Aspen anomaly
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Aspen anomaly is a geological structure in Colorado, United States. It consists of a low-seismic velocity anomaly in the mantle which underpins the highest sector of the Rocky Mountains.
The Aspen anomaly is a seismic velocity anomaly in the mantle beneath central Colorado (in the region of Aspen, Colorado[1]),[2] which appears to reach down into the upper mantle.[3] Helium with isotope ratios indicative of mantle origin emanates from the terrain above the anomaly.[4][5]
The Aspen anomaly coincides with the highest region of the Rocky Mountains (such as the San Juan Mountains and the Sawatch Range[6]) and divergent drainages (Arkansas River, Colorado River and Gunnison River) which have cut deep gorges. This region underwent significant uplift during the Cenozoic[3] starting from 10-5 million years ago and was subsequently eroded by the Colorado River.[7] Ongoing present-day uplift of the San Juan Mountains may be linked to the Aspen anomaly.[5]
River knickpoints in Gore Canyon and Black Canyon may mark the point at which the rivers pass through the edge of the region above the anomaly.[8] The Colorado River may be influenced by the anomaly all the way to Lees Ferry, Arizona.[9]
Hot springs and geysers above the anomaly are a major source of carbon dioxide and other gases, some linked to chemolithotrophic bacterial communities.[4] Cenozoic volcanism is also associated with the anomaly,[10] such as potentially the Twin Lakes pluton close to Leadville, Colorado.[11]