CRUST STRUCTURE AND COMPOSITION IN THE SOUTHERN SIBERIAN CRATON ( influence zone of Baikal rifting ), FROM MAGNETOTELLURIC DATA
M.I. Epov, E.V. Pospeeva, and L.V. Vitte
A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Magnetotelluric (MT) soundings, resistivity, rift-related faults, collision zone, igneous and metamorphic rocks
Pages: 293-306
Abstract
The magnetotelluric (MT) profile traverses the southeastern edge of the Siberian craton and the adjacent Paleozoic Ol'khon collision zone, both being within the influence area of the Baikal rifting. The processed MT data have been integrated with data on the crust structure and composition, as well as with magnetic, gravity, and seismic patterns. Large resistivity lows are interpreted with reference to new geothermal models of rifted crust in the Baikal region. The northwestern and southeastern flanks of the profile corresponding to the craton and the collision zone, respectively, differ markedly in the crust structure and composition and in the intensity of rifting-related processes, the difference showing up in the resistivity pattern. The high-grade metamorphic and granitic crust of the craton basement in the northwestern profile flank is highly resistive but it includes a conductor (less than 50 ohm·m) below 16-20 km and a nearly vertical conductive layer in the upper crust. The crust in the southeastern part, within the collision zone, is lithologically heterogeneous and heavily faulted. High resistivities are measured mainly in the upper crust composed of collisional plutonic and metamorphic complexes. Large and deep resistivity lows over the greatest part of the section are due to Cenozoic activity and rift-related transcrustal faults that vent mantle fluids constantly recharged from deeper mantle.
|
