Comprehensive refertilization of lithospheric mantle beneath the North China Craton: further Os—Sr—Nd isotopic constraints

摘要

Mantle peridotitic xenoliths in Cenozoic basalts from Hannuoba, on the northern margin of the Archaean North China Craton, have variable Re (0.01-0.30 ppb) and Os (2.7-6.2 ppb) abundances and ~l87Os/ ~188Os (0.1138-0.1236) ratios. These xenoliths yield a range of Proterozoic Re depletion ages of 0.8-2.2 Ga that show a general correlation with olivine Fo. Mantle xenoliths in Cenozoic basalts from the centre and southern margin of the North China Craton also overwhelmingly show Proterozoic Re depletion ages that correlate with olivine Fo. These Re—Os age features are completely different from those of Palaeozoic kimberlite-borne peridotitic xenoliths, which have Archaean ages. This age distinction between xenoliths associated with Palaeozoic and Cenozoic volcanism indicates that the present-day lithospheric mantle was dominantly not newly accreted during the Phanerozoic but instead was transformed from the ancient lithospheric mantle by interaction with melts. The Re—Os data in combination with the geochemical and Sr—Nd isotopic features of peridotitic xenoliths from the Cenozoic basalts of the North China Craton demonstrate the presence of multiple stages of mantle metasomatic overprints in the lithospheric mantle. This study thus further indicates that lithospheric transformation through melt—rock interaction could be an important mechanism for compositional refertilization during the Phanerozoic.