P-T AND H2O CONCENTRATION OF MESOZOIC GRANITOID FORMATION IN THE MONGOL-OKHOTSK ZONE, BASED ON MELT INCLUSION INVESTIGATIONS, MONGOLIA, SIBERIA

Abstract

Constraints on the ranges of some parameters of granitoid formation in the Mongol-Okhotsk zone (MOZ) have been determined, based on melt inclusion investigations: temperature from 1235° to 500 °C, pressure -from 8000 to 90 bars, and H 2 O concentration - from 13.9 to 0.2 mass %. Increasing value range of temperature, pressure and H 2 O concentration in the melt of granitoid magma crystallisation up to the limiting values in the crystal conditions have been found with decreasing depth of granitoid facies occurrences. Values, around the main modal values of corresponding distributions, are common for batholiths. The maximum values are mainly related to small, rare-met al ore-bearing intrusions. The maximum water pressures and concentrations in the melt are found in rare-met al granitoid massifs. The possibility of forming the rare-met al granitoids by fluid-magmatic differentiation (metamagmatic transformations) of early palingenic granitoid melts, and the participation of fluids with high hydrocarbon content is shown. Fluid-magmatic differentiation is of great importance in the formation of rare-met al ore-magmatic systems.