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  • Earth Sciences; Mineralogy; Mineral Resources; Geology  (1)
  • Elasmobranchia; Scyliorhinidae; taphonomy; exceptional preservation; collagen; Late Eocene; Washing− ton State; USA.  (1)
  • Fluid inclusions; Granulite; Charnockite; Cathodoluminescence; LA-ICPMS; Quartz  (1)
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  • 1
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    Fluid/rock interaction and mass transfer in continental subduction zones: constraints from trace elements and isotopes (Li, B, O, Sr, Nd, Pb) in UHP rocks from the Chinese Continental Scientific Drilling Program, Sulu, East China (2018)
    Springer-Verlag | Berlin/Heidelberg
    Details
    Publikationsdatum: 2021-03-29
    Beschreibung: In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu, China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite are characterized by a 〉10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B may show different patterns of enrichment and of isotopic fractionation.
    Schlagwort(e): Fluid/rock interaction; Elemental transfer; Isotopic fractionation; Subduction and exhumation; Sulu ; 551 ; Earth Sciences; Mineralogy; Mineral Resources; Geology
    Sprache: Englisch
    Materialart: article , publishedVersion
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    CITATION GEO-LEO
  • 2
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    Catshark egg capsules from a Late Eocene deep-water methane-seep deposit in western Washington State, USA (2018)
    Details
    Publikationsdatum: 2021-03-29
    Beschreibung: Fossil catshark egg capsules, Scyliorhinotheca goederti gen. et sp. nov., are reported from a Late Eocene deep−water methane−seep calcareous deposit in western Washington State, USA. The capsules are preserved three−dimensionally and some show mineralized remnants of the ribbed capsule wall consisting of small globular crystals that are embedded in a microsparitic matrix. The globules are calcitic, but a strontium content of 2400–3000 ppm suggests that they were origi− nally aragonitic. The carbonate enclosing the egg capsules, and the capsule wall itself, show 13C values as low as −36.5‰, suggesting that formation was induced by the anaerobic oxidation of methane and hence in an anoxic environ− ment. We put forward the following scenario for the mineralization of the capsule wall: (i) the collagenous capsules expe− rienced a sudden change from oxic to anoxic conditions favouring an increase of alkalinity; (ii) this led to the precipitation of aragonitic globules within the collagenous capsule wall; (iii) subsequently the remaining capsule wall was mineralized by calcite or aragonite; (iv) finally the aragonitic parts of the wall recrystallized to calcite. The unusual globular habit of the early carbonate precipitates apparently represents a taphonomic feature, resulting from mineralization mediated by an organic matrix. Taphonomic processes, however, are at best contributed to an increase of alkalinity, which was mostly driven by methane oxidation at the ancient seep site
    Schlagwort(e): Elasmobranchia; Scyliorhinidae; taphonomy; exceptional preservation; collagen; Late Eocene; Washing− ton State; USA. ; 551
    Sprache: Englisch
    Materialart: article , publishedVersion
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    CITATION GEO-LEO
  • 3
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    Deciphering fluid inclusions in high-grade rocks (2018)
    Details
    Publikationsdatum: 2021-03-29
    Beschreibung: The study of fluid inclusions in high-grade rocks is especially challenging as the host minerals have been normally subjected to deformation, recrystallization and fluid-rock interaction so that primary inclusions, formed at the peak of metamorphism are rare. The larger part of the fluid inclusions found in metamorphic minerals is typically modified during uplift. These late processes may strongly disguise the characteristics of the “original” peak metamorphic fluid. A detailed microstructural analysis of the host minerals, notably quartz, is therefore indispensable for a proper interpretation of fluid inclusions. Cathodoluminescence (CL) techniques combined with trace element analysis of quartz (EPMA, LA-ICPMS) have shown to be very helpful in deciphering the rock-fluid evolution. Whereas high-grade metamorphic quartz may have relatively high contents of trace elements like Ti and Al, low-temperature re-equilibrated quartz typically shows reduced trace element concentrations. The resulting microstructures in CL can be basically distinguished in diffusion patterns (along microfractures and grain boundaries), and secondary quartz formed by dissolution-reprecipitation. Most of these textures are formed during retrograde fluid-controlled processes between ca. 220 and 500 °C, i.e. the range of semi-brittle deformation (greenschist-facies) and can be correlated with the fluid inclusions. In this way modified and re-trapped fluids can be identified, even when there are no optical features observed under the microscope.
    Schlagwort(e): Fluid inclusions; Granulite; Charnockite; Cathodoluminescence; LA-ICPMS; Quartz ; 551
    Sprache: Englisch
    Materialart: article , publishedVersion
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    CITATION GEO-LEO
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