云南苍山变质带前寒武纪正变质岩的邓尚贤地球化学特征及其形成时代

摘要

Two types of metabasites have been recognized on the basis of elemental geochemical studies in the Cangshan metamorphic belt in Yunnan. The Ti-Zr-Y diagram and REE patterns indicate that one is a metatholeiite formed in an E-MORB setting, and another is a metamorphosed alkaline basaltic dyke formed in a within-plate rnsetting. The metatholeiites show higher 143Nd/144Nd (0.5126～0.5128) and alkaline meta basaltic dykes show larger variation range of 143Nd/144Nd (0.5118～ 0.5127).Sm-Nd isochron trend suggest that the metatholeiites were formed in the period of late Paleoproterozoic to Mesoproterozoic (2.0～1.4Ga), and the metamorphosed alkaline basaltic dykes were formed during Mesoproterozoic to Neoproterozoic (1.3～0.8Ga). The published rnSm-Nd isochron of 2 408 Ma is actually a false isochron, and does not reflect an actual geological event due to too rnnarrow interval of Sm/Nd ratios.%元素地球化学研究结果表明，苍山变质带内发育两类正变质基性岩：一类为形成于富集型MORB构造环境的变拉斑玄武岩，另一类为形成于板内构造环境的变碱性玄武质岩墙。Sm-Nd同位素体系研究表明，变拉斑玄武岩形成于晚古元古代至中元古代(2.0～1.4Ga)；变碱性玄武质岩墙形成于中新元古代(1.3～0.8Ga)。已发表的Sm-Nd等时线年龄(2408 Ma)其Sm/Nd比值变化很小，故没有实际的地质意义。