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Russian Geology and Geophysics

2013 year, number 3


T.V. Donskaya, D.P. Gladkochub, A.M. Mazukabzov, S.L. Presnyakov, T.B. Bayanova
Keywords: Granites, trondhjemites, UPb geochronology, geochemistry, accretionary orogen, Paleoproterozoic, Siberian craton
Pages: 283-296


Detailed geochemical, isotope, and geochronological studies were carried out for the granitoids of the Chuya and Kutima complexes of the Baikal marginal salient of the Siberian craton basement. The obtained results indicate that the granitoids of both complexes are confined to the same tectonic structure (Akitkan fold belt) and are of similar absolute age. UPb zircon dating of the Kutima granites yielded an age of 2019 16 Ma, which nearly coincides with the age of 2020 12 Ma obtained earlier for the granitoids of the Chuya complex. Despite the close ages, the granitoids of these complexes differ considerably in geochemical characteristics. The granitoids of the Chuya complex correspond in composition to calcic and calc-alkalic peraluminous trondhjemites, and the granites of the Kutima complex, to calc-alkalic and alkali-calcic peraluminous granites. The granites of the Chuya complex are similar to rocks of the tonalitetrondhjemitegranodiorite (TTG) series and are close in CaO, Sr, and Ba contents to I -type granites. The granites of the Kutima complex are similar in contents of major oxides to oxidized A-type granites. Study of the Nd isotope composition of the Chuya and Kutima granitoids showed their close positive values of εNd(T) (1.93.5), which indicates that both rocks formed fr om sources with a short crustal history. Based on petrogeochemical data, it has been established that the Chuya granitoids might have been formed through the melting of a metabasic source, wh ereas the Kutima granites, through the melting of a crustal source of quartzfeldspathic composition. Estimation of the PT-conditions of granitoid melt crystallization shows that the Chuya granitoids formed at 735776ºC (zircon saturation temperature) and >10 kbar and the Kutima granites, at 819920ºC and >10 kbar. It is assumed that the granitoids of both complexes formed in thickened continental crust within an accretionary orogen.