Provenances of the Paleozoic Terrigenous Sequences of the Oldoi Terrane of the Central Asian Orogenic Belt: Sm-Nd isotope Geochemistry and U-Pb Geochronology (LA-ICP-MS)

The results of Sm-Nd isotope geochemical investigations of the Paleozoic terrigenous sequences of the Oldoi terrane and U-Pb dating of detrital zircons by the LA-ICP-MS technique showed that the clastic material was mainly derived from Late Precambrian granitoids and Early to Middle Paleozoic granitoids and volcanics, which were formed owing to the reworking of the Late Precambrian continental crust. During the Silurian, the main source of terrigenous material in the sedimentation basin was the erosion of Late Precambrian and Early Paleozoic granitoids. In the Devonian, provenances became more diverse, and the sedimentation basin was additionally supplied by the decomposition products of Middle Paleozoic granitoids and silicic volcanics. The age ranges obtained for detrital zircons from the sandstones of the Middle-Late Devonian Oldoi Formation and the Early Carboniferous Tipara Formation are almost identical to the stratigraphic ages of the formations, which indicates that terrigenous sedimentation in the Oldoi terrane had been accompanied, at least since the Middle Devonian, by vigorous magmatic activity and occurred in an environment of a mature island arc or an active continental margin.