Density Patterns of the Upper Mantle Under Asia and the Arctic: Comparison of Thermodynamic Modelling and Geophysical Da
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Pure and Applied Geophysics
Density Patterns of the Upper Mantle Under Asia and the Arctic: Comparison of Thermodynamic Modelling and Geophysical Data TATIANA S. SOKOLOVA,1
ALENA I. SEREDKINA,2
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. Keywords: Density, upper mantle, Asia, Arctic, olivine, pyroxene.
1
Institute of the Earth’s Crust SB RAS, Irkutsk 664033, Russia. E-mail: [email protected] 2 Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS, Troitsk, Moscow 108840, Russia.
and PETER I. DOROGOKUPETS1 1. Introduction
Current knowledge about the composition and structure of the Earth is based on geophysical research and experimental and theoretical modelling. It is well known that silicates (olivine, pyroxene and garnet) are predominate phases in the composition of the upper mantle to depths of 670 km (Ringwood 1975; Chudinovskikh and Boehler 2001; Pushcharovsky and Pushcharovsky 2010; Wu et al. 2019). The association of olivine and pyroxene (Ol ? Px) is estimated to be more than 80 wt% of the total volume of the upper mantle, according to the pyrolytic model (Ringwood 1975). The olivine-pyroxene association also has fundamental significance for other known models of mantle composition (peridotitic
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