青藏高原东部地块的属性与演化

doi:10.13745/j.esf.sf.2023.2.5

摘要/Abstract

摘要：

利用大量地方地震台站的数据获得了青藏高原地壳上地幔0.5°×0.5°×10 km的高精度三维速度结构,揭示了青藏高原地壳上地幔结构的大量细节,为了解大陆碰撞与高原演化的动力学作用提供了新的证据。根据地震层析成像三维波速数据,计算取得了青藏高原岩石圈底界面深度的三维图,由此发现青藏高原东、西两部属性有本质区别:东部以高波速、较高电阻率和密度的厚岩石圈为主,厚度在150~180 km范围变化;西部以低波速、较低电阻率和密度的薄岩石圈为主,厚度在130~155 km范围变化。上述表明高原东部没有大规模软流圈上涌,而西部发生了大规模软流圈上涌,上涌幅度在20~30 km左右。高原东西部分界线的两个端点坐标分别为(85°E,20°N)和(98°E,40°N)。结合古地磁数据可知,青藏高原东部地块在空间上是40 Ma以来西部陆-陆俯冲作用与东南亚洋-陆俯冲作用之间的作用力转变的过渡带。

关键词: 青藏高原, 东部地块, 地震层析成像, 岩石圈底界面, 属性演化

Abstract:

Using high-quality seismic data collected from a large number of local seismic stations, we have achieved high-resolution imaging of the three-dimensional velocity structure of the crust and upper mantle in the Qinghai-Tibetan Plateau with an accuracy of 0.5°×0.5°×10 km, which revealed in great detail the crustal and upper mantle structure of the Qinghai-Tibetan Plateau and provided new evidence for understanding the dynamics of continental collision and plateau evolution. Then, based on the 3D seismic P-wave velocity data, a 3D depth map of the lithosphere-asthenosphere boundary beneath the Qinghai-Tibetan Plateau is obtained. It is found that there are fundamental differences in geological attributes between the eastern and western parts of the plateau: The eastern part is dominated by thick lithosphere with high wave velocity, high resistivity and density, and a thickness range of 150-180 km; whereas the west is dominated by thin lithosphere with low wave velocity, low resistivity and density, and thickness ranging between 130-155 km. Furthermore, there is no large-scale asthenospheric upwelling in the eastern part whereas ~20-30 km upwelling has occurred in the west. The coordinates of the two endpoints of the east-west boundary are (20°N, 85°E) and (40°N, 98°E) respectively. According to the paleomagnetic data, the eastern massif in the Qinghai-Tibetan Plateau is a stress transition zone situated between the western continent-continent subduction zone and Southeast Asia ocean-continent subduction zone since 40 Ma.

Key words: Qinghai-Tibetan Plateau, eastern massif, seismic tomography, lithospheric thickness, attribute evolution

中图分类号:

P313.1

刘晓宇, 杨文采, 陈召曦, 瞿辰, 于常青. 青藏高原东部地块的属性与演化[J]. 地学前缘, 2023, 30(3): 233-241.

LIU Xiaoyu, YANG Wencai, CHEN Zhaoxi, QU Chen, YU Changqing. Attributes and evolution of the eastern massif in the Qinghai-Tibetan Plateau[J]. Earth Science Frontiers, 2023, 30(3): 233-241.

图/表 6

图1 地幔岩石P波速度随温度变化曲线(a)及地下温度与浅壳幔岩石熔融温度的对比图(b)(据文献[16]修改)

Fig.1 (a) Change of P-wave velocity of mantle with temperature, and (b) comparison of the temperature of the lithosphere and melting temperature of shallow crust-mantle at different depths. Modified after [16].

图2 成像采用的地震观测台站和震源分布平面图(a)及射线覆盖面积平面图(b) (a)—地震和台站分布;(b)—射线覆盖。图中红色三角形为地方地震台网的台站位置,绿色圆圈为3级以上震源位置。

Fig.2 (a) Locations of the selected seismic stations (red triangles) and earthquake (intensity > MS 3) epicenters (green circles), and (b) raypath coverage map

图3 地震层析成像检测板试验与P波速度扰动图 (a)—不同深度的检测板试验结果,深度分别为120、165、210和260 km;(b)—深度120 km的波速扰动,对应上地壳;(c)—深度150 km的波速扰动;(d)—深度180 km的波速扰动。

Fig.3 Results of checkboard resolution test at different depths for P-wave tomography (a) and map view of P-wave velocity perturbations at different depths (b-d)

图4 青藏高原岩石圈厚度与主要山脉分布对比图线条AB标记东部地块的西边界,线条CD标记东部地块的东边界。

Fig.4 Distribution of main mountain ranges compared to lithospheric-thickness distribution in the Qinghai-Tibetan Plateau. Lines AB and CD mark boundaries of the eastern massif.

图5 青藏高原的地下电阻率分布与地表布格重力异常图 (a)—青藏高原地下100 km的电阻率平面图;(b)—青藏高原地表布格重力异常平面图。线条AB标记东部地块的西边界,线条CD标记东部地块的东边界。

Fig.5 (a) Distribution of resistivity 100 km underground in and (b) surface Bouguer gravity anomaly map of the Qinghai-Tibetan Plateau. Lines AB and CD mark the boundaries of the eastern massif.

图6 根据古地磁数据恢复的东南亚地块演化系列图(80~10 Ma)(据文献[31]修改) 黑色箭头标记陆块运动方向,红色字母“E”标记青藏东部地块位置,其两侧直线标记此地块边界。

Fig.6 Evolution of the Southeast Asian plate restored from paleomagnetic data (80-10 Ma). Arrows mark the movement direction of the plate; letter “E” marks the location of the eastern Qinghai-Tibetan massif, with the flanking black lines marking the boundaries of the massif. Modified after [31].

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