Rocky Mountain HighIf you drive from the Mississippi River to Denver, you increase in elevation by o

Rocky Mountain HighIf you drive from the Mississippi River to Denver, you increase in elevation by over a thousand meters despite not crossing any major active faults. Head farther west and you cross major faults – entering the Rocky Mountain front, but there are plenty of faults in that area.How then, did an area like Denver get so high? Geologists have been wondering about this issue for decades and recent research out of CU Boulder offers a new exploration; this rock. That’s why, despite this being a post about the lovely landscape of Colorado, I’m showing a rock for this post.This rock is an phlogopite-bearing peridotite from Italy. The majority of the rock is made of the mineral olivine, the most common mineral in the upper mantle. The dark crystals you see are phlogopites, a type of silicate mineral containing iron, magnesium, and hydrogen in its structure. Hydrogen is the lowest mass element, so when it is included in the structure of a mineral it tends to lower the mineral’s density.For this work, the geologists mapped xenoliths like this one – rocks from the mantle brought up to the surface by volcanoes. They found that in areas that are at lower elevation, volcanoes brought up minerals containing olivine and garnet – a common mineral assemblage in the mantle. But, as they approached Colorado, they found that the garnets were replaced by phlogopites and amphiboles, minerals with water in their structure.For hundreds of millions of years, an oceanic plate called the Farallon plate was sinking beneath the west coast of the North American continent. As it entered the mantle, it was heated, driving off water contained in the sediments and altered rocks of the oceanic crust. That water caused the formation of volcanoes, including the Sierra Nevada Mountains in California, and it also could have supplied water farther inland as well.Hydrated mantle is less dense than dry mantle, so a boost of water to the mantle underneath Colorado would make it buoyant and cause it to start rising upward, thus explaining the extra elevation beneath Denver.This paper proposes that the mountain views and landscapes of Colorado are due to the dark crystals in a rock just like this one. Neat.-JBBImage credit:http://bit.ly/1GtMIT6Original paper:http://geology.gsapubs.org/content/early/2015/03/03/G36509.1.abstractPress release version:http://cires.colorado.edu/news/press/highplains/ -- source link

More pics about