吉林中部大口钦地区杨家沟组物源分析:来自地球化学特征及碎屑锆石U-Pb年代学证据  

Provenance analysis of Yangjiagou Formation in Dakouqin area,central Jilin Province:evidence from geochemistry and detrital zircon U-Pb geochronology

作　　者：李翱鹏[1,2] 王春阳 吕鹏 刘万臻[1,2] 王福亮 苏斌[1] LI Aopeng;WANG Chunyang;L Peng;LIU Wanzhen;WANG Fuliang;SU Bin(Geological Survey Institute of Jilin Province,Changchun 130102,China;Northeast Geological Science&Technology Innovation Center,China Geological Survey,Shenyang 110034,China;The Fourth Geologic Survey of Jilin Province,Tonghua 134000,Jilin,China)

机构地区：[1]吉林省地质调查院,长春130102 [2]中国地质调查局东北地质科技创新中心,沈阳110034 [3]吉林省第四地质调查所,吉林通化134000

出　　处：《世界地质》2025年第1期35-55,共21页World Geology

基　　金：中国地质调查局东北地质科技创新中心区创基金项目(QCJJ2022-18)。

摘　　要：关于古亚洲洋最终闭合的时间一直是地学界争论的热点问题之一,吉林中部地区在古生代期间主要受古亚洲洋构造体系的控制,是研究上述问题的理想场所。笔者对吉林中部大口钦地区杨家沟组岩屑杂砂岩和粉砂质板岩开展了系统的锆石U-Pb年代学和岩石地球化学研究,确定了杨家沟组的沉积时限和物源特征。地层最大沉积年龄采用最年轻的碎屑锆石加权平均年龄进行限定,杨家沟组的2个岩屑杂砂岩样品(PM001-38-TW1和PM001-135-TW1)的沉积下限年龄分别为(255±5)Ma和(251±2)Ma,与二叠系-三叠系沉积界限年龄(251.902±0.024)Ma相符合。结合捕获自周围晚三叠世二长花岗岩[(235~227)Ma]锆石的年龄和侵入到杨家沟组中二长花岗岩的年龄(223±2)Ma,认为研究区杨家沟组应形成于晚二叠世。全岩主、微量元素数据表明杨家沟组岩屑杂砂岩和粉砂质板岩的w(SiO_(2))为65.13%~70.73%,w(Al_(2)O_(3))为14.75%~17.29%,w(K_(2)O)为2.43%~3.87%,w(Na_(2)O)为1.59%~3.26%,K_(2)O/Na_(2)O为0.75~2.34,相对富集轻稀土元素,亏损重稀土元素,LREE/HREE=6.98~9.09,Eu/Eu*=0.56~0.70。CIA-ICV图解、物源区属性图解以及构造背景判别图解表明,杨家沟组物源沉积物经历了中等程度的风化作用,成熟度相对较高,其物源主要以长英质岩石为主,形成于活动大陆边缘或大陆岛弧背景下。杨家沟组的碎屑锆石年龄可划分为5组:古元古代(1819~1785 Ma)、中-新元古代(1491~561 Ma)、寒武纪-石炭纪(522~301 Ma)、早-中二叠世(295~259 Ma)和晚二叠世-中三叠世(258~238 Ma)。结合前人对区域上岩浆作用的研究表明,杨家沟组具有双向物源特征(华北板块和兴蒙造山带)。杨家沟组的源区性质及古生物学证据表明其形成于碰撞造山向构造稳定环境转化的阶段。综合研究区的岩浆作用特征,认为古亚洲洋在吉林中部的最终闭合发生在晚二叠世-中三叠世。The timing of the final closure of the Paleo-Asian Ocean is one of the controversial issues in the field of geoscience.The central Jilin Province,which was controlled by the evolution of the Paleo-Asian tectonic regime during the Paleozoic,is an ideal place to resolve the above issue.The authors conducted systematic zircon U-Pb geochronological and geochemical studies on lithic sandstones and silty slates from Yangjiagou Formation in the Dakouqin area,central Jilin Province,and determined the deposition time and provenance characteristics of Yangjiagou Formation.The maximum depositional age of the formation can be constrained by the youngest weighted average age of detrital zircons,and therefore the lower depositional ages of the two lithic sandstones samples(PM001-38-TW1 and PM001-135-TW1)from Yangjiagou Formation were determined to be(255±5)Ma and(251±2)Ma,which are consistent to the Permian and Triassic boundary(251.902±0.024)Ma.Combined with the ages of zircons that captured from the surrounding Late Triassic monzogranite dated(235-227)Ma,and the timing of the monzogranite aged(232±2)Ma which intruded in,the Yangjiagou Formation in the study area would deposit during the Late Permian.Whole rock major and trace element geochemical data of the lithic sandstones and silty slates from Ya ngjiagou Formation indicate that w(SiO_(2))ranges from 65.13%to 70.73%,w(Al_(2)O_(3))form 14.75%to 17.29%,w(K_(2)O)form 2.43%to 3.87%,w(Na_(2)O)form 1.59%to 3.26%,and the ratio of K_(2)O/Na_(2)O is from 0.75 to 2.34.The light rare earth elements are relatively enriched,while the heavy rare earth elements are depleted,with LREE/HREE and Eu/Eu*ratios of 6.98-9.09 and 0.56-0.70,respectively.Based on the CIA-ICV diagram,the source composition discrimination diagram and the tectonic setting discrimination diagram,the sedimentary provenance of Yangjiagou Formation has experienced a relatively moderate weathering with a high maturity.The Yangjiagou Formation whose source rocks are mainly felsic,were deposited in active continental m

关 键 词：物源分析 地球化学特征 锆石U-PB年代学 杨家沟组 大口钦地区 吉林省中部 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]