Momentum

Allen McGrew is a video "rock star." The associate professor of geology shares his field research into the extreme stretching of the Earth’s crust in northeastern Nevada on the RuGGEd YouTube channel, which has received thousands of views from students, science educators and geoscience professionals.

The videos are produced with colleagues from the University of Colorado Boulder and Great Basin College under a National Science Foundation grant totaling nearly $400,000. The University of Dayton received $200,000 from the grant.

The growing collection of Nevada geology tutorials are linked to an interactive Google map, so geology students and tourists can download the material before field trips or hikes. The channel also has videos about laboratory practices featuring University of Dayton geology students, and videos of the researchers discussing results at Geological Society of America conferences.

The research highlighted on the YouTube channel centers on a large section of the western U.S. —between Salt Lake City and Reno, Nevada — that has roughly doubled in width over the last 40 million years due to extreme stretching and extension of the Earth’s crust. Focusing on a well-exposed section of crust in the Ruby Mountains-East Humboldt Range-Wood Hills metamorphic core complex, McGrew and his colleagues are examining rocks that were brought to the surface from 12 to 24 miles deep by large, geological faults. Using radiometric age-dating, their goal is to determine the timing and rate of the extension, which is the subject of scientific debate.

“These rocks were deep and they were hot,” McGrew said. “They were probably at least 600 degrees Celsius at their original depths. As they are brought up by these faults, they cool as they get closer to the surface. We use that cooling as a fingerprint for this ‘unroofing’ — the rate at which these rocks were brought up to the surface. You can apply this technique to different minerals and they will begin recording this history at different temperatures, so you can develop a fairly continuous cooling history from over 500 degrees to about 50 degrees Celsius. Then, when they get to the surface they begin eroding and they show up in surface deposits, so you can really track the complete history of their journey.”

Some geologists believe 90% of the extension occurred after 17 million years ago, when the North American tectonic plate began to drift over the “Yellowstone hot spot,” a long-lived volcanic center. However, McGrew and others have argued that the extension actually began about 40 million years ago during a series of large geological events, including a widespread outburst of volcanism across Nevada.

“What we’ve been able to show is that the latter view is basically correct,” he said.

McGrew has done field work in northeastern Nevada since he joined the University faculty in 1995. Under the NSF grant, he has made regular trips to the Ruby Mountains, accompanied by five University of Dayton undergraduate students, as well as several from CU Boulder and Great Basin College in nearby Elko, Nevada. He is interested in the geological history of the mountains, but the area is also of great economic interest because it sits in the heart of North America’s largest gold-producing province.

Currently, he is completing the age-dating and working with his colleagues — James Metcalf of CU Boulder and Carrie Bruno Meisner of Great Basin College — to synthesize data and prepare their findings for publication.