ARCHEAN MAGMATIC ROCKS IN THE LAKE NOTOZERO AREA OF THE NORTHWESTERN BELOMORE - ISOTOPIC GEOCHRONOLOGY AND PETROLOGY

The Notozero Complex of plutonic rocks is located in the margin of the Belomorian Belt where it borders the Karelian granite-greenstone terr ain. It consists of calc-alkalic and tholeiitic rocks dominated by gra nites. The plutons were intruded under the conditions of low-pressure granulite metamorphism (P = 4 - 5 kbar, T = 950 - 850 degrees C) at 27 30 - 2710 Ma, The petrochemical and geochemical features of the rocks suggest that all tholeiitic rocks and some of the calc-alkalic were fo rmed as a result of the melting of crustal rocks (I-type granites), si milar to those of active continental margins. The low K2O content of t he calc-alkalic rocks and the negative Nh anomaly of the basics sugges t that subducted material took part in their formation. The rocks unde rwent garnet amphibolite facies metamorphism (T = 730 - 660 degrees C, P = 7 - 6 kbar) at 2700 - 2680 Ma, synchronously with metamorphism th at occurred in northwestern Belomor'e during the collision stage of th e region's history.