Crustal evolution in the South Tianshan Terrane: Constraints from detrital zircon geochronology and implications for continental growth in the Central Asian Orogenic Belt

The South Tianshan Terrane (STT) is located in the boundary between the south-western Central Asian Orogenic Belt (CAOB) and the Tarim Craton and is a key area for understanding the geologic and tectonic history of the craton and the orogenic belt. In this paper, we report detrital zircon ages from the Late Palaeozoic and Mesozoic clastic sedimentary rocks from the southern part of STT. In combination with the U-Pb ages for felsic igneous and meta-igneous rocks exposed in the STT and adjacent tectonic units, we identify several distinct age populations. Provenance analysis suggests that the detrital zircon grains were predominately derived from the felsic magmatic rocks in the Tarim Craton and South Tianshan Terrane. The pre-Neoproterozoic age populations may be associated with the early history of the Tarim Craton. Several pulses of Neoproterozoic magmatism are revealed by our dataset, presumably related to the assembly and break-up of the supercontinent Rodinia. The 995 to 901Ma detrital zircon grains were likely sourced from magmatic rocks associated with the assembly of Neoproterozoic Tarim to Australia. Among the age population of 886 to 752Ma, the older group might be related to the subduction-related magmatism after the assembly of Rodinia, and the younger one records a protracted magmatic event in a continental rift-related setting associated with the break-up of Rodinia. Two younger Neoproterozoic age populations (736 to 694Ma and 665 to 610Ma), showing narrow spreads with weak peaks, represent the waning stages of igneous activities related to the break-up of Rodinia. Regarding the Palaeozoic evolution, together with other evidence, our data indicate a two-stage subduction model for the SW Palaeo-Asian Ocean. The 490 to 384Ma age population corroborates the existence of Early Palaeozoic continental arc magmatism at the northern margin of Palaeozoic Tarim generated by the bidirectional subduction of the South Tianshan Ocean. After a similar to 30My period of tectonomagmatic quiescence, the second stage is marked by the northward subduction of the South Tianshan Terrane during Late Devonian to Early Carboniferous. The final collision of Tarim and the south-western CAOB likely occurred during the Late Carboniferous, followed by syn- and post-collisional magmatism, as represented by the 320 to 265Ma age population. Based on the detrital zircon ages in conjunction with the Hf isotopic features of zircons from Palaeozoic igneous rocks, our study does not support the model of large-scale Phanerozoic net continental growth in the South Tianshan Terrane.