1. How Laramide-Age Hydration of North American Lithosphere by the Farallon Slab Controlled Subsequent Activity in the Western United States
Humphreys, Hessler, Dueker, Farmer, Erslev, and Atwater
International Geology Review, 45, 2005
Jeffrey Roth
February 22, 2007
ASU Earthscope Seminar

2. Motivation: western U.S. tectonics and magmatic activity
The motivation for this study comes from the observation of the anomalously large extent of uplift and magmatism associated with the U.S. Cordilleron. Clearly visible in this satellite image are the broad, uplifted Colorado Plateau, the Rio Grande Rift, the extended Basin and Range, and the Rocky Mountains.

3. North America: Topography
Looking at a large area in this topography map of the U.S., you can see that the structures associated with the Cordilleron extend half way across the continent, when you include the uplifted topography of the great plains.

4. Observations Seismic velocity ~100 km depth
low resolution: S-wave model of Grand (1997)
high resolution: P-wave models
Surface heat flow
High correlation between datasets
The upper plot is a compilation of seismic velocity models. The lower plot is a surface heat flow model. High correlation is observed between heat flow with upper mantle seismic velocity and Cenezoic volcanism; Authors suggest that this implies near-vertical ascent of mantle melt at depth leads to volcanism and high heat flow at surface.
Humphreys et al., 2003

5. Data & Methods Travel time data
Corrected delays used in tomographic inversion
Regions of slow wave propagation beneath central New Mexico, Colorado, and Yellowstone
Regions of fast wave propagation in the east and west, and central Wyoming
Data used in the inversion. (A) Station locations; (B) Observed delay times; (C) Station corrections (elevation, sediment and crustal thickness); (D) Corrected delays.
Humphreys et al., 2003

6. Results Low-velocity volumes: Jemez volcanic trend
West-central Colorado (Rocky Mtns)
-Results: low-velocity volume beneath jemez volcanic trend and west-central colorado (Rocky Mtns)

7. Implications Flattening slab cools and hydrates lithosphere
Removal of slab exposes hydrated lithosphere to hot asthenosphere
Widespread magmatism
Uplift due to decreased density from heating and unloading from slab removal
Hypothesized model for Cordilleron uplift and magmatism.
Humphreys et al., 2003

8. Additional Thoughts Why not continue squeeze tests below 200 km?
What is the mechanism for Farallon slab flattening and detachment?
Possible impact of proposed Yellowstone plume impingement ~80Ma?