Detrital zircon ages and Hf isotopic compositions of metasedimentary rocks in the Wuqia area of Southwest Tianshan, NW China: implications for the early Paleozoic tectonic evolution of the Tianshan orogenic belt

ABSTRACT

The Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of −22.0 to +11.3 and two-stage model ages (TDM₂) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (−15.0 to −0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.

KEYWORDS:

• Detrital zircon age
• Lu–Hf isotope composition
• material source
• metasedimentary rocks
• Chinese southwestern Tianshan

Acknowledgments

We thank X.H. Wang, Y. Sun, J.L. Li, J. Ma, B. Yang, T. Zhang, and Z.L. Ding for assistance during fieldwork. We are grateful for the laboratory assistance provided by Y.W. Tang and Z.H. Dai at the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry Chinese Academy of Sciences, Guiyang, China. Authors give our sincerest thanks to three anonymous reviewers for their critical and detailed reviews and enlightening suggestions that improved the manuscript greatly.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Material

Supplemenatal data for this article can be accessed here.

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China (U1403292, 41472196, and 41502085); the National Key Technology Research and Development Program of the Ministry of Science and Technology of China [2015BAB05B04, 2018YFC0604005] and the China Geological Survey basic research fund for commonwealth research institution of state goverment (JYYWF20183702, JYYWF20180602)