SUBDUCTION-RELATED ANATECTIC GRANITOIDS OF THE URALS

Abstract

The most intense subduction-related anatexis in the Urals occured in the late Early Carboniferous (340-320 Ma). It is characterized by high water saturation (PH2O = 0.7 1.OPtot) of the generated melts, caused by additional supply of water into the zone of anatexis. Anatexis occurs in the zone of stability of main hydroxyl-bearing minerals - biotite and hornblende accumulated in restite. Anatectic melt is either of tonalite or granodiorite composition. This composition of melt is due to a basite substratum whose degree of melting provides about 40% of melt sufficient for separation from the substratum. Outmelting of granitoid melts is accompanied by water basite magmatism. The products of this magmatism are represented by high-Sr hornblende gabbros, which are the source of heat and matter (substratum) for anatexis. Gabbroids and products of crystallization of anatectic melt share the mineral composition: Hbl + B1 + An20-45 + Ep± ± Kfs ± Q + Sph + Ap + I1m ± Mt. Prolonged basite magmatism increased the crust thickness from below, thus causing its underplating in a suture megablock, in the adjacent island-arc zones, and in the regions of development of subduction-related tonalite-granodiorite massifs in the continent-marginal zones.