Detrital-zircon geochronology from the metasedimentary rocks of the Suizhou Group in the southern foot of the Tongbaishan Orogen and their geological significance

扬子克拉通北缘的随州-枣阳地区是整个秦岭-桐柏山-大别山-苏鲁造山带及其前陆地区受晚三叠世(印支期)扬子板块向华北板块深俯冲并发生高压-超高压变质作用影响最小的地区,因而扬子克拉通北缘的前寒武纪基底在这里得到了较多的保存.它们不仅为研究扬子克拉通北缘新元古代构造环境提供了难得的样品,也为研究造山带内变质杂岩的原岩性质提供了参照物.出露的前寒武纪基底包括新元古代的变质火山-沉积岩系(随州群)以及大量的超镁铁质-锾铁质岩床群.本文用LA-ICP-MS锆石U-Pb法对随州群中变质沉积岩中的碎屑锆石进行了系统的年代学研究,结果表明:①随州群变质沉积岩中最年轻碎屑锆石的年龄约为720Ma,表明随州群的主要沉积作用应晚于该时间；②年龄介于700～1000Ma时间段的锆石颗粒构成了随州群变质沉积岩中最大的碎屑锆石群体,峰值在800Ma左右,说明新元古代,尤其是新元古代中、晚期形成的岩浆岩是随州群沉积岩最重要的一个物源；③随州群变质沉积岩中也出现了较多1700～ 2100Ma年龄段的锆石颗粒,说明古元古代中、晚期形成的岩浆岩也是随州群沉积岩的重要物源之一；④随州群沉积岩具有古元古代早期,甚至太古代年龄的碎屑锆石,说明扬子克拉通北缘可能存在层位相当的物源.The Suizhou-Zaoyang area (northern margin of the Yangtze Craton), the least affected area of the whole Qinling-Tongbaishan-Dabieshan-Sulu orogen and their foreland by the deep subduction of the Yangtze Craton beneath the North China Craton and concomitant HP-UHP metamorphism during Triassic, relatively well preserved Precambrian basement of the northern Yangtze Craton. These low-grade metamorphosed Precambrian rocks not only provide an ideal opportunity to study the palaeo-tectonic setting of the northern Yangtze Craton, but also are rare-references for resuming protolithes of the metamorphic complex in the orogen. The Precambrian rocks exposed here include Neoproterozoic volcanic-sedimentary rock series (Suizhou Group) and voluminous Neoproterozoic ultramafic-mafic sill swarms. In this work, we used LA-ICP-MS zircon U-Pb technique dating detrital zircons from the metasedimentary samples of the Suizhou Group, yielding results as follow; (1) The youngest age of detrital-zircon from the metasediments of the Suizhou Group is about 720Ma, which means that the formed age of the Suizhou Group was mainly later than this time; (2) Zircon grains with ages from about 700Ma to 1000Ma are maximum detrital zircon group, with peak value at about 800Ma, showing that the magmatic rocks formed in Neoproterozoic era, especially medium to late stage of the Neoproterozoic, were foremost source of the Suizhou Group; (3) There are many zircon grains with ages from 1700Ma to 2100Ma, showing that the magmatic rocks formed in the medium to late stage of the Paleoproterozoic were also one of important sources; (4) Existing of detrital-zircon with ages of early stage of Paleoproterozoic and Archaean imply that this era of stratum may exist in the northern margin of the Yangtze Craton.国家自然科学基金项目; 地质矿产调查评价专项http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000317531300015&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)32564-5802