on its northern flank, the Afyon Zone on its eastern border, and the Lycian Nappes on its southern flank. The discovery of magnesiocarpholite-kyanite assemblages in the Mesozoic 'cover' sequence of the southern Menderes Massif leads to the very first consideration that a major high-pressure (HP) metamorphic event affected the massif during its Alpine evolution. Estimations of minimum pressure-temperature conditions about 10-12 kbar and 440 °C suggest a minimum burial of 30 km for the metasedimentary rocks of the Menderes Massif, similar to that for the Eocene Dilek Blueschists, which belong to the Cycladic complex. This finding of high-pressure rocks within the Menderes 'cover' series, as well as the recent description of low-grade high-pressure parageneses in the basal thrust sheets of the overlying Lycian nappe complex, has strong implications for the tectono-metamorphic evolution of these units. The characteristics of this high-pressure metamorphism and the deformation features observed in the southern Menderes Massif allow consideration of a fast burial during Alpine subduction and nappe stacking. Three high-pressure units were piled up during the Eocene collision of the Sakarya continent and the Tauride-Menderes block. The lowermost unit consists of the imbricated 'core' and 'cover' of the Menderes Massif. The intermediate unit is the Cycladic Blueschist complex (Dilek and Samos regions) and the uppermost unit is made of the Lycian Nappes. The retrogression of high-pressure parageneses from the Menderes Massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented N-S to NE-SW during the high-pressure event and its exhumation. We propose a tectono-metamorphic model in three main stages: (1) the southward translation of the high

  6. Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California

    Science.gov (United States)

    Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.

    2007-01-01

    Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic, leuco-some, and pegmatite ages to the period of Sevier belt thrusting and the period of most voluminous Sierran arc magmatism suggests that both burial by thrusting and regional magmatic heating contributed to metamorphism and

  7. A study of radioactive elements of various rocks in Pattani Province with gamma ray spectrometer

    Directory of Open Access Journals (Sweden)

    Kaewtubtim, P.

    2002-01-01

    Full Text Available The radioactivity of the three elements, potassium, uranium and thorium, in rocks of various types in Pattani Province was investigated by using a gamma ray spectrometer. It was found that potassium contents in igneous rocks, sedimentary rocks and metamorphic rocks were 6.29 %, 2.21% and 1.54 % respectively. Uranium equivalent contents in igneous rock, sedimentary rocks and metamorphic rocks were found to be 22.51 ppm, 11.25 ppm and 14.13 ppm, while thorium contents in these rocks were 21.78 ppm, 18.88 ppm and 18.15 ppm respectively. The results obtained were similar to those reported by Pungtip Ranglek (1995 for igneous rock at Liwong Pluton site in Thepha, Na Thawi, Chana and Saba Yoi Districts, Songkhla Province, and were about six times higher than those reported by Kittichai Wattananikorn (1994 for igneous rock in the northern part of Thailand.

  8. Metamorphic evolution of metadolerites from the Frido Unit ophiolites (Southern Apennine-Italy)

    Science.gov (United States)

    Cristi Sansone, Maria T.; Prosser, Giacomo; Rizzo, Giovanna; Tartarotti, Paola

    2010-05-01

    The Southern Apennines chain is a fold-and-thrust belt resulting from the convergence of the African and European plates and simultaneous roll-back of SE-directed Ionian subduction (Upper Oligocene-Quaternary). Ophiolites in the Southern Apennines are related to northwest subduction of the oceanic lithosphere pertaining to the Ligurian sector of the Jurassic western Tethys. The ophiolitic sequences are enclosed within remnants of the Liguride accretionary wedge now incorporated in the Southern Apennine chain and they crop out in the north-eastern slope of the Pollino Ridge (Calabria-Lucania border zone). Mafic and ultramafic rocks, with garnet-bearing felses, amphibolites, gneiss and granitoides occur as tectonic slices within a matrix mainly composed of calcschists and phyllites. Metadolerites occur as dikes cutting through serpentinized peridotites. Metadolerites have different kinds of texture reflecting various degree of crystallinity and strain: porphyritic or aphyric, intersertal/intergranular, blastophitic, cataclastic to mylonitic. In all metadolerites primary plagioclase and clinopyroxene can be observed. The metamorphic mineral assemblage consists of brown amphibole, green amphibole, chlorite, blue amphibole, pumpellyite, prehnite, quartz, epidote, white mica, lawsonite and plagioclase (Pl2 and Pl3). Accessory phases are opaque minerals, Fe-hydroxides and zircon. Metadolerites are cross- cut by veins filled with pumpellyite, chlorite, prehnite, tremolite, plagioclase, white, mica, quartz, lawsonite, epidote and zircon. The veins are straight, a few millimetres in thickness and occur isolated or in closely spaced sets. The vein morphology ranges from planar to sinuous and irregular. On the basis of metamorphic mineral phases three different types of metadolerite can be distinguished: i) rocks with a high content of prehnite crystals in cataclastic-mylonitic bands, exhibiting an intersertal or a blastophitic texture or a mylonitic fabric and in some cases a

  9. GRAPHITIZATION OF METASEDIMENTARY ROCKS IN THE WESTERN KONYA

    Directory of Open Access Journals (Sweden)

    Hüseyin KURT

    2000-01-01

    Full Text Available The Paleozoic-Mesozoic metasedimentary rocks in the study area are metacarbonate, metachert, metapelite, metasandstone and metaconglomerate. Graphite layers are 1cm to 2m thick, extend laterally for tens of meters and are intercalated with metasedimentary rocks. Generally, the graphite is black in color, with a well developed cleavage which is concordant with the cleavage of the host rocks. In addition, the crystal and flake graphites formed in metasedimentary rocks are mostly aligned parallel to the cleavage planes. These metamorphic rocks are subjected to shearing and granulation providing structural control for the development of graphite. It was probably this phenomenon that first led to emphasize the relationship between graphite and metasedimentary rocks. Graphite mineralization has been controlled by bedding, microfractures and granulations. Briefly, the metamorphism has converted carbonaceous matter into graphite .

  10. The Chicxulub crater - impact metamorphism of sulfate and carbonate lithologies

    Science.gov (United States)

    Deutsch, A.; Langenhorst, F.; Hornemann, U.; Ivanov, B. A.

    2003-04-01

    It is discussed whether in the aftermath of the Chicxulub event, impact-released CO_2 and SO_x have changed the Earth's climate, acting also as lethal thread for life. Undoubtedly, vaporization of carbonates and sulfates, which are major target lithologies at the Chicxulub impact site, occurred in the footprint of the projectile. What happened to these lithologies outside this very restricted zone was so far unconstrained. Petrologic observations on PEMEX and UNAM as well as on the CSDP cores allow to set up a general classification for shock-related pro-grade effects on sulfate and carbonate sedimentary rocks. Shock effects in lithic breccias are restricted to brecciation and formation of twins in calcite. Suevites mostly lack melted carbonate clasts; annealing effects in anhydrite fragments are absent. The underlying melt breccias contain anhydrite fragments still displaying a sedimentary texture, and limestone clasts, whose texture reflect crystallization from melt. Impact melt breccias from deeper levels frequently contain partially resorbed anhydrite clasts and a melt matrix with the Ca-rich mineral assemblage quartz + plagioclase + clinopyroxene; this mineral assemblage provides evidence for partial dissociation of CaSO_4. Large clasts of anhydrite consist of equant crystals with 120^o triple junctions, a feature indicative for re-crystallization in the solid state. Tagamites (impact melt rocks) are virtually free of clasts from sedimentary lithologies. These rocks have an extremely high formation temperature, which caused total dissociation of CaSO_4 and CaCO_3. Finally, up to 100 μm wide veins of anhydrite + calcite + quartz cut the matrix of all lithologies except the tagamites. They probably represent "degassing vents". The given scheme is in qualitative accordance with data of shock recovery and annealing experiments as well as with modeling results. In addition, it substantiates that annealing plays a fundamental role in the impact metamorphism of

  11. Cooling history of the Sanbagawa metamorphic belt inferred from fission track zircon ages

    Science.gov (United States)

    Shinjoe, H.; Tagami, T.

    1994-12-01

    The Sanbagawa metamorphic belt in central Shikoku, Japan, is a classic example of a high-pressure, intermediate facies series metamorphic belt. The lowest structural horizon of the Sanbagawa belt exposed in central Shikoku is the Oboke unit and this is overlain by the Besshi unit, which contains high-grade mineral zones. Seven fission track (FT) zircon ages were obtained from five fractions of felsic igneous pebbles in conglomerate, the matrix schist of conglomerate and an intercalated psammitic schist from the Oboke unit. The ages are in the range 56-69 Ma and are younger than 40Ar/ 39Ar ages previously reported from the Oboke unit (70-77 Ma). These concordant grain ages are interpreted as being post-metamorphic cooling ages because the samples analyzed are composed of zircon crystals of igneous and various detrital origins and, therefore, of variable provenance age. The cooling rate of the Oboke unit is less than 8°C/Ma, which is lower than that obtained for the Besshi unit. Our results of FT zircon dating are close to those of the melange zone of the Northern (Cretaceous) Shimanto belt (ca. 65 Ma). This suggests that the underplating of the high-pressure type Sanbagawa metamorphic rock occurred contemporaneously within the same subduction system as the growth of the Shimanto accretionary complex.

  12. Origin and significance of tourmalinites and tourmaline-bearing rocks of Menderes Massif, western Anatolia, Turkey

    OpenAIRE

    Yucel-ozturk, Yesim; Helvaci, Cahit; Palmer, Martin R.; Ersoy, E. Yalcin; Freslon, Nicolas

    2015-01-01

    In the western central portion of Anatolia lies the Menderes Massif – a large metamorphic crystalline complex made of Neoproterozoic to Precambrian basement rocks overlain by Palaeozoic to early Tertiary metasedimentary rocks, and with a multistage metamorphic evolution developed from the late Neo-Proterozoic to Eocene. We have undertaken a study of the petrology, geochemistry and boron isotope composition of these tourmaline occurrences aiming to constrain the processes responsible for the e...

  13. Metamorphic crystallization kinetics quantified through space and time

    Science.gov (United States)

    Kelly, E. D.; Carlson, W. D.; Ketcham, R. A.

    2012-12-01

    Numerical simulations of diffusion-controlled nucleation and growth of garnet porphyroblasts in regionally metamorphosed rocks constrain values for interfacial energy and rates of nucleation and Al intergranular diffusion, quantities that exert a strong control on the sizes and disposition of porphyroblasts in most metamorphic rocks. During simulation of a reaction, product crystals consume a rate-limiting component (Al) and gradients in Al concentration in the intergranular fluid develop between the product and reactant crystals. Low Al concentrations surrounding product crystals (low reaction affinity) reduce nucleation probability, creating a tendency toward spatial ordering of crystal centers in homogeneous portions of a rock. Also, as Al depletion zones impinge, crystals compete for Al, resulting in a tendency toward smaller sizes for neighboring crystals and larger sizes for those that grow in isolation. These phenomena produce distinctive textural effects that allow the simulations to be constrained by measurements of the sizes and locations of porphyroblasts in natural samples. The 13 rocks analyzed in this study were collected from 7 localities exhibiting a diverse range of crystallization conditions. In the simulations, unknown kinetic parameters governing nucleation and intergranular diffusion were adjusted iteratively to achieve fits between simulated and natural porphyroblastic textures. Model fits were assessed primarily from textural characteristics precisely measured by high-resolution X-ray computed tomography. The range of interfacial energies obtained for heterogeneous nucleation is 0.007-0.118 J/m2 for the sample suite, assuming shape factors in the range 0.1-1.0. Nucleation rates change through space and time due to growth and impingement of Al depletion zones. In some modeled rocks, the actual (whole-rock) rate rises steeply, achieves a steady state, and then falls rapidly as reactants are consumed; in others, the steady-state is not achieved

  14. Metamorphic evolution of the contact aureole of the Jhirgadandi ...

    Indian Academy of Sciences (India)

    The metamorphic evolution of the contact aureole around the Late Paleoproterozoic Jhirgadandi pluton in the eastern part of Parsoi Formation of Mahakoshal terrain, central India represents three distinct metamorphic zones, characterized by definite mineral assemblages. The contact-metamorphic event pro- duced the ...

  15. Metamorphic core complex formation by density inversion and lower-crust extrusion.

    Science.gov (United States)

    Martinez, F; Goodliffe, A M; Taylor, B

    2001-06-21

    Metamorphic core complexes are domal uplifts of metamorphic and plutonic rocks bounded by shear zones that separate them from unmetamorphosed cover rocks. Interpretations of how these features form are varied and controversial, and include models involving extension on low-angle normal faults, plutonic intrusions and flexural rotation of initially high-angle normal faults. The D'Entrecasteaux islands of Papua New Guinea are actively forming metamorphic core complexes located within a continental rift that laterally evolves to sea-floor spreading. The continental rifting is recent (since approximately 6 Myr ago), seismogenic and occurring at a rapid rate ( approximately 25 mm yr-1). Here we present evidence-based on isostatic modelling, geological data and heat-flow measurements-that the D'Entrecasteaux core complexes accommodate extension through the vertical extrusion of ductile lower-crust material, driven by a crustal density inversion. Although buoyant extrusion is accentuated in this region by the geological structure present-which consists of dense ophiolite overlaying less-dense continental crust-this mechanism may be generally applicable to regions where thermal expansion lowers crustal density with depth.

  16. The metamorphic basement of the Cordillera Frontal of Mendoza: New geochronologic and isotopic data

    International Nuclear Information System (INIS)

    Basei, Miguel; Ramos, Victor A.; Vujovich, Graciela I.; Poma, Stella

    1998-01-01

    The metamorphic rocks of the Cordillera Frontal exposed in the Cordon del Portillo, Mendoza were examined by Rb/Sr geochronology and Nd/Sm isotopic analysis. The Rb/Sr data defined a Devonian age for the last metamorphic episode, similar to the previous K/Ar and Ar/Ar ages obtained in this region and western Precordillera. The isotopic analysis identified three sets of model ages: 1.- The oldest corresponds to a set of meta sedimentary rocks with a model age of 1,400 to 1,700 Ma; 2.- A monzogranodiorite with a model age of 1,000 Ma; and 3.- Metabasites with model ages between 577 and 330 Ma. These rocks are interpreted as 1.- A typical Grenvillian derived basement; 2.- Late Paleozoic granitoids derived from a different Proterozoic basement; and 3.- Some Eopaleozoic metabasites tectonically inter fingered with the Grenvillian basement. These new data are coherent with the existence of a Laurentia derived terrane, Chilenia, that was separated by oceanic rocks from the basement of Pre cordillera during Eopaleozoic times. This last basement known as the Cuyania terrane, was also derived from Laurentia. (author)

  17. Tectonic origin and deformation process of the Mayer Kangri medium-high pressure metamorphic dome in Central Qiangtang of Tibet

    Science.gov (United States)

    Wang, Y.; Liang, X.

    2016-12-01

    The metamorphic characteristics, deformation process, geochronology of the medium-high pressure metamorphic rocks in blueschist bearing Central Qiangtang Metamorphic belt (CQMB) of Tibet were less well constrained. It is, however, commonly assumed that these rock slices in the margin also contain important implications on the evolution of the entire metamorphic belt. The well-exposed Mayer Kangri medium-high pressure metamorphic dome in north flank of the CQMB provides an unique opportunity to investigate the outer part of the CQMB, which could facilitate the study on the subduction-exhumation-post orogenic scenarios of the Triassic accretionary orogeny in Central Qiangtang. Field structural analyses indicate the Mayer Kangri metamorphic dome are bounded by low-angle normal faults (LANF) within the hanging wall of low-green schist facies mélange. It majorly consists of epidote-amphibolites, quartz-phengite schist, epidote-albite schist. The outcrop and micro structural observations of footwall metamorphic rocks show an open anticline with multiple foliation replacement, which largely differentiate themselves from the dextral strike-slip shearing of the hanging wall. Well-zoned amphiboles were found within the epidote-amphibolite after micro-structural observations and electron probe microanalyses (EPMA), which indicate that the amphibole zonation demonstrates a Hastingsite core, a Ferro-actinolite mantle and a Ferro-winchite rim in most cases. The mean temperature and pressure estimates of the zoned amphibolites change from 544 °, 0.98Gpa in the core, to 426°, 0.34Gpa in the mantle, and to ca.364° and 0.70 GPa in the rim. The detailed analyses on the stepwise-heating Ar-Ar results of the zoned amphiboles provide good constrains on the episodic deformation process of the CQMB. For Hast-cores, we obtained near plateau ages of 242.4-241.2 Ma, indicating the onset of the oceanic subduction is earlier than the Anisian stage of Middle Triassic. The subsequent

  18. Cordilleran metamorphic core complexes and their uranium favorability

    International Nuclear Information System (INIS)

    Coney, P.J.; Reynolds, S.J.

    1980-11-01

    The objective of this report is to provide a descriptive body of knowledge on Cordilleran metamorphic core complexes including their lithologic and structural characteristics, their distribution within the Cordillera, and their evolutionary history and tectonic setting. The occurrence of uranium in the context of possibility for uranium concentration is also examined. This volume contains appendices of the following: annotated bibliography of Cordilleran metamorphic core complexes; annotated bibliography of the uranium favorability of Cordilleran metamorphic core complexes; uranium occurrences in the Cordilleran metamorphic core complex belt; and geology, uranium favorability, uranium occurrences and tectonic maps of individual Cordilleran metamorphic core complexes; and locations, lithologic descriptions, petrographic information and analytical data for geochemical samples

  19. Re-Os geochronology of the Iimori Besshi-type massive sulfide deposit in the Sanbagawa metamorphic belt, Japan

    Science.gov (United States)

    Nozaki, Tatsuo; Kato, Yasuhiro; Suzuki, Katsuhiko

    2010-08-01

    Besshi-type Cu deposits are strata-bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents. Although there are numerous Besshi-type deposits in the Sanbagawa metamorphic belt, Japan, their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints. We report Re-Os data for the Iimori deposit, one of the largest Besshi-type deposits in western Kii Peninsula, in order to examine the robustness of the Re-Os isotope system for dating sulfide minerals in the high-P/T metamorphic belt and to elucidate the primary depositional environment of the Iimori sulfide ores. An 11-point Re-Os isochron plot yields an age of 156.8 ± 3.6 Ma. As this Re-Os isochron age is significantly older than the timing of the Sanbagawa peak metamorphism (110-120 or ˜90 Ma) and a well-defined isochron was obtained, the Re-Os age determined here is most likely the primary depositional age. Despite high-grade metamorphism at up to 520 ± 25 °C and 8-9.5 kbar, the Re-Os isotope system of the Iimori sulfides was not disturbed. Hence, we consider that the whole-rock Re-Os closure temperature for the Iimori sulfide ores was probably higher than 500 °C. As the accretion age of the Sanbagawa metamorphic belt is considered to be 120-130 or 65-90 Ma on the basis of radiolarian and radiometric ages, we estimated the time from the Iimori sulfide deposition on the paleo-seafloor to its accretion at the convergent plate boundary to be greater than 25 Myr. Consequently, the depositional environment of the Iimori sulfide ores was not in the marginal sea, but was truly pelagic.

  20. Uranium deposits in granitic rocks

    International Nuclear Information System (INIS)

    Nishimori, R.K.; Ragland, P.C.; Rogers, J.J.W.; Greenberg, J.K.

    1977-01-01

    This report is a review of published data bearing on the geology and origin of uranium deposits in granitic, pegmatitic and migmatitic rocks with the aim of assisting in the development of predictive criteria for the search for similar deposits in the U.S. Efforts were concentrated on the so-called ''porphyry'' uranium deposits. Two types of uranium deposits are primarily considered: deposits in pegmatites and alaskites in gneiss terrains, and disseminations of uranium in high-level granites. In Chapter 1 of this report, the general data on the distribution of uranium in igneous and metamorphic rocks are reviewed. Chapter 2 contains some comments on the classification of uranium deposits associated with igneous rocks and a summary of the main features of the geology of uranium deposits in granites. General concepts of the behavior of uranium in granites during crustal evolution are reviewed in Chapter 3. Also included is a discussion of the relationship of uranium mineralization in granites to the general evolution of mobile belts, plus the influence of magmatic and post-magmatic processes on the distribution of uranium in igneous rocks and related ore deposits. Chapter 4 relates the results of experimental studies on the crystallization of granites to some of the geologic features of uranium deposits in pegmatites and alaskites in high-grade metamorphic terrains. Potential or favorable areas for igneous uranium deposits in the U.S.A. are delineated in Chapter 5. Data on the geology of specific uranium deposits in granitic rocks are contained in Appendix 1. A compilation of igneous rock formations containing greater than 10 ppM uranium is included in Appendix 2. Appendix 3 is a report on the results of a visit to the Roessing area. Appendix 4 is a report on a field excursion to eastern Canada

  1. Rock fragmentation

    Energy Technology Data Exchange (ETDEWEB)

    Brown, W.S.; Green, S.J.; Hakala, W.W.; Hustrulid, W.A.; Maurer, W.C. (eds.)

    1976-01-01

    Experts in rock mechanics, mining, excavation, drilling, tunneling and use of underground space met to discuss the relative merits of a wide variety of rock fragmentation schemes. Information is presented on novel rock fracturing techniques; tunneling using electron beams, thermocorer, electric spark drills, water jets, and diamond drills; and rock fracturing research needs for mining and underground construction. (LCL)

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

    International Nuclear Information System (INIS)

    Eglinger, Aurelien

    2013-01-01

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

  3. Shape Metamorphism Using p-Laplacian Equation

    Energy Technology Data Exchange (ETDEWEB)

    Cong, Ge; Esser, Mehmet; Parvin, Bahram; Bebis, George

    2004-05-19

    We present a new approach for shape metamorphism, which is a process of gradually changing a source shape (known) through intermediate shapes (unknown) into a target shape (known). The problem, when represented with implicit scalar function, is under-constrained, and regularization is needed. Using the p-Laplacian equation (PLE), we generalize a series of regularization terms based on the gradient of the implicit function, and we show that the present methods lack additional constraints for a more stable solution. The novelty of our approach is in the deployment of a new regularization term when p --> infinity which leads to the infinite Laplacian equation (ILE). We show that ILE minimizes the supremum of the gradient and prove that it is optimal for metamorphism since intermediate solutions are equally distributed along their normal direction. Applications of the proposed algorithm for 2D and 3D objects are demonstrated.

  4. Growing Languages with Metamorphic Syntax Macros

    DEFF Research Database (Denmark)

    Brabrand, Claus; Schwartzbach, Michael Ignatieff

    2002-01-01

    "From now on, a main goal in designing a language should be to plan for growth." Guy Steele: Growing a Language, OOPSLA '98 invited talk.We present our experiences with a syntax macro language which we claim forms a general abstraction mechanism for growing (domain-specific) extensions of program......"From now on, a main goal in designing a language should be to plan for growth." Guy Steele: Growing a Language, OOPSLA '98 invited talk.We present our experiences with a syntax macro language which we claim forms a general abstraction mechanism for growing (domain-specific) extensions...... of programming languages. Our syntax macro language is designed to guarantee type safety and termination.A concept of metamorphisms allows the arguments of a macro to be inductively defined in a meta level grammar and morphed into the host language. We also show how the metamorphisms can be made to operate...

  5. The behaviour of monazite from greenschist facies phyllites to anatectic gneisses: An example from the Chugach Metamorphic Complex, southern Alaska

    Science.gov (United States)

    Gasser, Deta; Bruand, Emilie; Rubatto, Daniela; Stüwe, Kurt

    2012-03-01

    Monazite is a common accessory mineral in various metamorphic and magmatic rocks, and is widely used for U-Pb geochronology. However, linking monazite U-Pb ages with the PT evolution of the rock is not always straightforward. We investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses, which is exposed in the Eocene Chugach Metamorphic Complex of southern Alaska. We investigated textures, chemical compositions and U-Pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade, with particular focus on the relationship between monazite and other REE-bearing minerals such as allanite and xenotime. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. In lower amphibolites facies schists (~ 550-650 °C and ≥ 3.4 kbar), small, medium-Y monazite is wide-spread (Mnz1), indicating monazite growth prior and/or simultaneous with growth of garnet and andalusite. In anatectic gneisses, new low-Y, high-Th monazite (Mnz2) crystallised from partial melts, and a third, high-Y, low-Th monazite generation (Mnz3) formed during initial cooling and garnet resorption. U-Pb SHRIMP analysis of the second and third monazite generations yields ages of ~ 55-50 Ma. Monazite became unstable and was overgrown by allanite and/or allanite/epidote/apatite coronas within retrograde muscovite- and/or chlorite-bearing shear zones. This study documents polyphase, complex monazite growth and dissolution during a single, relatively short-lived metamorphic cycle.

  6. Water level fluctuations due to earth tides in a well pumping from slightly fractured crystalline rock

    International Nuclear Information System (INIS)

    Marine, I.W.

    1975-01-01

    J At the Savannah River plant of the Atomic Energy Commission near Aiken, South Carolina, there are three distinct groundwater systems: the coastal plain sediments, the crystalline metamorphic rocks, and a buried Triassic basin. The coastal plain sediments include several Cretaceous and Tertiary granular aquifers and aquicludes, the total thickness being about 305 m. Below these sediments, water occurs in small fractures in crystalline metamorphic rock (hornblende schist and gneiss with lesser amounts of quartzite). Water level fluctuations due to earth tides are recorded in the crystalline metamorphic rock system and in the coastal plain sediments. No water level fluctuations due to earth tides have been observed in wells in the Triassic rock because of the very low permeability. The water level fluctuations due to earth tides in the crystalline rock are about 10 cm, and those in the sediments are about 1.8 cm. The use of water level fluctuations due to earth tides to calculate porosity appears to present practical difficulties both in the crystalline metamorphic rock system and in the coastal plain sediments. In a 1-yr pumping test on a well in the crystalline metamorphic rock the flow was controlled to within 0.1 percent of the total discharge, which was 0.94 1/s. The water level fluctuations due to earth tides in the pumping well were 10 cm, the same as when this well was not being pumped. (U.S.)

  7. Geometric description and analysis of metamorphic tectonites (Pelagonian Zone, Internal Hellenides, Northern Greece)

    Science.gov (United States)

    Diamantopoulos, A.

    2009-04-01

    An assortment of alpine and pre-Permian metamorphic tectonites, belonging to the Pelagonian Zone of the Internal Hellenides, are analyzed from Askion, Vernon and Vorras mountains. They in fact compose the Upper plate of the Western Macedonia core complex, overlying Late Tertiary high-P rocks through large-scale detachment fautls (Diamantopoulos et al. 2007). This work wants to determine the architecture and the kinematic path of rocks in a 3D assumption. Field analysis concludes: a) Meta-sedimentary lithologies and amphibolites, meta-igneous lithologies, granitoid mylonites composed of augen fieldspar gneisses, Permo-Triassic fossiliferous rocks, meta-carbonates of Triassic-Jurassic age, a Jurassic mélange including meta-sedimentary lithologies, serpentinites and carbonate tectonic blocks, Mesozoic Ophiolites, Cretaceous limestones and conglomerates as well as flysch sediments compose the architecture of the study area, b) Multiple high and low-angle cataclastic zones of intense non-coaxial strain separate distinct pre-Permian lithologies, alpine from pre-alpine rocks, Triassic-Jurassic rocks from Permo-Triassic rocks, Jurassic mélange from flysch sediments, Jurassic mélange from Triassic-Jurassic rocks, Cretaceous rocks from the Jurassic mélange, Cretaceous limestones from flysch lithologies and Cretaceous rocks from serpentinites, c) Geometric analysis and description of asymmetric structures found in fault cores, damage zones and in the footwall-related rocks showed a prominent kinematic direction towards WSW in low-T conditions affected all the rock lithologies, d) Multiple S- and L- shape fabric elements in the pre-Permian and Permo-Triassic rocks appear an intricate orientation, produced by intense non-coaxial syn-metamorphic deformation, e) Sheath and isoclinal folds oriented parallel to the L-shape fabric elements as well as a major S-shape fabric element, producing macroscopic fold-like structures compose the main syn-metamorphic fabric elements in the

  8. A system of nomenclature for rocks in Olkiluoto

    International Nuclear Information System (INIS)

    Mattila, J.

    2006-06-01

    Due to international interest in the Finnish deep repository project at Olkiluoto (SW Finland) and the need for collaboration between scientists involved in site investigations for the disposal of spent nuclear fuel in other countries, a well-documented system of rock nomenclature is required, based on existing classification schemes and international recommendations. The BGS (British Geological Survey) rock classification scheme is the most comprehensive rock classification scheme and the basic principles behind it are utilised for the system of nomenclature for rocks in Olkiluoto. The BGS classification system is based on the use of descriptive names and a clear hierarchy, making it possible to classify rocks at different levels depending on the specific goals of the study, the level of available information, and the expertise of the user. Each rock type is assigned a root name, which is based on structural and textural characteristics or modal compositions of the rock and the root names are refined with qualifier terms as prefixes. Qualifier terms refer to the structure or modal composition of the rock. The bedrock at the Olkiluoto site consists of metamorphic and igneous rocks. The metamorphic rocks consist of migmatitic gneisses and (non-migmatitic) gneisses, which are further divided according to their structural characteristics and modal compositions, the former into stromatic, veined, diatexitic gneisses, the latter into mica, quartz, mafic and TGG gneisses. Igneous rocks consist of pegmatitic granites, K-feldspar porphyry and diabases. (orig.)

  9. The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

    Science.gov (United States)

    Slotznick, Sarah P.; Eiler, John M.; Fischer, Woodward W.

    2018-03-01

    As the most abundant transition metal in the Earth's crust, iron is a key player in the planetary redox budget. Observations of iron minerals in the sedimentary record have been used to describe atmospheric and aqueous redox environments over the evolution of our planet; the most common method applied is iron speciation, a geochemical sequential extraction method in which proportions of different iron minerals are compared to calibrations from modern sediments to determine water-column redox state. Less is known about how this proxy records information through post-depositional processes, including diagenesis and metamorphism. To get insight into this, we examined how the iron mineral groups/pools (silicates, oxides, sulfides, etc.) and paleoredox proxy interpretations can be affected by known metamorphic processes. Well-known metamorphic reactions occurring in sub-chlorite to kyanite rocks are able to move iron between different iron pools along a range of proxy vectors, potentially affecting paleoredox results. To quantify the effect strength of these reactions, we examined mineralogical and geochemical data from two classic localities where Silurian-Devonian shales, sandstones, and carbonates deposited in a marine sedimentary basin with oxygenated seawater (based on global and local biological constraints) have been regionally metamorphosed from lower-greenschist facies to granulite facies: Waits River and Gile Mountain Formations, Vermont, USA and the Waterville and Sangerville-Vassalboro Formations, Maine, USA. Plotting iron speciation ratios determined for samples from these localities revealed apparent paleoredox conditions of the depositional water column spanning the entire range from oxic to ferruginous (anoxic) to euxinic (anoxic and sulfidic). Pyrrhotite formation in samples highlighted problems within the proxy as iron pool assignment required assumptions about metamorphic reactions and pyrrhotite's identification depended on the extraction techniques

  10. Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow

    Science.gov (United States)

    Plümper, Oliver; Botan, Alexandru; Los, Catharina; Liu, Yang; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2017-09-01

    The transport of fluids through the Earth's crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self-generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth's crust, electrokinetic transport through reaction-induced nanopores (mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena.

  11. K-Ar geochronologic evidence for a triassic metamorphic event in the main Chiloe Island, south-central Chile

    International Nuclear Information System (INIS)

    Duhart, P.; Munoz, J

    2001-01-01

    Pioneers geological reconnaissance studies in the Chiloe Archipelago recognised a Palaeozoic metamorphic basement (Saliot, 1969; Watters and Fleming, 1972; Valenzuela, 1982; Valdivia, 1986). Currently in progress geologic studies (Munoz et al., 1999, Duhart et al., 2000; Antinao et al., 2000) interpreted these rocks as part of the Bahia Mansa Metamorphic Complex (Duhart et al., 2000), well exposed to the north and equivalent to the 'Serie Occidental' (Aguirre et al., 1972). Geochronologic data set indicate that this complex evolved during Devonian to Triassic times. In the main Chiloe Island, this metamorphic complex is mainly conform by metasedimentary and metavolcanic rocks covered by Tertiary sedimentary and volcanic rocks and Quaternary glacial, fluvial, estuarine, beach, eolian and fluvial deposits. According to north-west and north-south lineament observed in satellite images, regional magnetic maps and topographic features, the main Chiloe island have been divide in northern, central and southern segments (Munoz et al., 1999). These lineaments are interpreted as regional faults but their ages and cinematic are not well constrained. The central segment was interpreted as an uplifted tectonic block and recent studies in the northern part of this segment have identified an intrusive body herein named as 'Metalqui Pluton'. Although the age of this pluton is unknown yet, Cretaceous intrusive rocks in the same tectonic setting of the Metalqui Pluton have been reported in the Valdivia area (Munizaga et al., 1988; Duhart et al., 1998). Previous U-Pb radiometric ages for detrital zircons from pelitic schists in the northern segment indicated a maximum sediment deposition age during Early to Middle Devonian (Duhart et al., 1999). Also, Triassic K-Ar and 40 Ar/ 39 Ar ages have been determined for the main metamorphic and tectonic event. This contribution report Triassic K-Ar ages for the central segment and discuss their regional significance (au)

  12. Preliminary radiometric analyses of zircons from the Mount Copeland syenite gneiss, Shuswap metamorphic complex, British Columbia

    International Nuclear Information System (INIS)

    Okulitch, A.V.; Laveridge, W.D.; Sullivan, R.W.

    1981-01-01

    The isotopic ratios resulting from Pb and U analyses on three zircon fractions from syenite gneiss intrusive into metasediments of the Shuswap Metamorphic Complex are collinear on a concordia plot and yield upper and lower intercepts of about 773 Ma and 70 Ma. The upper intercept is tentatively interpreted as the minimum age of emplacement. The lower intercept is suggested to be the time of uplift and cooling associated with tectonic denudation of the Shuswap Complex. The implied age of the country rocks is pre-late Proterozoic and they may be correlatives of the Purcell Supergroup. (auth)

  13. Nanodiamond Formation at the Lithogenesis and Low-Stages of Regional Metamorphism

    Science.gov (United States)

    Simakov, S. K.; Melnik, N. N.; Vyalov, V. I.

    2018-02-01

    Samples of gilsonite from Adzharia, anthraxolite and graphite of coal from Taimyr, shungite from Karelia, and anthracite from Donbass are studied using Raman spectroscopy. Peaks at 1600 cm-1, indicating the presence of nanographite, are recorded in all samples. The anthracite sample from Donbass, 1330 cm-1, corresponds to the sp 3-line of carbon hybridization conforming to a nanodiamond. It is concluded that in nature diamonds can be formed at late stages of lithogenesis (catagensis, metagenesis), and for coals, it can occur at the zeolite stage of regional metamorphism of rocks, before the green schist stage.

  14. Science Rocks!

    Science.gov (United States)

    Prestwich, Dorothy; Sumrall, Joseph; Chessin, Debby A.

    2010-01-01

    It all began one Monday morning. Raymond could not wait to come to large group. In his hand, he held a chunk of white granite he had found. "Look at my beautiful rock!" he cried. The rock was passed around and examined by each student. "I wonder how rocks are made?" wondered one student. "Where do they come from?"…

  15. Role of fluids in the metamorphism of the Alpine Fault Zone, New Zealand

    International Nuclear Information System (INIS)

    Vry, J.K.; Storkey, A.C.; Harris, C.

    1999-01-01

    Full text: Models of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole-rock δD values (δD WR = -56 to -30 per mill, average -45 per mill, n 20), irrespective of rock type, degree of chloritisation, location along the fault, or across-strike distance from the fault in the garnet zone. The green, chlorite-rich fault rocks, which probably formed from Australian Plate precursors, record nearly-isothermal fluid/rock interaction with a greyschist-derived metamorphic fluid at high temperatures, near 450-500 deg C. δD of water in equilibrium with the green fault rocks (δD H20,green ) is 18 per mill; δD of water in equilibrium with the greyschists and greyschist-derived mylonites (δD H20, grey ) is 19 per mill at 500 deg C δD H20, green is -17 per mill; δD H20,grey is -14 per mill at 450 deg C. There is no indication of an influx of a meteoric or mantle-derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late-stage retrogression or veining, which might be attributed to down-temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that, in some regions, rise vertically rather than following the trace of the Alpine Fault up to the surface, due to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle-ductile transition. Such fluids could mix with meteoric fluids to deposit quartz-rich, possibly gold-bearing veins in the region - 5-10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) program. Copyright (1999) Geological

  16. The role of evaporites in the formation of gems during metamorphism of carbonate platforms: a review

    Science.gov (United States)

    Giuliani, Gaston; Dubessy, Jean; Ohnenstetter, Daniel; Banks, David; Branquet, Yannick; Feneyrol, Julien; Fallick, Anthony E.; Martelat, Jean-Emmanuel

    2018-01-01

    The mineral and fluid inclusions trapped by gemstones during the metamorphism of carbonate platform successions are precious markers for the understanding of gem genesis. The nature and chemical composition of inclusions highlight the major contribution of evaporites through dissolution or fusion, depending on the temperature of formation from greenschist to granulite facies. The fluids are highly saline NaCl-brines circulating either in an open system in the greenschist facies (Colombian and Afghan emeralds) and with huge fluid-rock metasomatic interactions, or sulphurous fluids (ruby, garnet tsavorite, zoisite tanzanite and lapis-lazuli) or molten salts formed in a closed system with a low fluid mobility (ruby in marble) in the conditions of the amphibolite to granulite facies. These chloride-fluoride-sulphate ± carbonate-rich fluids scavenged the metals essential for gem formation. At high temperature, the anions SO4 2-, NO3 -, BO3 - and F- are powerful fluxes which lower the temperature of chloride- and fluoride-rich ionic liquids. They provided transport over a very short distance of aluminium and/or silica and transition metals which are necessary for gem growth. In summary, the genetic models proposed for these high-value and ornamental gems underline the importance of the metamorphism of evaporites formed on continental carbonate shelves and emphasise the chemical power accompanying metamorphism at moderate to high temperatures of evaporite-rich and organic matter-rich protoliths to form gem minerals.

  17. Ostwald ripening of clays and metamorphic minerals

    Science.gov (United States)

    Eberl, D.D.; Srodon, J.; Kralik, M.; Taylor, B.E.; Peterman, Z.E.

    1990-01-01

    Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

  18. The Chinese Continental Drilling Program: Geochemical and Isotopic (O, Sr, Nd, Pb), Investigations on a Vertical Sequence of UHP metamorphism

    Science.gov (United States)

    Hoefs, J.; Xiao, Y.; Zhang, Z.; Romer, R. L.

    2004-12-01

    Various UHP metamorphic rocks - orthogneiss, paragneiss, eclogite, amphibolite, ultra-mafic rocks, and rare schist and quartzite - have been drilled within the main hole of the Chinese Continental Drilling Program (CCSD) in Donghai, Sulu. Petrographic studies indicate that all the rocks have been subjected to UHP metamorphism. R-mode factor analysis vs. depth, combined with rock associations and lithologies, indicate that the 2050-m-thick slab can be divided into 6 units in order of increasing depth. Geochemical characteristics of eclogites from different units suggest that their protoliths may be of diverse origins: eclogites from unit 1(0-530m) are probably of cumulate origin being similar to Bixiling and Maowu in Dabie Shan; the protolith of the eclogite from unit 2 (530-600m) is a Fe-Ti-rich gabbroic rock-body, whereas that of the eclogite within ultramafic rocks from unit 3 (600-690m) is of mantle origin; eclogites fom unit 4 (690-1160m) and unit 6 (1600-2050m) that interlayered with paragneiss are metamorphic supracrustal rocks. Geochemical characteristics of orthogneiss (unit 5, 1160-1600m) and paragneiss suggest that their protoliths are probably of granitic and of supracrustal sedimentary origins, respectively. Oxygen isotope data indicate that eclogites and gneiss from depths above 1600m of the main hole have depleted bulk d18O values of -5.3 to 4.5%, indicating significant meteoric water/rock interaction; by contrast, samples from depths between 1600-2050m show bulk d18O values greater than 5.8%, without any indication of a meteoric water/rock interaction. This suggests an "in situ" origin and structural coherence throughout subduction and exhumation. The lowest d18O values occur at depths of 1100-1200m, which corresponds to the boundary between eclogites and the about 400m-thick ortho- (granitic) gneiss layer (boundary between unit 4 and unit 5; this implies that the intrusion of the granitic body could be a heat source for initiating meteoric water/rock

  19. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    OpenAIRE

    Del Real, PG; Maher, K; Kluge, T; Bird, DK; Brown, GE; John, CM

    2016-01-01

    Magnesium carbonate minerals produced by reaction of H2O?CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic metho...

  20. Petrochemistry And Tectonic Setting Of Metabasic Rocks Of Isanlu ...

    African Journals Online (AJOL)

    The rock reveals a mid-amphibolite facies assemblage of hornblende (magnesio and pargasitic compositions), plagioclase (oligoclase – labradorite) with small amounts of quartz and biotite. Locally, this assemblage has suffered retrogression into the greenschist facies and preserve the metamorphic assemblage actinolite ...

  1. Lead isotopes in rocks of granulitic belt of the Kola Peninsula

    Energy Technology Data Exchange (ETDEWEB)

    Zykov, S.I.; Stupnikova, N.I.; Sidorenko, S.A.

    1984-01-01

    From the data on lead isotopes in eclogites of granulitic rocks of the Kola Peninsula Salnye tundras a multistage development of rocks is shown and the age of metamorphism granulitic facies is determined. Results of lead isotope dating have shown that, in all probability the time of metamorphism manifestation corresponds to 2780+-150 mln. years and granulitic rocks are the products of polymetamorphism which have endured metamorphic transformations 1800 mln. years ago. Besides, a supposition is made on a possible age of initial ancient rocks within 3700-4100 mln. years. In interpreting the isotopic dating data the dependence expressing variation in the /sup 207/Pb//sup 204/Pb ratio versus the values of /sup 208/Pb//sup 204/Pb and /sup 232/Th//sup 238/U ratios has been used.

  2. Multiple tectonic mode switches indicate short-duration heat pulses in a Mio-Pliocene metamorphic core complex, West Papua, Indonesia

    Science.gov (United States)

    White, L. T.; Hall, R.; Gunawan, I.

    2017-12-01

    The Wandaman Peninsula is a narrow (2 km) promontory in remote western New Guinea. The peninsula is almost entirely composed of medium- to high-grade metamorphic rocks considered to be associated with a Mio-Pliocene metamorphic core complex. Previous work has shown that the uplift and exhumation of the core complex has potentially brought some extremely young eclogite to the surface. These might be comparable to the world's youngest (4.3 Ma) eclogites found in the D'Entrecasteaux Islands at the opposite end of New Guinea. We show that tectonic history of this region is complex. This is because the metamorphic sequences in the Wandaman Peninsula record multiple phases of deformation, all within the last few million years. This is demonstrated through methodical collation of cross-cutting relations from field and microstructural studies across the peninsula. The first phase of deformation and metamorphism is associated with crustal extension and partial melting that took place at 5-7 Ma according to new U-Pb data from metamorphic zircons. This extensional phase ceased after a tectonic mode switch and the region was shortened. This is demonstrated by two phases of folding (1. recumbent and 2. open) that overprint the earlier extensional fabrics. All previous structures were later overprinted by brittle extensional faults and uplift. This extensional phase is still taking place today, as is indicated by submerged forests exposed along the coastline associated with recent earthquakes and hot springs. The sequence of metamorphic rocks that are exposed in the Wandaman Peninsula show that stress and thermal conditions can change rapidly. If we consider that the present is a key to the past, then such results can identify the duration of deformation and metamorphic events more accurately than in much older orogenic systems.

  3. Metamorphism, P-T-t Conditions of Formation, and Prospects for the Practical Use of Al2SiO5 Polymorphs, Chloritoid, and Staurolite (Yenisei Ridge)

    Science.gov (United States)

    Kozlov, P. S.

    2017-12-01

    The Yenisei Ridge is an accretion–collisional orogen located in the southwestern frame of the Siberian Craton in the interfluve between Podkamennaya Tunguska, Angara, Kan, and Yenisei rivers. The Precambrian mono- and polymetamorphic complexes composed predominantly of the Mesoarchean–Neoproterozoic metapelitic rocks have been studied. Based on the typification of metamorphic complexes by pressure, temperature, metamorphic gradient, as well as age of metamorphism, the location scheme of the fields of the Precambrian sedimentary–metamorphic rock which are prospective for searching deposits of high-alumina metamorphic minerals (andalusite, kyanite, and sillimanite, chloritoid, and staurolite) in the Trans-Angara segment of the Yenisei Region, was compiled. The Teya sillimanite and Panimbinsk andalusite deposits, which are confined to the fields of regional metamorphic complexes of iron-alumina metapelites of the And–Sill facies series, are recommended as a priority for the organization of prospecting works and the subsequent involvement to the metallurgical industry. These metapelites are classified as monomineral. Owing to widespread occurrence and abundance of andalusite and sillimanite, the above deposits have significant inferred resources. Stratiform deposits of garnet–staurolite and chloritoid high-alumina rocks are still insufficiently studied and should be investigated further. The prospects for the possible use of high-alumina andalusite and sillimanite together with Middle Tatarka and Kiya nepheline syenite massifs and the bauxites of the Chadobets uplift, already being explored in the region, for production of aluminum oxide, silumin, and aluminum, as well as, the prospects for the expansion of the raw material base of the Boguchansk Electrometallurgical Complex, brought into operation in 2016 in the Lower Angara region, are considered.

  4. Mapping contact metamorphic aureoles in Extremadura, Spain, using Landsat thematic mapper images

    Science.gov (United States)

    Rowan, L.C.; Anton-Pacheco, C.; Brickey, D.W.; Kingston, M.J.; Payas, A.

    1987-01-01

    In the Extremadura region of western Spain, Ag, Pb, Zn, and Sn deposits occur in the pieces of late Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke that have been regionally metamorphosed to the green schist facies. The plutons generally are well exposed and have distinctive geomorphological expression and vegetation; poor exposures of the metasedimentary host rocks and extensive cultivation, however, make delineation of the contact aureoles difficult. Landsat Thematic Mapper (TM) images have been used to distinguish soil developed on the contact metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are similar, except that muscovite is more common in the contact metamorphic soil; carbonaceous material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 1.6-micrometers wavelength region (TM 5), and weaker Al-OH, Mg-OH, and Fe3+ absorption features than do spectra of the slate-metagraywacke soil. The low-reflectance and subdued absorption features exhibited by the contact metamorphic soil spectra are attributed to the high absorption coefficient f the carbonaceous material caused by heating during emplacement of the granitic plutons. These spectral differences are evident in a TM 4/3, 4/5, 3/1 color-composite image. Initially, this image was used to outline the contact aureoles, but digital classification of the TM data was necessary for generating internally consistent maps of the distribution of the exposed contact metamorphic soil. In an August 1984, TM scene of the Caceras area, the plowed, vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of TM 4/5 and 3/1 values were determine for selected plower fields within and outside the contact aureoles; TM 5 produced results similar to TM 4/5. Field evaluation, supported by X-ray diffraction and petrographic

  5. Investigating the response of biotite to impact metamorphism: Examples from the Steen River impact structure, Canada

    Science.gov (United States)

    Walton, E. L.; Sharp, T. G.; Hu, J.; Tschauner, O.

    2018-01-01

    Impact metamorphic effects from quartz and feldspar and to a lesser extent olivine and pyroxene have been studied in detail. Comparatively, studies documenting shock effects in other minerals, such as double chain inosilicates, phyllosilicates, carbonates, and sulfates, are lacking. In this study, we investigate impact metamorphism recorded in crystalline basement rocks from the Steen River impact structure (SRIS), a 25 km diameter complex crater in NW Alberta, Canada. An array of advanced analytical techniques was used to characterize the breakdown of biotite in two distinct settings: along the margins of localized regions of shock melting and within granitic target rocks entrained as clasts in a breccia. In response to elevated temperature gradients along shock vein margins, biotite transformed at high pressure to an almandine-Ca/Fe majorite-rich garnet with a density of 4.2 g cm-3. The shock-produced garnets are poikilitic, with oxide and silicate glass inclusions. Areas interstitial to garnets are vesiculated, in support of models for the formation of shock veins via oscillatory slip, with deformation continuing during pressure release. Biotite within granitic clasts entrained within the hot breccia matrix thermally decomposed at ambient pressure to produce a fine-grained mineral assemblage of orthopyroxene + sanidine + titanomagnetite. These minerals are aligned to the (001) cleavage plane of the original crystal. In this and previous work, the transformation of an inosilicate (pargasite) and a phyllosilicate (biotite) to form garnet, an easily identifiable, robust mineral, has been documented. We contend that in deeply eroded astroblemes, high-pressure minerals that form within or in the environs of shock veins may serve as one of the possibly few surviving indicators of impact metamorphism.

  6. Extensional ductile tectonics of the Sioule metamorphic series (Variscan French Massif Central)

    Science.gov (United States)

    Faure, M.; Grolier, J.; Pons, J.

    1993-09-01

    In the Northern part of the Variscan French Massif Central, the Sioule series, from top to bottom, consists of a pre-Viséan granite, migmatite, gneiss and mica schist. Two ductile deformations have been recognized. The earlier phase is characterized by a north-east-south-west trending stretching lineation; the second phase, characterized by a north-west-south-east trending mineral, stretching and crenulation lineation, is better marked in the lower mica schist part than in the upper granito-gneissic part. This second phase occurred during retrogression of the metamorphic rocks; related shear criteria indicate a top to the south-west shear. The Namurian-Westphalian magmatic bodies such as the Echassières leucogranite, Pouzol-Servant microgranite and numerous north-east -south-west trending microgranite dykes are emplaced in extensional fractures related to the same north-west-south-east maximum stretching direction. The asymmetrical shapes of the two granitic massifs indicate that they intruded towards the south-east. The synkinematic retrogression of the metamorphic rocks, the shape of the magmatic bodies and a re-examination of the numerous available data support the interpretation that the deformation is due to the extensional tectonic regime related to the Variscan crustal re-quilibration. This interpretation is in agreement with the correlation of the Sioule series with the Chavanon series. The two series belong to a unique tectono-metamorphic unit left-laterally offset by the Stephanian motion of the Sillon Houiller fault. This study also shows that the Sillon Houiller did not play a significant part during the Namurian-Westphalian extensional tectonics of the Massif Central.

  7. Telescoping metamorphic isograds: Evidence from 40Ar/39A dating in the Orange-Milford belt, southern Connecticut

    Science.gov (United States)

    Kunk, Michael J.; Walsh, Gregory J.; Growdon, Martha L.; Wintsch, Robert P.

    2013-01-01

    New 40Ar/39Ar ages for hornblende and muscovite from the Orange-Milford belt in southern Connecticut reflect cooling from Acadian amphibolite facies metamorphism between ∼380 to 360 Ma followed by retrograde recrystallization of fabric-forming muscovite and chlorite during lower greenschist facies Alleghanian transpression at ∼280 Ma. Reported field temperature and pressure gradients are improbably high for these rocks and a NW metamorphic field gradient climbing from chlorite-grade to staurolite-grade occurs over less than 5 km. Simple tilting cannot account for this compressed isograd spacing given the geothermal gradient of ∼20 °C/km present at the time of regional metamorphism. However, post-metamorphic transpression could effectively telescope the isograds by stretching the belt at an oblique angle to the isograd traces. Textures in the field and in thin section reveal several older prograde schistosities overprinted by lower greenschist facies fabrics. The late cleavages commonly occur at the scale of ∼100 μm and these samples contain multiple age populations of white mica. 40Ar/39Ar analysis of these poly-metamorphic samples with mixed muscovite populations yield climbing or U-shaped age spectra. The ages of the low temperature steps are late Paleozoic, while the ages of the older steps are late Devonian. These results support our petrologic interpretation that the younger cleavage developed under metamorphic conditions below the closure temperature for Ar diffusion in muscovite, that is, in the lower greenschist facies. The correlation of a younger regionally reproducible age population with a pervasive retrograde muscovite ± chlorite cleavage reveals an Alleghanian (∼280 Ma) overprint on the Acadian metamorphic gradient (∼380 Ma). Outcrop-scale structures including drag folds and imbricate boudins suggest that Alleghanian deformation and cleavage development occurred in response to dextral transpression along a northeast striking boundary

  8. Prograde and retrograde metamorphic processes in high-pressure subduction zone serpentinites from East Thessaly, Greece

    Science.gov (United States)

    Koutsovitis, Petros

    2016-04-01

    The East Thessaly region, Central Greece, includes metaophiolitic mélange formations which extend from the eastern foothills of Mt. Olympus and Ossa, throughout the Agia basin, Mt. Mavrovouni (Sklithro region), South Pelion and reaching up to northeast Othris (regions of Aerino and Velestino). They appear in the form of dispersed and deformed thrust sheets having been variably emplaced onto Mesozoic platform series rocks of the Pelagonian tectonostratigraphic zone[1]. These formations consist mainly of serpentinites, as well as metasediments, metagabbros, metadolerites, rodingites, ophicalcites, talc-schists and chromitites. Based upon petrographic observations, mineral chemistry data and XRD patterns, the subduction zone-related serpentinites from the regions of Potamia, Anavra, Aetolofos and Kalochori-Chasanbali (Agia basin), as well as from the regions of Aerino and Velestino, are characterized by the progressive transformation of lizardite to antigorite and are distinguished into two groups. The first group includes serpentinites from the metaophiolitic formations of Potamia, Anavra, Aerino and Velestino, which are marked by destibillization of lizardite to antigorite, mostly along the grain boundaries of the lizardite mesh textured relics. The presence of lizardite and antigorite in almost equal amounts indicates medium-temperature blueschist facies metamorphic conditions (˜340-370 ° C; P≈10-11 kbar)[2,3,4]. The second serpentinite group appears in the regions of Aetolofos and Kalochori, characterized by the predominance of antigorite, the minor occurrence of lizardite and the complete replacement of spinel by Cr-magnetite. The absence of metamorphic olivine suggests that these serpentinites were most likely formed at slightly higher temperature and pressure conditions compared to the first serpentinite group, corresponding to medium or high temperature blueschist facies metamorphism (˜360-380 ° C; P≈12 kbar)[2,3,4]. These metamorphic conditions are

  9. Metamorphic and Ar/Ar geochronology constraints on the Alakeci shear zone: Implications for the extensional exhumation history of the northern Kazdag Massif, NW Turkey

    International Nuclear Information System (INIS)

    Bonev, N; Beccaletto, L; Robyr, M; Monie, P

    2008-01-01

    The Kazdag Massif exposes a metamorphic dome in the Biga Peninsula of northwest Turkey. An extensional origin has been proposed for the dome, limited on both flanks by detachments and/or shear zones. The northern flank is bounded by the extensional Alakeci Shear Zone (ASZ), whose P-T-t path is still poorly known. We therefore focus on its metamorphic conditions and related temporal history to precise its tectono-metamorphic evolution. The local tectonostratigraphy in structurally ascending order comprises: (i) the high-grade metamorphic core rocks of the Kazdag Massif (gneisses and micaschists intercalated with amphibolites and marbles); (ii) the two kilometer-thick ASZ; (iii) the overlaying unmetamorphosed pre-Cenomanian accretionary Cetmi melange; and (iv) Neogene sedimentary and volcanic cover rocks. ASZ mylonites were derived from both the core rocks and the melange lithologies. From the north to the south the mylonitic fabrics in the ASZ depict a top-to-the N-NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdag Massif. The northward transition from ductile to brittle-ductile regime through the ASZ shows that the deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium within the mylonitic gneisses and schists contains Qtz + Fs + Ms + Bt + Grt ± St ± Sill, with late retrogressive chlorite after biotite and garnet. Four samples of ASZ rocks yielded pressures between 6.9-5.7 kbar and temperatures between 706-587 deg. C. Three samples from the mylonitic rocks supplied in situ isochron 36 Ar/ 40 Ar mica ages between 31.2-24.2 Ma, which we interpret to date the cooling of the mylonites following the P-T decrease across the ASZ. The metamorphic and structural results support the extensional character of the ASZ, and sketch transition from

  10. Recreating Rocks

    DEFF Research Database (Denmark)

    Posth, Nicole R

    2008-01-01

    Nicole Posth and colleagues spent a month touring South African rock formations in their quest to understand the origin of ancient iron and silicate layers.......Nicole Posth and colleagues spent a month touring South African rock formations in their quest to understand the origin of ancient iron and silicate layers....

  11. The timing of the tectono-metamorphic evolution at the Neoproterozoic-Phanerozoic boundary in central southern Madagascar

    DEFF Research Database (Denmark)

    Giese, Jörg; Berger, Alfons; Schreurs, Guido

    2011-01-01

    In central southern Madagascar the crystalline basement is composed of mid-crustal rocks which have experienced polycyclic deformation and metamorphism coupled with repeated granitoid magmatism at the Neoproterozoic–Phanerozoic boundary. Based on the integration of in situ U–Th–Pb dating of monaz......In central southern Madagascar the crystalline basement is composed of mid-crustal rocks which have experienced polycyclic deformation and metamorphism coupled with repeated granitoid magmatism at the Neoproterozoic–Phanerozoic boundary. Based on the integration of in situ U–Th–Pb dating...... of monazite and structural relationships,twodistinct phases of major ductile deformation, the Andreaba and Ihosy phases can be distinguished in central southern Madagascar. Both these deformation phases occur between ~550 and 520 Ma. Coeval with, and outlasting deformation, granitic plutons and dykes were...... that the whole crustal section remained in a mid-crustal position. Metamorphic overprinting related to M2 is spatially limited and is heterogeneously distributed in central southern Madagascar. Newly developed M2 mineral assemblages are preferentially found in areas featuring Ihosy phase vertical foliation...

  12. Structural and metamorphic evolution of the Turku migmatite complex, southwestern Finland

    Directory of Open Access Journals (Sweden)

    Väisänen, M.

    1999-06-01

    Full Text Available The Turku migmatite complex in southwestern Finland is a representative area for the type of tectonic and metamorphic evolution seen within the Palaeoproterozoic Svecofennian Orogen in southern Finland. The orogeny can be divided into early, late and postorogenic stages. The early orogenic structural evolution of the crust is expressed by a D1/D2 deformation recorded as bedding-parallel S1 mica foliation deformed by tight to isoclinal D2 folds with subhorizontal axial planes and a penetrative S2 axial plane foliation. Syntectonic ca. 1890-1870 Ma tonalites were emplaced during D2 as sheet intrusions. This deformation is attributed to thrust tectonics and thickening of the crust. The late orogenic structural evolution produced the main D3 folding, which transposed previous structures into a NE-SW trend. The doubly plunging fold axis produced dome-and-basin structures. The attitude of the F3 folds varies from upright or slightly overturned to locally recumbent towards the NW. Granite dikes were intruded along S3 axial planes. Large D3 fold limbs are often strongly deformed, intensively migmatized and intruded by garnet- and cordierite-bearing granites. These observations suggest that these potassium-rich granites, dated at 1840-1830 Ma, were emplaced during D3. This late orogenic NW-SE crustal shortening further contributed to crustal thickening. Subvertical D4 shear zones that cut all previous rock types possibly controlled the emplacement of postorogenic granitoids. Steeply plunging lineations on D4 shear planes suggest vertical displacements during a regional uplift stage. Metamorphic grade increases from cordierite-sillimanite-K-feldspar gneisses in the northwest and from muscovite-quartz±andalusite rocks in the southeast to high-temperature granulite facies migmatites in the middle of the study area. Block movements during D4 caused the observed differences in metamorphic grade. Garnet and cordierite are mostly breakdown products of biotite

  13. Metamorphic and volcanic quartz of the siliciclastic Tipuma Formation, West Papua, Indonesia: an insight into Triassic palaeogeography of northern Australia

    Science.gov (United States)

    Gunawan, Indra; Hall, Robert; Augustsson, Carita

    2013-04-01

    The origin and Triassic evolution of the Bird's Head of West Papua has been a subject of active discussion. Many interpretations have been proposed for the Triassic evolution, from active margin to passive margin models. The Bird's Head region is underlain by Australian continental crust and has a relatively complete stratigraphy from Palaeozoic to Recent. The Tipuma Formation is a Mesozoic siliciclastic sequence and a potentially important reservoir. Its sedimentation may record parts of the region's Mesozoic tectonic history, including several phases of rifting. Little is known about the variations in lithologies and their composition, and nothing is known about its provenance. The Tipuma Formation is dominated by red to cream well-bedded mudstone, sandstone and conglomerate. It rests unconformably on the Kemum Formation and is overlain by the Cretaceous Jass Formation. It is difficult to assess the depositional age of the Tipuma Formation due to the absence of fossils. The suggested Triassic age is based solely on its stratigraphic position. The Tipuma Formation was previously thought to be deposited in a stable continental setting. Detrital modes indicate acid plutonic, metamorphic, and recycled sedimentary source rocks for the Tipuma Formation sandstones. Angular volcanic quartz and elongate euhedral zircons suggest a contribution from previously unrecognised contemporaneous acid volcanics. New interpretations suggest that the widespread Permo-Triassic volcanic activity in the Bird's Head was caused by subduction associated with an Andean-type active margin and that the Tipuma Formation was deposited in a fluvial setting close to the volcanic arc. Cathodoluminescence (CL) characteristics of quartz depend on variations in temperature, pressure, and geochemical environment during crystal growth and subsequent events. The CL colour spectra of quartz can be correlated with the formation conditions of the quartz. They can therefore be used as a provenance indicator

  14. New evidence for an old idea: Geochronological constraints for a paired metamorphic belt in the central European Variscides

    Science.gov (United States)

    Will, T. M.; Schmädicke, E.; Ling, X.-X.; Li, X.-H.; Li, Q.-L.

    2018-03-01

    New geochronological data reveal a prolonged tectonothermal evolution of the Variscan Odenwald-Spessart basement, being part of the Mid-German Crystalline Zone in central Europe. We report the results from (i) secondary ion mass spectrometry (SIMS) U-Pb dating of zircon, rutile and monazite, (ii) SIMS zircon oxygen isotope analyses, (iii) laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) zircon Lu-Hf isotope analyses and, (iv) LA-ICPMS zircon and rutile trace element data for a suite of metamorphic rocks (five amphibolite- and eclogite-facies mafic meta-igneous rocks and one granulite-facies paragneiss). The protoliths of the mafic rocks formed from juvenile as well as depleted mantle sources in distinct tectonic environments at different times. Magmatism took place at a divergent oceanic margin (possibly in a back-arc setting) at 460 Ma, in an intraoceanic basin at ca. 445 Ma and at a continental margin at 329 Ma. Regardless of lithology, zircon in eclogite, amphibolite and high-temperature paragneiss provide almost identical Carboniferous ages of 333.7 ± 4.1 Ma (eclogite), 329.1 ± 1.8 to 328.4 ± 8.9 Ma (amphibolite), and 334.0 ± 2.0 Ma (paragneiss), respectively. Rutile yielded ages of 328.6 ± 4.7 and 321.4 ± 7.0 Ma in eclogite and amphibolite, and monazite in high-temperature paragneiss grew at 330.1 ± 2.4 Ma (all ages are quoted at the 2σ level). The data constrain coeval high-pressure eclogite- and high-temperature granulite-facies metamorphism of the Odenwald-Spessart basement at ca. 330 Ma. Amphibolite-facies conditions were attained shortly afterwards. The lower plate eclogite formed in a fossil subduction zone and the upper plate high-temperature, low-pressure rocks are the remains of an eroded Carboniferous magmatic arc. The close proximity of tectonically juxtaposed units of such radically different metamorphic conditions and thermal gradients is characteristic for a paired metamorphic belt sensu Miyashiro

  15. The New Consort Gold Mine, Barberton greenstone belt, South Africa: orogenic gold mineralization in a condensed metamorphic profile

    Science.gov (United States)

    Otto, A.; Dziggel, A.; Kisters, A. F. M.; Meyer, F. M.

    2007-10-01

    The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to, the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary rocks of the overlying c. 3,260-3,230 Ma Fig Tree Group. This contact, locally referred to as the Consort Bar, formed during ductile D1 imbrication of the metavolcanosedimentary sequence and predates the main stage of the gold mineralization. The imbricate stack is situated in the immediate hanging wall of the basal granitoid-greenstone contact along the northern margin of the greenstone belt. It is characterized by a condensed metamorphic profile in which the metamorphic grade increases from upper greenschist facies conditions (510-530°C, 4 kbar) in rocks of the Fig Tree Group to upper amphibolite facies grades (600-700°C, 6-8 kbar) in the basal Onverwacht Group. Detailed structural and petrological investigations indicate that the Consort Bar represents a major structural break, which is largely responsible for the telescoping of metamorphic isograds within the structural sequence. Two stages of mineralization can be distinguished. Loellingite, pyrrhotite, and a calc-silicate alteration assemblage characterize an early high-T mineralization event, which is restricted to upper amphibolite facies rocks of the Onverwacht Group. This early mineralization may correlate with the local D1 deformation. The second and main stage of gold mineralization was associated with renewed ductile shearing during D2. The D2 deformation resulted in the reactivation of earlier structures, and the formation of a NNW trending, steeply dipping shear zone system, the Shires Shear Zone, which separates two regional SE plunging D1 synclines. The mineralized shear zones are intruded by abundant syn-kinematic pegmatite

  16. Art Rocks with Rock Art!

    Science.gov (United States)

    Bickett, Marianne

    2011-01-01

    This article discusses rock art which was the very first "art." Rock art, such as the images created on the stone surfaces of the caves of Lascaux and Altimira, is the true origin of the canvas, paintbrush, and painting media. For there, within caverns deep in the earth, the first artists mixed animal fat, urine, and saliva with powdered minerals…

  17. Self-organized rock textures and multiring structure in the Duolun crater

    Science.gov (United States)

    Wu, Siben; Zhang, Jiayun

    1992-01-01

    The Duolun impact crater is a multiring basin located 200 km north of Beijing. From the center to the edge of the crater there are innermost rim, inner ring, outer rim, and outermost ring. Recently, we have found some self-organized textures or chaos phenomena in shock-metamorphic rocks from the Duolun impact crater, such as turbulence in matrices of impact glass, oscillatory zoning, or chemical chaos of spherulites in spherulitic splashed breccia, fractal wavy textures or self-similar wavy textures with varied scaling in impact glass, and crystallite beams shaped like Lorentz strange attractors. The rare phenomena indicate that the shock-metamorphic rocks from Duolun crater are formed far from equilibrium. If impact cratering generates momentarily under high-pressure and superhigh-temperature, occurrence of those chaos phenomena in shock-metamorphic rock is not surprising.

  18. Rock Physics

    DEFF Research Database (Denmark)

    Fabricius, Ida Lykke

    2017-01-01

    Rock physics is the discipline linking petrophysical properties as derived from borehole data to surface based geophysical exploration data. It can involve interpretation of both elastic wave propagation and electrical conductivity, but in this chapter focus is on elasticity. Rock physics is based...... on continuum mechanics, and the theory of elasticity developed for statics becomes the key to petrophysical interpretation of velocity of elastic waves. In practice, rock physics involves interpretation of well logs including vertical seismic profiling (VSP) and analysis of core samples. The results...

  19. Chloritoid and barroisite-bearing pelitic schists from the eclogite unit in the Besshi district, Sanbagawa metamorphic belt

    Science.gov (United States)

    Zaw Win Ko; Enami, M.; Aoya, M.

    2005-04-01

    The Sanbagawa metamorphic rocks in the Besshi district, central Shikoku, are grouped into eclogite and noneclogite units. Chloritoid and barroisite-bearing pelitic schists occur as interlayers within basic schist in an eclogite unit of the Seba area in the Sanbagawa metamorphic belt, central Shikoku, Japan. Major matrix phases of the schists are garnet, chlorite, barroisite, paragonite, phengite, and quartz. Eclogite facies phases including chloritoid and talc are preserved only as inclusions in garnet. P- T conditions for the eclogite facies stage estimated using equilibria among chloritoid, barroisite, chlorite, interlayered chlorite-talc, paragonite, and garnet are 1.8 GPa/520-550 °C. Zonal structures of garnet and matrix amphibole show discontinuous growth of minerals between their core and mantle parts, implying the following metamorphic stages: prograde eclogite facies stage→hydration reaction stage→prograde epidote-amphibolite stage. This metamorphic history suggests that the Seba eclogite lithologies were (1) juxtaposed with subducting noneclogite lithologies during exhumation and then (2) progressively recrystallized under the epidote-amphibolite facies together with the surrounding noneclogite lithologies. The pelitic schists in the Seba eclogite unit contain paragonite of two generations: prograde phase of the eclogite facies included in garnet and matrix phase produced by local reequilibration of sodic pyroxene-bearing eclogite facies assemblages during exhumation. Paragonite is absent in the common Sanbagawa basic and pelitic schists, and is, however, reported from restricted schists from several localities near the proposed eclogite unit in the Besshi district. These paragonite-bearing schists could be lower-pressure equivalents of the former eclogite facies rocks and are also members of the eclogite unit. This idea implies that the eclogite unit is more widely distributed in the Besshi district than previously thought.

  20. Late Mesoproterozoic to Early Paleozoic history of metamorphic basement from the southeastern Chiapas Massif Complex, Mexico, and implications for the evolution of NW Gondwana

    Science.gov (United States)

    Weber, Bodo; González-Guzmán, Reneé; Manjarrez-Juárez, Román; Cisneros de León, Alejandro; Martens, Uwe; Solari, Luigi; Hecht, Lutz; Valencia, Victor

    2018-02-01

    In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined "El Triunfo Complex" located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at 650 °C and 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian ( 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from 457 to 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of

  1. Geochemical, Metamorphic and Geodynamic Evolution implications from subduction-related serpentinites and metarodingites at East Thessaly (Central Greece)

    Science.gov (United States)

    Koutsovitis, Petros

    2017-04-01

    In Central Greece, the East Thessaly region encompasses ophiolitic and metaophiolitic formations emplaced onto Mesozoic platform series rocks. Metaophiolitic thrust sheets are characterized either by the predominance of serpentinites or metabasites. Serpentinites have been distinguished into three groups, representing distinct metamorphic degrees. Group-1 serpentinites (East Othris region) are characterized by the progressive transformation of lizardite to antigorite, estimated to have been formed under greenschist facies conditions (˜320-340 ˚ C, P≈6-8 kbar) [1]. Group-2 serpentinites (NE Othris and Agia-Agiokampos region) are marked by the further prevalence of antigorite over lizardite, suggesting upper-greenschist to low-blueschist facies metamorphism (˜340-370 ˚ C, P≈9-11 kbar) [1]. Group-3 serpentinites (Agia-Agiokampos region) are characterized by the predominance of antigorite and Cr-magnetite, as well as by their relatively low LOI (10.9-12.6 wt.%), corresponding to blueschist facies metamorphism (˜360-400 ˚ C, P≈12 kbar) [1]. These metamorphic conditions are highly comparable with the P-T estimates from the Easternmost Thessaly metabasic rocks, strongly indicating that the entire metaophiolitic formation (excluding East Othris) underwent blueschist facies metamorphism. Serpentinites from East Thessaly were formed from serpentinization of highly depleted harzburgitic protoliths under extensive partial melting processes (>15%), pointing to a hydrous subduction-related environment. Group-1 serpentinites exhibit higher Mg/Si ratio values and LOI compared to serpentinite Groups-2 and -3. Differences in the trace element behavior amongst the three serpentinite groups are also consistent with increasing metamorphic conditions (e.g. Pb, La enrichments, Ti, Y, Yb depletions) [1]. The East Thessaly serpentinites reflect highly oxidizing conditions (-0.4Jurassic Pindos oceanic SSZ model appears to successfully interpret not only the geochemical and

  2. Rock Foundations

    National Research Council Canada - National Science Library

    1994-01-01

    .... Chapter 4 provides guidance on rock mass characterization and classification schemes. Chapters 5 and 6 provide guidance on related topic areas of foundation deformation and settlement and foundation bearing capacity, respectively...

  3. Garnet growth interruptions during high- and ultra high-pressure metamorphism constrained by thermodynamic forward models

    Science.gov (United States)

    Konrad-Schmolke, M.; Schildhauer, H.

    2013-12-01

    Growth and chemical composition of garnet in metamorphic rocks excellently reflect thermodynamic as well kinetic properties of the host rock during garnet growth. This valuable information can be extracted from preserved compositional growth zoning patterns in garnet. However, metamorphic rocks often contain multiple garnet generations that commonly develop as corona textures with distinct compositional core-overgrowth features. This circumstance can lead to a misinterpretation of information extracted from such grains if the age- and metamorphic relations between different garnet generations are unclear. Especially garnets from high-pressure (HP) and ultra high-pressure (UHP) rocks often preserve textures that show multiple growth stages reflected in core-overgrowth differences both in main and trace element composition and in the inclusion assemblage. Distinct growth zones often have sharp boundaries with strong compositional gradients and/or inclusion- and trace-element-enriched zones. Such growth patterns indicate episodic garnet growth as well as growth interruptions during the garnet evolution. A quantitative understanding of these distinct growth pulses enables the relationship between reaction path, age determinations in spatially controlled garnet domains or temperature-time constraints to be fully characterised. In this study we apply thermodynamic forward models to simulate garnet growth along a series of HP and UHP P-T paths, representative for subducted oceanic crust. We study garnet growth in different basaltic rock compositions and under different element fractionation scenarios in order to detect path-dependent P-T regions of limited or ceased garnet growth. Modeled data along P-T trajectories involving fractional crystallisation are assembled in P-T diagrams reflecting garnet growth in a changing bulk rock composition. Our models show that in all investigated rock compositions garnet growth along most P-T trajectories is discontinuous, pulse

  4. High-pressure granulite-facies metamorphism in central Dronning Maud Land (East Antarctica): Implications for Gondwana assembly

    Science.gov (United States)

    Palmeri, Rosaria; Godard, Gaston; Di Vincenzo, Gianfranco; Sandroni, Sonia; Talarico, Franco M.

    2018-02-01

    Central Dronning Maud Land (DML; East Antarctica) is located in a key region of the Gondwana supercontinent. The Conradgebirge area (central DML) consists of orthogneisses, derived from both volcanic and plutonic protoliths, and minor metasedimentary rocks, intruded by Cambrian syn- to post-metamorphic plutons and dykes. Mafic-ultramafic boudins in the metavolcanic and metaplutonic gneisses from Conradgebirge consist of amphibolites and high-grade garnet-bearing pyroxene- and amphibole-rich granofels. They occur either as discontinuous levels or as pods boudinaged within highly-strained and strongly-migmatized gneisses. Bulk-rock major and trace-element compositions, together with geochemical discriminant diagrams (e.g., Th/Yb versus Ta/Yb and V versus Ti), suggest derivation from enriched mantle source for the mafic rocks boudinaged in metaplutonic gneisses, whereas a calc-alkaline signature is common for the mafic boudins in metavolcanic rocks. The microstructural study and P-T modelling of an ultramafic metagabbroic rock reveal a prograde metamorphic evolution from amphibolite-facies (ca. 0.5 GPa; 500 °C) up to high-P granulite-facies conditions (ca. 1.5-1.7 GPa; 960-970 °C). Partial melting is testified by "nanogranitoid" inclusions enclosed in garnet. An almost isothermal decompression down to ca. 0.4 GPa and 750-850 °C produced well-developed An + Opx-bearing symplectites around garnet. A final isobaric cooling at nearly 0.4 GPa is testified by Grt coronas around high-T symplectites. The above reconstruction traces a clockwise loading-heating P-T evolution with a peak metamorphism at high-P granulite-facies conditions suggesting crustal thickening at nearly 570 Ma, followed by a tectonically assisted rapid exhumation, and then, by an isobaric cooling. 40Ar-39Ar dating of amphibole and biotite at 505-480 Ma testify mineral re-equilibration at upper crustal level (T < 650 °C) during the isobaric cooling. This tectono-metamorphic scenario seems

  5. Inverted Metamorphic Multijunction (IMM) Cell Processing Instructions

    Energy Technology Data Exchange (ETDEWEB)

    Duda, A.; Ward, S.; Young, M.

    2012-02-01

    This technical report details the processing schedule used to fabricate Inverted Metamorphic Multijunction (IMM) concentrator solar cells at The National Renewable Energy Laboratory (NREL). These devices are used as experimental test structures to support the research at NREL that is focused on increasing the efficiency of photovoltaic power conversion. They are not intended to be devices suitable for deployment in working concentrator systems primarily because of heat sinking issues. The process schedule was developed to be compatible with small sample sizes and to afford relatively rapid turn-around times, in support of research efforts. The report describes the use of electro deposition of gold for both the back and front contacts. Electro-deposition is used because of its rapid turn around time and because it is a benign metallization technique that is seldom responsible for damage to the semiconductors. The layer transfer technique is detailed including the use of a commercially available adhesive and the etching away of the parent gallium arsenide substrate. Photolithography is used to define front contact grids as well as the mesa area of the cell. Finally, the selective wet chemical etchant system is introduced and its use to reveal the back contact is described.

  6. High Radiation Resistance Inverted Metamorphic Solar Cell, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — The innovation in this SBIR Phase II project is the development of a unique triple junction inverted metamorphic technology (IMM), which will enable the...

  7. High Radiation Resistance Inverted Metamorphic Solar Cell Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The innovation in the proposed SBIR Phase I project is the development of a unique triple unction inverted metamorphic technology (IMM), which will enable the...

  8. Natural analogue for storage of radwaste in crystalline rocks

    International Nuclear Information System (INIS)

    Brookins, D.G.; Abashian, M.S.; Cohen, L.H.; Wollenberg, H.A. Jr.

    1982-01-01

    The Bryan-Eldora stock (Colorado) intruded the Precambrian Idaho Springs Formation metamorphic rocks 58 million years ago. Geochronologic-geochemical work by Hart et al. [S.R. Hart et al., in Radiometric Dating for Geologists, E.I. Hamilton, R.S. Farquhar, eds. (Wiley-Interscience, New York, 1968) pp. 73-110] has demonstrated that the heat from the cooling intrusive rocks was sufficient to affect mineral isotopic systematics up to 2000 m from the contact, and the nature of these isotopic perturbations can be explained by a simple diffusion model in turn based on various heat flow models. Our new studies are focused on elemental exchange between stock and intruded rock as a function of distance from the contact; the assumption is made that the stock is a very large, high heat source analogous to a waste form emplaced in the metamorphic rocks without benefit of canister or engineered backfill. Data for U, Th and the REE indicate actinide and lanthanide immobility except perhaps in the 0 to 2m contact zone where some infiltration of the country rocks by stock-derived fluids occurred. Beyond 4m no stock-derived U, Th, REE or *Pb are noted. Further, whole rock Rb-Sr and stable O isotopic data indicate conductive cooling as opposed to convective, water-induced cooling. The intruded rocks possess low porosity and permeability; this helped prevent elemental migration during the 10 5 to 10 6 years of stock crystallization. The petrographic and geochemical studies show that the Idaho Springs (or equivalent) metamorphic rocks are well suited for radwaste storage. 1 figure, 1 table

  9. Recycling argon through metamorphic reactions: The record in symplectites

    Science.gov (United States)

    McDonald, Christopher S.; Regis, Daniele; Warren, Clare J.; Kelley, Simon P.; Sherlock, Sarah C.

    2018-02-01

    The 40Ar/39Ar ages of metamorphic micas that crystallized at high temperatures are commonly interpreted as cooling ages, with grains considered to have lost 40Ar via thermally-driven diffusion into the grain boundary network. Recently reported laser-ablation data suggest that the spatial distribution of Ar in metamorphic micas does not always conform to the patterns predicted by diffusion theory and that despite high metamorphic temperatures, argon was not removed efficiently from the local system during metamorphic evolution. In the Western Gneiss Region (WGR), Norway, felsic gneisses preserve microtextural evidence for the breakdown of phengite to biotite and plagioclase symplectites during near isothermal decompression from c. 20-25 to c. 8-12 kbar at 700 °C. These samples provide an ideal natural laboratory to assess whether the complete replacement of one K-bearing mineral by another at high temperatures completely 'resets' the Ar clock, or whether there is some inheritance of 40Ar in the neocrystallized phase. The timing of the high-temperature portion of the WGR metamorphic cycle has been well constrained in previous studies. However, the timing of cooling following the overprint is still much debated. In-situ laser ablation spot dating in phengite, biotite-plagioclase symplectites and coarser, texturally later biotite yielded 40Ar/39Ar ages that span much of the metamorphic cycle. Together these data show that despite residence at temperatures of 700 °C, Ar is not completely removed by diffusive loss or during metamorphic recrystallization. Instead, Ar released during phengite breakdown appears to be partially reincorporated into the newly crystallizing biotite and plagioclase (or is trapped in fluid inclusions in those phases) within a close system. Our data show that the microtextural and petrographic evolution of the sample being dated provides a critical framework in which local 40Ar recycling can be tracked, thus potentially allowing 40Ar/39Ar dates

  10. Metamorphic mineral reactions: Porphyroblast, corona and symplectite growth

    OpenAIRE

    F. Gaidies; R. Milke; W. Heinrich; R. Abart

    2017-01-01

    Much of the Earth’s dynamics is related to mineral reactions in the solid-state. Classically, this is referred to as metamorphic crystallization (Kretz, 1994). Based on the chemical compositions of the phases involved in a metamorphic mineral reaction, two basic reaction types may be distinguished. Reactions that involve only structural re-arrangements, while the compositions of the reactant and product phases are identical, are referred to as partitionless and ‘polymorphic phase transformati...

  11. Evidence of volcanism in the Paleozoic metamorphic basement of the Sierra Madre Oriental, NE-Mexico

    Science.gov (United States)

    Torres Sanchez, S. A.; Ramirez Fernandez, J. A.; Jenchen, U.; Barboza Gudino, J. R.; Augustsson, C.

    2012-04-01

    The Paleozoic metamorphic basement of the Sierra Madre Oriental comprises a wide variety of protoliths including psammites, pelites, tuffs, lava flows, pillow lavas as well as ultramafic rocks, metamorphosed under subgreenschist to greenschist facies. All these units are grouped under the Granjeno Schist Formation (GSF). They are limited by faults in the core of the Huizachal-Peregrina Anticlinorium (HPA), and in the uplifts of Miquihuana (M), Bustamante (B) and Aramberri (A) in NE Mexico. The aim of this work is to compare the metavolcanic units in the different localities, looking for a genetic relationship between them. These units include four different lithologies: a) pale green fine grained interstratified horizons of basic to intermediate metatuffs, b) massive, green and coarse greenstones, representing massive metalavas, c) well preserved dark green pillow lavas, and d) pale to dark massive talc schists. They are mainly massive, interbedded with the metasediments and do not display the typical pervasive schistosity of GSF. Preliminary analysis of the metavolcanic units indicate that they are alkaline (AB/OIB). Their origin is still under debate, they could be originated during continental intraplate volcanism or from an ancient oceanic island (?). It has to be noted that the Silurian to Permian HPÁs sedimentary sequence, encloses only a rhyolitic body (Aserradero Fm.) that cannot be directly correlated with the metavolcanics. The metamorphism age (≈ 330±30 Ma) and protoliths of all localities are similar, but there are enough petrographic differences to interpret that the metamorphic conditions are not similar at all. It is proposed that the vulcanosedimentary sequence were deposited in a forearc basin along the Pangea western margin, and later metamorphosed during the subduction process through Carboniferous times.

  12. Metamorphic III–V Solar Cells: Recent Progress and Potential

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, Ivan; France, Ryan M.; Geisz, John F.; McMahon, William E.; Steiner, Myles A.; Johnston, Steve; Friedman, Daniel J.

    2016-01-01

    Inverted metamorphic multijunction solar cells have been demonstrated to be a pathway to achieve the highest photovoltaic (PV) conversion efficiencies. Attaining high-quality lattice-mismatched (metamorphic) semiconductor devices is challenging. However, recent improvements to compositionally graded buffer epitaxy and junction structures have led to the achievement of high-quality metamorphic solar cells exhibiting internal luminescence efficiencies over 90%. For this high material quality, photon recycling is significant, and therefore, the optical environment of the solar cell becomes important. In this paper, we first present recent progress and performance results for 1- and 0.7-eV GaInAs solar cells grown on GaAs substrates. Then, an electrooptical model is used to assess the potential performance improvements in current metamorphic solar cells under different realizable design scenarios. The results show that the quality of 1-eV subcells is such that further improving its electronic quality does not produce significant Voc increases in the four-junction inverted metamorphic subcells, unless a back reflector is used to enhance photon recycling, which would significantly complicate the structure. Conversely, improving the electronic quality of the 0.7-eV subcell would lead to significant Voc boosts, driving the progress of four-junction inverted metamorphic solar cells.

  13. Possible zircon U-Pb evidence for Pan-African granulite-facies metamorphism in the Mozambique belt of southern Tanzania

    International Nuclear Information System (INIS)

    Coolen, J.J.M.M.M.

    1982-01-01

    Four zircon fractions of garnet-bearing two-pyroxene granulite, from the Furua granulite complex of southern Tanzania, plot very close to concordia. A discordia yields a lower intercept at 652 +- 10 Ma, an age slightly higher than the Rb-Sr whole-rock and mineral ages reported from the surrounding amphibolite-facies rocks. The U-Pb systematics indicate the presence of a very small amount of older (2-3 Ga) radiogenic lead. The zircon data may be interpreted as indicating an event of granulite-facies metamorphism during the Pan-African thermotectonic episode. This interpretation is at variance with current models postulating that the granulite complexes in the Mozambique belt are relicts of older, possibly Archaean events of metamorphism. (Auth.)

  14. Knowledge representation of rock plastic deformation

    Science.gov (United States)

    Davarpanah, Armita; Babaie, Hassan

    2017-04-01

    The first iteration of the Rock Plastic Deformation (RPD) ontology models the semantics of the dynamic physical and chemical processes and mechanisms that occur during the deformation of the generally inhomogeneous polycrystalline rocks. The ontology represents the knowledge about the production, reconfiguration, displacement, and consumption of the structural components that participate in these processes. It also formalizes the properties that are known by the structural geology and metamorphic petrology communities to hold between the instances of the spatial components and the dynamic processes, the state and system variables, the empirical flow laws that relate the variables, and the laboratory testing conditions and procedures. The modeling of some of the complex physio-chemical, mathematical, and informational concepts and relations of the RPD ontology is based on the class and property structure of some well-established top-level ontologies. The flexible and extensible design of the initial version of the RPD ontology allows it to develop into a model that more fully represents the knowledge of plastic deformation of rocks under different spatial and temporal scales in the laboratory and in solid Earth. The ontology will be used to annotate the datasets related to the microstructures and physical-chemical processes that involve them. This will help the autonomous and globally distributed communities of experimental structural geologists and metamorphic petrologists to coherently and uniformly distribute, discover, access, share, and use their data through automated reasoning and enhanced data integration and software interoperability.

  15. 40Ar/ 39Ar mineral ages within metamorphic clasts from the Kuma Group (Eocene), central Shikoku, Japan: Implications for tectonic development of the Sambagawa accretionary prism

    Science.gov (United States)

    Takasu, A.; Dallmeyer, R. D.

    1992-06-01

    The Sambagawa metamorphic belt exposed in central Shikoku records a high- P/T metamorphism. It is comprised by the Oboke nappe and the structurally overlying, internally imbricated Besshi nappe complex. The Besshi nappe complex locally is unconformably overlain by the Kuma Group (Eocene) which consists of conglomerates and subordinate sandstones and mudstones. Clasts within Kuma conglomerates exposed in the Kamegamori district include low-grade schists (derived from the unconformably underlying Sambagawa complex) and high-grade metamorphic rocks of uncertain provenance (including garnet-amphibolite and oligoclase-bearing pelitic schist). 36Ar/ 40Ar vs. 39Ar/ 40Ar isotope correlation ages recorded by hornblende from two amphibolite clasts are 131.1 ± 4.9 Ma and 156.8 ± 4.3 Ma. These are interpreted to date post-metamorphic cooling through temperatures required for intracrystalline retention of argon, and are older than cooling ages previously reported from any presently exposed segments of the Sambagawa terrane. Plateau ages of 108.8 ± 0.7 Ma and 115.7 ± 0.6 Ma are recorded by muscovite from two clasts of schist. Muscovite within a proximal basement exposure of unconformably underlying Sambagawa pelitic schist records a plateau age of 78.7 ± 0.5 Ma. Combined with isotopic ages previously reported for the Sambagawa terrane, 40Ar/ 39Ar data from clasts in the Kuma Group suggest that metamorphic culmination within a high-grade source terrane occured at c. 185-145 Ma. Sectors of this complex cooled through c. 500°C at c. 150 Ma. Other portions cooled through c. 500°C at c. 130 Ma. Contrasts in the cooling ages likely reflect internal imbrication within the source terrane. The Besshi nappe complex reached peak metamorphic conditions at c. 100-90 Ma and experienced relatively rapid uplift and cooling at c. 85-75 Ma. The Besshi nappe complex was structurally emplaced onto the Oboke nappe which attained peak metamorphic conditions at c. 75 Ma. Subsequently, the

  16. Source rock

    Directory of Open Access Journals (Sweden)

    Abubakr F. Makky

    2014-03-01

    Full Text Available West Beni Suef Concession is located at the western part of Beni Suef Basin which is a relatively under-explored basin and lies about 150 km south of Cairo. The major goal of this study is to evaluate the source rock by using different techniques as Rock-Eval pyrolysis, Vitrinite reflectance (%Ro, and well log data of some Cretaceous sequences including Abu Roash (E, F and G members, Kharita and Betty formations. The BasinMod 1D program is used in this study to construct the burial history and calculate the levels of thermal maturity of the Fayoum-1X well based on calibration of measured %Ro and Tmax against calculated %Ro model. The calculated Total Organic Carbon (TOC content from well log data compared with the measured TOC from the Rock-Eval pyrolysis in Fayoum-1X well is shown to match against the shale source rock but gives high values against the limestone source rock. For that, a new model is derived from well log data to calculate accurately the TOC content against the limestone source rock in the study area. The organic matter existing in Abu Roash (F member is fair to excellent and capable of generating a significant amount of hydrocarbons (oil prone produced from (mixed type I/II kerogen. The generation potential of kerogen in Abu Roash (E and G members and Betty formations is ranging from poor to fair, and generating hydrocarbons of oil and gas prone (mixed type II/III kerogen. Eventually, kerogen (type III of Kharita Formation has poor to very good generation potential and mainly produces gas. Thermal maturation of the measured %Ro, calculated %Ro model, Tmax and Production index (PI indicates that Abu Roash (F member exciting in the onset of oil generation, whereas Abu Roash (E and G members, Kharita and Betty formations entered the peak of oil generation.

  17. Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada.

    Science.gov (United States)

    Tashiro, Takayuki; Ishida, Akizumi; Hori, Masako; Igisu, Motoko; Koike, Mizuho; Méjean, Pauline; Takahata, Naoto; Sano, Yuji; Komiya, Tsuyoshi

    2017-09-27

    The vestiges of life in Eoarchean rocks have the potential to elucidate the origin of life. However, gathering evidence from many terrains is not always possible, and biogenic graphite has thus far been found only in the 3.7-3.8 Ga (gigayears ago) Isua supracrustal belt. Here we present the total organic carbon contents and carbon isotope values of graphite (δ 13 C org ) and carbonate (δ 13 C carb ) in the oldest metasedimentary rocks from northern Labrador. Some pelitic rocks have low δ 13 C org values of -28.2, comparable to the lowest value in younger rocks. The consistency between crystallization temperatures of the graphite and metamorphic temperature of the host rocks establishes that the graphite does not originate from later contamination. A clear correlation between the δ 13 C org values and metamorphic grade indicates that variations in the δ 13 C org values are due to metamorphism, and that the pre-metamorphic value was lower than the minimum value. We concluded that the large fractionation between the δ 13 C carb and δ 13 C org values, up to 25‰, indicates the oldest evidence of organisms greater than 3.95 Ga. The discovery of the biogenic graphite enables geochemical study of the biogenic materials themselves, and will provide insight into early life not only on Earth but also on other planets.

  18. Rocking pneumonia.

    Science.gov (United States)

    Rijkers, Ger T; Rodriguez Gomez, Maria

    2017-01-01

    Ever since Chuck Berry coined the term "rocking pneumonia" in his 1956 song "Roll over Beethoven", pneumonia has been mentioned frequently in modern blues and rock songs. We analyzed the lyrics of these songs to examine how various elements of pneumonia have been represented in popular music, specifically the cause of pneumonia, the risk groups, comorbidity (such as the boogie woogie flu), the clinical symptoms, and treatment and outcome. Up to this day, songwriters suggest that pneumonia is caused mainly by the cold and rain and that treatment is hardly possible, aside from a shot of rhythm and blues.

  19. Intellektuaalne rock

    Index Scriptorium Estoniae

    2007-01-01

    Briti laulja-helilooja ja näitleja Toyah Willcox ning Bill Rieflin ansamblist R.E.M. ja Pat Mastelotto King Krimsonist esinevad koos ansamblitega The Humans ja Tuner 25. okt. Tallinnas Rock Cafés ja 27. okt Tartu Jaani kirikus

  20. Igneous Rocks

    Science.gov (United States)

    Doe, Bruce R.

    “Igneous Rocks was written for undergraduate geology majors who have had a year of college-level chemistry and a course in mineralogy … and for beginning graduate students. Geologists working in industry, government, or academia should find this text useful as a guide to the technical literature up to 1981 and as an overview of topics with which they have not worked but which may have unanticipated pertinence to their own projects.” So starts the preface to this textbook.As one who works part time in research on igneous rocks, especially as they relate to mineral deposits, I have been looking for such a book with this avowed purpose in a field that has a choking richness of evolving terminology and a bewildering volume of interdisciplinary literature. In addition to the standard topics of igneous petrology, the book contains a chapter on the role of igneous activity in the genesis of mineral deposits, its value to geothermal energy, and the potential of igneous rocks as an environment for nuclear waste disposal. These topics are presented rather apologetically in the preface, but the author is to be applauded for including this chapter. The apology shows just how new these interests are to petrology. Recognition is finally coming that, for example, mineral deposits are not “sports of nature,” a view held even by many economic geologists as recently as the early 1960's; instead they are perfectly ordinary geochemical features formed by perfectly ordinary geologic processes. In fact, the mineral deposits and their attendant alteration zones probably have as much to tell us about igneous rocks as the igneous rocks have to tell us about mineral deposits.

  1. Coronitic metagabbro and eclogite from the Grenville Province of western Quebec: interpretation of U-Pb geochronology and metamorphism

    International Nuclear Information System (INIS)

    Indares, A.; Dunning, G.

    1997-01-01

    We present new U-Pb and metamorphic data on high-pressure coronitic metagabbros from three distinct structural settings in the Parautochthonous belt of the Grenville Province in western Quebec. Intrusive ages are (i) 1217 -10 +15 Ma, for metagabbro close to the Grenville Front, correlative with the Sudbury dykes, defined in Ontario; (ii) 1403 -11 +14 Ma for an eclogitized lens at the base of the highest structural level (SL4), a new age for mafic magmatism in the western Grenville; and (iii) 1218 -34 +53 Ma for metagabbro from SL4, interpreted as correlative with metagabbros from the Algonquin and Shawanaga domains in Ontario. Metamorphism in all cases is Grenvillian, with the best constrained age of 1069 ± 3 Ma for the metagabbro of SL4. Metamorphic grade increases from the Grenville Front to the south. The mafic rocks preserve relict igneous textures overprinted by garnet + clinopyroxene that developed as coronas and (or) pseudomorphs after igneous phases. The highest grade metagabbros contain omphacite and some lack primary plagioclase, therefore being eclogites. However, interpretation of textures and mineral chemistry indicates that they were equilibrated during decompression (at 1350 MPa and 720 o C, sample 51: and at 1200 MPa and 740 o C, sample 29), so maximum depths of burial remain unconstrained. Their evolution is interpreted as follows: (i) high-pressure metamorphism by burial of the Laurentian margin under accreted terranes thrust toward the northwest between 1080 and 1060 Ma; (ii) residence at intermediate crustal levels, for a few tens of millions of years; and (iii) rapid exhumation by renewed thrusting that led to the emplacement of the high-pressure units over the northerly adjacent structural units of the Parautochthonous Belt. (author)

  2. PALEOARCHEAN MAFIC ROCKS OF THE SOUTHWESTERN SIBERIAN CRATON: PRELIMINARY GEOCHRONOLOGY AND GEOCHEMICAL CHARACTERIZATION

    Directory of Open Access Journals (Sweden)

    A. V. Ivanov

    2017-01-01

    Full Text Available The Siberian craton consists of Archean blocks, which were welded up into the same large unit by ca 1.9 Ga [Gladkochub et al., 2006; Rojas-Agramonte et al., 2011]. The history of the constituent Archean blocks is mosaic because of limited number of outcrops, insufficient sampling coverage because of their location in remote regions and deep forest and difficulties with analytical studies of ancient rocks, which commonly underwent metamorphic modifications and secondary alterations. In this short note, we report data on discovery of unusual for Archean mafic rocks of ultimate fresh appearance. These rocks were discovered within southwestern Siberian craton in a region near a boundary between Kitoy granulites of the Sharyzhalgai highgrade metamorphic complex and Onot green-schist belt (Fig. 1. Here we present preliminary data on geochronology of these rocks and provide their geochemical characterization.

  3. White Rock

    Science.gov (United States)

    2005-01-01

    14 November 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a portion of the famous 'White Rock' feature in Pollack Crater in the Sinus Sabaeus region of Mars. The light-toned rock is not really white, but its light tone caught the eye of Mars geologists as far back as 1972, when it was first spotted in images acquired by Mariner 9. The light-toned materials are probably the remains of a suite of layered sediments that once spread completely across the interior of Pollack Crater. Dark materials in this image include sand dunes and large ripples. Location near: 8.1oS, 335.1oW Image width: width: 3 km (1.9 mi) Illumination from: lower left Season: Southern Summer

  4. Geochemistry of the U,Th and others lithophile elements in highgrade methamorphic rocks from 'Macico de Guaxupe', south Minas Gerais

    International Nuclear Information System (INIS)

    Fernandes, J.F.

    1982-01-01

    A geochemical investigation on the Silvianopolis complex, Minas Gerais, Brazil, has been carried out with the determination of lithophile elements like U, Th, Rb, K, etc. in rocks of different metamorphic grade. It is verified that the geochemical mobilities of the elements is dependant on the rock type. The elemental abundances and ratios are compared using a statistical test. (ARHC) [pt

  5. Timing of isoclinal folds in multiply deformed high metamorphic grade region using FIA succession

    Science.gov (United States)

    Cao, Hui; Cai, Zhihui

    2013-04-01

    Multiply deformed and isoclinally folded interlayered high metamorphic grade gneisses and schists can be very difficult rocks for resolving early formed stratigraphic and structural relationships. When such rocks contain porphyroblasts a new approach is possible because of the way in which porphyroblast growth is affected by crenulation versus reactivation of compositional layering. The asymmetries of the overprinting foliations preserved as inclusion trails that define the FIAs can be used to investigate whether an enigmatic isoclinal fold is an antiform or synform. This approach also reveals when the fold first formed during the tectonic history of the region. Isoclinally folded rocks in the Arkansas River region of Central Colorado contain relics of fold hinges that have been very difficult to ascertain whether they are antiforms or synforms because of younger refolding effects and the locally truncated nature of coarse compositional layering. With the realization that rocks with a schistosity parallel to bedding (S0 parallel S1) have undergone lengthy histories of deformation that predate the obvious first deformation came recognition that large scale regional folds can form early during this process and be preserved throughout orogenesis. This extensive history is lost within the matrix because of reactivational shear on the compositional layering. However, it can be extracted by measuring FIAs. Recent work using this approach has revealed that the trends of axial planes of all map scale folds, when plotted on a rose diagram, strikingly reflect the FIA trends. That is, although it was demonstrated that the largest scale regional folds commonly form early in the total history, other folds can form and be preserved from subsequent destruction in the strain shadows of plutons or through the partitioning of deformation due to heterogeneities at depth.

  6. Fabrics produced mimetically during static metamorphism in retrogressed eclogites from the Zermatt-Saas zone, Western Italian Alps

    Science.gov (United States)

    McNamara, D. D.; Wheeler, J.; Pearce, M.; Prior, D. J.

    2012-11-01

    Lattice preferred orientations (LPOs) are commonly interpreted to form by dislocation creep. Consequently they are used to infer deformation at the metamorphic grade at which the minerals were stable, especially if those minerals show a shape fabric. Here we show that LPOs can occur through mimicry of a pre-existing LPO, so they formed statically, not during deformation. Omphacite and glaucophane LPOs occur in eclogite facies rocks from the Zermatt-Saas Unit of the Northwest Italian Alps. Barroisite grew during greenschist facies retrogression and has an LPO controlled significantly by the eclogite facies omphacite and glaucophane LPOs, rather than directly by deformation. Using spatially resolved lattice orientation data from the three key minerals, collected using electron backscatter diffraction, we deploy a new technique of interphase misorientation distribution analysis to prove this. Barroisite LPO develops by mimicry of omphacite (via a particular lattice orientation relationship) and by direct topotactic and epitactic replacement of glaucophane. LPO in turn influenced anisotropic grain growth, resulting in a barroisite grain shape fabric. Thus regional retrogression during exhumation of the Zermatt-Saas high-pressure rocks was, in large part, static, rather than dynamic as previously interpreted. In general the possibility of mimetic fabrics forming during metamorphic reactions must be borne in mind when interpreting direct structural observations and seismic anisotropy data in terms of deformation, in both crust and mantle.

  7. The Lost South Gobi Microcontinent: Protolith Studies of Metamorphic Tectonites and Implications for the Evolution of Continental Crust in Southeastern Mongolia

    Directory of Open Access Journals (Sweden)

    Matthew J. Heumann

    2013-08-01

    Full Text Available The Central Asian Orogenic Belt, or Altaids, is an amalgamation of volcanic arcs and microcontinent blocks that records a complex late Precambrian–Mesozoic accretionary history. Although microcontinents cored by Precambrian basement are proposed to play an integral role in the accretion process, a lack of isotopic data hampers volume estimates of newly produced arc-derived versus old-cratonic crust in southeastern Mongolia. This study investigates metamorphic tectonites in southern Mongolia that have been mapped as Precambrian in age, largely on the basis of their high metamorphic grade and high strain. Here we present results from microstructural analyses and U-Pb zircon geochronology on samples from Tavan Har (44.05° N, 109.55° E and the Yagan-Onch Hayrhan metamorphic core complex (41.89° N, 104.24° E. Our results show no compelling evidence for Precambrian basement in southeastern Mongolia. Rather, the protoliths to all tectonites examined are Paleozoic–Mesozoic age rocks, formed during Devonian–Carboniferous arc magmatism and subsequent Permian–Triassic orogenesis during collision of the South Mongolia arc with the northern margin of China. These results yield important insights into the Paleozoic accretionary history of southern Mongolia, including the genesis of metamorphic and igneous basement during the Paleozoic, as well as implications for subsequent intracontinental reactivation.

  8. Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria)

    Science.gov (United States)

    Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Vitale-Brovarone, Alberto; Fernandez, Laure; Hammor, Dalila; Laouar, Rabah; Ouabadi, Aziouz; Abdallah, Nachida; Mechati, Mehdi

    2017-09-01

    Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

  9. The Intermediate-P/T metamorphism from the Misan Formation in the Imjingang belt, Korean Peninsula and its meaning to the geological relationship between Korea and China

    Science.gov (United States)

    Lee, B. Y.; Oh, C. W.

    2016-12-01

    Korean Peninsula consists of three Precambiran massifs from north to south: the Nangrim, Gyeonggi and Yeongnam massifs. The Imjingang belt is distributed between the Nangrim and Gyeonggi massifs. The Ogcheon belt locates between the Gyeonggi and Yeongnam massifs. The Imjingang belt had been suggested as the extension of the Dabie-Sulu collision belt between the North and South China Cratons but no evidence of collision was found and recently the Hongseong-Odesan belt locating between the Imjingang and Ogcheon belts was suggested as the extension of the Dabie-Sulu collision belt based on the finding of eclogite and ultrahigh temperature metamorphic rocks. so it is necessary to study the metamorphism of the Imjingang belt to confirm whether the Imjingang belt is the collision belt or not. The Imjingang belt is divided into the Jingok and Samgot units. The Jingok unit locates on the northern part of the Imjingang belt and underwent intermediate-P/T metamorphism resulting the Barrovian paragenetic sequence; the garnet, staurolite, kyanite zones from north to south. The P-T conditions of the garnet and staurolite zones are ca. 500-630° and 3-9kbar (Kim, 2002). The Kyanite zone gives peak metamorphic P-T of ca. 665-710° and 9kbar (Kim,2002; Cho et al.,2007). To extend the previous research, we study the meta-sedimentary unit in the Misan Formation of the Samgot units locating on the southern part of the Imjingang belt. The meta-sedimentary unit consists of interlayered biotite schist and hornblende schist. The P-T conditions of estimated from the biotite schist is ca.714-826° and 11-16kbar representing that the Imjingang belt had undergone the intermediate-P/T metamorhism from the garnet zone through the staurolite and kyanite zones in the Jingok unit to the Samgot unit. Similar intermediate-P/T metamorphism was reported from the Ogcheon belt in which metamorphic grade increases northwards. Whereas the metamorphic grade in the Imjingang belt increases southwards

  10. Metamorphic P-T evolution and U-Th-total Pb monazite dating of metapelites from the Nellore schist belt, Southeastern India: Implications for the Proterozoic tectonics

    Science.gov (United States)

    Hrushikesh, Hari; Prabhakar, Naraga

    2017-04-01

    The Paleoproterozoic Nellore Schist Belt (NSB) in the southeastern margin of the eastern Dharwar Craton (India) is predominantly described as a collision zone formed by accretionary growth. Two lithological groups are distinguished within the NSB: (a) a lower Vinjamuru Domain (VD) mainly consists of amphibolite facies metagabbros and amphibolites, and (b) an upper Udayagiri domain with greenschist facies platformal metasedimentary sequences. The present study emphasizes on demonstrating the structural, metamorphic, and chronological history of the metapelites from Saidapuram and Malakonda areas of the VD. These metapelites are sporadically exposed as lensoidal bodies composed of garnet + staurolite + kyanite + biotite + muscovite + paragonite and garnet + staurolite + plagioclase + biotite + muscovite ± kyanite mineral assemblages along with quartz and ilmenite. Integration of deformation microtextures with the results of phase equilibrium modelling coupled with conventional thermobarometric studies indicate the presence of three stages of metamorphism (M1-M2-M3). The garnet + kyanite + muscovite + quartz ± biotite assemblage characterize the early metamorphic event (M1), which is syntectonic with F1 folding at P-T conditions 540-560 ˚ C and 6.0-6.4 kb. The P-T conditions of syn/post-D2 peak metamorphism (M2) represented by garnet + staurolite + muscovite + biotite + plagioclase + quartz ± kyanite assemblage were equilibrated at 600-620 ˚ C and 7.8-8.2 kb. The last episode of metamorphism (M3) coeval with D3 crenulation cleavage gave rise to chlorite + muscovite ± biotite retrograde mineral assemblage. Texturally constrained U-Th-total Pb monazite dating reveals three distinct populations clustering around 1.65-1.55, 1.45-1.35 and 0.80 Ga in the metapelites. The chemical ages (1.65-1.55 Ga) retrieved from monazite cores limit the upper amphibolite facies peak metamorphism in the pelitic rocks that presumably stabilized major part of the crust within the NSB

  11. Thermal Inertia of Rocks and Rock Populations

    Science.gov (United States)

    Golombek, M. P.; Jakosky, B. M.; Mellon, M. T.

    2001-01-01

    The effective thermal inertia of rock populations on Mars and Earth is derived from a model of effective inertia versus rock diameter. Results allow a parameterization of the effective rock inertia versus rock abundance and bulk and fine component inertia. Additional information is contained in the original extended abstract.

  12. The post-impact metamorphism textures of various type meteorites

    Science.gov (United States)

    Grokhovsky, V.; Muftakhetdinova, R.; Petrova, E.; Yakovlev, G.

    2017-09-01

    A review of the features of shock metamorphism is given of stone and iron meteorites after high-intensity shock loading; In the simulation experiments, possible structural changes in the meteorite matter are demonstrated with significant peak pressure and temperature. This allows obtaining structural changes from melting to plastic deformation of the test substance.

  13. Fluid inclusions in high-grade metamorphic rocks from S.W. Norway

    NARCIS (Netherlands)

    Swanenberg, H.E.C.

    1980-01-01

    In part one of this thesis, isochoric sections, based on a modified Redl i ch-Kwong equat ion, are presented for the systems C02, C02-N2, N2-CHll and H20-C0 2, This allows the P-T interpretation of fluid inclusion freezing data in terms of the above-mentioned reference systems. Part two deals with

  14. Fluid inclusions in high-grade metamorphic rocks from S.W. Norway

    NARCIS (Netherlands)

    Swanenberg, H.E.C.

    1980-01-01

    In part one of this thesis, isochoric sections, based on a modified Redl i ch-Kwong equat ion, are presented for the systems C02, C02-N2, N2-CHll and H20-C0 2, This allows the P-T interpretation of fluid inclusion freezing data in terms of the above-mentioned reference systems. Part two deals

  15. Metamorphic evolution and U-Pb zircon SHRIMP geochronology of the Belizário ultramafic amphibolite, Encantadas Complex, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    Hartmann Léo A.

    2003-01-01

    Full Text Available The integrated investigation of metamorphism and zircon U-Pb SHRIMP geochronology of the Belizário ultramafic amphibolite from southernmost Brazil leads to a better understanding of the processes involved in the generation of the Encantadas Complex. Magmatic evidence of the magnesian basalt or pyroxenite protolith is only preserved in cores of zircon crystals, which are dated at 2257 ± 12 Ma. Amphibolite facies metamorphism M1 formed voluminous hornblende in the investigated rock possibly at 1989 ± 21 Ma. This ultramafic rock was re-metamorphosed at 702±21 Ma during a greenschist facies eventM2; the assemblage actinolite + oligoclase + microcline + epidote + titanite + monazite formed by alteration of hornblende. The metamorphic events are probably related to the Encantadas Orogeny (2257±12 Ma and Camboriú Orogeny (~ 1989 Ma of the Trans-Amazonian Cycle, followed by an orogenic event (702±21 Ma of the Brasiliano Cycle. The intervening cratonic period (2000-700 Ma corresponds to the existence of the Supercontinent Atlantica, known regionally as the Rio de la Plata Craton.

  16. 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

  17. High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity

    Science.gov (United States)

    Le Guillou, Corentin; Rouzaud, Jean-Noël.; Bonal, Lydie; Quirico, Eric; Derenne, Sylvie; Remusat, Laurent

    2012-03-01

    The insoluble carbonaceous matter from 12 chondrites (CI, CM, CO, CV, EH, and UOC), was characterized by high resolution transmission electron microscopy (HRTEM). Besides ubiquitous nanoglobules, the insoluble organic matter from petrologic type 1 and 2 chondrites and Semarkona (LL 3.0) is composed of a highly disordered polyaromatic component. No structural differences were observed between these IOMs, in agreement with the limited thermal metamorphism they all experienced. In chondrites of petrologic type >3.0, the evolution of the IOM is controlled by the extent of thermal metamorphism. The polyaromatic layers, shorter than 1 nm in petrologic type ≤3.0 chondrites, grow up to sizes between 5 and 10 nm in petrologic type >3.6 chondrites, contributing to the increase of the degree of structural order. In addition, we find rare, but ubiquitous onion-like carbons, which may be the product of nanodiamond graphitization. The insoluble carbonaceous matter of the enstatite chondrite Sahara 97096 (EH 3) is different from the other meteorites studied here. It is more heterogeneous and displays a high abundance of graphitized particles. This may be the result of a mixture between (1) the disordered carbon located in the matrix, and (2) catalytic graphitized phases associated with metal, potentially originating from partial melting events. The structural and nanostructural evolution are similar in all IOMs. This suggests that the structure of the accreted precursors and the parent body conditions of their secondary thermal modifications (temperature, duration, and pressure) were similar. The limited degree of organization of the most metamorphosed IOMs compared with terrestrial rocks submitted to similar temperature suggests that the conditions are not favorable to graphitization processes, due to the chemical nature of the precursor or the lack of confinement pressure.

  18. Omphacite microstructures as time-temperature indicators of blueschist- and eclogite-facies metamorphism

    Science.gov (United States)

    Carpenter, Michael A.

    1982-03-01

    Omphacites from a wide range of geological environments have been examined by transmission electron-microscopy. Their microstructures are sufficiently variable as to be potential indicators of thermal history for blueschist and eclogite metamorphism. In particular, the average size of equiaxed antiphase domains (APD's) arising from cation ordering appears to be a characteristic feature of each environment and increases in the sequence: Franciscan, blueschist (1) ≈ Turkey, blueschist (2) Wine Complex, Canada, amphibolite (1) disordering (75 kcal mole-1), available estimates of peak metamorphic temperature ( T) are used, and a reasonable geological time-scale is taken as 104 108 years. According to this model, APD sizes are set in a relatively short interval of the total history of a rock when its temperature is close to its peak value. APD sizes are much more sensitive to temperature than to time and may be used as a geothermometer which has the advantage of not being reset by re-equilibration at low temperatures. Petrological implications arising from the model are that Allalin metagabbros were metamorphosed at a similar peak temperature to Zermatt-Saas blueschists, Franciscan eclogites reached higher temperatures than has been previously supposed and that the microstructures in some Sesia-Lanzo omphacites are consistent with a high temperature, pre-blueschist origin. Deviation from an ideal coarsening law with n=2 implies that the APD's are not simply stacking mistakes but have some associated structural or compositional modification locally. Excess titanium concentrated at APD's in Red Wine Complex omphacites may account for their anomalously low observed APD size.

  19. Geochronological synthesis of magmatism, metamorphism and metallogeny of Costa Rica, Central America

    International Nuclear Information System (INIS)

    Alvarado, Guillermo E.; Gans, Phillipe B.

    2012-01-01

    A comprehensive compilation of 651 (since 1968) radiometric ages determinations (415 40 Ar/ 39 Ar, 211 K/Ar, 5 U/Th, 4 Rb/Sr, 2 U/Pb, and 13 fission track thermochronology ages using zircon) have provided a complete picture of the igneous stratigraphy of Costa Rica, and information about the age of the major metamorphic and metallogenic events in the region. Igneous rocks of Late Jurassic to Middle Eocene age (∼ 160 to ∼ 41 Ma), mainly accreted ophiolites. The actual subduction zone was established, represented by volcano-sedimentary rocks of basic to felsic composition, at the beginning of Campanian time (∼ 71 Ma). However, voluminous subalkaline, primary volcanic rocks have appeared only after ∼ 29 Ma. Intrusive to hypabyssal granitic to gabboic plutons, stocks, equivalent dykes and sills, are widely exposed in the Talamanca range (∼ 12,4 - 7,8 Ma), hills of Escazu (∼ 6,0 - 5,9 Ma), and Fila Costena (∼ 18,3 - 16,8 and ∼ 14,8 - 11,1 Ma), Tapanti-Montes del Aguacate-Carpintera (∼ 4,2 - 2,2 Ma) and Guacimal (∼ 6,4 - 5,2 Ma). Arc rocks between 29 and 11 Ma (called Photo-Volcanic Front) are known in the San Carlos plains and in southern Costa Rica. The location and age of the igneous rocks have indicated that there was a 20 degrees counterclockwise rotation of the arc (termed as Proto-Volcanic Front) between 15 and 8 Ma, with a pole of rotation that has centered on southern Costa Rica. This rotation is attributed to deformation in the overriding plate (shortening in the south coeval with extension in the NW), accompanied by trench retreat in the south. At ∼ 3,45 Ma, arc-related volcanism has shut off in southern part of the region, but local acid-adakite volcanism has persisted in the Talamanca range (4,2 - 0,95 Ma) due to the subduction of the Cocos Ridge. The Paleo-Volcanic Front is represented by arc-related rocks (8 - 3,5 Ma) along the length of Costa Rica, parallel to but in front of the modern arc. This activity was followed by the

  20. Mechanical behaviour of the Oman metamorphic sole: rheology of amphibolites at lower crustal conditions during subduction initiation

    Science.gov (United States)

    Soret, Mathieu; Agard, Philippe; Ildefonse, Benoît; Dubacq, Benoît; Prigent, Cécile; Yamato, Philippe

    2017-04-01

    Amphibolites are commonly found in the middle to lower continental crust and along oceanic transform faults and detachments. Amphibolites are also the main component of metamorphic soles beneath highly strained peridotites at the base of large-scale ophiolites as exemplified in Oman. Metamorphic soles are crustal slivers stripped from the slab during early subduction and underplated below the upper plate (future ophiolite) mantle when the subduction interface is still young and warm (i.e. during the first million years -My- of intra-oceanic subduction). Understanding the rheological behaviour of amphibolitic rocks is therefore of major interest to model and quantify deformation and strain localisation in varied geodynamical environments. This contribution focuses on the deformation mechanisms of amphibole through a microstructural and petrological study of garnet-bearing and garnet-free clinopyroxene-bearing amphibolites, using EBSD analysis. The first aim is to test the influence of progres- sive changes in PT conditions during deformation and of the appearance/disappearance of anhydrous minerals (plagioclase, clinopyroxene and garnet) on the mechanical behaviour of mafic amphibolites. The second aim is to track deformation mechanisms during early subduction, through the study of these metamorphosed oceanic rocks, commonly 10-100 m thick, which range from high- to low-grade away from the contact with the peridotites (i.e. from 800 ± 100˚C - 0.9 ± 0.2 GPa to 500 ± 100˚C - 0.5 ± 0.1 GPa) and are essentially mafic at the top). Our study points out the existence of two major steps of deformation in the high-temperature amphibolite slices of the metamorphic soles during the early subdduction dynamics. These two steps witness important mechanical coupling and progressive strain localization at plate interface under cooling and hydrated conditions after subduction initiation. During the accretion of the first slice of metamorphic sole at 850 ± 50˚C (the garnet

  1. Metamorphic history and age of aluminous gneisses of the Belomorian belt of the Baltic shield

    International Nuclear Information System (INIS)

    Bibikova, E.V.; Borisova, E.Yu.; Makarov, V.A.; Drugova, G.M.

    1997-01-01

    Metamorphic conditions and age are determined for the early metamorphic stage of aluminous gneisses in the Chupa nappe in the Belomorian Mobile Belt. The granulite-facies metamorphic conditions during Late Archean time are determined based on the composition of garnet and biotie from the metapelites. The early metamorphic stage was dated at 2860 ± 30 Ma based on the U-Pb systematics of granulitic zircon from the metapelites. The U-Pb isotopic system of the zircon was strongly affected by Svecogennian metamorphism (at 1750 Ma). The geodynamic evolution of the Belomorian Mobile Belt is discussed in light of the data of this work

  2. Natural radioactivity of the rocks from the Moon and planets

    International Nuclear Information System (INIS)

    Surkov, Yu.A.

    1982-01-01

    Tha data on natural radioactivity of rocks (U, Th and K contents) from the Moon, Venus and Mars obtained by means of cosmic means are analyzed. The Moon rock radioactivity has been measured in situ (from orbital vehicles) as well as in the samples of lunar material delivered to the Earth and as for Venus and Mars rocks - by landing vehicles. It has been found that the main specific feature of the Moon and the Earth group planets is the presence of two geomorphological types of the structure of their surface composed by two different types of the matter. The ancient contineent regions are made up by feldspar rock - gabbroanorthosite at the Moon (and possibly at the Mars) and granite-metamorphic at the Earth (and possibly at the Venus). The younger ''marine'' regions are composed by basalt rock. The presence at the Moon of two types of crust (marine and continental ones) having a different nature is clearly reflected on the Moon radioactivity map where marine regions (15% of the total surface) which have high radioactivity and continental regions with a relatively low radioactivity can be seen. The discovery of rocks on the Venus surface highly enriched by U, Th and K speaks of their melting from the primary matter in the depth of the Earth. The Marsian rock by the natural radioelement content is close to igneous rocks of the Earth crust of the basic composition and lunar marine basalts

  3. Radwaste storage in crystalline rocks: a natural analog

    International Nuclear Information System (INIS)

    Brookins, D.G.; Abashian, M.S.; Cohen, L.H.; Wollenberg, H.A.

    1982-01-01

    The Eldora-Bryan Stock (Colorado) intruded the 1.4-1.6 billion year old metamorphic rocks of the Idaho Springs Formation 55 million years ago. The stock may be considered a giant analog of a radwaste form without canister or engineered backfill barriers. The authors' lanthanide studies show the following: (1) The intrusive rocks remained as a closed system. (2) Lanthanide/chondrite versus ionic radius plots show only local redistribution in the immediate contact zone, and that rocks in this zone have not gained lanthanides from the magma. (3) No whole rock perturbations for the lanthanides are noted at distances greater than 3 m from the contact. Stable oxygen isotopic variations show a narrow 9.0 +- 0.3 per mille range for the intrusive rocks and whole rock values from 7.6 to 10.0 per mille for the intruded rocks. The authors conclude: (1) The Idaho Springs Formation was not penetrated by hydrothermal fluids from the Eldora-Bryan magma except possibly on a local scale within 3 m of the contact. (2) The light lanthanides may be locally redistributed in the immediate contact zone, but without additions from the magma. (3) The oxygen isotopic data imply lack of hydrothermal fluids from the magma penetrating the intruded rocks, even in the highest temperature contact zones. Whole rock data imply closed system conditions for Rb, Sr, Th, U, Pb even where mineral ages have been lowered. Data for Co, Cr, Sc, Fe, Cs also indicate retention in whole rock systems and no exchange with the magma. The combined chemical, isotopic, petrographic and theoretical data and calculations indicate suitability of rocks of the Idaho Springs Formation, and thus of many types of crystalline rocks as well, for possible use for the storage of radioactive waste

  4. Timing of exhumation of the Ereendavaa metamorphic core complex (north-eastern Mongolia) - U-Pb and 40Ar/39Ar constraints

    Science.gov (United States)

    Daoudene, Yannick; Ruffet, Gilles; Cocherie, Alain; Ledru, Patrick; Gapais, Denis

    2013-01-01

    The occurrence of numerous NE-SW trending rift basins that locally bound metamorphic core complexes in Transbaikalia, northern Mongolia and north-eastern China indicates that the eastern domain of the Central Asian Orogenic Belt was affected by a large-scale NW-SE extensional tectonic event during late Jurassic to early Cretaceous times. Available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in Transbaikalia (134-121 Ma) and North China (136-110 Ma) suggesting dome exhumation during the early Cretaceous. In north-eastern Mongolia, the Ereendavaa Range, lined by the Onon Shear Zone, was recently interpreted as one of these metamorphic core complexes, of late Jurassic to early Cretaceous age, on the basis of U-Pb zircons data from two synkinematic pegmatite dykes. However, this wide time range remains to be discussed. The present work constrains the tectono-thermal evolution of the range by providing new MC-ICP-MS U-Pb zircons ages from pegmatite dykes and metamorphic igneous rocks, and mica and amphibole 40Ar/39Ar laser step-heating ages from metamorphic and magmatic rocks that crop out within the range. The results show that (1) the Ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late Jurassic times, (2) cooling of the range began at least at 137.9 ± 0.3 Ma as revealed by a 40Ar/39Ar plateau ages obtained from an hornblende sampled within the range core, and (3) exhumation along the Onon Shear Zone occurred from 130.3 ± 1.9 Ma down to 124.8 ± 0.3 Ma, as shown by ages of most of micas and amphiboles from the Shear zone. These more accurate ages are consistent with metamorphic core complex ages from adjacent areas. Furthermore, they argue for an extensional dynamic paroxysm at the scale of eastern Asia during a narrow time range in the early Cretaceous between ca. 130 Ma and ca. 120 Ma.

  5. Terrestrial impact melt rocks and glasses

    Science.gov (United States)

    Dressler, B. O.; Reimold, W. U.

    2001-12-01

    The effects of meteorite and comet impact on Earth are rock brecciation, the formation of shock metamorphic features, rock melting, and the formation of impact structures, i.e. simple craters, complex craters, and multi-ring basins. Large events, such as the 65-Ma Chicxulub impact, are believed to have had catastrophic environmental effects that profoundly influenced the development of life on Earth. In this review, an attempt is made to summarize some of the voluminous literature on impact melting, one important aspect of planetary impact, provide some comments on this process, and to make suggestions for future research. The products of impact melting are glasses, impact melt rocks, and pseudotachylites. Our treatise deals mainly with the geological setting, petrography, and major-element chemistry of melt rocks and glasses. Impact glasses, in several petrographic aspects, are similar to volcanic glasses, but they are associated with shock metamorphosed mineral and rock fragments and, in places, with siderophile element anomalies suggestive of meteoritic contamination. They are found in allogenic breccia deposits within (fall-back 'suevite') and outside (fall-out 'suevite') impact craters and, as spherules, in distal ejecta. Large events, such as the K/T boundary Chicxulub impact, are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris. Impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common. On a microscopic scale, however, impact glasses are commonly strikingly heterogeneous. Tektites are glasses ejected from craters over large distances. They are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal, sedimentary rocks. Four tektite strewn-fields are known, three of which can be tied to specific impact

  6. Metamorphic hemispherical microphone array for three-dimensional acoustics

    Science.gov (United States)

    Biswas, Shantonu; Reiprich, Johannes; Cohrs, Thaden; Stauden, Thomas; Pezoldt, Joerg; Jacobs, Heiko O.

    2017-07-01

    This article describes the realization of a metamorphic stretchable microphone array, which can be inflated by air to morph from a planar to a hemispherical shape. The array undergoes morphological changes to adjust their receive characteristic. To realize this device, a metamorphic printed circuit board technology (m-PCB) is described. The resulting products are millimeter-thin stretchable silicone embedded and electrically interconnected electronic structures with mechanical properties, which resemble a silicone membrane. The microphone array is used to localize a sound source in a 3D space. The results of the planar orientation (resting shape), and the 3D hemispherical orientation after air inflation are compared. The inflated hemispherical microphone array proofs to be better for 3D acoustic localization and/or beam-forming.

  7. Pathway to 50% Efficient Inverted Metamorphic Concentrator Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Geisz, John F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Steiner, Myles A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schulte, Kevin L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); France, Ryan M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); McMahon, William E [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perl, Emmett [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Horowitz, Kelsey A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Friedman, Daniel J [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-09-06

    Series-connected five (5J) and six junction (6J) concentrator solar cell strategies have the realistic potential to exceed 50% efficiency to enable low-cost CPV systems. We propose three strategies for developing a practical 6J device. We have overcome many of the challenges required to build such concentrator solar cell devices: We have developed 2.1 eV AlGaInP, 1.7 eV AlGaAs, and 1.7 eV GaInAsP junctions with external radiative efficiency greater than 0.1%. We have developed a transparent tunnel junction that absorbs minimal light intended for the second junction yet resists degradation under thermal load. We have developed metamorphic grades from the GaAs to the InP lattice constant that are transparent to sub-GaAs bandgap light. We have grown and compared low bandgap junctions (0.7eV - 1.2 eV) using metamorphic GaInAs, metamorphic GaInAsP, and GaInAsP lattice-matched to InP. And finally, we have demonstrated excellent performance in a high voltage, low current 4 junction inverted metamorphic device using 2.1, 1.7, 1.4, and 1.1 eV junctions with over 8.7 mA/cm2 one-sun current density that operates up to 1000 suns without tunnel junction failure.

  8. Cordilleran metamorphic core complexes and their uranium favorability. Final report

    International Nuclear Information System (INIS)

    Coney, P.J.; Reynolds, S.J.

    1980-11-01

    The objective of this report is to provide a descriptive body of knowledge on Cordilleran metamorphic core complexes including their lithologic and structural characteristics, their distribution within the Cordillera, and their evolutionary history and tectonic setting. The occurrence of uranium in the context of possibility for uranium concentration is also examined. Chapter 1 is an overview of Cordilleran metamorphic core complexes which describes their physical characteristics, tectonic setting and geologic history. This overview is accompanied by a tectonic map. Chapter 2 is a discussion of the mantled gneiss dome concept. The purpose of including this work is to provide a basic history of this concept and to describe the characteristics and distribution of gneiss domes throughout the world to enable one to compare and contrast them with the metamorphic core complexes as discussed in this report. Some gneiss domes are known producers of uranium (as are also some core complexes). Chapter 3 is an examination of the effects of the core complex process on adjacent sedimentary and volcanic cover terranes. Also included is a discussion of the kinematic significance of these cover terranes as they are related to process within the cores of the complexes. Some of the cover terranes have uranium prospects in them. Chapter 4 is a detailed discussion of uranium in Cordilleran metamorphic core complexes and includes the conceptual basis for the various types of occurrences and the processes that might favor concentration of uranium. The report is supported by a 5-part Appendix. The majority of the core complexes discussed in this report either do not appear or are not recognizable on existing published geologic maps

  9. Correlated evolution of phenotypic plasticity in metamorphic timing

    OpenAIRE

    Michimae, H.; Emura, T.

    2012-01-01

    Phenotypic plasticity has long been a focus of research, but the mechanisms of its evolution remain controversial. Many amphibian species exhibit a similar plastic response in metamorphic timing in response to multiple environmental factors; therefore, more than one environmental factor has likely influenced the evolution of plasticity. However, it is unclear whether the plastic responses to different factors have evolved independently. In this study, we examined the relationship between the ...

  10. CERN Rocks

    CERN Document Server

    2004-01-01

    The 15th CERN Hardronic Festival took place on 17 July on the terrace of Rest 3 (Prévessin). Over 1000 people, from CERN and other International Organizations, came to enjoy the warm summer night, and to watch the best of the World's High Energy music. Jazz, rock, pop, country, metal, blues, funk and punk blasted out from 9 bands from the CERN Musiclub and Jazz club, alternating on two stages in a non-stop show.  The night reached its hottest point when The Canettes Blues Band got everybody dancing to sixties R&B tunes (pictured). Meanwhile, the bars and food vans were working at full capacity, under the expert management of the CERN Softball club, who were at the same time running a Softball tournament in the adjacent "Higgs Field". The Hardronic Festival is the main yearly CERN music event, and it is organized with the support of the Staff Association and the CERN Administration.

  11. Carbide-metal assemblages in a sample returned from asteroid 25143 Itokawa: Evidence for methane-rich fluids during metamorphism

    Science.gov (United States)

    Harries, Dennis; Langenhorst, Falko

    2018-02-01

    We found that the particle RA-QD02-0115 returned by the Hayabusa spacecraft from near-Earth asteroid 25143 Itokawa contains the iron carbide haxonite (Fe21.9-22.7Co0.2-0.3Ni0.2-0.8)C6 and several Fe,Ni alloys, including multi-domain tetrataenite and spinodally decomposed taenite. Ellipsoidal to nearly spherical voids occur throughout the particle and suggest the presence of a fluid phase during textural and chemical equilibration of the host rock within the parent asteroid of 25143 Itokawa. The calculated solubility of carbon in Fe,Ni metal indicates that the carbide formed at temperatures larger than 600 °C during thermal metamorphism of the LL-chondritic mineral assemblage. Haxonite formed metastably with respect to graphite and cohenite, probably due to its high degree of lattice match with neighboring taenite, a low cooling rate at peak metamorphic temperatures, and the hindered nucleation of graphite. Thermodynamic equilibrium calculations indicate that the fluid present was dry (H2O-poor) and dominated by methane. The reactive fluid most plausibly had an atomic H/C ratio of 4-5 and was derived from the reduction of macromolecular, insoluble organic matter (IOM) that initially co-accreted with water ice. The initial presence of water is a necessary assumption to provide sufficient hydrogen for the formation of methane from hydrolyzed IOM. Metallic iron was in turn partially oxidized and incorporated into the ferromagnesian silicates during the high-temperature stage of metamorphism. An exemplary bulk reaction from unequilibrated material on the left to an equilibrated assemblage on the right may be written as: 330 CH0.8O0.2(IOM) + 500 H2O(ice/g) + 681 Fe(in alloy) + 566 FeSiO3(in Opx) → 300 CH4(g) + 32 H2(g) + 5 Fe23C6(in Hx) + 566 Fe2SiO4(in Ol) (Opx = orthopyroxene, Hx = haxonite, Ol = olivine, g = fluid species). The best estimate of the fluid/rock ratio in the region of the LL parent body where RA-QD02-0115 formed is about 3 × 10-3 and corresponds to

  12. Geotectonic significance of Neoproterozoic amphibolites from the Central Eastern Desert of Egypt: A possible dismembered sub-ophiolitic metamorphic sole

    Science.gov (United States)

    Farahat, E. S.

    2011-07-01

    Supra-subduction zone ophiolites in the Egyptian Central Eastern Desert (CED) occur as clusters in its northern (NCEDO) and southern (SCEDO) parts, displaying abundant island arc-boninitic and MORB/island-arc geochemical affinities, respectively. An amphibolite belt, including the investigated massive to slightly foliated Wadi Um Gheig (WUG) amphibolites, is exposed in the southeast most of the NCEDO thrusting over the El Sibai gneissic association and intruded by late- to post-orogenic granitoids and gabbros. The WUG rocks are metamorphosed under epidote amphibolite to common amphibolite facies. The amphiboles are calcic and represented by actinolitic hornblende to magnesio-hornblende in the epidote amphibolites and magnesio- to ferro-hornblende in the amphibolites. Plagioclase composition varies from pure albite (An3-8) in the epidote amphibolites to andesine and labradorite (An36-65) in the amphibolites. The estimated P-T conditions are in favor of their metamorphism under epidote amphibolite (c. 550-600 °C and 2-3 ± 1.5 kbar) and amphibolite (c. 618-720 °C and 3-6 ± 1.5 kbar) facies. The peak metamorphic conditions point to a burial depth of c.15-20 km. Geochemically, the WUG amphibolites show basaltic to andesitic compositions of tholeiitic affinity. They display LILE-enriched MORB-normalized patterns with negative Nb anomalies characteristic of the subduction-related rocks. However, their chondrite-normalized rare-earth element (REE) patterns vary from LREE-depleted (LaN/YbN = 0.29 to 0.49) to LREE-enriched (LaN/YbN = 2.97 to 3.74). Few samples show major and trace element contents typical of boninitic rocks, including U-shaped REE pattern. On the standard tectonic discrimination diagrams the WUG amphibolites plot mostly in the island-arc fields with some samples of MORB and boninitic affinities. Greenschist facies metamorphosed NCEDO obviously share these geochemical characteristics, implying formation in the same tectonic environment, i.e. forearc basin

  13. Resetting of Mg isotopes between calcite and dolomite during burial metamorphism: Outlook of Mg isotopes as geothermometer and seawater proxy

    Science.gov (United States)

    Hu, Zhongya; Hu, Wenxuan; Wang, Xiaomin; Lu, Yizhou; Wang, Lichao; Liao, Zhiwei; Li, Weiqiang

    2017-07-01

    Magnesium isotopes are an emerging tool to study the geological processes recorded in carbonates. Calcite, due to its ubiquitous occurrence and the large Mg isotope fractionation associated with the mineral, has attracted great interests in applications of Mg isotope geochemistry. However, the fidelity of Mg isotopes in geological records of carbonate minerals (e.g., calcite and dolomite) against burial metamorphism remains poorly constrained. Here we report our investigation on the Mg isotope systematics of a dolomitized Middle Triassic Geshan carbonate section in eastern China. Magnesium isotope analysis was complemented by analyses of Sr-C-O isotopic compositions, major and trace element concentrations, and petrographic and mineralogical features. Multiple lines of evidence consistently indicated that post-depositional diagenesis of carbonate minerals occurred to the carbonate rocks. Magnesium isotope compositions of the carbonate rocks closely follow a mixing trend between a high δ26Mg dolomite end member and a low δ26Mg calcite end member, irrespective of sample positions in the section and calcite/dolomite ratio in the samples. By fitting the measured Mg isotope data using a two-end member mixing model, an inter-mineral Δ26Mgdolomite-calcite fractionation of 0.72‰ was obtained. Based on the experimentally derived Mg isotope fractionation factors for dolomite and calcite, a temperature of 150-190 °C was calculated to correspond to the 0.72‰ Δ26Mgdolomite-calcite fractionation. Such temperature range matches with the burial-thermal history of the local strata, making a successful case of Mg isotope geothermometry. Our results indicate that both calcite and dolomite had been re-equilibrated during burial metamorphism, and based on isotope mass balance of Mg, the system was buffered by dolomite in the section. Therefore, burial metamorphism may reset Mg isotope signature of calcite, and Mg isotope compositions in calcite should be dealt with caution in

  14. The Punta del Este terrain and its volcano sedimentary cover, metamorphic and sedimentary: geology, geochemistry and geochronology

    International Nuclear Information System (INIS)

    Preciozzi, F.

    2015-01-01

    Gariep belt it develops over the West Africa coastal region of Namibia underlying on Namaqua metamorphic complex.It characterized by supra crustal rocks affected for a very low to low metamorphism and in two tecto no-stratigraphic units identified by Base i et al 2005 showing that sediments of Formation Rocha in Uruguay and the Group Oranjemund Gariep in S E Africa have similar ages in the provenance of the zircons, suggesting that they were probably deposited in the same basin. This unit exhibits detrital zircons around 600my, sedimentation and metamorphism and deformación occur in a narrow time interval from 600-610 to 574 m (Granite de Castillo intrusion) .Cam pal et al, 2005 proposed to the Cerros Aguirre Formation similar in a range of age of different events. To the east separated from the Punta del Este Terrane –Pelotas. Aigua .Florianopolis batholith s by the shear zone Alferez Cordillera (Preciozzi et al. 1999, Basei et al. 2000) Another option develops this granitic belt is an integral part of Land Punta del Este Terrane(Preciozzi in this work), being deployed on a thin cratonic granite edge. The climax of the post-brasilian magmatism is 580my, strongly related to trans current movements (eg shear zones Major Gercino-Alferez- Cordillera and Sierra Ballena.In South America an old west domain is formed by the Piedra Alta Terrane which integrate the Río de la Pl ata Craton, a central domain intensely reworked by Neoproterozoic events known so far as Nico Perez . The primary coverage is integrated by two volcano-sedimentary basins (San Carlos Formation and Cerros de Aguirre Formation)In this study are considered the Geology,Geochemistry and Geochronology of the different units of Rocha Formation

  15. Exhumation And Evolution Of Al-Taif Metamorphic Core Complex (Western Arabian Shield) During Dextral Transpressional Regime

    Science.gov (United States)

    El-Fakharani, Abdelhamid; El-Shafei, Mohamed; Hamimi, Zakaria

    2013-04-01

    Al-Taif metamorphic belt is a NE-trending belt decorating steeply dipping major transpressional shear zone in western central Arabian Shield. It comprises gneisses and migmatites that were syn-kinematically invaded under relatively high-grade metamorphic conditions by voluminous granitic bodies and a confluence of pegmatitic veins. Field mapping and outcrop investigation reveal that the belt was evolved during at least three Neoproterozoic deformations (D1-D3). D1 and D2 were progressive deformations, took place during a contractional regime, and resulted in SW-mildly plunging isoclinal folds, superimposed by NE- gently to moderately plunging folds. The prevailed tectonic regime during D3was primordially plastic, accompanied with a NE-oriented oblique shearing that was subsequently evolved as semi ductile-semi brittle shearing during an episode of exhumation. Mesoscopic kinematic indicators, as well as microstructural analysis of the collected rock samples, reflect dextral sense of shearing. Such style of shearing is most probably the conjugate trend of the NNW- to NW- oriented sinistral Najd Fault System. Various cross cutting structures and overprinting relations were detected at both the outcrop- and microscopic scales, including; ductile S2folia with ESE-plunging amphibole mineral lineations; narrow, steeply dipping ductile D2 shear zones; and semi brittle to brittle fault zones. S-C' fabrics, asymmetric strain shadows around porphyroclasts and drag fault indicate a top-to-the-NE sense of shear for most structures. The geometry and style of deformation, together with map pattern highlighted in this study attest a simple shear rotational strain origin for the domed mylonitic foliation (S1) and mineral elongation lineation (L1). This result is in congruent with the landform pattern recorded in the inner parts of the metamorphic core complexes.

  16. Tectono-metamorphic evolution of the Tavşanli zone, Western Anatolia: implications for mechanical coupling during subduction/obduction processes

    Science.gov (United States)

    Plunder, Alexis; Agard, Philippe; Chopin, Christian; Okay, Aral

    2013-04-01

    Obduction (i.e., emplacement of a dense oceanic lithosphere on top of a continent) and associated continental subduction provide insights into the rheology of the lithosphere and inter-plate mechanical coupling that usefully complements those inferred from normal oceanic subduction beneath continents. Structural and petrological data from the Tavşanlı zone are herein used to highlight processes occurring along the subduction interface from initial obduction stages (i.e., initiation of intra-oceanic subduction witnessed by metamorphic soles) to continental subduction (represented by high-pressure low-temperature, HP-LT rocks). The Tavşanlı zone (Western Anatolia) belongs to the İzmir-Ankara suture zone, which separates the Pontides and Anatolide-Tauride block. It represents a very well preserved late Cretaceous subduction interface, thanks to only mild, later collision. The Tavşanlı zone is divided in three main tectonic units related to (either continental or oceanic) subduction and obduction, respectively, which are from bottom to top: (i) the distal cover of the subducted north facing continental margin of the Anatolide-Tauride block (Orhaneli unit), which yields one of the lowest thermal gradients on earth (i.e., 5°C/km, with peak T and P of 430°C/22-24 kbar); (ii) an accretionary complex made of low-grade, subducted ocean-derived metamorphic rocks; (iii) the non-metamorphic obducted ophiolite, underlain by a thin metamorphic sole, which is found as klippen south of the İzmir-Ankara suture zone. Systematic sampling and structural work allow us to reappraise the nature, internal structure and P-T conditions of the accretionary complex sandwiched between the lower continental and upper oceanic plates. Two major tectonic units (termed complex 1 and 2) are recognised based on metamorphic grade and structural position with respect to the continental margin. Metamorphic conditions range from incipient HP-LT metamorphism (complex 1) to blueschist facies

  17. On the Magnitude and Orientation of Stress during Shock Metamorphism: Understanding Peak Ring Formation by Combining Observations and Models.

    Science.gov (United States)

    Rae, A.; Poelchau, M.; Collins, G. S.; Timms, N.; Cavosie, A. J.; Lofi, J.; Salge, T.; Riller, U. P.; Ferrière, L.; Grieve, R. A. F.; Osinski, G.; Morgan, J. V.; Expedition 364 Science Party, I. I.

    2017-12-01

    Shock metamorphism occurs during the earliest moments after impact. The magnitude and orientation of shock leaves recordable signatures in rocks, which spatially vary across an impact structure. Consequently, observations of shock metamorphism can be used to understand deformation and its history within a shock wave, and to examine subsequent deformation during crater modification. IODP-ICDP Expedition 364 recovered nearly 600 m of shocked target rocks from the peak ring of the Chicxulub Crater. Samples from the expedition were used to measure the magnitude and orientation of shock in peak ring materials, and to determine the mechanism of peak-ring emplacement. Here, we present the results of petrographic analyses of the shocked granitic target rocks of the Chicxulub peak ring; using universal-stage optical microscopy, back-scattered electron images, and electron back-scatter diffraction. Deformation microstructures in quartz include planar deformation features (PDFs), feather features (FFs), which are unique to shock conditions, as well as planar fractures and crystal-plastic deformation bands. The assemblage of PDFs in quartz suggest that the peak-ring rocks experienced shock pressures of 15 GPa throughout the recovered drill core, and that the orientation of FFs are consistent with the present-day orientation of the maximum principal stress direction during shock is close to vertical. Numerical impact simulations of the impact event were run to determine the magnitude and orientation of principal stresses during shock and track those orientations throughout crater formation. Our results are remarkably consistent with the geological data, and accurately predict both the shock-pressure magnitudes, and the final near-vertical orientation of the direction of maximum principal stress in the shock wave. Furthermore, analysis of the state of stress throughout the impact event can be used to constrain the timing of fracture and fault orientations observed in the core

  18. Late Cretaceous extension and exhumation of the Stong and Taku magmatic and metamorphic complexes, NE Peninsular Malaysia

    Science.gov (United States)

    François, T.; Md Ali, M. A.; Matenco, L.; Willingshofer, E.; Ng, T. F.; Taib, N. I.; Shuib, M. K.

    2017-08-01

    Fragmentation of large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts, as exemplified by the Stong and Taku magmatic and metamorphic complexes of northern Peninsular Malaysia. For this case, we have employed a field and microstructural kinematic study combined with low temperature thermo-chronology to analyse the tectonic and exhumation history. The results show that the Late Palaeozoic - Triassic Indosinian orogeny created successive phases of burial related metamorphism, shearing and contractional deformation. This orogenic structure was subsequently dismembered during a Cretaceous thermal event that culminated in the formation of a large scale Late Santonian - Early Maastrichtian extensional detachment, genetically associated with crustal melting, the emplacement of syn-kinematic plutons and widespread migmatisation. The emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range, represented by amphibolite- and greenschist- facies mylonites and as well as brittle structures, such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment. The formation of this detachment and a first phase of Late Cretaceous cooling was followed by renewed Eocene - Oligocene exhumation, as evidenced from our fission track ages. We infer that an initial Cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults. These Cretaceous processes played a critical role in the establishment of the presently observed crustal structure of Peninsular Malaysia.

  19. Organic tissues, graphite, and hydrocarbons in host rocks of the Rum Jungle Uranium Field, northern Australia

    Science.gov (United States)

    Foster, C.B.; Robbins, E.I.; Bone, Y.

    1990-01-01

    The Rum Jungle Uranium field consists of at least six early Proterozoic deposits that have been mined either for uranium and/or the associated base and precious metals. Organic matter in the host rocks of the Whites Formation and Coomalie Dolomite is now predominantly graphite, consistent with the metamorphic history of these rocks. For nine samples, the mean total organic carbon content is high (3.9 wt%) and ranged from 0.33 to 10.44 wt%. Palynological extracts from the host rocks include black, filamentous, stellate (Eoastrion-like), and spherical morphotypes, which are typical of early Proterozoic microbiota. The colour, abundance, and shapes of these morphotypes reflect the thermal history, organic richness, and probable lacustrine biofacies of the host rocks. Routine analysis of rock thin sections and of palynological residues shows that mineral grains in some of the host rocks are coated with graphitized organic matter. The grain coating is presumed to result from ultimate thermal degradation of a petroleum phase that existed prior to metamorphism. Hydrocarbons are, however, still present in fluid inclusions within carbonates of the Coomalie Dolomite and lower Whites Formation. The fluid inclusions fluoresce dull orange in blue-light excitation and their hydrocarbon content is confirmed by gas chromatography of whole-rock extracts. Preliminary analysis of the oil suggests that it is migrated, and because it has escaped graphitization through metamorphism it is probably not of early Proterozoic age. The presence of live oil is consistent with fluid inclusion data that suggest subsequent, low-temperature brine migration through the rocks. The present observations support earlier suggestions that organic matter in the host formations trapped uranium to form protore. Subsequent fluid migrations probably brought additional uranium and other metals to these formations, and the organic matter provided a reducing environment for entrapment. ?? 1990.

  20. Rollerjaw Rock Crusher

    Science.gov (United States)

    Peters, Gregory; Brown, Kyle; Fuerstenau, Stephen

    2009-01-01

    The rollerjaw rock crusher melds the concepts of jaw crushing and roll crushing long employed in the mining and rock-crushing industries. Rollerjaw rock crushers have been proposed for inclusion in geological exploration missions on Mars, where they would be used to pulverize rock samples into powders in the tens of micrometer particle size range required for analysis by scientific instruments.

  1. New Rb-Sr isotope data from the Mzumbe Gneiss Suite, the oldest granitoid in the Mzumbe Terrane, Natal Metamorphic Province

    International Nuclear Information System (INIS)

    Thomas, R.J.; Eglington, B.M.

    1990-01-01

    Although the rocks of the Mzumbe Gneiss suite display a close similarity to many Archaean, high-alumina tonalite-trondhjemite suites, an origin by the reactivation of a pre-existing Archaean or early Proterozoic infrastructure during the Namaqua-Natal orogenesis, can be effectively excluded. It is proposed that the Natal Metamorphic Provunce was formed by the generation and successive accretion of discrete fragments of juvenile crust onto the southern margin of the Kaapvaal craton between ∼1200 and 900 Ma. 1 fig., 9 refs

  2. SHRIMP zircon U-Pb ages and tectonic implications of igneous events in the Ereendavaa metamorphic terrane in NE Mongolia

    Science.gov (United States)

    Miao, Laicheng; Zhang, Fochin; Baatar, Munkhtsengel; Zhu, Mingshuai; Anaad, Chimedtseren

    2017-08-01

    The Ereendavaa metamorphic terrane in NE Mongolia has long been considered as a Pre-Altaid block or a Precambrian cratonic terrane with a Paleoproterozoic basement overlain by Neoproterozoic-Cambrian rocks, but the idea has not been supported by any isotopic dating. Sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb dating on gneisses, amphibolite and schists (mylonites) of the Ereendavaa terrane suggests that the terrane mainly formed during Early Paleozoic (495-464 Ma) and Late Paleozoic-Early Mesozoic (295-172 Ma). A minor amount of Precambrian rocks might have been involved in the formation of the protoliths of these rocks, as shown by Precambrian inherited zircons (1796-794 Ma). The new age data also suggest that the Ereendavaa terrane experienced at least two periods of magmatism: (1) Early Paleozoic (495-464 Ma) and (2) Late Paleozoic-Early Mesozoic (295-172 Ma), which are probably produced by the subduction of the Paleo Asian Ocean in the south and the subduction of the Mongol-Okhotsk Ocean in the north, respectively. The mylonitized granite (172 Ma) and undeformed pegmatite (163 Ma) are interpreted to be syn- and post-kinematic products. The new age data constrain the closure of the Mongol-Okhotsk Ocean at mid-Jurassic.

  3. PRINCIPLE ROCK TYPES FOR RADIOACTIVE WASTE REPOSITORIES

    Directory of Open Access Journals (Sweden)

    Sibila Borojević Šostarić

    2012-07-01

    Full Text Available Underground geological storage of high- and intermediate/low radioactive waste is aimed to represent a barrier between the surface environment and potentially hazardous radioactive elements. Permeability, behavior against external stresses, chemical reacatibility and absorption are the key geological parameters for the geological storage of radioactive waste. Three principal rock types were discussed and applied to the Dinarides: (1 evaporites in general, (2 shale, and (3 crystalline basement rocks. (1 Within the Dinarides, evaporite formations are located within the central part of a Carbonate platform and are inappropriate for storage. Offshore evaporites are located within diapiric structures of the central and southern part of the Adriatic Sea and are covered by thick Mesozoic to Cenozoic clastic sediment. Under very specific circumstances they can be considered as potential site locations for further investigation for the storage of low/intermediate level radioactive wast e. (2 Thick flysch type formation of shale to phyllite rocks are exposed at the basement units of the Petrova and Trgovska gora regions whereas (3 crystalline magmatic to metamorphic basement is exposed at the Moslavačka Gora and Slavonian Mts. regions. For high-level radioactive waste, basement phyllites and granites may represent the only realistic potential option in the NW Dinarides.

  4. Mechano-chemical coupling in stressed rocks

    Science.gov (United States)

    Dewers, Thomas; Ortoleva, Peter J.

    1989-06-01

    The free energy of a grain in a rock at depth varies as a function of the texture of its surroundings, either due to fluctuations in stress, strain energy, or interfacial factors. Herein we discuss methods Used to estimate the contribution by texture to grain free energy in deforming rocks, as well as implications for textural evolution when included in kinetic reaction-transport models. A key feature is the introduction of a formalism coupling rock flow and mineral reaction by means of a Navier-Stokes equation. The resulting set of equations describes mechano-chemical interactions under a wide range of conditions and may pose constraints on more descriptive models. Under certain circumstances, this free energy may lead to the autonomous enhancement of spatial ihhomogeneities in texture when coupled to reaction and transport in an intergranular fluid. We hold that such phenomena as metamorphic layering, spaced (solution) cleavage, geodes, and certain types of concretions are examples of mechano-chemical selforganization. The dynamics leading to formation of such texture may thus be understood in analogy with other examples of geochemical self-organization and may be quantified accordingly.

  5. Textural and chemical evolution of pyroxene during hydration and deformation: A consequence of retrograde metamorphism

    Science.gov (United States)

    Centrella, Stephen; Putnis, Andrew; Lanari, Pierre; Austrheim, Håkon

    2018-01-01

    Centimetre-sized grains of Al-rich clinopyroxene within the granulitic anorthosites of the Bergen Arcs, W-Norway undergo deformation by faults and micro-shear zones (kinks) along which fluid has been introduced. The clinopyroxene (11 wt% Al2O3) reacts to the deformation and hydration in two different ways: reaction to garnet (Alm41Prp32Grs21) plus a less aluminous pyroxene (3 wt% Al2O3) along kinks and the replacement of the Al-rich clinopyroxene by chlorite along cleavage planes. These reactions only take place in the hydrated part of a hand specimen that is separated from dry, unreacted granulite by a sharp interface that defines the limit of hydration. We use electron probe microanalysis (EPMA) and X-Ray mapping together with electron backscatter diffraction (EBSD) mapping to investigate the spatial and possible temporal relationships between these two parageneses. Gresens' analysis (Gresens, 1967) has been used to determine the mass balance and the local volume changes associated with the two reactions. The reaction to garnet + low-Al clinopyroxene induces a loss in volume of the solid phases whereas the chlorite formation gains volume. Strain variations result in local variation in undulose extinction in the parent clinopyroxene. EBSD results suggest that the density-increasing reaction to garnet + low-Al clinopyroxene takes place where the strain is highest whereas the density-decreasing reaction to chlorite forms away from shear zones where EBSD shows no significant strain. Modelling of phase equilibria suggest that the thermodynamic pressure of the assemblage within the shear zones is > 6 kbar higher than the pressure conditions for the whole rock for the same range of temperature ( 650 °C). This result suggests that the stress redistribution within a rock may play a role in determining the reactions that take place during retrograde metamorphism.

  6. Shock metamorphism in the Vredefort Collar: Evidence for internal shock sources

    Science.gov (United States)

    Lilly, P. A.

    1981-11-01

    Shock metamorphic microstructures in the Vredefort collar include planar features, crystallographically controlled cleavage, crystallographically controlled faults, and mosaic extinction. In addition, several recrystallization textures are developed in the quartzites of the collar, and quartz c axis distributions for both primary and recrystallized quartz grains are random. The degree of recrystallization decreases away from the core-collar contact. Two events of shock deformation have been identified in the collar, and using planar feature orientations, shock pressures have been estimated using the technique of Robertson (1975). The first shock (D1) subjected the lowermost Witwatersrand rocks to shock pressures of about 150 kbar and the uppermost beds to pressures of about 60 kbar. Following a period of extensive recrystallization of the quartzites came the second shock event (D2), which was weaker than the first and subjected the lowermost strata in the collar to pressures of between 75 and 100 kbar. The D2 event has been shown to be separated in time from the D1 event. The results are used to show that the shock sources were probably within the earth and that the Vredefort ring structure has formed as a result of endogenous processes rather than hypervelocity meteorite impact.

  7. Thermomechanics of an extensional shear zone, Raft River metamorphic core complex, NW Utah

    Science.gov (United States)

    Gottardi, Raphaël; Teyssier, Christian

    2013-08-01

    A detailed structural and microstructural analysis of the Miocene Raft River detachment shear zone (NW Utah) provides insight into the thermomechanical evolution of the continental crust during extension associated with the exhumation of metamorphic core complexes. Combined microstructural, electron backscattered diffraction, strain, and vorticity analysis of the very well exposed quartzite mylonite show an increase in intensity of the rock fabrics from west to east, along the transport direction, compatible with observed finite strain markers and a model of ``necking'' of the shear zone. Microstructural evidence (quartz microstructures and deformation lamellae) suggests that the detachment shear zone evolved at its peak strength, close to the dislocation creep/exponential creep transition, where meteoric fluids played an important role on strain hardening, embrittlement, and eventually seismic failure. Empirically calibrated paleopiezometers based on quartz recrystallized grain size and deformation lamellae spacing show very similar results, indicate that the shear zone developed under stress ranging from 40 MPa to 60 MPa. Using a quartzite dislocation creep flow law we further estimate that the detachment shear zone quartzite mylonite developed at a strain rates between 10-12 and 10-14 s-1. We suggest that a compressed geothermal gradient across this detachment, which was produced by a combination of ductile shearing, heat advection, and cooling by meteoric fluids, may have triggered mechanical instabilities and strongly influenced the rheology of the detachment shear zone.

  8. Petrology and SHRIMP U-Pb dating of Xitieshan eclogite, North Qaidam UHP metamorphic belt, NW China

    Science.gov (United States)

    Zhang, Cong; Zhang, Lifei; Roermund, Herman Van; Song, Shuguang; Zhang, Guibin

    2011-09-01

    Normal bimineralic and phengite-bearing eclogites have been recognized within mafic boudins (or lenses) enclosed in granitic and pelitic gneisses in the Xitieshan terrane, NW China. Bimineralic eclogite contains the primary M1 mineral assemblage Grt + Omp + Rt + Qtz+/-Zrn. Inclusions in M1 omphacite may be coesite pseudomorphs. Phengite eclogite consists of the M1 mineral assemblage Grt + Omp + Phn + Qtz + Rt+/-Zrn. Most eclogites are retrogressed to various degrees and contain hornblende, diopside and plagioclase, which commonly form symplectitic and/or kelyphitic intergrowths. The peak M1 P-T conditions of the Xitieshan eclogite are calculated to be P = 2.71-3.17 GPa and T = 751-791 °C, consistent with the presence of coesite pseudomorphs in omphacite. In addition, we have identified two stages of retrograde metamorphism; an early isothermal decompression stage (M2) followed by a later stage (M3) that developed under decreasing temperatures and pressures. During M2 internally-derived fluids played an important role, whereas during M3 and below externally-derived fluids dominated. The composition of garnet in M1changed little during M2 isothermal decompression (ITD), although pyrope contents in garnet locally decrease from core to rim where the grains have amphibole and pargasite + plagioclase coronas. Also the jadeite content (56%) of M1 omphacite decreased in the presence of active fluids during retrograde metamorphism. M1 phengite is replaced by the M2 assemblage Ms + Bt accompanied by K-feldspar + quartz. Amphibole compositions changed from magnesio-katophorite in M2 to pargasite in M3. Zircon U-Pb SHRIMP dating shows that the bimineralic eclogite has a magmatic protolith age of 877 ± 8 Ma and a metamorphic age of 439 ± 8 to 461 ± 4 Ma. We conclude that the Xitieshan metabasic rocks formed in the late Proterozoic and were subsequently subducted to depths of about 100 km, where they were metamorphosed to UHP eclogite during the late Ordovician (440-460 Ma

  9. Low Pressure-High Temperature Metamorphism and the Advection of Heat to the Continental Crust: A Case Study from Northwest New Guinea

    Science.gov (United States)

    Jost, B.; Webb, M.; White, L. T.

    2017-12-01

    In northwest New Guinea, Palaeozoic basement rocks forming part of the northern margin of the Australian continent are exposed in a rugged mountain range. This remote and understudied region provides a unique window into the complex Palaeozoic evolution and tectonic history of this region, which we help unravel with new field, petrographic, geochemical, and geochronological data. The basement rocks consist of extensive meta-turbidites that were subject to low pressure-high temperature metamorphism along their eastern margin. They are cross-cut by predominantly acidic granitoids. U-Pb zircon dating reveals that these granitoids intruded in three episodes in the Devonian-Carboniferous, the Carboniferous, and the Triassic. The first episode has not previously been reported in the region. The granitoids are strongly peraluminous, suggesting that partial melting of the meta-sedimentary country rock contributed to their petrogenesis (S-type). The occurrence and character of country rock xenoliths and migmatites supports this interpretation. Equilibrium thermodynamic modelling of the metapelites and the migmatites indicates that a substantial amount of heat was added to the lower and middle crust to cause partial melting and regional metamorphism at relatively low pressure. We propose repeated intrusion of hot magma as the mechanism responsible for advecting the necessary heat from the mantle. This likely occurred in an active continental margin setting during the Devonian-Carboniferous and the Triassic, possibly separated by an interval of magmatic quiescence during most of the Permian. New biostratigraphic and low-temperature thermochronological data reveal very recent Pliocene-Pleistocene uplift and unroofing of these basement rocks.

  10. Chemical and mineralogical data and processing methods management system prototype with application to study of the North Caucasus Blybsky Metamorphic Complexes metamorphism PT-condition

    Science.gov (United States)

    Ivanov, Stanislav; Kamzolkin, Vladimir; Konilov, Aleksandr; Aleshin, Igor

    2014-05-01

    There are many various methods of assessing the conditions of rocks formation based on determining the composition of the constituent minerals. Our objective was to create a universal tool for processing mineral's chemical analysis results and solving geothermobarometry problems by creating a database of existing sensors and providing a user-friendly standard interface. Similar computer assisted tools are based upon large collection of sensors (geothermometers and geobarometers) are known, for example, the project TPF (Konilov A.N., 1999) - text-based sensor collection tool written in PASCAL. The application contained more than 350 different sensors and has been used widely in petrochemical studies (see A.N. Konilov , A.A. Grafchikov, V.I. Fonarev 2010 for review). Our prototype uses the TPF project concept and is designed with modern application development techniques, which allows better flexibility. Main components of the designed system are 3 connected datasets: sensors collection (geothermometers, geobarometers, oxygen geobarometers, etc.), petrochemical data and modeling results. All data is maintained by special management and visualization tools and resides in sql database. System utilities allow user to import and export data in various file formats, edit records and plot graphs. Sensors database contains up to date collections of known methods. New sensors may be added by user. Measured database should be filled in by researcher. User friendly interface allows access to all available data and sensors, automates routine work, reduces the risk of common user mistakes and simplifies information exchange between research groups. We use prototype to evaluate peak pressure during the formation of garnet-amphibolite apoeclogites, gneisses and schists Blybsky metamorphic complex of the Front Range of the Northern Caucasus. In particular, our estimation of formation pressure range (18 ± 4 kbar) agrees on independent research results. The reported study was

  11. Cretaceous high-pressure metamorphic belts of the Central Pontides (northern Turkey): pre-collisional Pacific-type accretionary continental growth of Laurasian Margin

    Science.gov (United States)

    Aygul, Mesut; Okay, Aral I.; Oberhaensli, Roland; Sudo, Masafumi

    2014-05-01

    Cretaceous blueschist-facies metamorphic rocks crop out widely in the central part of the Pontides, an east-west trending mountain belt in northern Turkey. They comprise an accretionary wedge along to the southern Laurasian active continental margin and predate the opening of Black Sea basin. From North to South, the wedge consists of a low grade metaflysch unit with marble, Na-amphibole-bearing metabasite and serpentinite blocks. An extensional shear zone separates the accreted distal terrigenous sediments from HP/LT micaschists and metabasites of oceanic origin, known as Domuzdaǧ Complex. The shear zone reaches up to one km in thickness and consists of tectonic slices of serpentinite, metabasite, marble, phyllite and micaschist with top to the NW sense of shear. The Domuzdaǧ Complex predominantly consists of carbonaceous micaschist and metabasite with serpentinite, and minor metachert, marble and metagabbro. Metabasites consist mainly of epidote-blueschists sometimes with garnet. Fresh lawsonite-blueschists are found as blocks within the shear zone. Peak metamorphic assemblages in the micaschists are chloritoid-glaucophane and garnet-chloritoid-glaucophane-lawsonite in addition to phengite, paragonite, quartz, chlorite and rutile (P: 17 ± 1 Kbar, T: 390-450 °C). To the south, lithologies change slightly, with metabasite and thick, pale marble with few metachert and metapelitic horizons. The degree of metamorphism also changes. The metabasites range from high-pressure upper-greenschist facies with growth of sodic-amphibole to lower greenschist without any HP index mineral, suggesting a general decrease in pressure toward south within the prism. While Domuzdaǧ Complex represents deep-seated underplated oceanic sediments and basalts, the carbonate-rich southern parts can be interpreted as seamounts integrated into the accretionary prism. Ar/Ar dating on phengite separates both from terrigenous and oceanic metasediments give consistent plateau ages of 100 ± 2

  12. Genesis and petrology of Late Neoproterozoic pegmatites and aplites associated with the Taba metamorphic complex in southern Sinai, Egypt

    Energy Technology Data Exchange (ETDEWEB)

    Abdelfadil, K.M.; Asimow, P.D.; Azer, M.K.; Gahlan, H.A.

    2016-07-01

    We present new field, petrographical, mineralogical and geochemical data from late Neoproterozoic pegmatites and aplites in southern Sinai, Egypt, at the northernmost limit of the Arabian-Nubian Shield. The pegmatites cross-cut host rocks in the Taba Metamorphic Complex (TMC) with sharp contacts and are divided into massive and zoned pegmatites. Massive pegmatites are the most common and form veins, dykes and masses of variable dimensions; strikes range mainly from E-W through NW-SE to N-S. Mineralogically, the massive pegmatites are divided into K-feldspar-rich and albite-rich groups. Zoned pegmatites occur as lenses of variable dimensions, featuring a quartz core, an intermediate zone rich in K-feldspars and an outer finer-grained zone rich in albite. All compositions are highly evolved and display geochemical characteristics of post-collisional A-type granites: high SiO2, Na2O+K2O, FeO*/MgO, Ga/Al, Zr, Nb, Ga and Y alongside low CaO, MgO, Ba and Sr. They are rich in Rare Earth Elements (REE) and have extreme negative Eu anomalies (Eu/Eu*= 0.03–0.09). A genetic linkage between the pegmatites, aplites and alkali granite is confirmed by their common mild alkaline affinity and many other geochemical characteristics. These pegmatites and aplites represent the last small fraction of liquid remaining after extensive crystallization of granitic magma, injected along the foliation and into fractures of the host metamorphic rocks. The extensional tectonic regime and shallow depth of emplacement are consistent with a post-collisional environment. (Author)

  13. Neoproterozoic metamorphic events in the kekem area (central ...

    African Journals Online (AJOL)

    2009-06-11

    Jun 11, 2009 ... 4-3-1. Metasedimentary rocks. Representative major and trace element compositions of metasediments are given in Table 6. These rock types define a chemical trend parallel to that of average shales. (Fig 5), but with a slightly lower Al2O3/SiO2 ratio. Sillimanite-garnet-biotite gneisses display Fe2O3, MgO.

  14. U-Pb zircon geochronology and evolution of some Adirondack meta-igneous rocks

    Science.gov (United States)

    Mclelland, J. M.

    1988-01-01

    An update was presented of the recent U-Pb isotope geochronology and models for evolution of some of the meta-igneous rocks of the Adirondacks, New York. Uranium-lead zircon data from charnockites and mangerites and on baddeleyite from anorthosite suggest that the emplacement of these rocks into a stable crust took place in the range 1160 to 1130 Ma. Granulite facies metamorphism was approximately 1050 Ma as indicated by metamorphic zircon and sphene ages of the anorthosite and by development of magmatitic alaskitic gneiss. The concentric isotherms that are observed in this area are due to later doming. However, an older contact metamorphic aureole associated with anorthosite intrusion is observed where wollastonite develops in metacarbonates. Zenoliths found in the anorthosite indicate a metamorphic event prior to anorthosite emplacement. The most probable mechanism for anorthosite genesis is thought to be ponding of gabbroic magmas at the Moho. The emplacement of the anorogenic anorthosite-mangerite-charnockite suite was apparently bracketed by compressional orogenies.

  15. Metamorphic reactions, deformation localization and rheological evolution of gabbro to eclogite transformation: A case study from Lofoten Anorthosite Complex, Norway

    Science.gov (United States)

    Nasipuri, P.; Stunitz, H.; Menegon, L.; Ravna, E. J.; Kullerud, K.; Berger, A.

    2011-12-01

    Eclogitization of lower crustal rocks during subduction processes and subsequent retrogression during exhumation will produce a range of mineral assemblages over widely spaced P-T conditions affecting the rheological behavior of the rock significantly. In this contribution, we describe the formation of syn-kinematic mineral assemblages which promotes development of centimeter- to meter-scale shear zones in undeformed leucogabbro from Lofoten, Norway. Plagioclase (Pl0), olivine (Ol0) and orthopyroxene (Opx0) form the igneous texture in the leucogabbro. Opx1 and Grt1 corona indicate the onset of metamorphism (M1) during subduction processes. Cm- wide alternating bands of a mixture of Pl-Amphibole(Amph) ± Spl and GrtI(M1) - Opx -Omph (M2A) phase mixtures characterize prograde metamorphic shear zones in the leucogabbro. Elongated Omph overgrow deformed Opx grains (D1). Relicts of Opx grains are surrounded by recrystallized opx indicating that the Opx grains survived in the Omph stability field. Grt- Cpx - Pl symplectite (M2B) rim the Omph± Opx porphyroblasts. GrtII(M3) occurs along the contact of deformed Opx± Omph and Pl. Amph ± Spl (M4) overgrow the finer grained pyroxene. Conventional thermobarometry indicate that metamorphism (M1) starts at 7000C at 1 GPa pressure. The peak PT-condition (650-7500C, > 1.8 GPa) was attained during the formation of Omph. The retrograde PT-path is represented by Cpx-Pl symplectite (600-6500C, 1 GPa) and Grt corona (6000C, 0.8 GPa). Replacement of fine-grained Cpx by Amph represents the last stage of metamorphism. Crystal orientation of Opx relicts is different from the CPO of the newly formed Opx (10 - 15 μm in size) indicating that Opx did not recrystallize by progressive subgrain rotation. The dramatic grain size reduction without significant change in chemical composition is probably caused by cracking of Opx at the onset of deformation. Small new grains may nucleate from fragments. In the fine grained Pl+ Amph± Spl aggregates

  16. Aspects of the structural and late thermal evolution of the Redbank Thrust system, central Australia: constraints from the Speares Metamorphics

    International Nuclear Information System (INIS)

    Biermeier, C.; Wiesinger, M.; Stuewe, K.; Foster, D.A.

    2003-01-01

    We present new data on the field geology and late thermal evolution of the Redbank Thrust system in the Arunta Block of central Australia. Geochronological and field data from the Speares Meta-morphics are also used to relate the thermal evolution of the Redbank Thrust system to the structural evolution of the region. We show that several stages in the evolution might be discerned. An originally sedimentary sequence was intruded by mafic intrusions and then deformed during partial melting to form the principal foliation observed in the region (D1). This sequence was then folded during D2 into upright folds with north- to northeast-plunging fold axes. These events are likely to correlate with the Strangways and/or Argilke and Chewings Orogenies known from previous studies. Subsequently, the Redbank Thrust was initiated during D3. This event is recognised by deflection of the host rocks into the shear zone and might therefore have been associated with a component of strike-slip motion. It occurred probably at or before 1500-1400 Ma. Subsequent north-over-south thrust motion in the Redbank Thrust formed the intense mylonitic fabric and folded the mylonitic fabric during D4 into asymmetric folds with shallow fold axes. New 40 Ar/ 39 Ar K-feldspar ages from three samples collected from variably deformed branches of the Redbank Thrust and undeformed rocks in the Speares Metamorphics suggest that most parts of the Redbank Thrust system cooled relatively slowly after metamorphism and deformation in the Mesoproterozoic so that the D4 thrusting might have been very long-lived. Minimum ages of the K-feldspar age spectra show that the entire region cooled below 200 deg C by approximately 300 Ma. Apatite fission track ages from nine samples show that cooling through the apatite partial annealing zone occurred during Cretaceous time (ca 150-70 Ma) and modelled cooling histories are consistent with the cooling rates obtained from the K-feldspar data. They indicate that final

  17. Semantic modeling of plastic deformation of polycrystalline rock

    Science.gov (United States)

    Babaie, Hassan A.; Davarpanah, Armita

    2018-02-01

    We have developed the first iteration of the Plastic Rock Deformation (PRD) ontology by modeling the semantics of a selected set of deformational processes and mechanisms that produce, reconfigure, displace, and/or consume the material components of inhomogeneous polycrystalline rocks. The PRD knowledge model also classifies and formalizes the properties (relations) that hold between instances of the dynamic physical and chemical processes and the rock components, the complex physio-chemical, mathematical, and informational concepts of the plastic rock deformation system, the measured or calculated laboratory testing conditions, experimental procedures and protocols, the state and system variables, and the empirical flow laws that define the inter-relationships among the variables. The ontology reuses classes and properties from several existing ontologies that are built for physics, chemistry, biology, and mathematics. With its flexible design, the PRD ontology is well positioned to incrementally develop into a model that more fully represents the knowledge of plastic deformation of polycrystalline rocks in the future. The domain ontology will be used to consistently annotate varied data and information related to the microstructures and the physical and chemical processes that produce them at different spatial and temporal scales in the laboratory and in the solid Earth. The PRDKB knowledge base, when built based on the ontology, will help the community of experimental structural geologists and metamorphic petrologists to coherently and uniformly distribute, discover, access, share, and use their data through automated reasoning and integration and query of heterogeneous experimental deformation data that originate from autonomous rock testing laboratories.

  18. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    Science.gov (United States)

    García del Real, Pablo; Maher, Kate; Kluge, Tobias; Bird, Dennis K.; Brown, Gordon E.; John, Cédric M.

    2016-11-01

    Magnesium carbonate minerals produced by reaction of H2O-CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-isotope temperatures that average 23.7 ± 5.0 °C. Based on oxygen isotope thermometry, these clumped-isotope temperatures suggest

  19. Isotope-geochemical methods for investigating ores and enclosing rocks

    International Nuclear Information System (INIS)

    Berezovskij, F.I.; Gnatenko, O.V.; Zhukov, F.I.

    1985-01-01

    Isotope-geochemical methods for investigating ores and enclosing rocks as applied to uranium deposits are considered. Attention is paid to precision mass-spectrometric isotope analysis mass-spectrometric isotope analysis of light elements and to sample preparation for the analysis. Interpretation of the results of sulfur, carbon, oxygen and lead isotope investigations in uranium deposits of different genetic types allows to find definite regularities in isotope variations depending on phisico-chemical ore forming conditions. It is shown that the combination of isotope-geochemical investigations permits to make a reliable conclusion on the source of ore substance means of its transportation and deposition in the process of metamorphism

  20. Metabolism of thyroxine in Rana catesbeiana tadpoles during metamorphic climax

    International Nuclear Information System (INIS)

    Galton, V.A.; Munck, K.

    1981-01-01

    Previous studies have indicated that premetamorphic tadpoles do not convert T4 to T3 to a measurable extent (1). The present study was performed to determine whether a T4 5'-monodeiodinating system is acquired at later stages of development. [ 125 I]T4 metabolism in vivo was determined in tadpoles at most stages of prometamorphosis and metamorphic climax and, for comparison, in premetamorphic tadpoles. The conversion of [ 125 I]T4 to [ 125 I]T3, as indicated by the presence of an 125 I-labeled product in serum and liver preparations that cochromatographed with carrier T3, was sometimes observed in tadpoles near the end of prometamorphosis and was always evident in tadpoles that were either undergoing or had completed metamorphic climax. However, during this phase, no correlation could be drawn between the extent of T3 production and morphological development. The formation of T3 from T4 in vivo was significantly decreased in tadpoles pretreated with propylthiouracil. The T45'-monodeiodinating system could be induced in premetamorphic tadpoles by injecting them with either T4 or T3. This finding together with the observation that normal acquisition of this system occurs at the time when endogenous T4 and T3 levels are rising rapidly suggest that its development is under the control of the thyroid hormones

  1. Uranium, rare metals, and granulite-facies metamorphism

    Directory of Open Access Journals (Sweden)

    Michel Cuney

    2014-09-01

    The Tranomaro metasomatized marbles recrystallizing under granulite-facies conditions represent a demonstrative example of fluid transfer from granulite-facies supracrustals to traps represented by regional scale skarns. Such fluids may be at the origin of the incompatible element enrichment detected in leucosomes of migmatites from St Malo in Brittany (France and Black Hills in South Dakota. The northern French Massif Central provides us with an example of a potential association between incompatible element enrichment of granitic melts and granulite-facies metamorphism. U- and F-enriched fine-grained granites are emplaced along a crustal scale shear zone active during the emplacement within the St Sylvestre peraluminous leucogranitic complex. We propose that during granulite-facies metamorphism dominated by carbonic waves in a deep segment of the continental crust, these shear zones control: (i the percolation of F-, LILE-, rare metal-rich fluids liberated primarily by the breakdown of biotite; (ii the enhancement of partial melting by F-rich fluids at intermediate crustal levels with the generation of F-, LILE-, rare metal-rich granitic melts; (iii their transfer through the crust with protracted fractionation facilitated by their low viscosity due to high F-Li contents; and finally (iv their emplacement as rare metal intrusions at shallow crust levels.

  2. Building a Six-Junction Inverted Metamorphic Concentrator Solar Cell

    Energy Technology Data Exchange (ETDEWEB)

    Geisz, John F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Steiner, Myles A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schulte, Kevin L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); France, Ryan M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); McMahon, William E [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perl, Emmett [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Friedman, Daniel J [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-12-02

    We propose practical six-junction (6J) inverted metamorphic multijunction (IMM) concentrator solar cell designs with the potential to exceed 50% efficiency using moderately high quality junction materials. We demonstrate the top three junctions and their monolithic integration lattice matched to GaAs using 2.1-eV AlGaInP, 1.7-eV AlGaAs or GaInAsP, and 1.4-eV GaAs with external radiative efficiencies >0.1%. We demonstrate tunnel junctions with peak tunneling current >400 A/cm2 that are transparent to <2.1-eV light. We compare the bottom three GaInAs(p) junctions with bandgaps of 1.2, 1.0, and 0.7 eV grown on InP and transparent metamorphic grades with low dislocation densities. The solution to an integration challenge resulting from Zn diffusion in the GaAs junction is illustrated in a five-junction IMM. Excellent 1-sun performance is demonstrated in a complete 6J IMM device with VOC = 5.15 V, and a promising pathway toward >50% efficiency at high concentrations is presented.

  3. Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

    Science.gov (United States)

    Hasegawa, Akira; Nakajima, Junichi

    2017-12-01

    We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration

  4. Structure, stability, and tsunami hazard associated with a rock slope in Knight Inlet, British Columbia

    Science.gov (United States)

    van Zeyl, D. P.; Stead, D.; Sturzenegger, M.; Bornhold, B. D.; Clague, J. J.

    2015-06-01

    Rockfalls and rockslides during the past 12 000 years have deposited bouldery debris cones on the seafloor beneath massive rock slopes throughout the inner part of Knight Inlet. The 885 m high rock slope, located across from a former First Nations village destroyed in the late 1500s by a slide-induced wave, exposes the contact between a Late Cretaceous dioritic pluton and metamorphic rocks of the Upper Triassic Karmutsen Formation. The pluton margin is strongly foliated parallel to primary and secondary fabrics in the metamorphic rocks, resulting in highly persistent brittle structures. Other important structures include a set of sheeting joints and highly persistent mafic dykes and faults. Stability analysis indicates that planar and wedge rock slope failures up to about 500 000 m3 in volume could occur. We suspect that failures of this size in this setting would have the potential to generate locally hazardous waves. As several similar rock slopes fronted by large submarine debris cones exist in the inner part of Knight Inlet, it is clear that tsunami hazards should be considered in coastal infrastructure development and land-use planning in this area.

  5. Sapphirine granulites from Panasapattu, Eastern Ghats belt, India: Ultrahigh-temperature metamorphism in a Proterozoic convergent plate margin

    Directory of Open Access Journals (Sweden)

    C.V. Dharma Rao

    2012-01-01

    Full Text Available We report equilibrium sapphirine + quartz assemblage in biotite–orthopyroxene–garnet granulites from a new locality in Panasapattu of Paderu region in the Eastern Ghats granulite belt, which provide new evidence for ultrahigh-temperature (UHT metamorphism at 1030–1050 °C and 10 kbar in this region. The development of migmatitic texture, stabilization of the garnet–orthopyroxene–plagioclase–K-feldspar association, prograde biotite inclusions within garnet and sapphirine as well as sapphirine and cordierite inclusions within garnet in these granulites indicate that the observed peak assemblages probably formed during prograde dehydration melting of a Bt–Sill–Qtz assemblage, and constrain the prograde stage of the p–T path. The core domains of orthopyroxene porphyroblasts have up to w(Al2O3 9.6%, which suggest that the temperatures reached up to 1150 °C suggesting extreme crustal metamorphism. These conditions were also confirmed by the garnet–orthopyroxene thermobarometery, which yields a p–T range of 1012–960 °C and 9.4 kbar. The p–T phase topologies computed using isochemical sections calculated in the model system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (NCKFMASH for metapelites, garnet-free sapphirine granulites and garnet-bearing sapphirine granulites match the melt-bearing assemblages observed in these rocks. Isochemical sections constructed in the NCKFMASH system for an average sub-aluminous metapelite bulk composition, and contoured for modal proportions of melt and garnet, as well as for the compositional isopleths of garnet, predict phase and reaction relations that are consistent with those observed in the rocks. Garnet and orthopyroxene contain Ti-rich phlogopite inclusions, suggesting formation by prograde melting reactions at the expense of phlogopite during ultrahigh-temperature conditions. These p–T results underestimate ‘peak’ conditions, in part as a result of the modification

  6. Rocks Can Wow? Yes, Rocks Can Wow!

    Science.gov (United States)

    Hardman, Sally; Luke, Sue

    2016-01-01

    Rocks and fossils appear in the National Curriculum of England science programmes of study for children in year 3 (ages 7-8). A frequently asked question is "How do you make the classification of rocks engaging?" In response to this request from a school, a set of interactive activities was designed and organised by tutors and students…

  7. K-Ar ages of basic rocks in the Patia Valley, southwest Colombia

    Science.gov (United States)

    De Souza, Hughes A. F.; Espinosa, Armando; Delaloye, Michel

    1984-08-01

    The Patia Valley situated between the Western and Central Cordilleras of the southwest Colombian Andes contains two areas in which Mesozoic basic and ultrabasic rocks crop out in abundance. Late Cretaceous Diabase Group pillow basalts which make up much of the Western Cordillera are at least 81 ± 5 Ma in the E1 Tambo-E1 Peñol area. 105-97 Ma hornblende and whole-rock dates from the ophiolitic Los Azules complex indicate an Albian age of formation, although many dates are lower (65-62 Ma) owing the low-grade ocean-floor metamorphism. The metamorphic age distribution here supports an end of Cretaceous emplacement for the complex rather than the Early-Mid Cretaceous emplacement suggested for North Colombian ophiolites similarly aligned along the Romeral fault system. Tertiary dacites intruding the Low Azules complex are 36-15 Ma.

  8. Geochemistry and metamorphic evolution of a Ti-metagabbro in the Asnawa Group of the Shalair terrain (Sanandaj-Sirjan Zone), Kurdistan region, Iraq.

    Science.gov (United States)

    Yara, Irfan; Schulz, Bernhard; Tichomirowa, Marion; Mohammad, Yousif; Matschullat, Jörg

    2014-05-01

    Geochemistry and metamorphic evolution of a Ti-metagabbro in the Asnawa Group of the Shalair terrain (Sanandaj-Sirjan Zone), Kurdistan region, Iraq. We present geochemical data, mineral chemistry, petrography, and theP-T conditions of a Ti-metagabbro from the Asnawa Group in the Shalair Terrain (Sanandaj-Sirjan Zone).Geochemical data indicate that this Ti-metagabbro has tholeiitic characteristics with low-K contents. Factor analyses of the elements indicate fractionation of common mineral phases such as clinopyroxene, hornblende, plagioclase, Ti-bearing phases (rutile, ilmenite, titanite), and apatite. The normal mid-oceanic ridge basalt (N-MORB)-normalized incompatible trace element diagram shows close similarity with typical N-MORB pattern. Tectonomagmatic discrimination diagrams suggest a dominating MORB environment. The rock/chondrite-normalized REE diagram of the amphibolites also shows their N-MORB-type signature, with relative enrichment in LREE. The rock derived from mixed primitive and depleted mantel. The formation and preservation of the various metamorphic mineral assemblages and their mineral chemical characteristicsare strongly affected by the original magmatic whole-rock composition. This can be demonstrated by different microdomains, which contain different amphiboles and plagioclases. The metamorphic history can be subdivided into the stages M1-M2-M3. The first stage of metamorphism was recorded by crystallisation of actinolite replacing clinopyroxene and igneous amphibole (M1 stage, 410< T < 490°C; 1.8 < P <2.2 kbar). Increase of temperature resulted in the formation of hornblende pseudomorphism and hornblende and sphene coronae growing on previous amphibole or clinopyroxene and ilmenite, respectively (M2 stage, 540 < T <580°C; 4.5 < P < 5.5 kbar). The third stage (M3 stage, 730 < T °C < 780°C; 6.5 < P < 7.5 kbar) led to the formation of a ferro-tschermakite corona, around the M2 amphibole, and rutile that developed on the sphene and ilmenite

  9. Strontium and argon isotopic homogenization of pelitic sediments during low-grade regional metamorphism: the Pan-African Upper Damara Sequence of northern Namibia (South West Africa)

    International Nuclear Information System (INIS)

    Clauer, N.

    1979-01-01

    The fine mineral fractions 0 C and pressures up to 2 kbar. These events are dated at about 535 m.y. and 455 m.y. respectively (with lambda( 87 Rb) = 1.42 X 10 -11 yr -1 ). Anomalously high K-Ar ages on samples from specific stratigraphic horizons can be related to open system behaviour and K migration during the formation of stilpnomelane from ferromagnesian illites. This study shows that age dating of sedimentary rocks subjected to low-grade regional metamorphism can only yield meaningful results if the interpretation of isotopic analyses is based on a clear understanding of the mineralogical processes that led to the formation of these parageneses which characterize the rock unit dated. (Auth.)

  10. Mineralogy, geochemistry and low grade metamorphism of green tuffs of Karaj formation in Hesarbon area (south west Firoozkooh

    Directory of Open Access Journals (Sweden)

    Shiva Bahrami

    2017-03-01

    Full Text Available Green tuffs of middle Eocene age in Hesarbon area, south west of Firoozkuh (East of Central Alborz consist of a thick sequence of lithic-, crystal-,vitric-and calcareous-tuffs. Microscopic and x-ray diffraction studies show plagioclase (albite and oligoclase, alkali feldspar (sanidine, quartz, cristobalite, biotite and hornblende are the major minerals in the rocks studied. Secondary minerals such as analcime, chlorite, prehnite and clay minerals are mainly present in the groundmass of the rocks. Extensive tectonic activities have created a variety of structural features including numerous folds and faults and therefore, have caused the green tuffs to be crushed and converted to breccia tuffs in many parts. Veins and cavities are filled by considerable amounts of zeolitic minerals including heulandite group, clinoptilolite and natrolite along with calcite and secondary quartz. Based on geochemical data, they lie on the dacite and rhyodacite field showing a calc-alkaline nature in the corresponding diagrams. According to the chondrite and primitive mantle normalized diagrams of trace elements, negative anomalies of Eu, Nb, Ti, P and depletion of HFSE together with their position in the petrogenesis discrimination diagrams, it is most likely that these rocks are formed in the active continental margin of a subduction zone. The existence of analcime and prehnite in the groundmass demonstrate that these rocks have undergone some degrees of low-grade metamorphism due to the overburden of the layers in the temperature range 200-300 °C. The present study shows that zeolite minerals filling the fractures and cavities of tuffs are precipitated by hydrothermal fluids with a neutral pH to acidic

  11. Rock Slope Design Criteria

    Science.gov (United States)

    2010-06-01

    Based on the stratigraphy and the type of slope stability problems, the flat lying, Paleozoic age, sedimentary : rocks of Ohio were divided into three design units: 1) competent rock design unit consisting of sandstones, limestones, : and siltstones ...

  12. Rocks in Our Pockets

    Science.gov (United States)

    Plummer, Donna; Kuhlman, Wilma

    2005-01-01

    To introduce students to rocks and their characteristics, teacher can begin rock units with the activities described in this article. Students need the ability to make simple observations using their senses and simple tools.

  13. Rock slope design guide.

    Science.gov (United States)

    2011-04-01

    This Manual is intended to provide guidance for the design of rock cut slopes, rockfall catchment, and : rockfall controls. Recommendations presented in this manual are based on research presented in Shakoor : and Admassu (2010) entitled Rock Slop...

  14. Effect of crustal heterogeneities and effective rock strength on the formation of HP and UHP rocks.

    Science.gov (United States)

    Reuber, Georg; Kaus, Boris; Schmalholz, Stefan; White, Richard

    2015-04-01

    next step, we performed several hundred numerical simulations to understand the effects of km-scale heterogeneities and material parameters on pressure magnitudes, using a model setup that is otherwise very similar to the one of Li et al. (2010). Results show that significant non-lithostatic pressures occur if (lower) crustal rocks are dry or if km-scale (nappe-sized) heterogeneities with dryer rocks are present within the crust. Overpressure magnitudes can be up to 1 GPa or 100% and in some cases rock assemblages are temporarily in the coesite stability field at a depth of only 40 km, followed by rapid exhumation to the surface. Tectonic overpressures can vary strongly in magnitude versus time, but peak pressures are present sufficiently long for metamorphic reactions to occur. The presence of heterogeneities can affect the crustal-scaled deformation pattern, and the effective friction angle of crustal-scale rocks (or the dryness of these rocks) is a key parameter that determines the magnitude of non-lithostatic pressures. Our results thus reconcile previous findings and highlight the importance of having an accurate knowledge of the fluid-pressure, initial crustal structure and rock composition during continental collision. If rocks are dry by the time they enter a subduction zone, or are stronger/dryer than surrounding rocks, they are likely to develop significantly higher pressures than nearby rocks. This might explain the puzzling observation that some nappes have very high peak pressures, while juxtaposed nappes have much lower values, without clear structural evidence for deep burial and exhumation along a subduction channel of the high-pressure nappe. Our models might also give a partial explanation of why the reported timescales for high and ultra-high pressure stages of peak metamorphism are often very short. References: Burov, E., Francois, T., Agard, P., Le Pourhiet, L., Meyer, B., Tirel, C., Lebedev, S., Yamato, P., Brun, J.-P., 2014. Tectonophysics

  15. An innovative approach for testing bioinformatics programs using metamorphic testing

    Directory of Open Access Journals (Sweden)

    Liu Huai

    2009-01-01

    Full Text Available Abstract Background Recent advances in experimental and computational technologies have fueled the development of many sophisticated bioinformatics programs. The correctness of such programs is crucial as incorrectly computed results may lead to wrong biological conclusion or misguide downstream experimentation. Common software testing procedures involve executing the target program with a set of test inputs and then verifying the correctness of the test outputs. However, due to the complexity of many bioinformatics programs, it is often difficult to verify the correctness of the test outputs. Therefore our ability to perform systematic software testing is greatly hindered. Results We propose to use a novel software testing technique, metamorphic testing (MT, to test a range of bioinformatics programs. Instead of requiring a mechanism to verify whether an individual test output is correct, the MT technique verifies whether a pair of test outputs conform to a set of domain specific properties, called metamorphic relations (MRs, thus greatly increases the number and variety of test cases that can be applied. To demonstrate how MT is used in practice, we applied MT to test two open-source bioinformatics programs, namely GNLab and SeqMap. In particular we show that MT is simple to implement, and is effective in detecting faults in a real-life program and some artificially fault-seeded programs. Further, we discuss how MT can be applied to test programs from various domains of bioinformatics. Conclusion This paper describes the application of a simple, effective and automated technique to systematically test a range of bioinformatics programs. We show how MT can be implemented in practice through two real-life case studies. Since many bioinformatics programs, particularly those for large scale simulation and data analysis, are hard to test systematically, their developers may benefit from using MT as part of the testing strategy. Therefore our work

  16. Temporal and spatial distribution of Paleozoic metamorphism in the southern Appalachian Blue Ridge and Inner Piedmont delimited by ion microprobe U-Pb ages of metamorphic zircon

    Science.gov (United States)

    Merschat, Arthur J.; Bream, Brendan R.; Huebner, Matthew T.; Hatcher, Robert D.; Miller, Calvin F.

    2017-01-01

    Ion microprobe U-Pb zircon rim ages from 39 samples from across the accreted terranes of the central Blue Ridge, eastward across the Inner Piedmont, delimit the timing and spatial extent of superposed metamorphism in the southern Appalachian orogen. Metamorphic zircon rims are 10–40 µm wide, mostly unzoned, and dark gray to black or bright white in cathodoluminescence, and truncate and/or embay interior oscillatory zoning. Black unzoned and rounded or ovoid-shaped metamorphic zircon morphologies also occur. Th/U values range from 0.01 to 1.4, with the majority of ratios less than 0.1. Results of 206Pb/238U ages, ±2% discordant, range from 481 to 305 Ma. Clustering within these data reveals that the Blue Ridge and Inner Piedmont terranes were affected by three tectonothermal events: (1) 462–448 Ma (Taconic); (2) 395–340 Ma (Acadian and Neoacadian); and (3) 335–322 Ma, related to the early phase of the Alleghanian orogeny. By combining zircon rim ages with metamorphic isograds and other published isotopic ages, we identify the thermal architecture of the southern Appalachian orogen: juxtaposed and superposed metamorphic domains have younger ages to the east related to the marginward addition of terranes, and these domains can serve as a proxy to delimit terrane accretion. Most 462–448 Ma ages occur in the western and central Blue Ridge and define a continuous progression from greenschist to granulite facies that identifies the intact Taconic core. The extent of 462–448 Ma metamorphism indicates that the central Blue Ridge and Tugaloo terranes were accreted to the western Blue Ridge during the Taconic orogeny. Zircon rim ages in the Inner Piedmont span almost 100 m.y., with peaks at 395–385, 376–340, and 335–322 Ma, and delimit the Acadian-Neoacadian and Alleghanian metamorphic core. The timing and distribution of metamorphism in the Inner Piedmont are consistent with the Devonian to Mississippian oblique collision of the Carolina superterrane

  17. Scattering from Rock and Rock Outcrops

    Science.gov (United States)

    2018-01-23

    of the open questions which exist for scattering from these types of surfaces and include increasing our basic understanding of: (1) geoacoustic...ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) Office of Naval Research 875 North Randolph Street ...ideal mean seafloor could be mapped to the local SCATTERING FROM ROCKS 5 Figure 4. (color online) SAS images of the calibration rock outcrop. Boxes

  18. On the meaning of peak temperature profiles in inverted metamorphic sequences

    Science.gov (United States)

    Duprat-Oualid, Sylvia; Yamato, Philippe

    2017-07-01

    Inverted metamorphic sequences (IMS) are common features of main thrust systems on Earth. They exhibit an upwards continuous increase in peak temperature conditions and thereby constitute evidence of the close relationship between the thermal field evolution and tectonic processes. Heat advection and shear heating are known to allow the formation of such metamorphic signatures. Heat diffusion also plays an important role in temperature distribution on both sides of the thrust. Other advection processes such as erosion or accretion may also cause a local peak temperature inversion. Each one of these processes therefore affects the thermal field around the thrust. However, despite the crucial importance of all these processes for the interpretation of the inverted peak temperature signatures, their respective influences have never been quantified and compared all together. To address this issue, we propose an innovative coupled approach. (i) We use two-dimensional numerical models that simulate various thrust systems, allowing for a wide diversity of setups. To illustrate this study, we focus on intracontinental thrust systems for which all processes listed are likely to play a key role in the thermal evolution. We perform a parametric study including kinematic settings (i.e. convergence, erosion and accretion), thermal properties, mechanical strength and heat sources. (ii) Dimensionless numbers based on parameters are used to quantify the relative contributions of each process to the thermal budget evolution. Hence, the three thermal processes (i.e. heat diffusion, heat advection and shear heating) are compared with each other via three dimensionless combinations of the Peclet and Brinkman numbers: RDif, RAdv and RPro, respectively. Erosion and accretion are compared separately, based on a fourth dimensionless number Rea. (iii) We analytically examine the inverted peak temperature recorded along profiles that are perpendicular to the thrust zone defined in our

  19. U-Th-PbT Monazite Gechronology in the South Carpathian Basement: Variscan Syn-Metamorphic Tectonic Stacking and Long-Lasting Post-Peak Decompressional Overprints

    Science.gov (United States)

    Săbău, G.; Negulescu, E.

    2012-12-01

    Dating metamorphic events appears to be unsatisfactorily addressed by most of the widely-employed and otherwise accurate and productive isotopic techniques, because the phases and systems investigated do not directly relate to the metamorphic events themselves. An adequate answer to this challenge is instead provided by microprobe-assisted chemical U-Th-PbT monazite geochronology, by its spatial resolution, truly in situ character and the possibility to reference analyses against well-defined textural environments and features, as well as a qualitative timeframe derived therefrom. Though chemical U-Th-PbT monazite geochronology is increasingly applied to seek answers ranging form a general characterization to fine details of the thermotectonic evolution of magmatic and metamorphic rocks, there are so far, unlike in the case of isotopic geochronological methods, no clearly defined standard analytical and data processing protocols. Two main reasons for this have to be mentioned, namely that chemical U-Th-PbT chronology is actually a proxy for isotopic geochronology, and the quantification of the errors and their propagation cannot be directly assessed because apparent ages are related to the measured element concentrations by an implicit function, the law of radioactive decay. Current approaches rely on treating calculated individual age values as primary data, a priori grouping of analyses supposed (and subsequently tested) to be coeval, and their statistical processing in order to obtain age values. An alternative approach we applied in basement units of the South Carpathians consists in an explicit approximation of the age formula and associated errors propagated from element concentrations to age values, and individual treatment of each age datum. The separation of the age clusters from the overall age spectrum of each sample was operated by tracing the variations of the normalized age gradient on the age spectrum sorted by increasing age values, and fine

  20. Punctuated HT/UHT metamorphism during prolonged Archean orogenesis in the Pikwitonei Granulite Domain revealed by garnet petrochronology

    Science.gov (United States)

    Dragovic, Besim; Guevara, Victor; Caddick, Mark; Couëslan, Chris; Baxter, Ethan

    2017-04-01

    Fundamental to every modern continent's early (Archean) history is the generation of high temperature conditions required to produce the dense, strong, relatively anhydrous rocks that comprise most of Earth's stable cratonic crust. While the thermal gradients supported in Archean terranes are better understood, the timescales over which these conditions occur are more enigmatic. Garnet petrochronology allows for the interrogation of a semi-continuous record of these tectonometamorphic conditions, by linking pressure-temperature-fluid conditions (using phase equilibria modeling, trace element thermometry, stable isotope geochemistry) to a precise chronologic/chronometric record (e.g. high-precision Sm-Nd geochronology, geospeedometry of major and trace element diffusion profiles). Here, we utilize techniques from this burgeoning field of study to elucidate the rates and conditions of high temperature/ultra-high temperature (HT/UHT) metamorphism in the 2.7 Ga Pikwitonei Granulite Domain (PGD). The PGD represents over 150,000 km2 of dominantly granulite-facies metamorphic rocks situated at the NW edge of the Superior Province. Peak temperatures in the region range from 760°C in the southernmost part of the PGD, to 900-960˚C in the central/western PGD ( 40-60 km apart). Previous studies have suggested that metamorphism was long-lived in the region, occurring over 100 Ma, from 2.71-2.60 Ga [1, 2, 3]. High-precision garnet geochronology on microsampled garnets provides a detailed growth history of several lithologies across the region. Where necessary, bulk garnet analysis (i.e. dating based upon multiple whole garnet crystals rather than portions thereof) was also performed. While cooling from HT/UHT will result in some degree of intra-mineral age resetting, a detailed isotopic study of a range of large garnet porphyroblasts from the PGD (those which would be variably reset depending on peak T, grain size, and initial cooling rate) can retain information about both

  1. The Potential for Metamorphic Thermal Pulses to Develop During Compaction-Driven Fluid Flow

    Science.gov (United States)

    Tian, Meng; Ague, Jay J.; Chu, Xu; Baxter, Ethan F.; Dragovic, Nora; Chamberlain, C. Page; Rumble, Douglas

    2018-01-01

    Compaction-driven fluid flow below the brittle-ductile transition may be a means of transporting fluids during metamorphism. In particular, when a decompaction weakening mechanism is introduced to account for the rock viscosity reduction due to fluid overpressures, channeling instabilities evolve into high-porosity/permeability fluid conduits that focus mass and energy transfer. In this study, we consider a crustal rheology that accounts simultaneously for upward-increasing viscosity and decompaction weakening to examine the nucleation and evolution of fluid channelization in two dimensions (2-D). The model shows that plume-shaped flow patterns can develop on time scales as short as 104 years, during which the plume tails act as fluid conduits and the plume heads act as fluid dispersion zones near the brittle-ductile transition. Collection of fluids into conduits is accomplished by a basal fluid catchment zone characterized by strong lateral fluid pressure gradients but low porosity/permeability. Relatively narrow ranges of viscous activation energy (˜100 kJ mol-1) and decompaction weakening factor (˜10-4) are constrained if the fluid conduits are of kilometer scale in width. Significant thermal excursions (˜65 °C) can be induced if a high flow rate, potentially from rapid intermittent dehydration, is realized within channels. Moreover, if the focused fluids emanate from external anomalously hot sources (e.g., magma intrusion), thermal pulses (>100°C), and steep lateral temperature gradients (>50°C km-1) can be generated. Given the focusing efficiency estimated from our 2-D compaction model, simple 3-D modeling further shows that tubular conduits have the potential to cause thermal pulses >200°C within 104 years.

  2. A Geothermochronologic Investigation of the Coyote Mountains Metamorphic Core Complex (AZ)

    Science.gov (United States)

    Borel, M.; Gottardi, R.; Casale, G.

    2017-12-01

    The Coyote Mountains metamorphic core complex (CM-MCC) makes up the northern end of the Baboquivari Mountain complex, which is composed of Mesozoic rocks, Tertiary granites, pegmatites, and metasediments. The CM-MCC expose the Pan Tak granite, a 58 Ma intrusive muscovite-biotite-garnet peraluminous granite. The Pan Tak and other intrusions within the Baboquivari Mountains have been interpreted as anatectic melts representing the culmination of a Laramide crustal shortening orogenic event started in the Late Cretaceous ( 70 Ma). Evidence of this magmatic episode includes polysynthetic twinning in plagioclase, myrmekitic texture in alkali feldspars, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary tectonic fabric, associated with the exhumation of the CM-MCC along the Ajo road décollement and associated shear zone. In the shear zone, the Pan Tak mylonite display N-dipping foliation defined by gneissic layering and aligned muscovite, and N-trending mineral stretching lineation. Various shear sense indicators are all consistent with a top-to the-N shear sense. Preliminary argon geochronology results suggest that the shear zone was exhumed 29 Ma ago, an age similar to the onset of detachment faulting in other nearby MCCs (Catalina, Rincon, Pinaleño). In the Pan Tak mylonite, quartz grains display regime 2 to 3 microstructures and shows extensive recrystallization by subgrain rotation and grain boundary migration. The recrystallized grain size ranges between 20 and 50 µm in all samples. Quartz crystallographic preferred orientation measured using electron backscatter diffraction (EBSD) shows that recrystallization was accommodated by dominant prism and minor rhomb slip, suggesting deformation temperature ranging from 450°C to 550°C. These preliminary results constrain the timing of uplift and exhumation, and thermomechanical evolution of the CM-MCC, and improve our understanding of recycling of the continental crust in

  3. Thermochronology of the Sulu ultrahigh-pressure metamorphic terrane: Implications for continental collision and lithospheric thinning

    Science.gov (United States)

    Liu, Li-Ping; Li, Zheng-Xiang; Danišík, Martin; Li, Sanzhong; Evans, Noreen; Jourdan, Fred; Tao, Ni

    2017-08-01

    The thermal history of the Dabie-Sulu orogenic belt provides important constraints on the collision process between the South China and North China blocks during the Mesozoic, and possible lithospheric thinning event(s) in the eastern North China Block. This study reports on the thermal evolution of the Sulu ultrahigh-pressure metamorphic (UHP) terrane using zircon U-Pb geochronology and multiple thermochronology methods such as mica and hornblende 40Ar/39Ar, zircon and apatite fission track, and zircon and apatite (U-Th)/He dating. 40Ar/39Ar and zircon (U-Th)/He data show that the UHP terrane experienced accelerated cooling during 180-160 Ma. This cooling event could be interpreted to have resulted from extensional unroofing of an earlier southward thrusting nappe, or, more likely, an episode of northward thrusting of the UHP rocks as a hanging wall. A subsequent episode of exhumation took place between ca. 125 Ma and 90 Ma as recorded by zircon (U-Th)/He data. This event was more pronounced in the northwest section of the UHP terrane, whereas in the southeast section, the zircon (U-Th)/He system retained Jurassic cooling ages of ca. 180-160 Ma. The mid-Cretaceous episode of exhumation is interpreted to have resulted from crustal extension due to the removal of thickened, enriched mantle. A younger episode of exhumation was recorded by apatite fission track and apatite (U-Th)/He ages at ca. 65-40 Ma. Both latter events were linked to episodic thinning of lithosphere along the Sulu UHP terrane in an extensional environment, likely caused by the roll-back of the Western Pacific subduction system.

  4. Pb, Sr and Nd isotope geological characteristics and its evolution of Jianchaling rock

    International Nuclear Information System (INIS)

    Pang Chunyong; Chen Minyang; Xu Wenxin

    2003-01-01

    It has been a long time debatable subject on the raw material source and its genesis of Jianchaling ultrabasic rock, because the original rock phases, the original mineral compositions, texture and structure, even part of the chemical components of the rocks had been changed completely after many periods and phases of metamorphism. According to the content of Pb, Rb, Sr, Nd elements and their Pb, Sr, Nd isotope compositions of the rocks, together with the isotope geological age of late magmatic activities, the authors analyze the evolution of Pb, Sr, Nd isotope compositions, The inferred initiate Nd isotope ratio of ultrabasic rocks is 0.510233, lower than that of meteorite unity at a corresponding period, its ε Nd(T)>O; The initiate Sr ratios inferred by the isotope geological age ranges from 0.702735 to 0.719028; Projecting the lead isotope compositions on the Pb tectonic evolution model, the result indicates that the raw material of Jianchaling ultrabasic rock coming from the deplete upper mantle. The ultrabasic magma which enrich of Mg, Ni and less S intruded the crust and formed the Jianchaling ultrabasic rock at late Proterozoic era (927 Ma±). The forming time of serpentinite is mostly equal to the granitoid intruding time, showing the intrusion o flate acidic magma caused a large scale alteration of the ultrabasic rocks and formed the meta-ultrabasic phase rock observed today. (authors)

  5. Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

    Science.gov (United States)

    Meqbel, Naser; Weckmann, Ute; Muñoz, Gerard; Ritter, Oliver

    2016-12-01

    We report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid- to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above

  6. Low- to high-grade metamorphic transition in the Southern part of Karnataka Nucleus, India

    Science.gov (United States)

    Naqvi, S. M.

    1988-01-01

    The southern part of Karnataka Nucleus has a strong imprint of 2.6 Ga metamorphism. This has affected the schist belts of Karnataka Nucleus from greenschist to upper amphibolite facies. The higher grades of metamorphism are in the Holenarasipur, Nuggihalli, Krishnarajpet, Hadnur and Melkote schist belts. In the high grade transition zone, around Sargur only keels of schist belts are preserved and occur as highly dismembered, disconnected belts with the top and bottom of the stratigraphic column obliterated due to high grade metamorphism and accompanying migmatization. Absence of high-grade metamorphic minerals in the sediments of the Dharwar schist belts supports the contention that high grade metamorphism post-dated the Dharwar sedimentation and occurred around 2.6 Ga ago. Sargur type metamorphism occurred at upper crustal levels and charnockite type metamorphism occurred in lower crustal levels. The P-T conditions for the mineral assemblage in metapelites of Sargur Group indicate burial depths up to at least 15 km suggesting that they were subducted and later obducted during the development of Early Proterozoic Mobile Belt along the southern border of the Karnataka Nucleus.

  7. The eclogites of the Marun Keu complex, Polar Urals (Russia): fluid control on reaction kinetics and metasomatism during high P metamorphism

    Science.gov (United States)

    Molina, José F.; Austrheim, Håkon; Glodny, Johannes; Rusin, Anatolij

    2002-03-01

    studied area presents a large variety of veins and metasomatic mineral sequences developing in the host-rock adjacent to the veins. High P minerals (garnet (Alm 40-60, Pyr 25-40, Gro 11-23), omphacite, phengite, paragonite) occur in both vein infillings and wall-rock mineral sequences, indicating that metasomatism was caused by the infiltration of out of equilibrium fluids (mostly silica-rich, alkali-rich compositions) during the eclogite-facies metamorphism. In zones of high fracture density, vein networks divide the host-rock into decimetre-scale blocks with omphacite-rich rinds replacing amphibolite cores. In contrast, metasomatic replacement of mafic eclogites by dendritic amphibole with barroisite composition ( M4Na˜0.64 apfu, based on 23 oxygens) also occurred at eclogite-facies conditions. We outline the importance of considering such metasomatic processes for the correct evaluation of P- T- t metamorphic histories. The Marun-Keu complex is another example that highlights the important control exerted by fluids on reaction kinetics during high P metamorphism and further points to an important metasomatic effect of these fluids.

  8. Recognition of the Kaweka Terrane in northern South Island, New Zealand : preliminary evidence from Rb-Sr metamorphic and U-Pb detrital zircon ages

    International Nuclear Information System (INIS)

    Adams, C.J.; Mortimer, N.; Campbell, H.J.; Griffin, W.L.

    2011-01-01

    Detrital zircon U-Pb ages and Rb-Sr metamorphic ages from low-grade Torlesse Supergroup metasedimentary rocks from North Canterbury and Marlborough provide preliminary evidence for a continuation of the Kaweka Terrane of the central North Island into the Torlesse Composite Terrane of the South Island. This would extend from the south side of the Wairau Fault in the upper Wairau River valley southwards to the Lake Tennyson and Lake Sumner areas, and as far as Hawarden. Rb-Sr ages indicate Jurassic metamorphism, 170±24 Ma, with initial 87 Sr/ 86 Sr ratios at that time 0.7073 ± 0.0007 i.e. similar to their North Island counterparts. These Kaweka Terrane rocks have detrital zircon ages that follow the distinctive pattern of the Torlesse rocks in general, i.e. substantial (>30%) Permian-Triassic and Precambrian-Early Palaeozoic groupings, but they also have minor youngest age components c. 175-165 Ma which constrain a maximum Early-Middle Jurassic depositional age. In detail, significant, older zircon components are Late Permian-Early Triassic (260-240 Ma) and Late Triassic (220-210 Ma), but the Precambrian-Early Palaeozoic detrital zircon ages are more scattered. The Kaweka Terrane thus forms a linear belt (c. 500 km) along the length of the Torlesse Composite Terrane in both North and South Islands. In the South Island it coincides with the Esk Head Belt, i.e. east of the Rakaia Terrane (Triassic-Late Permian) and west of the Pahau Terrane (Early Cretaceous-Late Jurassic). (author). 61 refs., 4 figs., 2 tabs.

  9. Origin of Eclogites from the Sanbagawa Metamorphic Belt, Southwestern Japan: Geochemical and Sr-Nd Isotopic Evidence

    Science.gov (United States)

    Utsunomiya, Atsushi; Jahn, Bor-Ming; Okamoto, Kazuaki; Ota, Tsutomu; Shinjoe, Hironao

    2010-05-01

    The Sanbagawa belt is a celebrated Cretaceous high-P/T metamorphic belt occurring in SW Japan. Although most metamorphic rocks from the Sanbagawa belt are non-eclogitic, several eclogite-facies metagabbro bodies are exposed in the Besshi area of the Shikoku island. These bodies were earlier recognized as tectonic blocks derived from the lower crust of the former hanging wall (= mantle wedge) in the subduction zone (Takasu et al., 1994). However, more recent studies of field occurrence and metamorphic petrology led to a suggestion that these bodies represent subducted oceanic materials along with their surrounding schists, but not tectonic blocks from mantle wedge (Ota et al., 2004; Terabayashi et al., 2005; Aoya et al., 2006). Furthermore, the protoliths of these eclogites were considered to have formed in a seamount (Aoya et al., 2006) or an oceanic plateau (Terabayashi et al., 2005). In this study, we aim to resolve the controversy about the protoliths and tectonic setting of eclogites and associated rocks using geochemical and Sr-Nd isotopic tracer techniques. All samples were collected from the Iratsu body, the best exposure of eclogitic rocks in the Besshi area. Eclogites, garnet clinopyroxenites and garnet amphibolites from the Iratsu body have flat to LREE-enriched REE patterns, and show Nb and Zr-Hf depletion in the conventional spidergrams. They have Sr-Nd isotopic characteristics of OIB (epsilon Nd (t) = -1 - +4), hence are different from the surrounding mafic schists which are akin to MORB. The overall geochemical and isotopic signatures suggest that the protoliths of the Iratsu body formed in a subduction setting and were produced by melting of mixed sources between a depleted and an enriched mantle components. The geochemical feature of garnet clinopyroxenites (strong Zr-Hf depletion and Ti enrichment) may be explained by accumulation of clinopyroxene + plagioclase + magnetite. A relevant experimental study indicates that the mineral assemblage

  10. Deformation and metamorphism of gold-sulphide lodes in the ...

    Indian Academy of Sciences (India)

    is key to understand the effect of deformation on movement of ore-bearing fluids, were .... the effect of polyphase deformation on these rocks. The earliest deformation D1 resulted in ..... Transverse section showing the disposition of ore bodies at depth, subparallel to the trend of the F2 fold axis. Dashed/dotted lines indicate ...

  11. Reconstruction of multiple P-T-t stages from retrogressed mafic rocks: Subduction versus collision in the Southern Brasília orogen (SE Brazil)

    Science.gov (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Pedrosa-Soares, Antônio; Hermann, Jörg; Dussin, Ivo; Pinheiro, Marco Aurélio P.; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2017-12-01

    The identification of markers of subduction zones in orogenic belts requires the estimation of paleo-geothermal gradients through pressure-temperature-time (P-T-t) estimates in mafic rocks that potentially derive from former oceanic units once. However, such markers are rare in supracrustal sequences specially in deeply eroded and weathered Precambrian orogens, and reconstructing their metamorphic history is challenging because they are commonly retrogressed and only preserve a few mineral relicts of high-pressure metamorphism. Metamorphosed mafic rocks from Pouso Alegre region of the Neoproterozoic Southern Brasília Orogen outcrop as rare lenses within continental gneisses. They have previously been classified as retrograde eclogites, based on the presence of garnet and the characteristic symplectitic texture replacing omphacite. These rocks were interpreted to mark the suture zone between the Paranapanema and São Francisco cratons. To test the possible record of eclogitic conditions in the Pouso Alegre mafic rocks, samples including the surrounding felsic rocks have been investigated using quantitative compositional mapping, forward thermodynamic modeling and in-situ dating of accessory minerals to refine their P-T-t history. In the metamorphosed mafic rocks, the peak pressure assemblage of garnet and omphacite (Jd20, reconstructed composition) formed at 690 ± 35 °C and 13.5 ± 3.0 kbar, whereas local retrogression into symplectite or corona occurred at 595 ± 25 °C and 4.8 ± 1.5 kbar. The two reactions were coupled and thus took place at the same time. A zircon U-Pb age of 603 ± 7 Ma was obtained for metamorphic rims and linked to the retrogression stage. Monazite and metamorphic zircon U-Th-Pb ages for the surrounding rocks are at ca. 630 Ma and linked to peak pressure conditions similar to the one recorded by the mafic rocks. The low maximal pressure of 14 kbar and the high geothermal gradient do not necessarily support subduction process

  12. Tectonic constraints on a deep-seated rock slide in weathered crystalline rocks

    Science.gov (United States)

    Borrelli, Luigi; Gullà, Giovanni

    2017-08-01

    Deep-seated rock slides (DSRSs), recognised as one of the most important mass wasting processes worldwide, involve large areas and cause several consequences in terms of environmental and economic damage; they result from a complex of controlling features and processes. DSRSs are common in Calabria (southern Italy) where the complex geo-structural setting plays a key role in controlling the geometry of the failure surface and its development. This paper describes an integrated multi-disciplinary approach to investigate a DSRS in Palaeozoic high-grade metamorphic rocks of the Sila Massif; it focuses on the definition of the internal structure and the predisposing factors of the Serra di Buda landslide near the town of Acri, which is a paradigm for numerous landslides in this area. An integrated interdisciplinary study based on geological, structural, and geomorphological investigations-including field observations of weathering grade of rocks, minero-petrographic characterisations, geotechnical investigations and, in particular, fifteen years of displacement monitoring-is presented. Stereoscopic analysis of aerial photographs and field observations indicate that the Serra di Buda landslide consists of two distinct compounded bodies: (i) an older and dormant body ( 7 ha) and (ii) a more recent and active body ( 13 ha) that overlies the previous one. The active landslide shows movement linked to a deep-seated translational rock slide (block slide); the velocity scale ranges from slow (1.6 m/year during paroxysmal stages) to extremely slow (responsible for the formation of this landslide. In particular, the landslide shows a strongly tectonic constraint: the flanks are bounded by high-angle faults, and the main basal failure surface developed inside an E-W southward-dipping thrust fault zone. The entire active rock mass (total volume of approximately 6 Mm3) slid at one time on a failure surface that dipped < 27°, and the maximum depth, as determined by inclinometer

  13. The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism.

    Science.gov (United States)

    Krężel, Artur; Maret, Wolfgang

    2017-06-09

    Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn 2+ ions at picomolar concentrations, extensive subcellular re-distribution of Zn 2+ , the loading of exocytotic vesicles with zinc species, and the control of Zn 2+ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn 2+ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn 2+ and Cu⁺ match the biological requirements for controlling-binding and delivering-these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn 2+ and Cu⁺. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

  14. The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

    Directory of Open Access Journals (Sweden)

    Artur Krężel

    2017-06-01

    Full Text Available Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn2+ ions at picomolar concentrations, extensive subcellular re-distribution of Zn2+, the loading of exocytotic vesicles with zinc species, and the control of Zn2+ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn2+ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn2+ and Cu+ match the biological requirements for controlling—binding and delivering—these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn2+ and Cu+. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms.

  15. Correlated evolution of phenotypic plasticity in metamorphic timing.

    Science.gov (United States)

    Michimae, H; Emura, T

    2012-07-01

    Phenotypic plasticity has long been a focus of research, but the mechanisms of its evolution remain controversial. Many amphibian species exhibit a similar plastic response in metamorphic timing in response to multiple environmental factors; therefore, more than one environmental factor has likely influenced the evolution of plasticity. However, it is unclear whether the plastic responses to different factors have evolved independently. In this study, we examined the relationship between the plastic responses to two experimental factors (water level and food type) in larvae of the salamander Hynobius retardatus, using a cause-specific Cox proportional hazards model on the time to completion of metamorphosis. Larvae from ephemeral ponds metamorphosed earlier than those from permanent ponds when kept at a low water level or fed conspecific larvae instead of larval Chironomidae. This acceleration of metamorphosis depended only on the permanency of the larvae's pond of origin, but not on the conspecific larval density (an indicator of the frequency of cannibalism) in the ponds. The two plastic responses were significantly correlated, indicating that they may evolve correlatively. Once plasticity evolved as an adaptation to habitat desiccation, it might have relatively easily become a response to other ecological factors, such as food type via the pre-existing developmental pathway. © 2012 The Authors. Journal of Evolutionary Biology © 2012 European Society For Evolutionary Biology.

  16. The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

    Science.gov (United States)

    Krężel, Artur; Maret, Wolfgang

    2017-01-01

    Recent discoveries in zinc biology provide a new platform for discussing the primary physiological functions of mammalian metallothioneins (MTs) and their exquisite zinc-dependent regulation. It is now understood that the control of cellular zinc homeostasis includes buffering of Zn2+ ions at picomolar concentrations, extensive subcellular re-distribution of Zn2+, the loading of exocytotic vesicles with zinc species, and the control of Zn2+ ion signalling. In parallel, characteristic features of human MTs became known: their graded affinities for Zn2+ and the redox activity of their thiolate coordination environments. Unlike the single species that structural models of mammalian MTs describe with a set of seven divalent or eight to twelve monovalent metal ions, MTs are metamorphic. In vivo, they exist as many species differing in redox state and load with different metal ions. The functions of mammalian MTs should no longer be considered elusive or enigmatic because it is now evident that the reactivity and coordination dynamics of MTs with Zn2+ and Cu+ match the biological requirements for controlling—binding and delivering—these cellular metal ions, thus completing a 60-year search for their functions. MT represents a unique biological principle for buffering the most competitive essential metal ions Zn2+ and Cu+. How this knowledge translates to the function of other families of MTs awaits further insights into the specifics of how their properties relate to zinc and copper metabolism in other organisms. PMID:28598392

  17. Radiation-Hardened, Substrate-Removed, Metamorphic InGaAs Detector Arrays, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — High-performance radiation-hardened metamorphic InGaAs imaging arrays sensitive from the ultraviolet (UV) through the short-wavelength infrared (SWIR) will be...

  18. Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites

    Science.gov (United States)

    Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.

    2018-04-01

    The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths

  19. Tectono-metamorphic evolution of the upper plate of the Eo-Alpine nappe-stack: constraints from the Oberhof Window (Carinthia, Austria)

    Science.gov (United States)

    Hollinetz, Marianne Sophie; Huet, Benjamin; Iglseder, Christoph; Rantitsch, Gerd; Grasemann, Berhard

    2017-04-01

    The Upper Austro-Alpine Unit in the Eastern Alps corresponds to a nappe-stack that formed during the Eo-Alpine Cretaceous event. It is dominated by crystalline rocks that show Variscan, Permo-Triassic, Eo-Alpine and Neo-Alpine metamorphic imprints. Understanding the tectono-metamorphic evolution of the Eo-Alpine nappe-stack is therefore hampered by a complex polyphase history. Most published studies focused on the subducted lower plate that contains the eclogite-bearing nappes (Koralpe-Wölz nappe system) but the upper plate (Ötztal-Bundschuh nappe system and Drauzug-Gurktal nappe system) is less understood. Our contribution focuses on the tectono-metamorphic evolution of the Bundschuh nappe (Oberhof Window, Carinthia, Austria). This nappe contains metasediments intruded by granites of Ordovician age. Characteristically, these rocks underwent Variscan amphibolite-facies. They were later covered by Carboniferous to Mesozoic sediments and, all together, overprinted by greenschist to amphibolite-facies metamorphism in the upper plate of the Eo-Alpine wedge. During this event, the Bundschuh nappe was overthrusted by the nappes of the Drauzug-Gurktal nappe system. The core of the window is occupied by the middle-grained "Oberhof orthogneiss". LA-ICP-MS U/Pb zircon dating yielded a late Ordovician age for its protolith. The orthogneiss is overlain by the transgressive Carboniferous metasediments comprising meta-conglomerate, graphite schist and quartzite. The Bundschuh nappe is overthrusted by garnet-micaschist, amphibolite, hornblende-garbenschist, calc-micaschist, quarzite and graphitic schist interpreted as parts of the basal Drauzug-Gurktal nappe system. Deformation is characterized by isoclinal folds with an E-W/SE-NW trending fold-axes and top-to-the-East/South-East shearing. This kinematics is related to normal faulting in the upper part of the Eo-Alpine orogenic wedge. The graphite schist contains an assemblage of isolated round garnet and abundant chloritoid in

  20. Clinopyroxene as a key for tracing a history of crystallization and recrystallization of coronitic metagabbro in high-grade metamorphic terranes

    Science.gov (United States)

    Egorova, Svetlana; Stepanova, Alexandra

    2017-04-01

    The evaluation PT-parameters of magmatic crystallization is usually complicated for metagabbros in high-grade metamorphic terranes. Sometimes intensively metamorphosed coronitic gabbronorites preserve relics of primary magmatic mineral assemblage that could give valuable information on the conditions of melt crystallization. However, to use the composition of this relict minerals one should be sure that relict magmatic minerals in coronotic metagabbros did not change their primary composition despite the fact of high-grade metamorphic overprinting. Clinopyroxene is the most important concentrator of REE in igneous and metamorphic mafic rocks because its trace element composition is a sensitive indicator of physico-chemical conditions of the clinopyroxene-bearing-rocks formation. The Belomorian mobile belt (BMB) of the eastern part of the Fennoscandian Shield is high-garde metamorphic terrane. High-Mg coronitic metagabbronorites are widespread in BMB. In spite of metamorphic alteration at high-pressure amphibolite (to eclogite) facies conditions they often preserve relicts of primary igneous mineral assemblages that consist of olivine, orthopyroxene, clinopyroxene (augite) and plagioclase. Corona textures usually developed between mafic minerals and plagioclase. In general, coronas consist of orthopyroxene, clinopyroxene (Na-rich diopside), hornblende (with or without spinel inclusions) and garnet. Trace element composition of relict (primary-igneous?) and corona-forming (around magmatic orthopyroxene) clinopyroxenes from paleoproterozoic coronitic metagabbronorites of the BMB was studied using SIMS Cameca IMS 4f. Igneous clinopyroxenes from fresh olivine gabbronorites of age ca. 2.45 Ga in the Karelian craton were used as reference composition for igneous clinopyroxenes. The major element contents in relict clinopyroxenes from coronitic metagabbronorites determined using EDS EPMA is very similar to the igneous clinopyroxene from gabbronorites of the Karelian craton

  1. Pseudotachylitic breccia in mafic and felsic rocks

    Science.gov (United States)

    Kovaleva, Elizaveta; Huber, Matthew S.

    2017-04-01

    -gabbro, demonstrating clast transport between lithologies. PT melt in meta-gabbro has a two-phase structure: a phase free of granitic clasts, and a phase that contains granitic clasts. This also indicates that melt in both rock types was mobile during the same period of time, and that physical mixing and chemical exchange occurred between the two melts. Thus, PTB cuts across the contact between granite and gabbro, and is not restricted by the contact (e.g., Reimold and Colliston, 1994). These differences in nucleation and propagation of PTB based on rock type must be considered when discussing the formation mechanisms of impact-generated PTB. References: Gibson R.L., Reimold W.U., Ashley A.J., Koeberl C. (2002) Metamorphism of the Moon: A terrestrial analogue in the Vredefort dome, South Africa? Geology 30:475-478. Gibson R.L., Reimold W.U., Wallmach T. (1997) Origin of pseudotachylite in the lower Witwatersrand Supergroup, Vredefort Dome (South Africa): constraints from metamorphic studies. Tectonophysics 283:241-262. Reimold W.U., Colliston W.P. (1994) Pseudotachylites of the Vredefort Dome and the surrounding Witwatersrand Basin, South Africa. Geological Society of America Special Papers 293:177-196.

  2. The variability and controls of rock strength along rocky coasts of central Spitsbergen, High Arctic

    Science.gov (United States)

    Strzelecki, Mateusz Czesław

    2017-09-01

    This paper presents the results of the Schmidt Hammer Rock Tests (SHRTs) across a range of rocky coastal landforms. Northern Billefjorden (central Spitsbergen), represents typical High Arctic microtidal fjord environment. Sheltered location and prolonged sea-ice conditions limit wave action. Coastal cliffs, shore platforms and skerries are developed in various rock types including limestone, sandstone, anhydrite/gypsum, dolomite and metamorphic outcrops. SHRT demonstrated a broad variety of relationships between rock strength and distance from shoreline, presence of sediment cover, distribution of snow patches and icefoot, and accumulations of seaweed and driftwood. In general, rock cliff surfaces were the most resistant in their lower and middle zones, that are thermally insulated by thick winter snowdrifts. More exposed cliff tops were fractured and weathered. The differences in rock strength observed along the shore platforms were highly dependent on thickness of sediment cover and shoreline configuration promoting stronger rock surfaces in areas exposed to the longest wave fetch and washed from gravel deposits. Rock strength of skerry islands is influenced by tidal action controlling the duration of tide inundation and movement of sea-ice scratching boulder surfaces. The results presented in this paper emphasize the richness of rock coast geomorphology and processes operating in High Arctic settings.

  3. Ultrapotassic rocks geology from Salgueiro region, Pernambuco state, Brazil

    International Nuclear Information System (INIS)

    Silva Filho, A.F. da; Guimaraes, I.P.

    1990-01-01

    The Cachoeirinha-Salgueiro belt has Proterozoic age and is located in the Borborema Province, NE Brazil. The ultrapotassic rocks from Salgueiro region intrudes the Cachoeirinha-Salgueiro belt rocks. The ultrapotassics from Salgueiro region constitutes of three units; Serra do Livramento pluton, and two dyke swarms called respectively beige alkali feldspar granites and green alkali feldspar syenite/quartz-syenite. The Serra do Livramento pluton shows E-W direction, boudin shape, width between 0,15 and 2,10 km, and it is intruded into metamorphic rocks and into the Terra Nova complex. Detailed geological mapping at the Serra das Duas Irmas allowed us to establish the dyke swarm chronology. The mapping reveals seven intrusion episodes, into the Terra Nova pluton, of green alkali feldspar syenite/quartz-syenite and five episodes of bege alkali feldspar granite. They alternate between them in space and time, and there are evidence that they were intruded under the tectonic control of the Pernambuco lineament. A systematic whole-rock Rb-Sr geochronology was done in the green alkali feldspar syenite/quartz-syenite, and an age of 514,8 ± 20,3 Ma was obtained. The initial ratio is 0,710615 + 0,000441. The age obtained shows small error and an initial ratio compatible with a strong crustal contamination. (author)

  4. Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China)

    Science.gov (United States)

    Malaspina, Nadia; Hermann, Jörg; Scambelluri, Marco; Compagnoni, Roberto

    2006-08-01

    Release of metamorphic fluids within the slab and/or from the slab to the mantle wedge in subduction environments can produce important metasomatic effects. Ultrahigh-pressure (UHP) metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones. We present a petrologic and geochemical study of eclogites (s.l.) from the Dabie Mountains (China). The investigated samples were collected in the North Dabie Complex, where eclogite-facies rocks are significantly overprinted by granulite-facies metamorphism and partial melting. The studied eclogites are included in meta-lherzolitic bodies, which are in turn hosted by leucocratic gneisses. The textural relations among the various rock-forming minerals enabled us to identify several re-crystallisation stages. The peak (UHP) paragenesis consists of garnet, clinopyroxene and rutile. UHP garnet and clinopyroxene display oriented inclusions of polycrystalline rods of rutile + ilmenite and of albite, K-Ba-feldspar and quartz, respectively. Garnet and clinopyroxene are both rimmed by an inclusion free zone that formed after the peak, still at high-pressure conditions. Such optical zoning does not correspond to a difference in major element concentrations between garnet core and rim. This observation provides evidence that the major element composition of garnet was reset during exhumation, thus preventing thermobarometric determination of peak metamorphic conditions. Further decompression is documented by the formation of limited ilmenite + amphibole and granulite-facies coronas consisting of clinopyroxene, orthopyroxene, plagioclase and amphibole around garnet. In order to investigate the stability of observed mineral parageneses, a series of reconnaissance piston cylinder synthesis experiments were carried out in an identical bulk composition. The experimental study indicates that the peak metamorphic paragenesis is stable at P˜3.5 GPa and T ≥ 750

  5. PETROGENESIS OF THE METACARBONATE AND RELATED ROCKS OF THE SILGARÁ FORMATION, CENTRAL SANTANDER MASSIF, COLOMBIAN ANDES: AN OVERVIEW OF A “REACTION CALCIC EXOSCARN”

    Directory of Open Access Journals (Sweden)

    Castellanos O.M

    2008-06-01

    Full Text Available Metacarbonate rocks (pure and impure marbles, carbonate-silicate rocks, calc-silicate rocks and carbonate-bearing silicate rocks form a very complex group within the metamorphic sequence of the Silgará Formation at the central Santander Massif (CSM. These rocks are interpreted as derived from a sedimentary sequence (including limestones and dolostones, carbonate-bearing mudstones,  sandstones, tuffaceous and evaporitic sediments and marlstones overprinted by near-isochemical regional metamorphism. They usually appear as scarce intercalations from millimeter up to meter scale, within the high-grade pelitic rocks, in the lower part of the metamorphic section, although the proportion of metacarbonate rocks can be higher and different marble layers are exploited. We report for the first time the occurrence of a "reaction calcic exoskarn", which corresponds to
    such metacarbonate rocks, taking into account that a skarn can be developed during regional metamorphism and by different metasomatic processes, adjacent to intrusive bodies, along faults and shear zones, and what defines these rocks as a skarn is its mineralogy, which includes a variety of calc-silicate and associated minerals, usually dominated by garnet and pyroxene. Therefore, this paper focus attention to the occurrence of metacarbonate and
    related rocks, which occurs as small scale reactions zones that show a gradational contact from garnet-bearing pelitic rocks to marbles or carbonate-silicate rocks, giving particular interest to the calc-silicate rocks, which are characterized by the presence of elongated grains of banded clinopyroxene (diopside and scapolite and massive
    or scattered garnet. Several reaction-zones occur in the contact between impure calcite marble and garnet-bearing metapelite and the sequence of mineral assemblages in these reaction zones is: biotite + plagioclase K-feldspar garnet (Zone I, biotite + plagioclase K-feldspar garnet staurolite epidote

  6. Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif

    Science.gov (United States)

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

    2018-05-01

    Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15-20 kbar, 560-630 °C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 ± 13 Ma.

  7. A conceptual model for the development of pristine drainage systems during exhumation of metamorphic core complexes

    Science.gov (United States)

    Trost, Georg; Neubauer, Franz; Robl, Jörg

    2017-04-01

    Metamorphic core complexes (MCCs) are defined as large scale geological features of domal shape. The essential characteristic comprises metamorphic rocks, which have been exhumed from lower crustal levels and now are exposed to the surface. The updoming process occurs at different tectonic settings of high strain zones initially exposing pristine gently dipping fault planes to Earth's surface. Consequently, the dome shape highly influences the type of adaption of the drainage systems to the active landforms. However, drainage systems and their characteristic metrics in regions shaped by MCCs have only been sparsely investigated and were not examined regarding the distinction between different MCC-types (A-type, B-type, C-type). In this study we investigate the drainage patterns of MCCs formed by different tectonic settings and build up a conceptual model for the development of the drainage systems under these conditions. We apply the χ-method to detect variations in uplift, as well as spatial unconformities in the drainage patterns. The χ-method is a mathematical approach to transform stream longitudinal profiles to the χ space where the slope of steady state profiles is solely dependent on uplift rate and bedrock erodibility. From this transformation we calculate color-coded χ-maps and χ-profiles of the main streams draining the MCCs. The applied method allows the interpretation of channel metrics in terms of (a) spatial gradients in uplift rate and (b) the time dependent evolution of drainage divides including drainage divide migration. Our results show a high variation in the shape and greatest elevation of the χ-profiles. This indicates the migration of active uplift zones along the dome axes. Even though only MCCs younger than Miocene age are investigated, the shape of the χ-profiles clearly points to different development stages of these areas. K-profiles plotted over the detachment underlying an active updoming process show concave shaped

  8. Metamorphic history at Lagoa Real: implications for uranium mineralization

    International Nuclear Information System (INIS)

    Lobato, L.M.

    1987-01-01

    Metasomatism and attendant mineralization associated with shear zones have beem recently studied in detail by several investigators. It has emerged from these studies that whereas ground preparation by shearing is essential to the percolation of mineralizing solutions, the ultimate Loci of mineralization reflect chemical controls via fluid/rock interactions. Uranium mineralization at Lagoa Real can be conveniently understood through this perspective. (E.G.) [pt

  9. Rock magnetic investigation and its geological significance for vein-type uranium deposits in southern China

    Science.gov (United States)

    Ge, Kunpeng; Liu, Qingsong; Deng, Juzhi; Nobes, David; Wang, Yang; Wang, Yanguo; Chen, Xiao

    2017-04-01

    To characterize the metallogenic environment of a typical vein-type uranium deposit, samples from diabase dykes, alteration zones including metamorphic diabase and uranium ore, and granites were systematically investigated for six boreholes from southeastern China. Rock magnetic results indicate that coarse-grained magnetites (pseudosingle domain, PSD, and multidomain, MD) are dominant magnetic carriers in diabase. In contrast, the uranium ore is dominated by fine-grained magnetites (superparamagnetic, SP, and single-domain, SD). The concentration of magnetic particles in fresh granites is low. Magnetic properties of metamorphic diabases exhibit much greater variability of magnetic properties and higher degrees of sulfuration than unaltered diabase and granite, due to contact metasomatism and reduction effects close to the vein. Compared with diabase, magnetic remanence of the uranium ore is much lower, but displays much higher stability. The Koenigsberger ratio Q peaks in the uranium ore with a value of ˜1.00. Using the systematic rock magnetic results to constrain the interpretation, the contribution of the intersection zone of diabase dyke and silicified fault to magnetic anomalies was further modeled, and the effects of the ore body are significant for magnetic exploration. Overall, rock magnetic investigations of vein-type uranium deposit provide a better understanding of the interactions between different rock types, and further facilitate regional magnetic surveys on the ground.

  10. Metamorphism, metasomatism and mineralization at Lagoa Real, Bahia, Brazil

    International Nuclear Information System (INIS)

    Lobato, L.M.

    1985-09-01

    Uranium deposits cumulatively in the 100,000 tonne U 3 O 8 range occur within ductile shear zones transecting Archean basement gneisses of the Sao Francisco Craton, at the Lagoa Real region of south-central Bahia, Brasil. The gneisses, dated at 2.6-3.0Ga, are at amphibolite and granulite facies and overlie to the west, the Proterozoic Espinhaco metasedimentary sequence along a thrust fault. Petrography and mineral chemistry show that in the zones of alteration/mineralization, the original K-feldspar + quartz + albite/oligoclase + hastingsite assemblage, is replaced by albite + aegirine - angite + andradite + hematite assemblages, with or without uraninite. This information along with oxygen isotope, whole rock geochemistry and fluid inclusion studies indicate that the alteration process involves removal of Si, K, Rb, Ba and addition of Na under oxidizing conditions. V, Pb and Sr were introduced along with U via interaction with saline SO 2 - rich, isotopically light fluids under varying water/rock ratios and at temperatures of 500 - 550 0 C. 87 Sr/ 86 Sr systematics suggest that it is unlikely that Sr, and by extension uranium, were introduced by fluids originating from the basement gneisses. Geological constraints and the general alteration pattern are consistent with the release of the mineralizing fluids in response to the overloading of the basement rocks onto the Sedimentary Espinhaco via a thrust mechanism. (Author) [pt

  11. Carbon dioxide generation and drawdown during active orogenesis of siliciclastic rocks in the Southern Alps, New Zealand

    Science.gov (United States)

    Menzies, Catriona D.; Wright, Sarah L.; Craw, Dave; James, Rachael H.; Alt, Jeffrey C.; Cox, Simon C.; Pitcairn, Iain K.; Teagle, Damon A. H.

    2018-01-01

    Collisional mountain building influences the global carbon cycle through release of CO2 liberated by metamorphic reactions and promoting mechanical erosion that in turn increases chemical weathering and drawdown of atmospheric CO2. The Southern Alps is a carbonate-poor, siliciclastic mountain belt associated with the active Australian Pacific plate boundary. On-going, rapid tectonic uplift, metamorphism and hydrothermal activity are mobilising carbon. Here we use carbon isotope measurements of hot spring fluids and gases, metamorphic host rocks, and carbonate veins to establish a metamorphic carbon budget. We identify three major sources for CO2 within the Southern Alps: (1) the oxidation of graphite; (2) consumption of calcite by metamorphic reactions at the greenschist-amphibolite facies boundary, and (3) the dissolution of groundmass and vein-hosted calcite. There is only a minor component of mantle CO2 arising on the Alpine Fault. Hot springs have molar HCO3-/Ca2+ ∼9, which is substantially higher than produced by the dissolution of calcite indicating that deeper metamorphic processes must dominate. The total CO2 flux to the near surface environment in the high uplift region of the Southern Alps is estimated to be ∼6.4 × 108 mol/yr. Approximately 87% of this CO2 is sourced from coupled graphite oxidation (25%) and disseminated calcite decarbonation (62%) reactions during prograde metamorphism. Dissolution of calcite and mantle-derived CO2 contribute ∼10% and ∼3% respectively. In carbonate-rich orogens CO2 production is dominated by metamorphic decarbonation of limestones. The CO2 flux to the atmosphere from degassing of hot springs in the Southern Alps is 1.9 to 3.2 × 108 mol/yr, which is 30-50% of the flux to the near surface environment. By contrast, the drawdown of CO2 through surficial chemical weathering ranges between 2.7 and 20 × 109 mol/yr, at least an order of magnitude greater than the CO2 flux to the atmosphere from this orogenic belt

  12. Death Valley turtlebacks: Mesozoic contractional structures overprinted by Cenozoic extension and metamorphism beneath syn-extensional plutons

    Science.gov (United States)

    Pavlis, T. L.; Miller, M.; Serpa, L.

    2008-07-01

    -thrust belts. Our work to the east of Death Valley suggests these thrusts were part of a NW trending thrust system that overprinted an older NE trending fold-thrust system that tracks into the Death Valley region from Nevada. These NW trending thrusts probably underlie all of the southern Black Mountains (south of the turtlebacks) and we suggest that pre-extensional structural relief along these basement thrusts placed basement at shallow crustal levels throughout what is now the Black Mountains; a conclusion consistent with the absence of rocks younger than Cambrian beneath Tertiary unconformities throughout the southern Death Valley region. In Late Miocene time, a major detachment system formed and the turtlebacks represent a mid-crustal shear zone developed during that time period, but this system is older, and structurally beneath younger detachments systems that comprise the Amargosa fault system. During motion on the detachment, an ~2km thick plutonic sheet was emplaced along the shear zone forming the Miocene plutonic assemblages of the Black Mountains, and produced upper amphibolite facies metamorphic assemblages along the floor of the pluton in what are now the Copper Canyon and Mormon Point turtlebacks, but the Badwater Turtleback escaped this metamorphism due to a different structural position. Motion continued along the floor of the pluton but syn-extensional folding produced structural relief along folds with axes parallel to the extension direction. Ultimately a new detachment system cut obliquely across the older extensional system, removing the roof of the pluton, but cutting down to its floor in the turtlebacks. This fault system formed a complex detachment system updip in the famous 'Amargosa Chaos', and removing the entire cover sequence from the Black Mountains (~10-12km of crustal section). The turtlebacks are therefore a composite structure in which extension contemporaneous with folding, presumably as a result of distributed transcurrent motion during

  13. Fluid induced metamorphism and strength of the middle to lower continental crust - field and textural examples from Bergen Arcs, Western Norway

    Science.gov (United States)

    Austrheim, H.; Putnis, A.; Putnis, C. V.

    2011-12-01

    Fluids may change the rheology of the lithosphere both by changing the deformation mechanism of minerals and by inducing metamorphic reactions. In the present account the influence of fluid-induced metamorphic reactions on the mineralogical and structural evolution of a thickened continental crust is described from anorthositic granulites in the Lindås Nappe, Bergen Arcs, Norway, where the Grenvillian age (~930 My) granulites (T 800°C, P≤10kbar) are transformed to Caledonian age (~420My) eclogite (~650°C and ≤ 20kbar) and amphibolite facies assemblages. The anorthosite complex ranges in composition from pure anorthosite via gabbroic anorthosite to gabbro with lenses of peridotite and pyroxenites which allow us to study the mineral reactions and assess relative rock strength in a wide range of compositions. The complex is locally banded with up to meter thick garnet-pyroxene rich layers alternating with plagioclase rich layers. In other localities the granulite facies structure is defined by oriented disc-shaped corona textures in a plagioclase rich matrix. The eclogites (garnet, omphacite, amphibole, kyanite, white micas ± plagioclase) and amphibolites (plagioclase, hornblende, kyanite, and white micas) are formed along fluid pathways such as fractures and shear zones. Breccias, where rotated blocks of granulites are surrounded by anastamosing eclogite- and amphibolite facies shear zones, outcrop over areas of km2. Pseudotachylytes are developed in the granulites while the hydrated rocks in the shear zone respond by ductile deformation. A hierachy of rock strength can be inferred from these field observations. Notably the relict granulites form rotated angular blocks within the shear zones suggesting that granulites, independent of composition, are stronger than hydrous eclogitites and amphibolites. The garnet pyroxenite layer forms rigid blocks in eclogites suggesting that the mafic parts of the granulite complex must have been stronger than the

  14. Detrital zircon analysis of Mesoproterozoic and neoproterozoic metasedimentary rocks of northcentral idaho: Implications for development of the Belt-Purcell basin

    Science.gov (United States)

    Lewis, R.S.; Vervoort, J.D.; Burmester, R.F.; Oswald, P.J.

    2010-01-01

    The authors analyzed detrital zircon grains from 10 metasedimentary rock samples of the Priest River complex and three other amphibolite-facies metamorphic sequences in north-central Idaho to test the previous assignment of these rocks to the Mesoproterozoic Belt-Purcell Supergroup. Zircon grains from two samples of the Prichard Formation (lower Belt) and one sample of Cambrian quartzite were also analyzed as controls with known depositional ages. U-Pb zircon analysis by laser ablation - inductively coupled plasma - mass spectrometry reveals that 6 of the 10 samples contain multiple age populations between 1900 and 1400 Ma and a scatter of older ages, similar to results reported from the Belt- Purcell Supergroup to the north and east. Results from the Priest River metamorphic complex confirm previous correlations with the Prichard Formation. Samples from the Golden and Elk City sequences have significant numbers of 1500-1380 Ma grains, which indicates that they do not predate the Belt. Rather, they are probably from a relatively young, southwestern part of the Belt Supergroup (Lemhi subbasin). Non-North American (1610-1490 Ma) grains are rare in these rocks. Three samples of quartzite from the Syringa metamorphic sequence northwest of the Idaho batholith contain zircon grains younger than the Belt Supergroup and support a Neoproterozoic age. A single Cambrian sample has abundant 1780 Ma grains and none younger than ~1750 Ma. These results indicate that the likely protoliths of many high-grade metamorphic rocks in northern Idaho were strata of the Belt-Purcell Supergroup or overlying rocks of the Neoproterozoic Windermere Supergroup and not basement rocks.

  15. Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus (Echinodermata: Echinoidea

    Directory of Open Access Journals (Sweden)

    Sutherby Josh

    2012-04-01

    Full Text Available Abstract Background A metamorphic life-history is present in the majority of animal phyla. This developmental mode is particularly prominent among marine invertebrates with a bentho-planktonic life cycle, where a pelagic larval form transforms into a benthic adult. Metamorphic competence (the stage at which a larva is capable to undergo the metamorphic transformation and settlement is an important adaptation both ecologically and physiologically. The competence period maintains the larval state until suitable settlement sites are encountered, at which point the larvae settle in response to settlement cues. The mechanistic basis for metamorphosis (the morphogenetic transition from a larva to a juvenile including settlement, i.e. the molecular and cellular processes underlying metamorphosis in marine invertebrate species, is poorly understood. Histamine (HA, a neurotransmitter used for various physiological and developmental functions among animals, has a critical role in sea urchin fertilization and in the induction of metamorphosis. Here we test the premise that HA functions as a developmental modulator of metamorphic competence in the sea urchin Strongylocentrotus purpuratus. Results Our results provide strong evidence that HA leads to the acquisition of metamorphic competence in S. purpuratus larvae. Pharmacological analysis of several HA receptor antagonists and an inhibitor of HA synthesis indicates a function of HA in metamorphic competence as well as programmed cell death (PCD during arm retraction. Furthermore we identified an extensive network of histaminergic neurons in pre-metamorphic and metamorphically competent larvae. Analysis of this network throughout larval development indicates that the maturation of specific neuronal clusters correlates with the acquisition of metamorphic competence. Moreover, histamine receptor antagonist treatment leads to the induction of caspase mediated apoptosis in competent larvae. Conclusions We

  16. Waste-rock interactions in the immediate repository

    International Nuclear Information System (INIS)

    McCarthy, G.J.

    1977-01-01

    The high level wastes (HLW's) to be placed underground in rock formations will contain significant amounts of radioactive decay heat for the first hundred-or-so years of isolation. Several physical-chemical changes analogous to natural geochemical processes can occur during this ''thermal period.'' The waste canister can act as a heat source and cause changes in the mineralogy and properties of the surrounding rocks. Geochemically, this is ''contact metamorphism.'' In the event that the canister is corroded and breached, chemical reactions can occur between the HLW, the surrounding rock and possibly the remains of the canister. In a dry repository which has not been backfilled (and thus pressurized) these interactions could be slow at best and with rates decreasing rapidly as the HLW cools. However, significant interactions can occur in years, months or even days under hydrothermal conditions. These conditions could be created by the combination of HLW heat, overburden pressure and water mobilized from the rocks or derived from groundwater intrusion. At the end of the thermal period these interaction products would constitute the actual HLW form (or ''source term'') subject to the low temperature leaching and migration processes under investigation in other laboratories. It is quite possible that these interaction product waste forms will have superior properties compared to the original HLW. Experimental programs initiated at Penn State during the last year aim at determining the nature of any chemical or mineralogical changes in, or interactions between, HLW solids and host rocks under various repository ambients. The accompanying figures describe the simulated HLW forms and the experimental approach and techniques. Studies with basalts as the repository rock are supported by Rockwell Hanford Operations and with shales by the Office of Waste Isolation

  17. Hydrogen in rocks: an energy source for deep microbial communities

    Science.gov (United States)

    Freund, Friedemann; Dickinson, J. Thomas; Cash, Michele

    2002-01-01

    To survive in deep subsurface environments, lithotrophic microbial communities require a sustainable energy source such as hydrogen. Though H2 can be produced when water reacts with fresh mineral surfaces and oxidizes ferrous iron, this reaction is unreliable since it depends upon the exposure of fresh rock surfaces via the episodic opening of cracks and fissures. A more reliable and potentially more voluminous H2 source exists in nominally anhydrous minerals of igneous and metamorphic rocks. Our experimental results indicate that H2 molecules can be derived from small amounts of H2O dissolved in minerals in the form of hydroxyl, OH- or O3Si-OH, whenever such minerals crystallized in an H2O-laden environment. Two types of experiments were conducted. Single crystal fracture experiments indicated that hydroxyl pairs undergo an in situ redox conversion to H2 molecules plus peroxy links, O3Si/OO\\SiO3. While the peroxy links become part of the mineral structure, the H2 molecules diffused out of the freshly fractured mineral surfaces. If such a mechanism occurred in natural settings, the entire rock column would become a volume source of H2. Crushing experiments to facilitate the outdiffusion of H2 were conducted with common crustal igneous rocks such as granite, andesite, and labradorite. At least 70 nmol of H2/g diffused out of coarsely crushed andesite, equivalent at standard pressure and temperature to 5,000 cm3 of H2/m3 of rock. In the water-saturated, biologically relevant upper portion of the rock column, the diffusion of H2 out of the minerals will be buffered by H2 saturation of the intergranular water film.

  18. Space Weathering of Rocks

    Science.gov (United States)

    Noble, Sarah

    2011-01-01

    Space weathering discussions have generally centered around soils but exposed rocks will also incur the effects of weathering. On the Moon, rocks make up only a very small percentage of the exposed surface and areas where rocks are exposed, like central peaks, are often among the least space weathered regions we find in remote sensing data. However, our studies of weathered Ap 17 rocks 76015 and 76237 show that significant amounts of weathering products can build up on rock surfaces. Because rocks have much longer surface lifetimes than an individual soil grain, and thus record a longer history of exposure, we can study these products to gain a deeper perspective on the weathering process and better assess the relative impo!1ance of various weathering components on the Moon. In contrast to the lunar case, on small asteroids, like Itokowa, rocks make up a large fraction of the exposed surface. Results from the Hayabusa spacecraft at Itokowa suggest that while the low gravity does not allow for the development of a mature regolith, weathering patinas can and do develop on rock surfaces, in fact, the rocky surfaces were seen to be darker and appear spectrally more weathered than regions with finer materials. To explore how weathering of asteroidal rocks may differ from lunar, a set of ordinary chondrite meteorites (H, L, and LL) which have been subjected to artificial space weathering by nanopulse laser were examined by TEM. NpFe(sup 0) bearing glasses were ubiquitous in both the naturally-weathered lunar and the artificially-weathered meteorite samples.

  19. Exploration of the enhanced geothermal system (EGS) potential of crystalline rocks for district heating (Elbe Zone, Saxony, Germany)

    Science.gov (United States)

    Förster, Andrea; Förster, Hans-Jürgen; Krentz, Ottomar

    2018-01-01

    This paper addresses aspects of a baseline geothermal exploration of the thermally quiescent Elbe Zone (hosting the cities of Meissen and Dresden) for a potential deployment of geothermal heat in municipal heating systems. Low-permeable to impermeable igneous and metamorphic rocks constitute the major rock types at depth, implying that an enhanced geothermal system needs to be developed by creating artificial flow paths for fluids to enhance the heat extraction from the subsurface. The study includes the development of geological models for two areas on the basis of which temperature models are generated at upper crustal scale. The models are parameterized with laboratory-measured rock thermal properties (thermal conductivity k, radiogenic heat production H). The uncertainties of modelled temperature caused by observed variations of k and H and inferred mantle heat flow are assessed. The study delineates highest temperatures within the intermediate (monzonite/syenite unit) and mafic rocks (diorite/monzodiorite unit) forming the deeper portions of the Meissen Massif and, specifically for the Dresden area, also within the low-metamorphic rocks (slates/phyllites/quartzites) of the Elbtalschiefergebirge. Boreholes 3-4 km deep need to be drilled to reach the envisioned economically favourable temperatures of 120 °C. The metamorphic and mafic rocks exhibit low concentrations of U and Th, thus being advantageous for a geothermal use. For the monzonite/syenite unit of high heat production ( 6 µW m-3) in the Meissen Massif, the mobilization of Th and U into the geothermal working fluid is assumed to be minor, although their various radioactive decay products will be omnipresent during geothermal use.

  20. Chronological study of the pre-jurassic basement rocks of southern Patagonia

    International Nuclear Information System (INIS)

    Pankhurst, R.J; Rapela, C.W; Loske, W.P; Fanning, C.M

    2001-01-01

    Southern Patagonia east of the Andes was the site of extensive rhyolite volcanism during the Jurassic rifting of Gondwana and subsequent shallow marine basin formation during the Cretaceous. Thus exposures of pre-Jurassic basement are extremely sparse. Nevertheless, extraction of the maximum amount of information from these scattered outcrops of granite and metamorphic rocks is crucial to assessment of the Palaeozoic and earliest Mesozoic history and crustal structure of the Pacific margin of the supercontinent. In particular, the identification and possible correlation of early terrane accretion on this margin depends on comparison of pre-Jurassic igneous and metamorphic events with adjacent areas. This is a preliminary report on work now in progress to this end (au)

  1. Earthquake triggering of landslides in highly jointed rock masses: Reconstruction of the 1783 Scilla rock avalanche (Italy)

    Science.gov (United States)

    Bozzano, Francesca; Lenti, Luca; Martino, Salvatore; Montagna, Alfredo; Paciello, Antonella

    2011-06-01

    The Scilla rock avalanche occurred on 6 February 1783 along the coast of the Calabria region (southern Italy), close to the Messina Strait. It was triggered by a mainshock of the “Terremoto delle Calabrie” seismic sequence, and it induced a tsunami wave responsible for more than 1500 casualties along the neighbouring Marina Grande beach. Based on subaerial and submarine surveys, a 5 × 106 m3 subaerial landslide was identified together with a 3 × 106 m3 submarine scar area, whereas block deposits are present in both the subaerial and submerged regions. A detailed geological reconstruction of the slope was obtained and a geomechanical characterisation of the metamorphic rocks involved in the landslide was performed. Based on this reconstruction, intense jointing conditions of the rock mass can be related to main fault zones parallel and normally oriented to the actual coastline. An engineering geology model of the landslide was devised according to an equivalent continuum approach to evaluate both stiffness and strength of the rock mass within the slope. A finite difference stress-strain numerical modelling of the Scilla landslide was performed under dynamic conditions to back-analyse the landslide trigger as well as local seismic amplifications. This modelling gave new insights into the physical interactions between seismic inputs and slopes, as it demonstrated the fundamental role played by i) the interaction between the seismic input and geological setting of unsheared rock slopes (i.e., without preexisting landslide masses), ii) cumulated strain effects due to seismic sequences, and iii) jointing conditions of the involved rock masses responsible for the seismic amplification of the landslide-prone volume, driving it toward failure conditions.

  2. Discovery of microscopic evidence for shock metamorphism at the Serpent Mound structure, south-central Ohio: Confirmation of an origin by impact

    Science.gov (United States)

    Carlton, R.W.; Koeberl, C.; Baranoski, M.T.; SchuMacHer, G.A.

    1998-01-01

    The origin of the Serpent Mound structure in south-central Ohio has been disputed for many years. Clearly, more evidence was needed to resolve the confusion concerning the origin of the Serpent Mound feature either by endogenic processes or by hypervelocity impact. A petrographic study of 21 samples taken from a core 903 m long drilled in the central uplift of the structure provides evidence of shock metamorphism in the form of multiple sets of planar deformation features in quartz grains, as well as the presence of clasts of altered impact-melt rock. Crystallographic orientations of the planar deformation features show maxima at the shock-characteristic planes of {101??3} and {101??2} and additional maxima at {101??1}, {213??1}, and {516??1}. Geochemical analyses of impact breccias show minor enrichments in the abundances of the siderophile elements Cr, Co, Ni, and Ir, indicating the presence of a minor meteoritic component.

  3. The offshore basement of Perú: Evidence for different igneous and metamorphic domains in the forearc

    Science.gov (United States)

    Romero, Darwin; Valencia, Kiko; Alarcón, Pedro; Peña, Daniel; Ramos, Victor A.

    2013-03-01

    As a result of new studies carried out in the offshore of Perú during the exploration and hydrocarbon evaluation of the forearc basins, new U-Pb SHRIMP and TIMS in zircons and some Ar-Ar data were obtained in the metamorphic and igneous basement. The understanding of this basement was critical to evaluate different hypotheses that have been proposed for the tectonic evolution of pre-Andean crust of Perú. Recent research performed in the basement rocks of the Marañón Massif in northern Perú, claimed that west of this area was a basement-free region in the Paleozoic, where the arc and forearc were developed in a mafic quasi-oceanic crust. However, petrographic studies and new preliminary ages indicate, for the first time, the nature and age of this sialic basement. Reconnaissance studies were performed in several offshore islands, as the Las Hormigas de Afuera Island west of Lima, and Macabí and Lobera islands along the edge of the continental platform. These data were complemented with the studies of some cutting samples obtained in recent exploration wells in northern Perú. The results of the present work show two large crustal domains in the Peruvian offshore forearc. A northern domain contains late Paleozoic igneous rocks that appear to be the southern offshore continuation of the Amotape-Tahuin block, which is interpreted as the southernmost remnant of the Laurentia Alleghenian orogen. The central offshore domain, known as the Paracas High, corresponds to the outer shelf high of previous studies. It contains orthogneisses of Grenville-age, probably recrystallized during an Ordovician magmatic episode. The new results show that the central offshore of Perú is an extension of the Grenville-age basement affected by Famatinian, early Paleozoic magmatism, well exposed in the southern domain in the Arequipa Massif along the coast of southern Perú.

  4. Heterogeneity of groundwater storage properties in the critical zone of Irish metamorphic basement from geophysical surveys and petrographic analyses

    Science.gov (United States)

    Comte, Jean-Christophe; Cassidy, Rachel; Caulfield, John; Nitsche, Janka; Ofterdinger, Ulrich; Wilson, Christopher

    2016-04-01

    Weathered/fractured bedrock aquifers contain groundwater resources that are crucial in hard rock basement regions for rural water supply and maintaining river flow and ecosystem resilience. Groundwater storage in metamorphic rocks is subject to high spatial variations due to the large degree of heterogeneity in fracture occurrence and weathering patterns. Point measurements such as borehole testing are, in most cases, insufficient to characterise and quantify those storage variations because borehole sampling density is usually much lower than the scale of heterogeneities. A suite of geophysical and petrographic investigations was implemented in the weathered/fractured micaschist basement of Donegal, NW Ireland. Electrical Resistivity Tomography provided a high resolution 2D distribution of subsurface resistivities. Resistivity variations were transferred into storage properties (i.e. porosities) in the saturated critical zone of the aquifer through application of a petrophysical model derived from Archie's Law. The petrophysical model was calibrated using complementary borehole gamma logging and clay petrographic analysis at multi-depth well clusters distributed along a hillslope transect at the site. The resulting distribution of porosities shows large spatial variations along the studied transect. With depth, porosities rapidly decrease from about a few % in the uppermost, highly weathered basement to less than 0.5% in the deep unweathered basement, which is encountered at depths of between 10 and 50m below the ground surface. Along the hillslope, porosities decrease with distance from the river in the valley floor, ranging between 5% at the river to less than 1% at the top of the hill. Local traces of regional fault zones that intersect the transect are responsible for local increases in porosity in relation to deeper fracturing and weathering. Such degrees of spatial variation in porosity are expected to have a major impact on the modality of the response of

  5. The lateral boundary of a metamorphic core complex: The Moutsounas shear zone on Naxos, Cyclades, Greece☆

    Science.gov (United States)

    Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai

    2013-01-01

    We describe the structure, microstructures, texture and paleopiezometry of quartz-rich phyllites and marbles along N-trending Moutsounas shear zone at the eastern margin of the Naxos metamorphic core complex (MCC). Fabrics consistently indicate a top-to-the-NNE non-coaxial shear and formed during the main stage of updoming and exhumation between ca. 14 and 11 Ma of the Naxos MCC. The main stage of exhumation postdates the deposition of overlying Miocene sedimentary successions and predates the overlying Upper Miocene/Pliocene conglomerates. Detailed microstructural and textural analysis reveals that the movement along the Moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher-temperature rocks. Paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20–77 MPa and a strain rate of 10−15–10−13 s−1 at 350 °C for quartz and ca. 300 °C for calcite. Chlorite geothermometry of the shear zone yields two temperature regimes, 300–360 °C, and 200–250 °C. The lower temperature group is interpreted to result from late-stage hydrothermal overprint. PMID:26523079

  6. Alteration halos around radioactive minerals in plutonic and metamorphic rocks of the northern Moldanubian area, Bohemian massif

    Czech Academy of Sciences Publication Activity Database

    Procházka, V.; Seydoux-Guillaume, A.-M.; Trojek, T.; Goliáš, V.; Korbelová, Zuzana; Matějka, D.; Novotná, P.

    2011-01-01

    Roč. 23, č. 4 (2011), s. 551-566 ISSN 0935-1221 Institutional research plan: CEZ:AV0Z30130516 Keywords : monazite * granites * paragneisses * radiation damage * alteration Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.486, year: 2011

  7. Rock kinoekraanil / Katrin Rajasaare

    Index Scriptorium Estoniae

    Rajasaare, Katrin

    2008-01-01

    7.-11. juulini kinos Sõprus toimuval filminädalal "Rock On Screen" ekraanile jõudvatest rockmuusikuid portreteerivatest filmidest "Lou Reed's Berlin", "The Future Is Unwritten: Joe Strummer", "Control: Joy Division", "Hurriganes", "Shlaager"

  8. Rock Equity Holdings, LLC

    Science.gov (United States)

    The EPA is providing notice of an Administrative Penalty Assessment in the form of an Expedited Storm Water Settlement Agreement against Rock Equity Holdings, LLC, for alleged violations at The Cove at Kettlestone/98th Street Reconstruction located at 3015

  9. Pop & rock / Berk Vaher

    Index Scriptorium Estoniae

    Vaher, Berk, 1975-

    2001-01-01

    Uute heliplaatide Redman "Malpractice", Brian Eno & Peter Schwalm "Popstars", Clawfinger "A Whole Lot of Nothing", Dario G "In Full Color", MLTR e. Michael Learns To Rock "Blue Night" lühitutvustused

  10. Solid as a rock

    International Nuclear Information System (INIS)

    Pincus, H.J.

    1984-01-01

    Recent technologic developments have required a more comprehensive approach to the behavior of rock mass or rock substance plus discontinuities than was adequate previously. This work considers the inherent problems in such operations as the storage of hot or cold fluids in caverns and aquifers, underground storage of nuclear waste, underground recovery of heat from hydrocarbon fuels, tertiary recovery of oil by thermal methods, rapid excavation of large openings at shallow to great depths and in hostile environments, and retrofitting of large structures built on or in rock. The standardization of methods for determining rock properties is essential to all of the activities described, for use not only in design and construction but also in site selection and post-construction monitoring. Development of such standards is seen as a multidisciplinary effort

  11. The Amphibole-Bearing Chondrite Meteorite LAP04840: Metamorphism and `Tectonics' in a Hydrous Asteroid

    Science.gov (United States)

    Treiman, A. H.; McCanta, M. C.; Essene, E. J.

    2006-12-01

    LAP04840 is an R-chondrite found in Antarctica, and is unique among meteorites in containing abundant amphibole and biotite. Its chondrules (>500 μm diam) sit in a granoblastic matrix of grains ~20 μm across. Amphibole and biotite grains are anhedral to subhedral, to ~100 μm, and concentrated in chondrules. Commonly, they fit among the olivine and opx grains in regions that would (in anhydrous chondrules) have been occupied by cpx, mesostasis, or glass. Minerals are unzoned, and have constant compositions: olivine Fo62Fa38, Opx En60Wo01, plagioclase An07Ab90, magnesio-hornblende, (Ca1.52Na0.81K0.44) (Mg3.60Fe1.27Mn0.01Ti0.04Cr0.08) (Si6.95Al1.02Fe0.03) O22 (OH1.94?F0.05Cl0.01), sodian phlogopite (low Ti, F, Cl), magnetite (Mt63Chr28Sp05Usp04) and Fe-Ni sulfides. This assemblage is consistent with amphibolite facies equilibrium. Amph-plg thermometry (Holland &Blundy, 1994) gives 675°C, which is consistent with limits of ~600metamorphism are simple. After accretion in the early solar nebula, a chondritic asteroid is heated principally by decay of ^{26}Al (Ghosh et al., 2006) in a single prograde event. An asteroid in the inner belt (<~3AU) would accrete little ice, would be dry, and could be heated to (and beyond) 950°C (Hutchison, 2004). The R chondrites fit nicely here; all but LAP are dry and contain strongly metamorphosed clasts (but no melt rocks). Depending on bulk composition, heating can continue to and beyond the basalt solidus, with core formation and widespread melting and differentiation. An asteroid in the outer belt would accrete abundant ice, which would dilute ^{26}Al and sink much of its heat in melting and vaporization even cores of large asteroids (100+ km radius) would barely reach 675

  12. Innovative rock bed construction

    Energy Technology Data Exchange (ETDEWEB)

    Cook, J.

    1983-06-01

    A general discussion of the use of rock beds for heating and cooling thermal storage is particularized for design and construction in Phoenix, Arizona. The rock bed parameters for three two-story condominium apartments constructed in 1982 are discussed, including sizing criteria and original construction details. A revised construction method using gabions that are self-supporting chain link cylinders provided a much more economical construction method as well as other advantages of speed and structural flexibility.

  13. Rock and Soil Rheology

    Science.gov (United States)

    Cristescu, Nicolae; Ene, Horia I.

    The first part of the volume contains theoretical considerations of the physical properties of soils and rocks. Articles on the mechanical and kinematical behavior of rocks as well as mathematical models are the base for the understanding of the physical properties of natural systems. In the second part articles deal with experiments and applications regarding creep deformation of clay, underground cavities, tunnels and deformation of sand and lamistrine sediments.

  14. Basic rocks in Finland

    International Nuclear Information System (INIS)

    Piirainen, T.; Gehoer, S.; Iljina, M.; Kaerki, A.; Paakkola, J.; Vuollo, J.

    1992-10-01

    Basic igneous rocks, containing less than 52% SiO 2 , constitute an important part of the Finnish Archaean and Proterozoic crust. In the Archaean crust exist two units which contain the majority of the basic rocks. The Arcaean basic rocks are metavolcanics and situated in the Greenstone Belts of Eastern Finland. They are divided into two units. The greenstones of the lower one are tholeiites, komatiites and basaltic komatiites. The upper consists of bimodal series of volcanics and the basic rocks of which are Fe-tholeiites, basaltic komatiites and komatiites. Proterozoic basic rocks are divided into seven groups according to their ages. The Proterozoic igneous activity started by the volominous basic magmatism 2.44 Ga ago. During this stage formed the layered intrusions and related dykes in the Northern Finland. 2.2 Ga old basic rocks are situated at the margins of Karelian formations. 2.1 Ga aged Fe-tholeiitic magmatic activity is widespread in Eastern and Northern Finland. The basic rocks of 1.97 Ga age group are met within the Karelian Schist Belts as obducted ophiolite complexes but they occur also as tholeiitic diabase dykes cutting the Karelian schists and Archean basement. The intrusions and the volcanics of the 1.9 Ga old basic igneous activity are mostly encountered around the Granitoid Complex of Central Finland. Subjotnian, 1.6 Ga aged tholeiitic diabases are situated around the Rapakivi massifs of Southern Finland, and postjotnian, 1.2 Ga diabases in Western Finland where they form dykes cutting Svecofennian rocks

  15. Clumped isotopes complement petrological data in the investigation of contact metamorphic aureoles: a case study from the Middle Triassic Monzoni intrusion (Northern Italy)

    Science.gov (United States)

    Müller, Inigo Andreas; Storck, Julian-Christopher; Brack, Peter; Bernasconi, Stefano M.

    2017-04-01

    Carbonate clumped isotope thermometry is a technique which measures the abundance of the 13C-18O-16O2 isotopologue in carbonate rocks. Its abundance is solely dependent on the formation temperature of the carbonate minerals, which makes this still novel method very attractive for research on paleoclimate or low temperature diagenetic processes. If carbonate rocks are exposed to high temperatures as during contact metamorphism or deep burial, the clumped isotope thermometer suffers from solid state reordering, destroying the primary temperature signal. However, this does not mean clumped isotopes cannot be applied on carbonates that were heated in high temperature regimes. In contrast it offers a great tool to track the extent a carbonate was heated and reveal secondary carbonate precipitation due to alteration by circulating fluids. We used carbonates from the contact aureole of the Monzoni intrusion in northern Italy to test the application of clumped isotopes in such an extreme environment. Our measurements show that solid state reordering of the clumped isotope signature and thus an increased temperature signal occurred already 3 km distal from the contact. In contrast, mineral paragenesis studies can only reconstruct the strong temperature decrease within 1.5 km from the contact, whereas carbonates exposed to temperatures below 300 °C do not form mineral assemblages allowing the reconstruction of temperatures. Towards the contact of the Monzoni intrusion clumped isotope data showed again decreasing temperatures and a change in their oxygen isotope composition. This probably reflects the later stage alteration of circulating fluids and subsequent precipitation of secondary carbonates. Our findings show that clumped isotopes are a powerful tool to estimate the extent of contact metamorphism in the cooler part of the aureole at temperatures up to 300 °C. Clumped isotope studies can complement petrological data in the low temperature range to improve thermal

  16. Correlating P-wave Velocity with the Physico-Mechanical Properties of Different Rocks

    Science.gov (United States)

    Khandelwal, Manoj

    2013-04-01

    In mining and civil engineering projects, physico-mechanical properties of the rock affect both the project design and the construction operation. Determination of various physico-mechanical properties of rocks is expensive and time consuming, and sometimes it is very difficult to get cores to perform direct tests to evaluate the rock mass. The purpose of this work is to investigate the relationships between the different physico-mechanical properties of the various rock types with the P-wave velocity. Measurement of P-wave velocity is relatively cheap, non-destructive and easy to carry out. In this study, representative rock mass samples of igneous, sedimentary, and metamorphic rocks were collected from the different locations of India to obtain an empirical relation between P-wave velocity and uniaxial compressive strength, tensile strength, punch shear, density, slake durability index, Young's modulus, Poisson's ratio, impact strength index and Schmidt hammer rebound number. A very strong correlation was found between the P-wave velocity and different physico-mechanical properties of various rock types with very high coefficients of determination. To check the sensitivity of the empirical equations, Students t test was also performed, which confirmed the validity of the proposed correlations.

  17. A study on the U speciation in groundwater of a hard rock aquifer in South India

    International Nuclear Information System (INIS)

    Thivya, C.; Chidambaram, S.; Thilagavathi, R.; Nepolian, M.; Adithya, V.S.; Tirumalesh, K.; Prasanna, M.V.

    2015-01-01

    Speciation of uranium indicates the contribution of this ion into different species. An attempt has been made to study the spatial and temporal variations of U speciation in the hard rock aquifer of South India. The major rock types have granulite facies with high grade metamorphic rocks and younger intrusive. It also comprises of Fissile hornblende biotite gneiss, Charnockite, Quartzite, Granite and Flood Plain Alluvium. A total of 108 samples were collected from the handpumps of the study area for two seasons (Pre monsoon and South West monsoon). The groundwater samples were analysed for U and other ions like Ca 2+ , Mg 2+ , Na + and K + , HCO 3 - , Cl - , SO 4 2- , PO 4 3- , NO 3 - , F - , H 4 SiO 4 , pH, EC and TDS using standard procedures

  18. The Behaviour of Chromium Isotopes during the Oxidative Weathering of Ultramafic Rocks

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie; Døssing, Lasse Nørbye; Mondal, Sisir K.

    Ore Group in the southern Singhbhum Craton (Orissa, India)[3]. A modern weathering profile was logged in an active open cast chromite mine (Sukinda valley). The Cr isotope data of samples from the weathering profile are fractionaed. While the least weathered horizons at the base of the profile reflect......The chromium isotope system has been proven to be a redox-sensitve proxy in ancient and modern environmental studies (e.g. [1], [2]). In this study we investigated Cr isotope fractionation during soil formation from Archean (3.1-3.3 Ga) ultramafic rocks, intruded into metamorphic rocks of the Iron...... are characterised by a Cr loss of up to 74 %. These data are consistent with the findings of Crowe et al. [2] who also studied the effects of weathering of ultramafic rocks in Indonesia on the Cr isotope system. These authors demonstrate that oxidation of Cr(III) to Cr(VI) in the soils is accompanied by isotopic...

  19. Magnetic fabric overprints in multi-deformed polymetamorphic rocks of the Gemeric Unit (Western Carpathians) and its tectonic implications

    Science.gov (United States)

    Hrouda, František; Faryad, Shah Wali

    2017-10-01

    In the Gemeric Unit of the Central West Carpathians, the magnetic fabric was investigated in Early Palaeozoic metasediments and metavolcanics, Permian to Early Triassic granites, and Late Palaeozoic (molasse) metasediments. In addition to Variscan greenschist facies metamorphism in the Early Palaeozoic basement, all rocks underwent Cretaceous (Alpine) low-grade metamorphism, which significantly modified their mineral composition and fabric; original magnetic minerals were destroyed at least partially and new, mostly paramagnetic, minerals were created. In the Early Palaeozoic metasediments, the magnetic fabric is entirely metamorphic/deformational in origin. In metavolcanics, the magnetic foliations are partly parallel to the Alpine metamorphic foliations developed in relatively incompetent lithologies such as tuffs and tuffites and partly to disjunctive foliations developed in competent rhyolites and its subvolcanic members. Their magnetic fabrics probably represent gradual transition from Variscan to Alpine fabrics. In the Permian granites, the magnetic foliations are near the Alpine mesoscopic disjunctive foliations crosscutting metamorphic schistosity in contact aureoles of granite. In the Late Palaeozoic (molasse) metasediments, the magnetic foliations are near the Alpine metamorphic foliations that are mostly parallel to the original bedding. On regional scale, the magnetic fabrics show curved pattern indicating complex interactions between the Gemeric and underlain Veporic units in the final stages of intendation and collision. The magnetic fabric pattern in the Gemeric Unit roughly resembles that in the Veporic Unit. This results from similar tectonic movements operating at least during Cretaceous collision in both the units. This tectonic process occurred subsequent to the closure of the Meliata ocean and was responsible for creation of the final structure of the Central Western Carpathians. Nevertheless, in contrast to the Veporic unit, where dominantly

  20. Development of III-Sb metamorphic DBR membranes on InP for vertical cavity laser applications

    Science.gov (United States)

    Addamane, S. J.; Mansoori, A.; Renteria, E. J.; Dawson, N.; Shima, D. M.; Rotter, T. J.; Hains, C. P.; Dawson, L. R.; Balakrishnan, G.

    2016-04-01

    Sb-based metamorphic DBR membranes are developed for InP-based vertical cavity laser applications. The reflectivity of the metamorphic DBR membrane is compared to the reflectivity of a lattice-matched DBR to characterize the optical quality of the DBR membrane. The metamorphic interface between InP and the III-antimonides is found to degrade the reflectivity of the DBR. Therefore, the growth temperature for the metamorphic DBR is optimized in order to obtain highly reflective (>99.8%) III-Sb thin-film membranes.

  1. Timing and duration of ultra-high temperature metamorphism in sapphirine-bearing metapelite granulite from Kodaikanal, Madurai block, South India: constraints from mineral chemistry and U-Th - total Pb EPMA age of monazite

    International Nuclear Information System (INIS)

    Bhadra, Subhadip

    2016-01-01

    The southern part of Peninsular India, popularly known as the Southern Granulite Terrane (SGT) witnessed a pervasive granulite faces metamorphism, ductile shearing and widespread migmatization during Pan-African orogeny, which marks the final assembly of the Gondwanaland during Cambrian (ca 500 Mu). The tectonic evolution of SGT, irrespective of its Gondwana connection, is far-reaching due to occurrences of ultra-high temperature (UHT) granulites in different parts of the SGT. In the present study, dynamics of melting and temporal evolution of sapphirine-bearing metapelite granulite, hosted within the Kodaikanal charnockite massif, during syn - to post - UHT metamorphic conditions are examined. The onset of UHT metamorphism in the rock is marked by the growth of Al-rich orthopyroxene (Al 2 O 3 ∼8 wt%) porphyroblast, sapphirine-cordierite symplectite via biotite dehydration melting. Embayment of orthopyroxene porphyroblast and accumulation of melt, now preserved as mesoperthites, in the pressure shadow region around the porphyroblast attest to syn-tectonic melting and crystallization. Monazites of varying sizes (40 to 100 mm) occur pervasively, either as inclusion in peritectic phases or in the biotite-mesoperthite rich matrix. Diagnostic chemical variation diagram, such as 4 (REE + Y + P) versus 4 (Th + U + Si), (Si + Y + REE) versus (Ca + P) suggests that the core and rims domains are linked by dominantly huttonitic (Th 4+ - Si 4+ = REE 3+ P 5+ ) and cheralite (Th 4+ + Ca 2+ = 2 REE 4+ ) substitutions. An increase in partitioning of Th towards the rim is also accompanied with a decrease in La/Sm ratio towards the rim. This together with core to rim chemical variation in monazite attests to monazite growth (core) and overgrowth (rim) during peak UHT metamorphism and subsequent cooling. U - Th - total Pb monazite ages constrain the timing of dehydration melting as well as peak UHT metamorphism at - 560 Ma and post-peak cooling at ∼510 Ma. This establishes a time

  2. On the age of the Onverwacht Group, Swaziland sequence, South Africa. [radioactive dating of stratified igneous rocks

    Science.gov (United States)

    Jahn, B.-M.; Shih, C.-Y.

    1974-01-01

    Some rocks of the Onverwacht Group, South Africa, have been analyzed for Rb and Sr concentrations and Sr isotopic composition. These rocks include volcanic rocks, layered ultramafic differentiates and cherty sediments. Whole rock data indicate that the Rb-Sr isotopic systems in many samples were open and yield no reasonable isochron relationships. However, the data of mineral separates from a basaltic komatiite define a good isochron of 3.50 (plus or minus .2) b.y. with an initial Sr-87/Sr-86 ratio of 0.70048 plus or minus 5. The orthodox interpretation of this age is the time of the low grade metamorphism. It is reasonable to assume that the age of 3.50 b.y. might also represent the time of initial Onverwacht volcanism and deposition. The initial Sr-87/Sr-86 ratio obtained above is important to an understanding of the Sr isotopic composition of the Archean upper mantle.

  3. Geophysical study in waste landfill localized above fractured rocks

    Directory of Open Access Journals (Sweden)

    Ariveltom Cosme da Silva

    2011-08-01

    Full Text Available Geophysical survey is an important method for investigation of contaminated areas used in the characterization of contrasting physical properties in the presence of pollutants. This work applied the geophysical methods of Electrical Resistivity and Self Potential in waste landfill, located in Caçapava do Sul city, RS. The landfill is located over fractured metamorphic rocks. Eight lines of electrical profiling with 288 measures of self potential were done. In addition, 83 measurements of direction and dip of fractures were taken. The application of spontaneous potential method permitted to detect the direction of groundwater flow. The electrical resistivity measurements allowed the identification of low-intensity anomalies associated with the presence of leachate. There is a relationship between anomalous zones and the directions of fractures.

  4. Exploring fractality in rocks: combined USANS and SANS measurements

    International Nuclear Information System (INIS)

    Triolo, A.; Triolo, F.; Triolo, R.; Lucido, G.

    1999-01-01

    Complete text of publication follows. The interest in the nanoscale structure of biomaterials, colloids, porous materials and, generally, in condensed matter is growing fast. For objects having dimensions of several hundred Angstrom, SANS instruments, nicely complementing conventional or synchrotron based SAXS instruments, have promoted both instrumentation and theoretical developments. Ultra Small Angle instruments (USANS and USAXS) have just covered the gap between the SANS range and the optical microscopy. Therefore new fields of investigation are now open, especially for USANS, due to the peculiar features of neutrons: high penetrability, large sensitivity to isotopic labelling, small absorption for most nuclei. New generation USANS instruments now allow reaching momentum transfers as low as 10 -5 A -1 , thus allowing exploring material science (ceramics etc), fundamental physics (phase separations, critical phenomena etc). A variety of rocks of different origin and texture (metamorphic, sedimentary and magmatic) are investigated and several model analysis' are compared. (author)

  5. Multifractal model of magnetic susceptibility distributions in some igneous rocks

    Directory of Open Access Journals (Sweden)

    M. E. Gettings

    2012-11-01

    Full Text Available Measurements of in-situ magnetic susceptibility were compiled from mainly Precambrian crystalline basement rocks beneath the Colorado Plateau and ranges in Arizona, Colorado, and New Mexico. The susceptibility meter used measures about 30 cm3 of rock and measures variations in the modal distribution of magnetic minerals that form a minor component volumetrically in these coarsely crystalline granitic to granodioritic rocks. Recent measurements include 50–150 measurements on each outcrop, and show that the distribution of magnetic susceptibilities is highly variable, multimodal and strongly non-Gaussian. Although the distribution of magnetic susceptibility is well known to be multifractal, the small number of data points at an outcrop precludes calculation of the multifractal spectrum by conventional methods. Instead, a brute force approach was adopted using multiplicative cascade models to fit the outcrop scale variability of magnetic minerals. Model segment proportion and length parameters resulted in 26 676 models to span parameter space. Distributions at each outcrop were normalized to unity magnetic susceptibility and added to compare all data for a rock body accounting for variations in petrology and alteration. Once the best-fitting model was found, the equation relating the segment proportion and length parameters was solved numerically to yield the multifractal spectrum estimate. For the best fits, the relative density (the proportion divided by the segment length of one segment tends to be dominant and the other two densities are smaller and nearly equal. No other consistent relationships between the best fit parameters were identified. The multifractal spectrum estimates appear to distinguish between metamorphic gneiss sites and sites on plutons, even if the plutons have been metamorphosed. In particular, rocks that have undergone multiple tectonic events tend to have a larger range of scaling exponents.

  6. RELATIONSHIP BETWEEN METAMORPHISM DEGREE AND LIBERATION SIZE OF COMPACT ITABIRITES FROM THE IRON QUADRANGLE

    Directory of Open Access Journals (Sweden)

    Rodrigo Fina Ferreira

    2015-06-01

    Full Text Available Iron ore exploited in Brazil can be classified into several lithological types which have distinct features. The progress of mining over time leads to scarcity of high grade iron ores, leading to the exploitation of poor, contaminated and compact ores. There is a growing trend of application of process flowsheets involving grinding to promote mineral liberation, essential condition for concentration processes. Several authors have correlated metamorphism processes of banded iron formations to mineralogical features observed on itabirites from the Iron Quadrangle, mainly the crystals size. This paper presents the implications of such variation in defining the mesh of grinding. Mineralogical characterization and grinding, desliming and flotation tests have been carried out with samples from two regions of the Iron Quadrangle subjected to different degrees of metamorphism. It was found a trend of reaching satisfactory liberation degree in coarser size for the itabirite of higher metamorphic degree, which has larger crystals. The flotation tests have confirmed the mineralogical findings.

  7. Carbonation by fluid-rock interactions at High-Pressure conditions: implications for Carbon cycling in subduction zones

    Science.gov (United States)

    Piccoli, Francesca; Vitale Brovarone, Alberto; Beyssac, Olivier; Martinez, Isabelle; Ague, Jay J.; Chaduteau, Carine

    2016-04-01

    Carbonate-bearing lithologies are the main carbon carrier into subduction zones. Their evolution during metamorphism largely controls the fate of carbon regulating its fluxes between shallow and deep reservoirs. In subduction zones, most works have focused on subtractive processes responsible for carbon release from subducting slabs. As an example, several recent works have stressed on the importance of carbonate dissolution as a mean to mobilize large amounts of carbon in subduction zones. By contrast, little is known on additive processes such as rock carbonation at high-pressure (HP) conditions. At shallow depths (e.g. ocean floor and shallow subduction zones, i.e. geo-biosphere and the atmosphere. We report the occurrence of eclogite-facies marbles associated with metasomatic systems in HP metamorphic unit in Alpine Corsica (France). We performed a field-based study on metasomatic marbles. We will present the petrology and geochemistry that characterize carbonate metasomatism together with fluid inclusions study and pseudosection modeling. Altogether, we bring strong evidences for the precipitation of these carbonate-rich assemblages from carbonic fluids during HP metamorphism. We propose that rock carbonation can occur at HP conditions by either vein-injection or chemical replacement mechanisms. Rock carbonation indicates that carbonic fluids produced by decarbonation reactions and carbonate dissolution may not be directly transferred to the mantle wedge, but may have a preferential and complex pathway within the slab and along slab/mantle interface. Rock carbonation by fluid-rock interactions has a potentially great impact on the residence time of carbon and oxygen and on carbonates isotopic signature in subduction zones. Lastly, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.

  8. The metamorphic basement of the southern Sierra de Aconquija, Eastern Sierras Pampeanas: Provenance and tectonic setting of a Neoproterozoic back-arc basin

    Science.gov (United States)

    Cisterna, Clara Eugenia; Altenberger, Uwe; Mon, Ricardo; Günter, Christina; Gutiérrez, Antonio

    2018-03-01

    The Eastern Sierras Pampeanas are mainly composed of Neoproterozoic-early Palaeozoic metamorphic complexes whose protoliths were sedimentary sequences deposited along the western margin of Gondwana. South of the Sierra de Aconquija, Eastern Sierras Pampeanas, a voluminous metamorphic complex crops out. It is mainly composed of schists, gneisses, marbles, calk-silicate schists, thin layers of amphibolites intercalated with the marbles and granitic veins. The new data correlate the Sierra de Aconquija with others metamorphic units that crop out to the south, at the middle portion of the Sierra de Ancasti. Bulk rock composition reflects originally shales, iron rich shales, wackes, minor litharenites and impure limestones as its protoliths. Moreover, comparisons with the northern Sierra de Aconquija and from La Majada (Sierra de Ancasti) show similar composition. Amphibolites have a basaltic precursor, like those from the La Majada (Sierra de Ancasti) ones. The analyzed metamorphic sequence reflects low to moderate weathering conditions in the sediments source environment and their chemical composition would be mainly controlled by the tectonic setting of the sedimentary basin rather than by the secondary sorting and reworking of older deposits. The sediments composition reveal relatively low maturity, nevertheless the Fe - shale and the litharenite show a tendency of minor maturity among them. The source is related to an acid one for the litharenite protolith and a more basic to intermediate for the other rocks, suggesting a main derivation from intermediate to felsic orogen. The source of the Fe-shales may be related to and admixture of the sediments with basic components. Overall the composition point to an upper continental crust as the dominant sediment source for most of the metasedimentary rocks. The protolith of the amphibolites have basic precursors, related to an evolving back-arc basin. The chemical data in combination with the specific sediment association

  9. Lu-Hf total-rock age for the Amîtsoq gneisses, West Greenland

    Science.gov (United States)

    Pettingill, H.S.; Patchett, P.J.

    1981-01-01

    Lu-Hf total-rock data for the Amîtsoq gneisses of West Greenland yield an age of 3.55±0.22Gy(2σ), based on the decay constant λ176Lu=1.96×10−11y−1, and an initial176Hf/177Hf ratio of 0.280482±33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 Gy, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial176Hf/177Hf lies close to a chondritic Hf isotopic evolution curve from 4.55 Gy to present. This is consistent with the igneous precursors to the Amîtsoq gneisses having been derived from the mantle at or shortly before 3.6 Gy. Anomalous relationships between Hf concentration and the176Lu/177Hf ratio may suggest that trace element abundances in the Amîtsoq gneisses are partly controlled by processes related to metamorphism.

  10. Clinopyroxenite dikes crosscutting banded peridotites just above the metamorphic sole in the Oman ophiolite: early cumulates from the primary V3 lava

    Science.gov (United States)

    Ishimaru, Satoko; Arai, Shoji; Tamura, Akihiro

    2013-04-01

    Oman ophiolite is one of the well-known ophiolites for excellent exposures not only of the mantle section but also of the crustal section including effusive rocks and the underlying metamorphic rocks. In the Oman ophiolite, three types of effusive rocks (V1, V2 and V3 from the lower sequences) are recognized: i.e., V1, MORB-like magma, V2, island-arc type lava, and V3, intra-plate lava (Godard et al., 2003 and references there in). V1 and V2 lavas are dominant (> 95 %) as effusive rocks and have been observed in almost all the blocks of northern part of the Oman ophiolite (Godard et al., 2003), but V3 lava has been reported only from Salahi area (Alabaster et al., 1982). It is clear that there was a time gap of lava eruption between V1-2 and V3 based on the presence of pelagic sediments in between (Godard et al., 2003). In addition, V3 lavas are fed by a series of doleritic dikes crosscutting V2 lava (Alley unit) (Alabaster et al., 1982). We found clinopyroxenite (CPXITE) dikes crosscutting deformation structure of basal peridotites just above the metamorphic sole in Wadi Ash Shiyah. The sole metamorphic rock is garnet amphibolite, which overlies the banded and deformed harzburgite and dunite. The CPXITE is composed of coarse clinopyroxene (CPX) with minor amount of chlorite, garnet (hydrous/anhydrous grossular-andradite) with inclusions of titanite, and serpentine formed at a later low-temperature stage. The width of the CPXITE dikes is 2-5 cm (10 cm at maximum) and the dikes contain small blocks of wall harzburgite. Almost all the silicates are serpentinized in the harzburgite blocks except for some CPX. The Mg# (= Mg/(Mg + Fe) atomic ratio) of the CPX is almost constant (= 0.94-0.95) in the serpentinite blocks but varies within the dikes, highest at the contact with the block (0.94) and decreasing with the distance from the contact to 0.81 (0.85 on average). The contents of Al2O3, Cr2O3, and TiO2 in the CPX of the dikes are 0.5-2.0, 0.2-0.6, and 0

  11. Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

    Science.gov (United States)

    Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.

    2010-01-01

    Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to <0.6 GPa @ 650??C, peak garnet granulite facies metamorphic conditions to 680-815??C @ 1.1-1.4. GPa, and a P-T path with a P increase of???0.5. GPa. These sections are compatible with water contents???0.28wt.%, local dehydration during garnet granulite metamorphism, and <0.3. GPa P increases during garnet growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern

  12. Combining Textural Techniques to Explore Effects of Diagenesis and Low-grade Metamorphism on Iron Mineralogy and Iron Speciation

    Science.gov (United States)

    Slotznick, S. P.; Webb, S.; Eiler, J. M.; Kirschvink, J. L.; Fischer, W. W.

    2016-12-01

    Iron chemistry and mineralogy in the sedimentary rocks provide a valuable tool for studying paleoenvironmental conditions due to the fact that iron atoms can take on either the +II or +III valence state under geological redox conditions. One method utilizing this redox chemistry is `iron speciation', a bulk chemical sequential extraction technique that maps proportions of iron species to redox conditions empirically calibrated from modern sediments. However, all Precambrian and many Phanerozoic rocks have experienced post-depositional processes; it is vital to explore their effects on iron mineralogy and speciation. We combined light and electron microscopy, magnetic microscopy, (synchrotron-based) microprobe x-ray spectroscopy, and rock magnetic measurements in order to deconvolve secondary overprints from primary phases and provide quantitative measurement of iron minerals. These techniques were applied to excellently-preserved shale and siltstone samples of the 1.4 Ga lower Belt Supergroup, Montana and Idaho, USA, spanning a metamorphic gradient from sub-biotite to garnet zone. Previously measured Silurian-Devonian shales, sandstones, and carbonates in Maine and Vermont, USA spanning from the chlorite to kyanite zone provided additional well-constrained, quantitative data for comparison and to extend our analysis. In all of the studied samples, pyrrhotite formation occurred at the sub-biotite or sub-chlorite zone. Pyrrhotite was interpreted to form from pyrite and/or other iron phases based on lithology; these reactions can affect the paleoredox proxy. Iron carbonates can also severely influence iron speciation results since they often form in anoxic pore fluids during diagenesis; textural analyses of the Belt Supergroup samples highlighted that iron-bearing carbonates were early diagenetic cements or later diagenetic overprints. The inclusion of iron from diagenetic minerals during iron speciation analyses will skew results by providing a view of pore

  13. P-T-t conditions, Nd and Pb isotopic compositions and detrital zircon geochronology of the Massabesic Gneiss Complex, New Hampshire: isotopic and metamorphic evidence for the identification of Gander basement, central New England

    Science.gov (United States)

    Dorais, Michael J.; Wintsch, Robert P.; Kunk, Michael J.; Aleinikoff, John; Burton, William; Underdown, Christine; Kerwin, Charles M.

    2012-01-01

    We present new evidence for the assignment of the Neoproterozoic Massabesic Gneiss Complex of New Hampshire to the Gander terrane rather than the Avalon terrane. The majority of Avalonian (sensu stricto) igneous and meta-igneous rocks as defined in Maritime Canada have positive whole-rock ɛNd compared to more negative values for Gander rocks, although there is a region of overlap in ɛNd between the two terranes. Our samples from areas in Connecticut previously thought to be Avalonian and samples from the Willimantic dome have the same isotopic signatures as Maritime Canada Avalon. In contrast, samples from the Clinton dome of southern Connecticut plots exclusively in the Gander field. The majority of the orthogneiss samples from Lyme dome (coastal Connecticut), Pelham dome (central Massachusetts) and Massabesic Gneiss Complex also plot in the Gander field, with a few samples plotting in the overlap zone between Gander and Avalon. U-Pb age distributions of detrital zircon populations from quartzites from the Massabesic Gneiss Complex more closely approximate the data from the Lyme Dome rather than Avalon. Additionally, the similarity of the P-T-t path for the rocks of the Massabesic Gneiss Complex (established by thermobarometry and 40Ar/39Ar dating of amphibole, muscovite, biotite and K-feldspar) with that established in the Ganderian Lyme dome of southern Connecticut strengthens the assignment of these rocks to a single Gander block that docked to Laurentia during the Salinic Orogeny. The identification of Ganderian isotopic signatures for these rocks all of which show evidence for Alleghanian metamorphism, supports the hypothesis that Neoproterozoic Gander lower crustal rocks underlie southern New Hampshire, Massachusetts, and Connecticut, and that all rocks of the overlying Central Maine trough that largely escaped high-grade Alleghanian metamorphism are allochthonous. We suggest that during the Alleghanian, the docking of Gondwana caused Avalon to wedge into

  14. Sedimentary Rocks and Dunes

    Science.gov (United States)

    2004-01-01

    25 November 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows buttes composed of light-toned, sedimentary rock exposed by erosion within a crater occurring immediately west of Schiaparelli Basin near 4.0oS, 347.9oW. Surrounding these buttes is a field of dark sand dunes and lighter-toned, very large windblown ripples. The sedimentary rocks might indicate that the crater interior was once the site of a lake. The image covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  15. Session: Hard Rock Penetration

    Energy Technology Data Exchange (ETDEWEB)

    Tennyson, George P. Jr.; Dunn, James C.; Drumheller, Douglas S.; Glowka, David A.; Lysne, Peter

    1992-01-01

    This session at the Geothermal Energy Program Review X: Geothermal Energy and the Utility Market consisted of five presentations: ''Hard Rock Penetration - Summary'' by George P. Tennyson, Jr.; ''Overview - Hard Rock Penetration'' by James C. Dunn; ''An Overview of Acoustic Telemetry'' by Douglas S. Drumheller; ''Lost Circulation Technology Development Status'' by David A. Glowka; ''Downhole Memory-Logging Tools'' by Peter Lysne.

  16. Age succession of metamorphism, paleovolcanism and granitoid magnetism processes in greenstone belts of Middle Dnieper region (Ukrainian shield)

    International Nuclear Information System (INIS)

    Shcherbak, N.P.; Artemenko, G.V.; Bartnitskij, E.N.; Strueva, O.M.

    1987-01-01

    Time succession of paleovolcanism, granatoid magmatism and metamorphism process is considered on the basis of geological, petrological and geochronological data obtained using U-Pb isochronous method by accessory zircons. Paleovolcanism process prevailed 3200-3000 billions of years ago, granatoid magmatism-3100-2950 millions of years ago and regional metamorphism-3000-2840 millions of years ago

  17. Stenian - Tonian and Ediacaran metamorphic imprints in the southern Paleoproterozoic Ubendian Belt, Tanzania: Constraints from in situ monazite ages

    Science.gov (United States)

    Boniface, Nelson; Appel, Peter

    2017-09-01

    In situ monazite geochronological data yield the timing of migmatitic metamorphism in southern Ubendian Belt. The mineral assemblage of garnet-biotite- sillimanite- K-feldspar- plagioclase-quartz- ilmenite, in migmatitic metapelitic gneisses was achieved during the Ediacaran metamorphic episode between 565 ± 4 Ma and 559 ± 8 Ma as manifested by dating of monazite grains that include garnet. The Ediacaran metamorphic event in the southern Ubendian Belt overprinted the Paleoproterozoic metamorphic event established at 1808 ± 9 Ma and the Mesoproterozoic metamorphic event at 944 ± 4 Ma (Tonian Period). The Stenian - Tonian and Ediacaran metamorphic imprints in the southern Ubendian Belt fall within the time window of metamorphism and deformation of the neighboring Irumide, southern Irumide, and Unango/Marrupa Complexes. The ca. 560 Ma old granulite facies imprinting in the southern Ubendian Belt is coeval with shear zone patterns in the neighboring Nyika Terrane in NE Malawi the event that was followed by eclogite facies metamorphism during the last stage of Gondwana amalgamation.

  18. Uranium deposits in the metamorphic basement of the Rouergue massif. Genesis and extension of related albitization processes

    International Nuclear Information System (INIS)

    Schmitt, J.M.

    1982-02-01

    Albitization processes in the Rouergue metamorphic basement, probably Permian aged is evidenced. Late development of uranium orebodies occured within albitized zones. The detection of the latter serves as a highly valuable indirect guide for prospecting this type of deposits in a metamorphic basement [fr

  19. High-precision UPb ages of metamorphic rutile: application to the cooling history of high-grade terranes

    Science.gov (United States)

    Mezger, K.; Hanson, G.N.; Bohlen, S.R.

    1989-01-01

    Metamorphic rutiles occurring in granulite and upper amphibolite facies metapelitic rocks of the Archean Pikwitonei granulite domain (Manitoba) and the Proterozoic Adirondack terrane (New York) give concordant and near concordant UPb ages. The Pb concentrations in rutile range from 2.85 to 168 ppm, U concentrations range from 10.9 to 390 ppm and the measured 206Pb 204Pb ratios range from 182 to 22,100 corresponding to 238U 204Pb ratios of 398-75,100. The proportions of radiogenic 208Pb are very low, ranging from 0.0 to 6.9% of total radiogenic Pb. The habits of the rutile crystals range from stubby to acicular, the physical properties vary from opaque/black to transparent/reddish-brown. Separate batches of black and reddish-brown rutile grains from the same samples have similar U and Pb concentrations, Pb-isotope ratios, and yield the same U Pb ages within analytical uncertainty. No correlation of U concentration and 206Pb 204Pb ratios with morphology or color of the rutiles was observed among the samples analyzed. Most rutiles yield concordant UPb ages which are reproducible within analytical uncertainty, i.e. generally ??2 Ma. The UPb ages for prograde rutile are younger than the time of peak metamorphism given by UPb ages for garnet and zircon, and also younger than UPb ages for sphene and monazite, and 40Ar 39Ar and KAr ages for hornblende but older than 40Ar 39Ar and KAr ages for biotite from the same area. This suggests that the rutile ages reflect cooling below closure temperatures. Within a single hand-specimen, and thus for an identical thermal history, larger rutile grains give older ages than do smaller grains. This suggests that volume diffusion is the most probable mechanism responsible for the ages being younger than the time of peak metamorphism. It also suggests that the dimensions for such diffusion are directly related to the dimensions of the rutile crystal and not to the dimensions of sub-grain domains, as is the case for Ar diffusion in

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

    Science.gov (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  1. Zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotopes from the metamorphic basement in the Wuhe Complex: Implications for Neoarchean active continental margin along the southeastern North China Craton and constraints on the petrogenesis of Mesozoic granitoids

    Directory of Open Access Journals (Sweden)

    Andong Wang

    2013-01-01

    Full Text Available We report zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotope data from mafic granulites and garnet amphibolites of the Wuhe Complex in the southeastern margin of the North China Craton (NCC. In combination with previous data, our results demonstrate that these rocks represent fragments of the ancient lower crust, and have features similar to those of the granulite basement in the northern margin of the NCC. A detailed evaluation of the Pb isotope data shows that Pb isotopes cannot effectively distinguish the role of the Yangtze Craton basement from that of the NCC basement with regard to the source and generation of magmas, at least for southeastern NCC. The age data suggest that the protoliths of the granulites or amphibolites in the Wuhe Complex were most likely generated in Neoarchean and that these rocks were subjected to Paleoproterozoic (1.8–1.9 Ga high-pressure granulite facies metamorphism. This study also shows that the Precambrian metamorphic basement in the southeastern margin of the NCC might have formed in a tectonic setting characterized by a late Neoarchean active continental margin.

  2. Linking rock fabric to fibrous mineralisation: a basic tool for the asbestos hazard

    Directory of Open Access Journals (Sweden)

    G. Vignaroli

    2011-05-01

    Full Text Available In recent years, many studies have addressed the effect on human health caused by asbestos exposures. As asbestos is a group of fibrous minerals that mainly occurs in mafic and ultramafic rocks (ophiolitic sequences, a close relationship between asbestos occurrence and the geological history of host rocks should be expected. By reviewing the existing literature and presenting characteristic examples, it is proposed a direct correspondence exists between the presence of fibrous minerals in ophiolites and the rock fabric systematics due to the combined activity of deformation, metamorphism/metasomatism, and rock/fluid interaction. Understanding the geological factors that may be at the origin of the nucleation/growth of fibrous minerals constitutes a necessary requirement for developing a methodological and analytical procedure to evaluate asbestos hazard (AH in the natural prototype (ophiolitic rocks. A parameterisation of the AH in function of the main geological processes that produce the rock fabric systematics in different tectonic/geodynamic settings is discussed. A geological multidisciplinary approach (based on geological-structural field evidence combined with textural, mineralogical, petrological, and geochemical investigations is proposed as the prerequisite for the evaluation of AH in natural environments. This approach, in particular, can provide a robust basis to formulate a procedural protocol finalised to the mitigation of asbestos effects in environments where these effects are still a real threat.

  3. The distribution of zirconium and hafnium in terrestrial rocks, meteorites and the moon

    Science.gov (United States)

    Ehmann, W. D.; Chyi, L. L.; Garg, A. N.; Ali, M. Z.

    1979-01-01

    It is shown that Zr and Hf are not always fractionated in terrestrial igneous differentiation or regional metamorphism. Data do support a Zr-Hf fractionation in the differentiation of the alkali olivine magma at St. Helena Island. A strong Zr-Hf fractionation exists among lunar rocks and minerals. Ilmenite is an excellent concentrator of Zr and Hf and always exhibits high Zr/Hf ratios. Chondritic meteorites exhibit rather uniform Zr abundances and Zr/Hf ratios but a distinct Zr-Hf fractionation is observed among the eucrite and diogenite achondrites.

  4. Northeast Church Rock Mine

    Science.gov (United States)

    Northeast Church Rock Mine, a former uranium mine 17 miles northeast of Gallup, NM in the Pinedale Chapter of the Navajo Nation. EPA is working with NNEPA to oversee cleanup work by United Nuclear Corporation, a company owned by General Electric (GE).

  5. Rock-hard coatings

    OpenAIRE

    Muller, M.

    2007-01-01

    Aircraft jet engines have to be able to withstand infernal conditions. Extreme heat and bitter cold tax coatings to the limit. Materials expert Dr Ir. Wim Sloof fits atoms together to develop rock-hard coatings. The latest invention in this field is known as ceramic matrix composites. Sloof has signed an agreement with a number of parties to investigate this material further.

  6. Rock-hard coatings

    NARCIS (Netherlands)

    Muller, M.

    2007-01-01

    Aircraft jet engines have to be able to withstand infernal conditions. Extreme heat and bitter cold tax coatings to the limit. Materials expert Dr Ir. Wim Sloof fits atoms together to develop rock-hard coatings. The latest invention in this field is known as ceramic matrix composites. Sloof has

  7. Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow

    NARCIS (Netherlands)

    Plümper, O.; Botan, Alexandru; Los, Catharina; Liu, Yang; Malthe-Sorenssen, Anders; Jamtveit, Bjørn

    2017-01-01

    The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a

  8. Selection of diet by metamorphic and juvenile western toads (Bufo boreas) in northeastern Oregon

    Science.gov (United States)

    Evelyn L Bull; Jane L. Hayes

    2009-01-01

    The decline of Bufo boreas, the Western Toad, in portions of its range has accentuated the need for more complete information on all life stages of this species. Our objectives were to describe the diet of recently metamorphosed and juvenile (one-year old) B. boreas and then compare it to the available arthropods. Metamorphs (n...

  9. Metamorphic reactions and preliminary P-T estimates of ultrahigh-temperature mafic granulite from Tonagh Island in the Napier Complex, East Antarctica

    OpenAIRE

    Tunogae,Toshiaki; Osanai,Yasuhito; Toyoshima,Tsuyoshi; Owada,Masaaki; Hokada,Tomokazu; Crowe,Warwick A.

    1999-01-01

    Metamorphic reactions and P-T conditions of mafic granulites from Tonagh Island in the Archean Napier Complex were examined to evaluate the nature of mafic granulite which has suffered ultrahigh-temperature (UHT) metamorphism. Although a peak mineral assemblage is preserved in plagioclase-orthopyroxene-clinopyroxene mafic granulites, initial mineral chemistry was completely reset by retrograde metamorphism. Evidence of UHT metamorphism was therefore inferred using lamella-bearing pyroxenes as...

  10. Rb-Sr and K-Ar isotopic evidence for neoproterozoic (Pan-African) granulite metamorphism from the basement of Mumbai offshore basin, India

    International Nuclear Information System (INIS)

    Rathore, S.S.; Vijan, A.R.; Singh, M.P.; Misra, K.N.; Prabhu, B.N.

    2000-01-01

    Precambrian basement from well HBM-1 in the Heera oil field of Mumbai offshore basin has been dated by Rb-Sr and K-Ar methods. Five granulitic basement samples from three conventional drill cores have yielded Rb-Sr isochron age of 502±25 Ma with an initial Sr ratio of 0.70855±0.00013. This age has been interpreted as the time of granulite facies metamorphism of the basement rocks in the region. Two whole rock samples from the basement of this well have yielded mutually concordant K-Ar ages of 505±16 Ma and 507±17 Ma. The K-Ar ages are significantly similar to Rb-Sr age obtained from this well, suggesting complete isotopic reequilibration around 500 Ma ago. The time of secondary thermal heating around 500 Ma ago in the basement of Heera field coincides with the widespread neoproterozoic (Pan-African) thermo-tectonic event extending from the Arabian Peninsula and eastern Africa covering Madagascar, southern India. Sri Lanka and East Antarctica. This study widens the limit of the Pan-African zone, which hitherto was thought to be confined to the western part (presently southern part) of the Indian subcontinent, towards further east. (author)

  11. Ordovician metamorphism in the Sierras Pampeana: New U-Pb SHRIMP ages in Central-East Valle Fertil and the Velasco batholith

    International Nuclear Information System (INIS)

    Rapela, C.W; Pankhurst, R.J; Baldo, E; Casquet, C.; Galindo, C; Fanning, C.M; Saavedra, J

    2001-01-01

    Magmatic activity, during which extensive I- and S-type granitoids were emplaced in the Famatinian belt and synchronous, though sparse, TTG plutons in the Pampean belt, preceded the accretion of the Precordillera terrane (PT) to the proto-Pacific margin of South America. These three types of granitoid were mainly emplaced in Early Ordovician times (470 90 Ma, Pankhurst et al., 2001). However, little is known about the timing and characteristics of regional metamorphism during the Famatinian orogeny. A key transect in this study is at 30 o 30 31 o 40 , where Grenvillian basement units of the PT are separated by the Bermejo valley from high-grade rocks of the Sierra de Valle Fertil. Geochronological studies have been carried out in the Sierra de Pie de Palo (PT), on the western side of the transect, by Ramos et al. (1998) and Casquet et al. (2001). We are now able to characterise metamorphism on the eastern side of the transect, i.e. the Gondwana margin. To this end we are presenting new U-Pb SHRIMP geochronological studies of western Sierra de Valle Fertil (Baldo et al., 2001), and central-eastern Sierra de Valle Fertil and Sierra de Velasco (this paper). The geology of the central and eastern sectors of the Sierra de Valle Fertil is dominated by a metaluminous sequence of hornblende-biotite tonalites/granodiorites, and suites of troctolitic, noritic and hornblende gabbros emplaced in high-grade metapelites, marbles and amphibolites. The locations of the three samples selected for the isotopic study SVF-3131 is a garnet migmatite composed of Grt + Bt + Pl + Qtz, with Zrn, Mnz, Ap as accessories (mineral symbols after Kretz, 1983). SVF-573 is a cordierite-garnet diatexitic migmatite: Crd (Mg 77-79) + Grt (Alm 57-69, Py 27-32) + Bt (TiO 2 = 3.2-4.5%) + Sil + Pl (An33-35) + Kfs + Qtz; accessories are Spl (included in Grt, ZnO 9-11%), Zrn, Mag, Ilm, Mnz. The widespread occurrence of Crd and Spl in the high-grade rocks indicates that anatexis in central-east Valle Fertil

  12. Drilling the leading edge of the mantle wedge and the underlying metamorphic sole of the Samail Ophiolite: Hole BT1B, Oman Drilling Project

    Science.gov (United States)

    Morishita, T.; Kelemen, P. B.; Coggon, J. A.; Harris, M.; Matter, J. M.; Michibayashi, K.; Takazawa, E.; Teagle, D. A. H.

    2017-12-01

    Hole BT1B (23°21.861' N, 58°10.957' E) was drilled by the Oman Drilling Project (OmDP) on the north side of Wadi Mansah in the Samail ophiolite, Oman. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole BT1B was cored from 6 to 23 March 2017, to a depth of 300.05 m. The outer surfaces of the cores were imaged and described onsite before being curated, boxed and shipped to the IODP drill ship Chikyu. Hole BT1B sampled carbonated peridotite (listvenite), 2 carbonate-veined serpentinite bands at 80-100 and 180-185 m depth, a few cm of ultracataclasite and 70 cm of fault gouge at 197 m depth, followed by 103 m metamorphic sole. Onboard Chikyu, BT1B underwent X-ray computed tomography (CT) and multi-sensor logging, imaging and spectroscopy, macroscopic and thin section observations, physical properties measurements, and XRF, XRD and ICP-MS analyses. 1st authors of abstracts reporting initial results are Beinlich (matrix characteristics), de Obeso (modeling mass transfer), Godard (XRF and ICP-MS whole rock data), Greenberger (infrared spectroscopy), Johnson (XRF core scanner), Kelemen (overall petrology), Manning (veins), and Michibayashi (X-ray CT). Listvenite is composed of carbonate + quartz + Fe-oxyhydroxides, + minor relict spinel ± chromian mica (fuchsite). The mineralogy suggests formation at < 150°C. The bulk rock density is similar to that of gabbro but the P-wave velocity is generally higher. Rock textures suggest viscous deformation, while additional brittle deformation is recorded by older veins and younger breccias and faults. The metamorphic sole consists of fine-grained to microcrystalline

  13. Late Cretaceous Localized Crustal Thickening as a Primary Control on the 3-D Architecture and Exhumation Histories of Cordilleran Metamorphic Core Complexes

    Science.gov (United States)

    Gans, P. B.; Wong, M.

    2014-12-01

    The juxtaposition of mylonitic mid-crustal rocks and faulted supracrustal rocks in metamorphic core complexes (MMCs) is usually portrayed in 2 dimensions and attributed to a single event of large-scale slip ± isostatic doming along a low-angle "detachment fault"/ shear zone. This paradigm does not explain dramatic along strike (3-D) variations in slip magnitude, footwall architecture, and burial / exhumation histories of most MMCs. A fundamental question posed by MMCs is how did their earlier thickening and exhumation histories influence the geometric evolution and 3-D slip distribution on the subsequent detachment faults? New geologic mapping and 40Ar/39Ar thermochronology from the Snake Range-Kern Mts-Deep Creek Mts (SKDC) complex in eastern Nevada offer important insights into this question. Crustal shortening and thickening by large-scale non-cylindrical recumbent folds and associated thrust faults during the late Cretaceous (90-80 Ma) resulted in deep burial (650°C, 20-25 km) of the central part of the footwall, but metamorphic grade decreases dramatically to the N and S in concert with decreasing amplitude on the shortening structures. Subsequent Paleogene extensional exhumation by normal faulting and ESE-directed mylonitic shearing is greatest in areas of maximum earlier thickening and brought highest grade rocks back to depths of~10-12 km. After ≥15 Ma of quiescence, rapid E-directed slip initiated along the brittle Miocene Snake Range detachment at 20 Ma and reactivated the Eocene shear zone. The ≥200°C gradient across the footwall at this time implies that the Miocene slip surface originated as a moderately E-dipping normal fault. This Miocene slip surface can be tracked for more than 100 km along strike, but the greatest amount of Miocene slip also coincides with parts of the footwall that were most deeply buried in the Cretaceous. These relations indicate that not only is the SKDC MMC a composite feature, but that the crustal welt created by

  14. Review of potential host rocks for radioactive waste disposal in the southeast United States-Southern Piedmont subregion

    International Nuclear Information System (INIS)

    1980-10-01

    A literature study was conducted on the geology of the Southern Piedmont province in the states of Maryland, Virginia, North Carolina, South Carolina, and Georgia. The purpose was to identify geologic areas potentially suitable for containment of a repository for the long-term isolation of solidified radioactive waste. The crystalline rocks of the Southern Piedmont province range in age from Precambrian to Paleozoic, and are predominantly slates, phyllites, argillites, schists, metavolcanics, gneisses, gabbros, and granites. These rock units were classified as either favorable, potentially favorable, or unfavorable as potential study areas based on an evaluation of the geologic, hydrologic, and geotechnical characteristics. No socio-economic factors were considered. Rocks subjected to multiple periods of deformation and metamorphism, or described as highly fractured, or of limited areal extent were generally ranked as unfavorable. Potentially favorable rocks are primarily the high-grade metamorphic gneisses and granites. Sixteen areas were classified as being favorable for additional study. These areas are primarily large igneous granite plutons as follows: the Petersburg granite in Virginia; the Rolesville-Castallia, Churchland, and Landis plutons in North Carolina; the Liberty Hill, Winnsboro, and Ogden plutons in South Carolina; and the Siloam, Elberton, and six unnamed granite plutons in Georgia

  15. The ophiolite of the Eohellenic nappe in the island of Skyros, Greece: Geotectonic environment of formation and metamorphic conditions inferred by mineralogical and geochemical data

    Science.gov (United States)

    Karkalis, Christos; Magganas, Andreas; Koutsovitis, Petros

    2014-05-01

    The island of Skyros is located in the Sporades-Aegean region. It includes an ophiolitic mélange sequence consisting of serpentinites, gabbroic and doleritic rocks, and also lavas which mostly appear in massive form, but in rare cases as deformed pillows. The ophiolitic mélange sequence also includes rodingites, ophicalcites, as well as radiolarites. This formation belongs to the Eohellenic tectonic nappe, which encompasses marbles, sandstones and schists and was emplaced onto the Pelagonian Zone during Early Cretaceous [1, 2]. Serpentinites were most likely formed after serpentinization of harzburgitic protoliths and consist of serpentine, bastite, spinel and magnetite. The chemistry of spinels (TiO2=0.14-0.25 wt.%, Al2O3=35.1-35.21 wt.%, Cr#=37.38-38.87), shows that the harzburgitic protoliths plausibly resemble back-arc basin peridotites [3]. Gabbros and dolerites present mostly subophitic textures, between the hornblende/clinopyroxene and plagioclase grains. Based upon their petrography and on their mineral chemistry hornblendes have been distinguished into magmatic and metamorphic hornblendes, with the first occurring mostly in gabbroic rocks. Magmatic hornblendes exhibit relatively high TiO2 (1.42-1.62 wt.%), Al2O3 (5.11-5.86 wt.%) and Na2O (1.01-1.09 wt.%) contents, with their presence implying that the magma was at least to some degree hydrous. Lavas are tholeiitic basalts with relatively high FeOt≡12 wt.% and low K2O and Th contents, consisting mostly albite, altered clinopyroxene and devitrified glass. Tectonomagmatic discrimination diagrams [4, 5] illustrate that the studied gabbros and lavas of Skyros are most likely associated with SSZ processes. Gabbroic rocks, subvolcanic dolerites and lavas have been subjected to greenschist/subgreenschist metamorphic processes, as confirmed by the presence of secondary amphiboles (metamorphic hornblende, actinolite/tremolite), epidote, pumpellyite and chlorite in all of the studied samples. On the other hand

  16. Soil/Rock Properties Laboratory

    Data.gov (United States)

    Federal Laboratory Consortium — Soil/Rock Properties LaboratoryLocation: Spokane SiteThe Soil/Rock Properties Laboratory is contained in the soils bay, a 4,700 sq. ft. facility that provides space...

  17. On the role of Yttrium during plurifacial Hercynian metamorphism as expressed in the Northern part of the Central galician schist Area (NW Spain)

    NARCIS (Netherlands)

    Hilgen, J.D.

    1981-01-01

    Recent investigations of the distribution of trace elements in metamorphic index minerals of metapelites have revealed, that the plurifacial character of the Hercynian metamorphism in this area is confirmed by the distribution of Yttrium in Hercynian garnets of the metamorphic series.

  18. Micro- to nano-scale mapping and characterization of low-temperature metamorphism in Archean subseafloor metabasalts with implications for early life

    Science.gov (United States)

    Grosch, Eugene; McLoughlin, Nicola

    2015-04-01

    In modern oceanic environments, the low-temperature alteration of subseafloor basaltic glass provides potential chemical energy argued to sustain deep microbial ecosystems. By analogy, it has been argued that early Archean subseafloor pillow lava sequences may provide an environment in which to seek evidence for the earliest traces of microbial life on Earth, and possibly on Mars. Microtextures in metavolcanic pillow lavas from the ca. 3.55 - 3.10 billion-year-old Barberton greenstone belt of South Africa have been argued to represent the remains of microbes that tunneled into Archean subseafloor volcanic glass [1]. The filamentous titanite microtextures occurring in a quartz-chlorite-epidote matrix have been argued to represent Earth's oldest trace fossil. However, distinguishing abiotic hydrothermal processes from candidate geochemical and micro-textural biosignatures preserved in early Archean rocks has proven to be a major scientific challenge. Also, very few PT-constraints on ocean-floor metamorphism are available in this greenstone belt. This quest for the earliest traces of life relies upon the ongoing development of in-situ analytical techniques in terms of instrument sensitivity and spatial resolution. Here we employ a wide-range of novel petrological tools and metamorphic thermodynamic modelling techniques to test the biogenicity of microtextures, provide the first constraints on metamorphic conditions on the host metabasalts, and contribute to the search for robust traces of life in the early Archean. This includes in-situ mapping of the microtextures by laser Raman confocal spectroscopy, high-spatial-resolution elemental (C, N, P) mapping and in-situ isotopic measurements by NanoSIMS (nanoscale secondary ion microprobe) to evaluate the candidate biosignatures [2]. We have also developed and applied a new quantitative microscale mapping technique combined with thermodynamic modelling to map out metamorphic conditions surrounding the candidate

  19. Sedimentological characteristics and depositional environment of Upper Gondwana rocks in the Chintalapudi sub-basin of the Godavari valley, Andhra Pradesh, India

    Science.gov (United States)

    Ramamohanarao, T.; Sairam, K.; Venkateswararao, Y.; Nagamalleswararao, B.; Viswanath, K.

    2003-03-01

    The Kota (Early to Middle Jurassic) and Gangapur (Early Cretaceous) rocks of the Chintalapudi sub-basin of Gondwana are poorly to very poorly sorted, positively to very positively skewed, and leptokurtic to very leptokurtic. The Kota rocks show a single prominent truncation line at the inflection of saltation/suspension at 2.0 φ of the river mode of transportation. The Gangapur rocks show two truncation lines of saltation/suspension, one at 0.5-1.7 φ and the other at 2.4-4.0 φ. These are inferred to be due to a high turbulent phase of the river. On the multigroup multivariant discriminant functions V1- V2 diagram, the bulk of the samples from Kota and Gangapur fall in the field of turbidite deposition. This study supports the view that the discrimination of river from turbidite deposits on this diagram is poor since both deposits are identical in terms of settling velocity distribution. On the C- M diagram, the Kota and Gangapur rocks show segments of rolling, bottom suspension, and graded suspension during river transport of sediment. The Q-R segments of graded suspension for these rocks have a C/ M ratio of 2.5, which is close to the ratio of the turbidites. The Kota and Gangapur rocks have nearly the same assemblage of heavy minerals. The provenance is inferred to consist of basic igneous rocks, acid igneous rocks, high-grade metamorphic rocks and sedimentary rocks.

  20. Eclogite Facies Relicts and Decompression Assemblages; Evidence for the Exhumation of a Large Coherent Metabasite Block From > 40 km Depth; Central Metamorphic Terrane, Eastern Klamath Mountains, Northern California

    Science.gov (United States)

    Barrow, W. M.; Fairhurst, R. J.; Metcalf, R. V.

    2007-12-01

    Recent exhumation models for eclogite terranes have focused on the exhumation of sialic rocks. Exhumed high pressure terranes are typically > 85% - 90% sialic material with only minor amounts of mafic and ultramafic rock. Most known metabasitic eclogites are blocks in mélange rather than large coherent bodies. The Central Metamorphic terrane (CMt) is a large (~300 km3) coherent, fault-bounded package of metabasites thought to represent a remnant of a downing plate subducted in an intra-oceanic convergent margin. Thermochronology indicates that the CMt was metamorphosed and later accreted to the base of the Trinity ophiolite along the Trinity fault during Early Permian extension (Hbl and Musc 40Ar/39Ar ages of 275 Ma - 294 Ma). Previous work suggested that the peak metamorphic temperatures and pressures were ~650°C and 0.4 to 0.8 GPa (Peacock and Norris, 1989) which is consistent with the amphibolite facies mineral assemblage. Trace element data confirm the NMORB-like composition of CMt metabasite protoliths. Newly discovered relict textures, however, suggest that CMt amphibolites record much deeper subduction burial with subsequent decompression exhumation. A decompression sequence consisting of rutile cores within ilmenite crystals mantled by titanite is observed in CMt amphibolite samples. Zr-in-rutile thermometry (Watson et al., 2006) combined with experimental data for rutile stability in metabasites (Ernst and Lui, 1998) suggests that relict rutile crystals preserve early P-T conditions of ~600°C and > 1.3 GPa consistent with eclogite facies metamorphism. Transition from eclogite facies is further supported by ilmenite-plagioclase-amphibole symplectites suggesting replacement of garnet (Bhowmik and Roy, 2003) during decompression. Amphibole compositions vary significantly and reflect lower grade (low Na, Al, Ti actinolite) overprint of earlier amphibolite facies compositions (high Na, Al, Ti magnesio- hornblende). Application of the Al-Ti hornblende

  1. Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

    Directory of Open Access Journals (Sweden)

    Torres-Sánchez Sonia Alejandra

    2017-08-01

    Full Text Available The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (LaN/YbN = 0.51 –20.0 and LaN/SmN = 0.72–9.1 and the enrichment in the highly incompatible elements Cs (0.1 ppm, U (2.8 ppm, and Zr (60 ppm as well as depletion in Ba (1 – 15 ppm, Sr (1 –184 ppm, Pb (0.1 –14 ppm, and Ce (0.1 –1.9 ppm the rocks have mid-ocean ridge and subduction zones characteristics. The serpentinite contains Al-chromite, ferrian chromite and magnetite. The Al-chromite is characterized by Cr# of 0.48 to 0.55 suggesting a MORB origin, and Cr# of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism. We propose at least two serpentinization stages of lithospheric mantle for the ultramafic rock of the Granjeno Schist, (1 a first in an ocean-floor environment at sub-greenschist to greenschist facies conditions and (2 later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite at greenschist to low amphibolite facies conditions during regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramafic rocks is related to an obduction and accretional event at the western margin of Pangea.

  2. Occurrence of Tourmaline in Metasedimentary Rocks of the Isua Supracrustal Belt, Greenland: Implications for Ribose Stabilization in Hadean Marine Sediments.

    Science.gov (United States)

    Mishima, Shinpei; Ohtomo, Yoko; Kakegawa, Takeshi

    2016-06-01

    Abiotic formation of RNA was important for the emergence of terrestrial life, but the acknowledged difficulties of generating and stabilizing ribose have often raised questions regarding how the first RNA might have formed. Previous researchers have proposed that borate could have stabilized ribose; however, the availability of borate on the early Earth has been the subject of intense debate. In order to examine whether borate was available on the early Earth, this study examined metasedimentary rocks from the Isua Supracrustal Belt. Garnet, biotite, and quartz comprise the major constituents of the examined rocks. Field relationships and the chemical compositions of the examined rocks suggest sedimentary origin. The present study found that garnet crystals contain a number of inclusions of tourmaline (a type of borosilicate mineral). All tourmaline crystals are Fe-rich and categorized as schorl. Both garnet and tourmaline often contain graphite inclusions and this close association of tourmaline with garnet and graphite has not been recognized previously. Garnet-biotite and graphite geothermometers suggest that the tourmaline in garnet experienced peak metamorphic conditions (~500 °C and 5 kbar). The mineralogical characteristics of the tourmaline and the whole rock composition indicate that the tourmaline formed authigenically in the sediment during diagenesis and/or early metamorphism. Clay minerals in modern sediments have the capability to adsorb and concentrate borate, which could lead to boron enrichment during diagenesis, followed by tourmaline formation under metamorphic conditions. Clay minerals, deposited on the early Archean seafloor, were the precursors of the garnet and biotite in the examined samples. The studied tourmaline crystals were most likely formed in the same way as modern tourmaline in marine sediments. Therefore, boron enrichment by clays must have been possible even during the early Archean. Thus, similar enrichment could have been

  3. Thermal ecology of the post-metamorphic Andean toad (Rhinella spinulosa) at elevation in the monte desert, Argentina.

    Science.gov (United States)

    Sanabria, Eduardo A; Rodríguez, César Y; Vergara, Cristina; Ontivero, Emanuel; Banchig, Mariana; Navas, Ana L; Herrera-Morata, Mario A; Quiroga, Lorena B

    2015-08-01

    Rhinella spinulosa is an anuran toad species distributed latitudinal and altitudinal (1200-5000m) from Peru to Argentina, inhabiting mountain valleys in the Andes. Considering the broad range of habitats where they live, it is important to understand the thermal physiological mechanisms, thermal tolerances and physiological adaptations for surviving in rigorous environments. We investigated the thermal parameters (field body temperature, selected body temperature, locomotor performance in field and laboratory conditions, and thermal extremes) during diurnal activity for a population of juvenile, post-metamorphosed toads (Rhinella spinulosa) from the Monte Desert of San Juan, Argentina. Post-metamorphic toads are active from approximately 1100-1900 (in contrast to nocturnal adult toads). Our findings show that these toads have a wide thermal tolerance range, ranging from a critical thermal maximum of 36.9°C to crystallization temperatures below 0°C. During their active period, toads always showed suboptimal thermal conditions for locomotion. Despite the suboptimal condition for the locomotion, diurnal activity is likely to confer thermal advantages, allowing them to search for food and increase digestion and growth rates. We also found that the toads are capable of super-cooling, which prevents mortality from freezing when the environmental temperatures drop below 0°C. The environmental temperatures are below zero at night, when toads are inactive and take refuge under rocks. In summary, this toad population demonstrates high thermal plasticity, as shown by a relatively high level of activity sustained over a wide range of ambient temperature (~35°C). These thermal adaptations allow this species of juvenile toads to inhabit a wide range of altitudes and latitudes. Copyright © 2015. Published by Elsevier Ltd.

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

    Science.gov (United States)

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

    2014-09-01

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

  5. Uranium in alkaline rocks

    International Nuclear Information System (INIS)

    Murphy, M.; Wollenberg, H.; Strisower, B.; Bowman, H.; Flexser, S.; Carmichael, I.

    1978-04-01

    Geologic and geochemical criteria were developed for the occurrence of economic uranium deposits in alkaline igneous rocks. A literature search, a limited chemical analytical program, and visits to three prominent alkaline-rock localities (Ilimaussaq, Greenland; Pocos de Caldas, Brazil; and Powderhorn, Colorado) were made to establish criteria to determine if a site had some uranium resource potential. From the literature, four alkaline-intrusive occurrences of differing character were identified as type-localities for uranium mineralization, and the important aspects of these localities were described. These characteristics were used to categorize and evaluate U.S. occurrences. The literature search disclosed 69 U.S. sites, encompassing nepheline syenite, alkaline granite, and carbonatite. It was possible to compare two-thirds of these sites to the type localities. A ranking system identified ten of the sites as most likely to have uranium resource potential

  6. Uranium in alkaline rocks

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, M.; Wollenberg, H.; Strisower, B.; Bowman, H.; Flexser, S.; Carmichael, I.

    1978-04-01

    Geologic and geochemical criteria were developed for the occurrence of economic uranium deposits in alkaline igneous rocks. A literature search, a limited chemical analytical program, and visits to three prominent alkaline-rock localities (Ilimaussaq, Greenland; Pocos de Caldas, Brazil; and Powderhorn, Colorado) were made to establish criteria to determine if a site had some uranium resource potential. From the literature, four alkaline-intrusive occurrences of differing character were identified as type-localities for uranium mineralization, and the important aspects of these localities were described. These characteristics were used to categorize and evaluate U.S. occurrences. The literature search disclosed 69 U.S. sites, encompassing nepheline syenite, alkaline granite, and carbonatite. It was possible to compare two-thirds of these sites to the type localities. A ranking system identified ten of the sites as most likely to have uranium resource potential.

  7. Rock and mineral magnetism

    CERN Document Server

    O’Reilly, W

    1984-01-01

    The past two decades have witnessed a revolution in the earth sciences. The quantitative, instrument-based measurements and physical models of. geophysics, together with advances in technology, have radically transformed the way in which the Earth, and especially its crust, is described. The study of the magnetism of the rocks of the Earth's crust has played a major part in this transformation. Rocks, or more specifically their constituent magnetic minerals, can be regarded as a measuring instrument provided by nature, which can be employed in the service of the earth sciences. Thus magnetic minerals are a recording magnetometer; a goniometer or protractor, recording the directions of flows, fields and forces; a clock; a recording thermometer; a position recorder; astrain gauge; an instrument for geo­ logical surveying; a tracer in climatology and hydrology; a tool in petrology. No instrument is linear, or free from noise and systematic errors, and the performance of nature's instrument must be assessed and ...

  8. Limados : Rock peruano

    OpenAIRE

    García Morete, Ramiro

    2013-01-01

    Incentivado por la corriente nuevaolera que llegaba de México, fue señalado por especialistas como pionero del punk. Aunque el plan, era tocar con lo que hubiera. Un recodo ínfimo de un período breve pero sorprendentemente poderoso, los 60 en un país que hizo del rock una expresión propia de su cultura. Facultad de Periodismo y Comunicación Social

  9. Deformations of fractured rock

    International Nuclear Information System (INIS)

    Stephansson, O.

    1977-09-01

    Results of the DBM and FEM analysis in this study indicate that a suitable rock mass for repository of radioactive waste should be moderately jointed (about 1 joint/m 2 ) and surrounded by shear zones of the first order. This allowes for a gentle and flexible deformation under tectonic stresses and prevent the development of large cross-cutting failures in the repository area. (author)

  10. Rock in Rio: forever young

    Directory of Open Access Journals (Sweden)

    Ricardo Ferreira Freitas

    2014-12-01

    Full Text Available The purpose of this article is to discuss the role of Rock in Rio: The Musical, as herald of megafestival Rock in Rio. Driven by the success that musicals have reached in Brazil, we believe that the design of this spectacle of music, dance and staging renews the brand of the rock festival, once it adds the force of young and healthy bodies to its concept. Moreover, the musical provides Rock in Rio with some distance from the controversal trilogy of sex, drugs and rock and roll, a strong mark of past festivals around the world. Thus, the musical expands the possibilities of growth for the brand.

  11. Hydrological characteristics of Japanese rock

    International Nuclear Information System (INIS)

    Ijiri, Yuji; Sawada, Atsushi; Akahori, Kuniaki

    1999-11-01

    It is crucial to evaluate the hydrogeological characteristics of rock in Japan in order to assess the performance of geosphere. This report summarizes the hydrogeological characteristics of various rock types obtained from broad literature surveys and the fields experiments at the Kamaishi mine in northern Japan and at the Tono mine in central Japan. It is found that the hydraulic conductivity of rock mass ranges from 10 -9 m/s to 10 -8 m/s, whereas the hydraulic conductivity of fault zone ranges from 10 -9 m/s to 10 -3 m/s. It is also found that the hydraulic conductivity tends to decrease with depth. Therefore, the hydraulic conductivity of rock mass at the depth of a repository will be smaller than above values. From the investigations at outcrops and galleries throughout the country, fractures are observed as potential pathways in all rock types. All kinds of crystalline rocks and pre-Neogene sedimentary rocks are classified as fractured media where fracture flow is dominant. Among these rocks, granitic rock is considered the archetype fractured media. On the other hand, andesite, tuff and Neogene sedimentary rocks are considered as intermediate between fractured media and porous media where flow in fractures as well as in rock matrix are significant. (author)

  12. Development of artificial soft rock

    International Nuclear Information System (INIS)

    Kishi, Kiyoshi

    1995-01-01

    When foundation base rocks are deeper than the level of installing structures or there exist weathered rocks and crushed rocks in a part of base rocks, often sound artificial base rocks are made by substituting the part with concrete. But in the construction of Kashiwazaki Kariwa Nuclear Power Station of Tokyo Electric Power Co., Inc., the foundation base rocks consist of mudstone, and the stiffness of concrete is large as compared with the surrounding base rocks. As the quality of the substituting material, the nearly same stiffness as that of the surrounding soft rocks and long term stability are suitable, and the excellent workability and economical efficiency are required, therefore, artificial soft rocks were developed. As the substituting material, the soil mortar that can obtain the physical property values in stable form, which are similar to those of Nishiyama mudstone, was selected. The mechanism of its hardening and the long term stability, and the manufacturing plant are reported. As for its application to the base rocks of Kashiwazaki Kariwa Nuclear Power Station, the verification test at the site and the application to the base rocks for No. 7 plant reactor building and other places are described. (K.I.)

  13. Inside a Crustal Earthquake - the Rock Evidence

    Science.gov (United States)

    Sibson, R. H.

    2012-12-01

    Exhumed fault rock assemblages provide insights into fault zone structure, rupture processes and physical conditions of seismogenesis which can be melded with high-resolution geophysical information on modern earthquakes. The transition from dominantly cataclasite-series to mylonite-series fault rocks at greenschist and greater grades of metamorphism is the basis of fault zone models and rheological strength profiles defining the FR-VS (frictional-viscous) transition which governs the base of the microseismically defined seismogenic zone, within which larger ruptures are mostly contained. In areas of crust deforming under moderate-to-high heat flow (e.g. Japan, California) there is good correlation between geothermal gradient and the base of microseismic activity in the crust. However, compositional variations (e.g. quartz- vs. feldspar-dominant rheology) plus other factors such as water content locally perturb the base of the seismogenic zone, creating strength asperities which may affect the nucleation of large ruptures (e.g.1989 M6.9 Loma Prieta earthquake). The level of shear stress driving rupturing within the seismogenic zone remains problematic. While some estimates (e.g. those inferred from pseudotachylyte friction-melts) are broadly consistent with expectations for the frictional strength of optimally oriented faults with 'Byerlee friction' (τ ~ 80-240 MPa at 10 km depth, depending on faulting mode), others (e.g. faults with associated hydrothermal extension veins) appear to slip at much lower levels of shear stress (max. τ 90% of global seismic moment release) and areas of active compressional inversion (e.g. NE Honshu). However, while fault overpressuring is more easily generated and sustained in compressional regimes, it may be more widespread than once thought. The presence of incrementally deposited hydrothermal veins along fault slip surfaces (often associated with subsidiary extension vein arrays) is not uncommon in fault assemblages exhumed from

  14. Eclogite-high-pressure granulite metamorphism records early collision in West Gondwana: new data from the Southern Brasilia Belt, Brazil

    DEFF Research Database (Denmark)

    Reno II, Barry Len; Brown, Michael; Kobayashi, Katsura

    2009-01-01

    constrain the age of. (1) retrograded eclogite from a block along the tectonic contact beneath the uppermost nappe in a stack of passive margin-derived nappes; (2) high-pressure granulite-facies metamorphism in the uppermost passive margin-derived nappe; (3) high-pressure granulite-facies metamorphism...... in the overlying arc-derived nappe. Rare zircons from a retrograded eclogite yield a Pb-206/U-238 age of 678 +/- 29 Ma. which we interpret as most likely to (late close-to-peak-P metamorphism and to provide a minimum age for detachment of the overlying passive margin-derived nappe from the subducting plate. Zircon...

  15. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Science.gov (United States)

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-12-04

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

  16. Pre-lithification tectonic foliation development in a clastic sedimentary rock sequence from SW Ireland

    Science.gov (United States)

    Meere, Patrick; Mulchrone, Kieran; McCarthy, David

    2017-04-01

    The current orthodoxy regarding the development of regionally developed penetrative tectonic cleavage fabrics in sedimentary rocks is that it postdates lithification of those rocks. It is well established that fabric development under these circumstances is achieved by a combination of grain rigid body rotation, crystal-plastic deformation and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal nature of cleavage development commonly observed in low grade metamorphic rocks. While there have been advocates for the development of tectonic cleavages before host rock lithification these are currently viewed as essentially local aberrations without regional significance. In this study we combine new field observations with strain analysis, element mapping and modelling to characterise Acadian (>50%) crustal shortening in a Devonian clastic sedimentary sequence from the Dingle Peninsula of south west Ireland. Fabrics in these rocks reflect significant levels of tectonic shortening are a product of grain translation, rigid body rotation and repacking of intra- and extra-formational clasts during deformation of an unconsolidated clastic sedimentary sequence. There is an absence of the expected domainal cleavage structure and intra-clast deformation expected with conventional cleavage formation. This study requires geologists to consider the possibility such a mechanism contributing to tectonic strain in a wide range of geological settings and to look again at field evidence that indicates early sediment mobility during deformation.

  17. Review of potential host rocks for radioactive waste disposal in the Piedmont Province of Georgia

    Energy Technology Data Exchange (ETDEWEB)

    Wenner, D.B.; Gillon, K.A.

    1980-10-01

    A literature study was conducted on the Piedmont province of Georgia to designate areas that may be favorable for field exploration for consideration of a repository for storage of radioactive waste. The criteria utilized in such a designation was based upon consideration of the rock unit having favorable geological, geotechnical, and geohydrological features. The most important are that the rock unit have: (1) satisfactory unit dimensions (> 100 km/sup 2/ outcrop area and at least 1500 meters (approx. 5000 feet) depth of a continuous rock type); and (2) acceptable geohydrological conditions. Among all rock types, it is concluded that the granites of the large post-metamorphic plutons and large, homogeneous orthogneissic units offer the most favorable geologic settings for exploration for siting a radioactive waste repository. Virtually all other rock types, including most metavolcanic and metasedimentary lithologies have unacceptable unit dimensions, generally unfavorable geohydrologic settings, and deleterious mechanical and physical geotechnical properties. After consideration of all major lithologies that comprise the Georgia Piedmont, the following units were deemed favorable: (1) the Elberton Pluton; (2) the Siloam Pluton; (3) the Sparta Pluton; (4) two unnamed plutons adjacent to the Snelson body of S.W. Georgia; (5) the Lithonia Gneiss; (6) basement orthogneisses and charnockites of the Pine Mountain Belt.

  18. The role of second phases for controlling microstructural evolution in polymineralic rocks: A review

    DEFF Research Database (Denmark)

    Herwegh, Marco; Linckens, Jolien; Ebert, Andreas

    2011-01-01

    We present a state-of-the-art review of the microstructural evolution in rocks under static and deformational conditions. First, the general concepts and processes are introduced using monomineralic aggregates. Then, they are expanded into the more complex context of polymineralic rocks with a do......We present a state-of-the-art review of the microstructural evolution in rocks under static and deformational conditions. First, the general concepts and processes are introduced using monomineralic aggregates. Then, they are expanded into the more complex context of polymineralic rocks...... with a dominant matrix phase. The first part of this contribution delivers information on sample strategies to quantify polymineralic microfabrics. Based on comparisons between microfabrics of monomineralic and polymineralic rocks, we use the common knowledge collected over the past decades for monomineralic......, and deformation mechanisms. We speculate on the effect of mineral reactions during the evolution of microstructures and rheology in polymineralic aggregates at different metamorphic conditions. At the end of the article, we demonstrate the great potential of grain-size evolution maps as microstructural tool...

  19. Review of potential host rocks for radioactive waste disposal in the Piedmont Province of Georgia

    International Nuclear Information System (INIS)

    Wenner, D.B.; Gillon, K.A.

    1980-10-01

    A literature study was conducted on the Piedmont province of Georgia to designate areas that may be favorable for field exploration for consideration of a repository for storage of radioactive waste. The criteria utilized in such a designation was based upon consideration of the rock unit having favorable geological, geotechnical, and geohydrological features. The most important are that the rock unit have: (1) satisfactory unit dimensions (> 100 km 2 outcrop area and at least 1500 meters (approx. 5000 feet) depth of a continuous rock type); and (2) acceptable geohydrological conditions. Among all rock types, it is concluded that the granites of the large post-metamorphic plutons and large, homogeneous orthogneissic units offer the most favorable geologic settings for exploration for siting a radioactive waste repository. Virtually all other rock types, including most metavolcanic and metasedimentary lithologies have unacceptable unit dimensions, generally unfavorable geohydrologic settings, and deleterious mechanical and physical geotechnical properties. After consideration of all major lithologies that comprise the Georgia Piedmont, the following units were deemed favorable: (1) the Elberton Pluton; (2) the Siloam Pluton; (3) the Sparta Pluton; (4) two unnamed plutons adjacent to the Snelson body of S.W. Georgia; (5) the Lithonia Gneiss; (6) basement orthogneisses and charnockites of the Pine Mountain Belt

  20. Stability and predictability in younger crystalline rock system: Japanese Islands case

    International Nuclear Information System (INIS)

    Yoshida, S.

    2009-01-01

    The Japanese Islands consist of igneous, sedimentary, and metamorphic rocks ranging in age from Paleozoic to Cenozoic. Among these, Carboniferous to Paleogene rocks occupy about 60% of the total area of the Japanese Islands. It should be noted that Quaternary volcanic rocks occupy only about 9% of the total area, although Quaternary volcanoes occur throughout the Japanese Islands. Long-term stability and predictability in the rock system are discussed in terms of volcanic activity, active faulting, and plate motion. Volcanic activity in the Japanese Islands is intimately related to subduction of the Pacific Plate and the Philippine Sea Plate. The volcanic front related to the Pacific and the Philippine Sea plates has been essentially fixed since about 6 Ma. The main active faults, which are distributed sporadically throughout the Japanese Islands, number about 150 and have been extensively investigated. The modes of the Pacific Plate and the Philippine Sea Plate have been essentially invariable since 10 Ma and 6 Ma, respectively. These lines of evidence imply that volcanism and tectonism in the Japanese Islands will scarcely change for hundreds of thousands of years into the future. It is clear that many places suitable for geological disposal will be present in this rock system. (author)

  1. Relationship between fluvial clastic sediment and source rock abundance in Rapti river basin of central Nepal Himalayas

    International Nuclear Information System (INIS)

    Tamrakar Naresh Kazi; Shresth Madhusudan Bhakta

    2008-01-01

    Many tributaries from carbonate sedimentary, metamorphic and igneous rocks of the Lesser Himalayan and clastic sedimentary rocks of the Sub-Himalayan Ranges carry gravelly sediments to the Rapti River. River bar sediments were analyzed for composition and texture to evaluate downstream changes in properties, and to establish relationship between proportion of clasts and the abundance of rock types in the source areas. Percent quartzite clast or granite clast increases whereas that of carbonate, schist or slate decreases along downstream. The largest grain size decreases downstream, whereas fatness index and sphericity tend to increase. Despite of little diminish in relative abundance of rock types in source areas along the river, the relative proportion of corresponding clast type shows rapid reduction (e.g. slate or phyllite or carbonate clasts) or rapid enhancement (e.g. granite clast). The relationships of quartzite clast and schist clasts with their corresponding source rocks are statistically significant suggesting that these clasts can provide clue to source rock abundance. About 85 to 94% of the gravel clasts represent rock types of the Lesser Himalayan Range suggesting that this range has been contributing enormous amount of sediments.

  2. Rock Pore Structure as Main Reason of Rock Deterioration

    Science.gov (United States)

    Ondrášik, Martin; Kopecký, Miloslav

    2014-03-01

    Crashed or dimensional rocks have been used as natural construction material, decoration stone or as material for artistic sculptures. Especially old historical towns not only in Slovakia have had experiences with use of stones for construction purposes for centuries. The whole buildings were made from dimensional stone, like sandstone, limestone or rhyolite. Pavements were made especially from basalt, andesite, rhyolite or granite. Also the most common modern construction material - concrete includes large amounts of crashed rock, especially limestone, dolostone and andesite. However, rock as any other material if exposed to exogenous processes starts to deteriorate. Especially mechanical weathering can be very intensive if rock with unsuitable rock properties is used. For long it had been believed that repeated freezing and thawing in relation to high absorption is the main reason of the rock deterioration. In Slovakia for many years the high water absorption was set as exclusion criterion for use of rocks and stones in building industry. Only after 1989 the absorption was accepted as merely informational rock property and not exclusion. The reason of the change was not the understanding of the relationship between the porosity and rock deterioration, but more or less good experiences with some high porous rocks used in constructions exposed to severe weather conditions and proving a lack of relationship between rock freeze-thaw resistivity and water absorption. Results of the recent worldwide research suggest that understanding a resistivity of rocks against deterioration is hidden not in the absorption but in the structure of rock pores in relation to thermodynamic properties of pore water and tensile strength of rocks and rock minerals. Also this article presents some results of research on rock deterioration and pore structure performed on 88 rock samples. The results divide the rocks tested into two groups - group N in which the pore water does not freeze

  3. Mineralogy and geochemistry of xenoliths in the Eocene volcanic rocks from southwest of Jandaq

    Directory of Open Access Journals (Sweden)

    Samineh Rajabi

    2013-04-01

    Full Text Available The Eocene volcanic rocks from the southwest of the Jandaq (Kuh-e-Godar-e-Siah, Central-East Iran micro-continent are andesitic basalt and andesite in composition. These rocks contain xenoliths with granulitic mineralogy. Mineral assemblage of these xenoliths is plagioclase + phlogopite + corundum + sillimanite + chlorite + phengite with granublastic, poiklioblastic and foliated textures in the pick metamorphic condition. Thermometry of phlogopite in these xenoliths suggests the average temperature 782oC. The characteristics of the xenoliths are consistent with the granolitic facies metamorphism of the Al-saturated Si-undersaturated crustal sediments at the lower crust condition. Melting of these granulites forms the magma which crystallized the S-type granitoids. Differentiation and crystallization of this magma causes the S-type granite formation. Therefore, the S-type granites in the study area are probably generated from melting of the granulites parts of which brought to the surface as xenoliths by Eocene magmatism in south of the Jandaq (Kuh-e-Godar-e-Siah. S-type granites in the study area are located along the Doruneh, Chupanan and Aeirakan faults in the Aeirakan area and Jandaq ophiolite. These granites are the source of uranium, thorium and uranium ore in southwest of the Aeirakan mountain.

  4. Integrating GIS-based geologic mapping, LiDAR-based lineament analysis and site specific rock slope data to delineate a zone of existing and potential rock slope instability located along the grandfather mountain window-Linville Falls shear zone contact, Southern Appalachian Mountains, Watauga County, North Carolina

    Science.gov (United States)

    Gillon, K.A.; Wooten, R.M.; Latham, R.L.; Witt, A.W.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.

    2009-01-01

    Landslide hazard maps of Watauga County identify >2200 landslides, model debris flow susceptibility, and evaluate a 14km x 0.5km zone of existing and potential rock slope instability (ZEPRSI) near the Town of Boone. The ZEPRSI encompasses west-northwest trending (WNWT) topographic ridges where 14 active/past-active rock/weathered rock slides occur mainly in rocks of the Grandfather Mountain Window (GMW). The north side of this ridgeline is the GMW / Linville Falls Fault (LFF) contact. Sheared rocks of the Linville Falls Shear Zone (LFSZ) occur along the ridge and locally in the valley north of the contact. The valley is underlain principally by layered granitic gneiss comprising the Linville Falls/Beech Mountain/Stone Mountain Thrust Sheet. The integration of ArcGIS??? - format digital geologic and lineament mapping on a 6m LiDAR (Light Detecting and Ranging) digital elevation model (DEM) base, and kinematic analyses of site specific rock slope data (e.g., presence and degree of ductile and brittle deformation fabrics, rock type, rock weathering state) indicate: WNWT lineaments are expressions of a regionally extensive zone of fractures and faults; and ZEPRSI rock slope failures concentrate along excavated, north-facing LFF/LFSZ slopes where brittle fabrics overprint older metamorphic foliations, and other fractures create side and back release surfaces. Copyright 2009 ARMA, American Rock Mechanics Association.

  5. Mineral chemistry and geothemobarometry of mantle harzburgites in the Eastern Metamorphic Complex of Khoy ophiolite -NW Iran

    Directory of Open Access Journals (Sweden)

    Morovvat Faridazad

    2017-02-01

    Full Text Available Introduction Khoy ophiolite at the global scale is in the middle part of the Alp-Himalaya orogenic belt and it is extended over 3900 Km2 which indicates remnant Neotethys oceanic lithosphere in the Mesozoic era (Kananian et al., 2010. In this paper, in addition to a review of previous investigations about Khoy ophiolite, we will try to determine the nature and kind of minerals, origin and partial melting rate as well as the equilibrium pressure and temperature of harzburgites from the Eastern Metamorphic Complex of Khoy ophiolite. Materials and methods Thin sections microscopy studies were carried out following field investigations. EPMA analysis was carried out with using a Superprobe JEOL, JXA 8200 Microprobe unit at the state of WDS and under condition of 15kv accelerating voltage, 10nA current beam, 1µm beam diameter and collection of natural and synthetic standards for calibration. Results The study area is located at the NW of Iran and north of the Khoy city in the west Azarbaijan province. This area is part of the ophiolitic complex of NW Iran and belongs to its Eastern Metamorphic Complex. This metamorphic zone has large tectonically segments of the metamorphic ophiolites which mainly include serpentinized peridotites with associated metagabbros. There are three types of peridotitic rocks in this area which are: Lherzolites, harzburgites and dunites. Lherzolites are composed of olivine (60-70%, orthopyroxene (10-30% and clinopyroxene (~10-20% with minor amounts (~2% of Cr-spinel mineral. Harzburgites are composed of olivine (70-80%, orthopyroxene (10-20% and clinopyroxene (~5% with minor amounts (~2% of Cr-spinel mineral. Dunites are composed of olivine (90-95%, orthopyroxene (5-10% with minor amounts (~1-2% of Cr-spinel mineral. Composition range of olivines is between Fo89.46 Fa10.37 to Fo89.86 Fa10.0 as well as NiO content range is 018-046 (wt %. The calculated Mg# of olivines is 0.90 and the composition of olivines in Fo-Fa diagram

  6. Death Valley turtlebacks: Mesozoic contractional structures overprinted by Cenozoic extension and metamorphism beneath syn-extensional plutons

    International Nuclear Information System (INIS)

    Pavlis, T L; Serpa, L; Miller, M

    2008-01-01

    -thrust belts. Our work to the east of Death Valley suggests these thrusts were part of a NW trending thrust system that overprinted an older NE trending fold-thrust system that tracks into the Death Valley region from Nevada. These NW trending thrusts probably underlie all of the southern Black Mountains (south of the turtlebacks) and we suggest that pre-extensional structural relief along these basement thrusts placed basement at shallow crustal levels throughout what is now the Black Mountains; a conclusion consistent with the absence of rocks younger than Cambrian beneath Tertiary unconformities throughout the southern Death Valley region. In Late Miocene time, a major detachment system formed and the turtlebacks represent a mid-crustal shear zone developed during that time period, but this system is older, and structurally beneath younger detachments systems that comprise the Amargosa fault system. During motion on the detachment, an ∼2km thick plutonic sheet was emplaced along the shear zone forming the Miocene plutonic assemblages of the Black Mountains, and produced upper amphibolite facies metamorphic assemblages along the floor of the pluton in what are now the Copper Canyon and Mormon Point turtlebacks, but the Badwater Turtleback escaped this metamorphism due to a different structural position. Motion continued along the floor of the pluton but syn-extensional folding produced structural relief along folds with axes parallel to the extension direction. Ultimately a new detachment system cut obliquely across the older extensional system, removing the roof of the pluton, but cutting down to its floor in the turtlebacks. This fault system formed a complex detachment system updip in the famous 'Amargosa Chaos', and removing the entire cover sequence from the Black Mountains (∼10-12km of crustal section). The turtlebacks are therefore a composite structure in which extension contemporaneous with folding, presumably as a result of distributed transcurrent motion

  7. Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    HARTMANN LÉO A.

    2003-01-01

    Full Text Available Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite or compositional (e.g. mantle spinel remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3 and narrow 1-3 m-wide shear zones (M4 containing asbestos.

  8. Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

    Science.gov (United States)

    Zheng, Nan; Ahrenkiel, S. Phillip

    2017-07-01

    Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and lattice images.

  9. Relaxation dynamics and residual strain in metamorphic AlSb on GaAs

    International Nuclear Information System (INIS)

    Ripalda, J. M.; Rivera, A.; Alen, B.; Gonzalez, Y.; Gonzalez, L.; Briones, F.; Sanchez, A. M.; Taboada, A. G.; Rotter, T. J.; Balakrishnan, G.

    2012-01-01

    We have observed the evolution of the accumulated stress during heteroepitaxial growth of highly lattice mismatched AlSb on GaAs by measuring the deformation of the substrate as a function of time. High resolution transmission electron microscopy images show almost all of the plastic relaxation is accommodated by an array of 90 deg. misfit dislocations at the interface. The in-plane lattice parameter of the resulting metamorphic AlSb is slightly smaller (0.3%) than the bulk value and perfectly matches the lattice parameter of bulk GaSb. It is, therefore, possible to grow nearly stress-free GaSb on GaAs using a metamorphic AlSb buffer layer.

  10. Relaxation dynamics and residual strain in metamorphic AlSb on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ripalda, J. M.; Rivera, A.; Alen, B.; Gonzalez, Y.; Gonzalez, L.; Briones, F. [IMM-Instituto de Microelectronica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, E-28760 Tres Cantos, Madrid (Spain); Sanchez, A. M. [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Taboada, A. G. [Laboratory for Solid State Physics, ETH Zurich, Schafmattstr. 16, CH-8093 Zurich (Switzerland); Rotter, T. J.; Balakrishnan, G. [Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

    2012-01-02

    We have observed the evolution of the accumulated stress during heteroepitaxial growth of highly lattice mismatched AlSb on GaAs by measuring the deformation of the substrate as a function of time. High resolution transmission electron microscopy images show almost all of the plastic relaxation is accommodated by an array of 90 deg. misfit dislocations at the interface. The in-plane lattice parameter of the resulting metamorphic AlSb is slightly smaller (0.3%) than the bulk value and perfectly matches the lattice parameter of bulk GaSb. It is, therefore, possible to grow nearly stress-free GaSb on GaAs using a metamorphic AlSb buffer layer.

  11. From stones to rocks

    Science.gov (United States)

    Mortier, Marie-Astrid; Jean-Leroux, Kathleen; Cirio, Raymond

    2013-04-01

    With the Aquila earthquake in 2009, earthquake prediction is more and more necessary nowadays, and people are waiting for even more accurate data. Earthquake accuracy has increased in recent times mainly thanks to the understanding of how oceanic expansion works and significant development of numerical seismic prediction models. Despite the improvements, the location and the magnitude can't be as accurate as citizen and authorities would like. The basis of anticipating earthquakes requires the understanding of: - The composition of the earth, - The structure of the earth, - The relations and movements between the different parts of the surface of the earth. In order to answer these questions, the Alps are an interesting field for students. This study combines natural curiosity about understanding the predictable part of natural hazard in geology and scientific skills on site: observing and drawing landscape, choosing and reading a representative core drilling, replacing the facts chronologically and considering the age, the length of time and the strength needed. This experience requires students to have an approach of time and space radically different than the one they can consider in a classroom. It also limits their imagination, in a positive way, because they realize that prediction is based on real data and some of former theories have become present paradigms thanks to geologists. On each location the analyzed data include landscape, core drilling and the relation established between them by students. The data is used by the students to understand the meaning, so that the history of the formation of the rocks tells by the rocks can be explained. Until this year, the CBGA's perspective regarding the study of the Alps ground allowed students to build the story of the creation and disappearance of the ocean, which was a concept required by French educational authorities. But not long ago, the authorities changed their scientific expectations. To meet the

  12. Design and accuracy analysis of a metamorphic CNC flame cutting machine for ship manufacturing

    Science.gov (United States)

    Hu, Shenghai; Zhang, Manhui; Zhang, Baoping; Chen, Xi; Yu, Wei

    2016-09-01

    The current research of processing large size fabrication holes on complex spatial curved surface mainly focuses on the CNC flame cutting machines design for ship hull of ship manufacturing. However, the existing machines cannot meet the continuous cutting requirements with variable pass conditions through their fixed configuration, and cannot realize high-precision processing as the accuracy theory is not studied adequately. This paper deals with structure design and accuracy prediction technology of novel machine tools for solving the problem of continuous and high-precision cutting. The needed variable trajectory and variable pose kinematic characteristics of non-contact cutting tool are figured out and a metamorphic CNC flame cutting machine designed through metamorphic principle is presented. To analyze kinematic accuracy of the machine, models of joint clearances, manufacturing tolerances and errors in the input variables and error models considering the combined effects are derived based on screw theory after establishing ideal kinematic models. Numerical simulations, processing experiment and trajectory tracking experiment are conducted relative to an eccentric hole with bevels on cylindrical surface respectively. The results of cutting pass contour and kinematic error interval which the position error is from-0.975 mm to +0.628 mm and orientation error is from-0.01 rad to +0.01 rad indicate that the developed machine can complete cutting process continuously and effectively, and the established kinematic error models are effective although the interval is within a `large' range. It also shows the matching property between metamorphic principle and variable working tasks, and the mapping correlation between original designing parameters and kinematic errors of machines. This research develops a metamorphic CNC flame cutting machine and establishes kinematic error models for accuracy analysis of machine tools.

  13. Enhanced Contacts for Inverted Metamorphic Multi-Junction Solar Cells Using Carbon Nanotube Metal Matrix Composites

    Science.gov (United States)

    2018-01-18

    AFRL-RV-PS- AFRL-RV-PS- TR-2017-0125 TR-2017-0125 ENHANCED CONTACTS FOR INVERTED METAMORPHIC MULTI-JUNCTION SOLAR CELLS USING CARBON NANOTUBE METAL...Rochester, NY 14604-5603 18 Jan 2018 Final Report APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED. AIR FORCE RESEARCH LABORATORY Space...ACCORDANCE WITH ASSIGNED DISTRIBUTION STATEMENT. DAVID WILT PAUL HAUSGEN, Ph.D. Program Manager Technical Advisor, Spacecraft Component Technology

  14. Study on microwave induced pyrolysis of low metamorphic coal and liquefaction residue

    Science.gov (United States)

    Li, Zhao; Wu, Kunyao; Cao, Jing; Wang, Yongfeng

    2017-05-01

    This paper mainly studies pyrolysis characteristic in the different heating of microwave of low metamorphic coal and Liquefaction Residue, which was focused on the effects of particle sizes, pyrolysis reaction time, and microwave powers. The product are analyzed by Gas chromatography- mass spectrometry (GC-MS), etc. The results showed that when heating time is 40 min and 800 W, yield of tar is about 15.51%.

  15. Complicated secondary textures in zircon record evolution of the host granitic rocks: Studies from Western Tauern Window and Ötztal-Stubai Crystalline Complex (Eastern Alps, Western Austria)

    Science.gov (United States)

    Kovaleva, Elizaveta; Harlov, Daniel; Klötzli, Urs

    2017-07-01

    Samples of metamorphosed and deformed granitic rocks were collected from two Alpine complexes with well-constrained metamorphic history: Western Tauern Window and Ötztal-Stubai Crystalline Complex. Zircon grains from these samples were investigated in situ by a combination of scanning electron microscope techniques, cathodoluminescence (CL) imaging and Raman spectroscopy. The aims were: to describe and interpret complicated secondary textures and microstructures in zircon; based on cross-cutting relationships between secondary microstructures, reconstruct the sequence of processes, affecting zircon crystals; link the evolution of zircon with the history of the host rocks. The results indicate that zircon in the sampled granitic rocks forms growth twins and multi-grain aggregates, which are unusual for this mineral. Moreover, various secondary textures have been found in the sampled zircon, often cross-cutting each other in a single crystal. These include: distorted oscillatory CL zoning with inner zones forming inward-penetrating, CL-bright embayments, which are the evidence of dry recrystallization via annealing/lattice recovery; CL mosaicism with no preservation of growth zoning, but abundant nano- and micro-scale pores and mineral inclusions, which are the evidence of recrystallization by coupled dissolution-reprecipitation and/or leaching; embayed zircon boundaries filled with apatite, monazite, epidote and mylonitic matrix, indicating mineral-fluid reactions resulting in zircon dissolution and fragmentation; overgrowth CL-dark rims, which contain nano-pores and point to transport and precipitation of dissolved zircon matter. We conclude that zircon in our meta-granites is sensitive to metamorphism/deformation events, and was reactive with metamorphic fluids. Additionally, we have found evidence of crystal-plastic deformation in the form of low angle boundaries and bent grain tips, which is a result of shearing and ductile deformation of the host rock. We

  16. Effects of the herbicide triclopyr on metamorphic northern red-legged frogs.

    Science.gov (United States)

    Yahnke, Amy E; Grue, Christian E; Hayes, Marc P; Pearman-Gillman, Schuyler

    2017-09-01

    Aquatic herbicides are used to manage invasive emergent plants in and around wetlands. Metamorphic frogs that emerge during the aquatic weed management season may be at risk of herbicide exposure. Metamorphic northern red-legged frogs (Rana aurora) were exposed to a triclopyr tank mix labeled for control of broadleaf emergent aquatic weeds such as invasive purple loosestrife (Lythrum salicaria). The tank mix consisted of Renovate® 3 (triclopyr triethylamine salt 44.4%), the modified vegetable oil surfactant Competitor®, and the marker dye Hi-Light ® . Metamorphs were exposed to the tank mix and a clean-water control for 96 h, and then reared in clean water for 60 d. Exposure to the tank mix resulted in no treatment-related mortalities, no effects on behavior immediately post exposure, and no effects on body or liver condition indices. Exposure to the tank mix resulted in lethargy during exposure and a 1-d delay in completion of metamorphosis. Deformities present in the rearing population confounded results for some endpoints. Observed effects were minimal, especially compared with the potential for ecological impacts from unmanaged invasive plants. Environ Toxicol Chem 2017;36:2316-2326. © 2017 SETAC. © 2017 SETAC.

  17. Formation Mechanism of Surface Metamorphic Layer on Turning End Face of GH4169 Superalloy

    Directory of Open Access Journals (Sweden)

    YAO Changfeng

    2017-12-01

    Full Text Available Turning experiments and Deform-3D finite element methods were used to study the formation mechanism of surface metamorphic layer on turning GH4169 processed. The investigations were carried out by analyzing the changing of cutting force, the temperature and strain field, the residual stress, micro-hardness, microstructure, as well as the distribution of the above all along the direction of the depth under various process parameters. The results show that the surface metamorphic layer is formed due to the thermal-mechanical coupled effects on the microstructure of the material in the machining process. The cutting force, heat and strain of surface material are increased with the increase of machining intensity. Besides the higher strength of machining, the greater changes of plastic deformation, metallographic and grain deformation are acquired. In the range of processing parameters, the temperature layer is 130-200 μm,the strain layer is 100-220 μm, the residual stress layer is 80-110 μm, the depth of hardening layer is 50-80 μm, and the depth of surface metamorphic layer is 2.5-5μm.

  18. EVOLUTIONARY CONCEPTION OF SNOW METAMORPHISM BASED ON CRYSTAL-MORPHOLOGY AND THEORY OF SYMMETRY

    Directory of Open Access Journals (Sweden)

    E. G. Kolomyts

    2012-01-01

    Full Text Available The paper presents a novel approach to the study of development of microstructures in snowpack based on the crystal-morphology and on the fundamental laws of natural symmetry. An empirical deterministic model describing the sublimation-metamorphic cycle in seasonal snow cover and the polymorphic variants of this cycle is suggested. Staging in the formation of crystal shapes and self-development of snow microstructure in snow layers is revealed. The crystal shapes are the result of successive process of superposition of ice crystal-chemical symmetry and dissymmetry of the soil – snow cover – atmosphere system, according to the known P. Curie principle. Morphological classification of snow crystals in seasonal snow cover is developed on the base of evolutionary model. Evolution of snow microstructure is conditioned by a marked degree by probabilistic conformity to natural laws, manifesting itself in the processes of auto-regulation of metamorphism. These processes include two types of regulation: the self-regulation of snow layers, on the one hand, and the regulation related to external conditions – under the influence of atmospheric perturbations, on the other hand. The accounting the processes of auto-regulation of snow metamorphism for allows development of new methods in short- and long-term avalanche forecast.

  19. Probabilistic approach to rock fall hazard assessment: potential of historical data analysis

    Directory of Open Access Journals (Sweden)

    C. Dussauge-Peisser

    2002-01-01

    Full Text Available We study the rock fall volume distribution for three rock fall inventories and we fit the observed data by a power-law distribution, which has recently been proposed to describe landslide and rock fall volume distributions, and is also observed for many other natural phenomena, such as volcanic eruptions or earthquakes. We use these statistical distributions of past events to estimate rock fall occurrence rates on the studied areas. It is an alternative to deterministic approaches, which have not proved successful in predicting individual rock falls. The first one concerns calcareous cliffs around Grenoble, French Alps, from 1935 to 1995. The second data set is gathered during the 1912–1992 time window in Yosemite Valley, USA, in granite cliffs. The third one covers the 1954–1976 period in the Arly gorges, French Alps, with metamorphic and sedimentary rocks. For the three data sets, we find a good agreement between the observed volume distributions and a fit by a power-law distribution for volumes larger than 50 m3 , or 20 m3 for the Arly gorges. We obtain similar values of the b exponent close to 0.45 for the 3 data sets. In agreement with previous studies, this suggests, that the b value is not dependant on the geological settings. Regarding the rate of rock fall activity, determined as the number of rock fall events with volume larger than 1 m3 per year, we find a large variability from one site to the other. The rock fall activity, as part of a local erosion rate, is thus spatially dependent. We discuss the implications of these observations for the rock fall hazard evaluation. First, assuming that the volume distributions are temporally stable, a complete rock fall inventory allows for the prediction of recurrence rates for future events of a given volume in the range of the observed historical data. Second, assuming that the observed volume distribution follows a power-law distribution without cutoff at small or large scales, we can

  20. Probabilistic approach to rock fall hazard assessment: potential of historical data analysis

    Science.gov (United States)

    Dussauge-Peisser, C.; Helmstetter, A.; Grasso, J.-R.; Hantz, D.; Desvarreux, P.; Jeannin, M.; Giraud, A.

    We study the rock fall volume distribution for three rock fall inventories and we fit the observed data by a power-law distribution, which has recently been proposed to describe landslide and rock fall volume distributions, and is also observed for many other natural phenomena, such as volcanic eruptions or earthquakes. We use these statistical distributions of past events to estimate rock fall occurrence rates on the studied areas. It is an alternative to deterministic approaches, which have not proved successful in predicting individual rock falls. The first one concerns calcareous cliffs around Grenoble, French Alps, from 1935 to 1995. The second data set is gathered during the 1912-1992 time window in Yosemite Valley, USA, in granite cliffs. The third one covers the 1954-1976 period in the Arly gorges, French Alps, with metamorphic and sedimentary rocks. For the three data sets, we find a good agreement between the observed volume distributions and a fit by a power-law distribution for volumes larger than 50 m3 , or 20 m3 for the Arly gorges. We obtain similar values of the b exponent close to 0.45 for the 3 data sets. In agreement with previous studies, this suggests, that the b value is not dependant on the geological settings. Regarding the rate of rock fall activity, determined as the number of rock fall events with volume larger than 1 m3 per year, we find a large variability from one site to the other. The rock fall activity, as part of a local erosion rate, is thus spatially dependent. We discuss the implications of these observations for the rock fall hazard evaluation. First, assuming that the volume distributions are temporally stable, a complete rock fall inventory allows for the prediction of recurrence rates for future events of a given volume in the range of the observed historical data. Second, assuming that the observed volume distribution follows a power-law distribution without cutoff at small or large scales, we can extrapolate these

  1. A smart rock

    Science.gov (United States)

    Pressel, Phil

    2014-12-01

    This project was to design and build a protective weapon for a group of associations that believed in aliens and UFO's. They collected enough contributions from societies and individuals to be able to sponsor and totally fund the design, fabrication and testing of this equipment. The location of this facility is classified. It also eventually was redesigned by the Quartus Engineering Company for use at a major amusement park as a "shoot at targets facility." The challenge of this project was to design a "smart rock," namely an infrared bullet (the size of a gallon can of paint) that could be shot from the ground to intercept a UFO or any incoming suspicious item heading towards the earth. Some of the challenges to design this weapon were to feed cryogenic helium at 5 degrees Kelvin from an inair environment through a unique rotary coupling and air-vacuum seal while spinning the bullet at 1500 rpm and maintain its dynamic stability (wobble) about its spin axis to less than 10 micro-radians (2 arc seconds) while it operated in a vacuum. Precision optics monitored the dynamic motion of the "smart rock."

  2. Rock Properties Model

    International Nuclear Information System (INIS)

    Lum, C.

    2004-01-01

    The purpose of this model report is to document the Rock Properties Model version 3.1 with regard to input data, model methods, assumptions, uncertainties and limitations of model results, and qualification status of the model. The report also documents the differences between the current and previous versions and validation of the model. The rock properties model provides mean matrix and lithophysae porosity, and the cross-correlated mean bulk density as direct input to the ''Saturated Zone Flow and Transport Model Abstraction'', MDL-NBS-HS-000021, REV 02 (BSC 2004 [DIRS 170042]). The constraints, caveats, and limitations associated with this model are discussed in Section 6.6 and 8.2. Model validation accomplished by corroboration with data not cited as direct input is discussed in Section 7. The revision of this model report was performed as part of activities being conducted under the ''Technical Work Plan for: The Integrated Site Model, Revision 05'' (BSC 2004 [DIRS 169635]). The purpose of this revision is to bring the report up to current procedural requirements and address the Regulatory Integration Team evaluation comments. The work plan describes the scope, objectives, tasks, methodology, and procedures for this process

  3. Rock critics as 'Mouldy Modernists'

    Directory of Open Access Journals (Sweden)

    Becky Shepherd

    2011-09-01

    Full Text Available Contemporary rock criticism appears to be firmly tied to the past. The specialist music press valorise rock music of the 1960s and 1970s, and new emerging artists are championed for their ‘retro’ sounding music by journalists who compare the sound of these new artists with those included in the established ‘canon’ of rock music. This article examines the narrative tropes of authenticity and nostalgia that frame the retrospective focus of this contemporary rock writing, and most significantly, the maintenance of the rock canon within contemporary popular culture. The article concludes by suggesting that while contemporary rock criticism is predominately characterised by nostalgia, this nostalgia is not simply a passive romanticism of the past. Rather, this nostalgia fuels a process of active recontextualisation within contemporary popular culture.

  4. The role of an evolving porosity in fluid-rock interaction - a synthesis of insights gained in six years of in-situ 4D microtomography experiments

    Science.gov (United States)

    Fusseis, Florian

    2017-04-01

    Effective fluid rock interaction relies on permeable pore space for fluid to move in. In dynamic (tectono-)metamorphic environments, pore space will be transient and subject to continuous modification. As a consequence, transport properties of rocks evolve throughout their metamorphic history, which complicates the interpretation of fossilised traces of fluid-rock interaction in natural rock samples. Thankfully, a large body of processes involved in fluid-rock interaction occur on time scales accessible in experiments, and over the past decades significant insights were gained in many now classical laboratory investigations. Until recently though, fluid-rock interaction could not be observed directly, and processes and rates were inferred through indirect measurements or post-mortem analyses. Studies that utilise x-rays or neutrons to continuously image fluid-mediated processes inside experimental vessels allow, on the one hand, to quantify their rates but also to assess and characterise transient porosity on the grain scale. In this presentation, I will synthesize the findings from several collaborative experimental studies that documented and quantified fluid-rock interaction in 4-dimensional x-ray microtomographic datasets. Most of these experiments were conducted in bespoke x-ray transparent vessels built in Edinburgh and all of them involved a dynamically evolving porosity as a key element of the studied processes. The latter are 1) the dehydration of gypsum single crystals and alabaster, 2) the carbonation of olivine aggregates, 3) pressure solution in polycrystalline salt, and 4) the dolomitisation of various carbonates. The microtomographic time series data enabled the direct observation of the above processes on the grain scale and were used to quantify their advance using sophisticated image analytical workflows. Each of the studies characterised porosity formation or alteration by a particular mechanism relevant to geological scenarios and it became

  5. Geochemistry, petrography, and zircon U-Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon-Tanana terrane

    Science.gov (United States)

    Dusel-Bacon, Cynthia; Day, Warren C.; Aleinikoff, John N.

    2013-01-01

    We report the results of new mapping, whole-rock major, minor, and trace-element geochemistry, and petrography for metaigneous rocks from the Mount Veta area in the westernmost part of the allochthonous Yukon–Tanana terrane (YTT) in east-central Alaska. These rocks include tonalitic mylonite gneiss and mafic metaigneous rocks from the Chicken metamorphic complex and the Nasina and Fortymile River assemblages. Whole-rock trace-element data from the tonalitic gneiss, whose igneous protolith was dated by SHRIMP U–Pb zircon geochronology at 332.6 ± 5.6 Ma, indicate derivation from tholeiitic arc basalt. Whole-rock analyses of the mafic rocks suggest that greenschist-facies rocks from the Chicken metamorphic complex, a mafic metavolcanic rock from the Nasina assemblage, and an amphibolite from the Fortymile River assemblage formed as island-arc tholeiite in a back-arc setting; another Nasina assemblage greenschist has MORB geochemical characteristics, and another mafic metaigneous rock from the Fortymile River assemblage has geochemical characteristics of calc-alkaline basalt. Our geochemical results imply derivation in an arc and back-arc spreading region within the allochthonous YTT crustal fragment, as previously proposed for correlative units in other parts of the terrane. We also describe the petrography and geochemistry of a newly discovered tectonic lens of Alpine-type metaharzburgite. The metaharzburgite is interpreted to be a sliver of lithospheric mantle from beneath the Seventymile ocean basin or from sub-continental mantle lithosphere of the allochthonous YTT or the western margin of Laurentia that was tectonically emplaced within crustal rocks during closure of the Seventymile ocean basin and subsequently displaced and fragmented by faults.

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

    Directory of Open Access Journals (Sweden)

    Mikko Nironen

    2011-08-01

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

  7. Rock.XML - Towards a library of rock physics models

    Science.gov (United States)

    Jensen, Erling Hugo; Hauge, Ragnar; Ulvmoen, Marit; Johansen, Tor Arne; Drottning, Åsmund

    2016-08-01

    Rock physics modelling provides tools for correlating physical properties of rocks and their constituents to the geophysical observations we measure on a larger scale. Many different theoretical and empirical models exist, to cover the range of different types of rocks. However, upon reviewing these, we see that they are all built around a few main concepts. Based on this observation, we propose a format for digitally storing the specifications for rock physics models which we have named Rock.XML. It does not only contain data about the various constituents, but also the theories and how they are used to combine these building blocks to make a representative model for a particular rock. The format is based on the Extensible Markup Language XML, making it flexible enough to handle complex models as well as scalable towards extending it with new theories and models. This technology has great advantages as far as documenting and exchanging models in an unambiguous way between people and between software. Rock.XML can become a platform for creating a library of rock physics models; making them more accessible to everyone.

  8. Analysis of magnetotelluric profile data from the Ruby Mountains metamorphic core complex and southern Carlin Trend region, Nevada

    Science.gov (United States)

    Wannamaker, Philip E.; Doerner, William M.; Stodt, John A.; Sodergen, Timothy L.; Rodriguez, Brian D.

    2002-01-01

    We have collected about 150 magnetotelluric (MT) soundings in northeastern Nevada in the region of the Ruby Mountains metamorphic core complex uplift and southern Carlin mineral trend, in an effort to illuminate controls on core complex evolution and deposition of world-class gold deposits. The region has experienced a broad range of tectonic events including several periods of compressional and extensional deformation, which have contributed to the total expression of electrical resistivity. Most of the soundings are in three east-west profiles across increasing degrees of core uplift to the north (Bald Mountain, Harrison Pass and Secret Pass latitudes). Two shorter lines cross a prominent east-west structure to the north of the northern profile. MT impedance tensor and vertical magnetic field rotations imply a N-NNE average regional geoelectric strike, similar to surface geologic trends. Model resistivity cross sections were derived using a 2-D inversion algorithm, which damps departures of model parameters from an a priori structure, emphasizing the transverse magnetic (TM) mode and vertical magnetic field data. Geological interpretation of the resistivity combines previous seismic, potential field and isotope models, structural and petrological models for regional compression and extension, and detailed structural/stratigraphic interpretations incorporating drilling for petroleum and mineral exploration. To first order, the resistivity structure is one of a moderately conductive, Phanerozoic sedimentary section fundamentally disrupted by intrusion and uplift of resistive crystalline rocks. Late Devonian and early Mississippian shales of the Pilot and Chainman Formations together form an important conductive marker sequence in the stratigraphy and show pronounced increases in conductance (conductivity-thickness product) from east to west. These increases in conductance are attributed to graphitization caused by Elko-Sevier era compressional shear deformation and

  9. Rock and soil rheology

    International Nuclear Information System (INIS)

    Cristescu, N.; Ene, H.I.

    1988-01-01

    The aim of the Euromech Colloquium 196 devoted to Rock and Soil Rheology is to review some of the main results obtained in the last years in this field of research and also to formulate some of the major not yet solved problems which are now under consideration. Exchange of opinions and scientific discussions are quite helpful mainly in those areas where some approaches are controversial and the progress made is quite fast. That is especially true for the rheology of geomaterials, domain of great interest for mining and petroleum engineers, engineering geology, seismology, geophysics, civil engineering, nuclear and industrial waste storage, geothermal energy storage, caverns for sports, culture, telecommunications, storage of goods and foodstuffs (cold, hot and refrigerated storages), underground oil and natural gas reservoirs etc. Some of the last obtained results are mentioned in the present volume. (orig./HP)

  10. Rock the Globe

    CERN Multimedia

    Laëtitia Pedroso

    2010-01-01

    Created in 2005, the Swiss rock band "Wind of Change" is now candidate for the Eurovision Song Contest 2011 with a new song " Night & Light " with the music video filmed at CERN.   With over 20 gigs under their belt and two albums already released, the five members of the band (Alex Büchi, vocals; Arthur Spierer, drums; David Gantner, bass; Romain Mage and Yannick Gaudy, guitar) continue to excite audiences. For their latest composition "Night & Light", the group filmed their music video in the Globe of Science and Innovation. Winning the Eurovision contest would be a springboard in their artistic career for these young musicians. The selection results will be available December 11, 2010.      

  11. Petrogenesis and Tectonic Implications of Paleoproterozoic Metapelitic Rocks in the Archean Kongling Complex from the Northern Yangtze Craton, South China

    Science.gov (United States)

    Li, Y.; Zheng, J.; Wang, W.; Xiong, Q.

    2015-12-01

    The Archean Kongling Complex in the northern Yangtze Craton is an ideal target to investigate the Precambrian accretion and evolution of continental crust in South China. This study aims to unravel the crustal evolution and tectonic setting of the Yangtze Craton during the Paleoproterozoic time, using integrated studies of petrography, zircon U-Pb and Hf isotopes and whole-rock geochemistry of Paleoproterozoic metapelitic rocks in the Kongling Complex. These rocks contain garnet, sillimanite, biotite, plagioclase, minor graphite and ilmenite. Zircons from the samples show nebulous sector-zoning and rim-core structure, suggesting both metamorphic origin and detrital origin with metamorphic overprints. The metamorphic zircons and metamorphic overprints have concordant 207Pb/206Pb age at ~2.0 Ga, while detrital grains yield three distinct concordant-age populations of >2.5 Ga, 2.4-2.2 Ga and 2.2-2.1 Ga. The age patterns indicate that the depositional age of the metasedimentary rocks was 2.1-2.0 Ga. Those 2.2-2.1 Ga detrital zircons with variable ɛHf(t) values (-7.28 to 2.97) suggest the addition of juvenile materials from depleted mantle to the crust during 2.2-2.1 Ga. The 2.4-2.2 Ga zircons have Hf model ages (TDM2) of ~2.6-3.5 Ga and >2.5 Ga zircons have TDM2 ages varying from 2.9 Ga to 3.3 Ga. The new data suggest that the Kongling Complex was originally a Paleoarchean (old up to 3.5 Ga) continental nucleus, which experienced multiple episodes of growth and reworking events at 3.3-3.2 Ga, 2.9 Ga, 2.7-2.6 Ga, 2.4-2.2 Ga and 2.2-2.1 Ga. In combination with available data, the new results in this study suggest a continent-arc-continent evolution model to explain the tectonic evolution of the Yangtze Craton during the Paleoproterozoic time: the western margin of Yangtze Craton was originally an individual continent, which underwent a reworking event during 2.4-2.2 Ga and a crust growth event caused by continent-arc collision during 2.2-2.1 Ga; it subsequently collided

  12. Geochemistry and petrogenesis of basaltic rocks from the Develidağ volcanic complex, Central Anatolia, Turkey

    Science.gov (United States)

    Kürkcüoglu, Biltan

    2010-01-01

    The Develidağ volcanic zone (DVZ) is a part of the Middle Miocene-Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia. The DVZ is located at the eastern side of the Plio-Quaternary Sultansazlığı pull-apart basin, that opened along the Ecemiş left-lateral strike-slip fault. Towards the south, the volcanic rocks of the DVZ overlie the Paleozoic metamorphic rocks of the Taurus range. Regional stratigraphic studies indicate that volcanic rocks of the DVZ crop out in a ˜N-S trending rectangular-shaped exposure in the middle of which Middle Miocene andesitic rocks are found surrounded by Upper Miocene basaltic rocks. The purpose of this paper is to present basic geochemical data for the DVZ rocks and discuss possible processes of magma generation. The Develidağ basalts are characterized by low LILE (Rb, K, Ba, Th) and high HFSE (Nb,Zr,Hf,Y) contents, whereas the andesites generally have high LILE and HFSE values except for Nb and Zr. Variable abundances of Pb (3.11-12.09 ppm) and U (0.36-2.64 ppm) are associated with high Ba content within the rock suites. Although low Nb/La (0.6-0.7) and relatively high Ba/Nb ratios indicate crustal involvement for the basalts, high Zr/Ba (0.5), Zr/Hf (42-47) and Th/U (3.13-4.69) values imply contributions from an asthenospheric source component. Furthermore, the high Zr/Hf values (>36) are the diagnostic feature of metasomatized mantle (Dupuy et al., 1992; Rudnick et al., 1993). Moreover, multi-element patterns show that Develidağ basalts have similar trace element signatures to those of the US Cascades tholeiites. The ratios of Zr/Hf, Zr/Ba, Nb/Th and Sr/Ce indicate that basaltic rocks are derived from a MORB-like mantle, and calculated melting model reflects generation from a spinel peridotite source (3-4% melting), but the combined effects of melting and assimilation and fractional crystallization (AFC) processes seem to be partially responsible for the relatively evolved rocks. Typical tholeiitic

  13. Metamorphic brines and no surficial fluids trapped in the detachment footwall of a Metamorphic Core Complex (Nevado-Filábride units, Betics, Spain)

    Science.gov (United States)

    Dyja-Person, Vanessa; Tarantola, Alexandre; Richard, Antonin; Hibsch, Christian; Siebenaller, Luc; Boiron, Marie-Christine; Cathelineau, Michel; Boulvais, Philippe

    2018-03-01

    The ductile-brittle transition zone in extensional regimes can play the role of a hydrogeological barrier. Quartz veins developed within an orthogneiss body located in the detachment footwall of a Metamorphic Core Complex (MCC) in the Nevado-Filábride units (Betics, Spain). The detachment footwall is composed mainly of gneisses, schists and metacarbonates from the Bédar-Macael sub-unit. Schist and metacarbonate bodies show evidence of ductile deformation at the time the gneiss was already undergoing brittle deformation and vein opening during exhumation. The vein system provides the opportunity to investigate the origin, composition and PVTX conditions of the fluids that circulated in the detachment footwall while the footwall units were crossing the ductile-brittle transition. The analysis of fluid inclusions reveals the presence of a single type of fluid: 30-40 mass% NaCl > KCl > CaCl2 > MgCl2 brines, with trace amounts of CO2 and N2 and tens to thousands of ppm of metals such as Fe, Sr, Li, Zn, Ba, Pb and Cu. δDfluid values between -39.8 and -16.7‰ and δ18Ofluid values between 4.4 and 11.7 ± 0.5‰ show that the brines have undergone protracted interaction with the host orthogneissic body. Coupled salinity and Cl/Br ratios (200 to 4400) indicate that the brines originate from dissolution of Triassic metaevaporites by metamorphic fluids variably enriched in Br by interaction with graphitic schists. This study highlights the absence of any record of surficial fluids within the veins, despite the brittle deformation conditions prevailing in this orthogneiss body. The fact that fluids from the detachment footwall were isolated from surficial fluid reservoirs may result from the presence of overlying schists and metacarbonates that continued to be affected by ductile deformation during vein formation in the gneiss, preventing downward circulation of surface-derived fluids.

  14. Rock Art in Kurdistan Iran

    Directory of Open Access Journals (Sweden)

    Jamal Lahafian

    2013-12-01

    Full Text Available Kurdistan, with great potential and prehistoric resources, has numerous petroglyphs in different areas of the province. During the last 14 years of extensive field study, more than 30 sites of rock art have been identified and introduced by the author. In this article, we summarize these rock art areas in Iranian Kurdistan.

  15. Beach rock from Goa Coast

    Digital Repository Service at National Institute of Oceanography (India)

    Setty, M.G.A.P.; Wagle, B.G.

    Beach rock is a common rock type in many parts of the southern hemisphere and also some areas north of the equator. Its distribution particularly in the Indian Ocean islands and atolls and coasts of India is reviewed. The mineralogic and faunal...

  16. Origin and provenance of basement metasedimentary rocks from the Xolapa Complex: New constraints on the Chortis-southern Mexico connection

    Science.gov (United States)

    Talavera-Mendoza, Oscar; Ruiz, Joaquín; Corona-Chavez, Pedro; Gehrels, George E.; Sarmiento-Villagrana, Alicia; García-Díaz, José Luis; Salgado-Souto, Sergio Adrian

    2013-05-01

    The U-Pb (LA-MC-ICPMS) geochronology of Xolapa metasedimentary rocks from Tierra Colorada, Guerrero to Puerto Ángel, Oaxaca in southern Mexico reveals that their protoliths accumulated in two distinctive cycles of sedimentation, one of Early Jurassic age and another of Late Cretaceous age. These ages are younger than thought and demonstrate that Xolapa metasedimentary rocks are not rocks from the Acatlán or Oaxacan complexes or their Paleozoic sedimentary covers as claimed. However, detrital zircon ages indicate that Xolapa sediments received contemporaneous detritus most likely from these assemblages suggesting a probably (para-)autochthonous origin for the Xolapa terrane. Xolapa rocks record two major tectonothermal events of 64-59 Ma and ~34 Ma; the first event produced the high-grade metamorphism and widespread migmatization that characterize Xolapa and the second event is likely related to extended heating produced by coeval arc plutonism. Pre-Jurassic assemblages of the Chortis block of Central America contain zircon populations that significantly coincide with those recorded in both, the Acatlán and Oaxacan complexes and their Paleozoic sedimentary covers as well as with those recorded in Xolapa metasediments, which suggests a spatial connection among these petrotectonic assemblages during much of the Mesozoic. It is proposed that Xolapa was generated in a basin floored by Permian rocks flanked on one side by southern Mexico terranes and on the other side by the Chortis block. Contraction of the basin tied to the approach and accretion of the Guerrero terrane arc assemblages during Late Cretaceous time produced crustal thickening and high-grade metamorphism and migmatization at mid-crustal levels. Diachronic exhumation of Xolapa began during Early Paleogene time very likely promoted by the detachment and migration of the Chortis block. The migration would additionally produce slicing of Xolapa assemblages generating its elongated and juxtaposed structure

  17. The UHP metamorphic Seve Nappe Complex of the Swedish Caledonides - a new occurrence of the microdiamond-bearing gneisses and their exhumation

    Science.gov (United States)

    Klonowska, Iwona; Janák, Marian; Majka, Jarosław; ‎ Froitzheim, Nikolaus; Gee, David G.

    2015-04-01

    The ultra-high pressure metamorphism (UHPM) in the Seve Nappe Complex of the Swedish Caledonides has been recently recognized within several lithologies including gneisses, eclogites and garnet pyroxenites (e.g. Janák et al. 2013, Klonowska et al. 2014a, Majka et al. 2014). Thermodynamic modelling and thermobarometric calculations indicate peak pressure conditions of >3GPa at c. 800-900°C (reaching the diamond stability field) for eclogites and garnet pyroxenites from northern Jämtland (e.g. Klonowska et al. 2014b). In addition to this, the first microdiamonds were found in paragneisses from the Snasahögarna Mt. in central Jämtland (Majka et al. 2014). Here we report a new discovery of microdiamond together with moissanite (SiC) from one of the world's most famous localities for thrusting, Mount Åreskutan, where long transport distances were recognized already in the 19th century (Törnebohm 1888). Garnet porphyroblasts in gneisses from the Åreskutan Mt. contain abundant mineral inclusions, mainly graphite, carbonates and quartz, together with fluid inclusions of CO2 concentrated in swarms. Among these inclusions three microdiamonds were found in two gneiss samples. In one of the samples moissanite was also discovered. Both minerals were identified by micro-Raman spectroscopy. In addition to these 'swarm' inclusions, biotite, kyanite, rutile, feldspars, zircon, monazite, ±phengite, ±muscovite, ±spinel, ±ilmenite, ±apatite occur in garnets. Phase equilibrium modelling for the phengite-bearing gneiss confirms its UHP history at temperatures of c. 800°C. Recent discoveries of UHP metamorphism within the Seve Nappe Complex derived from the Baltican outer margin (part of the Middle Allochthon) challenged us to present a new tectonic model incorporating exhumation of the deeply subducted continental rocks together with mantle lithosphere peridotites. Majka et al. (2014) introduced a new "under-pressure"-driven exhumation mechanism of rocks buried in

  18. Evidence of Failure on Low-Angle Normal Faults from Thermochronology and Paleomagnetism: A Case Study from South Mountains Metamorphic Core Complex, Arizona

    Science.gov (United States)

    Hoehn, J. R.; Smith, D. M.; Goodwin, L. B.; Feinberg, J. M.; Heizler, M. T.; Singer, B. S.; Jicha, B. R.

    2015-12-01

    The South Mountains metamorphic core complex records progressive extension and exhumation of Miocene granodiorite. Early mylonites are cut by younger brittle faults, including locally abundant, shallowly dipping, pseudotachylyte-lined slip surfaces. These frictional melt generation veins can be grouped based on mesoscopic character of both pseudotachylyte and host granodiorite mylonite. All vein types are subparallel to biotite-lined, host rock C-surfaces. Thin (clasts. Though largely parallel C-surfaces, these veins possess S-surface-parallel segments up to several cms long, and cut host rock with a strong S-C fabric. Type 3 veins lack mesoscopic foliation and cut host rock ranging from protomylonite to ultramylonite. They are similar in thickness to type 2 veins, but include fewer survivor clasts. Previous 40Ar/39Ar dates on pseudotachylyte veins (16.24 ± 0.23 Ma and 17.44 ± 0.20 Ma) show pseudotachylyte-producing seismicity occurred over at least 1 million years. Multi- diffusion-domain analysis of host rock K-feldspar demonstrates cooling below 150°C by 21.8 Ma. Assuming a geothermal gradient between 25°C and 50°C/km, pseudotachylyte veins were generated at a maximum depth of 2.5-5 km. Fabric intensity of anisotropy of magnetic susceptibility (AMS) corresponds to vein types. Paleomagnetic analyses yield 3 clusters of characteristic remanent magnetizations (ChRMs) that correlate to AMS/vein types. ChRMs of nonfoliated type 3 veins are close to the Miocene pole. By contrast, ChRMs for type 1 and 2 veins are deflected close to the foliation due to strong anisotropy of their magnetic mineral assemblages. Normal faults dipping oriented for slip according to Andersonian fault mechanics. Previous workers therefore have suggested they failed at steeper dips, then rotated to current orientations. The uniformity of South Mountains generation vein orientations records no rotation between formation of the oldest and youngest veins. The proximity of the ChRMs of type 3