Abstract A mass of lithospheric shortening occurred beneath the Tibetan Plateau due to the collision between the Indian and Eurasian plates. The extrusion of the upper crust beneath the Tibetan Plateau has been widely accepted, but whether the lithospheric mantle escapes laterally by creep deformation or rigid-block extrusion remains unclear. Based on the Pn travel time data, the velocity structure of the uppermost mantle in eastern and southeastern Tibetan Plateau was obtained by using the interstation travel-time difference method. The results show an obviously high Pn velocity beneath the Sichuan Basin and Qaidam Basin, indicating that the areas are stable blocks. The high Pn velocity beneath the eastern Lhasa terrane may be related to the underplating of the Indian lithospheric plate to the north. The Qilian block located in the north of the Kunlun fault appears as a normal Pn velocity, which indicates a mean lithospheric mantle thickness. A significantly low Pn velocity with an average of ~7.8 km/s in eastern and southeastern Tibetan Plateau, including the eastern Songpan–Ganzi terrane, the Chuan–Dian Diamond Block, and the northern part of Yunnan Province, indicates that the lithospheric mantle is relatively thin in these regions. Combined with other geologic and geophysical results, we propose that the lithospheric mantle of the plateau did not escape to eastern and southeastern Tibetan Plateau where the crust has been thickened by adding crustal material from the interior of the plateau.

中文翻译：

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青藏高原下的岩石圈地幔不会向东南逃逸

摘要 由于印度板块和欧亚板块的碰撞，青藏高原下方发生了大量的岩石圈缩短。青藏高原下上地壳的挤压已被广泛接受，但岩石圈地幔是否通过蠕变变形或刚性块挤压横向逃逸尚不清楚。基于Pn走时资料，采用站间走时差法得到青藏高原东部和东南部最上地幔的速度结构。结果表明，四川盆地和柴达木盆地下方有明显的高Pn速度，表明该区域为稳定块体。拉萨地体东部下方的高 Pn 速度可能与印度岩石圈板块向北的底侵有关。位于昆仑断裂以北的祁连地块表现为正常的Pn速度，表明岩石圈地幔的平均厚度。青藏高原东部和东南部，包括松潘-甘孜地体东部、川-滇钻石地块和云南省北部，平均约 7.8 km/s 的显着低 Pn 速度表明岩石圈地幔是这些地区比较薄。结合其他地质和地球物理结果，我们认为高原的岩石圈地幔没有逃逸到青藏高原东部和东南部，因为高原内部添加地壳物质而使地壳增厚。8 km/s 在青藏高原东部和东南部，包括东部松潘-甘孜地体、川滇钻石地块和云南省北部，表明这些地区的岩石圈地幔相对较薄。结合其他地质和地球物理结果，我们认为高原的岩石圈地幔没有逃逸到青藏高原东部和东南部，因为高原内部添加地壳物质而使地壳增厚。8 km/s 在青藏高原东部和东南部，包括东部松潘-甘孜地体、川滇钻石地块和云南省北部，表明这些地区的岩石圈地幔相对较薄。结合其他地质和地球物理结果，我们认为高原的岩石圈地幔没有逃逸到青藏高原东部和东南部，因为高原内部添加地壳物质而使地壳增厚。