Petrochemical characteristics of the Mesozoic-Cenozoic volcanic rock in Huanghua basin

Based on the data from typical core sampling, combined with K-Ar dating, petrochemistry,trace elemental geochemistry and isotopic compositions of the Mesozoic-Cenozoic volcanic rock in the Huanghua basin, Bohai region, the geochemical features of the volcanic rock were studied. The rocks fall into four groups: Cenozoic basalt,Mesozoic late Cretaceous basaltic-trachy-andesite, Mesozoic late Cretaceous trachy-dacite and liparite, and Mesozoic early Triassic dacite. The distribution pattern of the main elemental abundance of late Mesozoic shows a typical bimodal. Chronologically,for the volcanic rock,the amount of SiO2 decreases gradually,the contents of Fe-2 O-3,FeO,CaO,MgO,TiO2,P-2 O-5 and MnO increase little by little. The Cenozoic basalt is derived from the asthenospheric mantle. The late Cretaceous basaltic-trachy-andesite is derived from the enriched lithospheric mantle. In late Cretaceous and early Palaeogene,the felsic volcanic rock may be derived from fractional melting of the crust.