HYDRODYNAMIC MODEL OF SEDIMENTARY BASIN FORMATION BASED ON DEVELOPMENT AND SUBSEQUENT PHASE TRANSFORMATION OF A MAGMATIC LENS IN THE UPPER MANTLEA. T. Ismail-zadeh, B. M. Naimark, and L. I. Lobkovsky
We present a sedimentary basin formation mechanism based on the subsidence of an eclogite lens in the upper mantle. After the extension of the lithosphere a hot asthenospheric component is advected to the base of the lithosphere into the space created by that process. If the lithosphere/asthenosphere boundary prevents further magma uplift, a magmatic lens concentrates, due to its buoyancy, at the roof of the asthenospheric bulge. We assume that basalt melt in the asthenospheric bulge has not been transported onto the surface and stays in the magmatic lens. According to experimental data, basalt melts turn into eclogite of an increased density during the process of general cooling and crystallization at pressures of 18--22 kb and temperatures of 1000--1200$^\circ$C (at a depth of 60--80 km). Hence the eclogite lens causes crustal subsidence resulting in the sedimentary basin formation. A bicubic spline finite element method is used for a quantitative analysis of the proposed subsidence mechanism. The model region comprises a cross section through the lithosphere and the upper part of the asthenosphere. We assume the Newtonian rheology with variable density and viscosity. An approximate topography is calculated from the normal stress at the free-slip surface boundary for several sample models. The model can be applied to study intracratonic sedimentary basin evolution.