额尔古纳地块新元古代花岗岩榍石原位微区LA-ICP-MS U-Pb定年及其地质意义  

Titanite LA-ICP-MS U-Pb dating of the Neoproterozoic granites in the Erguna massif and their geological significance

作　　者：赵硕 张进[1] 李锦轶[1] 许文良[2] 曲军峰[1] 刘建峰[1] 郑荣国[1] 葛茂卉 ZHAO Shuo;ZHANG Jin;LI Jinyi;XU Wenliang;QU Junfeng;LIU Jianfeng;ZHENG Rongguo;GE Maohui(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing,100037;College of Earth Sciences,Jilin University,Changchun,130061)

机构地区：[1]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]吉林大学地球科学学院,长春130061

出　　处：《地质学报》2020年第3期757-767,共11页Acta Geologica Sinica

基　　金：国家重点研究开发计划项目(编号2017YFC0601301);中国地质科学院基本科研业务费专项经费(编号J1907);国家自然科学基金青年科学基金项目(编号41802068);中国地质调查项目(编号DD20190004)联合资助的成果。

摘　　要：本文首次报道了额尔古纳地块新元古代花岗岩榍石原位微区LA-ICP-MS U-Pb定年数据,以明确其形成时代,进而为准确厘定额尔古纳地块新元古代岩浆作用期次提供新的证据,并进一步揭示其地质意义。研究区内分别采自满归岩体和莫尔道嘎岩体的2个代表性样品中的榍石呈菱形自形-半自形晶,不具有变质榍石特有的杏仁孔或孔洞特征,暗示其为岩浆成因。对原生榍石的定年结果显示,满归岩体和莫尔道嘎岩体数据点的线性拟合性均较好,拟合线下交点年龄分别为873±22 Ma和783±31 Ma,均与206Pb/238U加权平均年龄(872±18Ma和789±17 Ma)相一致。同时结合已有研究成果表明,原定为额尔古纳地块新元古代最早期岩浆作用产物的满归岩体实际形成于~850 Ma,而非前人认为的957~927 Ma;莫尔道嘎岩体形成于~790 Ma,也并非前人认为的~762 Ma。综合校正后的岩体年龄以及近年来前人研究成果,现阶段额尔古纳地块新元古代岩浆作用期次可大致分为五个阶段,即915~905 Ma、~847 Ma、818~808 Ma、~792 Ma和~738 Ma。This paper first presents the LA-ICP-MS titanite in situ U-Pb dating results for the Neoproterozoic granites in the Erguna massif with the aim of constraining their chronology and providing new evidence for determining the ages of the Neoproterozoic magmatic events and their geological significance.Titanite grains from two representative samples of the Mangui and Moerdaoga plutons are euhedral-subhedral diamond in shape,and do not display the specific almond hole of metamorphic titanite in microphotographs,implying a magmatic origin.Titanite U-Pb dating results demonstrate that the analyses of both the plutons plot along a fine discordia line with lower intercept ages of 873±22 Ma and 783±31 Ma,which correspond to 206 Pb/238 U weighted mean ages of 872±18 Ma and 789±17 Ma respectively.Combined with the published data,it is concluded that Mangui pluton,the original earliest product of the Neoproterozoic magmatism in the Erguna massif,actually formed at-850 Ma,not 957~927 Ma as previously believed,whereas Moerdaoga pluton actually formed at^790 Ma,rather than^762 Ma as was previously suggested.At present,the modified and previously published ages demonstrate that the Neoproterozoic magmatism in the Erguna massif can be subdivided into five stages:915~905 Ma,~847 Ma,818~808 Ma,~792 Ma and^738 Ma.

关 键 词：额尔古纳地块 新元古代 岩浆作用 榍石U-Pb年龄 

分 类 号：P597.3[天文地球—地球化学] P588.121[天文地球—地质学]