中国大陆及周边地区现代岩石圈演化动力学模拟

Dynamic simulation of lithospheric evolution from the modern China mainland and its surrounding areas

采用有限元方法模拟了近20万年来青藏高原岩石圈形变演化过程,探讨了印度-欧亚大陆的碰撞对中国大陆岩石层形变和应力场的影响以及它们与强地震活动性的关系.结合现代GPS、地震和地质学观测的结果,对比分析了中国大陆在百万年、十万年和十年尺度上的形变和构造应力场的基本格局.研究表明:(1)印度-欧亚大陆的碰撞以及印度大陆的持续向北推进、挤压所产生的应力环境,一直主导了以青藏高原为核心的我国西部地域岩石圈构造、运动和演化,但其影响随着远离青藏高原地区而逐渐变小.(2)断层滑移和重力势作用对于青藏高原东西部以及塔里木盆地的影响相当大,它们导致青藏高原岩石层东西向形变速率增大,对青藏高原的中南部地区产生拉张效应,同时导致塔里木盆地出现整体的右旋趋势.(3)青藏高原区域水平方向形变速率和GPS观测结果吻合较好.但在垂直方向上,一些地区计算结果与观测数据相差较大,这说明单纯的挤压作用不是现代青藏高原隆升的惟一机制.现代青藏高原的隆升可能与其他驱动机制,如地幔对流、重力均衡以及剥蚀作用等有关.(4)印度板块的挤压作用基本上决定了中国大陆西部的主压应力场分布.(5)印度板块的碰撞对中国大陆的强地震活动性有重要影响,但华北地区是个例外,该地区的地震活动性很强而印度板块的挤压在该区域产生的影响却很小,说明其他的驱动力在一定程度上活化了华北地块.

Recent 0.2Ma evolution of lithosphere in the China mainland is modeled using finite element analysis. The effects of collision between Eurasia and Indian Plates on the strain and stress field in the China mainland are studied. Combining with GPS surveys, seismological data and geological analysis, we try to probe into the basic patterns of strain and stress field in this area on the time scales of several million years, 0.1 million years and tens of years. The results show that the India-Eurasia collision and the stress environment caused by the continuous northward extrusion of the Indian Plate play a key role in controlling the tectonic movement and lithospheric evolution of the Tibetan Plateau and its surrounding areas, while in the regions far away from the Tibetan Plateau, it becomes weak. Faults and gravity potential produce significant effects on the eastern and the western parts of the Tibetan Plateau and Tarim Basin. In the Tibetan Plateau, these effects increase the rate of lateral deformation; in the southern parts of Tibet, they create an extensional stress field, while in the Tarim Basin, they make it dextrorotate. The calculated horizontal velocities are well consistent with GPS surveys. However, in vertical dimension, quite large differences are observed in some areas, which means modern uplifting of the Qinghai-Tibetan Plateau depends not only on the Indian-Eurasian collision, but also on other kinds of mechanisms, such as mantle convections, isostatic effects and all kinds of erosions. The calculated stress field is consistent with the observed data. The Indo-Asian collision has mainly controlled the principle tensional stress field in the western part of China, but other kinds of mechanisms, such as gravity and mantle convections, have a very important impact on the eastern Tibetan Plateau. The Indo-Asian collision controls the seismicity of the western part of China, but except North China, where the seismicity is very active while the calculated stress level is very low. This puzzle probably means that other forces have made the North China block reactive.