Provenance of Early Late Ordovician marine carbonate red beds in the Tarim Block and implication for tectonic evolution of northern Gondwana

Abstract

As the largest oil-bearing basin in northwest China, the Tarim basin records multiple major tectonic-sedimentary transitions during the Early Paleozoic, which play an important role in understanding assembly processes of Gondwana. An important transition from the Middle to Late Ordovician was development of important unconformity T74, the end of a unified carbonate platform, and development of turbidites in eastern basin. However, due to unobvious terrigenous clastic record, there is still a lack of understanding of driving mechanism of the tectonic transition. Marine carbonate red beds (MCRBs) with detritus components are developed in the Tumuxiuke/Kanling Formation at the bottom of the Upper Ordovician. By detailed field observation, zircon U-Pb dating and Hf-isotope analyses, provenance and the tectonic implication of the MCRBs are studied. New zircon U-Pb dating results constrain the depositional age of the MCRBs at ca. 454Ma. Provenance tracing shows the Precambrian detrital zircons were mainly sourced from the basement of the Tarim block, and the early Late Ordovician detrital zircons were probably derived from ash from the Altyun Tagh orogenic belt. Based on syn-depositional magmatic zircon records and the magmatic-metamorphic records in the Altyn Tagh orogenic belt, the closure age of North Altyn Ocean, one branch of Proto-Tethys Ocean, can be constrained to the latest Middle Ordovician (~ca. 460 Ma). The collison of the Tarim block with the Central Altyn terrane occurred (ca. 460 Ma - 454 Ma), leading to the major tectonic-sedimentary transition in the Tarim block. The U-Pb age spectrum of detrital zircons also indicates that the Tarim block is closely related to the North Indian block in Gondwana. This study shows that carbonate rocks with low clastic flux can be applied as provenance research objects.