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 July 25, 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 July 25, 2014).

Share This




More Earth & Climate News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Goma Cheese Brings Whiff of New Hope to DRC

Goma Cheese Brings Whiff of New Hope to DRC

Reuters - Business Video Online (July 24, 2014) — The eastern region of the Democratic Republic of Congo, mainly known for conflict and instability, is an unlikely place for the production of fine cheese. But a farm in the village of Masisi, in North Kivu is slowly transforming perceptions of the area. Known simply as Goma cheese, the Congolese version of Dutch gouda has gained popularity through out the region. Ciara Sutton reports. Video provided by Reuters
Powered by NewsLook.com
Bill Gates: Health, Agriculture Key to Africa's Development

Bill Gates: Health, Agriculture Key to Africa's Development

AFP (July 24, 2014) — Health and agriculture development are key if African countries are to overcome poverty and grow, US software billionaire Bill Gates said Thursday, as he received an honourary degree in Ethiopia. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com
Higgins Breaks Record at Mt. Washington

Higgins Breaks Record at Mt. Washington

Driving Sports (July 24, 2014) — Subaru Rally Team USA drivers David Higgins and Travis Pastrana face off against a global contingent of racers at the annual Mt. Washington Hillclimb in New Hampshire. Includes exclusive in-car footage from Higgins' record attempt. Video provided by Driving Sports
Powered by NewsLook.com
Storm Kills Three, Injures 20 at Virginia Campground

Storm Kills Three, Injures 20 at Virginia Campground

Reuters - US Online Video (July 24, 2014) — A likely tornado tears through an eastern Virginia campground, killing three and injuring at least 20. Linda So reports. Video provided by Reuters
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