柴北缘茶卡北山伟晶岩型锂铍矿变质围岩时代及原岩特征OA北大核心CSTPCD
Age and protolith characteristics of metamorphic surrounding rock of Chakabeishan pegmatitic lithium-beryllium ore in the northern margin of Qaidam
茶卡北山锂铍矿床位于青海南山西部,区域构造上处于宗务隆山陆缘裂谷带东段.矿体赋存于花岗伟晶岩脉中,围岩为低角闪岩-高绿片岩相变质岩组合,该套变质岩作为锂铍矿体围岩,对于探讨柴北缘锂铍矿成矿规律及成矿预测具有重要意义.依据岩石组合,将其单独厘定为茶卡北山片岩岩组,通过对片岩开展锆石阴极发光图像特征研究和锆石U-Pb(LA-ICP-MS)测年,限定形成时代为南华纪—奥陶纪,为宗务隆山陆缘裂谷带新发现的新元古代—早古生代地层.锆石Hf同位素分析结果显示,εHf(t)值分布范围在-19.62～-3.07 之间,表明源区岩石源自古元古代—新太古代上地壳物质的部分熔融.片岩SiO2 含量介于 61.33%～70.57%之间,FeO含量为 3.58%～5.13%,TFe2O3 含量为 5.2%～7.95%,MgO含量为 1.89%～4.95%.球粒陨石稀土元素配分曲线表现为右倾,重稀土元素曲线趋于平缓,具有弱Eu亏损和轻稀土元素富集特征.微量元素富集Th、U、Nd、Zr、Hf、Nb、Ti等高场强元素,亏损Ba、Sr等亲石元素.综合岩石年龄和地球化学特征,认为茶卡北山片岩形成于新元古代—早古生代弧后盆地环境,原岩遭受弱风化剥蚀作用,化学组分稳定,确定为泥质砂岩,物质主要来源于岛弧环境的长英质火成岩,构造环境为大陆岛弧,与矿区含锂铍矿伟晶岩脉源区一致.
The Chakabeishan lithium beryllium deposit is located in the west of Nanshan,Qinghai Province.The region is tectonically located in the eastern segment of the Zongwulong Mountain continental margin rift belt.The orebody occurs in the granite pegmatite dike,and the surrounding rock is metamorphic rock assemblage of low amphibole-high green schist facies.The study value of this set of metamorphic rocks as the surrounding rock of lithium beryllium ore body is of great significance for discussing the regularity and prediction of lithium beryllium mineralization in the northern margin of Qaidam.Based on the rock assemblages,the schist formation was identified as the Chakabeishan Schist Formation.Based on zircon cathodoluminescence image characteristics and zircon U-Pb(LA-ICP-MS)dating tests,the formation age was determined to be Nanhuaian—Ordovician.Zircon Hf isotope analysis shows that the εHf(t)values range from-19.62 to-3.07,indicating that the rocks in the source area were partially melted from paleoproterozoic to Neoarchean upper crust.The contents of SiO2,FeO,TFe2O3,and MgO in schist Formation are 61.33%～70.57%,3.58%～5.13%,5.2%～7.95%and 1.89%～4.95%respectively.The REE partition curve of chondrites is right-leaning,and the REE curve tends to be flat,with weak europium deficit and light REE enrichment characteristics.High field strength elements such as Th,U,Nd,Zr,Hf,Nb and Ti are enriched in trace elements,while lithophilic elements such as Ba and Sr are depleted.Based on the chronology and geochemistry,the author believes that the Chakabeishan schist was formed in the Neoproterozoic and Early Paleozoic back-arc basin environment.The protolith suffered from weak weathering and denudation,and the chemical composition is stable.It is determined to be argillaceous sandstone,whose material is mainly derived from felsic igneous rocks in the island arc environment.The tectonic setting is a continental island arc,which is consistent with the source area of pegmatite dikes containing lithium beryllium ore.
郑英;李五福;张小永;韩杰;靳旭亮;缑明亮
青海省地质调查院,青海西宁 810012||青海省青藏高原北部地质过程与矿产资源重点实验室,青海西宁 810012
地质学
茶卡北山片岩碎屑锆石锆石U-Pb定年南华纪—奥陶纪构造环境
Chakabeishanschistdetrital zirconzircon U-Pb datingNanhuaian—Ordovician periodtectonic environment
《地质通报》 2024 (007)
1104-1119 / 16
青海省地质调查局项目《青海省天峻县贡卡休玛地区1∶2.5万区域地质矿产调查项目》(编号:2019048021jc013)和中国科学院广州地球化学研究所项目(第二次青藏高原综合科学考察研究项目)(编号:2019QZKK0702)
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