| dc.description.abstract | This study describes, analyzes, and interprets Chushiang fault propagation fold-related deformation bands (DBs) based on field and laboratory observations. DBs are common structural elements found in the late Pliocene to early Pleistocene Cholan sandstones distributed downstream of the Chichi weir along the Choshui River in the frontal part of the fold-thrust belt in central-western Taiwan. One fold train appears in the hanging wall of the east-dipping Chushiang left-lateral reverse fault. It is composed of a plunging, upright, gentle Shizhoutzu syncline and a plunging inclined asymmetric, tight Dingxizhou anticline with a wavelength of hundreds of meters. The DBs occur in moderately sorted, fine-to-coarse grained sandstone layers. Most of them appear long (> one meter) and thick (up to 2 cm) in area B, which is bounded by the anticline axial surface at one side and the syncline axial surface at the other and fall into three sets with orientations of 035°/45°SE (set 1), 135°/53°SW (set 2), and 000°/~85° W to 85°E (set 3), respectively. Our investigation shows that the orientation of the set 1 is sub-parallel to the Chushiang fault orientation. Besides that, the acute bisector of the sets 2 and 3 is sub-perpendicular to the Dingxizhou anticline fold axis, sub-parallel to the inferred direction of maximum contraction. In addition, DBs that appear in the area between the Chushiang fault trace and the Shizhoutzu syncline axial trace (area C) are obvious under microscopic but ambiguous on the outcrops because they are thin (few mm) and short (< 3 dm), and commonly evolve into fractures. However, in the eastern limb of the Dingxizhou anticline (area A), the DBs appear either sub-parallel to the bedding plane (type 1) or close to some minor fault with an orientation parallel to the fault trace (type 2). The type 2 are cataclastic DBs with the characteristic of crushed fine-grained minerals in the bands while the type 1 are disaggregation bands with the characteristic of grain reorganization through a process referred to as granular flow, this is grains are deformed by rolling and sliding. The DBs in area B are solution and cementation bands, which are dominated by clay minerals likely resulting from dissolution or cementation processes but remain the characteristic of crushed fine-grained quartz, likely inherited from cataclastic DBs, i.e. their counterpart in the past. The DBs in area C are slip DBs with the characteristic of slip surfaces easily identifiable as discontinuities within the band under the microscope and on the outcrops. Such evidence including the DB occurrences and textures indicates the origin of these DBs except the disaggregation bands is highly related to the Chushiang fault propagation fold activity. The factors controlling their development include lithology, proximity to the fault, and position on folds induced by faulting. In conclusion, the disaggregation bands in area A likely formed before the emergent anticline, three sets of cataclastic DBs followed during the anticline development, and most of cataclastic DBs evolved into the solution and cementation bands in area B and the slip bands in area C during the post-anticline (syncline forming) phase. | en_US |