Detrital Zircon U-Pb Geochronology from Greywackes in the Niujuanzi Ophiolitic Mélange, Beishan Area, NW China: Provenance and Tectonic Implications  

作　　者：Shengdong Wang Kexin Zhang Bowen Song Shucai Li Jianxing Li Jiyuan Yu Jianjun Bu 

机构地区：[1]Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China [2]Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China [3]State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China [4]Cores and Samples Center of Land and Resources, China Geological Survey, Langfang 065201, China [5]Xi'an Center of Geological Survey, Geological Survey of China, Xi'an 710000, China [6]Wuhan Center of Geological Survey, Geological Survey of China, Wuhan 430205, China

出　　处：《Journal of Earth Science》2018年第1期103-113,共11页地球科学学刊（英文版）

基　　金：funded by the Key Research and Development Project of the Ministry of Science and Technology (No.2016YFC0601005);the Chinese Geological Survey (Nos. 121201004000150013, 121201102000150012);the National Natural Science Foundation of China (Nos. 41472004, 41772107)

摘　　要：The Niujuanzi ophiolitic m^lange represents the remnant of oceanic crust between the Dunhuang massif and Mingshui-Hanshan massif. Greywacke from different tectonic slices in the Niu- juanzi ophiolitic mdlange were analyzed for detrital zircon U-Pb geochronology, trace dements and whole-rock trace elements to infer their provenance and the evolution of the Niujuanzi Ocean. Sample N-76s containing Carboniferous spores has the youngest zircon age of 323 Ma, while sample N-85s without fossils has the youngest zircon age of 449 Ma. The two samples were deposited no earlier than 323 and 449 Ma, respectively. The greywackes are depleted in large ion lithophile elements, and are relatively enriched in high field strength elements. The age spectra and trace element concentrations indicate that the sediments may have been deposited near the trench. The Hf, U, and Yb contents of zircons from sample N-76s vary widely, whereas those from sample N-85s have a narrow range. Sample N-76s contains both continental and oceanic zircons, while sample N-85s contains only continental zir-cons. The sediments were derived from the continental arc and accretionary wedge. The Paleozoic oce- anic crust zircons have ages of 430-500 Ma, indicating the timing of the expansion of the Hongliuhe- Niujuanzi-Xichangjing Ocean expansion. The oldest Paleozoic continental zircon has an age of 470 Ma, suggesting that the northward subduction of the oceanic crust may have started at that time.The Niujuanzi ophiolitic m^lange represents the remnant of oceanic crust between the Dunhuang massif and Mingshui-Hanshan massif. Greywacke from different tectonic slices in the Niu- juanzi ophiolitic mdlange were analyzed for detrital zircon U-Pb geochronology, trace dements and whole-rock trace elements to infer their provenance and the evolution of the Niujuanzi Ocean. Sample N-76s containing Carboniferous spores has the youngest zircon age of 323 Ma, while sample N-85s without fossils has the youngest zircon age of 449 Ma. The two samples were deposited no earlier than 323 and 449 Ma, respectively. The greywackes are depleted in large ion lithophile elements, and are relatively enriched in high field strength elements. The age spectra and trace element concentrations indicate that the sediments may have been deposited near the trench. The Hf, U, and Yb contents of zircons from sample N-76s vary widely, whereas those from sample N-85s have a narrow range. Sample N-76s contains both continental and oceanic zircons, while sample N-85s contains only continental zir-cons. The sediments were derived from the continental arc and accretionary wedge. The Paleozoic oce- anic crust zircons have ages of 430-500 Ma, indicating the timing of the expansion of the Hongliuhe- Niujuanzi-Xichangjing Ocean expansion. The oldest Paleozoic continental zircon has an age of 470 Ma, suggesting that the northward subduction of the oceanic crust may have started at that time.

关 键 词：detrital zircon U-Pb geochronology Niujuanzi ophiolitic melange Beishan. 

分 类 号：P2[天文地球—测绘科学与技术]