山东莒南地区下地壳的复杂组成和多期次生长与改造:麻粒岩捕虏体的再研究  

Complex composition and multi-stage juvenile accretion and reworking of the lower crust beneath Junan,East China s Shandong Province:granulite xenoliths revisited

作　　者：英基丰[1,2] 汤艳杰 YING JiFeng;TANG YanJie(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049

出　　处：《岩石学报》2022年第12期3735-3746,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41873036、91214203)资助.

摘　　要：山东莒南玄武质角砾岩中含有大量地幔橄榄岩、下地壳麻粒岩和辉石岩等深源捕虏体,对这些捕虏体开展研究有助于深化对华北克拉通东部岩石圈组成和演化历史的认识。我们对玄武岩中的金云母和新获得的2件麻粒岩捕虏体分别开展了^(40)Ar-^(39)Ar年代学以及锆石U-Pb年龄和Hf同位素测试。玄武岩中金云母巨晶的^(40)Ar-^(39)Ar年代学结果表明莒南玄武岩的形成年龄为59.04±0.17Ma,该年龄比玄武岩基质K-Ar法获得的年龄年轻约8Myr。锆石离子探针U-Pb年龄结果显示,莒南地区下地壳麻粒岩的原岩记录了多期次岩浆活动,包括3.33Ga、2.52Ga、1.98Ga和0.76Ga。锆石激光原位Hf同位素揭示出莒南地区下地壳经历了多阶段陆壳的增生和改造,其中3.7~3.8Ga是最重要的陆壳增生期,新元古代也存在因地幔物质的加入导致的下地壳生长。麻粒岩捕虏体所反映的下地壳主要是始太古代新生陆壳经多期壳内物质重循环而成。The abundant deep-seated xenoliths of peridotite,granulite,and pyroxenite entrapped in Junan basaltic breccia,Shandong province have been the key to increased understanding of the lower crust and upper mantle in eastern North China craton.We report high-precision ^(40)Ar-^(39)Ar dating data of the host basalt and new measurements of U-Pb and Hf isotopes of zircon from the granulite xenoliths.The ^(40)Ar-^(39)Ar dating of phlogopite megacryst yields an age of 59.04±0.17Ma,which is about 8Myr younger than the age determined by K-Ar method on basalt matrix.SIMS U-Pb analysis of zircon from the granulite xenoliths reveals that the protolith of these granulites recorded multiphase magmatism,aged at around 3.33Ga,2.52Ga,1.98Ga and 0.76Ga.The in-situ Hf isotope determination of the dated zircon suggests that the lower crust underneath Junan experienced multi-stage crustal accretion and reworking.Hf model age indicate that the lower crust was substantially accreted during 3.7~3.8Ga with subordinate crustal growth in Neoproterozoic.Intra-crustal recycling of the Neoarchaean juvenile crust,demonstrated by the multiphase magmatism leads to the formation of the protolith of the lower crust beneath Junan.

关 键 词：麻粒岩捕虏体 U-PB年龄 HF同位素 莒南 华北克拉通 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]