新疆阿尔泰造山带南缘萨勒巴斯推覆体的变形和变质作用

Deformation and Metamorphism of Salebasi Nappe in Southern Pidmont of Altay Orogenic Belt, Xinjiang, China

萨勒巴斯推覆体中发育一套深层次变形构造组合和倒转递增变质带,其中糜棱岩、混合岩、混合花岗岩的成因关系对研究挤压造山背景下,地壳深层次变形作用和成岩作用具有特殊的意义。研究表明:在大型滑脱推覆系统中,存在糜棱岩—混合岩—混合花岗岩成岩系列;成岩过程为:韧性变形—剪切加热—部分熔融;控制成岩过程的主导因素为构造动力条件。这一成岩过程能导致稀土元素发生分异,出现重稀土元素有规律地亏损,变质作用pTt轨迹显示造山过程中逆冲推覆作用导致的地壳叠置加厚和剪切加热的典型热演化模式,变形、变质高峰期后,高角度逆冲作用导致变形岩石经历减压、降温的退变质作用,形成由南向北的倒转递增变质带。

Some structural assemblages resulted from the deep - position deformation in the earth crust and a reverse progressive metamorphic belt are developed in the Salebasi nappe, in which the genetic relationship among mylonite, migmatite and migmatitic granite is very important for studying the deformation and lithogenesis within the deep - position 'of the earth crust in compressive orogenic background. The researches show that there is a lithogenic series of mylonite to migmatite to migmatitic granite in the large-scale detachment slipping system, and the lithogenic process is: beginning from ductile deformation through shear heating to partial melting. The major factor controlling this process is tectono - dynamic condition. The differentiation of rare earth elements could take place in the lithogenic process, which shows regular loss of heavy rare earth elements. The pTt path of metamorphism shows the typical heat evolution model of thickened crust and shear heating resulted from tectonic thrusting in orogeny process. After the climax of deformation and metamorphism, high angle thrusting made deformed rocks expericence regressive metamorphism by relief of pressure and falling of temperature, and form the reverse progressive metamorphic belt from south to north in the Salebasi nappe .