Waldien et al. (2021) present new bedrock geologic mapping, U-Pb geochronology, and 40Ar/39Ar thermochronology from the eastern Alaska Range in south-central Alaska to determine the burial and exhumation history of metamorphic rocks associated with the Alaska Range suture zone, interpret the history of faults responsible for the burial and exhumation of the metamorphic rocks, and speculate on the relative importance of the Alaska Range suture zone and related structures during Cenozoic reactivation. They also propose that ultramafic rocks in their Ann Creek map area in south-central Alaska (herein referred to as the “Ann Creek ultramafic complex”) correlate with the Pyroxenite Creek ultramafic complex in southwestern Yukon, and that this correlation is “consistent with other estimates of >400 km” of offset on the Denali fault. However, despite Waldien et al.’s (2021) claim that the purportedly offset ultramafic rocks are “similar” and that characteristics of the Ann Creek ultramafic complex “make a strong case” for a faulted portion of an Alaska-type ultramafic intrusion, their paper gives short shrift in describing the Pyroxenite Creek ultramafic complex and in discussing previous estimates of displacement on the Denali fault. In Addition, Waldien et al. (2021) are either unaware of or ignore several key references of the Pyroxenite Creek ultramafic complex and estimates of displacement on the Denali fault. As a result, Waldien et al.’s (2021) claim of a “correlation” between allegedly offset ultramafic rocks is suspect, and their reference to “other estimates of >400 km” of offset on the Denali fault is incorrect, or at the very least misleading.
Oligocene-Neogene lithospheric-scale reactivation of Mesozoic terrane accretionary structures in the Alaska Range suture zone, southern Alaska, USA: Comment