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

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 ¹⁸⁷Os/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.

采自太古宙华北克拉通北缘汉诺坝新生代玄武岩中的幔源橄榄岩捕虏体，其铼（Re）丰度介于0.01~0.30 ppb，锇（Os）丰度介于2.7~6.2 ppb，¹⁸⁷Os/¹⁸⁸Os比值介于0.1138~0.1236之间。这些捕虏体呈现出0.8~2.2 Ga的元古宙Re亏损年龄区间，且该年龄与橄榄石Fo值存在总体相关性。华北克拉通中部与南缘新生代玄武岩中的幔源橄榄岩捕虏体，同样以元古宙Re亏损年龄为主体，且该年龄与橄榄石Fo值亦存在相关性。上述Re-Os同位素年龄特征，与古生代金伯利岩载带的橄榄岩捕虏体所呈现的太古宙年龄特征完全不同。古生代与新生代火山作用相关的捕虏体之间的年龄差异表明，现今的岩石圈地幔主体并非在显生宙期间新生增生形成，而是通过熔体-岩石相互作用，由古老岩石圈地幔改造演化而来。结合华北克拉通新生代玄武岩中橄榄岩捕虏体的地球化学与Sr-Nd同位素特征，本次Re-Os同位素数据证实了岩石圈地幔中存在多期幔源交代叠加作用。本研究进一步指出，通过熔体-岩石相互作用实现的岩石圈地幔改造，可能是显生宙期间地幔组分再肥沃化的重要机制之一。