Approach to the mineralogy of the lower mantle by a combined method of a laser-heated diamond anvil cell experiment and analytical electron microscopy

Abstract

A combined method of a laser-heated diamond anvil cell (DAC) experiment and analytical electron microscopy to study the mineralogy of the lower mantle was explored. Particularly, the use of ultramicrotomy to make ultrathin foils for analytical transmission electron microscopy (ATEM) of the ultrahigh pressure materials was explored with the aim of obtaining the exact chemical compositions of those materials with submicron size. Ultrathin foils with a thickness down to about 30 nm were obtained for ultrahigh pressure materials synthesized by a laser-heated DAC, although some areas of the foils were lost. Reliable chemical compositions were obtained with these foils using the experimentally obtained k-factors. The preliminary results on the mutual solubilities between (Mg,Fe)SiO3 and CaSiO3 perovskites with this method indicate that the (Mg,Fe) solubility in CaSiO3 perovskite increases dramatically (up to 0.34 cations per foumula unit at 78 GPa and 1900 °C) with increasing the bulk iron content and/or pressure, while the Ca solubility in coexisting (Mg,Fe)SiO3 perovskite remains very limited (0.01–0.02 cations per formula unit) under the same conditions.