Abstract
Nine pieces of gabbroic xenoliths from Hannuoba were examined for their major and trace elements and Nd, Sr and Pb isotopes. The results show that the gabbroic xenoliths are of more mafic basaltic composition. Their abundances show narrow variations in major elements. The trace element contents are highly variable in contrast with those of host basalts and lherzolite xenoliths. The gabbroic xenoliths are rich in Nd (0.51159–0.51249), Sr (0.70491–0.70768) and low in radiogenic Pb(16.283–17.046, 15.191–15.381 and 36.999-37.476), significantly different from basalts and lherzolites in isotopic space. The calculated Nd and Pb model ages are about 3.0–3.5 Ga. The rocks have relatively low equilibriumT(~850°C) andP (0.8–0.9 GPa). They could be interpreted to be the product of upper mantle melting at the boundary between the lower crust and the upper mantle. Their chemical and isotopic variations can be ascribed to different degrees of melting, segregation and long-term evolution.
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