大别山镁铁质下地壳的Pb同位素成分だ醋粤窕匝业闹圃.doc

大别山镁铁质下地壳的Pb同位素成分 だ醋粤窕匝业闹圃 关键字：大别,大别山,别山,镁铁质,铁质,下地,地壳,同位,同位素,成分 大别山镁铁质下地壳的Pb同位素成分 だ醋粤窕匝业闹圃 本文为Word文档，感谢你的关注！ 　　摘要：北大?e高温超高压杂岩带中榴辉岩的岩石学和地质年代学研究已经证明它们为华南板块新元古代镁铁质下地壳岩石经三叠纪深俯冲变质成因。基于此，开展了北大别榴辉岩的Pb同位素地球化学研究。结果表明：北大别榴辉岩表现出与北大别片麻岩相似的低放射性成因Pb同位素特征，并具有更低的N（208Pb）/N（204Pb）值；其初始Pb同位素组成分别为N（206Pb）/N（204Pb）i=15217～17.522，N（207Pb）/N（204Pb）i=15077～15540和N（208Pb）/N（204Pb）i=35219～38082，表现出目前已知的大别造山带3个含榴辉岩的超高压变质岩片中最低的Pb同位素组成，这进一步证明北大别榴辉岩的原岩来自于俯冲镁铁质下地壳；北大别榴辉岩表现出较宽的Pb同位素组成变化范围，其中最低的Pb同位素组成源自于具有低w（U）/w（Pb）值、低w（Th）/w（U）值演化特征的晚太古代至古元古代镁铁质下地壳，而相对较高的Pb同位素组成则继承于新元古代底侵的幔源岩浆，表明北大别榴辉岩的Pb同位素特征是幔源岩浆混染古老镁铁质下地壳的结果。与大别山中生代埃达克质岩的Pb同位素对比研究表明，早白垩纪拆沉再循环的陆壳物质中不仅含有镁铁质下地壳岩石，还含有长英质下地壳物质，大别山深部的长英质下地壳随镁铁质下地壳一起拆沉并再循环进入地幔。 　　关键词：地球化学；榴辉岩；Pb同位素；镁铁质下地壳；新元古代；地壳混染；大陆深俯冲；北大别 　　P597文献标志码：A 　　Abstract： The eclogites from the North Dabie hightemperature and ultrahighpressure complex zone in central China have been previously documented by petrology and geochronology to be transformed from the Neoproterozoic mafic lower continental crust underneath South China block during the Triassic continental deep subduction. An integrated study of Pb isotopic geochemistry on the whole rocks and omphacites of the eclogites from North Dabie was carried out， providing new insight into the Pb isotopic compositions of the mafic lower continental crust. The results show that the eclogites here display low radiogenic Pb isotopic characteristics similar to the surrounding gneisses with even lower N（208Pb）/N（204Pb）； （N（206Pb）/N（204Pb））i， （N（207Pb）/N（204Pb））i and （N（208Pb）/N（204Pb））i of the eclogites are 15.21717.522， 15.07715.540 and 3521938.082， respectively， showing the lowest Pb isotopic compositions in the three eclogitebearing ultrahighpressure metamorphic slices of Dabie orogen， and documenting a mafic lowercrustal origin of their protoliths； the variation range of Pb isotopic compositions of the eclogites is large， and the lowest Pb isotopic compositions are demonstrated to be derived from the Paleoproterozoi