滇西富碱斑岩及其中包体岩石的地幔流体交代作用特征

滇西富碱斑岩体中,有多处产出深浅来源不同的包体岩石。针对寄主岩石和包体岩石的岩相学和岩石化学成分的对比研究发现:寄主岩石较包体岩石更富S iO2,A l2O3,N a2O和K2O,而包体岩石较寄主岩石更富C aO,M gO,F e2O3和F eO,岩石蚀变以角闪石化、钠黝帘石化和硅化为主,结合具超基性岩性的包体岩石发育碎裂结构,碎裂粒间出现与交代成因角闪石共生的微晶硅质、碳质、碳酸盐和金云母等表现地幔流体显交代作用的特征矿物组合,由此判定交代主岩和包体岩石的流体富含碱质和硅质,是与富碱岩浆同源的来自富集地幔源区的地幔流体,其交代作用的功能和能量明显优于一般意义上的地壳流体作用,而此交代作用促进了成矿元素和挥发份的聚集,且富碱斑岩与地幔流体的交代作用之间存在有利的时差关系。

THE CHARACTERISTICS OF THE MANTLE FLUID METASOMATISM OF THE ALKALI-RICH PORPHYRIES AND ITS XENOLITHS IN WESTERN YUNNAN

Xenoliths derived from different depth were found in the alkali-rich porphyries in western Yunnan.The petrographic features and petrochemistry data from the porphyries(host rocks) and its xenoliths were studied.The research showed that the host rocks were rich in SiO_2,Al_2O_3,Na_2O and K_2O,the xenoliths were rich in CaO,MgO,Fe_2O_3 and FeO respectively.And amphibolization,saussuritization and silicification were main alteration characters.Cataclastic texture was found in the ultrabasic xenoliths.The texture was filled with microcrystalline siliceous matters,carbonaceous matter,carbonates and phlogolites,and these matters were intergrowth with amphibole resulted from replacement.The mineral assemblages indicates the characters of mantle fluids of obvious metasomatism.It is considered that the silicon-alkali-rich fluids,were mantle fluids.The fluids were consanguineous with alkali-rich magma and originated from enriched mantle,and its function and energy are much powerful than crust fluids.This paper revealed the deep geologic process of large-scale mineralization in studied areas.