Rocky Mountain High: Mystery of the Origins of the Rockies Solved!
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March 02, 2011

Rocky Mountain High: Mystery of the Origins of the Rockies Solved!

Barns_grand_tetons The formation of the Rocky Mountains in Colorado has puzzled scientists for decades. Some 600 miles inland and far removed from the nearest tectonic plate, the only comparable inland mountain range is the Himalaya, which were formed by the collision of the Indian plate with the Eurasian

"But there really was no India slamming into North America," said Craig Jones, a research fellow of the Cooperative Institute for Research in Environmental Sciences (CIRES) and a professor of geological sciences at the University of Colorado at Boulder. "Just how the Rockies have formed is an enigma."

But based on new research,  Jones and his team of researchers have proposed a new model of the mountains' formation that not only explains the origin of the Rockies, but also explains other geological phenomena: such as why a swath of gold, silver and other precious metal deposits stretches across Colorado, and why a marine basin deepened in the states of Colorado and Wyoming just before the Rockies rose. The sediments of this marine basin are the Pierre Shale, a layer of dark-gray shale lying along the Front Range of Colorado.

"Pierre Shale has this nasty tendency to bow up people's basements," Jones said. "Why more than a mile of this stuff was dumped into this area has been puzzling."

Previously scientists believed that the oceanic plate subducting - moving under - North America rose to rub against the continent's bottom all the way from the ocean to Colorado. The theory was this action pushed the landmass into mountains much like a rug piles up underfoot, said Jones. But the hypothesis just doesn't explain the facts, he said. "That model predicted removal of material that is still found to lie underneath California and Arizona," he said. "That in and of itself was unsatisfying."

The new model hinges on an unusually thick lithosphere – the stiff part of the Earth's surface that make up the tectonic plates – under Wyoming. The protrusion of this keel into more fluid mantle flowing below, created a suction that pulled down Southern Wyoming and Colorado and formed a basin, Jones said. This basin, or hole, in which Pierre Shale built up, amplified mountain-building forces far inland and forced the formation of the Rockies, he said.

"A huge basin develops and all of a sudden these mountains come rocketing out of it," Jones added. "We end up with the counter-intuitive visage of mountains rising up out of a hole. "

The hypothesis, if confirmed, could not only unravel the geological origin of the Rockies, but could also illuminate the mechanisms that have led to mountain ranges worldwide. "We are adding a new collection of processes that can control how mountain belts develop that previously haven't really been appreciated," Jones said. "Considering these processes might explain other puzzling mountain belts."

The Daily Galaxy via University of Colorado at Boulder

Comments

This is very interesting and instructive. If the Rockies were indeed formed in this manner is it possible that the Himalaya also could have been formed in this way instead of by the collision of the Indian and Eurasian plates? I'm simply curious about the degree of certainty which can be attributed to these mechanisms as means of range formation.

I am still unclear as to how the mountains formed from the basin being pulled down - are you suggesting that the earth rebounded like a cork in response to the land being pulled down?

Er, Himalaya are quite clearly being made by collision with India. You could ask if the Tien Shan could be created by this mechanism--and the answer is almost certainly not. As to the certainty of our new hypothesis--I would say not much certainty at this point; this is the way science goes. But by advancing this idea, we are suggesting a number of tests that in and of themselves will help us to understand how subduction of ocean floors interacts with overlying continents.

As to the second question, no it is not a rebound like a cork, more like the suction pulls western US towards eastern US, with the Southern Rockies caught in between and squished. A slightly better (but more convoluted) analogy has a layer of molasses on a rubber sheet over water. If you pull down on the rubber a bit, the molasses starts to flow into the hole, thickening and shortening the molasses in the region, which is the same bulk deformation that produced the Rockies. [If you really want to make the analogy better, you have a layer of firm whipped cream on top of the molasses, then you will get mountains popping up out of the basin].

The whipped-cream analogy seems apropos. So is it then the case that the upper lithosphere is drawn up due to collision, like the whipped-cream (Southern Rockies), while the lower lithosphere sinks and forms basins, like the molasses (Pierre Shale--or is this much deeper in the crust?) Why is the lithosphere thicker under Wyoming? Does the tomography indicate a detached eclogite under this area? Thanks.

Guys, I know researchers say, the Himilayas were forced upward by the colliding continent of India, and the Rockies were forced upward by massive subducting plates. Here's the problem with both inferences...what force of energy moved the specific crusts of rock, that is the continent of India, and the massive Pacific Plate to these extraordinary levels?


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