冀北异剥钙榴岩的岩石学、地球化学及锆石SHRIMP年代学研究  

PETROLOGY,GEOCHEMISTRY AND ZIRCON SHRIMP GEOCHRONOLOGY OF RODINGITES FROM THE NORTH HEBEI PROVINCE,CHINA

作　　者：严刚[1] 倪志耀[1] 翟明国[2] 卢俊生[1] 赵太平[3] 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]中国科学院地质与地球物理研究所,北京100029 [3]中国科学院广州地球化学研究所,广东广州510460

出　　处：《矿物岩石》2008年第1期21-30,共10页Mineralogy and Petrology

基　　金：国家自然科学基金项目(40472041,40234050)

摘　　要：对产于红旗营子群黑云斜长片麻岩或黑云斜长变粒岩之中的冀北异剥钙榴岩进行岩石学研究表明，其主要矿物成分有富钙石榴石、钠长石或钡冰长石以及角闪石等，另有少量异剥辉石（透辉石）残留，其形态多呈大小不等的透镜状或团块状。异剥钙榴岩的化学成分总体表现为SiO2（36．63％～44．46％）明显不饱和，富CaO（17．81％～27．78％）、FeO^＊（9．76％～18．36％）和贫MgO（0．77％～4．56％）的特征。异剥钙榴岩化作用除导致岩石的CaO升高而SiO2降低外，REE总量和某些不活动性微量元素（Zr，Hf，Nb，Ta，Y和V等）含量也相应增加，但REE配分模式变化太大。冀北异剥钙榴岩的原岩可能为蛇绿岩型异剥辉长岩，经历过早期的钙交代和晚期的钡交代。前者以岩石中发育富钙石榴石为标志，后者则形成钡冰长石，是富钡流体交代钠长石的结果。冀北异剥钙榴岩的锆石SHRIMP年龄为396．4Ma±5．3Ma。The rodingites from the north Hebei Province occurred as separate tectonic lenses within biotite plagioclase gneisses or leptynites of the Hongqiyingzi Group. Their mineral assemblage was characterized by major components of Ca-rich garnet, albite or hyalophane and amphibole and minor mineral of residual diallage （diopside）. Rodingites were SiO2-undersaturated, CaO-and FeO^＊ -rich and MgO- poor, and the compositional varieties of SiO2 ,CaO,FeO^＊ and MgO were 36.63%-44.46%0, 17.81% -27.78%0,9.76%-18.36% and0.77%-44.56%0 respectively. Geochemical characteristics of rodingites indicated that CaO content may rise while SiO2 decrease during rodingitization,and ∑REE and some immobile elements,such as V,Y,Zr, Hf,Nb and Ta, may be changed, but REE distribution pattern does not change basically. The protolith of rodingites may be the ophiolitic diallage gabbro,and two main stages have been identified in the formation of rodingites. The early stage is the calcic metasomatism characterized by existence of Ca-rich garnet,the late stage is the barium metasomatism characterized by formation of hyalophane,which is the result of barium metasomatism between barium-rich fluid and albile. Zircon SHRIMP isotopic dating of rodingite reveals a weighted mean age of 396.4 Ma±5.3 Ma, which is considered as rock-forming age of the rodingite.

关 键 词：异剥钙榴岩 岩石学 地球化学 锆石SHRIMP年代学 冀北 

分 类 号：P597.2[天文地球—地球化学] P597.3[天文地球—地质学]