Analysis of the Thermal Structure of Lithospheric Mantle and Lithospheric Isostasy in China Continent

Abstract

AbstractIt is shown that there are several phenomena in continental areas which can not be explained by traditional isostasy models. The essential reason for this problem comes from the thermal‐caused lithospheric mantle density variation effects on the isostasy models: in traditional isostasy models, effects from mantle lithosphere are excluded. Incorporating the lithospheric mantle effect into the isostasy model, we analyzed the isostasy state of 20 tectonic units in China mainland. It is shown that, in some areas, such as the Tarim Basin, Beishan and Qaidam Basin, although the results derived from the 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 the Tibetan Plateau and its surrounding regions, the results derived from the lithospheric isostasy model are more close to observed elevations and consistent with vertical velocities of crustal movement in most tectonic units. In general, the lithospheric isostasy model with effects of the mantle density variations being taken into account is always better than the traditional crustal isostasy models. Basing on the analysis on isostatic states, following conclusions can be derived. (1) The degree of isostatic state is relatively higher in stable areas; (2) The present‐day crustal movements of the Tibetan Plateau and its surroundings are mainly controlled by regional tectonics and deep dynamic processes. The isostatic adjustment plays only a minor role in 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 the 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.