Abstract:

In this paper, a 3-D visco-elastic finite element model is used to describe the long-term average movement of China's continent. The boundary conditions of the model are taken in reference to the average plate velocity obtained from geological information, as well as the subduction of the Philippines and Pacific Plates into the continent and the collision between the Indian Plate and China's continent. The results of GPS may reflect the contemporary movement of China's continent. The difference between the contemporary movement and the long-term average crustal movement can then be recognized by the comparison of the modeling result and the GPS result. The two kinds of results show much consistency and little difference. It indicates in one point that each short-term movement of the continent might be a small dynamic adjustment process near the long-term average state, and can be attributed to the continuous adjustment of the continental crust to reach an equilibrium state in response to the movements of the surrounding plates. The modeled stress field shows that the stress is higher in the western and southern parts and lower in the eastern and northern parts, consistent with the stress field obtained by the other studies. The subduction of the Pacific and Philippine plates has led to a complex effect on the eastern part of the continent. In Northeast and North China, the E-W-directed stress is dominated by compression due to the compression of the ocean plate and the obstacle of the block to the north. However, the S-N-directed stress becomes gradually to be extensional, as the S-N-directed displacement becomes greater from north to south. Because of the difference of motion rate between North China and South China, North China is subjected to extensional stress. This is consistent with the results of Shen et al. (2000) and DING Guo-yu (1986). In South China, the S-E-directed compressive stress is predominant, but alternating compressive and extensional stresses are predominant in the vicinity of the eastern boundary of the continent. Three cross sections are cut along the X-direction of the model to observe the stress and displacement on X-Z plane. In contrast to the compression of the Indian plate, the subduction of the ocean plates gives rise to the complicated distributions of stress and displacement on the profiles. Although the whole continent, and especially the western part of the continent, is dominated by compressive stress, alternating high, low and high stress regions may occur from west to east in the eastern part of the continent, and extensional stress may to different extent occur in the region from Huanghai sea to Taiwan. Because of the differences of the rheological properties of the media in various layers of the model, stress will gradually concentrate in the high viscocity layers of the model as time goes on. Due to the subduction of the ocean plates, small-scale high stress region with high stress gradient may occur at depth of the lithosphere beneath the eastern boundary of the continent. In addition, some convection circles may occur in the lithosphere beneath the eastern boundary of the continent, but the features of stresses in various quadrants are different due to the complexity of the crust and upper mantle. Further study is needed to test this conclusion. The modeling results in this paper indicate that the subduction of the Pacific and Philippine Plates into the continental lithosphere has very important effect on the orientation and features of the stress field in eastern China's continent. LI Zu-ning et al. (2002) proposed that the ignorance of the effects of the subduction of Pacific and Philippine plates is the main reason that causes the incompatibility of their modeling result to the results of GPS and seismic observations in China's continent. Obviously, a better understanding of the dynamic background of China's continent can be gained only by taking the effects of the Pacific and Philippine Plates into consideration.

Key words: China’s continent, finine-element method, layered visco-elastic

摘要：

利用三维黏弹性有限元模型,模拟出中国大陆的长期平均运动状态.其位移场与当前GPS结果比较有很强的一致性和较小的差异性,这从一方面说明了各时期板块边界的运动状态可能只是在均衡状态附近的幅度不大的震荡.进一步分析其应力场,由于海洋板块的俯冲,在大陆东部边界产生挤压、引张、挤压应力相间的情形,华北地区出现引张力作用,与其他研究结果一致.分析大陆东部的剖面,进一步证明大陆东部应力性质的变化,并且由于大陆岩石圈本身分层流变性会使应力逐渐集中到黏滞性较大的地壳部分.模拟显示在大陆岩石圈剖面中形成规模不等的位移对流环,还有待进一步的研究.

关键词: 中国大陆, 有限元法, 分层黏弹性