北京西山南部中生代早期的构造变形相和古地热异常

EARLY MESOZOIC DEFORMATION FACIES AND PALEOGEOTHERMAL ANOMALY IN SOUTHERN PART OF THE WESTERN HILLS, BEIJING

北京西山房山变质核杂岩的盖层下部，在一套由元古界及早古生界岩层组成的韧性流变中间层中发育一套反映伸展体制下近水平剪切造成的固态流变构造，其形成于中生代早期。区域构造变形相分析表明这套固态流变构造在空间上分布具不均一性，从变质核杂岩中心向外约２５ｋｍ，从固态流变变形相过渡为脆裂剪切变形相。对其变形强度、变形时的温度和围压的相关性研究表明，构造变形对温度具有敏感性，固态流变构造基本上发育在３００℃以上的古地温异常区。结合岩浆作用和变质作用特点，可以认为幔源热活动是本区古地热异常的主因，是陆内造山的触发因素。

There is a rheid tectonic community developed in a ductile flow middle slab consisting of Proterozoic and Early Paleozoic sequences between the Archean core and upper sedimentary cover of the Fanshan metamorphic core complex, Beijing. The characteristics of these structures reflected a subhorizontal shear under an extensional regime during the Early Mesozoic epoch. A regional analysis of deformation facies shows that its space distribution is inhomogenous. From the core outward about 25km, the rheid deformation facies has gradually changed to a brittle shear facies. A correlation analysis of strain, temperature and confining pressure during its deformation shows that the deformation is temperature sensitive. The rheid deformation developed at the anomaly area with temperature high than 300℃. By combining the characteristics of magmatism and metamorphism, it is suggested that mantle drived thermal activity is the main cause of this paleogeothermal anomaly and may be a trigger factor of intracontinental orogeny.