Cambrian to Triassic geodynamic evolution of central Qiangtang, Tibet

Abstract

Central Qiangtang is a tectonic mélange between the northern Qiangtang terrane (NQT) and the southern Qiangtang terrane (SQT), and it preserves a complete Cambrian to Triassic geological record related to Tethyan evolution (e.g., high-pressure metamorphic rocks and ophiolites); thus, this region is the key to understanding the geodynamic processes that occurred during the dispersion of Gondwana and the accretion of Laurussia. Given previous studies on sedimentary, paleomagnetic and seismic records, this paper presents an integrated interpretation of ophiolites, magmatism, metamorphism and tectonism and reconstructs the Cambrian-Triassic tectonic evolution of central Qiangtang as described below. (1) Following the Neoproterozoic-early Cambrian Pan-African orogeny and associated postcollisional extension, the southward subduction of the Proto-Tethys oceanic plate produced Andean-type magmatism along the northern margin of Gondwana. A back-arc basin between the NQT and SQT further opened during the late Cambrian-early Ordovician, accompanying with trench retreat and overriding plate extension resulting from slab rollback. (2) With the middle Ordovician-late Silurian successive incorporation of micro-continental terranes (e.g., Qaidam-Kunlun and Tarim terranes) into the northern margin of Gondwana, the back-arc basin closed through subduction polarity reversal from southward to northward. (3) During the late Devonian-early Carboniferous, the southward subduction of an oceanic plate to the north of the NQT separated the NQT and SQT through back-arc extension. Consequently, the NQT drifted northward rapidly and the back-arc basin gradually evolved into a mature ocean basin (i.e., Longmu Co-Shuanghu Paleo-Tethys Ocean, LSPTO). (4) Subsequently, a late Carboniferous-early Permian continent-continent collision between the NQT and the South China Block (SCB) resulted in the northward subduction of the LSPTO, and the ongoing subduction probably induced the opening of a back-arc basin between the NQT and the SCB during the late Permian. (5) Finally, diachronous collision between the NQT and SQT closed the LSPTO during the early-middle Triassic, and the termination of the collisional orogenic event was evidenced by strong late Triassic magmatism related to postcollisional extension in the Qiangtang Block. In this paper, we propose that the opening and closure of back-arc basins controlled the Cambrian-Triassic tectonic evolution of central Qiangtang, which provides significant insights into the dispersion of Gondwana and the accretion of Laurussia.