Onset Timing and Slip History of the Teton Fault, Wyoming: A Multidisciplinary Reevaluation

Abstract

The dramatic relief of the Teton Range in northwestern Wyoming results from motion along the Teton normal fault. New apatite (U‐Th)/He (AHe) and fission track (AFT) ages of samples collected in the footwall yield fundamental constraints on contrasting models of Teton fault activity and consequent relative footwall uplift. Low‐elevation samples in the immediate footwall of the fault range from 12.5 to 6.5 Ma. AHe ages of samples from subvertical transects range from 57.8 to 6.5 Ma (Rendezvous), 54.0 to 6.8 Ma (Grand), and 20.5 to 7.1 Ma (Moran), with all three transects yielding an expected trend of decreasing age with decreasing elevation. AFT ages obtained from the three transects range from 55.4 to 45.7 Ma (Rendezvous), 43.2 to 13.3 Ma (Grand), and 38.0 to 11.7 Ma (Moran). Inverse thermal history modeling indicates that the onset of relatively rapid cooling, as a proxy for relative footwall uplift, initiated first in the northern part of the range (15–13 Ma) and then migrated south as fault displacement continued (7 Ma to present at Rendezvous). Thus, this work suggests that although the Teton fault likely initiated due to Basin and Range extension, this structure remains active. Normal fault displacement models also suggest a minimum of ~6 km displacement for footwall uplift of ~2 km. If evaluated in the context of established normal fault length‐displacement relationships, this yields a length of ~180 km, substantially longer than current estimates of Teton fault length and putting the northern end of the fault well into, and potentially beyond, the bounds of Yellowstone National Park.

Tectonothermal Evolution of the Broadly Rifted Zone, Ethiopian Rift

“…This is perhaps unsurprising because as normal fault systems grow and accumulate displacement, their footwalls experience predictable uplift and denudational histories (Densmore et al, ; Harbor, ) that result in the development of expected patterns of topography (Densmore et al, ). Indeed, other authors have exploited these fault growth‐denudation relationships by using along‐strike cooling history patterns, as recorded by low‐temperature thermochronology age spectra, to investigate the mechanisms by which normal fault systems have evolved (Brown et al, ; Curry et al, ; Mortimer et al, ).…”

“…Here we present a conceptual model whereby along‐strike variations in inversely modeled thermal histories, generated using AFT and AHe data, may be utilized to elucidate normal fault array growth (Figure ). Similar to previous approaches (Brown et al, ; Curry et al, ; Mortimer et al, ), which used variations in age spectra alone to investigate fault system evolution, it is the along‐strike difference in the onset of footwall cooling that is the primary diagnostic indicator for distinguishing between end‐member fault growth models. However, unlike previous models, this approach both accounts for compositional, morphological, and radiation damage effects on AFT and AHe data by incorporating annealing and diffusion models during thermal history modeling (section ), as well as allows for the estimation of displacement accumulation trends at various stages of fault evolution (Figure ).…”

“…Low‐temperature thermochronometers, such as apatite fission track (AFT) analysis, are alternative, yet powerful, tools to constrain periods of rift basin development by determining the timing of denudation and cooling associated with rift‐related footwall uplift (e.g., Fitzgerald, ; Stockli, ; Storti et al, ). While the well‐understood behavior of the AFT system makes it a robust method for constraining the timing and degree of cooling related to extensional tectonism (Kohn et al, ), in certain cases, its temperature sensitivity (~60–120 °C) can be too high to adequately record small‐amplitude variations in footwall cooling histories associated with normal fault slip (Brown et al, ). Such was the case for previous thermochronology studies in the BRZ (Balestrieri et al, ; Philippon et al, ), where AFT data provided minimum age constraints for the formation of the Beto Basin (between 14 and 10 Ma) and the Galana Basin (~10–8 Ma), bound by the Amaro Horst along its western margin.…”

Postglacial slip distribution along the Teton normal fault (Wyoming, USA), derived from tectonically offset geomorphological features

“…This may indicate that the longer-term slip accumulation is roughly symmetric. As indicated by low-temperature thermochronological data, the Teton fault may have formed at 15-13 Ma and accumulated ~6 km of displacement since then (Brown et al, 2017). Notably, the original Teton fault was probably much longer (as much as 180 km) and potentially linked to the normal fault bounding the Gallatin Range north of the Yellowstone Plateau before its central part was erased by the activity of the Yellowstone hotspot (Brown et al, 2017).…”

“…Recent thermochronological studies in the Teton Range suggest that the onset of rapid cooling (which may be considered as a proxy for fault movement) began at ca. 15-13 Ma in the Mount Moran area in response to Basin and Range extension (Brown et al, 2017;Hoar, 2019). As a consequence of the diverse estimates for timing and amount of slip on the Teton fault, estimates for the long-term vertical slip rate of the Teton fault vary from 0.5 to 1.2 mm/yr.…”