The most intense subduction-related anatexis in the Urals occurred in the late Early Carboniferous (340–320 Ma). It is characterized by high water saturation (PH2O = 0.7−1.0Ptot) of the generated melts, caused by additional supply of water into the zone of anatexis. Anatexis occurs in the zone of stability of major 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 + Bt + An20–45 + Ep± Kfs ± Q ± Sph + Ap + Ilm ± 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 tonalite-granodiorite massifs in the continent-marginal zones.
