Depleted SSZ Type Mantle Peridotites in Proterozoic Eastern Sayan Ophiolites in Siberia

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.

Nd-Sr Isotopic Study of Magmatic Rocks and 40Ar/39Ar Dating of the Mafic Dike of the Proterozoic Ulan-Sar’dag Ophiolite Mélange (Southern Siberia, East Sayan, Middle Belt, Russia)

“…The ratio of ε Nd (T)-I Sr (T) did not correspond to the mantle sequence [49] (Figure 8). The model age determined from the Re-Os isotopy of mantle peridotites of the Ulan-Sar'dag massif was 1.38-2.38 Ga [31].…”

“…Generally, geochemical signatures for the magmatic rocks associated with Eastern Sayan ophiolites reveal a wide compositional series: mid-ocean ridge basalt (MORB)-type basalts (tholeiites), boninites, island-arc andesites and dacites, and ocean island basalt (OIB)-type basite rocks. There are numerous isotopic data of the island arc assemblage and ophiolites in a different segment of CAOB, but isotope geochemical data of Proterozoic Eastern Sayan ophiolites are limited [4,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. [35,36].…”

The Fuchuan Ophiolite in South China: Evidence for Modern‐Style Plate Tectonics During Rodinia Breakup

“…Significantly, the Yangtze Block of South China, Arabian Shield, Nubian Shield, Siberia Craton, and India which have abundant Neoproterozoic ophiolites (Figure 13c) were located on the margin of the Rodinia supercontinent (ca. 850 Ma), in paleogeographic reconstructions, adjacent to the circum‐continental supra‐subduction zone (Merdith et al., 2017; K. L. Wang et al., 2017; Wang, Cawood, & Pandit, 2021; Wang, Cawood, Pandit, Xia, et al., 2021). The relatively rigid plate margin and low mantle temperature promoted cold and deep subduction along the Rodinia margins that likely induced mantle flow into a much wider cell resulting in extensional stresses at greater distances from the trench (e.g., ∼3,000 km; Dal Zilio et al., 2018).…”

“…Significantly, the Yangtze Block of South China, Arabian Shield, Nubian Shield, Siberia Craton, and India which have abundant Neoproterozoic ophiolites (Figure 13c) were located on the margin of the Rodinia supercontinent (ca. 850 Ma), in paleogeographic reconstructions, adjacent to the circum-continental supra-subduction zone (Merdith et al, 2017;K. L. Wang et al, 2017;Wang, Cawood, Pandit, Xia, et al, 2021).…”

Multistage Magmatism in Ophiolites and Associated Metavolcanites of the Ulan-Sar’dag Mélange (East Sayan, Russia)

“…The Ulan-Sar'dag ophiolitic mélange may constitute an independent branch [38]. At the present time, this ophiolitic mélange is still poorly studied and only briefly described in Russian and international publications [44][45][46]. The focus of this paper is to describe the petrography, mineralogy, geochemistry, and geochronology of the mantle and cumulative peridotites, gabbros, and volcanic-sedimentary sequence of the USM.…”