福建紫金山矿集区浸铜湖花岗斑岩的成因及构造意义

Petrogenesis and Tectonic Implications of the Jintonghu Granitic Porphyry in Zijinshan Orefield,Fujian Province

华南中生代花岗岩成因研究对指示华南岩石圈演化机制具有重要意义,也是成岩成矿作用研究的重要内容。利用原位LA-ICP-MS锆石U-Pb年代学、微量元素及Hf同位素组成分析,对紫金山矿田内浸铜湖铜钼矿床发育的花岗斑岩开展研究,获得其成岩年龄为(101.1±1.9)Ma,属早白垩世。浸铜湖花岗斑岩锆石Hf同位素εHf(t=101 Ma)为-6.1~0.7,两阶段Hf模式年龄(TDM2)为1.09~1.51 Ga,不支持其形成于华夏陆壳基底物质或壳源(变质)沉积岩的直接熔融。锆石Ce4+/Ce3+值指示岩浆氧逸度较低,表明其成因类似于华南分异的I型花岗岩,主要源于火成岩的部分熔融作用,可能有少量地幔物质的加入。华南晚中生代古太平洋板块受俯冲作用影响,发育大规模岩浆活动,其构造背景为活动大陆边缘环境。

Genesis of Mesozoic granites in South China is important for studying the evolution of the lithosphere,as well as the regional granite petrogenesis and related mineralization.In this contribution,in-situ LA-ICP-MS U-Pb,trace element and Hf isotope analyses of zircon were conducted to constrain the emplacement age and petrogenesis of the granitic porphyry at the Jintonghu Cu-Mo deposit,western Fujian,China.The Jintonghu granitic porphyry is U-Pb dated to be Early Cretaceous(101.1±1.9 Ma).The zirconεHf(t)values(-6.1 to0.7)and the two-stage Hf model ages(1.09 to 1.51 Ga)preclude the possiblilty that the parental magmas of the Jintonghu granitic porphyry was dominantly sourced from the basement materials or metasedimentary rocks.The low zircon Ce4+/Ce3+ratios suggest that the Jintonghu granitic porphyry mimics fractionated I-type granites in the Nanling Range,and the magmas were likely derived from older felsic igneous domains with little juvenile material contributions.Interpretations of the elemental and isotopic data suggests that the Jintonghu granite was most likely derived from partial melting of old deep-seated magmatic rocks due to the subduction of Paleo-Pacific Plate in an active continental marginal setting.