What is it about?
There has been a long debate on the deep structure of cratons which form the core of continents. These old and stable Precambrian cores are underlain by high-velocity roots or keels that can extend to depths greater than 200 km. Here we show that the deep parts of cratons experience a peculiar deformation.
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Why is it important?
These results suggest that olivine, a major constituant of the Earth upper mantle is aligned preferentially in the horizontal plane, but is azimuthally random at large scale beneath cratons. Most cratons are located on "slow" plates with horizontal motion smaller than 4 cm/year. This "slow" motion may therefore not produce sufficient shearing at the base of continental plates to align at large scale olivine crystals. The 3D model is updated with new data on a regular basis and can be downloaded from : http://perso.ens-lyon.fr/eric.debayle/ or https://ds.iris.edu/ds/products/emc-3d2017_09sv/
Perspectives
This model is compatible with previous observations suggesting that radial anisotropy extends deeper beneath continents than beneath oceans (Gung et al, Nature, 2003) but involves a different story that needs to be tested in the future.
Eric Debayle
CNRS - University of Lyon - Université Claude Bernard - ENS Lyon
Read the Original
This page is a summary of: An automatically updatedS-wave model of the upper mantle and the depth extent of azimuthal anisotropy, Geophysical Research Letters, January 2016, Wiley,
DOI: 10.1002/2015gl067329.
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