Article
Article name	GEOTHERMOBAROMETRY OF LHERZOLITES BASED ON A CLINOPYROXENE COMPOSITIONS ANALYSIS OF THE CaO-MgO-Al2O3-SiO2 MODEL SYSTEM
Authors	Kirdyashkin A.. , Golitsyna Z.. research assistant, zoe.zhurko@igm.nsc.ru Banushkina S.. research assistant, banushkinasv@igm.nsc.ru
Bibliographic description
Category	Earth science
DOI	549.07
DOI	10.21209/2227-9245-2020-26-2-14-22
Article type
Annotation	The possibility of diagnosing the conditions for the formation of mineral associations in terms of temperature and pressure values, which, in turn, can be calculated by the enstatite and Ca-chermakite minals percentage in the clinopyroxene is described in this article. This problem has an inverse solution as well – the clinopyroxene composition in the CaO-MgO-Al2O3-SiO2 system is determined by the unique values of temperatures and pressures. The clinopyroxene is found in all types of deep-seated rocks and also has the broadest composition variations, which makes it a universal physicochemical conditions indicator for the formation of mineral associations. Analysis of the Northern Lesotho lherzolites samples demonstrates the strict pattern of changes in the clinopyroxene composition depending on the values of temperatures and pressures. The experimental studies data of the Cpx – Gr (clinopyroxene – garnet) phase relationships of the CaO-MgO-Al2O3-SiO2 model system are presented in the pressure range 12…30 kbar and temperatures 1325…1650 ° C. The compositions retaining this pattern was obtained in our laboratory conditions on a piston-cylinder type high-pressure apparatus, at pressures and temperatures close to the conditions for the formation of lherzolites. It consists in increasing the enstatite and Ca-chermakite components percentage with temperature rise and their decrease with pressure rise. Thus, a significant change in clinopyroxene compositions both as a function of temperature, and pressure was revealed. The polynomial dependence of the clinopyroxene composition on pressure and temperature is presented. The polynomial dependence calculation of clinopyroxene compositions on temperature and pressure turned out to be valid for data of other authors. They are in good agreement and complement our data sampling, and the pattern presented in the form of a polynomial is preserved
Key words	phase diagram; geothermobarometry; minal; garnet lherzolites; analysis of phase relationships; phase equilibrium; melting; eutectic reaction; high pressures; polynomial
Article information	Golitsyna Z., Kirdyashkin A., Banushkina S. Geothermobarometry of Lherzolites Based on a Clinopyroxene Compositions Analysis of the CaO-MgO-Al2O3-SiO2 Model System // Transbaikal State University Journal, 2020, vol. 26, no. 2, pp. 14–22. DOI: 10.21209/2227-9245-2020-26-2-14-22.
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Full article	GEOTHERMOBAROMETRY OF LHERZOLITES BASED ON A CLINOPYROXENE COMPOSITIONS ANALYSIS OF THE CaO-MgO-Al2O3-SiO2 MODEL SYSTEM