Geology question for Ed Frank

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Geology question for Ed Frank

Post by dbhguru » Sun Jul 14, 2013 10:53 pm


I need some help with geology. Today Monica and I went into the Jemez mountains of northern New Mexico. As I surenyou know, they are of recent volcanic origin. One description of them I read states that they and the Sangre de Cristo mountains of New Mexico are the southern terminus of the Rocky Mountains. I had understood that the Sangres were, but not the Jemez mountains. What criteria is used to judge where the Rockies end? The Jemez apparently date back only about 1.5 million years and I think I read that the last volcanic activity was between 50,000 and 60,000 years ago. What defines the Rocky Mountains? How has the thinking changed from when the Rockies were defined as the result of the Laramide Orogeny?

Robert T. Leverett
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Friends of Mohawk Trail State Forest
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Re: Geology question for Ed Frank

Post by edfrank » Sun Jul 14, 2013 11:27 pm


Basically, yes. The Sangre de Cristo mountains of New Mexico are the southernmost range of the Rocky Mountains. They were uplifted as part of the Laramide orogeny occurring from between 80 to 55 Ma. The Jemez Mountains were formed by inner continental volcanism with major activity dating from 1.4 million years ago and continuing until the present. They are not part of the Laramide orogeny, therefore they are a separate mountain range even though they but up against the southern end of the rockies. The thinking on the origin of the Rockies as the result of the Laramide orogeny hasn't really changed. There has been some arguments about the time range of the orogeny, but most agree with the standard dates and none are are argued as being any younger than 35 million years in any part of the range, so it is quite distinct from the volcanism that formed the Jemez Mountains.

"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

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