Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (3): 154-167.DOI: 10.13745/j.esf.sf.2020.4.44

Previous Articles     Next Articles

Zircon U-Pb dating and trace element geochemistry in syenite porphyry and granite xenoliths from Liuhe, western Yunnan, China

DUAN Wenjing1(), ZHAO Fufeng1,*(), REN Kefa1, LIU Xianfan1, DENG Jianghong1, YANG Mimi1, CHU Yating2   

  1. 1. Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Ministry of Natural Resources; College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China
    2. CECEP Construction Engineering Design Institute Limited Company, Chengdu 610059, China
  • Received:2018-11-08 Revised:2019-04-06 Online:2020-05-20 Published:2020-05-20
  • Contact: ZHAO Fufeng

Abstract:

The Liuhe syenite porphyry is a typical representative of the Cenozoic alkali-rich porphyry in western Yunnan. It is famous for various xenoliths developed at different depths, including granite xenoliths of the same period. The deep geological processes represented by these xenoliths have important constraints on the formation and evolution of alkali-rich magma. In this paper, we focused on zircon trace element analyses, and combined with the studies on syenite porphyry main elements, zircon U-Pb dating, Ti thermometer and zircon oxygen fugacity of the Liuhe syenite porphyry and its granite xenoliths to explore the formation and evolution process of alkali-rich magma. The zircon U-Pb dating results suggested that the activity time of Liuhe alkali-rich magma is 37.89±0.96 to 35.87±0.58 Ma, almost synchronous with that of granite inclusions representing the same period of silicon-rich acidic magma at 38.21±0.44 to 36.21±0.36 Ma. The zircon trace element diagram showed that zircons from syenite porphyry mainly overlapped with the potassium-magnesium lamprophyre range, suggesting that alkali-rich magma source has mantle properties; whereas zircons from granite xenoliths overlapped in part with the granite range. The overlapping part confirmed a common growth environment during syenite porphyry and granite xenoliths zircon crystallization. The estimated Ce(Ⅳ)/Ce(Ⅲ) ratio and Ti temperature calculations showed that oxygen fugacity of the alkali-rich magma and zircon crystallization temperature changed greatly between 36.42 and 36.41 Ma, indicating the effect of mixing alkali-rich and entrapped granitic magma; while decreasing oxygen fugacity oscillation reflects magma supplement from a later mantle source. In summary, we speculate that the Himalayan alkali-rich magma from enriched mantle source in the Liuhe area underplates and melts the overlying felsic rocks to form granitic magma, and a small amount of which mix with alkali-rich magma to form syenite porphyry.

Key words: syenite porphyry from Liuhe, zircon U-Pb dating, trace element geochemistry, crust-mantle magma mixing, deep geological process

CLC Number: