No abstract

No abstract

No abstract

. Dobretsov et al. [1985] first described the rock complexes in Eastern Sayan as ophiolites. Ophiolites formed in Dunzhugur island arc and were obducted onto Gargan block, a Neoarchean crystalline basement of the Tuva-Mongolian Massif (TMM), as a single nappe [Khain et al., 2002;Kuzmichev, 2004]. Zircons from plagiogranite were dated at 1021±5 Ma by multigrain TIMS and 1020±1 Ma by Pb-Pb single-grains evaporation method [Khain et al., 2002]. Later [Kuzmichev, Larionov, 2013] analysed 12 grains of detrital zircons from gravelstone of the Dunzhugur formation and obtained 206 Pb/ 238 U ages from 844±8 to 1048±12 Ma. Careful examination of these data shows that 206 Pb/ 238 U ages for concordant zircons only vary from 962±11 to 1048±12 Ma. Two groups of data give Concordia ages of 974±11 and 1028±10 Ma. Rocks of the Dunzhugur complex are characterized by slightly negative to slightly positive εNd(t) values from -1.0 to +1.5 and Late Palaeoproterozoic depleted mantle Nd model ages of 1.8-1.6 Ga [Sklyarov et al., 2016]. The Dunzhugur complex was intruded by tonalite plutons of the Sumsunur complex dated at 785±11 Ma [Kuzmichev et al., 2001] and 811±7 Ma [Kovach et al., 2012]. These tonalites have strongly negative ɛNd(t) values from -13.2 to -12.3 and Nd model ages of 2.5-2.4 Ga, suggesting formation of these melts from a mixture of N.L.

No abstract