Resolving the Cenozoic History of Rock Exhumation Along the Central Rocky Mountain Trench Using Apatite Low‐Temperature Thermochronology

Abstract

AbstractThe Rocky Mountain Trench (RMT) extends through the Canadian Cordillera from the Yukon to northwest Montana. The RMT's impressive length and continuous nature have been interpreted to be the result of faulting, and localized erosion, along a continent‐scale zone of crustal weakness located beneath the RMT, possibly associated with the ancient continental margin. Despite the continuous nature of the RMT, its kinematics vary along strike from dextral strike‐slip faults in the north to normal faults in the south. The central RMT is thought to be the transition between these two structural zones. We use low‐temperature thermochronology to compare the cooling histories across the central RMT in eastern British Columbia. We report apatite fission track ages from 23 samples and apatite (U‐Th)/He ages from 25 samples along with thermal‐history models. Our results reveal three phases of rapid cooling that followed the Cretaceous‐Paleocene cordilleran thrusting in the Eocene, the early–mid Miocene, and from the late Miocene to recent. We find that the Malton Gneiss Complex exhumed as a horst structure 20–10 Ma bounded by the North Thompson Albreda Fault and the RMT. Normal faulting along the NTAF continued in the late Miocene as well as west side down normal faulting along the RMT. Our data suggest that extends along the southern RMT continued northward to at least this portion of the central RMT in multiple episodes during the Cenozoic. We suggest transtension occurred in our study area that was driven by orogenic collapse and lithospheric mantle delamination.