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Grain- to multiple-grain-scale deformation processes during diffusion creep of forsterite + diopside aggregate: 1. Direct observations.

Authors :
Maruyama, G.
Hiraga, T.
Source :
Journal of Geophysical Research. Solid Earth. Aug2017, Vol. 122 Issue 8, p5890-5915. 26p.
Publication Year :
2017

Abstract

We uniaxially deformed fine-grained (~ 1 μm) forsterite + diopside (5 and 20 vol %) aggregates in the diffusion creep regime. Prior to deformation, line markers were milled on a lateral surface of a cylindrical sample to detect single- to multiple-grain-scale deformation. We performed deformation experiments and observations of the marker-etched surface after sample cooling multiple times on the same specimens. The strain measured at the scale of several tens of grains from macroscopic shortening of the markers parallel to the compression axis is consistent with the total strain of the sample. However, microscopically, the markers are intensely segmented and rotated at the grain scale increasing with the sample strain. Meanwhile, essentially, no deformation is observed within the grains in most of the samples. The surface microstructures, including the deformation of the markers, reveal the serial operations of grain boundary migration, grain boundary sliding, rigid body grain rotation, and grain neighbor switching, which correspond well to processes expected in diffusion-controlled superplasticity. This sequence is commonly observed in both samples consisting of forsterite grains of tabular and equiaxed grain shapes, which have been shown to develop notable crystallographic preferred orientation (CPO) and random (or weak) CPO, respectively, during diffusion creep. Intragranular regions of relatively larger forsterite grains in the specimens deformed at stresses near the transition between deformation mechanisms from diffusion creep to dislocation creep reveal marker deformation and formation of surface creases and subgrain boundaries, which indicate intragranular dislocation processes. Overall, the surface microstructures reflect the deformation state of the materials well. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
21699313
Volume :
122
Issue :
8
Database :
Academic Search Index
Journal :
Journal of Geophysical Research. Solid Earth
Publication Type :
Academic Journal
Accession number :
125244394
Full Text :
https://doi.org/10.1002/2017JB014254