摘要
Re-Os同位素体系为研究地幔的成分-结构-演化提供了新的地球化学示踪和定年的工具．上地幔Os同位素组成演化的球粒陨石模型是Re-Os体系用于地幔物质定年的基础,尤其在采用Re亏损模式年龄和Os同位素代理等时线年龄时．综合了铁陨石和各类球粒陨石、地幔橄榄岩包体和蛇绿岩豆荚状铬铁矿的Re-Os同位素体系研究的近期成果,为认识对流上地幔Os同位素组成的演化提供了制约．对河北遵化蛇绿岩豆荚状铬铁矿岩的研究,获得新太古代(2．5 Ga)时形成豆荚状铬铁矿的对流上地幔的187Os／188Os=0．110 2,与球粒陨石型模式的一致．文献中常用的球粒陨石模式的参数如下: 地球形成时(4．558 Ga)初始值187Os／186Os为0．095 31,现代值分别采用碳质球粒陨石的187Os／186Os比值为0．127 0和原始上地幔(PUM)的187Os／186Os比值为0．129 6,PUM与普通球粒陨石和顽火球粒陨石的187Os／186Os比值接近．
The Re-Os isotope system is a new technique of geochemical dating and tracing, specially in the basic subject of the composition-structure-evolution of the earth＇s mantle. The chondritic model of the evolution of Os isotope compositions in the upper mantle is the important background of Re-Os isotope dating for the mantle-derived materials, especially using Re depleted model age and Os proxy isochron methods. The comprehensive studies of various meteorites, mantle-derived peridotitic xenoliths and ophiolitic podiform chromites offered strong constraints on the evolution of Os isotope compositions in the convective upper mantle. We offer the Os isotope composition of convective upper mantle in the Irate Archean, based on ophiolitic podiform chromitites from Zunhua, Hebei Province, which is 0. 110 2. This is consistent with the chondritic model. The parameters of the chondrite model in common use are.. the initial osmium isotope ratio is 0. 095 31 at 4. 558 Ga; the present osmium isotope ratios are 0. 127 0 of carbonaceous chondrite and 0. 129 6 of the primitive upper mantle respectively. The latter is similar to that of ordinary and enstatite chondrites.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2006年第1期23-30,共8页
Earth Science-Journal of China University of Geosciences
基金
国家自然科学基金项目(Nos.40473008
40572036)
