Mystery of Grand Canyon's Formation Revealed

This is a completely newmechanism for explaining regional uplifts. Obviously glacial in development but still able to lift sea level sedimentarystacks a couple of miles in the vertical as happened here.  It surely applies as well elsewhere.

The arid condition of thisregion has prevented a rapid destruction of the terrain which would hardlyexist al all had this happened in the Amazon. Thus we need to also consider wet eroded regions as equally prospectivefor this form of uplift.  Perhaps the Himalayas got an extra lift in a similar manner.

This gives us a goodexplanation and it may even hold up.

Mystery of Grand Canyon's FormationRevealed

Charles Q. Choi, OurAmazingPlanet Contributor

Date: 27 April 2011 Time: 01:23 PM ET

A magnificent mile deep gorge on the South Kaibab Trail along the SouthRim of Grand Canyon National Park. CREDIT:Andrea El-Wailly 

http://www.livescience.com/13903-grand-canyon-age-formation-colorado-plateau-uplift.html

The birth of the Grand Canyon andthe Colorado Plateau through which it carvedhave been a geological mystery. Now a giant anomalous structure discovered onthe underside of the plateau could shed light on how it was formed.

Over the past 70 million years, and possibly quite recently, therelatively flat Colorado Plateau of the southwesternUnited States -- a 130,000-square-mile (336,000 square kilometers)region that straddles Colorado, Utah, Arizona and New Mexico -- rose up about1.2 miles (2 km), was invaded by magma and was eroded away into deep valleys,creating a dramatic landscape including the GrandCanyon.

This kind of behavior is more expected with mountain belts, notplateaus, and so these events have perplexed geologists for more than acentury.

"Anyone who goes to the Grand Canyonand looks down should think, 'What is it that made it this way?' The mostimmediate answer is water, that a river cut this canyon, but what is it thatmade the rock it lies in, the earth, move up?" said researcher AlanLevander, a structural seismologist at Rice University.

Deep Earth 'drip'

To learn more about the rise of the Colorado Plateau, Levander and hiscolleagues analyzed new data from the EarthscopeTransportable Array of seismic stations. They focused on thelithosphere, the strong, long-lived crust and upper mantle of the planet,extending to a depth of about 90 miles (150 km), which sits on top of theasthenosphere, the hotter, weaker part of the mantle.

In the lithosphere under the Grand Canyonand much of the western half of the Colorado Plateau, scientists discovered ananomalously cold, dense region more than 120 miles (200 km) deep sinking intothe Earth. This anomaly is apparently pulling off the lower part of the crustabove it, activity that might lead to a major part of the unusual geologicalhistory in and around the Grand Canyon.

The researchers think the cold region was created by the asthenosphereinvading the lithosphere above it. As partially molten material expanded,cooled and solidified after flowing upward, it made the mantle portion of thelithosphere it invaded heavy enough to peel away and drip down. The morebuoyant asthenosphere then filled the space left above, where it expanded andcause the Colorado Plateau to uplift.

The scientists conjecture this "mantle drip" formed in justthe past 6 million years, and is just the most recent such anomaly occurringaround the edges of the Colorado Plateau in the past 20 million to 30 millionyears. The timing of this event has implications for the effort to pinpointthe age of theGrand Canyon.

How old is it?

"There are generally two schools of thought on the age of the Grand Canyon — one is that it formed in the last 6million or 7 million years, and the other is that it has a much longerhistory as a canyon. Our results suggest it's the younger date that's moreaccurate," Levander told OurAmazingPlanet.

Seismologist George Zandt of the University of Arizona,who did not take part in this study, agreed that "these findings wouldtend to support the idea of at least a young component of the uplift."However, they don't eliminate the possibility that there might have been anearlier phase of the uplift also, potentially keeping the idea of an older Grand Canyon alive, he added.

These drips are increasingly found all over the Earth, potentiallyincluding the western part of the Mediterranean, the central Andes and Tibet,and they could yield clues about how the upper mantle influences the surface ofEarth's continents.

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"They're a new component to our understanding of how continentsevolve that we're just trying to figure out now," Zandt toldOurAmazingPlanet.

Levander now proposes to go with more seismometer stations to image theU.S.anomaly "and see if we can pull out more details." He and hiscolleagues detailed their findings in the April 28 issue of the journal Nature.