Details of the Doublet Moho Structure beneath Lhasa, Tibet, Obtained by Comparison of P and S Receiver Functions
Details of the Doublet Moho Structure beneath Lhasa, Tibet, Obtained by Comparison of P and S Receiver Functions
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DOI：
10.1785/0120100163
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发表时间：
2011-06
影响因子：
3
通讯作者：
Xueqing Li;D. Wei;X. Yuan;R. Kind;Prakash Kumar;Hui-lan Zhou
中科院分区：
文献类型：
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作者：
Xueqing Li;D. Wei;X. Yuan;R. Kind;Prakash Kumar;Hui-lan Zhou
印度板块和亚洲板块自55Ma以来的碰撞形成了地球上最大的高原和最厚的地壳。然而，对于地壳增厚的方式，人们并没有达成普遍的一致意见。青藏高原的地壳厚度仍然很难确定。人们普遍认为，西藏地壳的厚度大约是正常厚度的两倍，并且向北变薄，但莫霍面深度的个体观测在空间上存在差异，并且在同一地点使用不同的技术，差异超过20 km。在这项工作中，我们比较了P和S接收函数LSA站，位于拉萨南部，以确定地壳厚度的台站。在下地壳60和80 km深度处，P波接收函数中清晰地显示出具有两个重要界面的双重莫霍面结构。然而，在S接收函数数据中不存在更深的相位（莫霍面）。在这里，我们通过一个以30°角向东倾斜的强莫霍面地形来模拟观测到的P和S接收函数。这一结果可能表明西藏莫霍面结构非常复杂，具有很强的横向变化，并表明只有通过二维密集地震实验才有可能获得详细的莫霍面深度图。莫霍面倾角局部垂直于印度板块运动方向，表明下地壳变形与下伏印度地幔岩石圈解耦。LSA站以东及下方极强的莫霍面变化也可能意味着壳幔相互作用，特别是下地壳到上地幔的分层或下沉。
The collision of the Indian and Asian plates since about 55 Ma has created the largest plateau with the thickest crust on Earth. There is, however, no general agreement on the modes of the crustal thickening. The crustal thickness of the Tibetan plateau still remains poorly determined. It is generally accepted that the Tibetan crust has roughly double normal thickness and that it thins somewhat toward the north, but individual observations of Moho depth vary spatially and for different techniques at the same place by greater than 20 km. In this work we compare P and S receiver functions at station LSA, located in the southern Lhasa terrane, to determine the crustal thickness beneath the station. A doublet Moho structure with two significant interfaces at about 60 and 80 km depth in the lower crust is seen clearly in the P receiver functions. The deeper phase (Moho) is, however, absent in the S receiver function data. Here we model the observed P and S receiver functions by a strong Moho topography that dips to the east at an angle of 30°. This result may indicate that the Moho structure beneath Tibet can be very complicated and has strong lateral variations and suggests that a detailed map of Moho depth is only possible with 2D dense seismic experiments. The Moho dips locally perpendicular to the direction of the Indian plate motion, suggesting that the lower crustal deformation is decoupled from the underlying Indian mantle lithosphere. The extremely strong Moho variation beneath and east of station LSA may also imply a crust-mantle interaction, specifically delamination or foundering of lower crust down to the upper mantle.