中山大学王洋团队在研究青藏高原东南部岩石圈变形及其深部动力过程中取得新进展。该研究于2024年10月15日发表于《中国科学：地球科学》杂志。

据研究人员介绍，青藏高原东南部(SE)是印度-欧亚斜向汇聚带的重要组成部分，具有复杂的地壳形变和频繁的地震活动。岩石圈复杂的变形特征及其动力学机制一直是人们争论的焦点。

本研究基于综合地球物理资料、活动构造和大地测量资料，分析了青藏高原东南部岩石圈变形特征和地球动力学过程。分析结果表明，青藏高原东南部上地壳绕喜马拉雅构造结东部顺时针旋转，表明Saging断裂与鲜水河—小江断裂之间存在分布变形。在下地壳，变形方向与地表构造的走向有明显不同。

以26°N为界，研究区北部地震各向异性观测主要来源于地壳，南部地震各向异性观测主要来源于软流圈地幔。此外，沿这一边界观察到明显的地壳和岩石圈厚度和地形变化。北部地区的厚度为60-70km，岩石圈厚度140-180km，平均海拔超过4000m，而南部地区的厚度约为30km，岩石圈厚度80-100km，平均海拔下降至2000m。

青藏高原东南部岩石圈力学性质较弱，具有较薄的等效弹性厚度。孕震层存在于地壳和上地幔中。两个中下地壳薄弱带的存在表明，在重力（地形）变化的驱动下，在地质时间尺度上存在潜在的物质流动。研究人员认为青藏高原东南部复杂的岩石圈变形是多种地球动力学过程的结果。在约26°N以北，岩石圈的变形可被归因于重力塌陷及其诱发的中下地壳流动，以及上地壳块体的挤压。在该边界以南，除了地块挤压和重力崩塌外，地幔流的牵引可能占主导地位，这可能受到缅甸板块和巽他板块的后退/回退，或海南地幔柱的地幔上涌的影响。

附：英文原文

Title: Lithospheric deformation and corresponding deep geodynamic process of the SE Tibetan Plateau

Author: Zhangjun LI, Yang WANG, Lijun LIU, Zhigang SHAO, Feng CHENG, Jinjiang ZHANG, Weijun GAN, Ming HAO

Issue&Volume: 2024/10/15

Abstract: As a crucial segment of the oblique Indian-Eurasian convergence zone, the southeast (SE) Tibetan Plateau exhibits intricate crustal deformation and frequent seismic activity. The complex lithospheric deformation characteristics and associated dynamic mechanisms have been subjects of intense debate. By integrating geophysical data, active tectonics, and geodetic observations, we analyze the lithospheric deformation features and geodynamic processes in SE Tibetan Plateau. Our analysis reveals that the upper crust in SE Tibetan Plateau undergoes clockwise rotation around the Eastern Himalayan syntaxis, indicating distributed deformation between the Sagaing and Xianshuihe-Xiaojiang faults. In the lower crust, deformation direction significantly differs from striking of surface structures. Approximately bounded by 26°N, the seismic anisotropy observations in the northern part of the study area mainly originates from the crust, while that in the southern part stems from the asthenospheric mantle. Additionally, significant variations in crustal and lithospheric thickness and topography are observed along this boundary. The northern region features a crustal thickness of 60–70km, lithospheric thickness of 140–180km, and average elevations exceeding 4000m, whereas the southern region shows a crustal thickness of about 30km, lithospheric thickness of 80–100km, and average elevations decreasing to 2000m. The lithosphere in SE Tibetan Plateau is mechanically weak, characterized by a thin equivalent elastic thickness. Seismogenic layers are present in both the crust and upper mantle. The existence of two middle-to-lower crustal weak zones suggests potential material flow over geological timescales driven by gravitational (topography) variations. We argue that complex lithospheric deformation in SE Tibetan Plateau results from multiple geodynamic processes. North of approximately 26°N, lithospheric deformation can be attributed to gravitational collapse and induced middle-to-lower crustal flow, and extrusion of upper crustal blocks. South of this boundary, in addition to block extrusion and gravitational collapse, tractions from mantle flow may dominate, possibly influenced by the retreat/rollback of the Burma and Sunda plates or mantle upwelling from the Hainan mantle plume.

DOI: 10.1007/s11430-024-1414-4

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-024-1414-4