Abstract:

Daba Mountain is a geometrically systemtric, flat-crested and truncated salient, of which the main-boundary fault, Chengkou arc fault, markedly change in the trend from N-W in north, to NW in middle, and to E-W in south, and obviously truncate with its interior structures. Moreover, the salient parallels to the thrust-transporting direction from NE to SW in Daba Mountain. Analyses of the mesoscopic and microscopic structures, metamorphic and strain patterns in the Chengkou salient, show its two-stage evolution and a weakening tendency in dextrally strike-slipping deformation from north to south. The early E-W linear trend was high-angle-to-vertically superposed by the late lineation that generally parallels to the Chengkou salient. In particular, a high-to-vertical lineation with a weakening tendency in deformation (e.g. the plunge of hinges, B-axis and strain of lens) was found at the southern segment of Chengkou salient, which is composed of asymmetrical minor-fold hinge and B-axis in lens accommodated by dextral strike-slip. Furthermore, the northern segment was under a middle-high greenschist facies metamorphic condition indicated by strain of quartz and feldspar, showing strong thrusting and dextrally strike-slipping by kinematic indictors. Whereas the southern segment was under a lower greenschist facies metamorphic condition, showing gentle dextrally strike-slipping and thrusting by kinematic indictors. A weakening tendency from north to south in Chengkou salient indicates an asymmetry in metamorphism and deformation. Asymmetry in metamorphism and deformation was attributed to the indention of the Hannan basement from south to north during the Late Triassic to Jurassic collisional orogen between the South and North China blocks, resulting a strong dextrally strike-slipping along Chenkou salient.

Key words: dextral strike-slip, structural features, asymmetry, salient, Chengkou arc fault, Daba Mountain, structural geology