Featured Research

from universities, journals, and other organizations

Earth's mantle plasticity explained: Missing mechanism for deforming olivine-rich rocks

Date:
March 6, 2014
Source:
CNRS
Summary:
The Earth's mantle is a solid layer that undergoes slow, continuous convective motion. But how do these rocks deform, thus making such motion possible, given that minerals such as olivine (the main constituent of the upper mantle) do not exhibit enough defects in their crystal lattice to explain the deformations observed in nature? Scientists have provided an unexpected answer to this question. It involves little known and hitherto neglected crystal defects, known as 'disclinations', which are located at the boundaries between the mineral grains that make up rocks.

Optical microscopy image in cross polarized light of a natural olivine polycrystal (Oman mylonite).
Credit: S. Demouchy, Montpellier

Earth's mantle is a solid layer that undergoes slow, continuous convective motion. But how do these rocks deform, thus making such motion possible, given that minerals such as olivine (the main constituent of the upper mantle) do not exhibit enough defects in their crystal lattice to explain the deformations observed in nature? A team led by the Unité Matériaux et Transformations (CNRS/Université Lille 1/Ecole Nationale Supérieure de Chimie de Lille) has provided an unexpected answer to this question. It involves little known and hitherto neglected crystal defects, known as 'disclinations', which are located at the boundaries between the mineral grains that make up rocks. Focusing on olivine, the researchers have for the first time managed to observe such defects and model the behavior of grain boundaries when subjected to a mechanical stress.

The findings, which have just been published in Nature, go well beyond the scope of the geosciences: they provide a new, extremely powerful tool for the study of the dynamics of solids and for the materials sciences in general.

Earth continuously releases its heat via convective motion in Earth's mantle, which underlies the crust. Understanding this convection is therefore fundamental to the study of plate tectonics. The mantle is made up of solid rocks. In order for convective motion to occur, it must be possible for the crystal lattice of these rocks to deform. Until now, this was a paradox that science was unable to fully resolve. While defects in the crystal lattice, called dislocations, provide a very good explanation of the plasticity of metals, they are insufficient to explain the deformations undergone by certain mantle rocks.

The researchers suspected that the solution was to be found at the boundaries between the mineral grains that make up rocks. However, they lacked the conceptual tools needed to describe and model the role played by these boundaries in the plasticity of rocks. Researchers at the Unité Matériaux et Transformations (CNRS/Université Lille 1/Ecole Nationale Supérieure de Chimie de Lille) in collaboration with researchers at the Laboratoire Géosciences Montpellier (CNRS/Université Montpellier 2) and the Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux (CNRS/Université de Lorraine/Arts et Métiers ParisTech/Ecole Nationale d'Ingénieurs de Metz) have now explained this role. They have shown that the crystal lattice of the grain boundaries exhibits highly specific defects known as 'disclinations', which had hitherto been neglected. The researchers succeeded in observing them for the first time in samples of olivine (which makes up as much as 60% of the upper mantle) by using an electron microscope and specific image processing. They even went further: based on a mathematical model, they showed that these disclinations provided an explanation for the plasticity of olivine. When mechanical stress is applied, the disclinations enable the grain boundaries to move, thus allowing olivine to deform in any direction. Flow in the mantle is thus no longer incompatible with its rigidity.

This research goes beyond explaining the plasticity of rocks in Earth's mantle: it is a major step forward in materials science. Consideration of disclinations should provide scientists with a new tool to explain many phenomena related to the mechanics of solids. The scientists intend to continue their research into the structure of grain boundaries, not only in other minerals but also in other solids such as metals.


Story Source:

The above story is based on materials provided by CNRS. Note: Materials may be edited for content and length.


Journal Reference:

  1. Patrick Cordier, Sylvie Demouchy, Benoît Beausir, Vincent Taupin, Fabrice Barou, Claude Fressengeas. Disclinations provide the missing mechanism for deforming olivine-rich rocks in the mantle. Nature, 2014; 507 (7490): 51 DOI: 10.1038/nature13043

Cite This Page:

CNRS. "Earth's mantle plasticity explained: Missing mechanism for deforming olivine-rich rocks." ScienceDaily. ScienceDaily, 6 March 2014. <www.sciencedaily.com/releases/2014/03/140306112228.htm>.
CNRS. (2014, March 6). Earth's mantle plasticity explained: Missing mechanism for deforming olivine-rich rocks. ScienceDaily. Retrieved September 21, 2014 from www.sciencedaily.com/releases/2014/03/140306112228.htm
CNRS. "Earth's mantle plasticity explained: Missing mechanism for deforming olivine-rich rocks." ScienceDaily. www.sciencedaily.com/releases/2014/03/140306112228.htm (accessed September 21, 2014).

Share This



More Earth & Climate News

Sunday, September 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Will Climate Rallies Spur Change?

Will Climate Rallies Spur Change?

Newsy (Sep. 21, 2014) — Organizers of the People's Climate March and other rallies taking place in 166 countries hope to move U.N. officials to action ahead of their summit. Video provided by Newsy
Powered by NewsLook.com
Thousands March in NYC Over Climate Change

Thousands March in NYC Over Climate Change

AP (Sep. 21, 2014) — Accompanied by drumbeats, wearing costumes and carrying signs, thousands of demonstrators filled the streets of Manhattan and other cities around the world on Sunday to urge policy makers to take action on climate change. (Sept. 21) Video provided by AP
Powered by NewsLook.com
Climate Change Rally Held in India Ahead of UN Summit

Climate Change Rally Held in India Ahead of UN Summit

AFP (Sep. 20, 2014) — Some 125 world leaders are expected to commit to action on climate change at a UN summit Tuesday called to inject momentum in struggling efforts to tackle global warming. Duration: 00:41 Video provided by AFP
Powered by NewsLook.com
New Music With Recycled Instruments at Colombia Fest

New Music With Recycled Instruments at Colombia Fest

AFP (Sep. 19, 2014) — Jars, bottles, caps and even a pizza box, recovered from the trash, were the elements used by four musical groups at the "RSFEST2014 Sonorities Recycling Festival", in Colombian city of Cali. Duration: 00:49 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins