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In situ deformation experiments to study ductile strain localization (InSiDe-Strain)
Start date: Jul 1, 2013, End date: Jun 30, 2015 PROJECT  FINISHED 

Plate tectonics, by linking the evolution of the Earth’s surface to the dynamics of the deep interior, has provided a coherent framework to understand the formation of mountain ranges and oil-rich sedimentary basins, as well as the distribution of major catastrophic events such as volcanic eruptions and earthquakes. We now understand that it is an essential and unique feature of mantle convection but the processes behind still remain a major open question. Strain localization at the plate scale is crucial for the generation of plate tectonics from a convecting mantle but, while in the brittle field (producing faults) it is a well-known process, in the ductile regime –within 5/6 of the plates– it is still poorly understood. The most enigmatic point is the initiation of strain localization in a homogeneous and isotropic medium. How the deformation itself produces a heterogeneous weakening leading to localization: is it driven by shear heating or grain size reduction? Detailed microstructural observations on naturally-deformed rocks and existing laboratory experiments did not allow quantifying the processes that occur during plastic deformation thus the initiation of strain localization is still under debate. In this project we propose to obtain this data, which is essential for understanding and modeling strain localization due to microstructural evolution, via in situ experiments in SEM dedicated to the measurement of crystal orientations by indexation of EBSD patterns allowing for high-resolution characterization of the microstructural evolution during deformation. The proposed experiments will be performed on polycrystalline ice and magnesium, which (1) deform ductilely in the PT range of experimental conditions applicable in the SEM-EBSD, and (2) show strong anisotropy, hence, can model the viscoplastic deformation of major constituent minerals of the deep Earth’s interior (olivine and quartz). Results will be constrained by comparison with observations in natural shear zones.
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