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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Exhumation history of a section of the Sikkim Himalayas, India: records in the metamorphic mineral equilibria and compositional zoning of garnet
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Exhumation history of a section of the Sikkim Himalayas, India: records in the metamorphic mineral equilibria and compositional zoning of garnet

机译：印度锡金喜马拉雅山一部分的掘尸历史：石榴石的变质矿物平衡和组成分区记录

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摘要

The exhumation history of pelitic migmatite samples from the High Himalayan Crystalline Complex (HHC) near the South Tibetian Detachment System in the Sikkim-Darjeeling section has been determined on the basis of thermo-barometric analyses, retrograde breakdown reactions and compositional zoning of garnet. The peak metamorphic condition is estimated to be ～10.4 kbar, 800 ℃ from thermo-barometric and phase equilibrium constraints. The observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and, hence, extremely rapid (～15 mm/yr) exhumation up to the depth of ～15 km. Numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process, ～2 mm/yr, up to at least ～5 km depth, to lead to the development of the observed compositional zoning of garnet. The dramatic change of the exhumation velocity (V_z) might reflect a process of tectonic thinning followed by erosion and/or horizontal flow at shallow depth. Assuming that the V_z did not change significantly below 5 km depth, these results suggest that the HHC samples studied in this work exhumed from a depth of ～34 km within ～8 Ma.
机译：在热气压分析，逆行分解反应和石榴石组成分区的基础上，确定了锡金-大吉岭断面南藏系分离体系附近的喜马拉雅高结晶复合体（HHC）的黄泥云母样品的发掘历史。根据热压和相平衡的限制，峰值变质条件在800℃时估计为〜10.4 kbar。观察到的石榴石向尖晶石和堇青石的逆行分解需要接近等温，因此，直到〜15 km的深度都极快地（〜15毫米/年）发掘。数值模拟表明，最初的快速发掘必须遵循一个非常慢的过程，即〜2 mm / yr，直到至少〜5 km的深度，才能导致观察到的石榴石成分区划的发展。挖掘速度（V_z）的剧烈变化可能反映了构造变薄的过程，随后是浅深度的侵蚀和/或水平流动。假设V_z在5 km深度以下没有明显变化，这些结果表明，在这项工作中研究的HHC样本在〜8 Ma内从〜34 km的深度发掘出来。

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