Wedge-Thrust Folding in the Micangshan Constrains from Low-Temperature Thermochronology Model and Its Significance

Basin-mountain system comprises multistage-evolving structures whose behavior is either controlled by internal factors, e.g., tectonic frameworks, or external ones, e.g., intensity of erosion and sedimentation, resulting in a coupling between structures and surface processes. Documenting the coupling has thus the potential to yield critical insights on the dynamics of the whole basin-mountain system. The Micangshan located at the eastern margin of the Tibetan Plateau is an intracontinental mountain belt, which was shaped during multiple phases of intense mountain building and associated denudation throughout the Mesozoic and Cenozoic. However, the coupling between surface processes recorded by low-temperature thermochronometer and mountain-building has been controversial. Based on seismic profile, apatite fission track (AFT) data, a simplified one-dimensional, tilted topography model resulted by wedge-thrust folding across the Micangshan was developed. In the model, the paleo-topography and paleo-geothermal gradient immediately before initiation of the wedge-thrust folding deformation can be estimated by using present sample elevations, the cooling ages and the closure-temperature of each sample. By the coefficient of determination and suitable geological features (e.g., geothermal gradient), we can decipher the coupling/uncoupling relationship between the tectonic construction and the landscape evolution (e.g., a specific slope in topography). Our model shows that the inherited structure as a wedge-thrust folding, played a predominant role during the Late-Cretaceous uplift and exhumation in the Micangshan. It suggests a steady state, slow uplift and exhumation with rate of 0.03∼0.05 mm/a during Late Cretaceous time across much of the Micangshan, with a southern (or basin-ward) ∼4° tilted topography.