Experimental Study of the Phase Diagram of CaMgSi_2O_6-CaAl_(0 5)Si_2O_6 System at 3.0 GPa

摘要

Stoichiometric end members are the main components of natural clinopyroxenes. However, the study of the compositions of natural clinopyroxenes and experimental works have revealed the presence of excess SiO_2 in the form of the jadeite-type Ca_(0.5)AlSi_2O_6, called a "calcium Eskola molecule" (hereafter, CEM). Particular attention has been devoted to this end member in connection with the issue of the "eclogite barrier" Researchers have supposed that the component mentioned above can be used as an indicator of pressure in rocks of eclogite paragenesis. However, the experimental data on the stability of nonstoichiometric clinopyroxenes are inconsistent. The problem may be solved by plotting a correct phase diagram for the CaMgSi_2O_6-Ca_(0.5)AlSi_2O_6 system at 3.0 GPa.