Abstract
Abstract Classically held mechanisms for removing mountain topography (e.g., erosion and gravitational collapse) require 10-100 Myr or more to completely remove tectonically generated relief. Here, we propose that mountain ranges can be completely and rapidly (<2 Myr) removed by a migrating hotspot. In western North America, multiple mountain ranges, including the Teton Range, terminate at the boundary with the relatively low relief track of the Yellowstone hotspot. This abrupt transition leads to a previously untested hypothesis that preexisting mountainous topography along the track has been erased. We integrate thermochronologic data collected from the footwall of the Teton fault with flexural-kinematic modeling and length-displacement scaling to show that the paleo-Teton fault and associated Teton Range was much longer (min. original length 190-210 km) than the present topographic expression of the range front (~65 km) and extended across the modern-day Yellowstone hotspot track. These analyses also indicate that the majority of fault displacement (min. 11.4-12.6 km) and the associated footwall mountain range growth had accumulated prior to Yellowstone encroachment at ~2 Ma, leading us to interpret that eastward migration of the Yellowstone hotspot relative to stable North America led to removal of the paleo-Teton mountain topography via posteruptive collapse of the range following multiple supercaldera (VEI 8) eruptions from 2.0 Ma to 600 ka and/or an isostatic collapse response, similar to ranges north of the Snake River plain. While this extremely rapid removal of mountain ranges and adjoining basins is probably relatively infrequent in the geologic record, it has important implications for continental physiography and topography over very short time spans.
Highlights
Studies of mountain ranges commonly invoke erosion and extensional collapse to explain the reduction of topographic relief [1,2,3,4,5] and rarely do such studies consider less common, but geologically significant mechanisms such as supercalderas
New inverse thermal history models based on a compilation of new and previously existing apatite (U-Th)/He (AHe)+apatite fission track (AFT) data is combined with new models of variable geothermal gradients alongstrike of the Teton Range to define the timing of Teton fault slip and the total magnitude of exhumation, as a function of cooling
These results are combined with flexural-kinematic modeling to determine the total displacement magnitude accrued on the Teton fault at multiple transects, and to identify the maximum accumulated displacement (Dmax) that occurred in the vicinity of Mount Moran, which leads us to interpret that area as the approximate center of the paleo-Teton fault
Summary
Studies of mountain ranges commonly invoke erosion and extensional collapse to explain the reduction of topographic relief [1,2,3,4,5] and rarely do such studies consider less common, but geologically significant mechanisms such as supercalderas. In regions that have experienced a prolonged history of explosive volcanism and regions impacted by supercalderas eruptions, it is useful to consider whether or not these cataclysmic mechanisms could denude or even completely diminish mountain topography where it intersects the caldera boundaries. In the northern Basin and Range of Idaho and Wyoming, the NNW striking crustal-scale normal faults and their associated uplifted footwall mountain blocks and adjoining halfgrabens terminate where they intersect the anomalous low relief of the Snake River Plain (SRP; Figure 1). The Teton, Gallatin, Madison, and Centennial ranges all abut and appear to be truncated by the 2.0-0.6 Ma Yellowstone caldera and two studies [9, 10]
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