Engr 597 Tectonics
Formation of the Rocky Mountains
• How did they form?
• Sevier orogeny
• Laramide orogeny
• prevailing theory (flat slab subduction)
1. Very low angle subducting slab
2. rubbing against underside of North American plate
3. first proposed by william dickinson (1978)
4. another good paper Peter Bird (1988)
• Alternative theories
1. Craig jones - suction model
2. (maxson, Tikoff 1996) - Hit and run collision model "I 'll come back to it"
Within the North American cordillera there lies an expansive region of mountain ranges, basins, and plateaus, stretching from Mexico through America and Canada all the way to Alaska. This region rises up from the ground like …show more content…
The first piece of evidence that points to a non-traditional formation of the Rocky Mountains is the rock composition of the ranges in this area. The rock composition in these areas is not sedimentary like we would expect to see in the traditional convergent boundrie folding type of orogenic event. But rather, it is composed mostly of basal igneous rock that seems to have inexplicably risen up from deeper portions of the crust (Pendick and Denial, 1997). The second, and most problematic, question as to the formation of the Rocky Mountains is, how did the mountains form so far within the interior of the continent? The central and eastern portion of the Rocky Mountains is thought to have formed during the Laramide orogeny; which is believed to pre-date the Jurassic and early Cretaceous accretion of the terrenes that make up the North American cordillera. Meaning that this portion of the Rocky Mountains had to have formed 700-1500 km inboard from the nearest convergent plate boundary (English et al. …show more content…
Bird tested this theory by using Computer modeling. In his simulation bird based the earth on the 'Jelly Sandwich ' theory which states that the earth 's crust is floating on a layer of partially molten upper mantle which is then underlain by a dense layer of mantle called mantle lithosphere. In Bird 's computer models he was able to adjust variables such as the strength of the lithosphere and the amount of friction generated between the two plates. After testing Bird concluded that even in simulations with relatively low amounts of friction the strain created was still great enough to deform the upper portion of the lithosphere by 5-10%. Which he believed would have been more than enough to create the Rock Mountains and explain its strange features (Bird,