东秦岭黄水庵钼矿床的碳酸岩成因与地质意义:来自痕量元素和Sr-Nd-Pb同位素的约束  

Genesis and geological significance of the carbonatite in the Huangshui an Mo deposit in Eastern Qinling area of China:Constraints from trace elements and Sr-Nd-Pb isotopes

作　　者：付鑫宁 唐利[1] 姚梅青 胡昕凯 赵玉[1] FU Xinning;TANG Li;YAO Meiqing;HU Xinkai;ZHAO Yu(School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083

出　　处：《成都理工大学学报（自然科学版）》2021年第5期525-538,共14页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家重点研发计划项目(2016YFC0600504);大学生创新创业训练计划项目(S201911415003);拔尖青年教师创新能力培养项目(2652019047)。

摘　　要：通过痕量元素和Sr-Nd-Pb同位素研究,探讨东秦岭黄水庵碳酸岩的岩浆源区、岩石成因和构造背景,对三叠纪时期秦岭造山带的构造演化和钼多金属成矿作用研究提供指示。黄水庵钼矿床位于东秦岭钼矿带内,是一种独特的碳酸岩脉型钼矿床,辉钼矿主要呈放射状集合体和细脉状产于碳酸岩脉中。黄水庵碳酸岩主要由淡粉红色方解石(>70%)和石英(<15%)组成。痕量元素方面显示碳酸岩具有富集轻稀土元素和大离子亲石元素、亏损高场强元素的特征。Sr-Nd-Pb同位素表明碳酸岩具有相对较高的(87 Sr/86 Sr)i值(0.7061~0.7065)和偏低的εNd(t)值(-16.4~-14.7),Nd同位素的两阶段模式年龄为2183~2322 Ma,岩浆源区与金属成矿物质来源均表现为富集地幔EMI与下地壳的混合特征。综合年代学和Sr-Nd-Pb-Hf同位素研究结果,认为黄水庵碳酸岩脉(209.5~207 Ma B.P.)形成于秦岭造山带后碰撞阶段,由于地壳增厚,富含钼等金属的下地壳发生拆沉作用并与EMI地幔端元混合,在低程度部分熔融的情况下形成富含Mo、Pb、S和REE的硅酸盐-碳酸岩熔体,经不混溶作用和结晶分异形成黄水庵碳酸岩。Through the study of trace elements and Sr-Nd-Pb isotopes,the magmatic origin,petrogenesis and tectonic background of Huangshui an carbonatite rock in the Eastern Qinling Mountains are studied so as to provide an indication for the study of tectonic evolution and molybdenum polymetallic mineralization of the Qinling orogenic belt in the Triassic period.Huangshui an molybdenum deposit in east Qinling molybdenum belt is a unique carbonatite dike type molybdenum deposit,and molybdenite mainly occurs in carbonatite dike by radiating aggregate and veinlets.The Huangshui an carbonatite rock is mainly composed of pale pink calcite(>70%)and quartz(<15%).Geochemical analysis shows that the carbonatite is rich in LREE and large ion lithophile elements,and deplete of high field strength elements.Sr-Nd-Pb isotopic data display high(87 Sr/86 Sr)i values(0.706144~0.706512)and lowεNd(t)values(-16.43~-14.71),with two-stage Nd model ages of 2322~2183 Ma,suggesting that the sources of magma and metals are characterized by the mixture of EMI and lower crust end members.Based on available data of geochronology and Sr-Nd-Pb-Hf isotopes,it is proposed that the Huangshui an carbonatite(209.5~207 Ma B.P.)was formed in the post-collision stage of Qinling orogenic belt.The metal-enriched lower crust(molybdenum and other metals)is delaminated and mixed with the end member of EMI due to the crust thickening.Silicate-carbonate melts rich in Mo,Pb,S and REE are formed under the condition of low degree partial melting,and Huangshui an carbonatite rocks are formed through immiscible and crystallization differentiation.

关 键 词：碳酸岩 痕量元素 SR-ND-PB同位素 黄水庵 东秦岭 

分 类 号：P618.63[天文地球—矿床学] P588.15[天文地球—地质学]