Major and trace element studies on garnets from Palaeozoic kimberlite-borne mantle xenoliths and megacrysts from the North China craton

Palaeozoic kimberlites from Mengyin, Shandong and Fuxian, Liaoning, eastern China, contain plenty of mantle xenoliths (peridotites, eclogites) and meg acrystic minerals. In-situ electron and ion microprobe analyses on garnets from these xenoliths and megacrysts as well as relevant theoretical modelin g reveal that these garnets were more or less affected by kimberlitic silic ate melts prior to the encapsulation, in which eclogitic garnet from Fuxian , Liaoning Province, was little affected by mantle metasomatism, representi ng the primitive depleted mantle composition. In contrast, garnet from Meng yin, Shandong Province, and all megacrystic garnets were completely modifie d by metasomatic melts/fluids and reached perfectly chemical equilibrium, t hus reflecting the characteristics of the enriched mantle. It is inferred t hat old lithospheric mantle beneath the North China craton was fairly stron gly modified by metasomatism before Palaeozoic kimberlite emplacement.