米仓山楔入冲断构造模型低温热年代学证据及其意义

基于低温热年代学特征的构造重建（或解译）与浅部地表过程模型在诠释盆-山结构与演化过程中受到越来越广泛的重视与应用.青藏高原东缘米仓山-川北前陆盆山系统楔入冲断构造模型与浅部地貌建造（非）耦合的检验校正为米仓山造山带构造变形及其动力学模型研究提供了契机.基于稳态楔入冲断构造低温热年代学模型研究表明，米仓山-川北前陆盆-山结构带盆山地貌的建造和低温热年代学（磷灰石裂变径迹和（U-Th）/He）特征具有明显的耦合性，二者统一于（盆地向）具~4°古地貌斜坡的楔入冲断构造模型.现今米仓山地区低温热年代学不具有明显的海拔高程和年龄线性关系，但当古地貌具有~4°坡度时低温热年代学与古地貌具有明显的线性相关性，揭示晚白垩世米仓山东西段具有一致（或相似）的稳态抬升剥露特征，东西段剥露速率分别为0.05 mm/a 和0.03 mm/a.古地貌坡度与古地温梯度具有较好的相关性（R²=95%~98%），相关古地温梯度（25~35 ℃/km）符合米仓山稳态剥露地质结构特征.米仓山造山带楔入冲断构造模型的发育可能受控于多套滑脱层系（尤其是深部和浅部滑脱层系）和扬子板块能干性基底对造山带盆地向扩展变形过程的阻挡作用.

Wedge-thrust folding in the Micangshan constrained by low-temperature thermochronometer 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 into 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 and apatite fission track (AFT) data, a simplified one-dimensional titled topography model of 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° titled topography.