摘要
嫩江洋作为古亚洲洋东段的重要分支,其闭合时限对限定中亚造山带东段的构造演化具有重要意义.对大兴安岭北部大乌苏地区出露的二叠纪岩体进行了岩石学、年代学和地球化学研究,探讨其构造产出背景,进而为约束嫩江洋的闭合时限及大兴安岭北部地区构造演化提供新的证据.锆石U-Pb年代学结果显示,二长花岗岩加权平均年龄为292±4 Ma,形成于早二叠世.岩石属弱过铝质I型花岗岩,样品稀土分配模式曲线呈右倾型,大离子亲石元素Rb、Ba、K富集,高场强元素Nb、P、Ti亏损,呈现后造山花岗岩特征,可能形成于伸展环境.大乌苏二长花岗岩具有中等程度的Eu负异常(δEu=0.46~0.47),Th/U比值为5.61~5.94,Nb/Ta比值为7.98~8.14,Ti/Zr比值为6.11~6.36,且Mg^(#)值(22~23)较低.上述地球化学特征暗示其应形成于下地壳的部分熔融,在上升过程中发生了程度较高的结晶分异作用.综合区域上已发表的年代学资料,将区内石炭纪—二叠纪岩浆作用划分为360~350 Ma、345~292 Ma、289~260 Ma三期.通过对比各期岩浆岩的时空分布、岩石组合和地球化学特征,认为上述三期岩浆岩呈现了俯冲—碰撞后—造山后伸展的连续变化特点,记录了嫩江洋的闭合过程.研究认为大乌苏二长花岗岩应属于第二期岩浆作用的产物,产于额尔古纳-兴安地块与松嫩地块碰撞后的伸展环境,由此限定嫩江洋应闭合于早石炭世末期.
Nenjiang Ocean is an important branch of the eastern section of Paleo-Asian Ocean,and its closure time is of great significance to define the tectonic evolution of the eastern section of Central Asian orogenic belt.The paper studies the petrology,chronology and geochemistry of the Permian rock mass in Dawusu area,northern Daxinganling Mountains,and discusses its tectonic background,which provides new evidence for the constrains on the closure time of Nenjiang Ocean and tectonic evolution in northern Daxinganling Mountains.The zircon U-Pb geochronology results show that the weighted mean age of monzogranite is 292±4 Ma,corresponding to Early Permian.The monzogranite belongs to weak peraluminous I-type granite,with the REE distributions in right-inclined pattern,enriched LILEs(Rb,Ba and K)and depleted HFSEs(Nb,P and Ti),showing the characteristics of post-orogenic granites,which may be formed in extensional environment.Geochemically,the rock shows moderately negative Eu anomaly(δEu=0.46-0.47),with the Th/U ratio of 5.61-5.94,Nb/Ta ratio of 7.98-8.14,Ti/Zr ratio of 6.11-6.36,and low Mg^(#) value(22-23),indicating that it was formed in the partial melting of lower crust,with a high degree of crystallization differentiation occurred during the ascent.Based on the published regional chronological data,the Carboniferous-Permian magmatism can be divided into three stages:360-350 Ma,345-292 Ma and 289-260 Ma.By comparing the spatiotemporal distribution,lithological assemblage and geochemical characteristics of magmatic rocks of each stage,it is concluded that the magmatic rocks of the three stages show a continuous change of subduction-postcollision-postorogenic extension,which records the closure process of Nenjiang Ocean.It is believed that Dawusu monzogranite is the product of the second-stage magmatism,formed in the extensional environment after the collision between Erguna-Xing’an block and Songnen block,which defines that Nenjiang Ocean should be closed at the end of Early Carboniferous.
作者
马维
马婧轩
洪阳百合
文韵琪
MA Wei;MA Jing-xuan;HONG Yang-bai-he;WEN Yun-qi(No.6 Geological Team of Liaoning Province,Dalian 116200,Liaoning Province,China;College of Resources and Civil Engineering,Northeastern University,Shenyang 110819,China;College of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)
出处
《地质与资源》
CAS
2024年第3期267-279,共13页
Geology and Resources
基金
国家自然科学基金“碱性岩浆作用中铌钽元素富集机制的研究:以辽东地区赛马铌钽矿床为例”(42102087)
中国博士后科学基金“辽东地区碱性岩型铌钽矿床成因研究”(2022M712966)。
关键词
嫩江洋
早二叠世
地质年代学
地球化学
大乌苏地区
大兴安岭
Nenjiang Ocean
Early Permian
geochronology
geochemistry
Dawusu area
Daxinganling Mountains
