PT-CONDITIONS AND MECHANISMS OF INTERACTI ON OF CONTRASTING MAGMAS INTHE SHALUTIN PLUTON, TRANSBAIKALIA (FROM THE RESULTS OF STUDY OF INCLUSIONS IN MINERALS)

In the structure of the Shalutin Pluton (Transbaikalia) sites made up of co-existing quartz-syenites and basic magmas have been revealed. In the place of their contact a zone of remelting of quartz-syenite mate rial and of intense chemical and mechanical interaction of regenerated granitoid and intruded basic magmas is observed. Numerous combined di kes containing variable amounts of regenerated acidic melt and basic m atter branch off from the contact zones to host quartz syenites. With thermobarogeochemical methods, the PT-parameters of rock crystallizati on have been studied. It is shown that the crystallization temperature s of basic rocks steadily fall as their hybridization degrees increase : from 850-900 degrees C in the least altered differentiates to 760-79 0 degrees C in quartz gabbros, which, along with geochemical data, poi nts to a supply of alkalies and water into the basic melt at the initi al stages of magmas interaction. Though The temperature of heating of sialic material in the contact zones reached 800 degrees C and higher, the crystallization temperatures of regenerated magmas turned out to be much lower than the solidus temperatures of host quartz syenites (6 40-660 degrees C against 700-720 degrees C). This, most likely, points to a supply of the significant amounts of volatiles into the remeltin g zones in the course of basic-magma crystallization. Far the host qua rtz syenites and quartz syenites of the remelting zones stratification of magmatic fluid into two immiscible phases - water-salt and water-c arbon dioxide - has been established.