Fragmented Indian plate and vertically coherent deformation beneath eastern Tibet
Fragmented Indian plate and vertically coherent deformation beneath eastern Tibet
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DOI：
10.1029/2012jb009210
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发表时间：
2012-11
影响因子：
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通讯作者：
S. Ceylan;J. Ni;John Chen;Qie Zhang;F. Tilmann;E. Sandvol
中科院分区：
文献类型：
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作者：
S. Ceylan;J. Ni;John Chen;Qie Zhang;F. Tilmann;E. Sandvol
[1] 利用 INDEPTH-IV 和 Namche-Barwa 地震实验的基模瑞利波，周期为 20 至 143 s，我们研究了西藏东部下方的岩石圈结构。我们发现了一个约 200 公里宽的高速体，起始于约 60 公里深度，大致位于班公-尼庄缝合线下方的中心，这很可能是印度大陆岩石圈的下冲断层的一部分。西藏东部下方印度岩石圈的近水平俯冲似乎伴随着其横向撕裂成至少两个碎片，以及随后在~91°E-33°N最西部分的断裂。我们在北羌塘地体和松潘-甘孜地体下方观察到的最上地幔低速带很可能是由于相对于西藏南部岩石圈更温暖和更薄。我们将东昆仑断裂北支和南支在岩石圈深处集中的低速区归因于剪切引起的应变加热。北羌塘地体和松潘-甘孜地体下方143 s（~200 km峰值敏感深度）各个时期的方位快方向是一致的，表明地壳和上地幔之间存在垂直相干变形。此外，昆仑山以下的低速带延伸至> 200 km，这表明柴达木盆地南缘目前存在大陆向南俯冲的情况。
[1] Using fundamental mode Rayleigh waves from the INDEPTH-IV and Namche-Barwa seismic experiments for periods between 20 and 143 s, we have investigated the lithospheric structure beneath eastern Tibet. We have found a ∼200-km-wide high velocity body, starting at ∼60 km depth and roughly centered beneath the Bangong-Nijuang Suture, which is most likely a piece of the underthrusting Indian continental lithosphere. The sub-horizontal underthrusting of the Indian lithosphere beneath eastern Tibet appears to be accompanied by its lateral tearing into at least two fragments, and subsequent break-off of the westernmost portion at ∼91°E-33°N. The uppermost mantle low velocity zone we observe beneath the N. Qiangtang and Songpan-Ganzi terranes is most probably due to warmer and thinner lithosphere relative to southern Tibet. We attribute the low velocity zones concentrated along the northern and southern branches of the eastern Kunlun fault at lithospheric depths to strain heating caused by shearing. The azimuthal fast directions at all periods up to 143 s (∼200 km peak sensitivity depth) beneath the N. Qiangtang and Songpan-Ganzi terranes are consistent, suggesting vertically coherent deformation between crust and uppermost mantle. Furthermore, the low velocity zone below the Kunlun Shan reaching down to >200 km argues against a present southward continental subduction along the southern margin of Qaidam Basin.