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北美大陆西部变质核杂岩体具有变质、深成岩的特征,其上可观察到缓倾糜棱岩组构和叠加有区域低角正断层形成过程中产生的脆性构造,这种正断层被认为是滑脱断层。滑脱断层下伏于高角断裂、脆性膨胀板状岩体,其上位移为第三纪引张时期产生的断距为50公里的正断层位移。变质核杂岩体中的糜棱岩组构和滑脱断层造成的脆性构造反映出产生缓倾正断层位移,地壳剪切带和下文称为滑脱断层带的这种韧-脆性演化过程。按照剪切带演化模型,滑脱断层和有关的脆性变形出现于滑脱断层带的上层,而且沿断层带向下逐渐成为韧性变形从而造成糜棱岩的出现。滑脱断层上的正断层位移导致形成中地
The metamorphic core complex in the western North America has the characteristics of metamorphism and plutonic rocks. The gentle mylonitial structure and the brittle structure in the superimposed low-angle normal faults can be observed, which is considered as Slipping off the fault. The detachment fault lies beneath the high-angle fault and brittle expansive plate-shaped rock mass, and the uplift is the normal fault displacement with a 50-km fault interval during the extension of the Tertiary. The brittle structure caused by the mylonite and detachment faults in the metamorphic core complex reflects this ductile-brittle evolution that results in slow-dip normal fault displacements, crustal shear zones and the so-called slip-out fault zone. According to the shear band evolution model, the detachment fault and the related brittle deformation appear in the upper strata of the slip-off fault zone, and gradually become ductile deformation down the fault zone, resulting in the appearance of mylonites. The normal fault displacement on the slip fault resulted in the formation of mid-earth