北京周口店侵入体特征及其侵位机制

FEATURES AND EMPLACEMENT OF THE ZHOUKQUDIAN STOCK, BEIJING

北京西部周口店花岗质岩株是一个多次脉动侵入的同心带状复式岩体。第一次侵入的石英闪长岩零星分布于岩体边缘;第二次侵入的花岗闪长岩为岩株主体,从中心到边缘分为三个逐渐过渡的同心相带。岩石的化学分析表明,从第一次的石英闪长岩到第二次的边缘相至中央相,SiO_2增加很快,Na_2O和K_2O增加缓慢,而MgO、FeO、Fe_2O_3、CaO、Al_2O_3则减少。岩石化学和矿物学特征表明,该岩体为Ⅰ型花岗岩体。岩体和热变质岩的构造特征表明,该岩株是底辟作用侵位的产物。

The Zhoukoudian granitoid stock in western Beijing is a concentric complex which was formed by repeated pulsative intrusions. The first intrusion is finegrained quartz diorite which scattered in the margin,and the second is granodio-rite which is the main part of the pluton. From the center to the margin, the latter is again divided into three gradually transitional concentric phase zones. Chemical analyses of the rocks indicate that SiO2 increases very quickly, and Na2O and K2O rise slowly, while MgO, FeO, Fe2O3, CaO and A12O3 decrease from the early intrusive body through the margin of the late intrusion to the center. Petrochemical and mineralogical features indicate that it is I-type granitoid rock. Structure features of the pluton and aureole rocks show that the emplacement of the stock was a diapiric process.