赣杭铀成矿带马荃盆地安山岩年龄、地球化学特征及岩石成因  

Age,geochemical characteristics and petrogenesis of andesites in Maquan basin,Ganhang uranium metallogenic belt

作　　者：祝东 刘帅[1,2] 巫建华[2] 杨东光 黄美化[1,2] 马树松 ZHU Dong;LIU Shuai;WU Jianhua;YANG Dongguang;HUANG Meihua;MA Shusong(College of Earth Science,East China Institute of Technology,Nanchang 330013,Jiangxi,China;State Key Laboratory Breeding Base of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,Jiangxi,China;No.243 Geological Party,China National Nuclear Corporation,Chifeng 024000,Inner Mongolia,China)

机构地区：[1]东华理工大学地球科学学院,江西南昌330013 [2]东华理工大学核资源与环境国家重点实验室,江西南昌330013 [3]核工业二四三大队,内蒙古赤峰024000

出　　处：《地质通报》2023年第5期828-845,共18页Geological Bulletin of China

基　　金：国家自然科学基金项目《赣南-粤北相邻区河口-南迳加里东期火山岩研究与铀成矿关系》(批准号:41662006)和《相山铀矿田深部地质环境三维建模与多元地学信息融合分析研究》(批准号:41862013)

摘　　要：赣杭铀成矿带位于扬子板块和华夏板块拼接部位,马荃盆地是该带中段的一个产铀火山盆地,铀矿体赋存在安山岩中。但其岩石类型、岩石系列归属存在一定争议,且缺少较精确的岩石年龄。以马荃盆地内中性火山岩为研究对象,对其进行了年代学、岩石学、地球化学特征研究。研究表明,火山岩SHRIMP锆石U-Pb年龄为137.1±1.1 Ma(n=15,MSWD=1.5),为早白垩世早期岩浆活动的产物。马荃盆地中性火山岩呈块状构造,斑状结构,以斜长石斑晶为主,并发育少量辉石、角闪石、黑云母斑晶,具有富碱、高钾、低铁、贫钛特征,以及富集轻稀土元素和大离子亲石元素(Rb、Ba、K),亏损高场强元素(Nb、Ta、Ti)等地球化学特征,应为安山岩,属于典型高钾钙碱性系列火山岩。安山岩(^(87)Sr/^(86)Sr)_(i)=0.70855~0.70882,εNd(t)=-9.77~-7.02,(^(206)Pb/^(204)Pb)_(i)=18.17~18.27,(^(207)Pb/^(204)Pb)_(i)=15.56~15.62,(^(208)Pb/^(204)Pb)_(i)=38.43~38.61,(^(87)Sr/^(86)Sr)_(i)-(^(206)Pb/^(204)Pb)_(i)和(143 Nd/144 Nd)_(i)-(^(206)Pb/^(204)Pb)_(i)及(143 Nd/144 Nd)_(i)-(^(87)Sr/^(86)Sr)_(i)图解指示,马荃盆地安山岩源区具有EMⅡ型富集地幔的特征。构造环境判别图指示,马荃盆地安山岩形成于板内伸展环境。综合研究表明,马荃盆地安山岩是在早白垩世早期拉张构造背景下,由地幔流体交代形成的EMⅡ型富集地幔部分熔融喷出地表的产物。The Ganhang uranium metallogenic belt is located at the junction of the Yangzi plate and the Huaxia plate.The Maquan basin is a uranium-bearing volcanic basin in the middle of this belt,and the uranium ore body is hosted in andesite.However,there is controversy over the rock types and lithological affiliation,and there is a lack of precise rock ages.Therefore,this paper focuses on the study of neutral volcanic rocks in Maquan basin,with the aim of investigating their chronology,petrology,and geochemical characteristics.The results show that the SHRIMP zircon U-Pb age of neutral volcanic rocks is 137.1±1.1 Ma(n=15,MSWD=1.5),which is a product of Early cretaceous magmatism.The neutral volcanic rocks in Maquan basin have a massive and porphyritic texture,with plagioclase as the main phenocryst,and contain a small amount of pyroxene,hornblende,and biotite.They are rich in alkali,high in potassium,low in iron,and poor in titanium,and they are enriched in light rare earth elements and large ion lithophile elements(Rb,Ba,K),but lack high field strength elements(Nb,Ta,Ti).These geochemical characteristics indicate that they are andesites,belonging to the typical high-potassium calc-alkaline volcanic rock series.The andesites have(^(87)Sr/^(86)Sr)_(i)=0.70855~0.70882,εNd(t)=-9.77~-7.02,(^(206)Pb/^(204)Pb)_(i)=18.17~18.27,(^(207)Pb/^(204)Pb)_(i)=15.56~15.62,(^(208)Pb/^(204)Pb)_(i)=38.43~38.61.The(^(87)Sr/^(86)Sr)_(i)-(^(206)Pb/^(204)Pb)_(i)and(143 Nd/144 Nd)_(i)-(^(206)Pb/^(204)Pb)_(i)as well as(143 Nd/144 Nd)_(i)-(^(87)Sr/^(86)Sr)_(i)diagrams indicate that the andesite source region in Maquan basin has the characteristics of enriched mantle EMⅡ.The tectonic discrimination diagrams indicate that the andesites in Maquan basin were formed in an intraplate extensional environment.The comprehensive study shows that the andesites in Maquan basin were produced by partial melting of enriched mantle EMⅡmobilized by mantle fluids in an early cretaceous extensional tectonic setting.

关 键 词：安山岩 锆石U-PB年龄 地球化学 EMⅡ型富集地幔 早白垩世早期 马荃盆地 

分 类 号：P619.14[天文地球—矿床学] P588.144[天文地球—地质学] P534.53