Long-lived interplay of Taiwan's Central Range topography and foreland basin architecture

The influence on strain in thrust belts from effects of variability in climate and crustal rheology has been suggested or implied for a number of compressive orogens around the world. While the interplay of boundary conditions provides a diverse array of possible responses to transient changes in any of those conditions, few orogens are sufficiently characterized to effectively isolate a causal link between observed changes in thrust belts and a single process or parameter. Taiwan is one of the few places where extremely dense networks of instrumentation and an impressive history of geologic characterization work actually allows for a synthesis of the wealth of information collected there. The recognition of a strong spatial correlation between the structural and stratigraphic architectures of the Western Foothills belt, Hsueshan Range and central western Foreland suggest a direct link between the ancestral Taihsi basin, modern Taichung basin and the Puli Topographic Embayment. The spatial correlation of differences in strain and erosion located far inboard of the active mountain-front demonstrates how the accretion and subsequent incorporation of an anisotropic foreland into the orogen profoundly affects its long-term evolution. Based in part on shallow seismic reflection data and river incision rates from OSL dates along the Peikang river near Puli, new cross sections and kinematic interpretations were created to provide feasible structural solutions for the observed surface uplift rates, river incision rates and subsurface survey data. The resulting sections show that underplating of material from below the decollement is a likely mechanism contributing to the observed patterns of surface deformation and both co-seismic and inter-seismic surface uplift in Puli. One of these models in particular has important implications for the long-term development of the orogenic wedge, implying a long-lived region of sub-critical taper within the orogen as well as a necessarily long-lived region of focused erosion. This model supports the hypothesis of the importance of inherited foreland structures, by requiring underplating to occur at spatial scales that correlate to the spacing and stratigraphic levels of observed normal faults in the foreland as well as providing a timing for the initiation of underplating. The model provides a new kinematic solution specific to central Taiwan for how this structural inheritance may function through time, taking into consideration the growing body of work that suggests several faults may be active within the toe of the orogen at any time, and that activity on any one of these faults is intermittent through time in a constant re-balancing of the effects of topographic growth and spatially focused erosion.