新疆包古图中酸性岩浆侵位的P-T-fO_2条件及岩体地球化学研究  

Emplacement of the Intermediate and Acid Magmatic Rocks in Xinjiang:Constraints from the P-T-fO_2 and Geochemistry

作　　者：魏少妮[1] 朱永峰[1] 

机构地区：[1]北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室,北京100871

出　　处：《地质学报》2010年第7期1017-1029,共13页Acta Geologica Sinica

基　　金：国家"十一五"科技支撑计划重点项目(编号2006BAB07B08)资助的成果

摘　　要：西准噶尔包古图地区I号、II号、V号和VII号岩体(花岗闪长斑岩和白岗岩)侵位于下石炭统火山-沉积地层中。侵入岩分为新鲜花岗闪长斑岩、绢云母-绿泥石化花岗闪长斑岩和硅化花岗闪长斑岩三种,三类岩石具有相似的重稀土组成,而轻稀土的分异程度依次增强。与新鲜样品相比,蚀变花岗闪长斑岩的Rb、Th、U和Nb、Zr、Hf等元素明显富集,而Sr和Ti含量略低。花岗闪长斑岩具有较低的初始87Sr/86Sr比值(0.703634～0.703760)和较高的初始143Nd/144Nd比值(0.512575～0.512660),指示亏损地幔源区。包古图I号、II号花岗闪长斑岩结晶于中温(695～766℃)、低压(1.1～2.9kbr)条件下,具有较高的氧逸度(LogfO2=-15～-17),岩石形成之后经历了一个氧逸度升高的演化过程。绢云母-绿泥石化和硅化过程中成矿元素Cu的含量明显升高,说明了流体作用对成矿的控制意义。The Baogutu porphyry body I,II,V and VII（granodioritic and alaskite）intrude into the Lower Carboniferous volcanic-sedimentary strata.Granodioritic porphyry can be divided into three types：fresh granodioritic porphyry,sericited-chlorited granodioritic porphyry and silicified granodioritic porphyry.They have similar HREE patterns but LREE differentiation is gradually strengthened.Compared with fresh samples,altered granodioritic porphyries are enriched in Rb,Th,U,Nb,Zr and Hf,and have lower Sr and Ti concentrations.Granodioritic porphyries have low initial 87Sr/86Sr ratio（0.70352 ~ 0.70365）and high 143Nd/144Nd ratio（0.512555 ~ 0.512635）indicating depleted mantle source.Porphyry body I and II were formed at a medium temperature（695 ~ 766℃）and low pressure（1.1 ~ 2.9kbr）;the calculated oxygen fugacity for the porphyry bodies（ranging from-15 to-17）indicates that the fugacity gradually increased after rock formation.Ore-forming element Cu was distinctively concentrated during sericitization-Chloritization and silicification,suggesting constraint of hydrothermal process on mineralization.

关 键 词：地球化学 氧逸度 花岗闪长斑岩 包古图 新疆 

分 类 号：P584[天文地球—岩石学]