【摘要】 龙门山造山带重力场研究表明它处于不均衡的状态,为此,构建了横贯松潘—甘孜块体、龙门山造山带和四川盆地的二维剖面的数值模型,采用黏弹性模型对重力场响应对研究区构造演化过程及动力学效应进行探讨.研究结果表明:(1)重力均衡调整导致了深部物质的垂向复杂动力学响应.在印度板块碰撞挤压效应与青藏高原东缘重力势能差的共同作用下,使得高原东缘深部物质在龙门山深处向东运移时潜入地幔,构成了青藏高原物质向东运移的另一种补偿方式;(2)流变结构及应变能的计算结果表明,龙门山上、中地壳层能量集中危险度较高的地段与汶川大震的孕震及发震方式基本一致,龙门山两侧介质属性、构造格局和流变属性的差异对汶川大地震的孕育和发生均起到了重要作用;(3)进一步开展由包含地表剥蚀的重力均衡调整效应与挤压缩短共同作用下的动力学模型,可以为合理地解释龙门山及周缘地带动力学响应提供重要的参考依据.更多还原

【Abstract】 The Longmenshan orogenic belt is in a very non-isostatic state,which means its crust is in an unstable state.In this paper,2-D Finite Element Method is used with viscoelastic model to study the geodynamical mechanism of gravitational isostasy through the profile across the Songpan-Garze block,Longmenshan faults and Sichuan basin.The results show that:(1) The motion mode of deep materials is much changed by the isostatic adjustment.The interaction effects of the India plate collision and the gravity potential energy cause the dynamics of the sub-vertical downward asthenospheric flow at the bottom of the Longmenshan lithosphere,and lead to the exceptionally steep topography at the eastern Tibetan margin as a result of gravitational buoyancy.(2) The distribution of strain-energy,the rheological structure and other results are calculated numerically,which show that the sections with high risk factors coincide with the areas of the Wenchuan earthquake.The different geophysical structures,as well as the different rheological model on both east and west side of Longmenshan faults zone played important roles in the seismogenic mechanism of the Wenchuan earthquake.(3) We suggest that crustal shortening together with isostatic adjustment,including the rapid erosion-related unloading,is a key component of the geodynamic processes on the eastern Tibetan Plateau margin.更多还原