桂东早古生代地层碎屑锆石U-Pb同位素年代学及其对华夏陆块加里东期构造事件性质的约束  

Detrital Zircon U-Pb Geochronology of the Early Paleozoic Strata in Eastern Guangxi and Its Constraint on the Caledonian Tectonic Nature of the Cathaysian Continental Block

作　　者：李青[1,2] 段瑞春[3,4] 凌文黎[3,4] 胡明安[1] 张军波[3,4] 杨振[1] 

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]广西地质矿产勘查开发局,广西南宁530023 [3]中国地质大学地球科学学院,湖北武汉430074 [4]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2009年第1期189-202,共14页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(Nos.40373015;40673025);国家自然科学基金研究群体科学基金项目(No.40521001);广西自治区"广西贵港龙山-龙头山地区金铜多金属矿床成矿系列与找矿预测研究"项目

摘　　要：对广西东部大瑶山-大明山地区分别位于早古生代不整合面之下和之上的寒武纪和泥盆纪地层进行了系统的碎屑锆石U-Pb同位素年代学研究.除少数为早太古宙锆石外,寒武纪地层碎屑锆石的年龄主要有2.7～2.6、～1.8、1.4～1.1和～1.0Ga四组峰值及分别为250Ma和105Ma的热液改造年龄记录;泥盆纪地层碎屑锆石除少数具有古太古代年龄外,其余主要形成于～1.7和～1.0Ga,并记录了强烈的～100Ma的热改造事件.这些特征表明,研究区具有华夏陆块的属性,扬子与华夏陆块的边界应位于该区西北以远;经加里东构造事件后,研究区沉积盆地的物源区发生了改变,因而加里东期岩浆作用在本区并没有显示.结合前人研究成果分析,加里东事件可能指示了已裂开古陆块与华夏陆块间发生的斜向碰撞,而大瑶山-大明山地区为沿垂直于该碰撞方向挤压形成的被动盆地.区域地层中部分碎屑锆石U-Pb同位素组成的重置和热液锆石的形成,反映了研究区在印支期和燕山期存在大规模流体参与的热改造事件,这些热液对流作用应是导致本地区乃至整个华南褶皱带陆缘Au-Cu多金属矿带形成的重要原因之一.A comprehensive U-Pb geochronological study of detrital zircons from the Cambrian and Devonian strata in Dayaos-han-Damingshan area, eastern Guangxi has been conducted. The strata contact through an unconformity surface, indicating an early Paleozoic depositing hiatus in the region. The Cambrian detrital zircons are characterized by age spectrums of 2.7-2.6, -1.8, 1.4-1.1 and -1.0 Ga with minor Meso-to Neoarchean grains as well as hydrothermal event records of 250 and 105 Ma. The Devonian detrital zircons, only few of which were formed in Paleoarcheozoic age, were dominated by -1.7 and 1.0 Ga grains and recorded a pronounced thermal event at -100 Ma. The geochronology suggests that the study area possessed a Cathaysian attribute in continental accretion and tectonic evolution during the Pre-Devonian, and thus infers that the continental boundary between the Yangtze and Cathaysian blocks was located northwestern to the Dayaoshan-Damingshan terrain. Contrasting characters in geochronology of the Cambrian and Devonian strata indicate a shift in sedimentary provenance after the depositing hiatus. However, zircons with timing intervening the Cambrian and Devonian are absent, which suggests that Cale donian magmatism was minimal or lacking in the region and its proximity. Combined with previous studies, it is inferred that Caledonian folding was likely resulted from an oblique collision between the Cathaysia and a continental block which had moved apart later. This collision also resulted in a development of passive basin in Dayaoshan-Damingshan area by extruding along the vertical direction of pressing. Isotopic resetting and hydrothermal reaction are thought to account for the Mesozoic ages recog- nized in a number of detrital zircons. This observation suggests that large scale eonvecting hydrothermal fluids were involved in the Indosinian and Yanshanian magmatic and tectonic activities. Thus the convecting hydrothermal liquids are regarded as one of the key factors resulting in the mineralization of the late Mesozoi

关 键 词：广西大瑶山 早古生代 碎屑锆石 U-PB年代学 加里东期构造事件 

分 类 号：P581[天文地球—岩石学]