CaS: A key medium for C-O-S-Ca cycles in Earth

Abstract

Oldhamite (CaS) is a rare mineral, which is only observed naturally in enstatite meteorites.No occurrence of CaS has been documented from other groups of meteorites and terrestrial samples. However, in experiments at 1.5 GPa/1510 K and 0.5 GPa/1320 K, when the lgfo2 is lower than -10.57 (FMQ-0.52), CaS was produced in this study by a two-melt mechanism involving the reaction between molten pyrrhotite-pentlandite-bearing orthopyroxenite and molten CaCO3. CaS can be easily oxidized to form CaSO4 or hydrolyzed to produce calcium hydroxide, which may explain why it has never been found in geological samples from Earth. We speculate that part of the anhydrite and gypsum in black smokers along mid-ocean ridges are related to the oxidation or hydrolysis of CaS in the underlying mantle. CaS can be produced when the Siberian mantle plume intruded into the lithosphere.Comment: The third versio