Integrated 3-D structural mapping in southern Taiwan Slate Belt: Implications for basal accretion and orogenic growth

The structural architecture of orogenic wedges, when integrated with paleo-thermal data, provides constraints on how materials are accreted at depth and subsequently exhumed to the surface. However, limited surface exposure hampers direct observation of structural architecture and obscures the broader tectonic processes. In this study, we integrated light detection and ranging (LiDAR)−based 3-D lineament mapping, satellite imagery, unmanned aerial vehicle surveys, and field investigations to examine structural architecture in the densely vegetated southern Taiwan Slate Belt, where the wedge growth processes remain under debate. Four types of structural lineaments were classified: bedding (LA), metamorphic foliation (LB), fractures (LC), and normal-sense sliding scarps (LD). The delineated lineaments (LA and LB), together with lithological mapping, reveal the presence of a 10-km-wavelength fault-breached synclinal geometry and provide the first evidence for the 3-D trace of a critical out-of-sequence thrust. These results demonstrate that LiDAR data can effectively map foliations and faults in densely vegetated, intensely deformed terrains where fieldwork is challenging. Integrating new structural observations with Raman spectroscopy of carbonaceous material and dating results shows that the thermo-tectonic evolution of the southern Slate Belt is influenced by basal accretion and nappe stacking, with associated out-of-sequence thrusts and penetrative strain contributing to crustal deformation and wedge growth.