赞皇前寒武纪变质杂岩区变质反应结构与变质作用P-T-t轨迹  

Metamorphic reaction textures and metamorphic P-T-t loops of the Precambrian Zanhuang metamorphic complex,Hebei,North China

作　　者：肖玲玲[1] 蒋宗胜[1] 王国栋[1] 万渝生[2] 王涛[2] 吴春明[1] 

机构地区：[1]中国科学院研究生院地球科学学院,北京100049 [2]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2011年第4期980-1002,共23页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40672129;90714006;40730315);中国科学院知识创新工程重要方向课题(XMXX280734)联合资助

摘　　要：赞皇变质杂岩位于华北克拉通中部造山带中南段、太行山东麓低山区。出露于该变质杂岩区中南部的含石榴石的斜长角闪片麻岩、泥质片麻岩,均保存了三期矿物组合:进变质、峰期变质和退变质矿物组合。这两大类变质岩石中,进变质阶段矿物组合(M1)以石榴石变斑晶核部的包裹体矿物组合为代表,变质高峰期矿物组合(M2)由石榴石变斑晶"边部"和基质矿物组成,退变质阶段矿物组合(M3)主要是环绕石榴石边部发育的"白眼圈"状后成合晶矿物组合。泥质片麻岩中的石榴石变斑晶均保存了明显的成分环带,且在边部很窄的范围内XMn有所增加、Mg/(Mg+Fe)有所降低,指示存在变质高峰期后的退变质过程。温度与压力计算结果表明,赞皇斜长角闪片麻岩所经历的进变质阶段(M1)温度约为640～710℃、压力约为8.2～8.6kbar;高峰期(M2)变质温度超过810℃,压力大于12.1kbar;退变质阶段(M3)的温压范围为590～670℃和3.2～5.6kbar。此前的研究已说明泥质片麻岩的进变质阶段(M1)变质温度为660～690℃,压力为9.0～9.2kbar;高峰期(M2)变质温度超过780℃,压力大于12.5kbar。变质高峰属于中压相系的顶部至高压相系的底部。斜长角闪片麻岩、泥质片麻岩均记录了典型的顺时针P-T轨迹,并显示近等温减压(ITD)的退变质片段。对泥质片麻岩中多颗锆石的变质增生边的SHRIMPU-Pb定年表明,变质高峰期时代为1821±17Ma。变质作用历史说明赞皇变质岩区卷入了华北克拉通东部陆块和西部陆块之间的俯冲-碰撞、随后的快速隆升过程,为华北克拉通中部造山带早元古代末期(～1850Ma)存在的造山事件提供了新的证据。The Zanhuang metamorphic complex is exposed in the lowland of the eastern slope of Mt.Taihangshan,and is located in the central-south segment of the nearly NS-striking Trans-North China Orogen.Garnet-bearing metapelitic gneisses and plagioclase-amphibole gneisses are exposed in the south and middle parts of the complex.These rocks preserve different metamorphic mineral assemblages formed during the prograde,peak and post-peak decompression stages,respectively.The prograde metamorphic assemblages （M1） are mineral inclusions preserved in the garnet porphyroblasts,the peak metamorphic assemblages （M2） are represented by the ＂garnet-rims＂ and the matrix minerals,whereas the retrograde assemblages （M3） are composed of amphibole＋plagioclase＋quartz symplectites rimming the garnet porphyroblasts in the plagioclase-amphibole gneisses.As for the metapelitic gneisses,the retrograde assemblages （M3） of biotite＋plagioclase＋quartz symplectites rim the garnet porphyroblasts.All garnet porphyroblasts preserve prograde chemical zoning in the metapelitic gneisses,and increasing of XMn and decreasing of Mg/（Mg＋Fe） in the quite narrow zones of the garnet rims reflect the post-peak decompression process.Thermobarometric computation shows that the metamorphic conditions of the plagioclase-amphibole gneisses are 640~710℃ at 8.2~8.6kbar for the M1 stage,810℃ at 12.1kbar for the metamorphic peak M2 stage,and 590~670℃ at 3.2~5.6kbar for the retrograde M3 stage,respectively.Furthermore,earlier work shows that the metamorphic conditions of the metapelitic gneisses are 660~690℃ at 9.0~9.2kbar for the M1 assemblages,and are 780℃ at 12.5kbar for the metamorphic peak M2 assemblages,respectively.The peak metamorphism of this terrane lies between the top of the medium-P/T series and the bottom of the high-P/T series.SHRIMP U-Pb dating of the metamorphic domains of zircons separated from a metapelitic gneiss specimen yielded a weighted mean age of 1821±17Ma.These rocks are deciphered to have undergone m

关 键 词：P-T轨迹 泥质片麻岩 斜长角闪片麻岩 温压计 华北克拉通中部带 赞皇变质杂岩 

分 类 号：P588.3[天文地球—岩石学]