FLEXURE OF THE CONTINENTAL LITHOSPHERE WITH MULTILAYERED RHEOLOGY

In this paper, a model of flexure of the continental lithosphere is derived taking into account crustal and mantle rheologies. Bending of the continental lithosphere is modelled with a double yield stress envelope: three layers (brittle, elastic and ductile) for the crust and three analogous layers for the mantle portion. The deformation of the layers is controlled by the rheological properties of quartz-rich crustal rocks and olivine-rich mantle rocks. The influence of various factors such as the depth of Moho, strain rates, thermal structure of the lithosphere, boundary conditions, and topographic load, is examined. Results show that the mechanical strength of the continental lithosphere in the horizontal and vertical directions is primarily controlled by the present thermal structure of the plate, boundary forces and moments, and the applied topographic load. This explains why mountainous regions may be more locally compensated than adjacent regions. We also thus are able to explain why many continental plates have apparent effective rigidities much smaller than those predicted on the basis of their geological ages. The model is then applied to the Tien Shan-Tarim area (Central Asia), and original topography and gravity data are used to constrain parameters of the model. We found that the model satisfactorily matches the data and is also able to predict the thermal state of the plate and the location of the deep seismicity.