THERMAL STATE OF LITHOSPHERE IN MONGOLIA

Abstract

The thermal state of lithosphere in Mongolia has been modeled on the basis of measured regional heat flows and predicted temperatures at depths from 0 to 50 km. The highest temperatures of 1100-1200 C and heat flows of 70-90 mW/m2 and higher occur in active thermal regions beneath the Hovsgol rift basin (Cenozoic rift) and the Onon graben (Mesozoic rift). In regions of moderate geothermal activity in central Mongolia, heat flow is in the range of 50-60 mW/m2, and temperatures at the Moho are within 600-700 °C. Low-activity regions of southern Mongolia show heat flows as low as 40-50 mW/m2 and Moho temperatures below 500 °C. 3He/4He ratios in subsurface fluids indicate predominantly mantle origin of heat flow in rift basins, deep thermoactive faults, and provinces of Cenozoic volcanism and a greater crustal (radiogenic) component in the rest of the territory. The thermal evolution of the lithosphere in Mongolia controlled its structural and compositional changes, especially at shallow depths. The reported results can be used in geothermal modeling for the Mongolian region of southeastern Asia.