Revisit to time and tectonic environment of the Aksu blueschist terrane in Northern Tarim, NW China: New evidence from zircon U-Pb age and Hf isotope

Abstract

It is of significant importance to understand the Precambrian tectonic evolution and reconstruction of the Neoproterozoic supercontinent of Tarim block in northwestern China by the study of the timing and tectonic background of the Aksu blueschist and the mafic dyke swarms intruding it. In this study, we carry out U-Pb dating and Hf isotope analysis on zircons from both the meta-clastic rocks of the Aksu blueschist and the mafic dyke swarms. There are two significant age peaks in the U-Pb age spectra of the detrital zircons from the schist, i. e. , the older zircon group concentrates at ∼1.9Ga, with minor Archaean component; another group peaking at ∼820Ma and representing the oldest deposit time of the Aksu blueschist. The mafic dyke swarms intruding the Aksu blueschist yields a zircon U-Pb age of ∼760Ma. Hence, the time of the Aksu blueschist facies metamorphism can be quite precisely defined in the range of 820 ∼ 760Ma. The peaks of the detrital zircon Hf crust-model age spectra appears at 2.2 ∼ 2.3Ga, 2.6Ga and 3.2 ∼ 3.3Ga respectively, implying that Aksu blueschist terrane may be continental margin magmatic arc developed on the Early Precambrian Tarim basement.