Article
Article name MELTING FEATURES OF PHASES IN THE DIOPSIDE - CALCIUM MOLECULE OF ESCOLA SECTION IN THE PRESSURE RANGE 1 KGS/SM2 - 20 KBAR
Authors Banushkina S.. research assistant, banushkinasv@igm.nsc.ru
Surkov N.. candidate of geological and mineralogical sciences, associate professor, senior researcher, diagrams@igm.nsc.ru
Golitsyna Z.. research assistant, zoe.zhurko@igm.nsc.ru
Bibliographic description
Category Earth science
DOI 549.07
DOI 10.21209/2227-9245-2019-25-7-6-17
Article type scientific
Annotation Stoichiometric minals are the main components of natural clinopyroxenes. It was assumed that the excess silica found in the results of some studies in clinopyroxene dissolves as the minal “calcium molecule of Escola” Ca0,5AlSi2O6 (CaEs). It was suggested to use the minal CaEs as a pressure indicator. So, attempts have been made to determine the dependence of non-stoichiometric clinopyroxenes compositions on (p, t0)-parameters. Nevertheless, the absence of clinopyroxene non-stoichiometry and complicated structure of phase diagram for the section diopside CaMgSi2O6 (Di) – Calcium Molecule of Escola Ca0,5AlSi2O6 (CaEs) has been shown in the subsequent experiment works at 20–30 kbar. In studies at 1 atm the existence of jadeite-similar minal CaEs as incorrect has been also recognized. It has been determined that there is the phase α-diopside (αDi) in the investigated section. It is close in composition to diopside, does not contain alumina, and does not belong to clinopyroxene solid solution of diopside series. Besides, due to the presence of αDi in this section the additional eutectic is observed. In this regard, a study was made of phase relations in the section of diopside CaMgSi2O6 (Di) – Calcium Molecule of Escola Ca0,5AlSi2O6(CaEs) at pressures 10-15 kbar, and the phase diagram for 1 atm - 20 kbar has been constructed. The phase α-diopside has been found. The phases An, Qtz, Cpx, αDi coexist in a solidus. In the diopside part of section at 10 kbar the clinopyroxene solid solutions field is observed. It is replaced by the phase volume Cpx+αDi. The melting happens at the eutectic reaction An+Cpx+αDi+Qtz=L at temperatures 1200...1210 0C. This eutectic trend well coincides with data previously known. The compositions of coexisting phases correspond to stoichiometry.
Key words Key words: phase diagram; minal; non-stoichiometric clinopyroxenes; Calcium Molecule of Escola;α-diopside; analysis of phase relationships; phase volume; melting; eutectic reaction; high pressures; geothermobarometry
Article information Banushkina S., Surkov N., Golitsyna Z. Melting features of phases in the diopside - Calcium molecule of Escola section in the pressure range 1 atm - 20 kbar // Transbaikal State University Journal, 2019, vol. 25, no.7, pp. 6-17
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Full articleMELTING FEATURES OF PHASES IN THE DIOPSIDE - CALCIUM MOLECULE OF ESCOLA SECTION IN THE PRESSURE RANGE 1 KGS/SM2 - 20 KBAR