Reconstructing the Olongbuluke Terrane (northern Tibet) in the end-Neoproterozoic to Ordovician Indian margin of Gondwana

The end-Proterozoic to Ordovician paleogeographic relationship of the northern Tibetan terranes with the Gondwana is poorly constrained. Most models have hypothetically regarded them as outboard ribbons isolated in the Proto-Tethyan Ocean. In this study, we employed zircon U-Pb geochronologic data from sedimentary units below and above a Neoproterozoic-Cambrian unconformity in the Olongbuluke Terrane (OLT) to show a transition in source from the OLT to the Gondwana at end-Neoproterozoic. The Precambrian sandstones contain the OLT originated zircons with consistent age spectra characterized by crystallization ages of 2700-1750 Ma. By contrast, Cambro-Ordovician sandstones yield a broad age range of 3580-490 Ma, dominated by a primary age cluster peaking at similar to 980 Ma. This age distribution displays a strong similarly with those for coeval sediments in the South China, Qiangtang and Himalaya, indicating a common source from the Indian Gondwana. The shared source requires the OLT to have a paleogeographic continuity with the northern India being a member of peri-Gondwana assemblages. Chronological studies assigned an end-Neoproterozoic age of similar to 580 to 550 Ma for the uppermost unit below the unconformity, while the lowest Cambrian has an initial depositional age of similar to 515 Ma, constraining a similar to 550 to 515 Ma age interval for the stratigraphic break. We invoke the similar to 550 to 515 Ma as the timing for the accretion of OLT onto the Greater Indian lithosphere, synchronous with the final assembly of Gondwana in the Indo-Australian portion. In combination with correlation of age spectra for the OLT with those for other tectonic units in the northern Tibet, our interpretation infers that the northern Tibetan terranes should have been subjected to the evolution of the Greater Indian lithosphere in the early-Paleozoic. This refined tectonic scenario provides a pioneering perspective to view the dynamic mechanism of tectonic evolution for the northern Tibet in the global Gondwana amalgamation context.