V. S. Shkodzinskiy (Diamond and Precious Metal Geology Institute of Siberian Branch of Russian Academy of Sciences)

ORIGIN OF GRANITE AND ORE-BEARING HYDROTHERMS OF THE EARTH

The confirmed existence of trends in magmatic fractionation in the mantle and in the crystalline crust, the correspondence of the isotopic age and crystallization temperature of their various rocks to the sequence of formation during fractionation, the sharp chemical nonequilibrium of mantle rocks with metallic iron of the Earth's core, and other data indicate hot heterogeneous accretion of the Earth and the existence of a global magma ocean. Lowpressure crystallization and fractionation of the near-bottom parts of the early still shallow magma ocean under the impact of the load of its forming upper parts led to the formation of large amount of acid residual melts. These melts resulted in the formation of acid crystalline crust. Its frictional heating and melting under the influence of tectonic deformations and subsequent decompression during ascent lead to the formation of granite magma. With an increase in the depth of their solidification, an independent fluid phase appears with an increasing degree of crystallization, when high concentrations of ore and volatile components that carry it out are reached in a small amount of residual melt. This the reason for significantly greater ore content of deep-seated hydrotherms as compared to shallow ones and the relationship of rich hydrothermal deposits with deep parts of granitoid intrusions.
Keywords: magma ocean, fractionation, frictional heat release, granite, ore-bearing hydrotherms.