黄骅盆地中新生代火山岩岩相及岩石化学特征

Petrographic and Petrochemical Characteristics of the Mesozoic-Cenozoic Volcanic Rocks in Huanghua Basin

通过对渤海地区黄骅盆地中新生代火山岩进行典型的岩芯取样、岩相及全岩分析 ,并结合K Ar法测年、微量元素和同位素地球化学分析 ,得出以下结论 :主要岩石类型有新生代老第三纪玄武岩、中生代晚白垩世玄武粗安岩、中生代晚白垩世粗面英安岩和流纹岩和中生代早三叠世英安岩。晚中生代火山岩岩石的主量元素丰度呈双峰分布 ,从老到新 ,火山岩主元素中SiO2 减少 ,Fe2 O3、FeO、CaO、MgO、TiO2 、P2 O5、MnO有所增加。新生代玄武岩可能源自亏损的软流圈地幔 ,晚白垩世玄武粗安岩源自玄武质组分亏损和受到富集改造的岩石圈地幔 ,晚白垩世及早三叠世长英质火山岩可能源自地壳组分的部分熔融。

Based on data collected from typical boreholes and petrographic and petrochemical characteristics,combined with K Ar dating,trace element geochemistry and isotopic composition of the Mesozoic Cenozoic volcanic rocks in Huanghua basin of Bohai region,this paper has discussed geochemical features of these volcanic rocks.The rocks fall into four groups,namely Cenozoic basalt,Late Cretaceous basaltic trachyandesite,Late Creatceous trachydacite and liparite,and Early Triassic dacite.The distribution of the abundances of major elements in Late Mesozoic shows a typical bimodal pattern.With the evolution of the volcanic rocks,the amount of SiO 2 decreased gradually,whereas the content of Fe 2O 3,FeO,CaO,MgO,TiO 2,P 2O 5 and MnO increases step by step.The Cenozoic basalt was derived from the asthenospheric mantle.The Late Cretaceous basaltic trachyandesite was derived from the enriched lithospheric mantle.In Late Cretaceous and Early Palaeogene,the felsic volcanic rocks might have been derived from fractional melting of the crust.