福建漳州角美花岗岩与闪长质包体的岩石成因及意义

Petrogenesis and implications of granites and associated dioritic enclaves in Jiaomei area,Zhangzhou,Fujian Province

本文选择福建沿海漳州地区的角美花岗岩和包体进行了锆石U—Pb年代学和Hf同位素地球化学研究。结果表明，黑云母花岗闪长岩（106．4±1．8Ma）和岩体中的闪长质包体（105．6±1．0Ma和106．5±1．0Ma）具有相同的锆石U—Pb年龄，为同期岩浆作用的产物，它们都是高钾钙碱性系列偏铝质岩石。花岗闪长岩具有相对较为均一的锆石Hf同位素组成（εHf（t）：2．2～3．7），表明其为新生地壳部分熔融的产物。闪长质包体具有更亏损的锆石Hf组成（εHf（t）=0．9～5．5）。地球化学数据结合野外证据表明岩体形成过程中经历了岩浆混合作用。福建沿海地区96～106Ma岩浆作用的发育处于古太平洋板片俯冲造成的伸展背景。

Zircon U-Pb ages and Hf isotopes of the host biotite granodiorite （ 106.4 ±1.8Ma） and associated dioritic enclaves （105. 6±1.0Ma and 106.5 ±1.0Ma） of the Jiaomei pluton from Zhangzhou, Fujiang Province, indicate that they are coeval magmatism. They are both high-K calc-alkaline metaluminous rocks, with similar major and trace element compositions. The granodiorite has relatively homogeneous zircon Hf isotopes （ εHf （t） = 2. 2 - 3.7 ）, suggesting their origin of partial melting of the juvenile crust. The dioritic enclaves show varied and high Hf isotopic compositions with εHf（t） ranging from 0. 9 to 5. 5, implies tbat they were resulting from magma mixing between lithospheric mantle-derived basaltic and crust-derived magmas. The age and nature of the 106Ma to 96Ma magmatism from Jiaomei area, along with other literature results, revealed that the rocks generated in an extensional tectonic setting, which may have resulted from the Cretaceous subduetion of the Paleo-Pacific Plate beneath the Fujian coastal area of southwestern China.