湘南宝山地区燕山期成矿花岗岩岩浆作用研究  

Study on Yanshanian metallogenic granitoids magmatism in Baoshan deposit, southern Hunan Province

作　　者：曹亮[1,2] 许国锋 刘磊 邵拥军[1,2] CAO Liang;XU GuoFeng;LIU Lei;SHAO YongJun(Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,Central South University,Changsha 410083,China;School of Geosciences and Info-Physics,Central South University,Changsha 410083,China)

机构地区：[1]中南大学有色金属成矿预测与地质环境监测教育部重点实验室,长沙410083 [2]中南大学地球科学与信息物理学院,长沙410083

出　　处：《岩石学报》2023年第3期886-906,I0001-I0003,共24页Acta Petrologica Sinica

基　　金：国家重点研发计划(2018YFC0603901);湖南省科技创新团队项目(2021RC4055)联合资助。

摘　　要：本文对湘南宝山花岗闪长斑岩进行了系统的锆石和磷灰石U-Pb定年、岩石地球化学以及锆石Hf同位素研究,并探讨了宝山花岗闪长斑岩的岩石成因和构造意义。锆石和磷灰石的LA-ICP-MS U-Pb定年显示,宝山花岗闪长斑岩的成岩年龄为160Ma。综合元素和同位素地球化学证据,宝山花岗闪长斑岩的成因可能为新生地壳与古老地壳的混合熔融,同时宝山花岗闪长斑岩中发现的890±20Ma的继承锆石,验证了新元古代新生地壳的参与。磷灰石的主微量元素研究显示花岗闪长斑岩具有较高的氧逸度和Cl含量,Sr/Th比值具有较大变化,而La/Sm比值变化不大等特征,表明形成花岗闪长斑岩岩浆的母岩受到俯冲板片脱水形成的流体交代作用影响。在上述过程中,富含Cl和H2O的流体从板片中释放出来,引发地幔楔熔融,并对矿床中成矿金属元素进行提取。由于古太平洋板块俯冲引发的伸展-减薄运动,在地幔上涌过程中,新元古代新生地壳发生部分熔融,这些高温岩浆底侵老地壳源区,诱发老地壳部分熔融,进而发生了强烈的壳-壳混合作用,产生花岗闪长质岩浆。In order to explore its petrogenesis and tectonic setting, an integrated study, including zircon and apatite U-Pb dating, geochemistry and zircon Hf isotope analyses, has been conducted on granodiorite porphyry in the Baoshan deposit, southern Hunan Province. The results suggested that the formation age of the granodiorite porphyry is ca.160 Ma. According to the element and isotope results, the mixed melting model of a juvenile crust and an ancient crust is proposed. Meanwhile, the 890±20 Ma inherited zircons are discovered in the granodiorite porphyry, indicating the involvement of a Neo-Proterozoic juvenile crust in its parental magma evolution. The apatite major and trace elements of the granodiorite porphyry are characterized by high oxygen fugacity and Cl contents, large change of Sr/Th ratio, but weak change of La/Sm ratio, indicating that the magma origin region of the granodiorite porphyry was influenced by the fluid metasomatism due to the subducted slab dehydration. During this process, the fluid with enriched Cl and H2O is released from the slab, which triggered mantle wedge melting and extracted of ore-forming elements in this deposit. Because of extension-thinning activities triggered by the subduction of an ancient Pacific plate, the Neoproterozoic juvenile crust partly melted during the mantle material upwelling. These high-temperature magmas intruded into the old crust and induced partial melting. A strongly crust-crust mixing model, which formed granodioritic magma, is proposed. Therefore, Baoshan granodiorite porphyry was formed in the extensional thinning tectonic environment caused by the subduction of the paleo-Pacific plate.

关 键 词：宝山矿床 花岗闪长斑岩 锆石 磷灰石 岩浆混合作用 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]