The lithospheric S-wave velocity structure beneath the NE Tibetan Plateau and its surrounding craton basins
The lithospheric S-wave velocity structure beneath the NE Tibetan Plateau and its surrounding craton basins
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DOI：
10.3389/feart.2022.1066265
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
Weilai Wang;Guangyao Cai;Jianping Wu;L. Fang
中科院分区：
文献类型：
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作者：
Weilai Wang;Guangyao Cai;Jianping Wu;L. Fang
详细研究岩石圈和软流圈的空间分布，对进一步认识板块碰撞效应和造山运动过程是十分必要的。通过接收函数和面波的联合反演，获得了研究区1,843个地震台站下至200公里深度的三维横波速度结构结果。分析了沉积厚度、地壳厚度、下地壳波速和岩石圈厚度。根据地壳厚度估算了下地壳低速带的分布。结果表明，秦岭构造带下地壳中存在低速体，但它们并不连通，表明它们在地壳尺度上可能不能作为青藏高原东北部物质挤出的通道。根据剖面结果和岩石圈-岩石圈边界的深度分布，四川盆地和鄂尔多斯盆地下方存在较厚的岩石圈，研究区东部岩石圈较薄，厚度约60-80 km，表明研究区东部岩石圈遭受了严重的破坏和重组。松潘-甘孜地块岩石圈存在拆沉作用，表现出软流圈物质垂向运动的特征。在东北高原地幔岩石圈顶部存在较厚的低速带，而在相对稳定的四川盆地和鄂尔多斯地块之下则不存在。与两侧的四川盆地和鄂尔多斯盆地相比，秦岭构造带在100-160 km深度处存在低速带，可能是软流圈物质。结合SKS波的偏振方向特征，可以清楚地观察到秦岭构造带之下存在着近似东西向的软流圈物质运动。因此，秦岭构造带之下的软流层可能是青藏高原东北部物质挤出的重要通道。
It is essential to investigate the spatial distribution of the lithosphere and asthenosphere in detail, to further obtain the understanding of the effect of plate collision and the process of orogenic movement. From the joint inversion of receiver functions and surface waves, the three-dimensional S-wave velocity structure results down to 200 km depth in the study area were obtained at 1,843 seismic stations. Analysis was performed on the sedimentary thickness, crustal thickness, lower crustal wave velocity, and lithospheric thickness. According to the crustal thickness, we evaluated the distribution of low-velocity zones in the lower crust. The results show that there are low-velocity bodies in the lower crust in the Qinling tectonic belt, but they are not connected, indicating that they may not be able to be used as a channel for material extrusion from the NE Tibetan Plateau at the crustal scale. According to the section results and the depth distribution of the lithosphere-astenosphere boundary, a relatively thick lithosphere exists below the Sichuan Basin and Ordos Basin, and the lithosphere in the east of the study area is relatively thin with a thickness of about 60–80 km, indicating that the lithosphere in the east of the study area has been severely destructed and restructured. The delamination has been observed in the lithosphere under the Songpan-Ganzi Block, showing characteristics of vertical movement of asthenosphere materials. There is a relatively thick low-velocity zone at the top of the mantle lithosphere of the NE plateau; however, it does not exist under the relatively stable Sichuan Basin and the Ordos Block. Compared with the Sichuan Basin and the Ordos Basin at both sides, the Qinling tectonic belt has a low-velocity zone at the depth of 100–160 km, which may be asthenosphere material. In combination with the polarization direction characteristics of the SKS wave, it is clearly observed that asthenospheric material movement exists in an approximate east-west direction beneath the Qinling tectonic belt. Therefore, the asthenosphere beneath the Qinling tectonic belt may serve as an important channel for material extrusion in the NE Tibetan Plateau.