Polyphase deformation, dynamic metamorphism, and metasomatism of Mount Everest’s summit limestone, east central Himalaya, Nepal/Tibet
Polyphase deformation, dynamic metamorphism, and metasomatism of Mount Everest’s summit limestone, east central Himalaya, Nepal/Tibet
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DOI：
10.1130/l473.1
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发表时间：
2016-02
期刊：
影响因子：
2.4
通讯作者：
Travis L. Corthouts;D. Lageson;C. Shaw
中科院分区：
文献类型：
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作者：
Travis L. Corthouts;D. Lageson;C. Shaw
从横跨珠峰（珠穆朗玛峰组）的石灰岩的横断面上采集的新样品表明，多个不同的变形事件被离散地划分在这个组中。珠穆朗玛峰组（珠峰峰顶）最高暴露处的样本保留了发育良好的糜棱叶理和显微结构，与≥250 °C的变形温度一致。热年代学和显微结构的结果表明，这些织物根深蒂固的喜马拉雅造山作用的初始收缩阶段，地壳增厚时，容纳褶皱和推覆的特提斯沉积序列。与此相反，珠穆朗玛峰组底部（南峰顶）附近的样品保留了伸展剪切变形，表明温度为1500 °C时的交代作用，并含有白云母+云母+黑云母+电气石+金红石的同运动次生矿物组合。剪切组构保存在南峰会样品与珠穆朗玛峰拆离活动，而第二相的结晶是石灰岩原岩和挥发性，富硼流体渗透到珠穆朗玛峰组的基础，交代作用之间的反应的结果。同运动白云母的40 Ar/ 39 Ar定年结果表明，其次级组合的结晶时间约为2000年。剪切组构形成于≥18 Ma。本文首次证明，珠峰顶灰岩记录了喜马拉雅造山运动中与离散阶段相关的多期变形，并首次证明，珠峰上藏南拆离带的最高构造带在珠峰组底部表现为离散脆性拆离带之前，最初是一个分布的剪切带。
New samples collected from a transect across the summit limestone of Mount Everest (Qomolangma Formation) show that multiple distinct deformational events are discretely partitioned across this formation. Samples from the highest exposures of the Qomolangma Formation (Everest summit) preserve a well-developed mylonitic foliation and microstructures consistent with deformation temperatures of ≥250 °C. Thermochronologic and microstructural results indicate these fabrics were ingrained during initial contractile phases of Himalayan orogenesis, when crustal thickening was accommodated by folding and thrusting of the Tethyan Sedimentary Sequence. In contrast, samples from near the base of the Qomolangma Formation (South Summit) preserve extensional shear deformation, indicate metasomatism at temperatures of ∼500 °C, and contain a synkinematic secondary mineral assemblage of muscovite + chlorite + biotite + tourmaline + rutile. Shear fabrics preserved in South Summit samples are associated with activity on the Qomolangma detachment, while the crystallization of secondary phases was the result of reactions between the limestone protolith and a volatile, boron-rich fluid that infiltrated the base of the Qomolangma Formation, resulting in metasomatism. The 40 Ar/ 39 Ar dating of synkinematic muscovite indicates the secondary assemblage crystallized at ca. 28 Ma and that shear fabrics were ingrained at ≥18 Ma. This paper presents the first evidence that Everest’s summit limestone records multiple phases of deformation associated with discrete stages in Himalayan orogenesis, and that the structurally highest strand of the South Tibetan detachment on Everest was initially active as a distributed shear zone before it manifested as a discrete brittle detachment at the base of the Qomolangma Formation.