Stishovite – the variability of gehesis under earth’s conditions: physico-geochemical aspects

Abstract

Experimental data of studying the stishovite (SiO2) genesis under the Earth’s conditions are systemized. ThePT-diagram of SiO2state up to 350 GPa and 3200°C was drawn. The phase fields of quartz, coesite, stishvite, phase SiO2of CaCl2-type, seifertite (α-PbO2-type) and phase SiO2of pyrite-type were designated. The early accumulation of the Earth’s mass in the period of meteorite accretion was accompanied with impact-in-waves genesis and underground disposal of stishovite which was completely assimilated with the global magma ocean of pyrolite composition. Crystallization of the magma ocean has been completed with a stratification of the mantle with the seismic boundaries between upper mantle, transition zone and lower mantle. The fractional ultrabasic-basic evolution of the mantle magmas was accompanied by peritectic reactions of ringwoodite+akimotoite and bridgmanite with stishovite formation. These reactions are revealed in physical-chemical experiments at 20 and 26 GPa. These reactions in the diamond-parental carbonate-silicate-carbon melts provided formation of stishovite with its capturing into diamonds as paragenic inclusions. The stishovite genesis is also connected with the global mantle convection as at subduction of the lithospheric plates with silica to the layer D”, so at uplift of the superplumes from the layer D” up to the Earth’s crust. The impact-meteoritic genesis of stishovite is restarted with formation of the Earth’s crust.