Detrital Zircon U-Pb Geochronology from Greywackes in the Niujuanzi Ophiolitic Mélange, Beishan Area, NW China: Provenance and Tectonic Implications
Shengdong Wang, Kexin Zhang, Bowen Song, Shucai Li, Jianxing Li, Jiyuan Yu, Jianjun Bu
Journal of Earth Science ›› 2018, Vol. 29 ›› Issue (1) : 103-113.
Detrital Zircon U-Pb Geochronology from Greywackes in the Niujuanzi Ophiolitic Mélange, Beishan Area, NW China: Provenance and Tectonic Implications
The Niujuanzi ophiolitic mélange represents the remnant of oceanic crust between the Dunhuang massif and Mingshui-Hanshan massif. Greywacke from different tectonic slices in the Niujuanzi ophiolitic mélange were analyzed for detrital zircon U-Pb geochronology, trace elements 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 zircons. The sediments were derived from the continental arc and accretionary wedge. The Paleozoic oceanic 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.
detrital zircon / U-Pb geochronology / Niujuanzi ophiolitic mélange / Beishan
|
|
|
|
|
|
|
|
|
|
|
|
Gausu Geological Survey Geological Map of Mazongshan Sheet, People’s Republic of China (1: 250 000) (Unpublished), 2001.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
/
〈 |
|
〉 |