麻山群孔兹岩系的地球化学特征  

GEOCHEMISTRY OF MASHAN-GROUP KHONDALITE SERIES

作　　者：姜继圣[1] 

机构地区：[1]长春地质学院,130061

出　　处：《地球化学》1993年第4期363-372,共10页Geochimica

摘　　要：系统的地球化学研究,揭示出麻山群孔兹岩系岩石具有与典型的太古后碎屑沉积物相同的稀土分布模式。稀土总量高,轻稀土富集,重稀土亏损,具明显的负铕异常。它们的微量元素分布,也表现出太古后沉积物的典型特征。结合这些岩石富钾贫钠的性质以及原岩中大量石英砂岩的存在,认为它们的原始沉积物主要来源于一个被风化和剥蚀的富钾花岗质深成侵入体。它们是稳定克拉通构造环境下形成的陆棚浅海沉积物。并根据麻山群的形成时代,对佳木斯地块的太古地壳演化进行了探讨。The Mashan-group khondalite series was formed from aluminium-rich and gra-phite-bearing metasediments including highly aluminous garnetsillimanite schists,sil-limanite-garnet-cordierite gneisses,quartzose schists-felsic gneisses,graphite schists,marbles,calc-silicate rocks,and some impersistent layers of intermediate to basicgranulites.An attempt has been made to elucidate the geochemistry of the Mashangroupkhondalite series and the implications for its provenance and tectonic setting.These rocks are characterized by high Al and K,low Na and Ca,and K_2O>Na_2O.There are remarkable negtive correlations between the contents of SiO_2 andthe abundances of Al_2O_3 and TiO_2,and positive correlations between Al_2O_3 and Ti_2O.Compositional variations show that they are typically sedimentary in origin.The REE distribution patterns in Mashan-group metamorphic rocks are charac-terized by LREE enrichment,HREE depletion and significant negtive Eu anomalieswith Eu/Eu~*=0.34—0.65,typical of the post-Archean terrigenous sediments(suchas PAAS and NASC).Most of them have very high total REE abundances,about 3times those of PAAS and NASC.In terms of its trace elements the Mashan-group khondalite series is enrichedin large ion lithophile elements(LILE)and high field strength elements(HFSE)but depteted in ferromagnesian trace elements,also indicating their distribution pat-terns are typical of post-Archean sedimentary rocks.The REE patterns characterized by strong Eu depletion,high K_2O/Na_2O ratiosand large amounts of quartzose sandstone in protoliths suggest that the Mashan-groupkhondalite series must have been derived from weathering and erosion of K-richgranitic plutons which constitute the precursor of later widespread granitic crutchat the end of Archean.The observed Eu depletion is thought to have been inherited from the K-richgranitic source,wich was derived from partial melting of an early crust of the Jiamusimassif.

关 键 词：地球化学 孔兹岩系 麻山群 稀土族 

分 类 号：P588.21[天文地球—岩石学]