Zircon U-Pb ages, geochemistry and geologi-cal significance of gneissic granodiorite in northern Lenghu, Qinghai Province

GU Pingyang; ZHA Xianfeng; CHEN Ruiming; DONG Zengchan; ZHUANG Yujun; ZHA Fangyong; HU Chaobin; LI Peiqing

2017 Vol. 36, No. 9

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GU Pingyang, ZHA Xianfeng, CHEN Ruiming, DONG Zengchan, ZHUANG Yujun, ZHA Fangyong, HU Chaobin, LI Peiqing. Zircon U-Pb ages, geochemistry and geologi-cal significance of gneissic granodiorite in northern Lenghu, Qinghai Province[J]. Geological Bulletin of China, 2017, 36(9): 1542-1552.

Citation:

GU Pingyang, ZHA Xianfeng, CHEN Ruiming, DONG Zengchan, ZHUANG Yujun, ZHA Fangyong, HU Chaobin, LI Peiqing. Zircon U-Pb ages, geochemistry and geologi-cal significance of gneissic granodiorite in northern Lenghu, Qinghai Province[J]. Geological Bulletin of China, 2017, 36(9): 1542-1552.

Zircon U-Pb ages, geochemistry and geologi-cal significance of gneissic granodiorite in northern Lenghu, Qinghai Province

1.
Key Laboratory of Western China's Mineral Resources and Geological Engineering, Ministry of Education, Earth Science & Resources College of Chang'an University, Xi'an 710054, Shaanxi, China
2.
Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Xi'an Geological Survey Center, Xi'an 710054, Shaanxi, China

Received Date: 09 December 2015

Revised Date: 18 March 2017

Publish Date: 25 September 2017

Abstract

Abstract

The gneissic granodiorite in northern Lenghu of Qinghai Province is characterized by low SiO₂ and MgO, and high Al₂O₃, Na₂O and CaO, with alumina saturation index A/CNK of 0.92~0.797. These features suggest that this gneissic granodiorite belongs to the high-K calci-alkaline peraluminous rocks and metaluminous rocks. The chondrite-normalized REE values show right-in-clined patterns with slightly negative Eu anomaly. The primitive mantle normalized trace element spidergrams are characterized by en-riched LILE(such as Rb, Th and U) and depleted HFSE(such as Nb, Ta and Zr), which is comparable with the characteristics of oro-genic magmatic rocks, suggesting a volcanic arc tectonic setting associated with subduction. Moreover, the gneissic granodiorite is characterized by rich Na₂O and A1₂O₃, high Sr, Sr/Yb and LREE, and inconspicuous differentiation of HREE. These features imply that the rocks in northern Lenghu of Qinghai were probably formed by the melting of basaltic rocks with amphibole as a residua phase. With the U-Pb isotopic age of 470.2±1.2Ma(n=19, MSWD=0.68) of granodiorite, the authors believe that north Al-tun oceanic crust subducted toward Oulongbuluke block in Early Ordovician.
- gneissic granodiorite /
- LA-ICP-MS zircon U-Pb dating /
- substance records /
- geochemistry

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