地幔岩石圈热结构差异与中国大陆岩石圈均衡分析

It is shown that there are several phenomena in continental areas which can not be explained by traditional isostacy models. The essential reason for this problem comes from the thermally-caused lithospheric mantle density variation effects on the isostacy models: in traditional isostasy models, the effects from mantle lithosphere are excluded. Incorporating lithospheric mantle effect into isostasy model, we analyzed the isostasy state of 20 tectonic units in China continent. It is shown that, in some areas, such as Tarim Basin, Beishan and Qaidam Basin, although the results derived from traditional Airy model and lithospheric isostasy model are close, the lithospheric isostasy model can explain the nature of the mass balance in a more reasonable way. Except for Tibetan Plateau and its surrounding regions, the results derived from lithospheric isostasy model are closer to observed elevations and consistent with vertical velocities of crustal movement in most tectonic units. In general, the lithospheric isostasy model, which takes into account the effects of mantle density variations, is always better than the traditional crustal isostasy models. Based on the analysis of isostatic states, the following conclusions can be derived. (1) The degree of isostatic state is relatively higher in stable areas; (2) The present-day crustal movement of Tibetan Plateau and its surroundings is mainly controlled by regional tectonics and deep dynamic processes. The isostatic adjustment plays just a minor role for the current crustal vertical movement; (3) The tectonic units in which significant vertical movements are observed are in the stage of isostatic adjustment. The magnitudes of isostasy forces are represented by the amount of crustal vertical movement. (4) There is a good correlation between the rate of present-day crustal vertical movement and the differences between the observed elevations and those calculated with lithospheric isostasy model in stable areas. Based on this relationship, we can obtain the information of the kinematic and geodynamic characteristics by analyzing isostasy states; (5) Mantle contribution to lithospheric isostasy is so important that it should be taken into account in isostasy analysis.