THERMAL MODEL FOR LITHOSPHERIC THINNING AND ASSOCIATED UPLIFT IN THE NEOTECTONIC PHASE OF INTRAPLATE OROGENIC ACTIVITY AND CONTINENTAL RIFTS

Abstract

Many regions of recent tectonic activity are characterized by the existence of mantle inhomogeneties which are revealed by various geophysical methods. It is found that the lithosphere beneath the continental rifts and many recent uplifts (high plateaus) is abnormally thin. This thinning of the lithosphere is connected with the process of intensive convective heating. A study of the thermal evolution of the lithosphere, when the convective heat flow is supplied to its base, is performed in the framework of a Stefan's type problem. Solutions are derived giving the relationship between the evolution of the thickness of the lithosphere and the value of the heat flow at the base of the lithosphere at the neotectonic reactivation stage. The results of computations show that the thickness of the lithosphere can be reduced to one half of its initial value in a time interval of an order of several million years when the value of convective heat flow from the anomalous mantle is of an order of 40–100 mW/m². Important data on the evolution of the lithosphere can be obtained from the comparative analysis of the composition of volcanic rocks at different stages of continental rifting. It has been found that the source of magmas has a general tendency to migrate to a shallower depth with time. This process suggests successive thinning of the lithosphere. Based on this deduction, we can use these data to evaluate the time dependence of heat flow from the anomalous mantle.