Deep structure of the Ulaanbaatar area (Mongolia) from the gravimetric data

Abstract

The medium-scale gravity survey over the Ulaanbaatar area (Central Mongolia) has yielded the Bouguer gravity anomaly map. Based on interpretation of these data, 3D models have been built for large density inhomogeneities in the Earth’s crust - Ulaanbaatar (Tola) depression and Bogdo granite massif. It has been identified that the basement of the depression has a block structure and complicated by two basins: western and central (Selbe) The sediment thickness averages about 150 m in the western basin and may reach 300 m in the Selbe. The thickness of granitoids in the Bogdo massif reaches 4.5 km, the area of its projection on the earth's surface is twice the area of the exits. The data on the form and dimensions of these density inhomogeneities may be used in engineering seismology to update seismic hazard estimates for the town of Ulaanbaatar and to conclude about the prospects for metallogenic specialization of granitoids whose features concerning some minerals are related to peculiar massif form and identified by geological-geophysical and geochemical studies