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.

产于华北克拉通（North China Craton）北缘太古宙（Archaean）背景下汉诺坝新生代（Cenozoic）玄武岩中的幔源橄榄岩捕虏体（mantle peridotitic xenoliths），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，各项参数均存在显著变化。该类捕虏体的元古宙（Proterozoic）铼亏损年龄范围为0.8–2.2 Ga（十亿年），且该年龄与橄榄石Fo值（olivine Fo）整体呈显著相关关系。华北克拉通中部与南缘新生代玄武岩中的幔源捕虏体，绝大多数同样呈现与橄榄石Fo值相关的元古宙铼亏损年龄特征。此类铼-锇（Re-Os）年龄特征，与赋存于古生代（Palaeozoic）金伯利岩中的橄榄岩捕虏体所具有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捕虏体之间的年龄差异表明，现今岩石圈地幔（lithospheric mantle）在显生宙（Phanerozoic）期间并非主要通过新生增生形成，而是由古老岩石圈地幔经熔体-岩石相互作用（melt–rock interaction）改造而来。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（geochemical）数据与锶-钕（Sr-Nd）同位素特征，本研究证实岩石圈地幔中存在多期幔交代叠加作用（mantle metasomatic overprints）。本研究进一步表明，通过熔体-岩石相互作用实现的岩石圈改造，是显生宙期间岩石圈组分再富集（compositional refertilization）的重要机制之一。