滇西首例火成碳酸岩的发现与厘定  

Discovery and determination of the first igneous carbonatite in western Yunnan Province,SW China

作　　者：高雅俊 宋文磊 周家喜 雷碧东 杨金昆 许丹妮 罗开 GAO YaJun;SONG WenLei;ZHOU JiaXi;LEI BiDong;YANG JinKun;XU DanNi;LUO Kai(Key Laboratory of Critical Minerals Metallogeny in Universities of Yunnan Province,School of Earth Sciences,Yunnan University,Kunming 650500,China;Key Laboratory of Sanjiang Metallogeny and Resources Exploration&Utilization,MNR,Yunnan University,Kunming 650500,China;State Key laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China;Exploration Branch of Yunnan Gold&Mineral Group Co.,Ltd,Kunming 650299,China)

机构地区：[1]云南大学地球科学学院,云南省高校关键矿产成矿学重点实验室,昆明650500 [2]云南大学,自然资源部三江成矿作用及资源勘查利用重点实验室,昆明650500 [3]西北大学地质学系,大陆动力学国家重点实验室,西安710069 [4]云南黄金矿业集团股份有限公司勘查分公司,昆明650299

出　　处：《岩石学报》2024年第9期2638-2652,共15页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42273070);云南省新一轮找矿突破战略行动暨地勘基金项目(Y202403);云南省科技厅重点项目(202401AS070127);云南省教育厅科学研究基金项目(2023Y0187);关键金属成矿与找矿预测硕士生导师团队项目(2023-15)联合资助。

摘　　要：火成碳酸岩(又称碳酸岩)是由地幔派生的富碳酸盐矿物且贫硅的火成岩石,地表出露较少。碳酸岩是研究地幔性质及其演化过程的岩石“探针”,并且蕴藏着丰富的稀土和铌等关键金属矿产资源。因此,对它的研究具有重要的科学和经济价值。本次工作首次在云南保山龙陵地区发现火成碳酸岩岩体,规模较大,岩体出露面积约为60000m 2。出露于保山地块与腾冲地块之间的龙陵-潞西褶皱带内。新发现的碳酸岩主要由方解石和白云石等矿物组成,其次还含有大量的磷灰石、磁铁矿、黑云母、辉石、独居石和斜锆石等副矿物。结合岩相学、矿物学和全岩地球化学组成,可将新发现的碳酸岩划分为钙质、镁质和含铁钙质三类。不同岩性的CaO(29.57%~51.66%)、Fe_(2)O^(T)_(3)(0.72%~21.15%)和MgO(1.76%~16.90%)含量变化大。微量元素特征显示,碳酸岩总体富集Sr(3431×10^(-6)~9753×10^(-6))、Ba(197×10^(-6)~2428×10^(-6))、Pb(14.4×10^(-6)~425×10^(-6))和∑REE(841×10^(-6)~2341×10^(-6))等大离子亲石元素,相对亏损Nb(1.09×10^(-6)~12.48×10^(-6))、Ta(0.12×10^(-6)~4.74×10^(-6))和Hf(0.07×10^(-6)~7.85×10^(-6))等高场强元素。稀土配分模式为右倾型,(La/Yb)N比值介于58~104之间,富集LREE,具有弱铕负异常(δEu=0.68~0.74)。碳酸岩中主要造岩矿物方解石、白云石和磷灰石也表现出与全岩相似的元素地球化学特征。碳酸盐矿物的δ^(13)C V-PDB值(-7.45‰~-3.54‰)大多落入“初始火成碳酸岩”范围,但δ^(18)O V-SMOW值(10.79‰~20.06‰)偏高,很可能源于岩浆期后热液蚀变。上述全岩、矿物化学和C-O同位素特征与全球大多数碳酸岩基本一致,证实坡头岩体为典型的火成碳酸岩。钙质碳酸岩中斜锆石的LA-ICPMS测年结果显示,其U-Pb等时线谐和年龄为160.7±2.0Ma(MSWD=1.8),^(206)Pb/^(238)U加权平均年龄为159.7±1.8Ma(MSWD=2.4),表明其形成于中侏罗世,为三叠纪碰撞造山作用后�Igneous carbonatite(also known as carbonatite)is a mantle-derived,carbonate-rich,and silica-poor igneous rock rarely exposed on the surface.Carbonatite serves as a“probe”rock for studying mantle properties and evolution,and it hosts abundant critical metal mineral resources such as rare earth elements(REEs)and niobium.Therefore,the research on it has important scientific and economic value.In this study,a large-scale carbonatite rock mass was discovered for the first time in the Baoshan area of Yunnan.The exposed area of rock mass is about 60000m 2,exposed within the Longling-Luxi fold belt between the Baoshan block and the Tengchong block.These carbonatites are primarily composed of carbonate minerals such as calcite and dolomite,and they also contain significant amounts of apatite,magnetite,biotite,pyroxene,monazite,and baddeleyite.Based on petrography,mineralogy,and whole-rock chemical composition,carbonatite can be classified into calciocarbonatite,magnesiocarbonatite,and ferruginous calciocarbonatite.The different lithologies show significant variations in CaO(29.57%~51.66%),Fe_(2)O^(T)_(3)(0.72%~21.15%),and MgO(1.76%~16.90%).Trace element characteristics reveal that the carbonatites are generally enriched in large-ion lithophile elements(LILEs)such as Sr(3431×10^(-6)~9753×10^(-6)),Ba(197×10^(-6)~2428×10^(-6)),Pb(14.4×10^(-6)~425×10^(-6)),and∑REE(841×10^(-6)~2341×10^(-6)).Still,they are relatively depleted in high field strength elements(HFSEs)like Nb(1.09×10^(-6)~12.48×10^(-6)),Ta(0.12×10^(-6)~4.74×10^(-6))and Hf(0.07×10^(-6)~7.85×10^(-6)).The REE distribution pattern is right-leaning,with(La/Yb)N ratios ranging from 58 to 104,showing enrichment in light rare earth elements(LREEs)and a weak negative Eu anomaly(δEu=0.68~0.74).The major rock-forming minerals in the carbonatites,such as calcite,dolomite,and apatite,also exhibit geochemical characteristics similar to those of the whole rock.Theδ^(13)C V-PDB values of the carbonatite minerals(-7.45‰to-3.54‰)mostly fall within the range

关 键 词：坡头 碳酸岩 全岩地球化学 C-O同位素 斜锆石U-Pb年龄 云南保山 

分 类 号：P588.15[天文地球—岩石学]