Carbonization of Carbonates and Fractionation of Stable Carbon Isotopes in a Dynamic Slip Zone
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onization of Carbonates and Fractionation of Stable Carbon Isotopes in a Dynamic Slip Zone Yu. A. Morozova, *, V. S. Sevastianovb, **, A. Yu. Yurchenkoc, ***, and O. V. Kuznetsovab, **** a
Schmidt Institute of Physics of the Earth, Russian Academy Sciences, Moscow, 123242 Russia Institute of Geochemistry and Analytical Chemistry, Russian Academy Sciences, Moscow, 119991 Russia c Center for Hydrocarbon Recovery, Skolkovo Institute of Science and Technology, Moscow, 143026 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected]
bVernadsky
Received July 15, 2019; revised January 28, 2020; accepted January 29, 2020
Abstract—Data obtained on carbonates and metaterrigenous rocks of the Devonian complex of the SultanUizdag Range, northwestern Uzbekistan, which are carbonized in local deformation zones, are used in a generalized interpretation of the genesis of carbonaceous matter by means of decomposition of carbonates under the effect of seismogenic movements. The release of free carbon is facilitated by synchronous Fe–Mg metasomatism and by the reducing conditions in the presence of hydrogen. Based on literature data on experimental modeling of carbonization processes at high-speed shear deformations of carbonates in a hydrogen medium, a possible scenario is considered for the generation of hydrogen on the surfaces of quartz dislocations in the presence of water in metaterrigenous rocks in association with carbonates. The variation of carbon isotope composition over the volume of the carbonate and terrigenous rocks is extremely heterogeneous, with the 13C isotope enriched in the fracture zones and 12C enriched in the near-fracture volumes of decompression-damaged rocks. It is hypothesized that deformations can affect the fractionation of stable carbon isotopes. With regard for literature data, it is demonstrated that isotope exchange can proceed between the free carbon and carbonate carbon. Various aspects are discussed of the influence of mineral-phase and structural–textural transformations of carbonate rocks at their thermomechanical decomposition under shearing on the geomechanical behavior of the fracture, manifestations of mechanical instability in it, and causes of frictional weakening. Keywords: carbonates, thermomechanical decomposition, carbonization, fractionation of carbon isotopes, seismogenic fault, dynamic slip DOI: 10.1134/S0016702920090062
INTRODUCTION Targeted instrumental–analytical studies of textural and compositional transformation in localized deformation zones, which usually occur in the crust in shear geomechanical environments (pure and simple shearing, transpression, and transtension) span a broad circle of problems resolved at interfaces between geology, petrology, seismology, and geomechanics. Such studies are focused on the deformation facies (tectonites and seismites) of rocks of different genesis and composition, which are produced and modified under elevated pressure, temperature, normal and tangential stress, def
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