The role of lower-crustal hydration in the tectonic evolution of the Colorado Plateau

- Seismic and thermodynamic modeling are used to constrain Colorado Plateau uplift.
- Part of the modern Colorado Plateau elevation is supported by crustal hydration.
- Hydration and a related buoyancy are impacted by upper mantle processes.

Geologists have long debated the timing and mechanism for uplift of the Colorado Plateau with numerous hypotheses proposed to explain each. We use surface wave tomography to examine the lithospheric structure of the Colorado Plateau and surrounding regions and combine these data with thermodynamic modeling to better constrain lower crustal composition, water content, and density. Our results show that about 15% (~ 290 m) of the modern plateau elevation can be supported isostatically by hydration of the lower crust, which reduces the overall density of the lithosphere. Hydration of the Colorado Plateau lithosphere likely occurred due to dewatering of the Farallon slab during flat-slab subduction. Subsequent warming and extension have likely further reduced the density of the crust along the plateau margins by as much as 110 kg/m3. This is likely a result of extension encroaching into the plateau and small-scale convection occurring within the mantle surrounding the plateau, and may help explain the high topography on the margins of the plateau.