Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

High pressure experiments reproduce mineral structures 1,800 miles deep

24.09.2010
Crystal structure of post-perovskite explains anisotropic seismic wave propagation

University of California, Berkeley, and Yale University scientists have recreated the tremendous pressures and high temperatures deep in the Earth to resolve a long-standing puzzle: why some seismic waves travel faster than others through the boundary between the solid mantle and fluid outer core.

Below the earth's crust stretches an approximately 1,800-mile-thick mantle composed mostly of a mineral called magnesium silicate perovskite (MgSiO3). Below this depth, the pressures are so high that perovskite is compressed into a phase known as post-perovskite, which comprises a layer 125 miles thick at the core-mantle boundary. Below that lies the earth's iron-nickel core.

Understanding the physics of post-perovskite, and therefore the physics of the core-mantle boundary, has proven tough because of the difficulty of recreating the extreme pressure and temperature at such depths.

The researchers, led by Yale post-doctoral fellow Lowell Miyagi, a former UC Berkeley graduate student, used a diamond-anvil cell to compress an MgSiO3 glass to nearly 1.4 million times atmospheric pressure and heated it to 3,500 Kelvin (more than 3,000 degrees Celsius, or nearly 6,000 degrees Fahrenheit) to create a tiny rock of post-perovskite. They then further compressed this to 2 million times atmospheric pressure and zapped the substance with an intense X-ray beam from the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory to obtain a diffraction picture that reveals the deformation behavior of post-perovskite.

They found that the orientation of post-perovskite's crystals in the deformed rock allowed some seismic waves – those polarized parallel to the core-mantle boundary – to travel faster than those polarized perpendicular to it. This anisotropic structure may explain the observations of seismologists using seismic waves to probe the earth's interior.

"For the first time, we can use mineral physics with diamond-anvil cells at the ALS to get information about how this mineral, post-perovskite, performs under intense pressure," said co-author Hans-Rudolf Wenk, a Professor of the Graduate School in UC Berkeley's Department of Earth and Planetary Science and Miyagi's Ph.D. thesis advisor. "People had suggested this as an explanation for the anisotropy, but now we have experimental evidence."

"Understanding how post-perovskite behaves is a good start to understanding what's happening near the mantle's lower reaches," Miyagi said. "We can now begin to interpret flow patterns in this deep layer in the earth."

The study, which appears in the Sept. 24 issue of the journal Science, has important implications for understanding how the earth's internal heating and cooling processes work.

"This will give seismologists confidence in their models by matching what these observations predict with the seismic data they get," said coauthor Waruntorn "Jane" Kanitpanyacharoen, a UC Berkeley graduate student.

Post-perovskite was first recognized as a high-pressure phase in the mantle in 2004, and subsequent experiments in diamond-anvil cells have produced the mineral. Wenk and his colleagues in 2007 conducted experiments that they thought had determined the deformation behavior of post-perovskite, but which now appear to have been related to the phase transformation to post-perovskite. This transition takes place at about 1,300,000 times atmospheric pressure (127 gigaPascals) and 2,500 Kelvin (4,000 degrees Fahrenheit).

The current experiment showed that post-perovskite's crystal structure is deformed by pressure into a more elongated shape. Because seismic waves travel faster in the stretched direction, this matches the observed difference in velocity between seismic waves polarized horizontally and vertically traveling through the post-perovskite zone above the earth's core.

If scientists can gain a better understanding of the core-mantle boundary's behavior, it will give them clues as to how Earth's internal convection works there, where cool tectonic plates descend from the ocean floor through the mantle eventually nearing the dense, liquid-iron outer core, heat up, and begin moving upward again in a repeated cycle that mixes material and heat through the mantle.

Other authors of the paper include UC Berkeley researcher Pamela Kaercher and Kanani K. M. Lee, assistant professor of geology and geophysics at Yale.

The work was funded by the National Science Foundation, with support for the ALS from the U.S. Department of Energy.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Earth Sciences:

nachricht In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>