北京房山变质核杂岩的基本特征及其成因探讨

CHARACTERISTICS OF FANGSHAN METAMORPHIC CORE COMPLEX,BEIJING AND A DISCUSSION ABOUT ITS ORIGIN

北京房山变质核杂岩是典型的板内变质核杂岩。由核部的结晶基底及顶部的变余糜棱岩带、固态流变的中间层和脆性剪裂的上部盖层组成三层结构。核部有强力侵位的早白垩世的房山花岗闪长岩株。地壳的韧性伸展表现于下古生界及其前的盖层岩系中，形成于印支期前，反映了强烈的区域古地热异常。印支期的南北向挤压造就了区域构造格局。燕山期的岩浆侵入使变质核杂岩定型。新生代的差异性隆升使核杂岩最终出露地表。幔源热异常、基底热隆及岩浆的强力侵位是核杂岩形成的主要因素．

he Fangshan metamorphic core complex is a typical kind of intraplate one.It consists of three layers: a crystalline basement core with a blastomylonite zone on the top,a ductile flow middle slab and an upper cover deformed by brittle shear. The Fangshan granodiorite pluton of Lower Cretaceous occupies the middle of core. The ductile extension of the crust occuring in the rock cover of the Lower Paleozoic and older age formed during the Pre-Indosinian period and reflects a strong paleogeothermal anomaly.The N-S directed compression during the Indosinian movement formed the regional structural configuration. The magmatic intrusion of the Yanshanian movement led the final formation of the metamorphic core complex. The differential uplift during the Cenozoic caused the cropping of the core complex onto the surface.It is suggested that a combination of a mantle origined geothermal anomaly,thermo-uplift of the basement and the active intrusion of magma may be the main factor of the origin of the metamorphic core complex.