汉诺坝幔源橄榄岩包体的微量元素和Re-Os同位素地球化学:SCLM的性质和形成时代  

The trace element and Re-Os isotopic geochemistry of mantle-derived peridotite xenoliths from Hannuoba: Nature and age of SCLM beneath the area.

作　　者：夏琼霞[1] 支霞臣[1] 孟庆[1] 郑磊[1] 彭子成[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5期1215-1224,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金(编号:40173009);国家高等教育博士点科研基金(编号:1999035816)

摘　　要：本文报道了汉诺坝新生代碱性玄武岩中地幔橄榄岩包体的主量、微量元素和Re-Os同位素。14个尖晶石橄榄岩Re、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,与^(187)Re/^(188)Os比值相关性不好,但与熔体亏损指标如重稀土元素Yb的含量、全岩Al_2O_3的百分含量有很好的线性关系,可能反映了地幔熔融后的Re或/和Os的活动。全岩Al_2O_3、CaO、TiO_2含量均与MgO有很好的负相关性,全岩原始地幔标准化REE丰度模式呈现了LREE亏损,表明该区橄榄岩包体是由软流圈地幔经过部分熔融,亏损了玄武质组分后形成的。由Os同位素代理等时线得到该区陆下岩石圈地幔的形成年龄为1.7～2.0Ga,表明尖晶石相橄榄岩所代表的岩石圈地幔是中元古代的陆下岩石圈地幔减薄后的残留体。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 similar to 0.193 ng/g and 1.237 similar to 4.304 ng/g, respectively, and the Os-187/(188) Os ratio is 0.1183 similar to 0.1244. The osmium isotope compositions do not correlate well with Re-187/Os-188, but correlate well with indices of basaltic melt extraction, such as the content of Yb and the weight percent of Al2O3, which may reflect mobility of Re and/or Os after mantle partial melting. The negative correlations between Al2O3, CaO, TiO2 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 similar to 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.

关 键 词：RE-OS同位素 微量元素 橄榄岩包体 汉诺坝 

分 类 号：P588.125[天文地球—岩石学] P597.3[天文地球—地质学]