Crustal structure beneath Namche Barwa, eastern Himalayan syntaxis: New insights from three-dimensional magnetotelluric imaging
Crustal structure beneath Namche Barwa, eastern Himalayan syntaxis: New insights from three-dimensional magnetotelluric imaging
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东喜马拉雅构造带南迦巴瓦峰下方的地壳结构：三维大地电磁成像的新见解
DOI：
10.1002/2016jb013825
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发表时间：
2017
影响因子：
3.9
通讯作者：
Zeng Weihua
中科院分区：
文献类型：
--
作者：
Lin Changhong;Peng Miao;Tan H;ong;Xu Zhiqin;Li Zhong-Hai;Kong Wenxin;Tong Tuo;Wang Mao;Zeng Weihua
喜马拉雅山脉的东端，命名为Namche Barwa，由于其独特的地质和地貌特征，被认为是青藏高原地球动力学的重要天然实验室。在Namche Barwa周围的83个站点测量的大地电磁（MT）数据通过三维（3-D）反演成像，以更好地揭示喜马拉雅东部的地壳结构。结果表明，Namche Barwa下方存在复杂且不均匀的电性结构。分布在南迦巴瓦周围的中地壳和下地壳中的电导体，如果被认为是一个相对大规模区域中流动的某些部分，则为“地壳流动”模型提供了额外的证据。Namche Barwa内部下方的近地表电阻率模型符合温泉和流体包裹体的位置，脆-韧性转变以及先前热液研究的300°C-400°C等温线。电阻率相对较高的上地壳（>800 Ωm）下面是导电性较强的中下地壳（<80 Ωm）。浅部热构造的电性特征表明存在一个含水熔融的堆积体，一个局部的传导性陡倾减压熔融带，与解释Namche Barwa变质岩折返机制的“构造动脉瘤”模型一致。研究结果还表明，地表过程和局部构造响应在Namche Barwa的演化中起着至关重要的作用。还讨论了另一种假设，即主要持续热源解释了Namche Barwa下方的局部热流变结构。
The eastern terminations of the Himalayan orogeny, named Namche Barwa, are considered a vital natural laboratory in the Tibetan plateau for geodynamics due to its distinctive geological and geomorphological characteristics. Magnetotelluric (MT) data measured at 83 sites around the Namche Barwa are imaged by three‐dimensional (3‐D) inversion to better reveal the crustal structure of the eastern Himalaya. The results show a complex and heterogeneous electrical structure beneath the Namche Barwa. The electrical conductors distributed in the middle and lower crust around the Namche Barwa provide additional evidence for the “crustal flow” model if they are considered as some parts of the flow in a relatively large‐scale region. The near‐surface resistivity model beneath the inner part of Namche Barwa conforms with the locations of hot spring and fluid inclusions, the brittle‐ductile transition, and the 300°C–400°C isotherm from previous hydrothermal studies. Relatively resistive upper crust (>800 Ωm) is underlain by a more conductive middle to lower crust (<80 Ωm). The electrical characteristics of the thermal structure at shallow depth indicate an accumulation of hydrous melting, a localized conductive steep dipping zone for decompression melting consistent with the “tectonic aneurysm” model for explaining the exhumation mechanism of metamorphic rocks at Namche Barwa. The results also imply that both surface processes and local tectonic responses play a vital role in the evolution of Namche Barwa. An alternative hypothesis that the primary sustained heat source accounts for the local thermal‐rheological structure beneath Namche Barwa is also discussed.