TETON FAULT EVOLUTION PART 1: ONSET TIMING AND SLIP HISTORY

The dramatic relief of the Teton Range in northwestern Wyoming results from motion along the Teton normal fault, which separates the range from the Jackson Hole valley to the east. New apatite (U-Th)/He (AHe) and fission track (AFT) ages of samples collected in the footwall of the Teton fault yield fundamental constraints on contrasting models of Teton fault activity and consequent relative footwall uplift. Samples were collected both at low elevation along strike and along three subvertical transects near Rendezvous Mountain, Grand Teton/Garnet Canyon, and Mount Moran. Low elevation samples (<200 m above Jackson Hole valley) in the immediate footwall of the fault range from 12.5 to 6.5 Ma and yield an average of 8.29 Ma. AHe ages of samples from the subvertical transects range from 57.9 to 6.5 Ma (Rendezvous), 35.5 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 40.1 Ma (Grand), and 38.0 to 11.7 Ma (Moran). Inverse thermal history modeling of the subvertical transects indicate 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, Moran) and then migrated south as vertical fault displacement continued to accumulate (Grand Teton cooling 10 Ma to present; Rendezvous cooling 7 Ma to present). Only inverse thermal history models of the Mount Moran transect show a pattern of decelerating cooling rate after 8 Ma, which is also interpreted to reflect a southward migration of displacement accumulation. Thus, this work suggests that although the Teton fault likely initiated due to Basin and Range extension, this structure remains active, with modeled cooling rates of >10° C Myr-1 for the southernmost Rendezvous transect over the last 7 Ma.