Density Patterns of the Upper Mantle Under Asia and the Arctic: Comparison of Thermodynamic Modelling and Geophysical Data

Abstract

Based on the modified thermodynamic model, we calculate the density of olivine-pyroxene mixtures at different proportions of molecular masses in minerals at temperatures of 1000–1700 K and pressures up to 17 GPa. The calculated density of the olivine-pyroxene mixtures is compared with the PREM model and the average density patterns of the Asian and Arctic regions estimated from the data on the Rayleigh wave group velocity dispersion in upper mantle conditions. Taking into account the characteristic temperature profiles of different tectonic units in Asia (Tibetan plateau, Khangay dome, Baikal rift and southern Siberian Platform) and the Arctic (Chukotka fold belt, Barents Sea, northern Greenland and Eurasia Basin), we discuss density patterns and features of the mantle composition underneath structures and to depths of 200 km, where the most significant variations in their density patterns are observed. The results obtained suggest some insights into the geodynamic evolution of the lithosphere in the study area. The calculated density characteristics of the components in the upper mantle and the modelling of their composition are compared with average density patterns under the tectonic units, in order to show the possibilities of previously developed equations of state. It has been shown that the composition (0.9(Mg0.9Fe0.1)2SiO4 + 0.1MgSiO3) describes the PREM model well, in addition to the average velocity patterns of the study regions. Variations in mineralogical compositions are revealed between stable structures and the areas with high levels of tectonic and seismic activity. The present paper could be of interest to geophysicists and mineralogists as it researches overlapping topics for both sciences, indicating the relationship between seismicity and features of the deep structure of the upper mantle.