云南瑶山群新元古代变基性岩的识别及其地质意义  

Identification of Neoproterozoic Metabasic Rocks in Yaoshan Group,Yunnan Province and Its Geological Implications

作　　者：刘昊茹 蔡永丰[1,2] 赵锴 华洁文 周云 Liu Haoru;Cai Yongfeng;Zhao Kai;Hua Jiewen;Zhou Yun(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541004,China;Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi,Guilin University of Technology,Guilin 541004,China)

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [2]桂林理工大学有色金属矿产勘查与资源高效利用省部共建协同创新中心,广西桂林541004

出　　处：《地球科学》2023年第12期4495-4507,共13页Earth Science

基　　金：国家自然科学基金项目(Nos.41502180,42072259);广西隐伏金属矿产勘查重点实验室项目(No.桂科隐19-185-17-04)。

摘　　要：云南瑶山群处于扬子地块西南缘,带内零星出露一些呈透镜状、似层状或碎片状的变基性岩,目前对它们的分布特征、形成时代及其构造背景仍不明确.对采自瑶山群中的变基性岩进行了锆石U-Pb年代学和元素地球化学分析.年代学测试结果表明2个代表性变基性岩的形成年龄分别为766±3 Ma和771±4 Ma,为首次在瑶山群识别出了新元古代中期基性岩浆活动信息.元素地球化学分析结果显示,变基性岩的SiO_(2)含量为48.41%~49.00%,Fe_(2)O_(3)^(T)和MgO含量分别为10.30%~10.48%和10.05%~10.15%,具有较高的Mg指数(Mg^(#)=69.3~69.5);样品相对富集轻稀土元素(LREE),轻、重稀土元素分馏程度相对较强((La/Yb)_(N)=1.97~2.19),Eu异常不明显(δEu=0.90~0.94),Nb呈负异常,亏损Ti、P,其微量元素组成特征整体上与岛弧玄武岩的地球化学特征类似.综合分析认为该变基性岩形成于岛弧环境,表明扬子地块西南缘存在新元古代时期的洋壳俯冲作用事件,这一研究结果对约束哀牢山构造带甚至整个华南地区新元古代构造演化提供了新的资料.Numerous Neoproterozoic igneous rocks were identified along the northwestern and southeastern Yangtze block,whereas the synchronous mafic rocks have been poorly reported along the southwestern Yangtze block so far.The Yaoshan Group,located at the southwestern Yangtze block,preserves small amounts of matabasic rocks and metagabbro which occurred as lens,layers and fragments.Their formation timing,petrogenesis and dynamic implication are still unclear.In this study,it presents zircon U-Pb geochronological,geochemical and petrological data for the metabasic rocks in the Yaoshan Group.The data show that the metabasic rocks have zircon U-Pb ages of 766±3 Ma and 771±4 Ma,for the first time to identify Neoproterozoic metabasic rocks in the Yaoshan Group.Geochemical data suggest that the metabasic rocks have SiO_(2)of 48.41%-49.00%and Fe_(2)O_(3)^(T),MgO range in 10.30%-10.48%and 10.05%-10.15%,respectively.They have relative high Mg-number(69.3-69.5).They are characterized by enrichment in LREE((La/Yb)_(N)=1.97-2.19),no obvious Eu anomalies(δEu=0.90-0.94),negative Nb anomalies,and depletion in Ti-P on primitive mantle-normalized trace element diagrams.Such geochemical signatures are similar to those of arc volcanic rocks.Together with other geological observations,it is proposed that the tectonic setting of the metabasic rocks is island arc which is dynamically related to ocean subduction along the southwestern margin of the Yangtze block.These results provide new evidence to understand the Neoproterozoic tectonic evolution of the Ailaoshan tectonic belt and even the whole South China.

关 键 词：变基性岩 俯冲作用 新元古代 哀牢山构造带 瑶山群 岩石学 地球化学 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]