康滇地轴冕宁杂岩的Sm-Nd同位素地质年代学初步研究

通过冕宁杂岩的稀土元素、微量元素及Sm—Nd同位素组成分析发现：杂岩核部二辉片麻岩微量元素以Th富集为特征，而典型的太古代灰色片麻岩则为Th亏损；分布于杂岩边部的英云闪长质片麻岩及花岗质片麻岩与灰色片麻岩宏观特征相似，且有Th，Nb亏损，但强不相容元素强烈富集，配分型式强烈右倾，也有别于太古代灰色片麻岩。两类岩石的Nd模式年龄均小于2000Ma，推测该杂岩的部分岩石原岩(二辉片麻岩及斜长角闪岩)形成时代可能为早元古代晚期，它们在晋宁期强烈的构造岩浆活动中发生角闪岩相变质。岩石的Nd模式年龄(2008Ma～766Ma)显示该区在元古代有较大规模的地壳增长，基底岩石的形成时代有别于扬子地台周边地区。

PRELIMINARY STUDY OF Sm-Nd ISOTOPIC GEOCHRONOLOGY FOR MIANNING COMPLEX IN KANGDIAN AREA

It is well-knowen that Kangdian axis has been regarded as an old crystalline basement for many years.Mianing Complex is one famous example because its rock assemblage include tonatite and granodiorite and granitic gneiss and high-grade metamorphic two-pyroxene gneiss.In this paper ,earth element and trace elemet and Sm-Nd isotope analytical results have been obtained,the results display the Th content of whole rock is enriched,which is very different from typical Archean Gray Gneisses Meantime, all Nd modal age are less than 2 000 Ma,so the formation age of complex is not more than Paleoproterozoic,it may be inferred as magmatic intrusions produced in Jinning tectonic movement.However,from mang Nd modal ages,three period are seen clearly:1 800 Ma~2 000 Ma,1 450 Ma~1 650 Ma,750 Ma~850 Ma,they may display crustal growth in Kangdian area.