The Chersky Range Ophiolite Belt, Northeast Russia

Abstract

Mafic and ultramafic rocks are found in isolated complexes along the Chersky Range, eastern Sakha Republic (Ya kutia), Russia. Five of the six exposures are located on the eastern side of a Devonian-Ordovician carbonate platform and appear to be thrust over it; the sixth, the Debin fragment, is located to the west. On the basis of lithology, geochemical composition, and structural position, the ultramafic rocks and their associated mafic volcanics and deep-marine sedimentary rocks are interpreted as ophiolites or ophiolite fragments derived from back-arc or oceanic crust located to the east of the Chersky Range. Faunal and radiometric dating indicate that the oceanic crust has an age of about 370-430 Ma, Early to Middle Devonian. The ages of metamorphic minerals suggest that the ophiolites were obducted and metamorphosed during the amalgamation of the Kolyma-Omolon superterrane, about 170-174 Ma (Callovian, late Middle Jurassic), at which time olistostromes containing fragments of the ophiolite were formed. This age predates the formation of the Uyandina-Yasachnaya volcanic arc, believed to represent the final closure of the ocean basin between the Kolyma-Omolon superterrane and the North Asian craton. It is possible that the southernmost ophiolite, the Debin fragment, has a different history from the other Chersky Range ophiolites and was emplaced as a result of the accretion of the Kolyma-Omolon superterrane.