摘要:
断层泥作为断裂脆性剪切变形的产物,记录了断层滑动方式和活动时间等信息,尤其是断层泥中石英颗粒表面微形貌特征的识别和统计,可以为估算断层活动相对时间提供证据。青川断裂作为秦岭构造带的南界,晚新生代以来发生右旋走滑运动,沿断裂带出露完整的断层破碎带,断层泥非常发育。本文以该断裂带中段:木鱼—大安段发育的青灰色和紫红色断层泥为研究对象,在野外调查的基础上,重点对断层泥中石英颗粒表面的微形貌进行了扫描电子显微镜观察,发现两类(II和III类)中-深度溶蚀石英形貌和一类(Ia 类)弱溶蚀石英形貌,未见 Io 类破裂微形貌。石英微形貌类型的统计结果指示青川断裂中段最新活动时间在晚更新世,全新世没有明显活动,与断裂带全新世河流阶地未发生构造扰动的现象一致。
Abstract:
Fault gouge, as the product of the brittle shear deformation in fault zone, records the information of fault slipping mode and activity time. The micromorphology textures of quartz in fault gouge, in particular, can be used to semi-quantitatively estimate a relative time of fault activity. The Qingchuan fault, as the southern boundary of the Qinling Tectonic Belt, has been of right-lateral strike-slip since late Cenozoic, and the complete fracture zone including well-developed fault gouge is exposed along the fault. In this paper, the authors chose the pewter gravelly fault gouge and purple fault gouge from the middle segment of Qingchuan Fault Zone (Muyu-Da’an segment) as the study objects on the basis of field investigation, with the emphasis placed on the SEM (scanning electron microscope) observation for surface textures of quartz grains. The quartz micromorphology shows two categories of medium-strong dissolved morphology (II and III) and one type of weak dissolved morphology (Ia) in purple fault gouge, with no rupturing morphology observed. This statistical result indicates that the latest activity time of the middle segment of Qingchuan fault was in late Pleistocene, and no obvious activity happened in Holocene. This viewpoint is well consistent with structural geomorphology investigations along the active fault zone.
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