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8 September 2017

Big earthquake in southwestern Mexico, M8.1

The M8.1 southwestern Mexico earthquake is discussed and placed in context.


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9 April 2014

Faults disrupting the contact between the Muleros Andesite and Mesilla Valley Formation shale

Hark! What gleams on yonder contact? Well, there’s no glaciers to polish anything ’round these here parts (southernmost New Mexico + westernmost Texas), so I reckon it must be fault polish. Let’s test that hypothesis by looking for slickensides… Sure enough! There they are! Unlike the deformation we saw yesterday, this faulting of the contact between the Muleros Andesite (Eocene) and the Mesilla Valley Formation shale (Cretaceous) into which it …


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8 April 2014

Deformation associated with the intrusion of the Muleros Andesite

Yesterday, I showed off a few views of the contact between the Cretaceous aged Mesilla Valley Formation shale and the hypabyssal Muleros Andesite which intruded into it during the Eocene at Mt. Cristo Rey (on the US/Mexico border where Texas meets New Mexico). Today, I’d like to look at some of the structure associated with the contact zone. First off, take a look at this image, which is looking orthogonal …


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7 April 2014

Contact between Muleros Andesite and Mesilla Valley Formation shale at Mt. Cristo Rey

There are two rock units in this photo. One is igneous, one is sedimentary. Can you find the contact between them? It’s somewhere along this dashed line… The Mesilla Valley Formation is Cretaceous shale with some sandstone. The Muleros Andesite (pretty much identical to the Campus Andesite you find at UTEP) is Eocene. Here’s a closer, more precisely-constrained, look at it: …but that one is in the shade. It’s bolder …


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9 April 2012

Pliegue de Viernes? No, pero es una roca ígnea de México

I got an email a few weeks back from Moritz K., a PhD student at the Universidad Nacional Autónoma de México (UNAM) in Querétaro. He wanted to offer up a potential Friday fold. Here’s what he had to say: I wanted to send you a couple of pictures of folds I took in my PhD field area in southern Mexico in a tonalitic/dioritic, strongly banded sequence in the Totoltepec pluton …


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13 February 2012

Recumbent fold in Sierra de Juarez, Mexico

Callan looks south across the border from Texas. Above the drug-war-ravaged town of Juarez, the Sierra de Juarez Mountains feature an enormous recumbent synform.


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11 February 2012

A campus underlain by porphyritic andesite

The campus of the University of Texas at El Paso is a beautiful place. You can look south into Mexico, a scant half mile away. It’s got rocky hills rising up between buildings and between stadiums (stadia?), and a utterly unique campus architecture based on the Himalayan nation of Bhutan. Here’s a look at the rocks beneath the university… The main rock type is a porphyritic andesite – probably a …


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17 October 2011

Hawk migration in Mexico

Two images that have me scheming to go down to Veracruz, Mexico, next September for a weekend of hawk-watching: …Impressive, no? Better yet, check this out: …Oh. Yeah.


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