WorldWideScience

Sample records for metamorphism

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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 ...

  7. 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

  8. 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

  9. 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.

  10. 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...

  11. 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

  12. 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.

  13. 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.

  14. 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...

  15. 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...

  16. 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

  17. 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...

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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...

  4. 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.

  5. 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 ...

  6. 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 ...

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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 ...

  17. 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)

  18. 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

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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,

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  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. 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)

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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

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

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    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

  10. 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

  11. 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.

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

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    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.

  13. 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

  14. 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)

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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 ...

  5. 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

  6. 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

  7. 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...

  8. 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.

  9. 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

  10. 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...

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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...

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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%.

  9. 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.

  10. 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...

  11. 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

  12. 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.)

  13. 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

  14. 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.

  15. 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).

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros Junior, Edgar Batista; Marques, Rodson Abreu, E-mail: edgarjr@ymail.com, E-mail: rodson.marques@ufes.br [Universidade Federal do Espirito Santo (UFES), Alegre, ES (Brazil). Departamento de Geologia; Jordt-Evangelista, Hanna; Queiroga, Glaucia Nascimento, E-mail: hanna@degeo.ufop.br, E-mail: glauciaqueiroga@yahoo.com.br [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Schulz, Bernhard, E-mail: bernhard.schulz@mineral.tu-freiberg.de [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)

    2016-01-15

    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. Metamorphic P-T paths of metapelitic granulites from the Larsemann Hills, East Antarctica

    Science.gov (United States)

    Tong, Laixi; Liu, Xiaohan; Wang, Yanbin; Liang, Xirong

    2014-04-01

    Through detailed textural observations, a peak M1 assemblage garnet + orthopyroxene + cordierite + K-feldspar has been identified in a structurally early Al-rich metapelitic granulite lens from the Larsemann Hills, East Antarctica. The M1 assemblage has been overprinted by M2 cordierite corona and M3 orthopyroxene + cordierite symplectite on garnet grains. Quantitative modeling for the peak M1 assemblage via the THERMOCALC program in the KFMASH system suggests that it was formed by the crossing of the univariant reaction garnet + biotite = cordierite + orthopyroxene + K-feldspar + melt under P-T conditions of 6-8 kbar and 840-880 °C, followed by post-peak near isobaric cooling. However, the average P-T calculations for the boron-bearing pelitic granulite indicate that peak M1 conditions reached ~ 9.0 kbar and ~ 900 °C, and the overprinting M2 assemblage formed under P-T conditions of ~ 7.0 kbar and 800-850 °C, reflecting a post-peak near isothermal decompression. P-T estimates show that M3 conditions reached 4-5 kbar and 700-750 °C. These imply that the M1 metamorphic evolution of the region displays contrasting P-T paths, while M2 to M3 evolution indicates a decompression-cooling process. The available chronological data support that the M1 metamorphic evolution occurred during the late Proterozoic (1000-900 Ma) Grenvillian high-grade compression tectonic event (D1), and was accompanied by strong magmatism, showing a close affinity to the northern Prince Charles Mountains and the Rayner complex. However, the overprinted M2 to M3 metamorphic evolution formed during the early Palaeozoic (~ 530 Ma) Pan-African high-grade tectonic events (D2-D3), and was associated with an important intracontinental reworking. This study presents an example for interpreting a complex polymetamorphic history.

  14. 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.

  15. 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.

  16. A versatile digitally-graded buffer structure for metamorphic device applications

    Science.gov (United States)

    Ma, Yingjie; Zhang, Yonggang; Chen, Xingyou; Gu, Yi; Shi, Yanhui; Ji, Wanyan; Du, Ben

    2018-04-01

    Exploring more effective buffer schemes for mitigating dislocation deficiencies is the key technology towards higher performance metamorphic devices. Here we demonstrate a versatile metamorphic grading structure consisting of 38-period alternated multilayers of In0.52Al0.48As and In0.82Al0.18As on InP substrate, thicknesses of which in each period were gradually varied in opposite directions from 48.7 and 1.3 nm to 1.3 and 48.7 nm, respectively, akin to a digital alloy. Both preferentially dislocation nucleation and blocking of threading dislocation transmission are observed near the In0.82Al0.18As/In0.52Al0.48As interfaces, which help relax the strain and lower the residual defect density. A 2.6 μm In0.83Ga0.17As pin photodetector is fabricated on this pseudo-substrate, attaining a low dark current density of 2.9  ×  10‑6 A cm‑2 and a high detectivity of 1.8  ×  1010 cmHz1/2W‑1 at room temperature, comparable with the states of the art that on linearly-graded buffer layers. These results indicate such digitally-graded buffer structures are promising for enhancing performances of metamorphic devices, and can be easily generalized to other lattice-mismatched material systems.

  17. 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

  18. Forecast of promising areas for uranium prospection at the metamorphic Massif of Isla de la Juventud

    International Nuclear Information System (INIS)

    Gongora, L.E.; Macola, E.; Sanchez, J.; Torres, J.C.; Alaminos, C.; LLanes, A.; Morales, M.

    1995-01-01

    A mineralization conceptual model for uranium of the metamorphic Massif of Isla de la Juventud was established taking into account the study of the geological and metallogenic characteristic of the territory. The determined indications of mineralization were plotted on the geological map in order to conform a forecasting map and the selection of 22 hypothetical promising areas was carried out. As result of the field words three really promising areas were selected. A group of exploration techniques needed to evaluate the targets areas is presented

  19. Structures, microfabrics and textures of the Cordilleran-type Rechnitz metamorphic core complex, Eastern Alps☆

    Science.gov (United States)

    Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai; Genser, Johann

    2013-01-01

    Rechnitz window group represents a Cordilleran-style metamorphic core complex, which is almost entirely located within nearly contemporaneous Neogene sediments at the transition zone between the Eastern Alps and the Neogene Pannonian basin. Two tectonic units are distinguished within the Rechnitz metamorphic core complex (RMCC): (1) a lower unit mainly composed of Mesozoic metasediments, and (2) an upper unit mainly composed of ophiolite remnants. Both units are metamorphosed within greenschist facies conditions during earliest Miocene followed by exhumation and cooling. The internal structure of the RMCC is characterized by the following succession of structure-forming events: (1) blueschist relics of Paleocene/Eocene age formed as a result of subduction (D1), (2) ductile nappe stacking (D2) of an ophiolite nappe over a distant passive margin succession (ca. E–W to WNW–ESE oriented stretching lineation), (3) greenschist facies-grade metamorphism annealing dominant in the lower unit, and (4) ductile low-angle normal faulting (D3) (with mainly NE–SW oriented stretching lineation), and (5) ca. E to NE-vergent folding (D4). The microfabrics are related to mostly ductile nappe stacking to ductile low-angle normal faulting. Paleopiezometry in conjunction with P–T estimates yield high strain rates of 10− 11 to 10− 13 s− 1, depending on the temperature (400–350 °C) and choice of piezometer and flow law calibration. Progressive microstructures and texture analysis indicate an overprint of the high-temperature fabrics (D2) by the low-temperature deformation (D3). Phengitic mica from the Paleocene/Eocene high-pressure metamorphism remained stable during D2 ductile deformation as well as preserved within late stages of final sub-greenschist facies shearing. Chlorite geothermometry yields two temperature groups, 376–328 °C, and 306–132 °C. Chlorite is seemingly accessible to late-stage resetting. The RMCC underwent an earlier large-scale coaxial

  20. 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)

  1. Miocene metamorphism of pan-African granites in the Edough Massif (NE Algeria)

    International Nuclear Information System (INIS)

    Hammor, D.; Lancelot, J.

    1998-01-01

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

  2. Research of the chemical activity of microgrinding coals of various metamorphism degree

    Science.gov (United States)

    Burdukov, A. P.; Butakov, E. B.; Kuznetsov, A. V.

    2017-09-01

    In this paper, we investigate the effect of mechanically activating grinding of coals of various degrees of metamorphism by two different methods - determination of the flash time in a vertical tubular furnace and thermogravimetric analysis. In the experiments, the coals that had been processed on a vibrating centrifugal mill and a disintegrator, aged for some time, were compared. The experiments showed a decrease in the ignition temperature of mechanically activated coals - deactivation of fuel, as well as the effect of mechanical activation on the further process of thermal-oxidative degradation.

  3. Uranium mineralization possibilities in metamorphic Massif of Isla de Juventud, Cuba

    International Nuclear Information System (INIS)

    Gongora Dominguez, L.E.; Llanes Castro, A.I.; Pena Fortes, B.; Capote Rodriguez, G.

    1996-01-01

    The geologic and metallogenic characteristic of the metamorphic Massif shows the presence of possible uranium vein type mineralization as a result of a hidrotermal genetic process. Metalliferous fluids rising along the fault system were responsible for the deposition of the uranium in the reduction zones, i.e. presence of pyrite, organic matter and others. This type of uranium minerization is proposed for the Bibijagua area and for the Revolucion and Lela area the same type is expected. The gamma spectrometric analysis was used to evaluate the geological samples

  4. 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.

  5. Record of high-pressure overprint in metamorphic soles of the Tavşanli zone, Western Anatolia

    Science.gov (United States)

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

    2013-04-01

    Large obducted ophiolites correspond to the emplacement of dense oceanic lithosphere on top of a continent and thereby provide insights into rheological and thermal coupling between plates or fluid budgets. Obducted ophiolites thrust onto the continental margin of the Anatolide-Tauride block (Western Anatolia, south of the Izmir-Ankara suture zone) are dated through their metamorphic sole at ca. 90-95Ma and derive from the same intra-oceanic Neotethyan subduction. We herein focus on the metamorphic soles of the Tavşanlı zone, which show a variable high-pressure low-temperature (HP-LT) overprint of the initial amphibolitic metamorphic conditions (Önen & Hall, 1993; Dilek & Whitney, 1997; Okay et al, 1998). Systematic sampling was done in both the already studied areas as well as new locations. PT conditions were estimated at 8 kbar and 700°C for the amphibolitic stage with the assemblage hornblende + plagioclase ± garnet ± epidote. The HP-LT metamorphic overprint reached incipient blueschist to blueschist facies PT conditions. Development of the characteristic assemblage glaucophane + lawsonite yields PT estimates of >6-7 kbar and 300°C. The high-pressure stage is similar to the one observed for the underlying accretionary-complex unit of the Tavşanlı zone (Plunder et al, this meeting). This HP overprint was not observed in other obduction contexts such as Oman or New Caledonia but was documented in Fransciscan Complex amphibolites (Wakayabashi, 1990). The record of two metamorphic events can be understood as: (1) rapid cooling of the subduction zone after initiation and the exhumation of the metamorphic sole; (2) reburial after or during exhumation of the amphibolite initially welded at the base of the ophiolite. Several observations (i.e., lack of tectonic contact between the ophiolitic body and the metamorphic sole, PT estimates,...) point to cooling as the most likely hypothesis. Metamorphic soles allow to highlight: (1) the dynamics of obducted

  6. 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

  7. 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.

  8. 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)

  9. Geochemistry and origin of piemontite-quartz schists in the Sanbagawa Metamorphic Belt, central Shikoku, Japan

    Science.gov (United States)

    Izadyar, J.; Tomita, K.; Shinjoe, H.

    2003-05-01

    In the Sanbagawa Metamorphic Belt of central Shikoku, geochemical characteristics are used to demonstrate that piemontite-quartz schists had a manganiferous sedimentary protolith. The Sanbagawa Metamorphic Belt was formed during a Cretaceous regional intermediate high-pressure type of metamorphism which is present throughout Southwest Japan. Based on a detailed mineralogical study of the Asemi-gawa and Besshi areas in central Shikoku, the Sanbagawa piemontite-quartz schists can be divided into talc-bearing and talc-free types. Phlogopite occurs only in talc-bearing assemblages and the modal percentage of piemontite in talc-bearing types is higher than in talc-free types. Plotting analyses of piemontites and garnets from talc-bearing and talc-free types in the Al 2O 3-Fe 2O 3-Mn 2O 3-MnO(Al-Fe 3+-Mn 3+-Mn 2+) diagram, for the Asemi-gawa and Besshi areas separately, shows that the piemontite which accompanies talc is richer in Mn 3+ and poorer in Fe 3+. Also, garnets from talc-bearing assemblage contain a slightly higher amount of Mn 2+ and a lower amount of Al than talc-free types. The Al 2O 3-SiO 2-Fe 2O 3+FeO plot shows that Sanbagawa piemontite-quartz schists have a composition between deep-sea pelagic clay and pure silica. By the use of Pearson's product moment correlation coefficient method, and plotting elements against each other after removing silica and volatiles, it is possible to distinguish four components which are able to explain the variance of the samples. These components are: (first component: Al 2O 3, TiO 2, MgO, Na 2O, K 2O, Zr, Rb, Y, Nb and to lesser degree Fe 2O 3, FeO, Ni, Th, Ba); (second component: SiO 2); (third component: MnO) and (fourth component: CaO). Al 2O 3, TiO 2, Zr and other elements with positive coefficient relations with them have a detrital origin. Biogenic origins are considered for CaO and SiO 2 and it was concluded that MnO was derived from an hydrothermal source. Because the Sanbagawa Metamorphic Belt has been subjected

  10. 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.

  11. Granulites and charnockites of the Gruf Complex: Evidence for Permian ultra-high temperature metamorphism in the Central Alps

    Science.gov (United States)

    Galli, A.; Le Bayon, B.; Schmidt, M. W.; Burg, J.-P.; Caddick, M. J.; Reusser, E.

    2011-05-01

    We present a detailed field and petrological study of charnockites and ultra-high temperature (UHT) granulites from the Gruf Complex, eastern Central Alps. Charnockites occur as up to 0.5 km wide and 8 km long, internally boudinaged, opx-bearing sheet-like bodies within the regionally dominant migmatitic biotite-orthogneisses. Granulites occur as garnet-orthopyroxene-biotite-alkali feldspar-bearing schlieren (± sapphirine, sillimanite, cordierite, corundum, spinel, plagioclase, and quartz) within charnockites and as residual enclaves both in the charnockites and the migmatitic orthogneisses. Thermobarometric calculations, P-T pseudosections and orthopyroxene Al content, show that both charnockites and granulites equilibrated at metamorphic peak conditions of T = 920-940 °C and P = 8.5-9.5 kbar. Peak assemblages were subsequently overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel at T = 720-740 °C and P = 7-7.5 kbar. We suggest that granulites and charnockites are lower crustal relicts preserved in the migmatitic orthogneisses. Garnet diffusion modelling shows that metamorphic garnet-opx ± sapphirine ± sillimanite peak assemblages and post-peak reaction textures always involving cordierite developed during two separate metamorphic cycles. Peak assemblages reflect UHT metamorphism related to post-Varican Permian extension, but post-peak coronae and symplectites formed during the mid-Tertiary, upper amphibolite facies, Alpine regional metamorphism. Fluid-absent partial melting of pelitic and psammitic sediments during the Permian UHT event lead to the formation of charnockitic magmas and granulitic residues. Intense melt loss and thorough dehydration of the granulites (although retaining biotite) favoured the partial preservation of peak mineral assemblages during Alpine metamorphism.

  12. 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

  13. 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

  14. 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

  15. Comparative analysis of strain fields in layers of step-graded metamorphic buffers of various designs

    Science.gov (United States)

    Aleshin, A. N.; Bugaev, A. S.; Ruban, O. A.; Tabachkova, N. Yu.; Shchetinin, I. V.

    2017-10-01

    Spatial distribution of residual elastic strain in the layers of two step-graded metamophic buffers of various designs, grown by molecular beam epitaxy from ternary InxAl1-xAs solutions on GaAs(001) substrates, is obtained using reciprocal space mapping by three-axis X-ray diffractometry and the linear theory of elasticity. The difference in the design of the buffers enabled the formation of a dislocation-free layer with different thickness in each of the heterostructures, which was the main basis of this study. It is shown that, in spite of the different design of graded metamorphic buffers, the nature of strain fields in them is the same, and the residual elastic strains in the final elements of both buffers adjusted for the effect of work hardening subject to the same phenomenological law, which describes the strain relief process in single-layer heterostructures.

  16. Following the Amphibolite to Greenschist Metamorphic Path through the Structural Parameters of Spinels from Amsaga (Mauritania

    Directory of Open Access Journals (Sweden)

    Davide Lenaz

    2018-01-01

    Full Text Available We investigated the crystal and structural behavior of several Cr-bearing spinels from the Archean chromitites of Amsaga (Mauritania. The chemical and structural data testified a retrograde metamorphism from amphibolite to greenschist facies, witnessed by relative changes in the amount of all the major oxides (Cr, Al, Mg, Fe2+, Fe3+, the relative proportion of Fe3+/Fetot as well as the structural parameters, including the cell edge and the oxygen coordinate. The general agreement between electron microprobe and Mössbauer data indicates that the analyzed spinels are stoichiometric. The structural data revealed that the oxygen positional parameter of amphibole-bearing samples is the highest observed among Cr-bearing spinels with similar Cr# and Mg#. Consequently, it is suggested that a structural study of detrital Cr-spinels could be important in discriminating an amphibole-chromitite source from an ophiolite source.

  17. 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

  18. Device characterization for design optimization of 4 junction inverted metamorphic concentrator solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Geisz, John F.; France, Ryan M.; Steiner, Myles A.; Friedman, Daniel J. [National Renewable Energy Laboratory, Golden, CO 80401 (United States); García, Iván [National Renewable Energy Laboratory, Golden, CO 80401 USA and Instituto de Energía Solar, Universidad Politécnica de Madrid, Avda Complutense s/n, 28040 Madrid (Spain)

    2014-09-26

    Quantitative electroluminescence (EL) and luminescent coupling (LC) analysis, along with more conventional characterization techniques, are combined to completely characterize the subcell JV curves within a fourjunction (4J) inverted metamorphic solar cell (IMM). The 4J performance under arbitrary spectral conditions can be predicted from these subcell JV curves. The internal radiative efficiency (IRE) of each junction has been determined as a function of current density from the external radiative efficiency using optical modeling, but this required the accurate determination of the individual junction current densities during the EL measurement as affected by LC. These measurement and analysis techniques can be applied to any multijunction solar cell. The 4J IMM solar cell used to illustrate these techniques showed excellent junction quality as exhibited by high IRE and a one-sun AM1.5D efficiency of 36.3%. This device operates up to 1000 suns without limitations due to any of the three tunnel junctions.

  19. Progress in GaAs Metamorphic HEMT Technology for Microwave Applications. High Efficiency Ka-Band MHEMT Power MMICs

    Science.gov (United States)

    Smith, P. M.; Dugas, D.; Chu, K.; Nichols, K.; Duh, K. H.; Fisher, J.; MtPleasant, L.; Xu, D.; Gunter, L.; Vera, A.

    2003-01-01

    This paper reviews recent progress in the development of GaAs metamorphic HEMT (MHEMT) technology for microwave applications. Commercialization has begun, while efforts to further improve performance, manufacturability and reliability continue. We also report the first multi-watt MHEMT MMIC power amplifiers, demonstrating up to 3.2W output power and record power-added efficiency (PAE) at Ka-band.

  20. New P-T and U-Pb constraints on Alpine Schist metamorphism in south Westland, New Zealand

    International Nuclear Information System (INIS)

    Scott, J.M.; Auer, A.; Muhling, J.R.; Czertowicz, T.A.; Cooper, A.F.; Billia, M.A.; Kennedy, A.K.

    2015-01-01

    Metamorphic mineral compositions of a staurolite-bearing greyschist from the middle reaches of the Moeraki River valley in south Westland reveal peak equilibration at c. 558±50 degrees C and c. 6.1±1.2 kbar. Two c. 83 Ma U-Pb monazite age populations from the cores of monazite-apatite-allanite-epidote corona structures in mylonitised schists from near Fox Glacier confirm that Alpine Schist metamorphism occurred during the Late Cretaceous. The published spread in Late Cretaceous metamorphic ages indicates that metamorphism was diachronous or was a protracted event. Further dating is required to pin down the cryptic transition into the Jurassic-Early Cretaceous metamorphosed Otago Schist, but the Alpine Schist must extend at least 11 km east of the Alpine Fault in south Westland and overprint the suture between the Pounamu and Rakaia terranes. The P-T-t results imply that the Late Cretaceous crust represented by portions of the Alpine Schist was probably of similar thickness to that beneath the Southern Alps today, but with dehydration and partial melting occurring near the base. The crust under Westland and Otago may be dry and therefore strong. (author).

  1. 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,

  2. 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

  3. Charnockites and UHT metamorphism in the Bakhuis Granulite Belt, western Suriname : Evidence for two separate UHT events

    NARCIS (Netherlands)

    Klaver, Martijn; de Roever, Emond W F; Nanne, Josefine A M; Mason, Paul R D; Davies, Gareth R.

    The Bakhuis Granulite Belt in western Suriname is an ultrahigh-temperature (UHT) metamorphic terrain in the centre of the Paleoproterozoic (Transamazonian) Guiana Shield. Next to the UHT granulites, the belt contains a 30 by 30km body of orthopyroxene-bearing granitoids: the Kabalebo charnockites.

  4. 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.

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

    NARCIS (Netherlands)

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

    2017-01-01

    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

  6. 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

  7. Relationships among developmental stage, metamorphic timing, and concentrations of elements in bullfrogs (Rana catesbeiana)

    Energy Technology Data Exchange (ETDEWEB)

    Snodgrass, J.W.; Hopkins, W.A.; Roe, J.H. [Towson University, Towson, MD (United States). Dept. for Biological Science

    2003-07-01

    We collected bullfrog (Rana catesbeiana) larvae from a coal combustion waste settling basin to investigate the effects of developmental stage and timing of metamorphosis on concentrations of a series of trace elements in bullfrog tissues. Bullfrogs at four stages of development (from no hind limbs to recently metamorphosed juveniles) and bullfrogs that metamorphosed in the fall or overwintered in the contaminated basin and metamorphosed in the spring were analyzed for whole-body concentrations of Al, V, Cr, Ni, Cu, As, Pb, Cd, Zn, Ag, Sr, and Se. After the effects of dry mass were removed, tissue concentrations of six elements (Al, V, Cr, Ni, Cu, As, and Pb) decreased from the late larval stage through metamorphosis. Decreases in concentrations through metamorphosis ranged from 40% for Cu to 97% for Al. Tissue concentrations of these elements were also similar or higher in spring; Al and Cr concentrations were 34 and 90% higher in the spring, respectively, whereas As, Ni, Cu, and Pb concentrations were {lt} 10% higher. Concentrations of Cd, Se, and Ag varied among seasons but not among stages; Cd and Ag concentrations were 40 and 62% lower, respectively, and Se concentrations were 21% higher in spring. Concentrations of Zn varied only among stages; concentrations decreased gradually through late larval stage and then increased through metamorphosis. Concentrations of Sr varied among stages, but this variation was dependent on the season. Concentrations of Sr were higher in larval stages during the spring, but because concentrations of Sr increased 122% through metamorphosis in the fall and only 22% in the spring, concentrations were higher in fall metamorphs when compared with spring metamorphs. Our results indicate that metamorphosis and season of metamorphosis affects trace element concentrations in bullfrogs and may have important implications for the health of juveniles and the transfer of pollutants from the aquatic to the terrestrial environment.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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

  19. Crystallography of hornblende amphibole in LAP04840 R chondrite and implication for its metamorphic history

    International Nuclear Information System (INIS)

    Ota, Kouhei; Mikouchi, Takashi; Sugiyama, Kazumasa

    2009-01-01

    LAP04840 is an unusual R chondrite that includes abundant hornblende amphibole. LAP04840 shows a texture of equilibrated chondrite composed of 59.3% olivine, 13.5% orthopyroxene, 13.3% hornblende, 6.2% plagio-clase, 6.0% Fe-Ni sulfide, and 1.7% accessory minerals. Hornblende replaces olivine and pyroxene in both chondrules and matrices, suggesting its secondary origin. All major phases in LAP04840 are homogeneous: olivine (Fa 37 ), orthopyroxene (En 70 Wo 1 ), and plagioclase (An 8 Or 2 ). Hornblende is also nearly homogeneous, but the total sum by electron microprobe analysis is 96-98 wt%, suggesting the presence of Fe 3+ and a hydroxyl group. Synchrotron Fe-XANES analysis gives a Fe 3+ /ΣFe ratio of ∼0.6 and micro-FT-IR analysis confirms the presence of a hydroxyl group. Thus, the structural formula is (Na 0.40 K 0 . 04 ) (Ca 1.46 Mn 0.02 Fe 0.06 2+ Na 0.46 ) (Al 0.08 Fe 0.43 2+ Fe 0.75 3+ Cr 0.08 Mg 3.60 ) (Si 7.02 Al 0.98 )O 22 (OH) 2 . Single crystal X-ray diffraction of LAP04840 hornblende gives the following lattice constants: a=9.7957(9) A, b=18.0788(12) A, c=5.2949(5) A, β=104.747(3)deg. The relatively short distances of [M(1)-O=2.069 A], [M(2)-O=2.081 A], and [M(3)-O=2.058 A] suggest the feasible preference of small Fe 3+ at these sites. The mineralogy and petrology of LAP04840 are consistent with its classification as an R6 chondrite. However, the presence of hornblende and biotite is quite unique among not only R chondrites but also asteroidal meteorites in general. The presence of these hydrous minerals suggests metamorphism under high pressure and an aqueous environment probably at depth in the parent body. A thermometer using hornblende and plagioclase equilibria gives T=670-690degC. Further, a barometer using Al content in hornblende gives P=∼0.1 GPa. Although these estimates bear some uncertainties, it is likely that the size of the R chondrite parent body was large enough to induce such metamorphism. (author)

  20. The next chapter in experimental petrology: Metamorphic dehydration of polycrystalline gypsum captured in 3D microtomographic time series datasets

    Science.gov (United States)

    Bedford, John; Fusseis, Florian; Leclere, Henry; Wheeler, John; Faulkner, Dan

    2016-04-01

    Nucleation and growth of new minerals in response to disequilibrium is the most fundamental metamorphic process. However, our current kinetic models of metamorphic reactions are largely based on inference from fossil mineral assemblages, rather than from direct observation. The experimental investigation of metamorphism has also been limited, typically to concealed vessels that restrict the possibility of direct microstructural monitoring. Here we present one of the first time series datasets that captures a metamorphic reaction, dehydration of polycrystalline gypsum to form hemihydrate, in a series of three dimensional x-ray microtomographic datasets. We achieved this by installing an x-ray transparent hydrothermal cell (Fusseis et al., 2014, J. Synchrotron Rad. 21, 251-253) in the microtomography beamline 2BM at the Advanced Photon Source (USA). In the cell, we heated a millimetre-sized sample of Volterra Alabaster to 388 K while applying an effective pressure of 5 MPa. Using hard x-rays that penetrate the pressure vessel, we imaged the specimen 40 times while it reacted for approximately 10 hours. Each microtomographic dataset was acquired in 300 seconds without interrupting the reaction. Our absorption microtomographic data have a voxel size of 1.3 μm, which suffices to analyse the reaction progress in 4D. Gypsum can clearly be distinguished from hemihydrate and pores, which form due to the large negative solid volume change. On the resolved scale, the first hemihydrate needles appear after about 2 hours. Our data allow tracking of individual needles throughout the entire experiment. We quantified their growth rates by measuring their circumference. While individual grains grow at different rates, they all start slowly during the initial nucleation stage, then accelerate and grow steadily between about 200 and 400 minutes before reaction rate decelerates again. Hemihydrate needles are surrounded by porous haloes, which grow with the needles, link up and

  1. 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.

  2. 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.

  3. Friction and sliding wear behavior of induction melted FeCrB metamorphic alloy coating

    International Nuclear Information System (INIS)

    Hu, Ge; Meng, Huimin; Liu, Junyou

    2014-01-01

    Induction melted FeCrB metamorphic coatings deposited onto Q235 steel were produced using ultrasonic frequency inductive cladding (UFIC) technique. The measurements of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), transmission electron microscopy (TEM), microhardness tester and ball-on-disc wear tester were used to determine the microstructure, microhardness and dry-sliding wear resistance coupled with wear mechanism of clad coatings. The experimental results show that C+ clad coating consists of austenite γ-Fe, interdentritic lamellar eutectics γ-Fe/(Cr,Fe) 2 B and borides (Cr,Fe) 2 B as the reinforcing phase whilst the phases of ferrite α-Fe, borides Cr 1.65 Fe 0.35 B 0.96 and eutectics α-Fe/Cr 1.65 Fe 0.35 B 0.96 are identified in M clad coating. The average microhardness of the C+ and M clad coating is more than 3-times than that of the substrate. The wear resistance of the C+ and M clad coating improves 5.18, 6.08 times compared with that of the substrate at applied load of 20 N, respectively, which contributes to the occurrence of the crystalline–amorphous phase transition by friction treatment and uniformly distributed borides embedded in the ductile solid solution matrix.

  4. Metamorphism of cosmic dust: Processing from circumstellar outflows to the cometary regolith

    International Nuclear Information System (INIS)

    Nuth, J.A. III.

    1989-01-01

    Metamorphism of refractory particles continues in the interstellar medium (ISM) where the driving forces are sputtering by cosmic ray particles, annealing by high energy photons, and grain destruction in supernova generated shocks. Studies of the depletion of the elements from the gas phase of the interstellar medium tell us that if grain destruction occurs with high efficiency in the ISM, then there must be some mechanism by which grains can be formed in the ISM. Most grains in a cloud which collapses to form a star will be destroyed; many of the surviving grains will be severely processed. Grains in the outermost regions of the nebula may survive relatively unchanged by thermal processing or hydration. It is these grains which one hopes to find in comets. However, only those grains encased in ice at low temperature can be considered pristine since a considerable degree of hydrous alteration might occur in a cometary regolith if the comet enters the inner solar system. The physical, chemical and isotopic properties of a refractory grain at each stage of its life cycle will be discussed

  5. Continuous Static Gait with Twisting Trunk of a Metamorphic Quadruped Robot

    Directory of Open Access Journals (Sweden)

    C. Zhang

    2018-01-01

    Full Text Available The natural quadrupeds, such as geckos and lizards, often twist their trunks when moving. Conventional quadruped robots cannot perform the same motion due to equipping with a trunk which is a rigid body or at most consists of two blocks connected by passive joints. This paper proposes a metamorphic quadruped robot with a reconfigurable trunk which can implement active trunk motions, called MetaRobot I. The robot can imitate the natural quadrupeds to execute motion of trunk twisting. Benefiting from the twisting trunk, the stride length of this quadruped is increased comparing to that of conventional quadruped robots.In this paper a continuous static gait benefited from the twisting trunk performing the increased stride length is introduced. After that, the increased stride length relative to the trunk twisting will be analysed mathematically. Other points impacting the implementation of the increased stride length in the gait are investigated such as the upper limit of the stride length and the kinematic margin. The increased stride length in the gait will lead the increase of locomotion speed comparing with conventional quadruped robots, giving the extent that natural quadrupeds twisting their trunks when moving. The simulation and an experiment on the prototype are then carried out to illustrate the benefits on the stride length and locomotion speed brought by the twisting trunk to the quadruped robot.

  6. 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.

  7. A self-reconfiguring metamorphic nanoinjector for injection into mouse zygotes

    Energy Technology Data Exchange (ETDEWEB)

    Aten, Quentin T. [Nexus Spine, LLC, Salt Lake City, Utah 84124 (United States); Jensen, Brian D.; Howell, Larry L. [Department of Mechanical Engineering, Brigham Young University, Provo, Utah 84602 (United States); Burnett, Sandra H. [Department of Microbiology and Molecular Biology, Brigham Young University, Provo, Utah 84602 (United States)

    2014-05-15

    This paper presents a surface-micromachined microelectromechanical system nanoinjector designed to inject DNA into mouse zygotes which are ≈90 μm in diameter. The proposed injection method requires that an electrically charged, DNA coated lance be inserted into the mouse zygote. The nanoinjector's principal design requirements are (1) it must penetrate the lance into the mouse zygote without tearing the cell membranes and (2) maintain electrical connectivity between the lance and a stationary bond pad. These requirements are satisfied through a two-phase, self-reconfiguring metamorphic mechanism. In the first motion subphase a change-point six-bar mechanism elevates the lance to ≈45 μm above the substrate. In the second motion subphase, a compliant folded-beam suspension allows the lance to translate in-plane at a constant height as it penetrates the cell membranes. The viability of embryos following nanoinjection is presented as a metric for quantifying how well the nanoinjector mechanism fulfills its design requirements of penetrating the zygote without causing membrane damage. Viability studies of nearly 3000 nanoinjections resulted in 71.9% of nanoinjected zygotes progressing to the two-cell stage compared to 79.6% of untreated embryos.

  8. Vitamin A Affects Flatfish Development in a Thyroid Hormone Signaling and Metamorphic Stage Dependent Manner

    Directory of Open Access Journals (Sweden)

    Ignacio Fernández

    2017-06-01

    Full Text Available Vitamin A (VA and retinoid derivatives are known morphogens controlling vertebrate development. Despite the research effort conducted during the last decade, the precise mechanism of how VA induces post-natal bone changes, and particularly those operating through crosstalk with the thyroid hormones (THs remain to be fully understood. Since effects and mechanisms seem to be dose and time-dependent, flatfish are an interesting study model as they undergo a characteristic process of metamorphosis driven by THs that can be followed by external appearance. Here, we studied the effects of VA imbalance that might determine Senegalese sole (Solea senegalensis skeletogenetic phenotype through development of thyroid follicles, THs homeostasis and signaling when a dietary VA excess was specifically provided during pre-, pro- or post-metamorphic stages using enriched rotifers and Artemia as carriers. The increased VA content in enriched live prey was associated to a higher VA content in fish at all developmental stages. Dietary VA content clearly affected thyroid follicle development, T3 and T4 immunoreactive staining, skeletogenesis and mineralization in a dose and time-dependent fashion. Gene expression analysis showed that VA levels modified the mRNA abundance of VA- and TH-specific nuclear receptors at specific developmental stages. Present results provide new and key knowledge to better understand how VA and TH pathways interact at tissue, cellular and nuclear level at different developmental periods in Senegalese sole, unveiling how dietary modulation might determine juvenile phenotype and physiology.

  9. Effect of High-Speed Milling Parameters on Surface Metamorphic Layer of TC17 Titanium Alloy

    Directory of Open Access Journals (Sweden)

    TAN Liang

    2017-12-01

    Full Text Available In order to provide the relatively accurate experimental basis for optimizing parameters and controlling surface metamorphic layer, ball end high-speed milling experiments of TC17 titanium alloy were carried out utilizing one of experimental design techniques based on the response surface methodology. The surface roughness prediction model was built, variance analyses were applied to check the significances of surface roughness model and input parameters, the effect of parameters on surface roughness was analyzed. Meanwhile, the residual stress, microhardness and microstructure under the condition of high, medium and low level of parameters were investigated. Results indicate that the model can predict the surface roughness effectively and feed per tooth and radial depth of cut have an obvious effect on surface roughness. Compressive residual stresses are detected on all milled surfaces and surface residual stresses are increased with the increase of the level of the milling parameters. The compressive residual stress layer is approximately 20 μm regardless of milling parameters level used. The process of thermal softening, then work hardening, and finally tending to stabilize are observed in the microhardness profiles. Grains of the surface layer are broken and bent, the thickness of plastic deformation layer is approximately 10 μm.

  10. 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.

  11. Engineering the metamorphic chemokine Lymphotactin/XCL1 into the GAG-binding, HIV-inhibitory dimer conformation

    OpenAIRE

    Fox, Jamie C.; Tyler, Robert C.; Guzzo, Christina; Tuinstra, Robbyn L.; Peterson, Francis C.; Lusso, Paolo; Volkman, Brian F.

    2015-01-01

    Unlike other chemokines, XCL1 undergoes a distinct metamorphic interconversion between a canonical monomeric chemokine fold and a unique β-sandwich dimer. The monomeric conformation binds and activates the receptor XCR1, while the dimer binds extracellular matrix glycosaminoglycans and has been associated with anti-human immunodeficiency virus (HIV) activity. Functional studies of WT-XCL1 are complex as both conformations are populated in solution. To overcome this limitation, we engineered a...

  12. Phosphate and feldspar mineralogy of equilibrated L chondrites: The record of metasomatism during metamorphism in ordinary chondrite parent bodies

    Science.gov (United States)

    Lewis, Jonathan A.; Jones, Rhian H.

    2016-10-01

    In ordinary chondrites (OCs), phosphates and feldspar are secondary minerals known to be the products of parent-body metamorphism. Both minerals provide evidence that metasomatic fluids played a role during metamorphism. We studied the petrology and chemistry of phosphates and feldspar in petrologic type 4-6 L chondrites, to examine the role of metasomatic fluids, and to compare metamorphic conditions across all three OC groups. Apatite in L chondrites is Cl-rich, similar to H chondrites, whereas apatite in LL chondrites has lower Cl/F ratios. Merrillite has similar compositions among the three chondrite groups. Feldspar in L chondrites shows a similar equilibration trend to LL chondrites, from a wide range of plagioclase compositions in petrologic type 4 to a homogeneous albitic composition in type 6. This contrasts with H chondrites which have homogeneous albitic plagioclase in petrologic types 4-6. Alkali- and halogen-rich and likely hydrous metasomatic fluids acted during prograde metamorphism on OC parent bodies, resulting in albitization reactions and development of phosphate minerals. Fluid compositions transitioned to a more anhydrous, Cl-rich composition after the asteroid began to cool. Differences in secondary minerals between H and L, LL chondrites can be explained by differences in fluid abundance, duration, or timing of fluid release. Phosphate minerals in the regolith breccia, Kendleton, show lithology-dependent apatite compositions. Bulk Cl/F ratios for OCs inferred from apatite compositions are higher than measured bulk chondrite values, suggesting that bulk F abundances are overestimated and that bulk Cl/F ratios in OCs are similar to CI.

  13. The first find of spinel peridotite in the Southern Kazakhstan: Structure, composition, and parameters of high-pressure metamorphism

    Science.gov (United States)

    Pilitsyna, A. V.; Tretyakov, A. A.; Alifirova, T. A.; Degtyarev, K. E.; Kovalchuk, E. V.

    2017-09-01

    Spinel peridotite, metamorphosed in high-pressure conditions, was first described within the Western part of the Central Asian Orogenic Belt. The spinel peridotite has the characteristics of Mg-Cr ultramafites indicating the mantle origin of its protolith. The preliminary estimation of the metamorphism peak for the model system MgO-Al2O3—SiO2-Cr2O3 (MASCr) is 10-19 kbar at 680-800°C.

  14. 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

  15. 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)

  16. Metamorphic chlorite and "vermiculitic" phases in mafic dikes from the Maláguide Complex (Betic Cordillera, Spain)

    Czech Academy of Sciences Publication Activity Database

    Ruiz Cruz, M. D.; Novák, Jiří Karel

    2003-01-01

    Roč. 15, č. 1 (2003), s. 1-14 ISSN 0935-1221 Grant - others:Ministerio de Educación y Cultura(ES) BTE-2000-1150; Research Group(ES) RNM-199 Institutional research plan: CEZ:AV0Z3013912 Keywords : low-grade metamorphism * vermiculite * Betic Cordillera Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.185, year: 2003

  17. 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)

  18. 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.

  19. 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...

  20. Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

    International Nuclear Information System (INIS)

    Rybalchenko, D. V.; Mintairov, S. A.; Salii, R. A.; Shvarts, M. Z.; Timoshina, N. Kh.; Kalyuzhnyy, N. A.

    2017-01-01

    Metamorphic Ga 0.76 In 0.24 As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In 0.24 Al 0.76 As/p-In 0.24 Ga 0.76 As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10 18 cm –3 and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.

  1. Unified Singularity Modeling and Reconfiguration of 3rTPS Metamorphic Parallel Mechanisms with Parallel Constraint Screws

    Directory of Open Access Journals (Sweden)

    Yufeng Zhuang

    2015-01-01

    Full Text Available This paper presents a unified singularity modeling and reconfiguration analysis of variable topologies of a class of metamorphic parallel mechanisms with parallel constraint screws. The new parallel mechanisms consist of three reconfigurable rTPS limbs that have two working phases stemming from the reconfigurable Hooke (rT joint. While one phase has full mobility, the other supplies a constraint force to the platform. Based on these, the platform constraint screw systems show that the new metamorphic parallel mechanisms have four topologies by altering the limb phases with mobility change among 1R2T (one rotation with two translations, 2R2T, and 3R2T and mobility 6. Geometric conditions of the mechanism design are investigated with some special topologies illustrated considering the limb arrangement. Following this and the actuation scheme analysis, a unified Jacobian matrix is formed using screw theory to include the change between geometric constraints and actuation constraints in the topology reconfiguration. Various singular configurations are identified by analyzing screw dependency in the Jacobian matrix. The work in this paper provides basis for singularity-free workspace analysis and optimal design of the class of metamorphic parallel mechanisms with parallel constraint screws which shows simple geometric constraints with potential simple kinematics and dynamics properties.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. The Sutter's Mill meteorite: Thermoluminescence data on thermal and metamorphic history

    Science.gov (United States)

    Sears, Derek W.; Beauford, Robert

    2014-11-01

    A piece of the Sutter's Mill meteorite, fragment SM2-1d, has been examined using thermoluminescence techniques to better understand its thermal and metamorphic history. The sample had very weak but easily measureable natural and induced thermoluminescence (TL) signals; the signal-to-noise ratio was better than 10. The natural TL was restricted to the high-temperature regions of the glow curve suggesting that the meteorite had been heated to approximately 300 °C within the time it takes for the TL signal to recover from a heating event, probably within the last 105 years. It is possible that this reflects heating during release from the parent body, close passage by the Sun, or heating during atmospheric passage. Of these three options, the least likely is the first, but the other possibilities are equally likely. It seems that temperatures of approximately 300 °C reached 5 or 6 mm into the meteorite, so that all but one of the small Sutter's Mill stones have been heated. The Dhajala normalized induced TL signal for SM2-1d is comparable to that of type 3.0 chondrites and is unlike normal CM chondrites, the class it most closely resembles, which do not have detectable TL sensitivity. The shape of the induced TL curve is comparable to other low-type ordinary, CV, and CO chondrites, in that it has a broad hummocky structure, but does not resemble any of them in detail. This suggests that Sutter's Mill is a unique, low-petrographic-type (3.0) chondrite.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. High-pressure granulites in the Fuping Complex of the central North China Craton: Metamorphic P-T-t evolution and tectonic implications

    Science.gov (United States)

    Qian, Jiahui; Yin, Changqing; Zhang, Jian; Ma, Li; Wang, Luojuan

    2018-04-01

    Mafic granulites in the Fuping Complex occur as lenses or boudins within high-grade TTG (Trondhjemite-Tonalite-Granodiorite) gneisses. Petrographic observations reveal four generations of mineral assemblage in the granulites: an inclusion assemblage of hornblende + plagioclase + ilmenite + quartz within garnet core; an inferred peak assemblage composed of garnet ± hornblende + plagioclase + clinopyroxene + rutile/ilmenite + quartz; a decompression assemblage characterized by symplectites of clinopyroxene ± orthopyroxene + plagioclase, coronae of plagioclase ± clinopyroxene ± hornblende around embayed garnet porphyroblasts or a two-pyroxene association; and a late amphibolite-facies retrogressive assemblage. Two representative samples were used for pseudosection modeling in NCFMASHTO model system to determine their metamorphic evolution. The results show that these granulites experienced a high-pressure stage of metamorphism with peak P-T conditions of 12-13 kbar and 760-800 °C (Pmax) and a post-peak history under P-T conditions of ∼9.0 kbar and 805-835 °C (Tmax), indicating a nearly isothermal decompression process (ITD) with a slight heating. Metamorphic evolution from the Pmax to the Tmax is predicted to be dominated by garnet breakdown through continuous metamorphic reactions of garnet + quartz ± diopside = hornblende + plagioclase + liquid and garnet + quartz + hornblende = plagioclase + diopside + liquid + orthopyroxene. Further metamorphic evolution after the Tmax is dominated by cooling, suggesting that high-pressure (HP) granulites may also exist in the Fuping Complex. Metamorphic zircons in the Fuping HP mafic granulites have left inclined REE patterns, Ti contents of 1.68-6.88 ppm and crystallization temperatures of 602-712 °C. SIMS zircon U-Pb dating on these zircons yields 207Pb/206Pb ages of 1891 ± 14 Ma and 1849 ± 6 Ma, interpreted to represent the cooling stage of metamorphism. The P-T-t evolution of the Fuping HP mafic granulites records

  1. 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

  2. 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.

  3. Dating an actively exhuming metamorphic core complex, the Suckling Dayman Massif in SE Papua New Guinea

    Science.gov (United States)

    Oesterle, J.; Seward, D.; Little, T.; Stockli, D. F.; Mizera, M.

    2016-12-01

    Low-temperature thermochronology is a powerful tool for revealing the thermal and kinematic evolution of metamorphic core complexes (MCCs). Most globally studied MCCs are ancient, partially eroded, and have been modified by deformation events that postdate their origin. The Mai'iu Fault is a rapidly slipping active low-angle normal fault (LANF) in the Woodlark Rift in Papua New Guinea that has exhumed a >25 km-wide (in the slip direction), and over 3 km-high domal fault surface in its footwall called the Suckling-Dayman massif. Some knowledge of the present-day thermal structure in the adjacent Woodlark Rift, and the pristine nature of this active MCC make it an ideal candidate for thermochronological study of a high finite-slip LANF. To constrain the thermal and kinematic evolution of this MCC we apply the U/Pb, fission-track (FT) and (U-Th)/He methods. Zircon U/Pb analyses from the syn-extensional Suckling Granite that intrudes the footwall of the MCC yield an intrusion age of 3.3 Ma. Preliminary zircon FT ages from the same body indicate cooling below 300 °C at 2.7 Ma. Ages decrease to 2.0 Ma with increasing proximity to the Mai'iu Fault and imply cooling controlled by tectonic exhumation. Almost coincident zircon U/Pb and FT ages from the nearby syn-extensional Mai'iu Monzonite, on the other hand, record extremely rapid cooling from magmatic temperatures to 300 °C at 2 Ma. As apparent from the preliminary He extraction stage, these syn-extensional plutons have young zircon and apatite (U-Th)/He ages. These initial results suggest that the Mai'iu Fault was initiated as an extensional structure by 3.3 Ma. We infer that it reactivated an older ophiolitic suture that had emplaced the Papuan Ultramafic body in the Paleogene. Rapid cooling of the Mai'iu Monzonite indicates that it was intruded into a part of the MCC's footwall that was already shallow in the crust by 2 Ma. This inference is further supported by the mineral andalusite occurring in the contact

  4. 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

  5. Possible giant metamorphic core complex at the center of Artemis Corona, Venus

    Science.gov (United States)

    Spencer, J.E.

    2001-01-01

    Hundreds of circular features on Venus known as coronae are characterized by annular fractures and commonly associated radial fractures and lava flows. Coronae are thought to have been produced by buoyant mantle diapirs that flatten and spread at the base of the lithosphere and cause fracturing, uplift, and magmatism. The interior of Artemis Corona, by far the largest corona at 2100 km diameter, is divided in half by a northeast-trending deformation belt that contains numerous rounded ridges resembling antiforms. The largest of these ridges, located at the center of Artemis Corona, is ???5 km high on its steep northwest flank where it is adjacent to a flat-bottomed, 10-km-wide trough interpreted as a rift valley. The 280-km-long antiformal ridge is marked by perpendicular grooves that cross the ???50-km-wide ridge and extend southeastward as far as 120 km across adjacent plains. The grooves abruptly terminate northwestward at the rift trough. The large antiformal ridge terminates southwestward at a transform shear zone that parallels the grooves. These features-rift valley, antiformal uplift, grooves, and transform shear zone-are morphologically and geometrically similar to grooved, elevated, submarine metamorphic core complexes on the inside corners of ridge-transform intersections of slow-spreading ridges on Earth. As with submarine core complexes, the grooved surface on Venus is interpreted as the footwall of a large-displacement normal fault, and the grooves are inferred to be the product of plastic molding of the footwall to irregularities on the underside of the hanging wall followed by tectonic exhumation of the molded grooves and conveyer-belt-like transport up and over the large antiform and across the southeastern plains. According to this interpretation, the trend of the grooves records the direction of extension, which is perpendicular to the thrusts at the leading edge of the annular thrust belt 1000 km to the southeast. Both may have formed at the

  6. Extreme metamorphism in a firn core from the Allan Hills, Antarctica, as an analogue for glacial conditions

    Science.gov (United States)

    Dadic, Ruzica; Schneebeli, Martin; Bertler, Nancy; Schwikowski, Margit; Matzl, Margret

    2015-04-01

    Understanding processes in near-zero accumulation areas can help to better understand the ranges of isotopic composition in ice cores, particularly during ice ages, when accumulation rates were lower than today. Snow metamorphism is a primary driver of the transition from snow to ice and can be accompanied by altered isotopic compositions and chemical species concentration. High degree snow metamorphism, which results in major structural changes, is little-studied but has been identified in certain places in Antarctica. Here we report on a 5-m firn core collected adjacent to a blue-ice field in the Allan Hills, Antarctica. We determined the physical properties of the snow using computer tomography (microCT) and measured the isotopic composition of δD and δ18O, as well as 210Pb activity. The core shows a high degree of snow metamorphism and an exponential decrease in specific surface area (SSA), but no clear densification, with depth. The micro-CT measurements show a homogenous and stable structure throughout the entire core, with obvious erosion features in the near-surface, where high-resolution data is available. The observed firn structure is likely caused by a combination of unique depositional and post-depositional processes. The defining depositional process is the impact deposition under high winds and with a high initial density. The defining post-depositional processes are a) increased moisture transport due to forced ventilation and high winds and b) decades of temperature-gradient driven metamorphic growth in the near surface due to prolonged exposure to seasonal temperature cycling. Both post-processes are enhanced in low accumulation regions where snow stays close to surface for a long time. We observe an irregular signal in δD and δ18O that does not follow the stratigraphic sequence. The isotopic signal is likely caused by the same post-depositional processes that are responsible for the firn structure, and that are driven by local climate

  7. 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

  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. 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

  10. The Heart of China revisited: II Early Paleozoic (ultra)high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage

    Science.gov (United States)

    Bader, Thomas; Franz, Leander; Ratschbacher, Lothar; de Capitani, Christian; Webb, A. Alexander G.; Yang, Zhao; Pfänder, Jörg A.; Hofmann, Mandy; Linnemann, Ulf

    2013-07-01

    Orogens with multiple (ultra)high-pressure ((U)HP) and (ultra)high-temperature ((U)HT) metamorphic events provide a complex but telling record of oceanic and continental interaction. The Early Paleozoic history of the "Heart of China," the Qinling orogenic collage, offers snapshots of at least three (U)HP and two (U)HT metamorphic events. The preservation of remnants of both oceanic and continental domains together with a ≥110 Myr record of magmatism allows the reconstruction of the processes that resulted in this disparate metamorphism. Herein, we first illuminate the pressure-temperature-time (P-T-t) evolution of the Early Paleozoic (U)HP and (U)HT events by refining the petrographic descriptions and P-T estimates, assess published, and employ new U/Th-Pb zircon, monazite, and titanite, and 40Ar-39Ar phengite geochronology to date the magmatic and metamorphic events. Then we explore how the metamorphic and magmatic events are related tectonically and how they elucidate the affinities among the various complexes in the Qinling orogenic collage. We argue that a Meso-Neoproterozoic crustal fragment—the Qinling complex—localized subduction-accretion events that involved subduction, oceanic-arc formation, and back-arc spreading along its northern margin, and mtantle-wedge exhumation and spreading-ridge subduction along its southern margin.

  11. Magnetotelluric investigation in and around southern part of Hidaka metamorphic belt in Hokkaido, Japan; Hidaka henseitai nanbuiki ni okeru MT kansoku

    Energy Technology Data Exchange (ETDEWEB)

    Sato, H.; Utsugi, M.; Hirano, K.; Doi, T.; Nishida, Y.; Arita, K. [Hokkaido University, Sapporo (Japan)

    1996-05-01

    An MT observation was conducted in the Hidaka district, Hokkaido, for the estimation of the 2D resistivity structure in the southern part of the metamorphic belt, when frequencies of the VLF, ELF, and ULF bands were used. An approximately 42km-long traverse line was set to cross the Hidaka metamorphic belt from east to west. As for the observation points, 48 VLF points, 16 ELF points, and 4 ULF points were provided. During the data processing, impedance tensor was calculated in the frequency domain for the determination of the apparent resistivity relative to frequency and the phase difference. As the result, it was found that there is a fairly large resistivity gap between observation spots MNS and KWR and that the boundary corresponds to the Hidaka metamorphic belt, that the metamorphic belt that is reflected as a conspicuous high-resistivity layer in the VLF-, ELF-MT slopes down toward the east and has a distribution as deep as 10km in the vicinity of observation point KWR, that this high-resistivity layer sandwiches a low-resistivity layer at a depth of 5-7km, and that on the east side of the metamorphic belt there is a medium-resistivity layer creeping under the belt from the east side toward the west side. 5 refs., 6 figs.

  12. Comparison of different pathways in metamorphic graded buffers on GaAs substrate: Indium incorporation with surface roughness

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Rahul, E-mail: rkp203@gmail.com [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Mukhopadhyay, P. [Rajendra Mishra School of Engineering Entrepreneurship, Indian Institute of Technology, Kharagpur 721302 (India); Bag, A.; Jana, S. Kr. [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Chakraborty, A. [Department of Electronics and Electrical Communication Engineering, Indian Institute of Technology, Kharagpur 721 302 (India); Das, S.; Mahata, M. Kr. [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Biswas, D. [Department of Electronics and Electrical Communication Engineering, Indian Institute of Technology, Kharagpur 721 302 (India)

    2015-01-01

    Highlights: • In(Al,Ga)As metamorphic buffers on GaAs have been grown. • Surface morphology, strain relaxation and compositional variation have been studied. • Al containing buffers shows inferior surface roughness. • Surface roughness modulates the indium incorporation rate. - Abstract: In this work, compositionally graded In(Al,Ga)As metamorphic buffers (MBs) on GaAs substrate have been grown by MBE through three different paths. A comparative study has been done to comprehend the effect of underlying MB on the constant composition InAlAs healing layer by analyzing the relaxation behaviour, composition and surface morphology of the grown structures. The compositional variation between the constant composition healing layers on top of graded MB has been observed in all three samples although the growth conditions have been kept same. Indium incorporation rate has been found to be dependent on underlying MB. By combining the result of atomic force microscopy, photo-luminescence and X-ray reciprocal space mapping, varying surface roughness has been proposed as the probable driving force behind different Indium incorporation rate.

  13. Comparison of different pathways in metamorphic graded buffers on GaAs substrate: Indium incorporation with surface roughness

    International Nuclear Information System (INIS)

    Kumar, Rahul; Mukhopadhyay, P.; Bag, A.; Jana, S. Kr.; Chakraborty, A.; Das, S.; Mahata, M. Kr.; Biswas, D.

    2015-01-01

    Highlights: • In(Al,Ga)As metamorphic buffers on GaAs have been grown. • Surface morphology, strain relaxation and compositional variation have been studied. • Al containing buffers shows inferior surface roughness. • Surface roughness modulates the indium incorporation rate. - Abstract: In this work, compositionally graded In(Al,Ga)As metamorphic buffers (MBs) on GaAs substrate have been grown by MBE through three different paths. A comparative study has been done to comprehend the effect of underlying MB on the constant composition InAlAs healing layer by analyzing the relaxation behaviour, composition and surface morphology of the grown structures. The compositional variation between the constant composition healing layers on top of graded MB has been observed in all three samples although the growth conditions have been kept same. Indium incorporation rate has been found to be dependent on underlying MB. By combining the result of atomic force microscopy, photo-luminescence and X-ray reciprocal space mapping, varying surface roughness has been proposed as the probable driving force behind different Indium incorporation rate

  14. Deep levels in metamorphic InAs/InGaAs quantum dot structures with different composition of the embedding layers

    Science.gov (United States)

    Golovynskyi, S.; Datsenko, O.; Seravalli, L.; Kozak, O.; Trevisi, G.; Frigeri, P.; Babichuk, I. S.; Golovynska, I.; Qu, Junle

    2017-12-01

    Deep levels in metamorphic InAs/In x Ga1-x As quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x = 0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.

  15. Body size and reproductive characteristics of paedomorphic and metamorphic individuals of the northern banded newt (Ommatotriton ophryticus

    Directory of Open Access Journals (Sweden)

    Eyup BAŞKALE

    2011-06-01

    Full Text Available

    Paedomorphs and metamorphs of the northern banded newt (Ommatotriton ophryticus were compared with respect to body size and some reproductive traits. Both morphs have a similar reproduction pathway in terms of egg number and incubation period, while hatching success and egg diameter appear to be different between morphs. This is most likely due to differences in female body size (paedomorphic females are smaller than metamorphic individuals of the same sex.

  16. 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.

  17. 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.

  18. 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

  19. 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).

  20. 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

  1. 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.

  2. 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

  3. Behavior of zircon in the upper-amphibolite to granulite facies schist/migmatite transition, Ryoke metamorphic belt, SW Japan: constraints from the melt inclusions in zircon

    OpenAIRE

    Kawakami, Tetsuo; Yamaguchi, Isao; Miyake, Akira; Shibata, Tomoyuki; Maki, Kenshi; Yokoyama, Takaomi D.; Hirata, Takafumi

    2013-01-01

    Behavior of zircon at the schist/migmatite transition is investigated. Syn-metamorphic overgrowth is rare in zircon in schists, whereas zircon in migmatites has rims with low Th/U that give 90.3 ± 2.2 Ma U–Pb concordia age. Between inherited core and the metamorphic rim, a thin, dark-CL annulus containing melt inclusion is commonly developed, suggesting that it formed contemporaneous with the rim in the presence of melt. In diatexites, the annulus is further truncated by the brighter-CL overg...

  4. K-Ar dating celadonite: A contribution to timing of a very low-grade metamorphism in the Central Andes of Chile

    International Nuclear Information System (INIS)

    Belmar, M; Schmidt, S.; Frey, M

    2001-01-01

    Clay minerals have been used in several studies to date very low-grade metamorphism processes and hydrothermal episodes. The technique of using the K-Ar isotopic dating was demonstrated by many authors (e.g. Hunziker et al., 1986; Clauer et al., 1995; Kirschner et al 1995; Zhao et al., 1997; Glasmacher et al., 2001). White mica and illitic materials of different size are usually analysed, whereasceladonite mineral with high potassium content has been low developed and few data are published. Successful dating of continental Andean celadonite could mean that is possible to date the very low-grade metamorphism (zeolites facies) in which celadonites are very often observed (au)

  5. 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

  6. 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

  7. Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France)

    Science.gov (United States)

    Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jérémie; Li, Xian-Hua; Lin, Wei; Blein, Olivier; Bruguier, Olivier; Poujol, Marc

    2018-02-01

    A structural and petrochronological study was carried out in the southern part of the Belledonne crystalline massif. A first tectonometamorphic event, Dx, corresponds to the eastward thrusting of the Chamrousse ophiolitic complex characterized by a low-temperature-moderate-pressure metamorphism reaching 0.535 ± 0.045 GPa and 427.5 ± 17.5 °C. A subsequent D1 deformation is defined by a penetrative S1 foliation that mostly dips toward the west and displays an E-W- to NE-SW-trending mineral and stretching lineation L1. D1 is associated with a top-to-the east shearing and is responsible for the crustal thickening accommodated by the eastward nappe stacking and the emplacement of the Chamrousse ophiolitic complex upon the Rioupéroux-Livet unit. This event is characterized by an amphibolite facies metamorphism (0.58 GPa ± 0.06; 608 ± 14 °C) that attains partial melting at the base of the nappe pile (0.78 ± 0.07 GPa; 680.5 ± 11.5 °C). LA-ICP-MS U-Pb dating of monazite grains from the mica schists of the Rioupéroux-Livet unit constrain the age of D1 to 337 ± 7 Ma. The D2 tectono-metamorphic event is characterized by NE-SW trending, upright to NE-verging synfolial folding. Folding associated with D2 is pervasively developed in all lithotectonic units with the development of a steeply-dipping S2 foliation. In particular, D2 involves the uppermost weakly metamorphosed Taillefer unit. LA-ICP-MS U-Pb dating performed on detrital zircon grains shows that the Taillefer conglomerates was deposited during the Visean. A zircon SIMS U-Pb age of 352 ± 1 Ma from a plagioglase-rich leucocratic sill of the Rioupéroux-Livet unit is interpreted as the age of magmatic emplacement. Our results suggest that the D2 event took place between 330 Ma and 310 Ma. We propose a new interpretation of the tectonometamorphic evolution of the southern part of the Belledonne massif, focusing on the Middle Carboniferous stages of the Variscan orogeny.

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. Physiological effects and cellular responses of metamorphic larvae and juveniles of sea urchin exposed to ionic and nanoparticulate silver.

    Science.gov (United States)

    Magesky, Adriano; Ribeiro, Ciro A Oliveiro; Pelletier, Émilien

    2016-05-01

    The widespread use of silver nanoparticles (AgNPs) would likely result in their discharge into wastewater and inevitable release in densely populated coastal areas. It is known that AgNPs can cause harmful effects to marine fauna, but how they affect development stages is still an open question. In order to understand in details how polymer-coated AgNPs (PAAm-AgNPs) (from 0.19 to 4.64mM as Ag) can affect critical stages of marine invertebrate development, metamorphic larvae and juveniles of sea urchins were used as biological models. Multidimensional scaling (MDS) approach based on Bray-Curtis similarity matrix with PERMANOVA showed organisms in a multivariate space undergoing through different physiological conditions as a function of time, chemical forms of silver, nominal concentrations, and presence or absence of food. Sublethal effects such as lethargy, oedema and immobility mainly characterized PAAm-AgNPs effects with juveniles and postlarvae, whereas necrosis and death arose in Ag(+) conditions in short-term tests. Chronically exposed metamorphic larvae had their morphogenic processes interrupted by PAAm-AgNPs and a high mortality rate was observed in recovery period. On the contrary, Ag(+) ions caused progressive mortality during exposure, but a quick recovery in uncontaminated seawater was observed. By means of fluorescent markers we showed that nanosilver could be transferred between consecutive stages (swimming larvae and postlarvae) and highlighted how important is food to enhance PAAm-AgNPs uptake. Using TEM we observed that unfed juveniles had nanosilver aggregates mostly restricted to their coelomic sinuses, while metamorphic larvae already had nano-contamination overspread in different tissues and blastocoel. Our main hypothesis for nanotoxicity of PAAM-AgNPs relies on the slow dissolution of nano-core over time, but in this study the effects of particulate silver form itself are also evoked. Main mechanisms governing tissular and cellular responses

  14. Pseudo- and real-inverted metamorphism caused by the superposition and extrusion of a stack of nappes: a case study of the Southern Brasília Orogen, Brazil

    Science.gov (United States)

    da Motta, Rafael Gonçalves; Moraes, Renato

    2017-10-01

    The Southern Brasília Orogen is a Neoproterozoic belt that occurs along the southernmost border of the São Francisco Craton where the Andrelândia Nappe System represents the subducted sedimentary domain and is divided into three allochthonous groups, of which the ages and P-T conditions of metamorphism are studied here. The basal unit, the Andrelândia Nappe, exhibits an inverted metamorphic pattern. The base of the structure, composed of staurolite, garnet, biotite, kyanite, quartz, and muscovite, marks the metamorphic peak, whereas at the top, the association of the metamorphic peak does not contain staurolite. The Liberdade Nappe, the middle unit, presents a normal metamorphic pattern; its base, close to the Andrelândia Nappe, shows paragneiss with evidence of in situ partial melting, and towards the top, coarse-grained staurolite schist is found. The staurolite-out and melt-in isograds are coincident and parallel to the main foliation. Thus, the shear zone that limits the nappes is syn-metamorphic, reheating the underlying Andrelândia Nappe and influencing the establishment of metamorphic inversion. This suggestion is supported by the monazite chemical ages, which indicates that the Andrelândia Nappe metamorphic peak (586 ± 15 Ma) is younger than that of the Liberdade Nappe (622.3 ± 7.6 Ma). The upper unit, the Serra da Natureza Klippe, bears a typical high-pressure granulite mineral assemblage that is composed of kyanite, garnet, K-feldspar, rutile, and leucosome, as well as a metamorphic peak at 604.5 ± 6.1 Ma. This tectonic assembly, with inverted and non-inverted metamorphic patterns and generation of klippen structures, is consistent with exhumation models and a strong indentor located in the lower continental crust.

  15. 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

    The term turtleback was first coined to describe the curvilinear fault surfaces that produced a distinctive geomorphic form in the Black Mountains east of Death Valley, and although it was decades before their full significance was appreciated, they remain one of the most distinctive features of the extensional structure of the Death Valley region. Historically the interpretation of the features has varied markedly, and misconceptions about their character continue to abound, including descriptions in popular field guides for the area. It the 1990's, however, the full history of the systems began to be apparent from several key data: 1) the dating of the plutonic assemblage associated with the turtlebacks demonstrated that late Miocene, syn-extensional plutonism was fundamental to their formation; 2) the plutonic assemblage forms an intrusive sheet structurally above the turtlebacks, indicating a tie between much of the high grade metamorphism and Cenozoic plutonism; 3) a modern analog for the syn-extensional plutonism in the Black Mountains was recognized beneath Death Valley with the imaging of a mid-crustal magma body; 4) the Neogene structural history was worked out in the turtlebacks showing that folding of early-formed shear zones formed the turtleback anticlinoria but overprinting by brittle faults produced the final form as they cut obliquely across the older structure; and 5) the pre-extensional structural history was clarified, demonstrating that Mesozoic basement-involved thrust systems are present within the turtlebacks, but have been overprinted by the extensional system. An unresolved issue is the significance of Eocene U-Pb dates for pegmatites within the region, but presumably these relate somehow to the pre-extensional history. Miller and Pavlis (2005; E. Sci. Rev.) reviewed many features of the turtlebacks, and our working model for the region is that the turtlebacks originated as mid-crustal ductile-thrust systems within the Cordilleran fold

  16. 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

  17. 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

  18. Temperature dependence of ballistic mobility in a metamorphic InGaAs/InAlAs high electron mobility transistor

    International Nuclear Information System (INIS)

    Lee, Jongkyong; Gang, Suhyun; Jo, Yongcheol; Kim, Jongmin; Woo, Hyeonseok; Han, Jaeseok; Kim, Hyungsang; Im, Hyunsik

    2014-01-01

    We have investigated the temperature dependence of ballistic mobility in a 100 nm-long InGaAs/InAlAs metamorphic high-electron-mobility transistor designed for millimeter-wavelength RF applications. To extract the temperature dependence of quasi-ballistic mobility, our experiment involves measurements of the effective mobility in the low-bias linear region of the transistor and of the collision-dominated Hall mobility using a gated Hall bar of the same epitaxial structure. The data measured from the experiment are consistent with that of modeled ballistic mobility based on ballistic transport theory. These results advance the understanding of ballistic transport in various transistors with a nano-scale channel length that is comparable to the carrier's mean free path in the channel.

  19. 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

  20. Evidence of contrasting low-grade metamorphic conditons from clay mineral assablages in Triassic Alpujárride-Maláguide transtional units in the Betic Cordilleras, Spain

    Czech Academy of Sciences Publication Activity Database

    Ruiz Cruz, M. D.; Franco, F.; Sanz de Galdeano, C.; Novák, Jiří Karel

    2006-01-01

    Roč. 41, 2 (2006), s. 621-638 ISSN 0009-8558 Institutional research plan: CEZ:AV0Z30130516 Keywords : low- grade metamorphism * clay minerals * Betic Cordilleras Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.974, year: 2006

  1. 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.)

  2. Evidence for diamond-grade ultra-high pressure metamorphism and fluid interaction in the Swartberget Fe-Ti garnet periodotite-websterite body, Western Gneiss Region, Norway

    NARCIS (Netherlands)

    Vrijmoed, J.C.; Van Roermund, H.L.M.; Davies, G.R.

    2006-01-01

    Based on mineral-chemical evidence we propose that the northernmost Scandian ultra-high pressure (UHP) metamorphic domain within the Western Gneiss Region of Norway can be extended 25 km northeastwards. A newly discovered, well preserved, fine-grained, Fe-Ti type garnet peridotite body at

  3. 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.

  4. The multi-stage tectonic evolution of the Xitieshan terrane, North Qaidam orogen, western China : From Grenville-age orogeny to early-Paleozoic ultrahigh-pressure metamorphism

    NARCIS (Netherlands)

    Zhang, Cong; Bader, Thomas; Zhang, Lifei; van Roermund, Herman

    The geodynamic evolution of the early Paleozoic ultrahigh-pressure metamorphic belt in North Qaidam, western China, is controversial due to ambiguous interpretations concerning the nature and ages of the eclogitic protoliths. Within this framework, we present new LA-ICP-MS U-Pb zircon ages from

  5. High-pressure metamorphism in the Aegean, eastern Mediterranean: Underplating and exhumation from the Late Cretaceous until the Miocene to Recent above the retreating Hellenic subduction zone

    Science.gov (United States)

    Ring, Uwe; Layer, Paul W.

    2003-06-01

    We report 40Ar/39Ar ages from various tectonic units in the Aegean and westernmost Turkey. On the basis of published geochronologic data and our 40Ar/39Ar ages we propose that the Aegean is made up of several high-pressure units, which were successively underplated from the Late Cretaceous until the Miocene. Ages for high-pressure metamorphism range from 80-83 Ma in parts of the Vardar-Izmir-Ankara suture zone in the north to 21-24 Ma for the Basal unit in the Cyclades and the external high-pressure belt on Crete in the south. Published seismic data suggest that high-pressure metamorphism is currently occurring underneath Crete. Younging of high-pressure metamorphism in a southerly direction mimics the southward retreat of the Hellenic subduction zone. We propose that distinct stages of high-pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat. By far most of the exhumation of the high-pressure units occurred early during the orogenic history in a forearc position.

  6. 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.

  7. 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)

  8. 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.

  9. 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

  10. Design of InP-based metamorphic high-efficiency five-junction solar cells for concentrated photovoltaics

    International Nuclear Information System (INIS)

    Huang, Yong; Yang, Hui

    2015-01-01

    We propose an InP-based upright five-junction (5J) solar cell structure for high conversion efficiency under concentration. In the structure, three bottom subcells are composed of lattice-matched (LM) InGaAsP materials, while two top subcells employ metamorphic InGaP materials. The two InGaP subcells are designed to have the same Ga composition of 30%. The first InGaP subcell is thinned so as to transmit half of the photon flux to the second InGaP subcell, thus forming an upright 5J InGaP(1.64 eV)/InGaP(1.64 eV)/InGaAsP(1.3 eV)/InGaAsP(1.02 eV)/InGaAs(0.74 eV) solar cell structure on the InP substrate. The subcell bandgap energies are chosen in such a way that a current matching condition can be achieved. Because no Al- or N-contained materials are used in the absorbers and only one metamorphic growth is required (with a lattice mismatch of 2.1%), the novel InP-based solar cell architecture is considered practically achievable with current growth technology. By comparing it with a InGaP/GaAs/Ge reference cell and adding additional nonideal factors in the modeling, an efficiency as high as 46.2% is estimated under concentration at ∼1500 suns. (paper)

  11. Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jheng-Sin; Clavel, Michael B.; Hudait, Mantu K., E-mail: mantu.hudait@vt.edu [Advanced Devices and Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States); Pandey, Rahul [Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Datta, Suman [Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Meeker, Michael; Khodaparast, Giti A. [Department of Physics, Virginia Tech, Blacksburg, Virginia 24061 (United States)

    2016-06-28

    The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current–voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77 K and 290 K demonstrated two bias-dependent transport mechanisms. The Shockley–Read–Hall generation–recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications.

  12. Design of InP-based metamorphic high-efficiency five-junction solar cells for concentrated photovoltaics

    Science.gov (United States)

    Huang, Yong; Yang, Hui

    2015-10-01

    We propose an InP-based upright five-junction (5J) solar cell structure for high conversion efficiency under concentration. In the structure, three bottom subcells are composed of lattice-matched (LM) InGaAsP materials, while two top subcells employ metamorphic InGaP materials. The two InGaP subcells are designed to have the same Ga composition of 30%. The first InGaP subcell is thinned so as to transmit half of the photon flux to the second InGaP subcell, thus forming an upright 5J InGaP(1.64 eV)/InGaP(1.64 eV)/InGaAsP(1.3 eV)/InGaAsP(1.02 eV)/InGaAs(0.74 eV) solar cell structure on the InP substrate. The subcell bandgap energies are chosen in such a way that a current matching condition can be achieved. Because no Al- or N-contained materials are used in the absorbers and only one metamorphic growth is required (with a lattice mismatch of 2.1%), the novel InP-based solar cell architecture is considered practically achievable with current growth technology. By comparing it with a InGaP/GaAs/Ge reference cell and adding additional nonideal factors in the modeling, an efficiency as high as 46.2% is estimated under concentration at ˜1500 suns.

  13. Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

    Science.gov (United States)

    Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

    2018-02-01

    This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems {010} and {110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system {001} and rotation axis [010]. The slip system {110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of

  14. 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

  15. 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

  16. U-Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism

    Science.gov (United States)

    Zhang, R.Y.; Yang, J.S.; Wooden, J.L.; Liou, J.G.; Li, T.F.

    2005-01-01

    We studied the Zhimafang ultrahigh-pressure metamorphic (UHP) peridotite from pre-pilot drill hole PP-1 of Chinese Continental Scientific Drilling project in the Sulu UHP terrane, eastern China. The peridotite occurs as lens within quartofeldspathic gneiss, and has an assemblage of Ol + Opx + Cpx + Phl + Ti-clinohumite (Ti-Chu) + Grt (or chromite) ?? magnesite (Mgs). Zircons were separated from cores at depths of 152 m (C24, garnet lhezolite), 160 m (C27, strongly retrograded phlogopite-rich peridotite) and 225 m (C50, banded peridotite), and were dated by SHRIMP mass spectrometer. Isometric zircons without inherited cores contain inclusions of olivine (Fo91-92), enstatite (En91-92), Ti-clinohumite, diopside, phlogopite and apatite. The enstatite inclusions have low Al2O3 contents of only 0.04-0.13 wt.%, indicating a UHP metamorphic origin. The weighted mean 206Pb/238U zircon age for garnet lherzolite (C24) is 221 ?? 3 Ma, and a discordia lower intercept age for peridotite (C50) is 220 ?? 2 Ma. These ages are within error and represent the time of subduction-zone UHP metamorphism. A younger lower intercept age of 212 ?? 3 Ma for a foliated wehrlite (C27) was probably caused by Pb loss during retrograde metamorphism. The source of zirconium may be partially attributed to melt/fluid metasomatism within the mantle wedge. Geochronological and geochemical data confirm that the mantle-derived Zhimafang garnet peridotites (probably the most representative type of Sulu garnet peridotites) were tectonically inserted into a subducting crustal slab and subjected to in situ Triassic subduction-zone UHP metamorphism. ?? 2005 Elsevier B.V. All rights reserved.

  17. 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

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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

  3. 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

  4. LA-ICP-MS trace element mapping: insights into the crystallisation history of a metamorphic garnet population

    Science.gov (United States)

    George, Freya; Gaidies, Fred

    2017-04-01

    In comparison to our understanding of major element zoning, relatively little is known about the incorporation of trace elements into metamorphic garnet. Given their extremely slow diffusivities and sensitivity to changing mineral assemblages, the analysis of the distribution of trace elements in garnet has the potential to yield a wealth of information pertaining to interfacial attachment mechanisms during garnet crystallisation, the mobility of trace elements in both garnet and the matrix, and trace element geochronology. Due to advances in the spatial resolution and analytical precision of modern microbeam techniques, small-scale trace element variations can increasingly be documented and used to inform models of metamorphic crystallisation. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in particular, can be used to rapidly quantify a wide range of elemental masses as a series of laser rasters, producing large volumes of spatially constrained trace element data. In this study, we present LA-ICP-MS maps of trace element concentrations from numerous centrally-sectioned garnets representative of the crystal size-distribution of a single sample's population. The study sample originates from the garnet-grade Barrovian zone of the Lesser Himalayan Sequence in Sikkim, northeast India, and has been shown to have crystallised garnet within a single assemblage between 515 ˚C and 565˚C, with no evidence for accessory phase reaction over the duration of garnet growth. Previous models have indicated that the duration of garnet crystallisation was extremely rapid (growth. In spite of straightforward (i.e. concentrically-zoned) major element garnet zonation, trace elements maps are characterised by significant complexity and variability. Y and the heavy rare earth elements are strongly enriched in crystal cores, where there is overprinting of the observed internal fabric, and exhibit numerous concentric annuli towards crystal rims. Conversely, the

  5. 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

  6. 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

  7. 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.)

  8. Tectono-metamorphic evolution of a hot orogen during Gondwanaland assembly: a case study from Palni hills metapelite granulite, south India

    Science.gov (United States)

    Bhadra, S.; Nasipuri, P.

    2012-04-01

    This study deals with the tectono-metamorphic evolution of Sapphirine-cordierite-bearing metapelite granulite at Perumalmalai, south India, that occurs as enclave within deformed migmatitic enderbite gneiss of Kodaikanal massif, Madurai granulite block (MB), south India. Pre-peak mineral paragenesis is represented by an inclusion assemblage of sillimanite + plagioclase + Ti-rich biotite ±quartz in Al-rich orthopyroxene. Dehydration melting of biotite marked the onset of ultra-high temperature metamorphism (M1A, ~1000 °C, 10 Kbar). Early stage of retrograde metamorphism (M1B) is characterized by the development of type1-symplectite and corona textures. In type1-symplectite an innermost vermicular sapphirine (Spr - XMg: 0.90, Al/Si: 6.17) - cordierite (Crd) symplectite on sillimanite is followed by cordierite (XMg: 0.94) moat. A meso-perthitic layer laced the interface between cordierite moat and orthopyroxene porphyroblast, the latter showing prominent rim-ward decrease in Al2O3 (up to 3 wt%). The cordierite rim at the interface between sillimanite and orthopyroxene characterizes corona texture. Type1-symplectite and corona domains are circumnavigated by Ti-poor biotite (TiO2: ~3.2 wt%) showing shape preferred alignment, and set in a feldspar matrix showing wide compositional range. By implication, leucosome crystallization was possibly prolonged and enhanced by deformation. Type1-symplectite and corona textures were resulted from melt-solid interaction or silica-metasomatism during early stage of retrogression, Opx+Sil = Spr+Crd → Opx+Sil+melt = Crd. The retrograde metamorphism is constrained at 9 kbar and 950°C, implying an early stage of near-isothermal decompression. Late stage retrograde metamorphism (M2) is also characterized by symplectite textures, type2-symplectite, with innermost sapphirine-cordierite symplectite followed by cordierite corona. Sapphirine in type2-symplectite domain (XMg: 0.89; Al/Si: 5.92), which occurs as inclusion in Opx, is

  9. 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

  10. Behaviour of uranium during late-Hercynian and alpine metamorphisms in the Aiguilles rouges and Belledonne (Valorcine, Lauziere) massifs. Western Alps

    International Nuclear Information System (INIS)

    Negga, H.S.

    1984-01-01

    The purpose of this research thesis is to define the origin of numerous uranium anomalies in the external crystalline Alpine massifs, more precisely the massif of the Aiguilles Rouges and the massif of Belledonne. The primary cause of uranium mineralization in the first massif appears to have been the retrograde metamorphism events of the late-Hercynian age. In the second massif, the same conditions of uranium mineralization appear to have been realised, but with a much higher calcium activity in the fluids. After having explained the choice of the selected areas, the sampling and the chemical analysis performed, the author describes the geological and structural framework of Western Alps: geological history of the paleozoic platform, regional geology of the studied massifs. The next part reports the petrographic and geochemical study, the analysis of the mineral chemistry, of the alteration and the metamorphism. Then the author describes the geochemistry of uranium and thorium within the studied structures

  11. Threading Dislocations in InGaAs/GaAs (001) Buffer Layers for Metamorphic High Electron Mobility Transistors

    Science.gov (United States)

    Song, Yifei; Kujofsa, Tedi; Ayers, John E.

    2018-03-01

    In order to evaluate various buffer layers for metamorphic devices, threading dislocation densities have been calculated for uniform composition In x Ga1-x As device layers deposited on GaAs (001) substrates with an intermediate graded buffer layer using the L MD model, where L MD is the average length of misfit dislocations. On this basis, we compare the relative effectiveness of buffer layers with linear, exponential, and S-graded compositional profiles. In the case of a 2 μm thick buffer layer linear grading results in higher threading dislocation densities in the device layer compared to either exponential or S-grading. When exponential grading is used, lower threading dislocation densities are obtained with a smaller length constant. In the S-graded case, lower threading dislocation densities result when a smaller standard deviation parameter is used. As the buffer layer thickness is decreased from 2 μm to 0.1 μm all of the above effects are diminished, and the absolute threading dislocation densities increase.

  12. 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

  13. 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

  14. Engineering Metamorphic Chemokine Lymphotactin/XCL1 into the GAG-Binding, HIV-Inhibitory Dimer Conformation.

    Science.gov (United States)

    Fox, Jamie C; Tyler, Robert C; Guzzo, Christina; Tuinstra, Robbyn L; Peterson, Francis C; Lusso, Paolo; Volkman, Brian F

    2015-11-20

    Unlike other chemokines, XCL1 undergoes a distinct metamorphic interconversion between a canonical monomeric chemokine fold and a unique β-sandwich dimer. The monomeric conformation binds and activates the receptor XCR1, whereas the dimer binds extracellular matrix glycosaminoglycans and has been associated with anti-human immunodeficiency virus (HIV) activity. Functional studies of WT-XCL1 are complex, as both conformations are populated in solution. To overcome this limitation, we engineered a stabilized dimeric variant of XCL1 designated CC5. This variant features a new disulfide bond (A36C-A49C) that prevents structural interconversion by locking the chemokine into the β-sandwich dimeric conformation, as demonstrated by NMR structural analysis and hydrogen/deuterium exchange experiments. Functional studies analyzing glycosaminoglycan binding demonstrate that CC5 binds with high affinity to heparin. In addition, CC5 exhibits potent inhibition of HIV-1 activity in primary peripheral blood mononuclear cells (PBMCs), demonstrating the importance of the dimer in blocking viral infection. Conformational variants like CC5 are valuable tools for elucidating the biological relevance of the XCL1 native-state interconversion and will assist in future antiviral and functional studies.

  15. Larval exposure to predator cues alters immune function and response to a fungal pathogen in post-metamorphic wood frogs.

    Science.gov (United States)

    Groner, Maya L; Buck, Julia C; Gervasi, Stephanie; Blaustein, Andrew R; Reinert, Laura K; Rollins-Smith, Louise A; Bier, Mark E; Hempel, John; Relyea, Rick A

    2013-09-01

    For the past several decades, amphibian populations have been decreasing around the globe at an unprecedented rate. Batrachochytrium dendrobatidis (Bd), the fungal pathogen that causes chytridiomycosis in amphibians, is contributing to amphibian declines. Natural and anthropogenic environmental factors are hypothesized to contribute to these declines by reducing the immunocompetence of amphibian hosts, making them more susceptible to infection. Antimicrobial peptides (AMPs) produced in the granular glands of a frog's skin are thought to be a key defense against Bd infection. These peptides may be a critical immune defense during metamorphosis because many acquired immune functions are suppressed during this time. To test if stressors alter AMP production and survival of frogs exposed to Bd, we exposed wood frog (Lithobates sylvaticus) tadpoles to the presence or absence of dragonfly predator cues crossed with a single exposure to three nominal concentrations of the insecticide malathion (0, 10, or 100 parts per billion [ppb]). We then exposed a subset of post-metamorphic frogs to the presence or absence of Bd zoospores and measured frog survival. Although predator cues and malathion had no effect on survival or size at metamorphosis, predator cues increased the time to metamorphosis by 1.5 days and caused a trend of a 20% decrease in hydrophobic skin peptides. Despite this decrease in peptides determined shortly after metamorphosis, previous exposure to predator cues increased survival in both Bd-exposed and unexposed frogs several weeks after metamorphosis. These results suggest that exposing tadpoles to predator cues confers fitness benefits later in life.

  16. 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

    The term turtleback was first coined to describe the curvilinear fault surfaces that produced a distinctive geomorphic form in the Black Mountains east of Death Valley, and although it was decades before their full significance was appreciated, they remain one of the most distinctive features of the extensional structure of the Death Valley region. Historically the interpretation of the features has varied markedly, and misconceptions about their character continue to abound, including descriptions in popular field guides for the area. It the 1990's, however, the full history of the systems began to be apparent from several key data: 1) the dating of the plutonic assemblage associated with the turtlebacks demonstrated that late Miocene, syn-extensional plutonism was fundamental to their formation; 2) the plutonic assemblage forms an intrusive sheet structurally above the turtlebacks, indicating a tie between much of the high grade metamorphism and Cenozoic plutonism; 3) a modern analog for the syn-extensional plutonism in the Black Mountains was recognized beneath Death Valley with the imaging of a mid-crustal magma body; 4) the Neogene structural history was worked out in the turtlebacks showing that folding of early-formed shear zones formed the turtleback anticlinoria but overprinting by brittle faults produced the final form as they cut obliquely across the older structure; and 5) the pre-extensional structural history was clarified, demonstrating that Mesozoic basement-involved thrust systems are present within the turtlebacks, but have been overprinted by the extensional system. An unresolved issue is the significance of Eocene U-Pb dates for pegmatites within the region, but presumably these relate somehow to the pre-extensional history. Miller and Pavlis (2005; E. Sci. Rev.) reviewed many features of the turtlebacks, and our working model for the region is that the turtlebacks originated as mid-crustal ductile-thrust systems within the Cordilleran fold

  17. 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

  18. The interacting effects of ungulate hoofprints and predatory native ants on metamorph cane toads in tropical Australia.

    Science.gov (United States)

    Cabrera-Guzmán, Elisa; Crossland, Michael R; González-Bernal, Edna; Shine, Richard

    2013-01-01

    Many invasive species exploit the disturbed habitats created by human activities. Understanding the effects of habitat disturbance on invasion success, and how disturbance interacts with other factors (such as biotic resistance to the invaders from the native fauna) may suggest new ways to reduce invader viability. In tropical Australia, commercial livestock production can facilitate invasion by the cane toad (Rhinella marina), because hoofprints left by cattle and horses around waterbody margins provide distinctive (cool, moist) microhabitats; nevertheless the same microhabitat can inhibit the success of cane toads by increasing the risks of predation or drowning. Metamorph cane toads actively select hoofprints as retreat-sites to escape dangerous thermal and hydric conditions in the surrounding landscape. However, hoofprint geometry is important: in hoofprints with steep sides the young toads are more likely to be attacked by predatory ants (Iridomyrmex reburrus) and are more likely to drown following heavy rain. Thus, anthropogenic changes to the landscape interact with predation by native taxa to affect the ability of cane toads in this vulnerable life-history stage to thrive in the harsh abiotic conditions of tropical Australia.

  19. The interacting effects of ungulate hoofprints and predatory native ants on metamorph cane toads in tropical Australia.

    Directory of Open Access Journals (Sweden)

    Elisa Cabrera-Guzmán

    Full Text Available Many invasive species exploit the disturbed habitats created by human activities. Understanding the effects of habitat disturbance on invasion success, and how disturbance interacts with other factors (such as biotic resistance to the invaders from the native fauna may suggest new ways to reduce invader viability. In tropical Australia, commercial livestock production can facilitate invasion by the cane toad (Rhinella marina, because hoofprints left by cattle and horses around waterbody margins provide distinctive (cool, moist microhabitats; nevertheless the same microhabitat can inhibit the success of cane toads by increasing the risks of predation or drowning. Metamorph cane toads actively select hoofprints as retreat-sites to escape dangerous thermal and hydric conditions in the surrounding landscape. However, hoofprint geometry is important: in hoofprints with steep sides the young toads are more likely to be attacked by predatory ants (Iridomyrmex reburrus and are more likely to drown following heavy rain. Thus, anthropogenic changes to the landscape interact with predation by native taxa to affect the ability of cane toads in this vulnerable life-history stage to thrive in the harsh abiotic conditions of tropical Australia.

  20. 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.

  1. A transamazonic age for magmatism, metamorphism and deformation on the northern limit of Jequie nucleous (Itaberaba, Bahia, Brazil)

    International Nuclear Information System (INIS)

    Fernandes, P.C.D.; Mcreath, I.; Lafon, J.M.

    1990-01-01

    A Rb/Sr isochron of 2154 ± 20 M.y., with Ro = 0,705 ± (MSWD=2,85) has been obtained for the Itaberaba and Pedra d'Agua granites, located on the northern limit between the Archean Jequie cratonic nucleous and the Early Proterozoic Salvador - Curaca mobile belt. The age so obtained dates peraluminous magmatism and Molybdenum mineralization, anatexis and granulite facies metamorphism, besides a N-S deformation phase (Fn+1). The Itaberaba and Pedra d'Agua massifs are the most important bodies in a context of extensive granite emplacement. A number of small granitic bodies can be found over the area. One of these dykes is emplaced in migmatitic kinzigites and has been dated along with the massifs above. It has shown itself to be the same age as those ones. Mingling between the dyke magma and anatectic leucosomes from the kinzigites has allowed dating anatexis in the migmatites. Crustal recycling processes have been involved in the generation of these granites, as suggested by petrographical/chemical features and high isotopic initial ratio. The age of the geological phenomena here described characterizes the area as a transitional interface between two tectonic blocks, helps typifying Early Proterozoic magmatism and metallogenesis in Central Bahia State and opens the discussion on the validity of 2,450 M. y. ages obtained previously. (author)

  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. Differential Gene Expression during Larval Metamorphic Development in the Pearl Oyster, Pinctada fucata, Based on Transcriptome Analysis

    Directory of Open Access Journals (Sweden)

    Haimei Li

    2016-01-01

    Full Text Available P. fucata experiences a series of transformations in appearance, from swimming larvae to sessile juveniles, during which significant changes in gene expression likely occur. Thus, P. fucata could be an ideal model in which to study the molecular mechanisms of larval metamorphosis during development in invertebrates. To study the molecular driving force behind metamorphic development in larvae of P. fucata, transcriptomes of five larval stages (trochophore, D-shape, umbonal, eyespots, and spats were sequenced using an Illumina HiSeq™ 2000 system and assembled and characterized with the transcripts of six tissues. As a result, a total of 174,126 unique transcripts were assembled and 60,999 were annotated. The number of unigenes varied among the five larval stages. Expression profiles were distinctly different between trochophore, D-shape, umbonal, eyespots, and spats larvae. As a result, 29 expression trends were sorted, of which eight were significant. Among others, 80 development-related, differentially expressed unigenes (DEGs were identified, of which the majority were homeobox-containing genes. Most DEGs occurred among trochophore, D-shaped, and UES (umbonal, eyespots, and spats larvae as verified by qPCR. Principal component analysis (PCA also revealed significant differences in expression among trochophore, D-shaped, and UES larvae with ten transcripts identified but no matching annotations.

  4. Strain induced effects on the transport properties of metamorphic InAlAs/InGaAs quantum wells

    International Nuclear Information System (INIS)

    Capotondi, F.; Biasiol, G.; Ercolani, D.; Grillo, V.; Carlino, E.; Romanato, F.; Sorba, L.

    2005-01-01

    The relationship between structural and low-temperature transport properties is explored for In x Al 1 - x As/In x Ga 1 - x As metamorphic quantum wells with x > 0.7 grown on GaAs by molecular beam epitaxy. Different step-graded buffer layers are used to gradually adapt the in-plane lattice parameter from the GaAs towards the InGaAs value. We show that using buffer layers with a suitable maximum In content the residual compressive strain in the quantum well region can be strongly reduced. Samples with virtually no residual strain in the quantum well region show a low-temperature electron mobility up to 29 m 2 /V s while for samples with higher residual compressive strain the low-temperature mobility is reduced. Furthermore, for samples with buffers inducing a tensile strain in the quantum well region, deep grooves are observed on the surface, and in correspondence we notice a strong deterioration of the low-temperature transport properties

  5. 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.

  6. Isotopic dating of low-grade metamorphic shales in northern Namibia (South West Africa) and implications for the orogenic evolution of the Pan-African Damara Belt

    International Nuclear Information System (INIS)

    Kroener, A.; Clauer, N.

    1979-01-01

    The fine mineral fractions (<2 μm) from pelitic sediments of the molasse-type Mulden Group in the Pan-African Damara belt of Namibia were dated by the Rb-Sr and K-Ar methods. The sediments contain two major parageneses of metamorphic origin which can be related to two separate low-grade regional tectono-thermal events of anchizonal intensity at about 535 (545) Ma and 455 (465) Ma respectively. (Auth.)

  7. 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.

  8. Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

    Directory of Open Access Journals (Sweden)

    B. R. Pinzer

    2012-10-01

    Full Text Available Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during temperature gradient metamorphism (TGM under a constant gradient of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, in addition to the exact locations of these phase changes. We calculated the average time that an ice volume stayed in place before it sublimated and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snowpack where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60% of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of {temperature gradient metamorphism} produced by directly observing the changing microstructure sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

  9. 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.

  10. CellDyM: A room temperature operating cryogenic cell for the dynamic monitoring of snow metamorphism by time-lapse X-ray microtomography

    Science.gov (United States)

    Calonne, N.; Flin, F.; Lesaffre, B.; Dufour, A.; Roulle, J.; Puglièse, P.; Philip, A.; Lahoucine, F.; Geindreau, C.; Panel, J.-M.; Roscoat, S. Rolland; Charrier, P.

    2015-05-01

    Monitoring the time evolution of snow microstructure in 3-D is crucial for a better understanding of snow metamorphism. We, therefore, designed a cryogenic cell that precisely controls the experimental conditions of a sample while it is scanned by X-ray tomography. Based on a thermoelectrical regulation and a vacuum insulation, the cell operates at room temperature. It is, thus, adaptable to diverse scanners, offering advantages in terms of imaging techniques, resolution, and speed. Three-dimensional time-lapse series were obtained under equitemperature and temperature gradient conditions at a 7.8 μm precision. The typical features of each metamorphism and the anisotropic faceting behavior between the basal and prismatic planes, known to occur close to -2°C, were observed in less than 30 h. These results are consistent with the temperature fields expected from heat conduction simulations through the cell. They confirm the cell's accuracy and the interest of relatively short periods to study snow metamorphism.

  11. Low-voltage InAsP/InAs HBT and metamorphic InAs BJT devices grown by molecular beam epitaxy

    Science.gov (United States)

    Averett, K. L.; Wu, X.; Koch, M. W.; Wicks, G. W.

    2003-04-01

    Two advances in InAs-based bipolar transistor technology are reported. Metamorphic InAs bipolar junction transistors (BJTs), grown on semi-insulating GaAs substrates, are reported for the first time, showing current gains comparable to similar structures grown homoepitaxially on InAs substrates. Measurements by atomic force microscopy report root-mean-square surface roughness as low as 0.661 nm, for a metamorphic BJT structure with a 5 μm thick InAs buffer. The quality of the epitaxial structure was investigated as a function of the buffer layer thickness, by measuring the reverse-leakage current density of metamorphic BJTs of 1, 2, and 5 μm InAs buffer layers, showing improved electrical characteristics with increasing buffer layer thickness. A second technological advance is also reported, concerning the development of a heterojunction bipolar transistor (HBT), with a strained, pseudomorphic InAs 1- yP y ternary for the wide-gap emitter. The common emitter current gain of a control BJT device was measured at β=110, and the HBT device, of identical doping structure achieved β=180.

  12. Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri Zones, NW Italy

    Science.gov (United States)

    Guergouz, Celia; Martin, Laure; Vanderhaeghe, Olivier; Thébaud, Nicolas; Fiorentini, Marco

    2018-05-01

    In order to improve the understanding of thermal-tectonic evolution of high-grade terranes, we conducted a systematic study of textures, REE content and U-Pb ages of zircon and monazite grains extracted from migmatitic metapelites across the amphibolite to granulite facies metamorphic gradient exposed in the Ivrea-Verbano and Strona-Ceneri Zones (Italy). This study documents the behaviour of these accessory minerals in the presence of melt. The absence of relict monazite grains in the metasediments and the gradual decrease in the size of inherited zircon grains from amphibolite to granulite facies cores indicate partial to total dissolution of accessory minerals during the prograde path and partial melting. The retrograde path is marked by (i) growth of new zircon rims (R1 and R2) around inherited cores in the mesosome, (ii) crystallisation of stubby zircon grains in the leucosome, especially at granulite facies, and (iii) crystallisation of new monazite in the mesosome. Stubby zircon grains have a distinctive fir-tree zoning and a constant Th/U ratio of 0.20. Together, these features reflect growth in the melt; conversely, the new zircon grains with R1 rims have dark prismatic habits and Th/U ratios ages obtained on both types are similar, indicating contemporaneous growth of stubby zircon and rims around unresorbed zircon grains, reflecting the heterogeneous distribution of the melt at the grain scale. In the Ivrea-Verbano Zone the interquartile range (IQR) of U-Pb ages on zircon and monazite are interpreted to represent the length of zircon and monazite crystallisation in the presence of melt. Accordingly, they provide an indication on the minimum duration for high-temperature metamorphism and partial melting of the lower crust: 20 Ma and 30 Ma in amphibolite and granulite facies, respectively. In amphibolite facies, zircon crystallisation between 310 and 294 Ma (IQR) is interpreted to reflect metamorphic peak condition and earlier retrograde history; conversely

  13. OXYGEN ISOTOPIC COMPOSITIONS OF THE ALLENDE TYPE C CAIs: EVIDENCE FOR ISOTOPIC EXCHANGE DURING NEBULAR MELTING AND ASTEROIDAL THERMAL METAMORPHISM

    Energy Technology Data Exchange (ETDEWEB)

    Krot, A N; Chaussidon, M; Yurimoto, H; Sakamoto, N; Nagashima, K; Hutcheon, I D; MacPherson, G J

    2008-02-21

    that CAIs 100, 160 and CG5 experienced melting in an {sup 16}O-rich ({Delta}{sup 17}O < -20{per_thousand}) nebular gas in the CAI-forming region. The Type C and Type-B-like portions of CAI 6-1-72 experienced melting in an {sup 16}O-depleted ({Delta}{sup 17}O {ge} -13{per_thousand}) nebular gas. CAIs ABC, TS26 and 93 experienced isotopic exchange during re-melting in the presence of an {sup 16}O-poor ({Delta}{sup 17}O {ge} -10{per_thousand}) nebular gas in the chondrule-forming region(s). Subsequently, Allende Type C CAIs experienced post-crystallization isotopic exchange with an {sup 16}O-poor reservoir that affected largely melilite and anorthite. Because pseudomorphic replacement of lacy melilite by grossular, monticellite and forsterite occurred during thermal metamorphism, some oxygen isotopic exchange of melilite and anorthite must have continued after formation of these secondary minerals. We suggest that some or all oxygen isotopic exchange in melilite and anorthite occurred during fluid-assisted thermal metamorphism on the CV parent asteroid. Similar processes may have also affected melilite and anorthite of CAIs in metamorphosed CO chondrites.

  14. Kyanite Formation and Element Fractionation in the High-Al Eclogites from the Sulu UHP Metamorphic Terrane

    Directory of Open Access Journals (Sweden)

    Yung-Hsin Liu

    2010-01-01

    Full Text Available Eclogite compositions are critical parameters for under standing chemical evolution in the Earth, particularly in subduction zones. A group of eclogites from the Sulu ultra-high pres sure (UHP metamorphic terrane in eastern China shows uncommon petrographic and compositional features. They are characterized by (1 zoisite porphyroblasts coexisting with inclusion-free, inclusion-containing, and net work kyanite, (2 high Al2O3 of 18.4 - 29.2% with high MgO of 8.59 - 11.3%, and (3 intensive HFSE-REE fractionations represented by [Zr/Sm]ch and [Ti/Gd]ch ratios of 0.1 - 3.9 and 1.1 - 9.0, respectively. High-pressure fluids played a major role on developing these features. Kyanite shows two textural varieties. KyI is inclusion-free and in apparent textural equilibrium with gar net and omphacite, implying formation from plagioclase break down. KyII includes kyanite networks and porphyroblasts; the former occurs mostly in gar net, whereas the latter encloses gar net and omphacite grains. KyII were crystallized at the expense of gar net and omphacite during eclogite-fluid interaction. The low [HREE]ch ratios of 1 - 2 indicate that the protoliths were arc cumulates. The well-de fined in verse Al2O3-SiO2 and Al2O3-CaO correlations are not the characteristics of igneous precursors; there fore, must reflect metamorphic modifications. The comparison to mafic cumulates shows that the low-Al samples are compositionally better representatives of protoliths. Mass balance calculations point to anolivine gabbronoritic protolith. The intensive HFSE-REE fractionations reflect compositional differences between two sample groups. Group I samples have superchondritic HFSE-REE ratios [(Nb/La, Zr/Sm, Ti/Gdch = 2 - 7] with depletions in LREE. In contrast, group II samples show HFSE depletions and LREE enrichments. These compositional differences were explained as reflecting element mobility during eclogite-fluid inter action. Released at temperatures > 750°C, the high

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

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    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

  16. 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

  17. 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.

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

    Science.gov (United States)

    Romero, Darwin; Valencia, Kiko; Alarcón, Pedro; Peña, Daniel; Ramos, Victor A.

    2013-03-01

    As a result of new studies carried out in the offshore of Perú during the exploration and hydrocarbon evaluation of the forearc basins, new U-Pb SHRIMP and TIMS in zircons and some Ar-Ar data were obtained in the metamorphic and igneous basement. The understanding of this basement was critical to evaluate different hypotheses that have been proposed for the tectonic evolution of pre-Andean crust of Perú. Recent research performed in the basement rocks of the Marañón Massif in northern Perú, claimed that west of this area was a basement-free region in the Paleozoic, where the arc and forearc were developed in a mafic quasi-oceanic crust. However, petrographic studies and new preliminary ages indicate, for the first time, the nature and age of this sialic basement. Reconnaissance studies were performed in several offshore islands, as the Las Hormigas de Afuera Island west of Lima, and Macabí and Lobera islands along the edge of the continental platform. These data were complemented with the studies of some cutting samples obtained in recent exploration wells in northern Perú. The results of the present work show two large crustal domains in the Peruvian offshore forearc. A northern domain contains late Paleozoic igneous rocks that appear to be the southern offshore continuation of the Amotape-Tahuin block, which is interpreted as the southernmost remnant of the Laurentia Alleghenian orogen. The central offshore domain, known as the Paracas High, corresponds to the outer shelf high of previous studies. It contains orthogneisses of Grenville-age, probably recrystallized during an Ordovician magmatic episode. The new results show that the central offshore of Perú is an extension of the Grenville-age basement affected by Famatinian, early Paleozoic magmatism, well exposed in the southern domain in the Arequipa Massif along the coast of southern Perú.

  19. 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

  20. 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

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. High-efficiency inverted metamorphic 1.7/1.1 eV GaInAsP/GaInAs dual-junction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Nikhil [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Schulte, Kevin L. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Geisz, John F. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Friedman, Daniel J. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; France, Ryan M. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Perl, Emmett E. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Norman, Andrew G. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Guthrey, Harvey L. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Steiner, Myles A. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA

    2018-01-29

    Photovoltaic conversion efficiencies of 32.6 +/- 1.4% under the AM1.5 G173 global spectrum, and 35.5 +/- 1.2% at 38-suns concentration under the direct spectrum, are demonstrated for a monolithic, dual-junction 1.7/1.1 eV solar cell. The tandem cell consists of a 1.7 eV GaInAsP top-junction grown lattice-matched to a GaAs substrate, followed by a metamorphic 1.1 eV GaInAs junction grown on a transparent, compositionally graded metamorphic AlGaInAs buffer. This bandgap combination is much closer to the dual-junction optimum and offers headroom for absolute 3% improvement in efficiency, in comparison to the incumbent lattice-matched GaInP/GaAs (~1.86/1.41 eV) solar cells. The challenge of growing a high-quality 1.7 eV GaInAsP solar cell is the propensity for phase separation in the GaInAsP alloy. The challenge of lattice-mismatched GaInAs solar cell growth is that it requires minimizing the residual dislocation density during the growth of a transparent compositionally graded buffer to enable efficient metamorphic tandem cell integration. Transmission electron microscopy reveals relatively weak composition fluctuation present in the 1.7 eV GaInAsP alloy, attained through growth control. The threading dislocation density of the GaInAs junction is ~1 x 10^6 cm-2, as determined from cathodoluminescence measurements, highlighting the quality of the graded buffer. These material advances have enabled the performance of both junctions to reach over 80% of their Shockley-Queisser limiting efficiencies, with both the subcells demonstrating a bandgap-voltage offset, WOC (=Eg/q-VOC), of ~0.39 V.

  7. Comparative Study of Photoelectric Properties of Metamorphic InAs/InGaAs and InAs/GaAs Quantum Dot Structures

    Science.gov (United States)

    Golovynskyi, Sergii; Seravalli, Luca; Datsenko, Oleksandr; Trevisi, Giovanna; Frigeri, Paola; Gombia, Enos; Golovynska, Iuliia; Kondratenko, Serhiy V.; Qu, Junle; Ohulchanskyy, Tymish Y.

    2017-05-01

    Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies. It was shown that the use of the InGaAs buffer spectrally shifted the maximum of the QD PL band to 1.3 μm (telecommunication range) without a decrease in the yield. Photosensitivity for the metamorphic QDs was found to be higher than that in GaAs buffer while the photoresponses for both metamorphic and pseudomorphic buffer layers were similar. The mechanisms of PV and PC were discussed for both structures. The dissimilarities in properties of the studied structures are explained in terms of the different design. A critical influence of the defects on the photoelectrical properties of both structures was observed in the spectral range from 0.68 to 1.0 eV for contact configuration (ii), i.e., in the case of electrically active GaAs wafer. No effect of such defects on the photoelectric spectra was found for configuration (i), when the structures were contacted to the top and bottom buffers; only a 0.83 eV feature was observed in the photocurrent spectrum of pseudomorphic structure and interpreted to be related to defects close to InAs/GaAs QDs.

  8. High-efficiency inverted metamorphic 1.7/1.1 eV GaInAsP/GaInAs dual-junction solar cells

    Science.gov (United States)

    Jain, Nikhil; Schulte, Kevin L.; Geisz, John F.; Friedman, Daniel J.; France, Ryan M.; Perl, Emmett E.; Norman, Andrew G.; Guthrey, Harvey L.; Steiner, Myles A.

    2018-01-01

    Photovoltaic conversion efficiencies of 32.6 ± 1.4% under the AM1.5 G173 global spectrum, and 35.5% ± 1.2% at 38-suns concentration under the direct spectrum, are demonstrated for a monolithic, dual-junction 1.7/1.1 eV solar cell. The tandem cell consists of a 1.7 eV GaInAsP top-junction grown lattice-matched to a GaAs substrate, followed by a metamorphic 1.1 eV GaInAs junction grown on a transparent, compositionally graded metamorphic AlGaInAs buffer. This bandgap combination is much closer to the dual-junction optimum and offers headroom for absolute 3% improvement in efficiency, in comparison to the incumbent lattice-matched GaInP/GaAs (˜1.86/1.41 eV) solar cells. The challenge of growing a high-quality 1.7 eV GaInAsP solar cell is the propensity for phase separation in the GaInAsP alloy. The challenge of lattice-mismatched GaInAs solar cell growth is that it requires minimizing the residual dislocation density during the growth of a transparent compositionally graded buffer to enable efficient metamorphic tandem cell integration. Transmission electron microscopy reveals relatively weak composition fluctuation present in the 1.7 eV GaInAsP alloy, attained through growth control. The threading dislocation density of the GaInAs junction is ˜1 × 106 cm-2, as determined from cathodoluminescence measurements, highlighting the quality of the graded buffer. These material advances have enabled the performance of both junctions to reach over 80% of their Shockley-Queisser limiting efficiencies, with both the subcells demonstrating a bandgap-voltage offset, WOC (=Eg/q-VOC), of ˜0.39 V.

  9. Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic-early Jurassic tectonics associated with the Paleo-Tethys Ocean

    Science.gov (United States)

    Wang, Yixuan; Liang, Xiao; Wang, Genhou; Yuan, Guoli; Bons, Paul D.

    2018-03-01

    The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic-early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P-T data, and Ar-Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E-W-trending, 2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist mélange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying mélange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and 404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at 0.7-1.1 GPa and 400 °C. Our Ar-Ar dating of amphibole reveals rim-ward decreasing in age bands, including 242.4-241.2 Ma, ≥202.6-196.8, and 192.9-189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang ( 244-220 Ma); (2) syn-collisional slab-break off (223-202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth ( 202.6-197 Ma); and (4) post-collision contraction and reburial (195.6-188.7 Ma).

  10. 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.

  11. New age data and geothermobarometric estimates from the Apuseni Mountains (Romania); evidence for Cretaceous amphibolite-facies metamorphism

    Science.gov (United States)

    Reiser, Martin; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard

    2014-05-01

    New Ar-Ar ms, Rb-Sr bt and Sm-Nd grt age data in combination with microprobe analyses and structural data from the Apuseni Mountains provide new constraints for the tectonic evolution of the Tisza and Dacia Mega-Units during the Late Jurassic-Late Cretaceous time interval, which is of special importance for the present day arrangement of tectonic units in the Alpine-Carpathian-Dinaridic region. Late Jurassic obduction of Transylvanian Ophiolites (155 Ma) partially reset Ar-Ar ms ages at the top of the Biharia Nappe System in the Dacia Mega-Unit. New Sm-Nd grt ages and P-T estimates yielded amphibolite-facies conditions of 500°C and about 0.8 GPa during the Early Cretaceous (125 Ma Sm-Nd age) for the Dacia Mega-Unit and during late Early Cretaceous times (104 Ma Sm-Nd age) for the Tisza Mega-Unit. This implies that not only the Dacia Mega-Unit, but also the Tisza Mega-Unit experienced a strong regional metamorphic overprint accompanying Alpine deformation. New 95 Ma Ar-Ar ms and 81 Ma Rb-Sr bt ages from the Bihor Nappe (Tisza Mega-Unit), in combination with fission track ages constrain rapid cooling of more than 20°C/Ma after the thermal maximum. The amplitude of cooling corresponds to data from the Dacia Mega-Unit, which started cooling 20 Ma earlier, but at a rate of only about 12°C/Ma. Kinematic indicators and stretching lineations show NE-directed, in-sequence nappe stacking for the Tisza and Dacia Mega-Units during "Austrian Phase" deformation (125-100 Ma). Following the Austrian Phase, the Dacia Mega-Unit was thrust over the Tisza Mega-Unit during the Turonian Phase (93-89 Ma). Constrained through NW-directed kinematic indicators and 94-80 Ma Rb-Sr bt ages, this tectonic phase is responsible for a pervasive retrograde greenschist-facies overprint and the geometry of the present-day nappe stack in the Apuseni Mountains.

  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. 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

  14. 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

  15. Low-grade metamorphism in the eastern Southern Alps: Distribution, conditions, timing and implications for the tectonics of the Alps and NW Dinarides

    Science.gov (United States)

    Neubauer, Franz; Heberer, Bianca; Genser, Johann; Friedl, Getrude

    2014-05-01

    Based on 40Ar/39Ar dating of newly-grown syntectonic metamorphic white mica (sericite), we recognize for the first time the timing of Alpine low-grade metamorphism in the eastern part of the Southalpine unit: (1) A Silurian phyllite of Seeberg inlier located to the south of the Periadriatic fault yields a plateau age at c. 75 Ma suggesting a Late Cretaceous age of previously recognized low-grade (Rantitsch & Rainer, 2003) metamorphism. (2) Within the Tolmin nappe, four sericite plateau ages of mainly Middle Triassic volcanics are at c. 51 Ma (Early Eocene). The Late Cretaceous age in the Seeberg inlier is considered to record ductile deformation during formation of a retro-wedge related to the Eo-Alpine orogeny in the Austroalpine units in the Eastern Alps exposed north of the future Periadriatic fault. The Eocene age at the boundary of very low-grade to low-grade metamorphism in the Tolmin nappe (Rainer et al., 2009) relates to the emplacement of the Southalpine nappe complex onto the Dinarides and is contemporaneous with the initial ductile deformation in the Dinarides during Adria-directed shortening and formation of a siliciclastic flysch belt in front of the SW-directed growing fold-thrust belt (Placer, 2008). Similar rare Late Cretaceous and dominant Eocene ages within post-Variscan units are virtually more widespread in the Southalpine unit and Dinarides as considered before. These regions include the Collio basin (Feijth, 2002) and the Eder unit (Läufer et al., 1996) in the western and central Southern Alps, in the internal NW Dinarides (Borojević Šoštarić et al., 2012) and the Mid Bosnian Schist Mountains (Pamić et al., 2004) and Lim Paleozoic unit in the central Dinarides (Ilic et al., submitted). Consequently, the Southalpine unit and Dinarides were affected by two stages of metamorphism, Late Cretaceous (ca. 80 to 75 Ma) and Eocene (ca. 51 - 40 Ma), both stages are related to back-thrusting. The ages of metamorphism are different from those in the

  16. Thrust Slip Rates as a Control on the Presence and Spatial Distribution of High Metamorphic Heating Rates in Collisional Systems: The "Hot Iron" Model Revisited

    Science.gov (United States)

    Thigpen, R.; Ashley, K. T.; Law, R. D.; Mako, C. A.

    2017-12-01

    In natural systems, two key observations indicate that major strain discontinuities such as faults and shear zones should play a fundamental role in orogenic thermal evolution: (1) Large faults and shear zones often separate components of the composite orogen that have experienced broadly different thermal and deformational histories, and (2) quantitative metamorphic and diffusional studies indicate that heating rates are much faster and the duration of peak conditions much shorter in natural collisional systems than those predicted by numerical continuum deformation models. Because heat transfer processes such as conduction usually operate at much slower time scales than rates of other tectonic processes, thermal evolution is often transient and thus can be strongly influenced by tectonic disturbances that occur at rates much faster than thermal relaxation. Here, we use coupled thermal-mechanical finite element models of thrust faults to explore how fault slip rate may fundamentally influence the thermal evolution of individual footwall and hanging wall thrust slices. The model geometry involves a single crustal-scale thrust with a dip of 25° that is translated up the ramp at average velocities of 20, 35, and 50 km Myr-1, interpreted to represent average to relatively high slip rates observed in many collisional systems. Boundary conditions include crustal radioactive heat production, basal mantle heat flow, and surface erosion rates that are a function of thrust rate and subsequent topography generation. In the models, translation of the hanging wall along the crustal-scale detachment results in erosion, exhumation, and retrograde metamorphism of the emerging hanging wall topography and coeval burial, `hot iron' heating, and prograde metamorphism of the thrust footwall. Thrust slip rates of 20, 35, and 50 km Myr-1 yield maximum footwall heating rates ranging from 55-90° C Myr-1 and maximum hanging wall cooling rates of 138-303° C Myr-1. These relatively rapid

  17. Fused embryos and pre-metamorphic conjoined larvae in a broadcast spawning reef coral [v2; ref status: indexed, http://f1000r.es/54p

    Directory of Open Access Journals (Sweden)

    Lei Jiang

    2015-03-01

    Full Text Available Fusion of embryos or larvae prior to metamorphosis is rarely known to date in colonial marine organisms. Here, we document for the first time that the embryos of the broadcast spawning coral Platygyra daedalea could fuse during blastulation and further develop into conjoined larvae, and the settlement of conjoined larvae immediately resulted in inborn juvenile colonies. Fusion of embryos might be an adaptive strategy to form pre-metamorphic chimeric larvae and larger recruits, thereby promoting early survival. However, future studies are needed to explore whether and to what extent fusion of coral embryos occurs in the field, and fully evaluate its implications.

  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. 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

  20. Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes

    Science.gov (United States)

    Buse, Ben; Schumacher, John C.; Sparks, R. Stephen J.; Field, Matthew

    2010-10-01

    Metamorphic assemblages within Karoo basalt xenoliths, found within volcaniclastic kimberlite of the B/K9 pipe, Damtshaa, Botswana, constrain conditions of kimberlite alteration. Bultfonteinite and chlorite partially replace the original augite-plagioclase assemblage, driven by the serpentinisation of the kimberlite creating strong chemical potential gradients for Si and Mg. Hydrogarnet and serpentine replace these earlier metamorphic assemblages as the deposits cool. The bultfonteinite (ideally Ca2SiO2[OH,F]4) and hydrogarnet assemblages require a water-rich fluid containing F-, and imply hydrothermal alteration dominated by external fluids rather than autometamorphism from deuteric fluids. Bultfonteinite and hydrogarnet are estimated to form at temperatures of ca. 350-250°C, which are similar to those for serpentinisation. Alteration within the B/K9 kimberlite predominantly occurs between 250 and 400°C. We attribute these conditions to increased efficiency of mass transfer and chemical reactions below the critical point of water and a consequence of volume-increasing serpentinisation and metasomatic reactions that take place over this temperature range. A comparison of the B/K9 kimberlite with kimberlites from Venetia, South Africa suggests that the composition and mineralogy of included xenoliths affects the alteration assemblages within kimberlite deposits.

  1. 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)

  2. Investigation of InP/InGaAs metamorphic co-integrated complementary doping-channel field-effect transistors for logic application

    Science.gov (United States)

    Tsai, Jung-Hui

    2014-01-01

    DC performance of InP/InGaAs metamorphic co-integrated complementary doping-channel field-effect transistors (DCFETs) grown on a low-cost GaAs substrate is first demonstrated. In the complementary DCFETs, the n-channel device was fabricated on the InxGa1-xP metamorphic linearly graded buffer layer and the p-channel field-effect transistor was stacked on the top of the n-channel device. Particularly, the saturation voltage of the n-channel device is substantially reduced to decrease the VOL and VIH values attributed that two-dimensional electron gas is formed and could be modulated in the n-InGaAs channel. Experimentally, a maximum extrinsic transconductance of 215 (17) mS/mm and a maximum saturation current density of 43 (-27) mA/mm are obtained in the n-channel (p-channel) device. Furthermore, the noise margins NMH and NML are up to 0.842 and 0.330 V at a supply voltage of 1.5 V in the complementary logic inverter application.

  3. 3D-reconstructions and virtual 4D-visualization to study metamorphic brain development in the sphinx moth Manduca sexta

    Directory of Open Access Journals (Sweden)

    Wolf Huetteroth

    2010-03-01

    Full Text Available During metamorphosis, the transition from the larva to the adult, the insect brain undergoes considerable remodeling: New neurons are integrated while larval neurons are remodeled or eliminated. One well acknowledged model to study metamorphic brain development is the sphinx moth Manduca sexta. To further understand mechanisms involved in the metamorphic transition of the brain we generated a 3D standard brain based on selected brain areas of adult females and 3D reconstructed the same areas during defined stages of pupal development. Selected brain areas include for example mushroom bodies, central complex, antennal- and optic lobes. With this approach we eventually want to quantify developmental changes in neuropilar architecture, but also quantify changes in the neuronal complement and monitor the development of selected neuronal populations. Furthermore, we used a modeling software (Cinema 4D to create a virtual 4D brain, morphing through its developmental stages. Thus the didactical advantages of 3D visualization are expanded to better comprehend complex processes of neuropil formation and remodeling during development. To obtain datasets of the M. sexta brain areas, we stained whole brains with an antiserum against the synaptic vesicle protein synapsin. Such labeled brains were then scanned with a confocal laser scanning microscope and selected neuropils were reconstructed with the 3D software AMIRA 4.1.

  4. 2D and 3D imaging of the metamorphic carbonates at Omalos plateau/polje, Crete, Greece by employing independent and joint inversion on resistivity and seismic data

    Directory of Open Access Journals (Sweden)

    Pangratis Pangratis

    2012-07-01

    Full Text Available A geophysical survey carried out at Omalos plateau in Chania, Western Crete, Greece employed seismic as well as electrical tomography methods in order to image karstic structures and the metamorphic carbonates (Tripali unit and Plattenkalk group which are covered by post-Mesozoic deposits (terra rossa, clays, sands and gravels. The geoelectrical sections image the metamorphic carbonates which exhibit a highly irregular relief. At the central part of the plateau the thickness of post-Mesozoic deposits (terra rossa, clays, sands and gravels ranges from 40-130 m. A 3D resistivity image was generated by inverting resistivity data collected on a grid to the south west at the Omalos plateau. The 3D resistivity image delineated a karstic structure at a depth of 25 to 55 m. On the same grid the depth to the top of the karstified carbonates ranges from 25-70 m. This is also verified on the resistivity sections and seismic velocity sections along lines 5 and 7 of the above mentioned grid which are derived from the cross-gradients joint inversion.

  5. 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.

  6. 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.

  7. Linking zircon age to metamorphic stage using U-Pb/REE depth-profiling of zircon combined with Lu-Hf garnet geochronology

    Science.gov (United States)

    Briggs, Sophie; Cottle, John; Smit, Matthijs; Arnush, Nicole

    2017-04-01

    The relatively novel approach of LASS-ICP-MS depth-profiling in zircon has enabled the analysis of sub-micrometer, isotopically/geochemically distinct zircon domains which are too thin to be analyzed by other in situ methods. The depth-profiling approach has proven to be particularly useful in targeting thin and discontinuous metamorphic zircon overgrowths, which are evidently capable of recording multiple short-duration tectonothermal events. Based on our knowledge of rare earth element (REE) partitioning between equilibrium zircon and garnet, it is possible to link LASS depth-profile data to specific metamorphic events, and discern the timing of garnet growth versus garnet breakdown. Here we test the potential of this approach by applying LASS-ICP-MS depth profiling in zircon to samples from the Alpine Schist (New Zealand) that have been dated previously by Lu-Hf garnet geochronology. Our results show that thin (Zealandia microcontinent from East Gondwana during 83 - 52 Ma. These results provide constraints on the P-T-t conditions recorded in the Alpine Schist during this period, with implications for the geodynamic processes involved in microcontinent formation.

  8. Materials Integration and Metamorphic Substrate Engineering from Silicon to Gallium Arsenide to Indium Phosphide for Advanced III-V/Silicon Photovoltaics

    Science.gov (United States)

    Carlin, Andrew M.

    ~10x, to a range of 1×107 cm-2, compared to current state of the art. This reduction can now enable future III-V/Si solar cells based on GaAsP metamorphic buffers in which the underlying Si substrate can participate as an active sub-cell, and such buffers have been demonstrated in this research. Second, in this same lattice constant range, novel GaP/SiGe interfaces on Si were grown and demonstrated to eliminate the small, but not negligible lattice misfit between GaP and Si, and provides a second pathway for future III-V/Si solar cell integration through subsequent metamorphic buffer growth. For the GaAs-InP range of lattice constants, multiple metamorphic buffer strategies, including those based on anion-specific quaternary GaInAsP, combinations of step and linearly-graded buffers, and buffers with multiple ternary alloys were all investigated. Micro-scale phase separation within quaternary anion-graded GaInAsP was identified as a mechanism to significantly inhibit proper lattice misfit strain relaxation, which was explained by thermodynamic arguments consistent with theoretical phase separation. This led to the creation of hybrid step and linearly graded InGaAs/InGaP metamorphic buffers through which phase separation was totally eliminated by avoiding specific compositions that were identified as sources for phase separation. These findings have enabled a realistic path for accessing the full range of bandgaps needed for future high efficiency III-V solar cells through optimized metamorphic III-V grading strategies.

  9. 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

  10. 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

  11. Hyperextension in the Caledonian margin of Baltica and its bearing on the structural and metamorphic evolution of Scandinavian Caledonides (Invited)

    Science.gov (United States)

    Andersen, T. B.

    2013-12-01

    The Scandinavian segment (~2000 km) of the Caledonian-Appalachian orogen formed by a head-on collision of Baltica and Laurentia. The collision followed rapid (>10 cm/yr) convergence, subduction and closure of the Iapetus Ocean in the Ordovician to the Middle Silurian. The collision culminated in a Himalayan type continental collision at 430 Ma, after which the continental subduction/convergence continued for 20 Myr. The terminal stage was characterized by syn- and post-orogenic extension and exhumation, which produced a template used in opening of the present-day Norwegian Sea. The Scandian collision produced a 'layer-cake' tectono-stratigraphy, but correlation of individual nappe units along strike is not trivial. The vestiges of the Iapetus can, however, be traced along the entire Scandinavian Peninsula and constitute the Iapetus suture. Rocks of assumed Laurentian origin structurally overlie the suture. The outboard units underwent several orogenic events that pre-date the Scandian collision and which took place outboard of Baltica. These will not be discussed further here. The Caledonian passive margin of Baltica was very wide, consisting of non-volcanic hyperextended segments as well as passive volcanic margin domains. Basement-cover pairs, in places with mafic dyke-swarms constitute most of these units. The Baltican and assumed Baltican units below the suture have evidence of diachronous and relatively locally developed pre-Scandian deformation and metamorphic events. In S. Norway large basement-cover units are separated by a melange with numerous solitary mantle peridotites and a number of detrital serpentinites. The melange can be traced along strike across S. Norway. Locally, an island-type ';Celtic' fauna is preserved in detrital serpentinite. Some mantle rocks were structurally emplaced, exhumed, eroded and juxtaposed with continental clastics and crust before the Early Ordovician. The melange was recently interpreted to represent an oceanic to

  12. 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

  13. 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

  14. Geochemistry and metamorphism of the Mouriscas Complex, Ossa-Morena/Central Iberian zone boundary, Iberian Massif, Central Portugal: Implications for the Cadomian and Variscan orogenies

    Science.gov (United States)

    Henriques, S. B. A.; Neiva, A. M. R.; Tajčmanová, L.; Dunning, G. R.

    2018-01-01

    The Mouriscas Complex is a deformed and metamorphosed predominantly mafic igneous complex of Ediacaran and Ordovician age and crops out at the Ossa-Morena/Central Iberian zone boundary in the Iberian Massif, Central Portugal. It comprises amphibolite with Neoproterozoic protoliths (ca. 544 Ma), protomylonitic felsic dykes derived from younger trondhjemitic protoliths (ca. 483 Ma) and garnet amphibolite derived of even younger dioritic protoliths (ca. 477 Ma). The protoliths of the Neoproterozoic amphibolites are calc-alkaline magmas of basic to intermediate compositions with intraplate and active continental margin affinities and are considered to represent the final phase of the Cadomian arc magmatism. They are interpreted to have originated as coarse-grained intrusions, likely gabbro or diorite and generated from the partial melting of meta-igneous lower crust and mantle. Their emplacement occurred near the Cadomian metamorphic event dated at ca. 540 Ma (P = 7-8 kbar and T = 640-660 °C) which is interpreted to represent a continental collision. During the Late Cambrian-Early Ordovician an extensional episode occurred in the central-southern Iberian Massif and was also observed in other areas of the Variscan Orogen. It led to mantle upwelling and to the development of an aborted intracratonic rift located at the Ossa-Morena/Central Iberian zone boundary and to the opening of the Rheic Ocean to the south of the area studied in present coordinates (i.e., between the Ossa-Morena and South Portuguese Zones). This event has been dated at ca. 477 Ma and was responsible for the melting of deep ancient mafic crust and mantle with formation of bimodal magmatism in an intra-plate setting, as indicated by the protoliths of the protomylonitic felsic dykes with trondhjemitic composition and of the garnet amphibolite. Subsequent Variscan metamorphism took place under amphibolite facies conditions (P = 4-5.5 kbar; T = 600-625 °C) at lower P-T conditions than the Cadomian

  15. 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

  16. Effects of the gate recess structure on the DC electrical behavior of 0.1-μm metamorphic high-electron-mobility transistors

    International Nuclear Information System (INIS)

    Oh, Jung-Hun; Son, Myung-Sik; Lee, Bok-Hyung; Baek, Yong-Hyun; Jang, Hae-Kang; Rhee, Jin-Koo; Hwang, In-Seok; Kim, Sam-Dong

    2004-01-01

    We examine the effects of the gate recess structure on the DC characteristics of 0.1-μm metamorphic high-electron-mobility transistors (MHEMTs). Compared to the wide gate recess structure, the narrow gate recess structure shows a significant increase in the drain-source saturation current from 440 to 710 mA/mm and in the extrinsic transconductance from 420 to 910 mS/mm. We propose that the observed variations in the DC characteristics are due to deep-level accepter-type interface traps formed between the silicon-nitride passivation layer and the Schottky barrier layer. We perform device simulations by using the hydrodynamic model based upon the proposed mechanism, and the simulation results show good agreement with the data obtained from the fabricated devices.

  17. 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.)

  18. Dynamic recrystallization and metamorphic evolution of ca. 1.85 Ga quartzofeldspathic and cordierite-garnet gneisses, western Gyeonggi Massif, Korea

    Science.gov (United States)

    Cho, Moonsup; Yang, Soh-young; Kim, Taehwan; Yi, Keewook

    2013-04-01

    Quartzofeldspathic orthogneisses together with cordierite-garnet gneisses occur in the Mt. Cheonggye area, western Gyeonggi Massif, where the transition from weakly-deformed gneiss to mylonite is revealed. These gneisses consist primarily of biotite, garnet, K-feldspar, plagioclase, and quartz with or without sillimanite (or kyanite) and cordierite. Microstructures in mylonites and gneisses were investigated to delineate the relationship between dynamic recrystallization and pressure-temperature (P-T) path, based on field and petrologic studies. For constraining the timing of deformation and metamorphism, zircon and monazite were dated using a sensitive high-resolution ion microprobe (SHRIMP) housed at the Korea Basic Science Institute. Recrystallization microstructures systematically vary in accordance with the degree of strain in weakly- to intensely-deformed gneisses or mylonites. Quartz shows the subgrain rotation (SGR) to grain boundary migration (GBM) recrystallization such as the ribbon structure, and K-feldspar is characterized by the core-and-mantle structure together with occasional development of myrmekite. Some isolated grains of K-feldspar appear to be the product of the solution-precipitation growth. Plagioclase was recrystallized by SGR and high-T GBM, forming fine-grained polygonal aggregates in weakly- and moderately-deformed gneisses. With increasing strain, plagioclase grains are connected with each other to form the interconnected weak layer. The microstructures described in the above suggest the deformation temperatures of ca. 490-650°C. Mineral assemblages and reaction textures in cordierite-garnet gneisses suggest a clockwise P-T path, evolving from the kyanite- to sillimanite-stable fields. The SHRIMP U-Th-Pb analyses of zircon and monazite in both cordierite-garnet gneisses and orthogneisses yielded the Paleoproterozoic metamorphic ages of ca. 1.86-1.85 Ga. Some zircons are overgrown by low Th/U rims dated at ca. 240-220 Ma. Monazite

  19. 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

  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. 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.

  2. 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.

  3. 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

  4. Thermal Structure and Tectono-Metamorphic Evolution of the Alboran Domain. New Insights From the Rif belt (Northern Morocco) and Correlations With the Betics (Southern Spain)

    Science.gov (United States)

    Negro, F.; Beyssac, O.; Goffe, B.; Saddiqi, O.; Bouybaouene, M.

    2005-12-01

    The Betico-Rifan Cordilleras represent the western termination of the Alpine Mediterranean orogen. The internal zone of this orogen is the Alboran Domain which consists in a complex stacking of metamorphic nappes including, locally, mantle-derived bodies: the Ronda and Beni Bousera peridotites. In order to assess the tectono-metamorphic evolution of theses nappes and their relation with the underlying peridotites, we have combined RSCM (Raman spectroscopy of carbonaceous material) thermometry and P-T estimates based on chlorite-phengite local equilibria together with a careful analysis of ductile deformation. In the inner Rif, the lower units (lower Sebtides) of the Alboran Domain are directly on top of the Beni Bousera peridotites. Our study shows that peak T was reached during thinning of these units, and that heating continued after this event. A Miocene thermal imprint is also recorded at the base of the upper units of the Alboran Domain (Ghomarides) and evidenced by an increase of T coeval with resetting of K-Ar ages. Retrograde P-T paths in the HP-LT units of the Sebtide Complex also agree with this thermal structure. The units located near the peridotites experienced heating during final decompression stages whereas the more distant units underwent mostly isothermal decompression. In addition analysis of ductile deformation shows that the whole complex was exhumed in a single tectonic event characterized by N-S to NW-SE stretching and top-to-the-N senses of shear. The same approach in the equivalent units (Alpujarrides) from Western Betics evidences a very similar thermal structure over the Ronda peridotites but tectonic dismembering of the orogenic prism was stronger in the Betics compared to the Rif. Finally, analysis of these observations at orogenic scale shows that the Alboran Domain underwent a strong thermal event during the Early Miocene. This event can be interpreted as the result of ascending hot mantle units coeval with thinning of the whole

  5. 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.

  6. Conditions for the formation and atmospheric dispersion of a toxic, heavy gas layer during thermal metamorphism of coal and evaporite deposits by sill intrusion

    Science.gov (United States)

    Storey, Michael; Hankin, Robin K. S.

    2010-05-01

    There is compelling evidence for massive discharge of volatiles, including toxic species, into the atmosphere at the end of the Permian. It has been argued that most of the gases were produced during thermal metamorphism of coal and evaporite deposits in the East Siberia Tunguska basin following sill intrusion (Retallack and Jahren, 2008; Svensen et al., 2009). The release of the volatiles has been proposed as a major cause of environmental and extinction events at the end of the Permian, with venting of carbon gases and halocarbons to the atmosphere leading to global warming and atmospheric ozone depletion (Svensen et al., 2009) Here we consider the conditions required for the formation and dispersion of toxic, heavier than air, gas plumes, made up of a mixture of CO2, CH4, H2S and SO2 and formed during the thermal metamorphism of C- and S- rich sediments. Dispersion models and density considerations within a range of CO2/CH4 ratios and volatile fluxes and temperatures, for gas discharge by both seepage and from vents, allow the possibility that following sill emplacement much of the vast East Siberia Tunguska basin was - at least intermittently - covered by a heavy, toxic gas layer that was unfavorable for life. Dispersion scenarios for a heavy gas layer beyond the Siberian region during end-Permian times will be presented. REFERENCES G. J. Retallack and A. H. Jahren, Methane release from igneous intrusion of coal during Late Permian extinction events, Journal of Geology, volume 116, 1-20, 2008 H. Svensen et al., Siberian gas venting and the end-Permian environmental crisis, Earth and Planetary Science Letters, volume 277, 490-500, 2009

  7. 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

  8. 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.

  9. Petrology and SHRIMP zircon geochronology of granulites from Vesleknausen, Lützow-Holm Complex, East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism

    Directory of Open Access Journals (Sweden)

    Toshiaki Tsunogae

    2014-03-01

    Full Text Available We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the Lützow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss (charnockite and minor biotite gneiss, mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750–850 °C, approximately 150 °C lower than those estimated for metasedimentary gneisses from Rundvågshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss, yielded a Concordia upper intercept ages of 2507.9 ± 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundvågshetta-Vesleknausen-Strandnibba region in southwestern Lützow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc magmatism. The Neoarchean magmatic terrane was tectonically mingled with other fragments (such as metasedimentary units in northern Lützow-Holm Bay by subduction/collision events during the assembly of Gondwana supercontinent, and subsequently underwent ∼850 °C granulite-facies metamorphosed during Neoproterozoic to Cambrian final collisional event.

  10. 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.

  11. 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

  12. 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

  13. 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

  14. Re-Os ages for Archean molybdenite and pyrite, Kuittila-Kivisuo, Finland and Proterozoic molybdenite, Kabeliai, Lithuania: Testing the chronometer in a metamorphic and metasomatic setting

    Science.gov (United States)

    Stein, H.J.; Sundblad, K.; Markey, R.J.; Morgan, J.W.; Motuza, G.

    1998-01-01

    Seven 187Re-187Os ages were determined for molybdenite and pyrite samples from two well-dated Precambrian intrusions in Fennoscandia to examine the sustainability of the Re-Os chronometer in a metamorphic and metasomatic setting. Using a new 187Re decay constant (1.666 x 10-11y-1) with a much improved uncertainty (±0.31%), we determined replicate Re-Os ages for molybdenite and pyrite from the Kuittila and Kivisuo prospects in easternmost Finland and for molybdenite from the Kabeliai prospect in southernmost Lithuania. These two localities contain some of the oldest and youngest plutonic activity in Fennoscandia and are associated with newly discovered economic Au mineralization (Ilomantsi, Finland) and a Cu-Mo prospect (Kabeliai, Lithuania). Two Re-Os ages for veinhosted Kabeliai molybdenite average 1486 ± 5 Ma, in excellent agreement with a 1505 ± 11 Ma U-Pb zircon age for the hosting Kabeliai granite pluton. The slightly younger age suggests the introduction of Cu-Mo mineralization by a later phase of the Kabeliai magmatic system. Mean Re-Os ages of 2778 ± 8 Ma and 2781 ± 8 Ma for Kuittila and Kivisuo molybdenites, respectively, are in reasonable agreement with a 2753 ± 5 Ma weighted mean U-Pb zircon age for hosting Kuittila tonalite. These Re-Os ages agree well with less precise ages of 2789 ± 290 Ma for a Rb-Sr whole-rock isochron and 2771 ± 75 Ma for the average of six Sm-Nd T(DM) model ages for Kuittila tonalite. Three Re-Os analyses of a single pyrite mineral separate, from the same sample of Kuittila pluton that yielded a molybdenite separate, provide individual model ages of 2710 ± 27, 2777 ± 28, and 2830 ± 28 Ma (Re = 17.4, 12.1, and 8.4 ppb, respectively), with a mean value of 2770 ± 120 Ma in agreement with the Kuittila molybdenite age. The Re and 187Os abundances in these three pyrite splits are highly correlated (r = 0.9994), and provide a 187Re-187Os isochron age of 2607 ± 47 Ma with an intercept of 21 ppt 187Os (MSWD = 1.1). It appears

  15. 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

  16. 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.

  17. 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

  18. Metamorphic P-T path and zircon U-Pb dating of HP mafic granulites in the Yushugou granulite-peridotite complex, Chinese South Tianshan, NW China

    Science.gov (United States)

    Zhang, Lu; Zhang, Lifei; Xia, Bin; Lü, Zeng

    2018-03-01

    Co-existing granulite and peridotite may represent relics of the paleo-suture zone and provides an optimal opportunity for better understanding of orogeny between two blocks. In this study, we carried out petrological and U-Pb zircon dating investigation on the HP mafic granulites associated with peridotite complex at Yushugou in Chinese South Tianshan. The studied samples include garnet-bearing high-pressure mafic granulites which can be subdivided into two types: Type I orthopyroxene-free and Type II orthopyroxene-bearing granulites and amphibolite. Type I granulite (Y21-2) has a mineral assemblage of garnet (33 vol.%), clinopyroxene (32 vol.%) and plagioclase (30 vol.%); and Type II granulite (Y18-8) has a mineral assemblage of garnet (22 vol.%), clinopyroxene (10 vol.%), orthopyroxene (14 vol.%), plagioclase (45 vol.%) and quartz. Garnet in both granulites exhibits core-rim structure characterized by increasing grossular and decreasing pyrope from core to rim. Petrographic observations and phase equilibrium modeling using THERMOCALC in the NCFMASHTO system for the mafic granulites (Y21-2 and Y18-8) show three stages of metamorphism: Stage I (granulite facies) was recognized by the large porphyroblastic garnet core, with P-T conditions of 9.8-10.4 Kbar and 860-900 °C (Y21-2) and 9.9-10.6 Kbar and 875-890 °C (Y18-8), respectively; Stage II (HP granulite facies) has peak P-T conditions of 12.1 Kbar at 755 °C (Y21-2) and 13.8 Kbar at 815 °C (Y18-8) using mineral assemblages combining with garnet rim compositions with maximum grossular and minimum pyrope contents; Stage III (amphibolite facies) was characterized by the development of calcic amphibole in granulites with temperature of 446-563 °C. Therefore, an anticlockwise P-T path characterized by simultaneous temperature-decreasing and pressure-increasing was inferred for the Yushugou HP mafic granulite. Studies of zircon morphology and inclusions, combined with zircon U-Pb dating and REE geochemistry

  19. 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

  20. Integration of offshore seismic data, exploration wells, and onland outcrops as constraints on the tectonics and uplift age of metamorphic core complexes, eastern Papua New Guinea

    Science.gov (United States)

    Fitz, G. G.; Mann, P.; Campos Aguiniga, H.

    2009-12-01

    High-grade metamorphic domes of the D’Entrecasteaux Islands (DEI) of eastern Papua New Guinea are located within continental crust at the tip of the westward propagating Woodlark spreading ridge. Multi-channel seismic data collected by the RV Maurice Ewing in 1992 was integrated with seismic data from 1974 and two wells drilled by the oil industry in 1973 to understand pattern and age of faults and clastic wedges in offshore basins surrounding the 2-2.5-km high DEI. The WNW-trending line of the DEI demarcates two areas of contrasting deformational and depositional histories. In the area of the Kiribisi and Trobriand basins north of the DEI, normal faults occupy a WNW-striking basin that began to rift in the early Miocene and continued to rift sporadically until the early Pliocene when all normal faults were buried by ~650 m of undeformed Plio-Pleistocene sediments. We infer that these basins formed as sub-basins within a larger forearc basin bounded to the north by the forearc high of the Trobriand Islands and to the south by the DEI. Uplift of the forearc high and inversion of normal faults near the high during the Pleistocene and suggests the possibility of present-day, southward subduction along the Trobriand trench. To the south of the DEI in the Goodenough basin, the Pleistocene section is thicker and deformed by active, WNW-striking normal faults with seafloor scarps and high-angle dips. Wedging of the Pleistocene clastic fill in a half-graben geometry along the Owen-Stanley fault in the Southern part of the Goodenough basin along the southern coastline of the bay indicates that most normal motion has now shifted to this fault system. The shift in extension from north of the DEI to the Owen-Stanley fault zone in post-Pliocene time likely signals the arrival of the propagating rift tip of the Woodlark basin. The presence of conglomerate with high-grade metamorphic clasts in the Pliocene section north of the DEI supports the idea that the uplift and erosion

  1. Zircon U-Pb geochronology and Hf isotopes from the Sanbagawa Metamorphic Belt, Western Shikoku, Japan: evidence for the prevalence for the Late Cretaceous protoliths

    Science.gov (United States)

    Walia, Monika; Knittel, Ulrich; Suzuki, Shigeyuki; Nishizaka, Naoki; Kimura, Kazunari; Lee, Yuan-Hsi; Lee, Hao-Yang

    2017-04-01

    Sanbagawa Metamorphic Belt lies to the south of Median Tectonic Line and is exposed on Kyushu, Shikoku and Honshu Islands in Japan. This belt has been the focus of many studies in recent years since the discovery of young detrital zircon grains (80 - 95 Ma). Samples for this study come from a 2000 m bore hole from north-western Shikoku drilled in an area considered to be part of the Jurassic to Early Cretaceous part of the Sanbagawa Belt. Dating of single zircon grains using the LA-ICP-MS U-Pb dating method shows that all but one sample contain zircons younger than 100 Ma and thus the protoliths are younger than the previously accepted age of metamorphism of the Sanbagawa Belt at ca. 110 Ma. The single sample that contains only zircons dated at 136 ± 3 Ma, apparently is of volcanic origin and could be a clast representing the source of 130-140 Ma zircons of the sample taken about 120m above this sample. In addition, three surface samples were analyzed. Two of these also contain zircons younger than 100 Ma, whereas the third sample contains only zircons older than 159 Ma. Hf-isotope values for the younger age group 82-116 Ma, ɛHf(T) range from -2.4 to +9.6. Zircon grains of 127-146 Ma ages have more positive ɛHf(T) values of +11.5 to +19.0 indicating depleted mantle source. We envisage these zircons to have been derived from the ocean side of a magmatic arc. All grains in the range 215-250 Ma are characterized by negative ɛHf(T) ranging from -2.3 to -15.2, suggesting re-melting of already existent crust. Within the detrital zircon populations contained in the Sanbagawa meta-sediments age groups are recognized that are also known from SE China. However, compared to those from mainland China, zircons from the Sanbagawa meta-sediments are usually characterized by higher ɛHf(T) values suggesting higher input of material derived from the depleted mantle.

  2. 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)

  3. 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

  4. 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

  5. Effects of Si doping on the strain relaxation of metamorphic (Al)GaInP buffers grown on GaAs substrates

    International Nuclear Information System (INIS)

    Li, K.L.; Dong, J.R.; Sun, Y.R.; Zeng, X.L.; Zhao, Y.M.; Yu, S.Z.; Zhao, C.Y.; Yang, H.

    2014-01-01

    We investigate the effects of Si doping on the strain relaxation of the compositionally step-graded (Al)GaInP buffers grown by metal-organic chemical vapor deposition on (0 0 1) GaAs substrates with different miscuts toward (1 1 1)A. It is found that in the 2° samples, high Si doping can reduce both the α and β dislocation densities by delaying and suppressing the formation of phase separation in the buffer. In contrast, in the 7° samples, Si dopants deteriorate the buffer quality through increasing the dislocation density accompanying with the tilt reduction along the [1 1 0] direction, and a striking feature, bunches of β dislocations away from the interfaces, is observed in the [1 1 0] cross-sectional transmission electron microscopy images. A cross-slip mechanism closely associated with the pinning effect of Si on α dislocation motion is proposed to explain the multiplication of β dislocations. These results indicate that selecting a moderate Si doping density and substrate miscut are critical for the design and fabrication of metamorphic optoelectronic devices.

  6. Comparison of different grading schemes in InGaAs metamorphic buffers on GaAs substrate: Tilt dependence on cross-hatch irregularities

    International Nuclear Information System (INIS)

    Kumar, Rahul; Bag, Ankush; Mukhopadhyay, Partha; Das, Subhashis; Biswas, Dhrubes

    2015-01-01

    Highlights: • InGaAs graded MBs with different grading scheme has been grown by MBE on GaAs. • Continuously graded MB exhibits smoother surface morphology. • Grading scheme has been found to have little impact on lattice relaxation. • Grading schemeaffects the lattice tilt significantly. • Cross-hatch surface irregularities affect the crystallographic tilt. - Abstract: InGaAs graded metamorphic buffers (MBs) with different grading strategies have been grown by molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. A detailed comparative analysis of surface using atomic force microscopy (AFM), and bulk properties using high resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RTPL) of grown MBs have been presented to comprehend the effectiveness of different grading scheme on InGaAs MBs. Conventional, statistical and fractal analysis on measured AFM data has been performed for in-depth investigation of these surfaces. The grading scheme has been found to have little impact on residual strain while it affects the epitaxial tilt significantly. Moreover, the tilt has been found to depend on growth front irregularities. Tilt magnitude in a graded MB has been found to vary with composition while tilt azimuth has been found to be almost same in the graded layers. PL Intensity and a shift in the PL peaks have been used to study the quality of the MB and residual strain comparatively.

  7. Comparison of different grading schemes in InGaAs metamorphic buffers on GaAs substrate: Tilt dependence on cross-hatch irregularities

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Rahul, E-mail: rkp203@gmail.com [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Bag, Ankush [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Mukhopadhyay, Partha [Rajendra Mishra School of Engineering Entrepreneurship, Indian Institute of Technology, Kharagpur 721302 (India); Das, Subhashis [Advanced Technology Development Centre, Indian Institute of Technology, Kharagpur 721302 (India); Biswas, Dhrubes [Department of Electronics & Electrical Communication Engineering, Indian Institute of Technology, Kharagpur 721 302 (India)

    2015-12-01

    Highlights: • InGaAs graded MBs with different grading scheme has been grown by MBE on GaAs. • Continuously graded MB exhibits smoother surface morphology. • Grading scheme has been found to have little impact on lattice relaxation. • Grading schemeaffects the lattice tilt significantly. • Cross-hatch surface irregularities affect the crystallographic tilt. - Abstract: InGaAs graded metamorphic buffers (MBs) with different grading strategies have been grown by molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. A detailed comparative analysis of surface using atomic force microscopy (AFM), and bulk properties using high resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RTPL) of grown MBs have been presented to comprehend the effectiveness of different grading scheme on InGaAs MBs. Conventional, statistical and fractal analysis on measured AFM data has been performed for in-depth investigation of these surfaces. The grading scheme has been found to have little impact on residual strain while it affects the epitaxial tilt significantly. Moreover, the tilt has been found to depend on growth front irregularities. Tilt magnitude in a graded MB has been found to vary with composition while tilt azimuth has been found to be almost same in the graded layers. PL Intensity and a shift in the PL peaks have been used to study the quality of the MB and residual strain comparatively.

  8. 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)

  9. 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.

  10. Design considerations for λ ˜ 3.0- to 3.5-μm-emitting quantum cascade lasers on metamorphic buffer layers

    Science.gov (United States)

    Rajeev, Ayushi; Sigler, Chris; Earles, Tom; Flores, Yuri V.; Mawst, Luke J.; Botez, Dan

    2018-01-01

    Quantum cascade lasers (QCLs) that employ metamorphic buffer layers as substrates of variable lattice constant have been designed for emission in the 3.0- to 3.5-μm wavelength range. Theoretical analysis of the active-region (AR) energy band structure, while using an 8-band k•p model, reveals that one can achieve both effective carrier-leakage suppression as well as fast carrier extraction in QCL structures of relatively low strain. Significantly lower indium-content quantum wells (QWs) can be employed for the AR compared to QWs employed for conventional short-wavelength QCL structures grown on InP, which, in turn, is expected to eliminate carrier leakage to indirect-gap valleys (X, L). An analysis of thermo-optical characteristics for the complete device design indicates that high-Al-content AlInAs cladding layers are more effective for both optical confinement and thermal dissipation than InGaP cladding layers. An electroluminescence-spectrum full-width half-maximum linewidth of 54.6 meV is estimated from interface roughness scattering and, by considering both inelastic and elastic scattering, the threshold-current density for 3.39-μm-emitting, 3-mm-long back-facet-coated QCLs is projected to be 1.40 kA/cm2.

  11. Continuous illumination through larval development suppresses dopamine synthesis in the suprachiasmatic nucleus, causing activation of α-MSH synthesis in the pituitary and abnormal metamorphic skin pigmentation in flounder.

    Science.gov (United States)

    Itoh, Kae; Washio, Youhei; Fujinami, Yuichiro; Shimizu, Daisuke; Uji, Susumu; Yokoi, Hayato; Suzuki, Tohru

    2012-04-01

    In order to better understand the endocrine aberrations related to abnormal metamorphic pigmentation that appear in flounder larvae reared in tanks, this study examined the effects of continuous 24-h illumination (LL) through larval development on the expression of tyrosine hydroxylase-1 (th1), proopiomelanocortin (pomc), α-melanophore-stimulating hormone (α-MSH) and melanin concentrating hormone (MCH), which are known to participate in the control of background adaptation of body color. We observed two conspicuous deviations in the endocrine system under LL when compared with natural light conditions (LD). First, LL severely suppressed th1 expression in the dopaminergic neurons in the anterior diencephalon, including the suprachiasmatic nucleus (SCN). Second, pomc and α-MSH expression in the pars intermedia melanotrophs was enhanced by LL. Skin color was paler under LL than LD before metamorphic pigmentation, and abnormal metamorphic pigmentation occurred at a higher ratio in LL. We therefore hypothesize that continuous LL inhibited dopamine synthesis in the SCN, which resulted in up-regulation of pomc mRNA expression in the melanotrophs. In spite of the up-regulation of pomc in the melanotrophs, larval skin was adjusted to be pale by MCH which was not affected by LL. Accumulation of α-MSH in the melanotrophs is caused by uncoupling of α-MSH synthesis and secretion due to inhibitory role of MCH on α-MSH secretion, which results in abnormal metamorphic pigmentation by affecting differentiation of adult-type melanophores. Our data demonstrate that continuous illumination at the post-embryonic stage has negative effects on the neuroendocrine system and pituitary in flounder. Copyright © 2012 Elsevier Inc. All rights reserved.

  12. Petrology and zircon U-Pb geochronology of metamorphic massifs around the middle segment of the Tan-Lu fault to define the boundary between the North and South China blocks

    Science.gov (United States)

    Shi, Yonghong

    2017-06-01

    The Tan-Lu fault (TLF) is a significant linear structure of eastern China. The middle segment of the TLF in the northern Anhui Province separates the North China Block (NCB) and South China Block (SCB). Lack of geological work makes the plate boundary here ambiguous. Detailed field survey and laboratory analyses have been conducted to constrain the formation and evolution of the TLF. To the west of the TLF, the Wuhe massif underwent a granulite facies metamorphism with T = 778-836 °C, P = 1.0-1.2 GPa during 2.41-2.43 Ga according to LA-ICP-MS U-Pb zircon dating. On the contrary, to the east of the TLF, the Zhangbaling massif suffered a greenschist to lower amphibolite facies metamorphism with the average metamorphic temperature at around 340-440 °C, with the protolith igneous ages of ca. 750 Ma. These differences indicate that the two massifs belong to the different blocks. Furthermore, the granitic gneiss in the central part of TLF gives three populations of zircon U-Pb age at 667-504 Ma, 228 ± 2 Ma and 211 ± 2 Ma, respectively. The later two groups of spectra correspond to the periods of subduction and exhumation of the Dabie massif (245-200 Ma). Combined with previous study, the precise plate boundary between NCB and SCB has been delineated as the Zhuding-Shimenshan fault, and the initial time of the motion for the TLF is also discussed.

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

    Science.gov (United States)

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

    2017-04-01

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

  14. 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

  15. 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

  16. A- and I-type metagranites from the North Shahrekord Metamorphic Complex, Iran: Evidence for Early Paleozoic post-collisional magmatism

    Science.gov (United States)

    Badr, Afsaneh; Davoudian, Ali Reza; Shabanian, Nahid; Azizi, Hossein; Asahara, Yoshihiro; Neubauer, Franz; Dong, Yunpeng; Yamamoto, Koshi

    2018-02-01

    The North Shahrekord Metamorphic Complex (NSMC) of the central Sanandaj-Sirjan Zone (SaSZ) consists of metagranitoid bodies, which were metamorphosed within high pressure-low temperature conditions. Whole rock chemistry shows relatively high amounts of SiO2 (65-77 wt%) and Al2O3 (12-15 wt%), low amounts of Nb, P, Sr, Ti, a high ratio of Ga/Al (4-9) and a negative Eu anomaly. The chemical compositions of metagranites are reasonably similar to A- and I-type granites. U-Pb zircon ages of three samples of metagranites indicate that crystallization of the granites occurred at 521.6 ± 9.1 to 513.5 ± 8.5 Ma, Middle Cambrian. The initial 87Sr/86Sr and 143Nd/144Nd ratios of samples vary from 0.7057-0.7239 and 0.511801-0.511890, respectively. High initial 87Sr/86Sr ratios and low εNd(t) values (- 3.39 to - 1.07) associated with high ratios of 206Pb/204Pb(t) = 17.8557-18.8045, 207Pb/204Pb(t) = 15.6721-15.7220, and 208Pb/204Pb(t) = 37.7490-38.4468 infer a significant contribution of continental crust in generating the source magma of the metagranite bodies. The results reveal that the metagranites were mainly produced through mixing of basaltic melts with components similar to metasedimentary sources. The new results show that crystallization of the metagranites occurred in Early Paleozoic times and much earlier than break-up and drifting of the SaSZ from the Arabian plate, suggesting that the metagranites were mainly produced in the western Iran after the closure of the Proto-Tethys Ocean. This model is consistent with the previously suggested models for formation of an Early Paleozoic granitoid belt along the northern rim of Gondwana.

  17. Effects of Si3N4 passivation on the dc and RF characteristics of metamorphic high-electron-mobility transistors depending on the gate-recess structures

    International Nuclear Information System (INIS)

    Oh, J H; Han, M; Baek, Y H; Moon, S W; Rhee, J K; Kim, S D

    2009-01-01

    Effects of the Si 3 N 4 passivation on the dc and RF characteristics of a 0.1 µm metamorphic high-electron-mobility transistor (HEMT) are investigated for narrow and wide gate-recess structures. Maximum drain-source saturation current (I dss,max ) and maximum extrinsic transconductance (g m,max ) are reduced by ∼14.8 and ∼11.6%, respectively, in the wide gate-recess structure after the passivation; on the other hand, only ∼5.7 and ∼4.9% reductions are measured from I dss,max and g m,max , respectively, in the narrow gate-recess structure. We examine the passivation-induced degradation by using a modified charge control model assuming the charged surface states on the Si 3 N 4 interface and a comparative study of the hydrodynamic device simulation with the experimental measurement. From the analysis, it is proposed that the difference of degradation in two different gate structures is due to an approximately three times higher charged surface state density of ∼4.5 × 10 11 cm −2 in the wide gate-recess structure than ∼1.6 × 10 11 cm −2 in the narrow gate-recess structure. The cut-off frequency (f T ) of the wide gate-recess structure also exhibits a greater reduction of ∼14.5%, while the f T of the narrow gate-recess structure is reduced by only ∼6.6% after the passivation. This is mainly due to the passivation-induced surface states of a higher density in the wide gate-recess structure. A great increase of the gate-to-drain parasitic capacitance in the wide gate-recess structure makes a major contribution to ∼13.5% degradation of the maximum frequency of oscillation

  18. Differential equilibration and intergranular diffusion of trace elements during rapid regional metamorphism: constraints from LA-ICP-MS mapping of a garnet population

    Science.gov (United States)

    George, F. R.; Gaidies, F.

    2017-12-01

    Trace element zoning contained within a metapelitic garnet population yields information pertaining to a more complex prograde reaction history than is evident in major element zoning patterns and other conventional analyses. In particular, while trace elements may not act as a rate-limiting component for garnet crystallization, their incorporation into garnet growth surfaces provides a nuanced insight into the crystallization history of the population, and the extent of equilibration of trace elements in the matrix. In this study, we present LA-ICP-MS raster maps of trace element concentrations from several population-representative, centrally sectioned garnets from a garnet-grade metapelite of the Sikkim Himalaya, India. Equilibrium forward modeling of garnet crystallization and simulation of diffusional modification indicates that the garnet population crystallized rapidly over <1 Myr between 515 °C/4.5 kbar and 565 °C/5.5 kbar, as a consequence of high heating rates during regional amphibolite-facies metamorphism. While the rate of diffusional homogenization of major divalent cations is interpreted to have exceeded the rate of interfacial advance (yielding simple prograde growth zoning), trace element distributions record a more complex transport history. In particular, yttrium and the heavy rare earth elements (HREE) document a transition from an overprinted sigmoidal core to concentric repeated HREE and yttrium annuli in all crystals. This suggests that there was a discrete increase in the length scale of equilibration along the advancing garnet interface at some point in the growth history. However, there is no evidence for a coeval change in HREE transport thorough the intergranular network. Conversely, spiral core-to-rim zoning of chromium indicates the element remains almost completely immobile in the matrix over the duration of garnet growth.

  19. 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.

  20. 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.

  1. Hygroscopic Metamorphic 4D Pleats

    Science.gov (United States)

    Yang, Shu

    There have been significant interests in morphing 2D sheets into 3D structures via programmed out-of-plane distortion, including bending, tilting, rotating, and folding as seen in recent origami and kirigami strategies. Hydrogel is one of the unique soft materials that can swell and shrink, thereby enabling real-time 4D motions in response to external stimuli, such as pH, temperature, and moisture. To achieve reliable folding behaviors, it often requires a large amount of water molecules or ions diffusing in and out of the hydrogel sheet, thus the entire sheet is immersed in an aqueous solution. Here, we demonstrate the design and folding of hierarchical pleats patterned from a combination of hydrophobic and hygroscopic materials, allowing us to spatially and locally control the water condensation induced by environmental humidity. In turn, we show out-of-plane deformation of the 2D sheets only in the patterned hygroscopic regions, much like the folding behaviors of many plants. By designing the dimension, geometry, and density of hygroscopic microstructures (as pixels) in the hydrophobic materials, we can display the enhanced water condensation together with the spatial guidance of obtained droplets as unified water-harvesting systems. When the water droplets become large enough, they roll off from the hierarchical sheet along the inclined plane that is programmed by the hygroscopic motion of hydrogel, and eventually wrapped by the folded sheet to keep them from evaporation. We acknowledge support from NSF/EFRI-ODISSEI, EFRI 13-31583.

  2. Evolution of borate minerals from contact metamorphic to hydrothermal stages: Ludwigite-group minerals and szaibélyite from the Vysoká - Zlatno skarn, Slovakia

    Science.gov (United States)

    Bilohuščin, Vladimír; Uher, Pavel; Koděra, Peter; Milovská, Stanislava; Mikuš, Tomáš; Bačík, Peter

    2017-09-01

    Borate minerals of the ludwigite group (LGM) and szaibélyite in association with hydroxylclinohumite, clinochlore, a serpentine mineral, magnesian magnetite, spinel, magnesite, dolomite and sulphide minerals, occur in a magnesian exoskarn in the R-20 borehole located in the Vysoká - Zlatno Cu-Au porphyry-skarn deposit, located within the Štiavnica Neogene stratovolcano, Western Carpathians, central Slovakia. The skarn is developed along the contact of Miocene granodiorite to quartz-diorite porphyry and a Middle-Upper Triassic dolomite-shale-psammite-anhydrite sedimentary sequence. The boron minerals were investigated by electron probe micro-analyser (EPMA) and micro-Raman techniques. The source of boron could have been from the granodiorite/quartz diorite intrusion; however some supply of B from adjacent evaporite-bearing sediments is also possible. Based on textural and compositional data, the minerals originated during two stages. (1) An early high-temperature, contact-metamorphic and metasomatic stage comprises coarse-crystalline aggregate of LGM (types 1 to 3) in association with hydroxylclinohumite, magnetite, and rarely spinel inclusions in LGM. Compositional variations of LGM show a crystallization sequence from early azoproite [≤17 wt% TiO2; 0.40 atoms pre formula unit (apfu) Ti, which correspond to ≤79 mol% of the Mg2(Mg0.5Ti0.5)O2(BO3) end-member], Ti-Al-rich members of LGM, "aluminoludwigite "[≤14 wt% Al2O3; ≤0.53 apfu, ≤53 mol% of Mg2AlO2(BO3) end-member] and Al-rich ludwigite in the central zone of crystals, to Ti-Al-poor ludwigite in outer parts of crystals. (2) Minerals of the late retrograde serpentinization and hydrothermal stage form irregular veinlets and aggregates, including partial alteration of hydroxylclinohumite to the serpentine-group mineral and clinochlore, replacement of LGM by szaibélyite, formation of the latest generation of Fe-rich, Ti-Al poor ludwigite in veinlets (type 4), and precipitation of dolomite, magnesite and

  3. The Keimoes Suite redefined: The geochronological and geochemical characteristics of the ferroan granites of the eastern Namaqua Sector, Mesoproterozoic Namaqua-Natal Metamorphic Province, southern Africa

    Science.gov (United States)

    Bailie, Russell; Macey, Paul Hugh; Nethenzheni, Sedzani; Frei, Dirk; le Roux, Petrus

    2017-10-01

    Voluminous granite gneisses and granites straddle the boundary between the Kakamas and Areachap Terranes in the eastern Namaqua Sector (NS) of the Mesoproterozoic Namaqua-Natal Metamorphic Province (NNMP). These rocks have been previously poorly defined and loosely grouped into the Keimoes Suite, but a recent U-Pb age study has suggested the suite be subdivided into syn-tectonic and post-tectonic groups relative to the main phase of the Namaqua Orogeny. This study adds new whole rock geochemical, isotopic and age data for these granites that confirms the subdivision is appropriate. The older group of syn-tectonic granite gneisses, dated between 1175 and 1146 Ma, have penetrative foliations and are largely derived from fractionated, leucogranitic metaluminous to peraluminous magmas with low maficity, low Ti, Mn and Ca. They were derived from mildly depleted sources (εNd(t): -1.47 to 1.78), with Meso-to Paleoproterozoic Nd model ages (1.57-1.91 Ga), and high initial Sr ratios (0.71970-0.75567) suggesting mixing between younger depleted and older, arc-like sources imparting an arc-like signature to the magmas. High initial Sr ratios appear to be an intrinsic character of these granites reflecting those of granites in the region and the highly radiogenic nature of the NS. The weakly to unfoliated late-to post-tectonic megacrystic granodiorites and monzogranites, including charnockites, intruded between 1110 and 1078 Ma and constitute the Keimoes Suite proper. They have I-type characteristics, being strongly metaluminous and locally hornblende- and orthopyroxene-bearing with moderate SiO2 and with arc-type affinities (LILE enrichment relative to the HFSE, Ta-Nb, Ti and P anomalies). However, the granitoids also have high Fe/Mg ratios, along with high HFSE, LILE and REE contents more indicative of A-type granites. They show an increasing maficity, metaluminous character, and general decreasing degree of fractionation with decreasing age. They are similar to the syn

  4. 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

  5. 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

  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. Lu-Hf geochronology on cm-sized garnets using microsampling: New constraints on garnet growth rates and duration of metamorphism during continental collision (Menderes Massif, Turkey)

    Science.gov (United States)

    Schmidt, Alexander; Pourteau, Amaury; Candan, Osman; Oberhänsli, Roland

    2015-12-01

    provides a precise age determination for prograde Barrovian metamorphism in the southern Menderes Massif, which so far was placed between 63 and 27 Ma on the basis of mica Rb-Sr and Ar-Ar dating. This study provides new constraints crucial to the understanding of the tectonic evolution of southwest Anatolia and the Aegean realm, as it yields a shorter outline for Alpine aged continental collision.

  8. Retrograde metamorphism of the eclogite in North Qaidam, western China: Constraints by joint 40Ar/39Ar in vacuo crushing and stepped heating

    Directory of Open Access Journals (Sweden)

    Rongguo Hu

    2015-09-01

    Full Text Available Two amphiboles and a syn-metamorphic quartz vein from the Yuka terrane, North Qaidam, western China, have been analyzed by joint 40Ar/39Ar crushing in vacuo and stepwise heating techniques. The crushing in vacuo results provide information to directly constrain the timing of fluid activity and the age of amphibolite-facies retrogression. The stepwise heating results could further be used to decipher the thermal history of the UHP rocks. Amphiboles from amphibolites and quartz vein within garnet-amphibolite lens analyzed by in vacuo crushing yield similarly shaped age spectra and exhibit relatively flat age plateaus for the last several steps. The characteristics of gas release patterns and geochronological data testify to the presence of significant excess 40Ar within the fluid inclusions. The age plateaux with weighted mean ages (WMA ranges from 488 to 476 Ma for amphiboles and 403 Ma for quartz (2σ. These data points constitute amphibole WMA yielding excellent isochrons with isochron ages of 469 and 463 Ma with initial 40Ar/36Ar ratios of 520 and 334, respectively. The isochron ages are interpreted to represent initial amphibolite-facies retrogression. The data points constituting the quartz age plateaux give an isochron age of 405 Ma with initial 40Ar/36Ar ratio of 295, recording a significant aqueous fluid flow episode during the early Devonian. Age spectra obtained by stepwise heating of amphibole residues remaining after crushing experiments are characterized by younger and relatively complex age spectra, which are probably influenced by the combined effects of resetting argon and/or mineral inclusions. Nevertheless, we note that the spectra shapes have features in common: excluding the last two steps, minimum apparent ages are found at temperatures of around 500 °C, corresponding to 319 and 249 Ma, perhaps representing the time of isotopic resetting or resulting from release gas from mineral inclusions of, e.g., biotite or feldspar

  9. Early Cretaceous overprinting of the Mesozoic Daqing Shan fold-and-thrust belt by the Hohhot metamorphic core complex, Inner Mongolia, China

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    Gregory A. Davis

    2010-10-01

    Full Text Available The Early Cretaceous Hohhot metamorphic core complex (mcc of the Daqing Shan (Mtns. of central Inner Mongolia is among the best exposed and most spectacular of the spatially isolated mcc’s that developed within the northern edge of the North China “craton”. All of these mcc’s were formed within the basement of a Late Paleozoic Andean-style arc and across older Mesozoic fold-and-thrust belts of variable age and tectonic vergence. The master Hohhot detachment fault roots southwards within the southern margin of the Daqing Shan for an along-strike distance of at least 120 km. Its geometry in the range to the north is complicated by interference patterns between (1 primary, large-scale NW-SE-trending convex and concave fault corrugations and (2 secondary ENE-WSW-trending antiforms and synforms that folded the detachment in its late kinematic history. As in the Whipple Mtns. of California, the Hohhot master detachment is not of the Wernicke (1981 simple rooted type; instead, it was spawned from a mid-crustal shear zone, the top of which is preserved as a mylonitic front within Carboniferous metasedimentary rocks in its exhumed lower plate. 40Ar–39Ar dating of siliceous volcanic rocks in basal sections of now isolated supradetachment basins suggest that crustal extension began at ca. 127 Ma, although lower-plate mylonitic rocks were not exposed to erosion until after ca. 119 Ma. Essentially synchronous cooling of hornblende, biotite, and muscovite in footwall mylonitic gneisses indicates very rapid exhumation and at ca. 122–120 Ma. Contrary to several recent reports, the master detachment clearly cuts across and dismembers older, north-directed thrust sheets of the Daqing Shan foreland fold-and-thrust belt. Folded and thrust-faulted basalts within its foredeep strata are as young as 132.6 ± 2.4 Ma, thus defining within 5–6 Ma the regional tectonic transition between crustal contraction and profound crustal extension.

  10. Growth, strain relaxation properties and high-κ dielectric integration of mixed-anion GaAs1-ySby metamorphic materials

    Science.gov (United States)

    Zhu, Y.; Clavel, M.; Goley, P.; Hudait, M. K.

    2014-10-01

    Mixed-anion, GaAs1-ySby metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs1-ySby materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs1-ySby. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs1-ySby structures. Selected high-κ dielectric materials, Al2O3, HfO2, and Ta2O5 were deposited using atomic layer deposition on the GaAs0.38Sb0.62 material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs0.38Sb0.62, indicating the potential of utilizing these dielectrics on GaAs0.38Sb0.62 for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al2O3 and HfO2 showed a conduction band offset of >2 eV on GaAs0.38Sb0.62, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs1-ySby material systems and the detailed band alignment analysis of multiple high-κ dielectric materials on a fixed Sb composition, GaAs0.38Sb0.62, provides a pathway to utilize GaAs1-ySby materials in future microelectronic and optoelectronic applications.

  11. 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.

  12. 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)

  13. Atividade da tripsina em rã-touro na fase pós-metamórfica Trypsin activity of the bullfrog in the post-metamorphic phase

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    Luís Gustavo Tavares Braga

    2004-08-01

    Full Text Available Com o objetivo de avaliar a atividade enzimática da tripsina no conteúdo intestinal da rã-touro (Rana catesbeiana Shaw, 1802, 320 animais com peso médio de 3,6 g foram distribuídos em baias-teste com temperatura e fotoperíodo controlados. As rãs selecionadas na fase pós-metamórfica receberam ração comercial extrusada ad libitum. Durante 87 dias de experimento, foram efetuadas 29 coletas em intervalos de 1 a 8 dias. As coletas do conteúdo intestinal foram feitas mediante a insensibilização das rãs em gelo e água e posterior isolamento do intestino delgado. Após cada coleta, todo o material foi congelado em nitrogênio líquido e armazenado em freezer, para posterior liofilização. A determinação da atividade da tripsina foi realizada utilizando-se Benzoil-D, L-Arginina p-nitroanilida (D, L-BApNA como substrato. A atividade da tripsina foi registrada no primeiro dia de experimento; a fase inicial foi marcada pelo aumento da atividade da tripsina até a estabilidade, quando os animais ainda estavam na fase de imago. O período subseqüente (até o final do experimento foi caracterizado pela manutenção da estabilidade da atividade e pela atividade específica da tripsina. Pode-se concluir que a rã-touro apresenta capacidade para digestão de alimentos de origem protéica, recomendando-se, na fase inicial, uso de ração rica em proteína.With the objective of evaluating the enzymatic activity of the trypsin in the intestinal content of the bullfrog (Rana catesbeiana Shaw, 1802, 320 animals with average weight of 3.6 grams were distributed in stall-test with temperature and photoperiod controlled. The frogs selected in the post-metamorphic phase were fed commercial extruded diet ad libitum. For 87 days of experiment, 29 collections were performed at intervals varying from one to eight days. The collections of the intestinal content were performed by the desensitization of the frogs in ice and water and subsequent isolation of

  14. Subduction Metamorphism of Ophicarbonates beyond the Stability of Antigorite: insights into Carbonate Dissolution vs. Decarbonation from the Almirez ultramafic massif (S. Spain)

    Science.gov (United States)

    Menzel, Manuel; Garrido, Carlos J.; López Sánchez Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

    2017-04-01

    Subduction zone processes play a key role in determining the time and length-scales of long-term element cycles like the deep carbon cycle. Recent improvements in thermodynamic modelling of fluid properties at high pressure and new experiments have underlined the importance of carbonate dissolution by subduction fluids from dehydration reactions for the transfer of carbon out of the subducting slab. However, natural case studies are scarce, in particular regarding the impact of fluids generated by serpentinite dehydration, which are considered as a major dissolution agent for carbon due to the high temperature of antigorite breakdown (about 650°C) and the potentially large volumes of hydrated peridotites occurring in the upper part of the subducting oceanic mantle lithosphere. Here we report the occurrence of meta-ophicarbonate lenses within prograde Chl-harzburgites in the Almirez ultramafic massif (Betic Cordillera, S. Spain). The presence of these lenses indicates that carbonate minerals were preserved beyond the stability conditions of antigorite and were not dissolved by deserpentinization fluids. The largest meta-ophicarbonate lens in the Almirez Chl-harzburgites measures 8 x 160 m and is composed of a high-grade assemblage of olivine, Ti-clinohumite, diopside, chlorite, dolomite, calcite and Cr-bearing magnetite with a granofelsic to banded appearance. In this assemblage we identified, for the first time in the Betic Cordillera, aragonite inclusions in olivine and diopside using coupled EBSD and chemical mapping. Calcite-dolomite thermometry and thermodynamic equilibrium modelling constrain the peak metamorphic conditions to 1.7 - 1.9 GPa and 680 °C at very low XCO2. These conditions compare well with P-T-estimates for the surrounding Chl-harzburgites. There is strong evidence that the protolith of the carbonate rocks within Chl-harzburgites was an ophicarbonate zone: bulk rock contents of Ni and Cr are similarly high in the carbonate rocks as in Atg

  15. Assessment of the hydraulic properties of fractured aquifers in crystalline and metamorphic formations in the region of Lacs (Central Côte d’Ivoire

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    Soro, G.

    2010-12-01

    Full Text Available Groundwater is the main source of water supply for rural populations in the Region des Lacs area in central Côte d’Ivoire (West Africa. The area is underlain by the metamorphic and crystalline fractured hard rock aquifers. This paper focuses on the assessment of their hydraulic properties. To this end, a data base comprising pumping tests data and the technical reports were gathered. 105 values of transmissivity (T and specific capacity (Q/s have been deduced after pumping tests interpretation by the Jacob recovery method. Statistical analyses of all these data have been done. Depth of wells range from 49.50 to 99 m with an average of 69 m. The thickness of the weathered zone has averaged 16.52 m and lies between 1.90 and 63.10 m. Wells average rate is 2.32 m3/s. The depths of open fractures are significantly in the first 60 meters of hard rock drilling and averaged 42.94 m. The transmissivity and specific capacity of each aquifer span over several orders of magnitude revealing the strong heterogeneity of the aquifer. Both variables are lognormal variables A significant empirical relationship between T and Q/s was found T = 0,937(Q/s^1.118 with a coefficient of determination (R^2 = 0.82. This relationship enabled the transmissivity data to be supplemented with the 95% prediction interval in order to assess the uncertainty associated with the estimates of transmissivity in the area of the study. These results are significant and can be used as an input in forthcoming modeling these aquifers and facilitate groundwater management policy.

    [fr] Dans la région des Lacs, centre de la Côte d’Ivoire (Afrique de l’Ouest, l’alimentation en eau potable des populations rurales est assurée en majorité par les eaux souterraines contenues dans les aquifères discontinus cristallin et cristallophyllien. L’objet de cet article est d’évaluer les propriétés hydrauliques de ces aquifères afin d’entreprendre des études pour la gestion

  16. 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.

  17. Terahertz radiation in In{sub 0.38}Ga{sub 0.62}As grown on a GaAs wafer with a metamorphic buffer layer under femtosecond laser excitation

    Energy Technology Data Exchange (ETDEWEB)

    Ponomarev, D. S., E-mail: ponomarev-dmitr@mail.ru; Khabibullin, R. A.; Yachmenev, A. E.; Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultrahigh Frequency Semiconductor Electronics (Russian Federation); Grekhov, M. M. [National Research Nuclear University “MEPhI” (Russian Federation); Ilyakov, I. E.; Shishkin, B. V.; Akhmedzhanov, R. A. [Russian Academy of Sciences, Institute of Applied Physics (Russian Federation)

    2017-04-15

    The results of time-domain spectroscopy of the terahertz (THz) generation in a structure with an In{sub 0.38}Ga{sub 0.62}As photoconductive layer are presented. This structure grown by molecular-beam epitaxy on a GaAs substrate using a metamorphic buffer layer allows THz generation with a wide frequency spectrum (to 6 THz). This is due to the additional contribution of the photo-Dember effect to THz generation. The measured optical-to-terahertz conversion efficiency in this structure is 10{sup –5} at a rather low optical fluence of ~40 μJ/cm{sup 2}, which is higher than that in low-temperature grown GaAs by almost two orders of magnitude.

  18. 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.

  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. 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

  1. Reply to comment on "Direct evidence of ancient shock metamorphism at the site of the 1908 Tunguska event" by Vannucchi et al. (Earth Planet. Sci. Lett. 409 (2015) 168-174)

    Science.gov (United States)

    Vannucchi, Paola; Morgan, Jason P.

    2015-04-01

    Our paper (Vannucchi et al., 2015) focuses on geologic evidence for shock metamorphism found at the epicentral region of the 1908 Tunguska event. None of the currently proposed bolide explanations for the 1908 event can produce the shock pressures indicated by the geological evidence described in Vannucchi et al. (2015). If the 1908 event would have generated these pressures over the epicentral region, an observable crater should have also formed. The comment by Melott and Overholt discusses the possibility that a 1908 cometary bolide strike in Tunguska cannot be excluded because of the absence of a detectable 14C increase at this site. They dispute the findings of a recent Liu et al.'s (2014) study that an East Asian comet impact recorded by eyewitness accounts in 773 AD was coincident with a detectable 14C increase in regional South China Sea corals that grew at that time. Their point, whether true or not, is fairly peripheral to our study because the bolide hypothesis for the 1908 Tunguska event, no matter the nature of the bolide itself, does not provide a viable explanation for the geological evidence of shock metamorphism found at the 1908 Tunguska site. Furthermore, as we discuss in our paper, the probability of a prior large impact-shock event having occurred at the site of the 1908 event is extremely low, suggesting that a terrestrial shock-generating mechanism may be linked to the resolution of the Tunguska enigma. Our preferred resolution is that a terrestrial hyper-explosive gas release event, a Verneshot (Morgan et al., 2004), created the large shock-event during the emplacement of the Siberian Traps. In this scenario, the 1908 Tunguska event was due to a much smaller gas-burst that re-used the lithospheric weakness created by the ancient Verneshot. Melott and Overholt's discussion regarding the existence and size of regional and global 14C anomalies related to cometary impacts seems, therefore, to be better addressed in response to the work of Liu et

  2. Thirty-five-nm T-Gate In0.52Al0.48As/In0.53Ga0.47As metamorphic HEMTs with an ultrahigh fmax of 610 GHz

    International Nuclear Information System (INIS)

    Choi, Do-Young; Kim, Sung-Ho; Choi, Gil-Bok; Jung, Sung-Woo; Jeong, Yoon-Ha

    2010-01-01

    Thirty-five-nanometer T-gate GaAs-based In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As metamorphic high electron mobility transistors (mHEMTs) are successfully fabricated using a zigzag-shaped T-gate. We obtain a maximum extrinsic transconductance (g m ) of 1060 mS/mm and a maximum oscillation frequency (f max ) of 610 GHz. These superior results are obtained by reducing the T-gate's length to 35 nm without the assistance of a supporting layer and by fabricating a wide-recessed-gate structure. The stand-alone 35-nm T-gate effectively improves the device performance because it doesn't cause additional parasitic capacitances. The wide-recessed-gate structure alleviates impact ionization in the channel, which suppresses the kink effect in the output characteristic and reduces the output conductance (g ds ). In addition, the wide-recessed-gate structure reduces the gate-to-drain capacitance (C gd ); consequently realizing a state-of-the-art f max . The f max of 610 GHz, to our knowledge, is the highest value reported to date for GaAs-based HEMTs.

  3. Ultraviolet light emitting diodes by ammonia molecular beam epitaxy on metamorphic (KAUST Repository

    Young, Erin C.

    2015-09-01

    © 2015. In this paper we demonstrate ultraviolet (UV) light emitting diodes (LEDs) grown on metamorphic AlGaN buffers on freestanding GaN (202-1) substrates by ammonia assisted molecular beam epitaxy (MBE). Misfit and related threading dislocations were confined to the stress relaxed, compositionally graded buffer layers, and single quantum well devices emitting at 355, 310 and 274. nm were grown on top of the graded buffers. The devices showed excellent structural and electrical (I-. V) characteristics.

  4. Evolution of the Archean continental crust in the nucleus of the Yangtze block: Evidence from geochemistry of 3.0 Ga TTG gneisses in the Kongling high-grade metamorphic terrane, South China

    Science.gov (United States)

    Qiu, Xiao-Fei; Ling, Wen-Li; Liu, Xiao-Ming; Lu, Shan-Song; Jiang, Tuo; Wei, Yun-Xu; Peng, Lian-Hong; Tan, Juan-Juan

    2018-04-01

    Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks are scattered within the Kongling high-grade metamorphic terrane (KHMT) in the northern South China block. A comprehensive geochronological and geochemical study is carried out on the Taoyuan granitic gneisses, a newly recognized TTG suite in the northwestern KHMT. This suite has long been regarded as a Mesoproterozoic magmatic pluton, but U-Pb zircon ages of 2994 ± 22 Ma and 2970 ± 15 Ma are obtained by LA-ICP-MS method in this study. The Taoyuan gneiss suite is trondhjemitic in composition, and has high SiO2 (67.80-74.93 wt.%), Na2O (5.11-5.81 wt.%) contents with Na2O/K2O ratios greater than unity, and low Ni (2.56-7.61 ppm), Cr (1.26-7.67 ppm), Yb (0.32-0.82 ppm) and Y (4.48-11.5 ppm) contents. Plots show large variation in La/Yb and Sr/Y ratios and pronounced depletion in Nb, Ta and Ti in the primitive mantle-normalized spiderdiagram. The gneiss suite also displays two-stage Nd model ages close to its crystallization age with corresponding εNd(t) values of -2.5 to +3.5. It is thus suggested that the Taoyuan gneisses, in fact, is part of the Archean Kongling basement complex. Geochemical evidence implies that the TTG rocks may be derived from partial melting of subducted oceanic crust from a garnetiferous amphibolite source with residual assemblage of garnet + amphibole + plagioclase. Our study further indicates that the nucleus of the Yangtze block might experience a juvenile continental crustal growth during Mesoarchean. We also suggest that the Yangtze block may have its own crustal evolutionary history independent from the North China craton and the Tarim block before Paleoproterozoic.

  5. 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.

  6. 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...

  7. Monitoring of stress relaxation and defect formation in metamorphic III-V semiconductor heterostructures for high-efficiency solar cells; Kontrolle von Spannungsrelaxation und Defektbildung in metamorphen III-V Halbleiterheterostrukturen fuer hocheffiziente Solarzellen

    Energy Technology Data Exchange (ETDEWEB)

    Schoene, Jan

    2009-07-21

    The paper discusses the further development of monolithic III-V multiple solar cells with three pn transitions for applications in concentrating PV systems. These triple solar cells consist of a GaInP upper cell, a GaInAs middle cell and a germanium lower cell, which are connected via electrically conducting and optically transparent tunnel diodes. Efficiencies are higher than 40 % with concentrated light. Demands on materials for III-V high-efficiency solar cells are extremely high. Especially in the metamorphic triple solar cell, for which compound semiconductors with different interatomic distances are deposited epitactically on each other, crystal defects may occur that impair the performance of the solar cell. The use of appropriate layer growing concepts may manipulate the formation of crystal defects and minimize their influence on solar cell performance. Both conventional and high-resolution transmission electron microscopy (TEM and HRTEM) as well as high-resolution X-ray diffraction (HRXRD) were applied successfully for investigating defect formation and layer stresses. In the investigations described, these methods were applied to develop a high-efficiency triple solar cell with a world first efficiency of 41.1 percent in concentrated light. [German] Diese Arbeit beschaeftigt sich mit der Weiterentwicklung von monolithischen III-V-Mehrfach-Solarzellen mit drei pn-Uebergaengen fuer die Anwendung in konzentrierenden Photovoltaiksystemen. Diese Tripelsolarzellen bestehen aus einer GaInP-Oberzelle, einer GaInAs-Mittelzelle und einer Germanium-Unterzelle, die mittels elektrisch leitender und optisch transparenter Tunneldioden verbunden sind. Derartige Solarzellen erzielen mittlerweile Rekordwirkungsgrade von mehr als 40 % unter konzentriertem Licht. Bei den III-V Hocheffizienzsolarzellen sind die Anforderungen an die Materialqualitaet ausserordentlich hoch. Insbesondere bei der metamorphen Tripelsolarzelle, bei der Verbindungshalbleiter mit unterschiedlichen

  8. Atividade da amilase em rã-touro durante a fase pós-metamórfica Amylase activy in the bulfrog during the post-metamorphic phase

    Directory of Open Access Journals (Sweden)

    Luís Gustavo Tavares Braga

    2005-10-01

    Full Text Available O objetivo deste trabalho foi avaliar a atividade da amilase no quimo da rã-touro, Rana catesbeiana Shaw 1802 (3,6 a 200 g. Oitenta e sete animais foram distribuídos em baias-testes com temperatura e fotoperíodo controlados. As rãs selecionadas na fase pós-metamórfica receberam ração comercial extrusada ad libitum. Durante 87 dias de experimento, foram efetuadas 29 coletas em intervalos de 1 a 8 dias. As coletas do conteúdo intestinal foram feitas mediante a insensibilização das rãs em gelo e água e isolamento posterior do intestino delgado das mesmas. Para os testes da atividade da amilase, foram utilizados kits enzimáticos comerciais. A atividade da amilase foi observada a partir do terceiro dia e apresentou aumento até alcançar estabilidade, quando os animais pesavam 4,35 g. Do sétimo dia até o final do experimento, ocorreu a manutenção da estabilidade da atividade (137,44 UI e atividade específica da amilase (14.688 UI mg-1.The objective of this work was to evaluate the amylase activity in the chime of the bullfrog Rana catesbeiana Shaw 1802 (3.6 to 200 g. Eighty-seven animals were distributed in test stalls with controlled temperature and photoperiod. The frogs selected in the post-metamorphic phase received commercial extruded diet ad libitum. During 87 days of the experiment, 29 samples were collected in intervals varying from one to eight days. The intestinal content samples were made by first desensitizing of the frogs in ice and water, and subsequently removing the small intestine. For the tests of amylase activity, commercial enzymatic kits were used. Amylase activity was observed since the third day and it increased until reaching stability, when the animals weighed 4.35 g. Amylase activity (137.44 UI and specific activity (14,688 UI mg-1 remained stable from the seventh day until the end of the experiment.

  9. 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)

  10. Efeito da densidade de estocagem no desempenho de rã-touro (Rana catesbeiana em recria Effects of stocking density on performance of bullfrog (Rana catesbeiana in the post-metamorphic phase

    Directory of Open Access Journals (Sweden)

    Alex Poeta Casali

    2005-12-01

    Full Text Available Este trabalho foi realizado com o objetivo de avaliar quatro densidades de estocagem na recria de rã-touro em mini-baias. As densidades estudadas foram: D1: 75 rãs/m² (inicial e 35 rãs/m² (final; D2: 105 rãs/m² (inicial e 50 rãs/m² (final; D3: 125 rãs/m² (inicial e 60 rãs/m² (final; e D4: 160 rãs/m² (inicial e 75 rãs/m² (final. No ensaio de desempenho, foram utilizadas 558 rãs com peso médio de 26,80 g durante 56 dias, distribuídas em um delineamento em blocos casualizados, com seis repetições. Houve efeito das densidades sobre o ganho de peso, que foram inversamente proporcionais. Menores densidades resultaram em maior consumo de alimento, de modo que, com o uso das densidades iniciais de 75 e 105 rãs/m², obteve-se maior consumo de alimento que o uso de 125 e 160 rãs/m². A conversão alimentar aparente também variou; a densidade inicial de 160 rãs/m² proporcionou a pior média desse parâmetro. Os tratamentos foram avaliados economicamente, segundo os custos com alimentação, a receita bruta e a receita líquida parcial proporcionados. Concluiu-se que a densidade final de 50 rãs/m² aumentou a receita líquida parcial, proporcionando resultados mais adequados para produção de rãs.This work was carried out with the objective of evaluate four stocking densities of bullfrog (post-metamorphic in mini-stalls. The densities studied were D1: 75 bullfrogs/m² (initial and 35 bullfrogs/m² (finishing; D2: 105 bullfrogs/m² (initial and 50 bullfrogs/m² (finishing; D3: 125 bullfrogs/m² (initial and 60 bullfrogs/m² (finishing; and D4: 160 bullfrogs/m² (initial and 75 bullfrogs/m² (finishing. The performance trial was carried out with 558 bullfrogs averaging initial weight of 26.80 g, during 56 days, according to a completely randomized blocks design with six replicates. Inversely proportional effects of densities on weight gain were observed. Smaller densities resulted in greater values of feed intake, and the initial

  11. SHRIMP chronology of the Magallanes Basin basement, Tierra del Fuego: Cambrian plutonism and Permian high-grade metamorphism Geocronología SHRIMP del basamento de la Cuenca de Magallanes, Tierra del Fuego: plutonismo Cámbrico y metamorfismo Pérmico de alto grado

    Directory of Open Access Journals (Sweden)

    Francisco Hervé

    2010-07-01

    Full Text Available Five new SHRTMP U-Pb zircon ages are reported for gneisses and foliated plutonic rocks belonging to the Tierra del Fuego igneous and metamorphic basement complex (TFIMC, obtained from the bottom of borehole cores through the Magallanes Basin. Three of the samples yielded weighted mean 206Pb/238U ages (523±7 Ma, 522±6 Ma and 538±6 Ma, interpreted as indicating Early Cambrian igneous crystallization of the host rocks. A migmatitic gneiss shows peaks at ca. 950-1,100 Ma and 560-650 Ma from inherited zircon grains in addition to two grains with ages of ca. 525 Ma, suggesting involvement of Grenvillian and Brasiliano material in the protolith of a Cambrian migmatite. A cordierite-sillimanite-garnet gneiss contains igneous zircons of Cambrian age and a population of U-rich metamorphic Permian zircons, indicating that a Permian high-grade metamorphic and anatectic (P=2-3 kbar, T=730-770°C event affected the Cambrian igneous rocks or sedimentary rocks derived from them. Cambrian/Ediacaran plutonic rocks are known from the basement of NW Argentina, the Sierra de la Ventana, the Cape Fold Belt in South Africa, and the Ross Orogen in Antarctica. The Permian metamorphic event is coeval with the deformation and low-grade metamorphism of the sedimentary successions that overlie the basement in many of these areas. In Tierra del Fuego at least 8 to 12 km of cover rocks were removed following the high-grade Permian metamorphic episode and the unconformable deposition of the Tobífera Formation volcanic rocks in the Middle to Late Jurassic. This eroded cover could nave been an important source of detritus for the conglomeratic Permian and Triassic? Successions of neighboring regions in South America, Africa and Antarctica.Cinco nuevas edades radiométricas logradas mediante análisis U-Pb en circón utilizando el SHRIMP, fueron determinadas en gneises y rocas plutónicas foliadas obtenidas desde el fondo de pozos de sondajes en la Cuenca de Magallanes y

  12. Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin Metamorfismo de bajo grado de sucesiones cambro-ordovícicas en el cinturón del Famatina, Andes Centrales de Argentina: Historia de enterramiento-exhumación ligada a la evolución del margen proto-andino de Gondwana

    Directory of Open Access Journals (Sweden)

    Gilda Collo

    2011-07-01

    Full Text Available The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Argentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar folding, with estimated temperatures between 290 and 400°C (KIcis: 0.16-0.27A°29, biotite blastesis and compositional homogeneity in dioctahedral micas and intermediate pressure conditions (white mica b parameter: 9.010Á-9.035Á, was recognized. The Achavil Formation (Middle-Upper Cambrian presents a main metamorphic event associated with temperatures between 200 and 290°C (KIcis: 0.26-0.41A°29 and intermediate- to low-pressure conditions (white mica b parameter values: 8.972Á-9.017Á. Some illitic substitution in dioctahedral micas also indicates lower metamorphic grade than the Negro Peinado Formation. For Upper Cambrian to Middle Ordovician sequences a burial metamorphic pattern, with a progressive decrease in metamorphic grade from Volcancito Formation to Cerro Morado Group (ca. 490-465 Ma; KIcis: 0.31-0.69A°29 and absence of tendency changes linked to strati-graphic discontinuities was proposed. Mica and chlorite are the main phyllosilicates in the oldest units, while Ilt/ Sme (R3 mixed-layer is almost the only one in the youngest. White mica b parameter indicates intermediate- to low-pressure conditions for all these sequences. This burial metamorphic pattern presents a marked break as the youngest Ordovician unit (La Aguadita Formation, after ca. 452 Ma records higher metamorphic conditions (IKcis: 0.28-0.19A°29 than units from the Ordovician arc, with estimated temperatures between 270 and 330°C and intermediate-pressure conditions. Our results indicate that basin contraction and inversion processes related to the Ordovician Ocloyic Orogeny involved at least two well-discriminated and not superposed metamorphic episodes in this region

  13. 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

  14. Polyphase white mica growth in low-grade metapelites from La Cébila Metamorphic Complex (Famatinian Belt, Argentina: evidence from microstructural and XRD investigations Crecimiento polifásico de mica blanca en metapelitas de bajo grado del Complejo Metamórfico La Cébila (Faja Famatiniana, Argentina: evidencias a partir de investigaciones microestructurales y de DRX

    Directory of Open Access Journals (Sweden)

    Sebastián O Verdecchia

    2011-07-01

    Full Text Available Two tectono-thermal metamorphic events, M1-D1 (S1, with associated white mica and chlorite: WM1-Chl1 and M2-D2 (S2, with development of WM2-Chl2, are established from polyphase white mica growth for low-grade units from the Ordovician metasedimentary successions of La Cébila Metamorphic Complex in the Famatinian belt (western-central Argentina. The thermobarometric characterization of the M1 main event was carried out by means of clay-mineral analysis and crystallo-chemical parameter measurements. Epizonal (temperatures between 300 and 400°C and low-pressure conditions are suggested for M1 event, based in Kübler index values ranging from 0.23 to 0.17 A°20, white mica b parameter values between 9.004 and 9.022 Á (mean of 9.014 Á, n=16 and Si contents between 3.13-3.29 a.p.f.u. Temperatures of ~180-270°C are estimated for the M2 event, with Kübler index values ranging from 0.31 to 0.46 A°20. The M1-D1 event of La Cébila could be linked to high-strain heating tectono-metamorphic Ordovician regime recorded in others complexes from Famatinian foreland region of Sierras Pampeanas.Dos eventos tectono-metamórficos fueron establecidos a partir de la blastesis superpuesta de mica blanca en sucesiones metasedimentarias ordovícicas de bajo grado del Complejo Metamórfico La Cébila, cinturón Famati-niano (centro oeste de Argentina: M1-D1 (S1, con blastesis asociada de mica blanca y clorita: WM1-Chl1 y M2-D2 (S2, con desarrollo de WM2-Chl2. La caracterización termobarométrica del evento principal M1 fue llevada a cabo a través del análisis de minerales de arcilla y de la medición de parámetros cristaloquímicos. Las condiciones de epizona con temperaturas entre 300 y 400°C, y baja presión fueron estimadas para el evento M1 sobre la base de valores de índice de Kübler de 0,23 a 0,17 A°20, parámetro b de la mica blanca entre 9,004 y 9,022 Á (valor medio de 9,014 Á, n=16 y contenidos de Si entre 3,13-3,29 a.p.f.u. Se estimaron

  15. Petrología y Estructura del Complejo Ígneo-Metamórfico Aluminé, Provincia de Neuquén, Argentina Petrology and Structure of the Aluminé Igneous-Metamorphic Complex, Neuquén province, Argentina

    Directory of Open Access Journals (Sweden)

    Ivana A Urraza

    2011-01-01

    andinas (cretácicas o más modernas y el sector sur donde dominan los granitoides preandinos de edades permotriásicas-jurásicas, emplazados en un basamento paleozoico. Si bien los diagramas geoquímicos permiten diferenciar los diferentes petrotipos definidos petrográficamente y sus tendencias evolutivas podrían indicar procesos de cristalización fraccionada, la distribución areal de los mismos, sus características petrográfico-microestructurales y la geocronología, indican que podrían corresponder a diferentes pulsos-eventos magmáticos separados en el tiempo, aunque desarrollados en un contexto de características tectónicas similares.In the present contribution, the partial results of a detailed study of the magmatic, metamorphic and tectonic events developed in the Aluminé Igneous-Metamorphic Complex (AIMC are given. We define the AIMC as the set of pre-andean and andean intrusive igneous and metamorphic rocks, outcropping in the área located between the Aluminé, Moquehue, Ñorquinco and Pulmarí lakes in the Neuquén province, Argentina. Based on field and petrographic observations and geochemical characteristics, the granitic rocks forming part of the AIMC have been classified as: 1. quartz diorites, 2. tonalites-granodiorites, 3. granodiorites and 4. granites. The geochemical parameters indícate that the defined lithologies derive from calcic to weakly calcalkaline magmas of metaluminous composition, typical of Type I Cordilleran batholiths associated with active continental margins. Intercalated between the magmatic rocks, some outcrops of metamorphic basement composed mainly of schists, gneisses, amphibolites and scarce quartzose sandstones. Andesites, tuffs and basalts cover in part the metamorphites and granitoids are exposed. The structure of the sector is characterized by the presence of three main sets of regional lineaments, with NE-SW, NW-SE and N-S orientations. These directions coincide with the orientations of the three groups of

  16. Petrographic and Geochemical Study of Low Grade Metamorphic ...

    African Journals Online (AJOL)

    interaction of water with ores and gangue minerals facilitate leaching and release of metals into the aquifer system ... of groundwater depends on its purpose of use i.e. for drinking, industry, irrigation etc. So, the ..... samples about one liter each were collected in pre-cleaned and numbered plastic bottles. The. © CNCS.

  17. High grade metamorphism in the Bundelkhand massif and its ...

    Indian Academy of Sciences (India)

    Journal of Earth System Science. Current Issue : Vol. 126, Issue 8 · Current Issue Volume 126 | Issue 8. December 2017. Home · Volumes & Issues · Special Issues · Forthcoming Articles · Search · Editorial Board · Information for Authors · Subscription ...

  18. Petrographic and Geochemical Study of Low Grade Metamorphic ...

    African Journals Online (AJOL)

    Hydrogeochemical data indicate that groundwater is relatively fresh and among major elements Na, Ca and Mg show relatively higher values compared to K. Water from metasediments is relatively harder among others. Na though shows higher values compared to Ca and Mg does not indicate any particular trend. Ca and ...

  19. Metamorphic GaAs/GaAsBi Heterostructured Nanowires.

    Science.gov (United States)

    Ishikawa, Fumitaro; Akamatsu, Yoshihiko; Watanabe, Kentaro; Uesugi, Fumihiko; Asahina, Shunsuke; Jahn, Uwe; Shimomura, Satoshi

    2015-11-11

    GaAs/GaAsBi coaxial multishell nanowires were grown by molecular beam epitaxy. Introducing Bi results in a characteristic nanowire surface morphology with strong roughening. Elemental mappings clearly show the formation of the GaAsBi shell with inhomogeneous Bi distributions within the layer surrounded by the outermost GaAs, having a strong structural disorder at the wire surface. The nanowire exhibits a predominantly ZB structure from the bottom to the middle part. The polytipic WZ structure creates denser twin defects in the upper part than in the bottom and middle parts of the nanowire. We observe room temperature cathodoluminescence from the GaAsBi nanowires with a broad spectral line shape between 1.1 and 1.5 eV, accompanied by multiple peaks. A distinct energy peak at 1.24 eV agrees well with the energy of the reduced GaAsBi alloy band gap by the introduction of 2% Bi. The existence of localized states energetically and spatially dispersed throughout the NW are indicated from the low temperature cathodoluminescence spectra and images, resulting in the observed luminescence spectra characterized by large line widths at low temperatures as well as by the appearance of multiple peaks at high temperatures and for high excitation powers.

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

    Indian Academy of Sciences (India)

    stage gold mineralization at the. Hutti mine, Dharwar craton, India; Miner. Deposita 40. 156–174. Kontak D J and Horne R J 2010 A multi-stage origin for the Meguma lode gold deposits, Nova Scotia, Canada: A possible global model for slate ...

  1. Contact metamorphism by an ophiolite peridotite from neyriz, iran.

    Science.gov (United States)

    Hall, R

    1980-06-13

    Ophiolites are conventionally regarded as fragments of former oceanic lithosphere. Mineralogical and field evidence indicates that peridotite of the Neyriz ophiolite was intruded at high temperature into folded crystalline limestones, forming skarns. This excludes the formation of the ophiolite at a mid-ocean ridge but is consistent with its origin by intrusion during continental rifting.

  2. 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 ...

  3. 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

  4. 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

  5. Contrasting metamorphism across Cauvery Shear Zone, south India

    Indian Academy of Sciences (India)

    The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating ...

  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. 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 ...

  8. 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 ...

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

    Indian Academy of Sciences (India)

    The granitoid pluton causes a high geothermal gradient resulted into the textural and miner- alogical changes in a narrow zone. The mineral assemblages of low pressure and low to high tem- perature conditions from outer to inner aureole along with textural and mineralogical changes. (figure 4) indicate the overprinting of ...