The Central Asia orogenic belt contains a wide range of structural elements, including micro continent, back arc system, ocean island/plateau, ophiolite and subduction accretion complex. But its final closing time has been controversial. Based on the magmatic age of the surrounding orogenic belt, the source of this set of clastic sediments is determined, which provides new important evidence for the evolution of the South Tianshan orogenic belt. The results show that the Jurassic detrital zircons from the study area were mainly derived from magmatic zircons and are deposited in a proximal source. The detrital zircon age of the Lower Jurassic Badaowan and Sangonghe Formation are concentrated in 290–260 Ma, and in 350–290 Ma and 460–390 Ma, respectively. The detrital zircon age of the Middle Jurassic Xishanyao Formation concentrates in 370–320 Ma and 450–390 Ma. There are very few zircons from the Precambrian period. These ages are consistent with the timing, indicating these clastic sediments were mainly originated from the southern margin of the Yili - Middle Tianshan Block. The Late Permian - Middle Triassic detrital zircons almost do not exist, implying that there were no contemporary magmatism related to collision or post-collision in the South Tianshan district, its complex evolution and orogenic stage are still a challenging topic. In the ancient active plate margin, the sedimentary records in the pre-arc basin can provide more information about the magmatic arc and basin-orogen coupling than the present exposed arc itself. The rhyolite, trachyte, and trachyandesite of the Dahalajunshan Formation were widely developed in the Yili - Middle Tianshan Block during the Early Carboniferous. During the formation of Wulang Formation in the Early Permian, a large number of rhyolite were developed. The age data of 75 detrital zircons were obtained from the sandstone (J1s-5) of the Sangonghe Formation, of which 74 zircons have a concordance degree of over 90%, and their age data also fall on the harmonic curv. In addition, the age of the youngest zircons increased gradually from Early to Middle Jurassic, indicating that the sediments in this period had the feature of uncovering. Our study provides a good reference for the analysis of provenance and regional tectonic evolution.
Detrital zircon age and Hf isotopic studies for metasedimentary rocks from the Chinese Altai: Implications for the Early Paleozoic tectonic evolution of the Central Asian Orogenic Belt
