Recycling of lower continental crust in the Trans-North China Orogen: Evidence from zircon dating of mantle composite xenoliths
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Abstract: 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 187 Os/ 188 Os (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. Supplementary material: Analytical methods and geochemical data are available at http://www.geolsoc.org.uk/SUP18334 .
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Abstract This paper reports the oxygen isotope compositions of olivine from dunite, wehrlite, harzburgite, and lherzolite xenoliths entrained by the Early Cretaceous high‐Mg diorites and Late Cretaceous basalts in the central and eastern North China Craton, with the aim of constraining processes that happened in the lithospheric mantle. Olivine oxygen isotope compositions were analyzed in situ using secondary ion mass spectrometry. Olivine δ 18 O of harzburgite and lherzolite xenoliths hosted in the Fushan and Tietonggou diorites with Archean and Paleoproterozoic rhenium‐depletion model ages ranges from 5.1‰ to 5.8‰, similar to olivine from spinel lherzolite xenoliths in the Late Cretaceous Fuxin basalts (olivine δ 18 O = 5.2–5.4‰) and typical mantle olivine. In contrast, olivine δ 18 O from dunite and wehrlite xenoliths ranges from 6.1‰ to 7.7‰, significantly higher than the typical mantle values. The olivine oxygen isotope data, combined with the petrologic observations, mineral compositions, and whole‐rock trace element and Sr‐Nd‐Os isotope compositions of the peridotite, suggest that the peridotites in Early Cretaceous high‐Mg diorites had been affected by interaction with melt derived from delaminated continental crust. These data provide compelling evidence for the recycling of continental crust in an intracontinental setting.
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