Crustal-scale wedge tectonics at the narrow boundary between the Tibetan Plateau and Ordos block
Crustal-scale wedge tectonics at the narrow boundary between the Tibetan Plateau and Ordos block
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DOI：
10.1016/j.epsl.2020.116700
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发表时间：
2021-01
影响因子：
5.3
通讯作者：
Xiaobo Tian;Z. Bai;S. Klemperer;Xiaofeng Liang;Zhen Liu;Xiao Wang;Xusong Yang;Yun-Bo Wei;
中科院分区：
文献类型：
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作者：
Xiaobo Tian;Z. Bai;S. Klemperer;Xiaofeng Liang;Zhen Liu;Xiao Wang;Xusong Yang;Yun-Bo Wei;
青藏高原部分以克拉通块为界，部分以构造热较年轻且较弱的地壳为界。青藏高原如何与毗邻的非克拉通地壳相互作用一直是一个争论，青藏高原目前是否正在扩大其面积，如果是的话，是通过逆冲作用还是通过下地壳流，或者两者兼而有之。据推断，西藏东北部边缘的缓坡包含了一条向外流向鄂尔多斯地块的下地壳水道，鄂尔多斯地块是华北克拉通的一部分。我们使用密集节点地震台记录的远震波形计算了接收器函数，该地震台从西藏东北部的龙西盆地穿越以六盘山（山脉）为标志的过渡带进入鄂尔多斯地块。我们的图像显示，陇西上地壳逆冲到鄂尔多斯地块上，形成了六盘山，而陇西下地壳则逆冲到鄂尔多斯之下，形成了 10 公里厚的地壳根。鄂尔多斯地壳形成插入陇西地壳的地壳尺度楔子，变形仅限于六盘山两侧<50 km的狭窄区域。陇西盆地和鄂尔多斯地块的交汇处形成了狭窄的山脉，而不是拓宽的高原。较大范围的平缓地貌可能是龙西盆地地壳变形可忽略不计的表现。即使位于柴达木盆地和四川盆地之间的西藏东北部的陇西盆地位于薄弱的下地壳之下，隧道水道流也不会延伸到六盘山以外，青藏高原也不会在鄂尔多斯地块下方向外生长。
The Tibetan plateau is bounded in part by cratonic blocks, and in part by tectonothermally younger and weaker crust. How the Tibetan plateau interacts with bordering non-cratonic crust is a continuing debate, whether the plateau is currently enlarging its area, and if so, whether by thrusting or by lower-crustal flow, or both. The gently sloping northeastern margin of Tibet has been inferred to incorporate a lower-crustal channel flow outward towards the Ordos block that is a part of the North China Craton. We calculated receiver functions using teleseismic waveforms recorded by a dense nodal seismic array crossing from the Longxi basin of northeastern Tibet across a transition zone marked by the Liupan Shan (mountains) into the Ordos block. Our image shows the Longxi upper crust overthrusts onto the Ordos block building the Liupan Shan, and the Longxi lower crust underthrusts beneath the Ordos forming a 10-km thick crustal root. The Ordos crust forms a crustal-scale wedge inserted into the Longxi crust, and deformation is limited to a narrow zone of <50 km either side of the Liupan Shan. Convergence between the Longxi Basin and Ordos block is producing a narrow mountain range rather than broadening the plateau. The larger-scale gentle topography is likely an expression of negligible crustal deformation of the Longxi basin. Even if the Longxi basin of NE Tibet, between the Qaidam and Sichuan basins, is underlain by a weak lower crust, tunneling channel flow does not extend beyond the Liupan Shan, and the Tibetan Plateau has not grown outward beneath the Ordos block.