胶北地块斜长角闪岩的岩石学与年代学研究  

Petrological and Geochronological Study of Amphibolite from Jiaobei Terrane

作　　者：陈爽 李旭平 段文勇 孙光明 冯庆达 Chen Shuang, Li Xuping , Duan Wenyong, Sun Guangming, Feng Qingda(College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, Chin)

机构地区：[1]山东科技大学地球科学与工程学院

出　　处：《地球科学》2018年第3期716-732,共17页Earth Science

基　　金：国家自然科学基金项目(No.41272072);山东科技大学校创新团队项目(No.2015TDJH101);国际(地区)合作与交流项目(No.41761144061)

摘　　要：胶北地块位于华北克拉通东部陆块,胶-辽-吉活动带的南端.胶北地区荆山杂岩中存在一组与高压基性麻粒岩密切共生的斜长角闪岩,是构成前寒武纪变质基底的重要组成部分.岩石学矿物学研究表明,斜长角闪岩记录了3个阶段的变质作用:峰期变质矿物组合(M1)为角闪石1+斜长石+榍石,根据NCKFMASHTO体系的成分视剖面图和角闪石压力计估算出温度条件T=660~715℃,压力条件P=0.65~0.71GPa;其后经历了退变质作用(M2),矿物组合为角闪石2+绿帘石+斜长石+绿泥石+钠长石,估算温压条件为537~630℃/0.41~0.58GPa;晚期发生前绿片岩相退变质作用(M3),其矿物组合为钠长石+葡萄石+绿泥石+方解石,其温压条件<400℃/0.35GPa.斜长角闪石的CL图像显示其具有较弱的阴极发光效应和弱震荡环带,Th/U比值相对较小(0.06~0.43),锆石形态和内部结构指示锆石形成于深熔作用过程,21个锆石的LA-ICP-MS定年研究的结果表明,斜长角闪岩记录的最老^(206)Pb/^(238) U年龄为2 075±25Ma,上交点年龄为1 845±23Ma(MSWD=0.35),该组年龄记录了斜长角闪岩峰期变质作用时代的上限.斜长角闪岩在原岩形成以后,可能曾经历麻粒岩相变质作用,并记录了在胶-辽-吉带~1.85Ga碰撞闭合过程中的深熔事件,此后经历了角闪岩相变质作用,及其二次退变质作用,终结于前绿片岩相的变质温压条件.Jiaobei terrane lies in the southern segment of the Paleoproterozoic Jiao-Liao-Ji belt,eastern block of the North China craton.There is a set of amphibolite closely related to the high-pressure mafic granulite in Jingshan complex of Jiaobei terrane,which is an important component of the Precambrian metamorphic basement.Our petrological and mineralogical study shows that amphibolite records three stages of metamorphism.The peak stage（M1）shows a mineral assemblage Amp1＋Pl＋Ttn.The temperature calculated by pseudosection modeling and estimated pressure conditions are T=660-715℃,P=0.65-0.71 GPa.The mineral assemblage at post-peak stage（M2）is Amp2＋Ep＋Pl＋Chl＋Ab,suggesting temperature and pressure conditions 537-630℃/0.41-0.58 GPa.The mineral assemblage at retrograde stage（M3）is Ab＋Prh＋Chl＋Cal.Prehnite and calcite veins indicate that the amphibolite underwent a prehnite-pumpellyite facies metamorphism with P-T conditions400℃/0.35 GPa.LA-ICP-MS U-Pb geochronology combined with cathodoluminescence（CL）imaging of 21 zircons are all characterized by relatively low Th/U ratios（0.06-0.43）,low luminescence and weakly oscillatory zoning.The morphological and internal structure features of zircons suggest that their growths were associated with partial melting,and they yielded ^（206） Pb/^（238） U weighted mean ages of 1 845±23 Ma（MSWD=0.35）.After formation of the mafic rock,it may have experienced granulite facies metamorphism,and then recorded the anataxis event during collisional convergence of the Jiao-Liao-Ji orogenic belt at^1.85 Ga.The investigated amphibolite recorded amphibolite facies metamorphism,and subsquently two episodes ofretrogressive metamorphism during the lift of the belt.

关 键 词：斜长角闪岩 矿物化学 年代学 变质作用:胶北地块 

分 类 号：P597[天文地球—地球化学]