Peak et al. (2021) concluded that their ZHe data revealed differences between eastern (EGC) and western (WGC) Grand Canyon regions in 1255–500 Ma basement cooling/exhumation such that the Grand Canyon Supergoup was not deposited in western Grand Canyon. Here, we agree that WGC and EGC had different 1255–500 Ma cooling histories, but we disagree that the ZHe data preclude deposition of the Grand Canyon Supergroup in WGC. Instead, a scenario of structurally controlled Unkar and Chuar Group deposition and magmatism across a wide region, including parts of WGC, is equally viable for the available thermochronometry, and is more viable geologically (Howard, 1991; Dehler et al., 2017; Mulder et al., 2017;).
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