Publishing House SB RAS:

Publishing House SB RAS:

Address of the Publishing House SB RAS:
Morskoy pr. 2, 630090 Novosibirsk, Russia



Advanced Search

Russian Geology and Geophysics

2001 year, number 7

STRUCTURE, COMPOSITION, AND FORMATION CONDITIONS OF METASEDIMENTARY-VOLCANOGENIC COMPLEXES OF THE KAN GREENSTONE BELT (northwestern Sayan region)

A. D. Nozhkin, O. M. Turkina, E. V. Bibikova, and V. A. Ponomarchuk
Keywords: Greenstone belt, amphibolites, gneisses, geochemistry, petrology, protoliths, geodynamics, East Sayan
Pages: 1058-1078

Abstract

In the northwestern Sayan region, within the Kan block - a fragment of the granite-greenstone province on the southwestern margin of the Siberian craton, - two greenstone belts, Idar and Kan, have been revealed. Study of the geologic sections and composition of the strata of the Kan greenstone belt (GSB) and reconstruction of the protoliths of metamorphic rocks by the wide spectrum of their trace, radioactive, and rare-earth elements have shown that rocks of tholeiite-basalt and andesite-dacite-rhyodacite associations are predominant in the metasedimentary-volcanogenic section. The overlapping metaterrigenous sediments include graywackes and aluminous pelites. The revealed types of rock associations and specific features of the trace-element composition of metasedimentary-volcanogenic rocks are typical of ancient greenstone belts. The complexes of the Kan GSB might have formed in the setting of an ensialic island arc, whose evolution was hindered by a zone of back-arc spreading. Results of the first isotope U-Pb and Ar-Ar dating of minerals show that the volcanic rocks of the Kan GSB accumulated in the Early Proterozoic and underwent intense metamorphism in the Early Cambrian. The trondjemites of the Upper Kan Massif also formed in the Early Cambrian.