Many post-orogenic settings exhibit a rugged topography, but the underlying mechanisms driving topographic rejuvenation are poorly understood. For example, the U.S. southern Colorado Front Range, a widely recognized and studied post-orogenic setting, contains deep canyons and steep channels even though the crustal deformation that built the range during the Laramide Orogeny ended at ca. 40 Ma. Two prevailing hypotheses are typically used to explain these topographically youthful features in the Colorado Front Range: (1) mantle dynamics and active tectonics during the late Cenozoic; and (2) enhanced erosional efficiency associated with Quaternary climatic changes. Here, we evaluate these end-member hypotheses through a tectonic geomorphological study of the upper Arkansas River Basin in southern Colorado. We perform river profile analysis on bedrock channels in the eastern Rockies and map and analyze fluvial terraces in the western High Plains. In the eastern Rockies, river knickpoints record a one- to two-stage increase in base-level fall rate downstream of the Colorado Front Range mountain front and an eastward increase in the magnitude of incision. In the western High Plains, Quaternary fluvial terraces also show an eastward increase in the total magnitude of incision. Supported by flexural and supplemental geomorphic analyses, these results suggest a previously undetected regional-scale, west-directed back-tilting associated with differential rock uplift. Based on the average timing of deformation, locations of major faults, and seismic activity, seismic tomographic data, and existing geodynamic models, we infer that this newly recorded westward tilting in the upper Arkansas Basin is the result of unsteady and potentially migrating dynamic topography that developed ca. 4 Ma.

中文翻译：

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河流剖面分析和河流阶地揭示了美国科罗拉多前岭南部的晚新生代变形

许多造山后环境呈现出崎岖的地形，但驱动地形复兴的潜在机制却知之甚少。例如，美国南部的科罗拉多前山脉是一个被广泛认可和研究的后造山环境，尽管拉拉米德造山运动期间形成该山脉的地壳变形终止于约 1970 年，但该山脉仍包含深峡谷和陡峭的通道。40马。两个流行的假设通常用于解释科罗拉多前岭这些年轻的地形特征：（1）新生代晚期的地幔动力学和活跃构造；(2)与第四纪气候变化相关的侵蚀效率增强。在这里，我们通过对科罗拉多州南部阿肯色河流域上游的构造地貌研究来评估这些端元假设。我们对落基山脉东部的基岩河道进行河流剖面分析，并绘制和分析西部高平原的河流阶地。在落基山脉东部，河流拐点记录了科罗拉多弗朗特山脉山前下游基准面下降率一到两个阶段的增加，以及切口程度向东的增加。在西部高地平原，第四纪河流阶地也表现出切口总规模向东增加的趋势。在弯曲和补充地貌分析的支持下，这些结果表明以前未检测到的区域规模、向西的后倾与差异岩石隆起有关。根据变形的平均时间、主要断层的位置、地震活动、地震层析数据和现有的地球动力学模型，我们推断阿肯色盆地上部新记录的向西倾斜是不稳定和潜在迁移的动态地形的结果，发达的约。4马。