Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Technique measures heat transport in the Earth's crust

01.04.2009
New spin on laser-flash analysis

Putting a new spin on an old technique, Anne M. Hofmeister, Ph.D., research professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis, has revolutionized scientists' understanding of heat transport in the Earth's crust, the outermost solid shell of our planet.

Temperature is an important driver of many geological processes, including the generation of magmas (molten rocks) in the deepest parts of the Earth's crust, about 30 to 40 kilometers below the surface. Yet, until recently, temperatures deep inside the Earth's crust were uncertain, mainly because of difficulties associated with measuring thermal conductivity, or how much heat is flowing through the rocks that compose the crust.

In conventional methods of measuring thermal conductivity, measurement errors arise as the temperature of a rock nears its melting point. At such high temperatures, heat is not just transported from atom to atom by vibrations, but also by radiation (light). Since conventional methods cannot separate heat flow carried by vibrations from that associated with radiation, most measurements of how efficiently rocks transport heat at high temperatures have been overestimated. Because of this experimental uncertainty, scientists have assumed rock conductivity to be constant throughout the crust in order to make advances in models describing Earth's geological behavior.

Laser-flash analysis

Using an industrial laser that is typically used for steel welding, Hofmeister was able to circumvent the problems that plagued the older methods. Her facility at WUSTL is the first in the world to employ such a laser for geoscience research.

Her technique, laser-flash analysis, provides much more accurate data on heat transport through rocks than conventional methods. In laser-flash analysis, a rock sample is held at a given temperature and then subjected to a laser pulse of heat, allowing Hofmeister to measure the time it takes for the heat to go from one end of the sample to the other. This measurement of thermal diffusivity, or how fast heat flows through matter, is another way to describe the thermal conductivity of a rock. Since measuring heat transport in the crust itself is impossible, Hofmeister used the laser to measure heat transport in individual rock samples at various temperatures and then averaged across samples to represent the dynamics of the crust. In collaboration with researchers from the University of Missouri - Columbia, Peter I. Nabelek, Ph.D., professor of geological sciences, and Alan G. Whittington, Ph.D., assistant professor of geological sciences, Hofmeister applied her findings to explain geological phenomena observed in the environment.

The results, published in Nature on March 19, 2009, suggest that rock conductivity is not constant as was previously assumed, but instead varies strongly with temperature. Hofmeister explains, "Our analysis shows that rocks are more efficient at conducting heat at low temperatures than was previously thought and less efficient at high temperatures. The process of moving heat around really depends on the temperature of the rocks."

Hofmeister and her collaborators found that the conductivity of rocks in the lower crust, where the external temperature is very high, is much lower — by as much as 50 percent — than was predicted by conventional methods. These results also suggest that the lower crust may be much hotter than scientists previously recognized. Since rocks become better insulators and poorer conductors at high temperatures, the lower crust acts like a blanket over the heat-generating mantle, the layer underlying the crust.

Magma machine

The observation that the lower crust is a good thermal insulator has broad implications for scientists' understanding of fundamental geological processes such as magma production.

Hofmeister explains, "The new methods change our understanding of how heat is transported in geological environments. This pertains to where you find magmas, where you cook metamorphic rock, and where lavas form on ocean ridges."

She and her colleagues used the new temperature-dependent data to inform computer models that predict the consequences of burying and heating up rocks during mountain belt formation, as occurs in the present-day Himalayas. While prior models relied upon extraordinary processes such as high levels of radioactivity to explain melting of the crust in the Himalayas, Hofmeister and her collaborators' work suggests that the thermal properties of the rocks themselves might be sufficient to generate magmas.

In particular, they find that the strain heating, or friction, caused by mountain belt formation can trigger crustal melting. Because the lower crust is such a good thermal insulator, strain heating is much faster, more efficient, and more self-perpetuating than previously recognized.

"The melt is more insulating than the rock," explains Hofmeister, "Once you get rocks melting, the thermal diffusivity goes down, which makes it harder to cool the rocks. They stay hot longer and there's the potential for more melting."

According to Hofmeister, the Himalaya situation described in the study is probably not unique. Because heat transport is such an important driver, many models of Earth's geological behavior will need to be revisited in light of Hofmeister and her collaborators' findings.

These advances bring Hofmeister much closer to accomplishing what she describes as her life-long career objective. "The goal for most of my career has been to determine the temperature inside the earth. It's the time dependence, how long it takes heat to flow through rocks, that is going to tell us how hot the interior is," she says.

According to Hofmeister, understanding the temperature of the Earth's interior is the first step towards understanding the thermal evolution of the earth.

Anne Hofmeister | EurekAlert!
Further information:
http://www.wustl.edu

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>