An uplifting story

Rocky Mountains Get Deep Study

American Association of Petroleum Geologists (AAPG)

Everyone knows that Colorado is a scenic, beautiful locale.

Scientists using state-of-the-art 3-D seismic technology are trying to explain in detail how it got to be that way.

The Colorado Rockies Experiment and Seismic Transects – perhaps better recalled by its acronym, CREST – is a project that will provide near 3-D teleseismic images of the geometry of the mantle anomaly in the central part of the state.

More specifically, CREST will investigate time-space correlation between Cenozoic rock uplift and denudation patterns, magmatism and the modern day mantle anomaly using a host of integrated geological and geophysical techniques.

The purpose is to understand when and why changes in lithospheric buoyancy occurred in the Rockies, how these changes have been expressed in terms of Cenozoic magmatism and the topographic evolution of the highest elevation region of the Rocky Mountains.

In other words, why those beautiful mountains are so beautiful.

“We hope to gain increased understanding on how intra-plate mountain building and continental lithosphere evolve under a wide variety of tectonic influences relevant to western North America, and generally on Earth, including compression, extension, magmatism and small-scale mantle convection,” said CREST principal investigator Rick Aster.

Looking for Answers

CREST’s focus on deep Earth imaging is intended to augment pre-existing data already gained in imaging projects, specifically since 2008, which included recorded earthquakes from around the world.

Aster, a professor of geophysics who is a department chair at the Geophysical Research Center and Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, said the CREST recorders started earlier this year and will remain in place for approximately another year, collecting seismic data to help explain how mantle processes beneath the Colorado Rocky Mountains have influenced their tectonic history.

Dating, geomorphology and other efforts, Aster said, will continue for several years after that.

“We also are surveying the gravity, geochemistry, pluton ages, geodynamics, exposure dates, stream incision and other geomorphic data, and other data from the region to assess the tectonic evolution of the region in consort with what we learn from the deep seismic imaging,” he said.

So what is it about Colorado that made researchers deduce the Rockies were at the climax of an enigma?

“The lithosphere in the Rocky Mountain region occupies an important transition between ancient lithosphere to the east and recently altered lithosphere to the west,” Aster said.

“The Rocky Mountains occupy one of the broadest plate boundary regions on Earth,” he added, “where we can see lots of mantle/lithosphere dynamic processes being played out that fundamentally help us learn how continents grow, evolve and erode, both from the top and bottom, throughout Earth history.”

Curtain Going Up

In theatrical terms, researchers view the history of Colorado’s Rockies as something of a three-act play: The initial uplift that began as a low-angle subduction of the Farrallon plate during the Laramide Orogeny; when the strike-slip San Andreas Fault did a version of the geologic merengue and started to form; finally, the post-Laramide “ignimbrite flare-up” in the San Juan Mountains.

The hope is that CREST will now be able to review the entire show. Aster hopes the project will be at the vanguard of a new set of multidisciplinary earth investigations in the region where geologists, geophysicists, geomorphologists and geochronologists can work in larger teams to more fully characterize and understand the history of this often baffling region.

Specifically, the imaging methods employed by CREST will be:

Seismic layering that shows up as velocity discontinuities (for example, Moho, at the base of the continental crust, a zone of complexity in the Rockies).

Tomograms that can reveal bulk mantle seismic velocity structure (for example, in the region of Aspen).

Work like CREST has been going on elsewhere internationally for years; North America is now a player of such investigations because of EarthScope, a National Science Foundation mega-project in which CREST is imbedded, and the IRIS PASSCAL instrument pool (managed at the Instrument Center on the NMT campus).

EarthScope will probe the deep structure of the entire conterminous United States with a 2,000-station moving network of seismographic stations called USArray. CREST will add an additional 59 stations, specifically in and around the Aspen anomaly.

In a sense, they’re both part of the same enigma – both hoping to unlock the same climax.

The partnership between CREST and USArray, however, constitutes one of the largest and densest seismic arrays currently deployed on earth – and represents an unprecedented scientific search for the meaning of one’s state’s beauty.

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