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

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.