Normal faulting from simple shear rifting in South Tibet, using evidence from passive seismic profiling across the Yadong-Gulu Rift
Normal faulting from simple shear rifting in South Tibet, using evidence from passive seismic profiling across the Yadong-Gulu Rift
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DOI：
10.1016/j.tecto.2013.03.019
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发表时间：
2013-10
期刊：
影响因子：
2.9
通讯作者：
Zhongjie Zhang;Yun Chen;X. Yuan;Xiaobo Tian;S. Klemperer;T. Xu;Z. Bai;Hongshuang Zhang;
中科院分区：
文献类型：
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作者：
Zhongjie Zhang;Yun Chen;X. Yuan;Xiaobo Tian;S. Klemperer;T. Xu;Z. Bai;Hongshuang Zhang;
青藏高原正经历着南北向缩短和东西向伸展的过程，表现为南北向正断层、地堑和裂谷的广泛发育。虽然南北缩短模式一直是大多数国际研究的主要焦点，但要了解西向东伸展的机制，需要了解藏南深部结构。南北走向的正断层的出现通常被认为是青藏高原在进入塌陷阶段之前被抬升到接近最大高度的标志。本文报道了藏南最年轻的裂谷之一亚东-古鲁裂谷（YGR）北方段地震学实验的接收函数。偏移接收函数图像显示，YGR是一条高角度正断层，其特征是从西向东两侧莫霍面隆起5 km，两侧地壳结构和壳内地震转换模式存在明显差异。这种高度不对称的岩石圈结构表明，整个地壳的伸展控制的简单/一般的剪切裂谷机制。青藏高原GPS速度场的观测结果以及上地壳、下地壳和岩石圈地幔之间剪切波分裂差异的观测结果表明，青藏高原上地壳底部的水平向剪切作用是造成该地区剪切裂陷的主要原因。我们建议，在YGR，简单的剪切裂谷容纳向北注入的印度岩石圈，这可能表明，开始的南北正断层并不表明重力崩溃的西藏岩石圈。
The Tibetan Plateau is undergoing north–south shortening accompanied by west–east extension, as evidenced by the widespread development of north–south trending normal faults, grabens and rifts. While the mode of the north–south shortening has been the main focus of most international studies, knowledge of the deep structure beneath South Tibet is required for understanding the mechanism of the west–east extension. The onset of the north–south trending normal faulting is commonly taken as an indicator that the Tibetan Plateau was uplifted to a near-maximum elevation before entering a collapsing stage. Here we report on the receiver functions of a seismological experiment across the northern segment of the Yadong-Gulu Rift (YGR), one of the youngest rifts in South Tibet. The migrated receiver function images reveal that the YGR is a high-angle normal fault characterized by a 5-km Moho rise from its western to eastern flank, together with distinct differences in the crustal structure and intracrustal seismic conversion patterns between the two flanks. This highly asymmetric lithospheric structure suggests whole-crustal extension controlled by a simple/general shear rifting mechanism. This simple/general shear rifting in the YGR is attributed to an eastward (horizontal) shear at the base of the upper crust, as evidenced by the observed Tibetan GPS velocity field and our observation of shear wave splitting discrepancy among the upper crust, lower crust and lithospheric mantle. We propose that in the YGR, simple shear rifting accommodates the northward injection of the Indian lithosphere, which may suggest that the onset of the north–south normal faulting does not indicate gravitational collapse of the Tibetan lithosphere.