Here we will Discuss the uplift of the Colorado plateau.  There has been at least 2 km of uplift across the plateau.  The uplift has been constrained to after 85 Ma due to widespread Cretaceous Marine sediments on the Plateau (the sediments would not have been able to have been deposited after the plateau was uplifted).  The upper bound of the uplift has been determined by paleobotany.  Fossil leaves were examined the shapes of the leaves lead to a determination of  paleo-climate, then from the climate an elevation was determined. It was concluded that the uplift had to occurr by 35 Ma.

There are two main theories about the uplift of the colorado plateau

1) Crustal thickening

2) Delamination of a subducted slab from the mantle
 

To see a cartoon illustrating these models, click here
 
 

• As was discussed on the page on geologic setting there has been only 1% crustal shortening across the plateau.  Even if the plateau sat on top of a thick crust (50 km), the crustal shortening would increase the thickness by 500m, which would lead to 70 m of uplift, not the 2km that really occurred.
• Geochemical evidence shows that there is still some old mantle beneath the slab, so not all of the slab could peel away (some would have to stay behind)
• Pn velocites might reveal if the Colorado Platueau has a high heat flow, which could point to mantle upwelling or delamination.  Pn velocities have been under debate.
• A numerical model (Spencer, 1996) shows that a partial delamination of the slab and some mantle lithosphere would be enough to account for the elevation of the plateau, but if you numerically put the slab back on would the plateau subside???

Refraction studies might help answer some questions about crustal thickness and Pn velocities.  These answers could help constrain the uplift models.