THE TEMPERATURES AND COMPOSITIONS OF MAGMAS OF TRACHYBASALT-COMENDITE ASSOCIATION IN THE TSAGAN-KHURTEI RIDGE, WEST TRANSBAIKALIA (by inclusions in minerals)

Silicate-melt and fluid inclusions have been studied in phenocrysts from mafic and silicic rocks of volcanic trachybasalt-comendite series from the Tsagan-Khurtei Ridge (West Transbaikalia). The results obtained permitted the liquidus temperatures of basic and silicic magmas to be estimated from the homogenization temperatures (T_hom) of melt inclusions. The compositions of melt inclusions were studied on Camebax-Micro and an IMS-4f ion microanalyzer. The highest T_hom (1280–1310 °C) are established for olivine phenocrysts from trachybasalts. The content of H₂O in basic magmas is about 0.1 wt.%, and the concentrations of F and Cl are < 0.4 and ∽0.02 wt.%, respectively. For comendites, three temperature ranges for different liquidus conditions of magmas have been established: 1100–1030, 920–870, and 780–745 °C. In the silicic melts with the highest T_hom, the contents of H₂O, Cl, and F are about 0.5, 0.1, and 0.5–0.6 wt.%, respectively. It is supposed that the highest liquidus temperatures correspond to the temperature of generation of comendite melts and, thus, point to great (probably, subcrustal) depths of their origin.