THE STRUCTURE OF THE MAGNETOACTIVE LAYER OF THE AMUR LITHOSPHERIC PLATE
A.N. Didenko1,2, M.Y. Nosyrev2, G.Z. Gilmanova2, M.D. Khutorskoy1
1Geological Institute of the Russian Academy of Sciences, Moscow, Russia
2Institute of Tectonics and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, Khabarovsk, Russia
Keywords: Curie Point Depth, plate boundaries, thermal anomalies and tectonic structures, Amur Plate
Abstract
Based on the results of spectral analysis of the anomalous magnetic field, the depths of the roof and the base of the magnetoactive layer of the Amur Plate and adjacent territories were calculated. The causes of variations in the depth of the magnetoactive layer base (CPD) from 14 to 38 km (average 24 km) were determined. Maximum CPD depths are observed within sedimentary basins (Erlian, Songliao, and Middle Amur) in the southwest and in the central part of the plate. The areas of minimum depths in the continental part are located in the northwest within the giant granitoid batholiths (Angara-Vitim, Khentei) and in the northeast within the Bureinsky province. The third area of minimum CPD values is located within the waters of the Sea of Japan. The relatively high elevation of the magnetoactive layer base in the waters of the Sea of Japan is associated with rifting processes in the back-arc basin, which began at the end of the Oligocene, and the generation of fluids and magma chambers above the Pacific slab that is sinking under the Amur Plate. Two high CPD areas standing in the continental part of the plate are associated with the presence of two thermal anomalies. The north-western one is explained by the presence of a thermal crustal anomaly due to the process of radioactive heat generation by granitoids of the giant Angara-Vitim, Khangai and Khentei batholiths. The Northeastern Bureinskaya area is explained by the presence of an anomalous temperature of the mantle here. A comparison of the newly constructed CPD map with the boundaries of the Amur Plate, previously determined mainly from seismic data, shows that the surface boundaries of the plate coincide mainly with the zones of the greatest CPD gradients. All of them are associated with areas of increased seismic energy generation, with the exception of one small area on the southern border of the Amur Plate at its junction with the Yangtze Plate. In our interpretation, plate boundaries are not just lines on the surface, they are fairly wide zones from tens to the first hundreds of kilometers that encircle the plate.
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