华北花岗岩类的大地构造岩石化学特征

华北花岗岩类为酸性深成岩.以正长花岗岩和二长花岗岩为主,按照地洼学说的大地构造分类,它们分属于地槽、地台和地洼三个演化阶段,其岩石化学各具特征. 从地槽、地台至地洼阶段,华北花岗岩类具有明显的化学演化规律.例如,在化学成分方面表现为K_2O含量递增,而MgO和CaO含量递减;在岩石化学指数方面.表现为里特曼碱性指数、长英指数、钾质指数和碱度递增.而铝质指数,镁质指数和钠质指数则递减等等.

GEOTECTONO-PETROCHEM ICAL CHARACTERISTICS OF GRANITOIDS IN NORTH CHINA

The granitoids in North China are acidic plutonic rocks with the majority of the orthoclase granite and monzonitic granite. According to the geotectonic classification of diwa theory, those granitoids belong to three evolutional stages respectively, i.e.the geosynclinal, platform and diwa stages, and possess different petrochemical characteristics in each stage.From the geosyelinal stage to platform stage and to diwa stage, the chemical evolutional regularities of the granitoids are shown obviously. For example, in the chemical compositions the K_2O content is increasing while the contents of MgO and CaO are decreasing; and in the petrochemical indices, the Rittman alkaline index, felsic index, potash inedx and alkalinity are increasing, but the aluminous, magnesian and soda indices are decreasing.