New details emerge on temperature, mobility of earth's lower crust in Rocky Mountains

January 17, 2018, Colorado State University
Moho temperature at depths varyingfrom 20 to 50 km. Credit: Colorado State University

Everything on the surface of the Earth rests on massive tectonic plates that resemble a jelly sandwich, with two rigid pieces—the upper crust and the upper mantle—enclosing a gooey middle layer of very hot rocks, which is the lower crust. The plates move ever so slowly around the globe over a deeper hot layer called the asthenosphere.

Temperature plays a fundamental role in determining the strength, thickness, and buoyancy of the lower crust. A research team led by Colorado State University has mapped the and viscosity of the lower crust for the first time and found that, under much of the western United States, the layer is hot enough to be near its initial melting point and, therefore, quite runny.

This new research shows that significant regions of the lower crust have little strength, and that over several million years, could lead to many mountains in the western U.S. being flattened.

"Having a map of the temperature gives us an understanding of how strong the plate is," said Derek Schutt, associate professor in CSU's Department of Geosciences. "What we found is that there are places where the crust is not strong enough to hold the topography."

Imagine three slices of Silly Putty, two frozen pieces lying on the top and bottom of one that is room temperature. When you push on the top layer, the warm Silly Putty will be squeezed flat. Similar mechanics are at work in the Earth's crust.

"Mountains are formed by forces pushing things around, and weak areas collapsing," according to Schutt.

Outside forces could potentially push on the crust and that force could be transferred deep inland, which is called orogenic float, he said. The new study suggests this process may occur more often than previously thought.

"That can cause mountains to form at a great distance from where you're pushing on things," Schutt said. "Because the lower crust is mobile, force can be transmitted over a large distance."

Scientists generally think of tectonic plates, or lithosphere, as being made up of the crust and a cold uppermost mantle. But in this new analysis, the team saw something akin to ball bearings slipping between the crust and mantle. While not unexpected, this study was able to map the extent of the areas resembling ball bearings.

"The 'ball bearings' keep separate what's happening in the mantle from what's happening in the crust," said Schutt.

Researchers calculated temperatures at the bottom of the crust, which varies in thickness, by measuring the velocity of seismic waves that travel near the interface between the lower crust and .

In the western U.S., the crust is very hot, which is what makes it so weak.

"We know in general that the lower crust in the western United States seems hot," said Schutt. "But this is the first time we've been able to really ascribe a temperature to a specific location."

The findings, he said, are not too surprising. But the research could lead to more insight about why mountains exist and, more specifically, why they exist in places where the temperatures in the lower are so high.

Schutt and the research team will continue to explore the causes of variations in tectonic plate strength as part of an ongoing project between Colorado State University, Utah State University, and Scripps Institution of Oceanography at the University of California, San Diego. This research is funded by the National Science Foundation's Earthscope Program.

Explore further: What is the temperature of the Earth's crust?

More information: Derek L. Schutt et al, Moho temperature and mobility of lower crust in the western United States, Geology (2018). DOI: 10.1130/G39507.1

Related Stories

What is the temperature of the Earth's crust?

September 19, 2016

As you may recall learning in geology class, the Earth is made up of distinct layers. The further one goes towards the center of the planet, the more intense the heat and pressure becomes. Luckily, for those of us living ...

Scientists reveal the mystery about the origin of gold

November 22, 2017

An international group of scientists, with the participation of the University of Granada (UGR), has shed new light on the origin of gold, one of the most intriguing mysteries for the scientific community.

Data mining finds more than expected beneath Andean Plateau

August 23, 2017

Seismologists investigating how Earth forms new continental crust have compiled more than 20 years of seismic data from a wide swath of South America's Andean Plateau and determined that processes there have produced far ...

Steep rise of the Bernese Alps

March 24, 2017

The striking north face of the Bernese Alps is the result of a steep rise of rocks from the depths following a collision of two tectonic plates. This steep rise gives new insight into the final stage of mountain building ...

How continents were recycled

August 23, 2017

Plate tectonics shape the Earth's dynamic surface. But when did these dynamics first emerge? And will the present-day continents last forever?

Recommended for you

After a reset, Сuriosity is operating normally

February 23, 2019

NASA's Curiosity rover is busy making new discoveries on Mars. The rover has been climbing Mount Sharp since 2014 and recently reached a clay region that may offer new clues about the ancient Martian environment's potential ...

Study: With Twitter, race of the messenger matters

February 23, 2019

When NFL player Colin Kaepernick took a knee during the national anthem to protest police brutality and racial injustice, the ensuing debate took traditional and social media by storm. University of Kansas researchers have ...

Researchers engineer a tougher fiber

February 22, 2019

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging ...


Adjust slider to filter visible comments by rank

Display comments: newest first

3 / 5 (2) Jan 17, 2018
Maybe it's just me?
An obscure and abstractly minor issue, perhaps having, at most, some facsimile of related relevance, petty though it may be, seems to have been curiously omitted from this article.
Stupid question...I know. Silly me.
not rated yet Jan 18, 2018
Look at the USGS earthquake map

-Note the unbroken arc of quakes from LA through las vegas, up through utah, yellowstone and ending in northwest Montana. LA is where the Pacific plate is hung up as it travels northward along the San Andreas.

It's almost as if the pressure is so great it's trying to tear off a large chunk of the western part of this country.

I've been watching this for years and I've never seen this much activity.
not rated yet Jan 18, 2018
If you turn on satellite view it does seem to follow a series of features separating terrain types.
not rated yet Jan 18, 2018
If you follow this arc north it appears to join up with a very clear separation which is apparently the Columbia river valley.

I'm sure there must be a name for this great arc?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.