云南苍山变质带前寒武纪正变质岩的地球化学特征及其形成时代  

Geochemical characteristics and formation time of Precambrain orthometamorphites in the Cangshan metamorphic belt, Yunnan

作　　者：邓尚贤[1] 王江海[1] 朱炳泉[1] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球化学》2001年第2期147-154,共8页Geochimica

基　　金：中国科学院"九五"重大 B项目资助! (KZ951- B1- 413);中国科学院院长基金资助项目

摘　　要：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～ 1.4 Ga)；变碱性玄武质岩墙形成于中新元古代 (1.3～ 0.8 Ga)。已发表的 Sm- Nd等时线年龄 (2 408 Ma)其 Sm/Nd比值变化很小，故没有实际的地质意义。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 setting. The metatholeiites show higher 143Nd/144Nd (0.512 6～ 0.512 8) and alkaline meta basaltic dykes show larger variation range of 143Nd/144Nd (0.511 8～ 0.512 7). Sm- Nd isochron trend suggest that the metatholeiites were formed in the period of late Paleoproterozoic to Mesoproterozoic (2.0～ 1.4 Ga), and the metamorphosed alkaline basaltic dykes were formed during Mesoproterozoic to Neoproterozoic (1.3～ 0.8 Ga). The published Sm- Nd isochron of 2 408 Ma is actually a false isochron, and does not reflect an actual geological event due to too narrow interval of Sm/Nd ratios.

关 键 词：变基性岩 地球化学 形成时代 苍山变质带 云南 前寒武纪 变质岩 钐-钕同位素 

分 类 号：P588.3[天文地球—岩石学] P59[天文地球—地质学]