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

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.