The structure of the magnetically active 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 FEB RAS Khabarovsk, Russia
Keywords: Amur Plate, Curie Point Depth, plate boundaries, thermal anomalies and tectonic structures
Abstract
Based on the results of spectral analysis of the anomalous magnetic field, the depths of the roof and the sole of the magnetically active layer of the Amur Plate and adjacent territories are calculated. The causes of variations in the depth of the sole of the magnetoactive layer (CPD) from 14 to 38 km (average 24 km) have been determined. Maximum CPD depths are observed within sedimentary basins (Erlian, Songliao, Sredneamursky) 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 bottom of the magnetically active layer in 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, sinking under the Amur Plate. Two areas of high CPD 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. Northeastern Bureinskaya – 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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