Rheology of Earth Materials :
Closing the gap between timescales in the laboratory and in the mantle

26 December 2023: New publication in Physics of the Earth and Planetary Interiors

Dislocations in naturally deformed olivine: Example of a mylonitic peridotite

Despite many years of interest in olivine deformation as a means of understanding the dynamics of the upper mantle, the microstructures of deformed samples in nature remain insufficiently documented. Yet they are essential witnesses to the behavior of olivine under natural conditions.
In this article, we study a peridotite specimen from an Oman ophiolite which has a mylonitic microstructure with remnant, strongly deformed, millimetric porphyroclasts coexisting with small newly formed olivine grains generated by dynamic recrystallization. Interestingly, even these small grains show evidence of dislocation creep. We show for the first time, thanks to detailed electron tomography characterization of dislocations, that in this sample naturally deformed under lithospheric conditions, dislocations move by mixed climb. This closer match between glide and climb velocities is probably a consequence of natural deformation conditions involving low stresses, which reduce glide velocity, and very low strain rates, which favor climb.

To learn more, please refer to:

S. Demouchy, A. Mussi, T. Weidner, E. Gardes & P. Cordier (2024) Dislocations in naturally deformed olivine: Example of a mylonitic peridotite. Physics of the Earth and Planetary Interiors, 346, 107125,  https://doi.org/10.1016/j.pepi.2023.107125

Free access to the article is provided by the publisher to anyone clicking on this link before February 14, 2024