The trace element and Re-Os isotopic geochemistry of mantle-derived peridotite xenoliths from Hannuoba: Nature and age of SCLM beneath the area.
The trace element and Re-Os isotopic geochemistry of mantle-derived peridotite xenoliths from Hannuoba: Nature and age of SCLM beneath the area.
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作者：
Xiao Qiong
本研究获得了汉诺坝新生代碱性玄武岩中夹带的地幔橄榄岩捕虏体的主量元素、微量元素和Re-Os同位素数据。 14个尖晶石橄榄岩样品的Re和Os含量分别为0.022～0.193ng/g和1.237～4.304ng/g，~(187)Os/~(188)Os比值为0.1183～0.1244。锇同位素组成与~(187)Re/~(188)Os相关性较差,但与玄武岩熔体萃取指标如Yb含量和Al_2O_3重量百分比相关性较好,这可能反映了地幔部分熔融后Re和/或Os的活动性。 Al_2O_3、CaO、TiO_2和MgO含量与整个岩石的贫化原始地幔标准化稀土元素模式之间的负相关性表明玄武岩熔体在部分熔融过程中从软流圈地幔中移出。橄榄岩捕虏体的锇代理等时线年龄为1.7～2.0Ga，因此该区现今由尖晶石二辉橄榄岩组成的上地幔很可能是中元古代SCLM岩石圈拆沉后的残余物。
The major elements, trace elements and Re-Os isotopic data of mantle peridotite xenoliths entrained in Hannuoba Cenozoic alkali basalts were obtained in this study. The contents of Re and Os of 14 samples of spinel peridotites are 0.022～0.193ng/g and 1.237～4.304ng/g, respectively, and the ~(187)Os/~(188)Os ratio is 0.1183～0.1244. The osmium isotope compositions do not correlate well with ~(187)Re/~(188)Os, but correlate well with indices of basaltic melt extraction, such as the content of Yb and the weight percent of Al_2O_3, which may reflect mobility of Re and/or Os after mantle partial melting. The negative correlations between Al_2O_3, CaO, TiO_2 and MgO contents and the depleted primitive mantle-normalized REE patterns of whole rock indicate the removal of basaltic melts from asthenosphere mantle during partial melting. The osmium proxy isochron age of the peridotite xenoliths is 1.7～2.0Ga, therefore the present upper mantle, consisting of spinel lherzolites, in this area is probably the residue of the Middle Proterozoic SCLM after lithosphere delamination.