大别山北部饶拔寨超镁铁岩体微量元素地球化学  

Trace element geochemistry of Raobazhai ultramafic complex, North Dabie Mountain

作　　者：支霞臣[1] 靳永斌[1] 孟庆[1] 高天山[1] 

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《岩石学报》2004年第3期463-472,共10页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程项目(编号:KZCX2-107);国家自然科学基金(编号:40173009);国家重点基础研究发展规划项目(编号:G1999075503)

摘　　要：本文报道了饶拔寨超镁铁岩体的5个钻孔15个岩心样品的主量元素和微量元素成分。该岩体由上、下两部分构成。岩性以方辉橄榄岩为主,纯橄榄岩和二辉橄榄岩次之。主量元素成分表明岩体由饱满地幔经过不同程度部分熔融,形成了亏损程度不同的大陆岩石圈地幔。总体上下部岩体较上部亏损程度大。原始地幔标准化REE等不相容微量元素丰度模式表明岩体在熔融作用后又经过了地幔交代作用,形成不同程度LREE和LILE的富集。样品中有角闪石和金云母等含水矿物,表明有实性地幔交代作用。对比LREE与LILE的富集特征,表明可能有两类地幔交代作用,有两种不同性质的交代介质,LREE和Sr等的富集可能与硅酸盐熔体有关,而Rb、Ba、K等的富集可能与俯冲带流体活动有关。总体上下部岩体的交代作用较上部岩体的强。The major and trace element compositions of 15 samples of 5 drill cores from Raobazhai ultramafic complex are reported here. The complex is composed of upper and lower parts. The ultramafic rocks are composted of predominantly harzburgite and subordinately dunite and lherzolite. It is deduced that the ultramafic complex is a part of sub-continental lithospheric mantle with different depletion of basaltic components by partial melting of fertile mantle in different degrees from the covariance among the major element compositions of the complex. Also, the complex experienced cryptical and modal mantle metasomatism that resulted in the enrichment of incompatible elements and formation of hydrated mineral phases such as amphibole and phlogopite after mantle partial melting. Comparing LREE and LILE enrichments, it is indicated that there exist two kinds of metasomatism by two different metamorphic agencies in the complex. The LREE enrichments were probably related with silicate melt from the asthenosphere by small degree partial melting, while the LILE (for example, Rb, Ba and K etc.) enrichments were probably related with the liquid from the subduction zone by devolatilization. The effect of metasomatism in lower part of the complex was stronger than that in upper part.

关 键 词：地幔交代作用 大陆岩石圈地幔 微量元素地球化学 饶拔寨超镁铁岩体 

分 类 号：P588.125[天文地球—岩石学] P595[天文地球—地质学]