Tonian rift sedimentation and granitic gneiss in the North Lhasa terrane, Tibet: A refined Neoproterozoic tectonic evolution model and its implications for paleogeography

Abstract

The Neoproterozoic paleogeographic affinity and basement characters of the Lhasa terrane remain enigmatic, constraining further understanding of the global supercontinent reconstruction. Here, an integrated petrological, geochronological, geochemical, and Sr-Nd-Hf isotopic study was undertaken on the newly discovered Tonian granitic gneisses in the Lhasa terrane. The granitic gneisses (ca. 855–844 Ma) show affinities to A-type granitoids and have positive zircon ε_Hf(t) (+3.1 to + 8.3) and whole-rock ε_Nd(t) (+4.0 to + 4.8) values. Their protoliths were probably generated by the partial melting of Mesoproterozoic crustal rocks. The U-Pb age data of detrital zircons from the biotite plagioclase gneisses associated with the granitic gneisses are also reported. The depositional age of the protoliths of the biotite plagioclase gneisses is constrained to be between the ages of the oldest intrusion body (ca. 855 Ma) and the youngest detrital zircon (ca. 917 Ma) therein, and their detrital zircon age distribution suggests a divergent tectonic setting. Integrating previous studies with the data presented in this contribution, we recommend that the northern Lhasa terrane experienced three Neoproterozoic tectonic stages: rift (ca. 930–850 Ma), subduction (ca. 850–650 Ma), and collision (ca. 650–610 Ma), which suggest an African paleogeographic affinity.