阿尔金断裂中段(阿克塞—芒崖段)的早期断层作用

Early Faulting along the Middle Part (From Akesai To Mang'ai) of the Altun Fault Zone

对于阿尔金断裂带中段阿克塞—芒崖地区开展的宏观构造分析、显微构造解析,并结合温压测定与测年分析,证明阿尔金断裂带的早期变形演化是一种韧性走滑剪切变形作用过程,沿断裂带形成了糜棱岩与糜棱状岩石。由变形构造、岩石组构和应变型式判别出与走滑断层作用相伴的中部地壳层次花状构造的存在。构成中部层次花状构造的岩石中同构造变形成因多硅白云母的出现说明韧性变形期间特殊的高围压条件(达0.43GPa),而白色云母(白云母和绢云母)与绿泥石组合指示了较低的温压条件(t:270～350℃;p:0.05～0.43GPa)。断裂带中的异常p/t变化主要归咎于高剪切应力引起的剪切加热与超压效应。依据同变形期矿物(白色云母)^(40)Ar-^(39)Ar记年初步证实早期韧性剪切变形发生于早白垩世(91～89Ma)。

Macroscopic, mesoscopic and microscopic structural analyses, together with p-t estimation and dating of fault rocks indicate an early faulting along the middle part of the Altun faulting, characterized by ductile strike-slip shearing. Mylonites and mylonitic rocks were formed along the fault zone. A flower structural pattern is revealed by deformation structures, fabric data and strain patterns associated with the ductile faulting. The occurrence of syntectonic phengite grains in the fault rocks from the flower structure suggests a high confining pressure condition (up to 0. 43 GPa), while the white mica-chlorite geothermometry gives low temperature condition (t:270-350℃ ; p:0. 05-0. 43 GPa). The abnormal p-t may be attributed to shear heating and overpres-suring due to high shear stress. 40Ar-39Ar dating of syntectonic minerals (white micas) suggests early ductile faulting along the middle part of the Altun fault zone at early Cretaceous (91-89 Ma).