Detrital zircon constraints on late Paleozoic tectonism of the Bogda region(NW China) in the southern Central Asian Orogenic Belt

The Chinese North Tianshan（CNTS） in the southern part of the Central Asian Orogenic Belt（CAOB） has undergone multistage accretion-collision processes during Paleozoic time,which remain controversial.This study addresses this issue by tracing the provenance of Late Paleozoic sedimentary successions from the Bogda Mountain in the eastern CNTS through U-Pb dating and Lu-Hf isotopic analyses of detrital zircons.New detrital zircon U-Pb ages（N=519） from seven samples range from 261±4 Ma to 2827±32 Ma.The most prominent age peak is at 313 Ma and subordinate ages vary from 441 Ma to 601 Ma,with some Precambrian detrital zircon ages（～7%） lasting from 694 Ma to 1024 Ma.The youngest age components in each sample yielded weighted mean ages ranging from 272±9 Ma to 288±5 Ma,representing the maximum depositional ages.These and literature data indicate that some previously-assumed "Carboniferous"strata in the Bogda area were deposited in the Early Permian,including the Qijiaojing,Julideneng,Shaleisaierke,Yangbulake,Shamaershayi,Liushugou,Qijiagou,and Aoertu formations.The low maturity of the sandstones,zircon morphology and provenance analyses indicate a proximal sedimentation probably sourced from the East Junggar Arc and the Harlik-Dananhu Arc in the CNTS.The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in the Harlik-Dananhu Arc.Zircon EHf（t） values have increased since ～408 Ma,probably reflecting a tectonic transition from regional compression to extension.This event might correspond to the opening of the Bogda intraarc/back arc rift basin,possibly resulting from a slab rollback during the northward subduction of the North Tianshan Ocean.A decrease of zircon εHf（t） values at ～300 Ma was likely caused by the cessation of oceanic subduction and subsequent collision,which implies that the North Tianshan Ocean closed at the end of the Late Carboniferous.