Genetic mineralogical study of olivine-bearing diorite xenoliths in Guzhen diorite,Handan-Xingtai area,Southern Hebei Province
The mantle xenoliths and xenocrysts contained in the Mesozoic intrusive rocks are the direct physical evidence from the lithospheric mantle.The lithospheric mantle thinning occurred in the center of the North China Craton,where this region is located,during the Mesozoic era.The dominant mechanism,effect degree and specific process of this event have not been reached consensus yet.In this study,olivine,pyroxene and other xenocrysts were found in the diorite xenoliths of Guzhen intrusions in Handan-Xingtai area,which are important research objects for the study of the destruction of the North China craton.Through genetic mineralogical study of different minerals in the xenoliths,their genesis and evolution process were discussed,and the thinning mechanism of Mesozoic lithosphere in North China Craton was constrained.The following conclusions are obtained:the chemical composition characteristics of olivine in the sample(w(CaO)=0.03％-0.07％,w(Al2O3)=0-0.03％,w(MnO)=0.30％-0.46％)and the imbalance with the host magma indicate that the olivine are the disintegrated products of mantle peridotite(xenocrysts).And the clinopyroxene are in equilibrium with the magma,belonging to the cumulates of early magma,which is recycled in the magmatic system;The low Fo value anomaly of olivine(Fo=75％-80％)and the compositional zone of clinopyroxene(relatively rich in magnesium in the core and iron in the rim)indicate the existence of mineral-magmatic reaction and its influence on the original magma.Amphibole and biotite are rich in magnesium,both of which belong to crust-mantle mixed origin,implying the existence of crust-mantle interaction.The extensive occurrence of mineral-magmatic Fe-Mg exchange reaction in the early magmatic period provides evidence for the origin of high magnesium diorite and the existence of delamination in this area.
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