大巴山国家地质公园构造地貌景观构造变形期次研究

Research on Tectonic Deformation Periods of Structural Landform Landscape in the Daba Mountain National Geopark

通过野外路线考察,典型地区填图,地质、地形图判读发现,大巴山国家地质公园主要构造地貌景观横向分布呈现由NE至SW即从造山带向前陆盆地方向逐渐减弱特征;纵向上明显受早期构造格局和岩石类型约束,在区域上呈现NW—SE向延展的平行岭谷地貌,山峰和谷地的走向与地质构造线基本一致。通过对主要构造地貌景观构造应力和变形期次判别探讨,确定构造地貌景观形成的构造期次大致为三期,应力主要来自于NE—SW、SE—NW向,反映该区不仅受到NE—SW向的冲断挤压变形作用,还受到SE—NW向的右旋剪切挤压变形作用,推测是由多期受力叠加改造而成。通过ESR及14C定年确定距今12 Ma以来,该区在500 kaBP、278 kaBP、29 kaBP分别出现三次规模较大的快速抬升运动,提供了与其构造景观形成密切相关的新构造运动年代学证据。

Field study, geological mapping of typical areas and interpretation of geological and topographic maps show that the main structural landforms of the area weaken horizontally in NE-SW direction, which is the direction from the orogenic belt to the foreland basin longitudinally constrained obviously by early tectonic framework and rock type. The present parallel ridge valley landforms extend in NW-SE direction. The trend lines of peaks and valleys are basically consistent with the geological structure. Based on the discussion on the tectonic stress and the tectonic deformation stages of the major constructed landscape in the study area, the authors hold that the tectonic structure of the landscape can be roughly divided into three periods, and the stress is mainly in NE-SW and SE-NW directions, suggesting that the study area experienced not only NE-SW trending thrust extrusion deformation but also SE-NW trending dextral shear extrusion deformation, presumably resulting from amulti-phase transformation from the superposition of the force. ESR and 14C dating shows that there have occurred three times of large-scale rapid uplifting since 12 Ma ago, which took place at 500 kaBP, 278 kaBP, and 29 kaBP respectively. The results obtained by the authors provide chronological evidence of neotectonism which was closely related to the formation of structural landscape.