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 (Thom) of melt inclusions. The compositions of melt inclusions were studied on Camebax-Micro and an IMS-4f ion microanalyzer. The highest Thom (1280-1310 degrees 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 degrees C. In the silicic melts with the highest Thom, 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.