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

Wuyi-Yunkai orogenic belt, located between Yangtze ancient plate and Cathaysian ancient plate, is the important type of hydrothermal uranium metallogenic belt in China, in this belt not only distributed caledonian and yanshanian intrusive rocks widely,but also distributed yanshanian volcanic rocks North-middle of the belt.Recent studies found that the porphyroclastics,in the original to Yanshanian, is now belongs to Caledonian in Hekou basin north of Xiazhuang uranium fields, it proved in the middle of Wuyi-Yunkai orogenic belt exist Caledonian volcanic activity. However, if in the early Paleozoic orogenic belt exist a subduction magmatism in the middle of Wuyi-yunkai orogenic belt? If they have certain genetic relationships with the uranium mineralization? All of these are problems to be solved.This project select the volcanic rocks from Hekou-Nanjing and the uranium deposits in north of Xianzhuang as research object, by the detail research in field to found out the yield characteristics, using the SHRIPMP zircon U-Pb dating technique to set the geological era of volcanic rocks,using the main and trace element,Sr-Nd-Pb-Hf istopic tracer technique to discriminant the material source and tectonic of the volcanic rocks and by means of S-O-H-C istopic tracer technique to explore the inner link between the volcanic rocks and uranium maneralization, then provide new evidence for the study the geological events of early Paleozoic south China and improve the uranium metallogenic theory.

位于华夏古板块和扬子古板块之间的武夷-云开造山带是我国重要热液型铀成矿带，该带不仅广泛分布加里东期和燕山期侵入岩，而且中、北部还广泛发育燕山期火山岩。新近的研究发现，下庄铀矿田北部河口盆地原归于燕山期的碎斑熔岩实属加里东期，证明武夷-云开造山带中部存在加里东期火山活动。然而在武夷-云开造山带中部早古生代是否存在俯冲岩浆活动？其与后期铀成矿是否有一定的成因联系？都是亟待解决的问题。本项目选择河口-南迳一带的火山岩和下庄北部的铀矿床为研究对象，通过野外深入调研,查明火山岩的产出特征，拟采用SHRIMP锆石U-Pb测年技术厘定火山岩的地质时代，利用主、微量元素、Sr-Nd-Pb-Hf联合示踪技术判别火山岩的物质来源和形成构造环境，并通过S-O-H-C同位素示踪技术等探讨加里东期火山岩与后期铀成矿的内在联系，为研究华南早古生代地质事件提供新的证据，为完善铀成矿理论提供技术支撑。

华南早古生代是否存在俯冲岩浆活动一直存有争议。基于华南出露广泛的加里东期花岗岩，而缺少同期火山岩，较早研究认为华南早古生代不存在俯冲岩浆活动。华南是否广泛存在加里东期火山岩？加里东造山带的构造演化背景究竟如何？都是有待进一步解决的问题。河口盆地首次发现的加里东期碎斑熔岩，开启了华南加里东期岩浆活动研究的窗口。本项目选择赣南-粤北河口-南迳一带的火山岩，通过实测剖面、采用地球化学、Sr-Nd-Pb同位素和SHRIMP锆石U-Pb同位素年代学方法，开展了火山岩时空分布、火山岩成因及构造背景判别研究。年代学和实测剖面研究表明，⑴流纹岩、英安岩和安山岩（442-436Ma）形成地质时代为晚奥陶世-早志留世早期；⑵晚奥陶世-早志留世早期流纹岩、英安岩和安山岩大多数具岛弧岩浆特征；⑶赣南南迳盆地火山岩系与龙头寨群变质岩系为整合接触的一套火山-变质岩系，将黄竹洞组灰色、灰绿色板岩、粉砂质板岩夹细粒石英砂岩之上的安山岩- 英安岩组合命名为南迳组，归入龙头寨群，置于其顶部；⑷龙头寨群变质板岩夹流纹岩、安山岩组合主体形成时代应为晚奥陶世-早志留世早期。.赣南-粤北加里东期火山岩研究意义在于：⑴查实了赣南-粤北及相邻区不仅存在广泛的加里东期花岗岩，还存在与其同期的火山岩，且火山岩多为岛弧火山岩，形成于活动大陆边缘，对进一步探讨华南加里东造山带为构造演化背景奠定了基础；⑵建立南迳组归入龙头寨群，明确了龙头寨群主体形成时代，打破了龙头寨群为冒地槽沉积的认识，为华南加里东造山带中段西部晚奥陶世—早志留世浅变质岩系属含有火山岩的优地槽型沉积提供了证据；⑶华南加里东造山带中段西部显现的优地槽型沉积、广泛分布的岛弧火山岩和龙头寨群活动大陆边缘沉积组合特征，皆为探讨晚奥陶世—早志留世早期华南加里东造山带是俯冲-碰撞造山提供了依据。