中天山基底岩系的韧性-脆韧性改造作用

造山带核部往往都存在一些古老的中深变质岩系,后期都受到多次构造作用的叠加,从而呈现出一种极其复杂的面貌。夹于中东阿尔卑斯造山带中的门德雷斯、克谢希尔、尼德、阿拉尼亚和比特利斯等变质地块(阿达米亚等,1976),以及我国大别群(陈江峰等,1993)、秦岭群(游振东等,1994)等都是如此。中天山地区存在类似情况,这里存在两类基底岩系,一类基本未变质,另一类则由中深变质岩系所组成。前一类以伊犁地块的基底为代表(车自成等,1994),出露地层由中晚元古界浅海碎屑岩、叠层石碳酸岩和上覆的冰债层组成,构成区内稳定型基底;另一类以巴伦台群为代表(车自成等,1994),由各类结晶片岩、片麻岩、混合岩和不同时代的岩体组成活动型基底。后者形成于中晚元古代,并受到多期构造热事件的改造,除明显的多期变形外,其同位素年龄也从元古代直至中生代呈现连续演化的趋势。

THE DUCTILE AND DUCTILE - BRITTLE MODIFICATION DEVELOPED IN BASEMENT COMPLEX OF MIDDLE TIANSHAN, WESTERN CHINA

The middle Tianshan is located in the core of the Tianshan Mts. Its basement complex is also composed of old metamorphic rocks of pre-sinian, being similar to many important orogenic zones. Studies of the basement complex, nearby the fault of the southern margin of the middle Tianshan Mts., revealed that this complex was remarkably modified by multiple thermal tectonic events, characterized by multiple superimposed deformation and its isotopic ages range from the Proterzoic to Mesozoic. Taken the southern margin of the middle Tianshan into consideration, its structural modification can be divided into four periods: (1) Ductile shear period (452-439Ma). It is characterized by mylonites and phyllonites resulted from strong strain in this period. (2 - 3) Ductile-brittle shear stage. A series of imbricate structures were developed and mylonites were formed due to less strain. (4) Brittle shear period. In this period, stride - sliping of the faults was active for a long time interval in the mesozoic-cenozoic, but the exact age is still uncertain. All facts mentioned above suggest that the orogenic belt of the middle Tianshan is a complicated mutiple metamorphism - deformation zone with a long evolutional period.