Experimental study of the differentiation of gabbro-syenite melt under superliquidus conditions

Abstract

ABSTRACTIn this work we present the results of experimental interaction of gabbro-syenite melt, corresponding to the average composition of Northern Timan rocks, with a complex hydrogen-containing fluid. The composition of the magmatic fluid was controlled to be close to natural conditions using a special cell in a high gas-pressure vessel. Under superliquidus conditions, the initial melt exsolves into melts of different composition, forming contrast, cryptic, and rhythmic melt stratifications. The experimental results agree with natural data in the petrochemical diagram. It follows from our experimental data that fluid-saturated melts in magmatic chambers are completely differentiated in the liquid state. In the absence of temperature gradients in the magma, gravitational migration of nanoclusters of different densities forms flotation, sedimentation, and rhythmic types of melt stratification. Transmission electron microscopy of the glasses formed in the cell was used to study the formation of nanoclusters in a fluid-saturated superliquidus anorthosite-granite model melt. Clusters with a size of 6 nm consist of a pseudo-crystalline anorthite core surrounded by fluid-saturated shells of the melt. The migration of fluid and fluid-enriched clusters to the upper part of the magmatic chamber results in the activation, from bottom to top, of the processes of crystallization in the magma.