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首页> 外文期刊>Contributions to Mineralogy and Petrology >Exhumation of the UHP Tso Morari eclogite as a diapir rising through the mantle wedge
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Exhumation of the UHP Tso Morari eclogite as a diapir rising through the mantle wedge

机译：挖掘出UHP Tso Morari榴辉岩作为通过地幔楔上升的底辟

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摘要

Ultrahigh-pressure (UHP) rocks such as the coesite-bearing eclogites, occurring as boudins within felsic gneisses of the Tso Morari dome in northwestern Himalayas, originated through subduction of the northern continental margin of India during its early Eocene collision with the Kohistan-Ladakh arc. These rocks are believed to be exhumed through a low-viscosity channel along the top surface of the subducting slab. However, details of the exhumation mechanism are poorly known. We present new constraints on the P-T evolution of hydrous and carbonate-rich samples of the Tso Morari eclogite between 2.2-2.3 GPa/400-425 degrees C and similar to 0.4 GPa/450 degrees C using thermobarometry and calculated P-T-M-CO2 phase equilibria. Our results indicate that the eclogites were strongly heated at high pressures from 400-425 degrees C at 2.2-2.3 GPa to 670-720 degrees C at 1.8-1.9 GPa during the early stages of exhumation. Diffusion modeling of Ca variation across the core-rim interface of garnet indicates that the heating stage lasted only <0.1 Myr, in accordance with geochronological constraints and fast exhumation rates. Our P-T path is at odds with exhumation of the eclogites along a subduction channel as model calculations indicate that the intermediate P-T conditions of 1.8-1.9 GPa/670-720 degrees C are not achieved along the subducting slab. Instead, the constrained P-T conditions are consistent with heating within the mantle wedge overlying the subducting slab. Therefore, we conclude that the Tso Morari eclogites were possibly exhumed as part of a low-density, felsic diapir rising through the mantle wedge. Based on low viscosity values (1.7 x 10(19)-5.0 x 10(19) Pa s) of mantle wedges associated with modern subduction zones, the calculated exhumation rate for the Tso Morari eclogite is extremely fast (29-147 mm/yr) and at par with that constrained for other northwestern Himalayan UHP rocks.
机译：喜马拉雅山Tso Morari穹顶长英质片麻岩中的布丁等超高压（UHP）岩石，如科安石榴辉岩，起源于印度北部始新世与科希斯坦-拉达克发生碰撞时对北大陆边缘的俯冲作用弧。据信这些岩石是沿着俯冲板顶面通过低粘度通道被挖出的。然而，掘尸机制的细节知之甚少。我们使用热压法和计算的P-T-M-CO2相平衡，在2.2-2.3 GPa / 400-425摄氏度与类似于0.4 GPa / 450摄氏度之间的Tso Morari榴辉岩含水和富含碳酸盐样品的P-T演化方面提出了新的限制条件。我们的结果表明，在发掘早期阶段，榴辉岩在400-425摄氏度（2.2-2.3 GPa）至670-720摄氏度（1.8-1.9 GPa）的高压下强烈加热。沿石榴石核心-边缘界面的Ca变化的扩散模型表明，根据地质学上的制约因素和快速的发掘速率，加热阶段仅持续了<0.1 Myr。我们的P-T路径与沿俯冲通道的榴辉岩发掘不一致，因为模型计算表明，沿俯冲平板未达到1.8-1.9 GPa / 670-720摄氏度的中间P-T条件。相反，受约束的P-T条件与覆盖俯冲板的地幔楔内的加热一致。因此，我们得出的结论是，Tso Morari榴辉岩可能是通过地幔楔上升的低密度，长统底辟的一部分。根据与现代俯冲带相关的地幔楔的低粘度值（1.7 x 10（19）-5.0 x 10（19）Pa s），Tso Morari榴辉岩的发掘速率非常快（29-147 mm / yr ），并且与其他西北喜马拉雅UHP岩石所受的约束相同。

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