桂南板城地区晚古生代硅质岩系砂岩夹层的碎屑锆石U-Pb年代学:对沉积物源的限定  

Detrital zircon U−Pb geochronology of Late Paleozoic sandstone intercalations of siliceous rock sequences in Bancheng area,southern Guangxi:Constraint on depositional provenance

作　　者：詹骏彦 覃小锋[1,2] 王宗起[3] 曹洁 庞保成[1,2] 赵国英[1,2] 石浩[1,2] 王震[1,2] ZHAN Junyan;QIN Xiaofeng;WANG Zongqi;CAO Jie;PANG Baocheng;ZHAO Guoying;SHI Hao;WANG Zhen(College of Earth Science,Guilin University of Technology,Guilin 541004,Guangxi,China;Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541004,Guangxi,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;Center of Oil&Gas Survey,China Geological Survey,Beijing 100029,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541004 [2]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [3]中国地质科学院矿产资源研究所,北京100037 [4]中国地质调查局油气资源调查中心,北京100029

出　　处：《中国地质》2020年第3期839-852,共14页Geology in China

基　　金：国家自然科学基金项目(41362006);广西自然科学基金项目(2013GXNSFAA019272);桂林理工大学人才引进科研启动基金项目(002401003364);中国地质调查局地质矿产调查项目(12120114039501、1212011085408、DD20160124)联合资助。

摘　　要：桂南板城地区位于钦-杭结合带的西南段,是研究华南地区古生代以来地质构造演化的关键地区。该区发育有一套上泥盆统至上二叠统连续沉积的硅质岩系,近年来经过笔者系统地野外地质调查发现,钦州市板城镇石梯水库一带出露的晚古生代硅质岩系中常夹有(粉)砂岩层。本文对晚古生代硅质岩系下部和上部两个粉砂岩夹层样品进行LA-MC-ICP-MS碎屑锆石U-Pb定年结果表明,碎屑锆石年龄频谱显示出407~573 Ma(早古生代)、644~954Ma(新元古代)、1124~1636 Ma(中元古代)和2368~2548 Ma(古元古代早期-新太古代晚期)4个主要的年龄组(区间),记录了物源区可能存在4期主要的区域构造热事件,与华夏板块云开地区发育的相应时期岩浆岩时代基本吻合,说明云开地区是晚古生代硅质岩系中砂岩的主要沉积物源区。晚古生代硅质岩系下部岩石和上部岩石的物源区存在明显区别,由下往上其沉积物源越来越复杂、年龄相对更老的特征表明,钦-杭结合带西南段的云开地块在加里东期造山作用结束后经历了快速剥蚀、隆升过程。晚古生代硅质岩系砂岩夹层的碎屑锆石年龄频谱记录了钦防海盆在晚古生代时期处于拉伸的构造背景。Situated in the southwestern segment of Qinzhou-Hangzhou joint belt,Bancheng area of southern Guangxi is a pivotal area in understanding the geological tectonic evolution history of South China since the Paleozoic.Late Devonian to late Permian siliceous rock sequences are outcropped in this area.In recent years,the authors conducted systematic field geological survey and found that there exist a series of siltstone intercalations in late Paleozoic siliceous rock sequences of the Shiti reservoir in Bancheng Town,Qinzhou City.In this paper,LA−MC−ICP−MS U−Pb isotopic dating was performed for detrital zircons from two siltstone intercalation samples of the lower and upper late Paleozoic siliceous rock sequences.Detrital zircon U−Pb age spectra shows that there are four main age groups of 407−573 Ma(early Paleozoic),644−954 Ma(Neoproterozoic),1124−1636 Ma(Mesoproterozoic)and 2368−2548 Ma(Early Paleoproterozoic-late Neoarchean),which recorded four major tectonic thermal events in this area.These four periods of tectonic thermal events are consistent with the ages of widely developed magmatic rocks in Yunkai area of the Cathaysia Block,indicating that Yunkai area might have been major depositional provenance for the siltstone intercalations of late Paleozoic siliceous rock sequences.The depositional provenances of the lower and upper late Paleozoic siliceous rock sequences are significantly different,and there is a general tendency toward increasing complex and relatively older age of detrital zircon from the lower to the upper of late Paleozoic siliceous rock sequences,indicating that the Yunkai Block has experienced rapidly erosion and uplift process after Caledonian orogeny in the southwestern segment of Qinzhou−Hangzhou joint belt.Detrital zircon U−Pb age spectra of the sandstone intercalations of late Paleozoic siliceous rock sequences imply that the Qinzhou-Fangchang Basin was in an extension tectonic setting in Late Paleozoic period.

关 键 词：晚古生代硅质岩系 砂岩夹层 碎屑锆石U-Pb定年 物源 地质调查工程 板城 广西 

分 类 号：P597.3[天文地球—地球化学]