Compositions of clinopyroxene solid solutions in Di-CaEs section of CMAS system at pressure up to 3.0 GPa

Abstract

Abstract The possibility of ‘excess’ silica dissolution in clinopyroxene as calcium molecule of Eskola (CaEs) end member has been known for a long time. At present time attempts to determine the dependence of such non-stoichiometric clinopyroxene compositions on (P, T)-parameters are continued. In this article Di-CaEs section of ‘dry’ CMAS system was investigated in P-T range of up to 3.0 GPa and up to 1550 oC. Experiments with synthetic clinopyroxene compositions were carried out on a vertical shaft electric resistance furnace with silicon carbide heaters (at atmospheric pressure) and were run by quenching method on the piston-cylinder apparatus (at high pressure). It was found that two independent stable pyroxene phases are formed: aluminous clinopyroxene and a high-magnesian alumina-free diopside. It was clarified that clinopyroxene solid solution is represented by a quad series of Di-En-CaTs-CaEs end members. It was shown that diopside phase belongs to Di-En solid solution. A tetrahedron of clinopyroxene compositions was constructed, occupying a central position in CMAS system. Experimental data obtained can serve as a necessary model for subsequent studying influence of alkalis, ferruginous component, etc. on stability of quartz-normative mineral associations and identical ‘real’ parageneses.