10.57647/j.ijes.2025.17558

Experimental study of Di-CaEs solid solution at pressures from 1 atm to 3.0 GPa

  1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia

Received: 2025-01-20

Revised: 2025-04-22

Accepted: 2025-06-19

Published Online: 2025-10-04

How to Cite

Viktorovna Banushkina, S., Friedrichovna Golitsyna, Z., & Anatolyevich Kirdyashkin, A. (2026). Experimental study of Di-CaEs solid solution at pressures from 1 atm to 3.0 GPa. Iranian Journal of Earth Sciences. https://doi.org/10.57647/j.ijes.2025.17558

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Abstract

The possibility of ‘excess’ silica dissolution in clinopyroxene (Cpx) as the calcium molecule of Eskola (CaEs) end member has been known for a long time. Currently, attempts to determine the dependence of non-stoichiometric Cpx compositions on (P, T)-parameters are ongoing. This article presents data on the analysis of Cpx compositions and the structural and textural features of a phase association obtained from an experimental study of the Di-CaEs cross-section in a ‘dry’ CMAS system. At atmospheric pressure, the temperature range is 960-1240±10 oC. At pressures of 1.0-3.0 GPa, the temperature range is 1170-1550±10 oC. Experiments with synthetic compositions were carried out in a vertical shaft electric resistance furnace with silicon carbide heaters (at atmospheric pressure) and by the quenching method on a piston-cylinder apparatus (at high pressure). It is noted that in the investigated cross-section, two independent stable pyroxene phases are formed: an aluminum-bearing Cpx and a high-magnesian aluminum-free diopside (Di). The composition of clinopyroxene solid solution Cpx(ss) is represented by a quad series of diopside (Di), enstatite (En), calcium molecule of Tschermak (CaTs), calcium molecule of Eskola (CaEs) end members. The diopside phase belongs to the Di-En series. The influence of P-T parameters and bulk chemical composition on the content of CaEs in Cpx is considered. The trend of eutectic equilibria exists in the temperature range from 1137±10 оС (at 1 atm) to 1300±10 оС (at 3.0 GPa). The experimental data obtained can be used in the future to build a physicochemical model of the evolution of quartz-normative rocks.

Keywords

  • CMAS system,
  • Experimental petrology,
  • Clinopyroxene solid solution,
  • CaEs end member,
  • Geothermobarometry

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