Detrital zircon populations of the South Qiangtang terrane, central Tibetan Plateau, and their implications for Tethyan evolution

Abstract

ABSTRACT Detrital zircon populations of the South Qiangtang terrane (SQT) provide vital information for reconstructing the Tethyan evolution of the Tibetan Plateau but are obscured by the undefined affiliation of detrital zircon samples and the superimposition of multiple Tethyan tectonothermal events. We outlined the SQT based on geological mapping and collated Cambrian-Triassic detrital zircon samples to investigate representative detrital zircon populations. Although diachronous strata have distinctive detrital zircon age distributions, the Cambrian-Permian strata record similar ca. 2.50 Ga, 950 Ma, 800 Ma, and 550 Ma populations, which can be used in future detrital zircon studies as Palaeozoic indicators for the SQT. We analyse the above detrital zircon data and compare them to those from adjacent microcontinents (e.g. North Qiangtang terrane, NQT). We note that (1) the Cambrian-Late Ordovician detrital zircons from Upper Triassic strata yield positive εHf(t) values, suggesting juvenile arc-related magmatism in the NQT, and (2) the late Palaeozoic strata in the SQT and NQT both contain Late Devonian-early Carboniferous detrital zircons but have different detrital zircon populations. Together with previous studies on Tethyan evolution, we support that the southward subduction of the Proto-Tethys oceanic plate opened two diachronous back-arc basins between the NQT and SQT during the late Cambrian-Ordovician and Late Devonian-early Carboniferous. The former closed during the late Silurian; the latter evolved into the Palaeo-Tethys Ocean. Subsequently, the northward subduction of the Palaeo-Tethys oceanic plate produced early-middle Permian arc magmatism in the NQT, and the slab pull force from the subducting oceanic plate caused middle-late Permian intraplate magmatism on the opposite passive margin.