Major reorganization of the Snake River modulated by passage of the Yellowstone Hotspot

The details and mechanisms for Neo-gene river reorganization in the U.S. Pacific Northwest and northern Rocky Mountains have been debated for over a century with key implications for how tectonic and volca-nic systems modulate topographic develop-ment. To evaluate paleo-drainage networks, we produced an expansive data set and prov-enance analysis of detrital zircon U-Pb ages from Miocene to Pleistocene fluvial strata along proposed proto-Snake and Columbia River pathways. Statistical comparisons of Miocene-Pliocene detrital zircon spectra do not support previously hypothesized drain-age routes of the Snake River. We use detrital zircon unmixing models to test prior Snake River routes against a newly hypothesized route, in which the Snake River circumnavi-gated the northern Rocky Mountains and entered the Columbia Basin from the north -east prior to incision of Hells Canyon. Our proposed ancestral Snake River route best matches detrital zircon age spectra through-out the region. Furthermore, this northerly Snake River route satisfies and provides con -text for shifts in the sedimentology and fish faunal assemblages of the western Snake River Plain and Columbia Basin through Miocene-Pliocene time. We posit that east-ward migration of the Yellowstone Hotspot and its effect on thermally induced buoyancy and topographic uplift, coupled with volca-nic densification of the eastern Snake River Plain lithosphere, are the primary mecha-nisms for drainage reorganization and that the eastern and western Snake River Plain were isolated from one another until the early Pliocene. Following this basin integra-tion, the substantial increase in drainage area to the western Snake River Plain likely over-topped a bedrock threshold that previously contained Lake Idaho, which led to incision of Hells Canyon and establishment of the modern Snake and Columbia River drainage network.