GEOCHEMICAL TYPES OF GRANITOIDS AND COMPO SITION OF THE EARTHS CRUST WITHIN THE KAN AND ARZYBEI-DERBIN BLOCKS (SOUTHWESTERN SIBERIAN PLATFORM)

The paper considers the early granitoids of the tonalite-trondhjemite series which were related to the granite-greenstone stage of formation of the earth's crust, In terms of parameters, they are correlated wit h the M-type granitoids of immature oceanic arcs and low-potassium I-g ranites of evolved island arcs, and in general are distinguished by st eeper REE spectra, high contents of Sr, and low contents of Y. Distrib ution of REE, Sr, Y, and Ta in the granitoids is controlled by an equi librium of the acid melts and garnet-clinopyroxene association of rest ite phases, which corresponds to the experimental data on dehydration melting of a mafic source at P > 16 kbar and T > 1025-1050 degrees C. This is evidence that the granitoids formed in a subduction-related en vironment. The average level of concentrations of a wide spectrum of e lements, including REE, Th, Sr, Th, Ba, and Zr, can be explained by pe culiarities of the composition of the melting source. Within the Kan b lock, certain differences in composition of the lower crust rock compl exes (as demonstrated by their metabasite component) are observed and regional zones anomalously enriched in alkalies and alkali-earth eleme nts are distinguished.