大兴安岭中段乐平统-中三叠统沉积物源分析:来自重矿物组合及碎屑锆石年代学证据  

Lopingian to Middle Triassic provenance analysis of sedimentary rocks in the middle segment of the Da Hinggan Mountains: Evidence from the heavy mineral assemblage and the detrital zircon U-Pb ages

作　　者：蔡芃睿 王涛[1] 王宗起[2] 李龙明[3] 王铭乾 贾建亮[1] 吴彦佳 CAI PengRui;WANG Tao;WANG ZongQi;LI LongMing;JIA JianLiang;WU Yanjia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Resources and Environment,Hefei University of Technology,Hefei 230009,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《岩石学报》2019年第11期3549-3564,共16页Acta Petrologica Sinica

基　　金：中国地质调查局公益性基础地质调查项目(DD20189613);基本科研业务费专项经费(JYYWF20180901)联合资助

摘　　要：黑龙江西部龙江地区位于中亚造山带东段,黑河-贺根山缝合带与西拉木伦缝合带之间,地层记录了两大古板块之间古亚洲洋闭合过程的信息。本文对龙江地区乐平统林西组和下-中三叠统老龙头组的砂岩样品进行碎屑重矿物和碎屑锆石U-Pb同位素年代学研究。碎屑重矿物组合以锆石+磷灰石+金红石+角闪石+绿帘石+重晶石的组合为特征,表明物源主要来自于中酸性岩浆岩,并有少量变质岩及沉积岩组分。林西组样品最年轻的锆石年龄为278±3Ma,老龙头组样品最年轻的锆石年龄为247±3Ma、243±4Ma及237±3Ma,结合前人的研究,限定了林西组沉积于乐平世,老龙头组沉积于早三叠世-中三叠世。碎屑锆石年龄谱明显分为五组:237~258Ma、270~329Ma、357~558Ma、680~1633Ma及1893~1966Ma。其中237~258Ma的碎屑锆石主要来自与古亚洲洋洋壳消亡前的俯冲增生过程相关的火山活动,270~329Ma的碎屑锆石主要来自大石寨组火山岩及其同期侵入岩,357~558Ma的碎屑锆石来自早古生代-晚古生代早期岩浆弧,680~1633Ma的碎屑锆石可能来自兴安及额尔古纳地块的变质基底,而较古老的~1800Ma的锆石年龄暗示了华北克拉通基底的物源信息。通过研究发现林西组及老龙头组样品前30%年轻的碎屑锆石年龄与地层沉积年龄之差都小于100Ma,结合对砂岩碎屑组成、重矿物组合及盆地与火山弧位置关系的研究,认为研究区乐平世-中三叠世沉积盆地具有汇聚背景,为弧前盆地。Longjiang area in western Heilongjiang Province is located in the eastern part of the Central Asian Orogenic Belt,between Heihe-Hegenshan suture zone and Xilamulun suture zone. Strata records the closure process of the Paleo-Asian Ocean between the two paleoplates. Clastic heavy minerals and U-Pb isotopic chronology of detrital zircons have been studied in sandstone samples from Linxi Formation of Upper Permian and Laolongtou Formation of Lower-Middle Triassic in Longjiang area. The clastic heavy mineral assemblages are characterized by zircon + apatite + rutile + amphibole + epidote + barite assemblages. This indicates that the provenances are mainly from intermediate-acid magmatic rocks with a small amount of metamorphic rocks and sedimentary rocks. The youngest zircon age of the Linxi Formation samples is 278 ± 3 Ma,while those of the Laolongtou Formation samples are 247 ± 3 Ma,243± 4 Ma and 237 ± 3 Ma,which limits that Linxi Formation was deposited in Late Permian and Laolongtou Formation was deposited in Early Triassic-Middle Triassic. The age spectrum of detrital zircons can be divided into five groups: 237 ~ 258 Ma,270 ~ 329 Ma,357~ 558 Ma,680 ~ 1633 Ma and 1893 ~ 1966 Ma. Among them,237 ~ 258 Ma detrital zircons mainly come from volcanic activities related to the subduction and accretion before the extinction of the Paleo-Asian ocean crust;270 ~ 329 Ma detrital zircons mainly come from volcanic rocks of the Dashizhai Formation and their contemporary intrusive rocks;357 ~ 558 Ma detrital zircons come from Early Paleozoic-Early Late Paleozoic magmatic arcs;and 680 ~ 1633 Ma detrital zircons may come from metamorphic basement of the Xingan and Erguna massifs. The older ~ 1800 Ma zircon age implies the source information of the North China Craton basement. It is found that the difference between the first 30% younger clastic zircon age of the Linxi and Laolongtou formations ’ samples and the sedimentary age of strata is less than 100 Ma. Based on the study of sandstone clastic composition,heavy mineral

关 键 词：中亚造山带 碎屑锆石年代学 碎屑重矿物 乐平世-中三叠世 物源分析 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]