摘要
北秦岭构造带早古生代构造格局和演化过程受到地质学界的长期关注,秦岭岩群在早古生代期间是否经历整体俯冲-深俯冲是存在较大争议的问题之一。西峡寨根地区界牌村附近寨根岩体围岩长英质片麻岩中出露了斜长角闪岩和长英质脉体,本文对其开展了详细的LA-ICP-MS锆石U-Pb定年、岩石地球化学、矿物化学和锆石包裹体分析,以期为该问题的探讨提供新的限定。锆石U-Pb年代学研究表明,界牌斜长角闪岩原岩年龄为820Ma,变质时代为(422±5)Ma,锆石中出现斜长石和石英包裹体。该岩石具有与区内榴辉岩相似的岩石地球化学特征,岩石中存在2类角闪石,分别形成于角闪岩相变质和之后的退变质阶段,长英质脉体中存在大量继承/捕获锆石。其中,1115~1576 Ma、502~517 Ma锆石来自秦岭岩群高压-超高压长英质片麻岩,908~935 Ma锆石来自寨根岩体,该岩石形成时代为(447±4)Ma,在420 Ma受到变质改造。长英质脉体具有富w(K_(2)O)、Rb和Ba,低w(CaO)、w(Fe_(2)O_(3)^(T))、w(MgO)和w(TiO_(2))的特征,表明其可能是秦岭岩群高压-超高压长英质片麻岩中(多硅)白云母脱水熔融的产物。综合本文和前人研究,界牌斜长角闪岩在早古生代期间只经历了角闪岩相变质作用,并非榴辉岩退变质产物,为秦岭岩群没有经历整体陆壳俯冲-深俯冲提供了进一步的证据。420~460 Ma期间,俯冲-深俯冲陆壳在折返抬升时由于幔源岩浆上涌以及广泛的部分熔融作用和岩浆侵入而破碎,最终与未发生俯冲的陆壳岩石发生混杂。
The tectonic evolution of the North Qinling in the early Paleozoic has been widely concerned for a long time,and whether the Qinling Group experienced overall continental deep subduction during the early Paleozoic is one of the controversial issues.In this paper,LA-ICP-MS zircon U-Pb dating,geochemistry,mineral chemistry and zircon inclusions of the amphibolite and felsic vein near the Zhaigen pluton,Jiepai village,Zhaigen country,have been carried out in order to better identify the early Paleozoic subduction history of the Qinling Group.LA-ICP-MS U-Pb dating yielded the protolith age of~820 Ma and metamorphic age of(422±5)Ma for the amphibolite.Plagioclase and quartz inclusions were discovered in zircons only.The amphibolite samples have similar geochemical characteristics with eclogites in the North Qinling.There are two types of amphibole in the amphibolite,which should be formed during the amphibolite facies metamorphism and the subsequent retrograde metamorphism,respectively.Lots of inherited/captured zircons are preserved in the felsic vein,among them,the 1115-1576 Ma and 502-517 Ma zircons may both inherited from the HP-UHP felsic gneiss of the Qinling Group,and the 908-935 Ma zircons may captured from the Zhaigen pluton.The felsic vein was formed at(447±4)Ma and underwent metamorphic modification at~420 Ma.In addition,the vein is characterized by higher w(K_(2)O),Rb and Ba,and low w(CaO),w(Fe_(2)O_(3)^(T)),w(MgO)and w(TiO_(2)),indicating that the vein may be the product of dehydration melting of phengite from the HP-UHP felsic gneisses of the Qinling Group.Combined with previous researches,it is concluded that the Jiepai amphibolite underwent amphibolite facies metamorphism only,which provides further evidence that the Qinling Group did not experience the overall continental subduction in the early Paleozoic.During 420-460 Ma,the subduction continental crust was fractured and broken due to the upwelling of mantle-derived magma,extensive partial melting and magmatic intrusion during the uplift processes
作者
李阔
宫相宽
孙敏佳
王一鸣
吴慧芸
尼加提·阿布都逊
LI Kuo;GONG Xiang-kuan;SUN Min-jia;WANG Yi-ming;WU Hui-yun;ABDURSUL·Nijat(Xinjiang Key Laboratory of Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt,Collaborative Innovation Center of Green Mining and Ecological Restoration for Xinjiang Mineral Resources,College of Geology and Mining Engineering,Xinjiang University,Urumqi 830017,China)
出处
《矿物学报》
CAS
CSCD
北大核心
2023年第5期674-692,共19页
Acta Mineralogica Sinica
基金
新疆维吾尔自治区高校科研计划项目(编号:XJEDU2021Y012)
国家自然科学基金项目(编号:41562010)。
