Allochthonous Marbles in High-Grade Metamorphic Terranes (A Case Study of Olkhon Terrane, West Baikal Area, Russia)

Abstract

For citation : Sklyarov E.V., Lavrenchuk A.V., 2017. Allochthonous marbles in high-grade metamorphic terranes (a case study of Olkhon terrane, West Baikal area, Russia). Geodynamics & Tectonophysics 8 (3), 561-563. doi:10.5800/ GT-2017-8-3-0291. Marbles are common constituents of high-temperature (HT) metamorphic terranes and shields. They have been traditionally considered as indicators of sedimentary or volcanic origin of related rocks involved into metamorphism which erases the primary features of the protoliths. This approach is correct in most cases, but carbonate and silicate-carbonate rocks, which often make linear bodies, may be allochthonous in some structurally and compositionally complex metamorphic terranes, as in the case of the Olkhon terrane.The Olkhon metamorphic terrane is a part of the Early Palaeozoic accretionary-collisional system in the northern Central Asian Orogenic Belt (CAOB). The terrane was produced by an Ordovician collision (470-460 Ma) as a collage of numerous chaotically mingled tectonic units that are composed of rocks of different ages (1870-1830, 840, 800, 640, 545, and 500-490 Ma) originated in different tectonic settings. All pre-collisional complexes in the Olkhon terrane have their analogs among the rocks formed during main events in the northern CAOB history [Donskaya et al., 2017]. The terrane history comprised several stages of thrusting, doming, and strike-slip faulting accompanied by high-temperature metamorphism and mafic and granitic magmatism [Fedorovsky, Sklyarov, 2010]. The processes of strike-slip tectonics were the most vigorous and diverse and defined the general structure of the Olkhon region with packages of tectonic units varying in composition, morphology, and structure. The tectonic units are separated by ductile shear zones of blastomylonites. The terrane has a complex mosaic structure but generally splits into the Southeastern and Northwestern major zones with (i) abundant

Metamorphic and chronological constraints on the early Paleozoic tectono‐thermal evolution of the Olkhon Terrane, southern Siberia

“…The marbles are mainly calcite‐type and locally form a marble mélange containing clasts of mafic granulite, amphibolite, gneiss, granite, and/or gabbro from a few centimetres up to tens of metres in size (Sklyarov et al, 2009). Some marble bodies resemble dykes ‘intruding’ amphibolites but have isotopic and geochemical compositions corresponding to sedimentary carbonates rather than mantle‐derived carbonatites (Sklyarov & Lavrenchuk, 2017). Nonetheless, the presence of marble as intercalations with gneisses, amphibolite, and granulite is a key determining factor in interpreting the region as a stratigraphically bedded volcano‐sedimentary sequence.…”