广西大明山地块寒武系碎屑锆石U-Pb年龄及其构造意义  

Detrital Zircon U-Pb Geochronology of Cambrian Sandstones in Damingshan,Central Guangxi and Its Tectonic Implications

作　　者：邹和平[1,2] 杜晓东[1,2] 劳妙姬[1,2] 丁汝鑫[1,2] 

机构地区：[1]中山大学地球科学系,广州510275 [2]广东省地质过程与矿产资源探查重点实验室,广州510275

出　　处：《地质学报》2014年第10期1800-1819,共20页Acta Geologica Sinica

基　　金：中国地质调查局地质大调查项目(批准号:1212011121064)资助的成果

摘　　要：大明山地区位处扬子地块与华夏地块结合带的西南段,对该区寒武系碎屑锆石开展U-Pb年龄谱研究可为新元古代—早古生代扬子地块与华夏地块结合带构造属性的进一步确定和对华南大地构造演化的深入研究提供新的依据。本次研究对该区2件寒武纪砂岩样品分选出的碎屑锆石进行了LA-ICPMS U-Pb年代测定和分析。锆石的透射光及阴极发光图像、Th/U比值、稀土元素特征说明其主要为岩浆岩锆石。222个谐和年龄数据显示出5个主要年龄区间：550~560Ma、750~780 Ma、950~1020 Ma、1560~1740Ma和2390~2450Ma,其中以950~1020Ma区间表现为最突出的峰值。对比大明山与大瑶山地区的寒武系碎屑锆石年龄谱系,两者表现出相似的分布特征。最明显的年龄峰值（980Ma）揭示物源区曾是Grenville期造山带的一部分。与扬子地块和华夏地块碎屑锆石年龄谱系进行比较,结合古水流及相关地质证据,认为所研究样品的碎屑锆石主要来自华夏地块。根据现有的资料,我们更倾向于认为寒武纪时扬子—华夏之间可能没有大洋的分割,而是一陆间海（intercontinental sea）格局。本次研究还在大明山寒武系中测得8颗具有太古宙年龄的古老锆石（≥2500Ma,其中1颗≥3200Ma）。这些锆石具振荡环带结构,Th/U比值均≥0.4,稀土分布多具有明显的Ce正异常与Eu负异常,指示其来自岩浆岩,反映物源区在太古宙发生过岩浆作用。结合前人研究获得的华夏地块太古宙锆石年龄信息,认为华夏地块可能存在太古宙地壳基底或接受过古老陆块的物源供给。The Damingshan-Dayaoshan area in Guangxi Province of South China is a major region in which the Cambrian strata are widely exposed.The united South China Block is composed of the Yangtze Block to the northwest and the Cathaysia Block to the southeast.The Damingshan area is located at the southwestern segment of the Qinzhou-Hangzhou Joint Belt between the Yangtze and Cathayian blocks.It is significant to study U-Pb geochronology of the detrital zircons from Cambrian sedimentary rocks in the area for inquiring into the Precambrian crustal evolution of South China,especially for further defining the Neoproterozoic-early Paleaozoic tectonic attribution of the belt between the Yangtze and Cathaysia blocks.Detailed LA-ICPMS U-Pb dating analyses have been carried out on detrital zircons from 2samples of Cambrian sandstones in the Damingshan area.The characteristics of transmitted light and Cathodoluminescence（CL）images,Th/U ratios and REE patterns indicate that these detrital zircons are mainly magmatic origin.U-Pb age determinations of 222 groups define five major populations with ages of 550~560Ma,750~780 Ma,950~1020 Ma,1560~1740Ma and 2390~2450Ma among which the most prominent peak age population is 950~1020Ma.Our studies also show that the U-Pb timing spectra of the detrital zircons from the Cambrian strata in the Damingshan area and the Dayaoshao area are nearly of the same characteristics and all of five major peaks of 2440 Ma,1680Ma,980 Ma,790Ma and 560 Ma,among which the most obvious age peak is at 980 Ma that correlates with the Grenville orogeny tectono-thermal events in the provenance.Comparing these dating data with the zircon U-Pb timing spectra of the Yangtze Block and the Cathaysia Block,combining with the correlative geologic evidence lines such as paleocurrent characteristics,it shows that the detrital zircons in the Cambrian sedimentary rocks of the DamingshanDayaoshan area were majorly derived from the Cathaysian Block.According to the data available,we are more inclined to accept the opinion that

关 键 词：大明山 寒武系 碎屑锆石U-PB年龄 华夏地块 扬子地块 

分 类 号：P597.3[天文地球—地球化学] P534.41[天文地球—地质学]