کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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6430624 | 1634804 | 2012 | 12 صفحه PDF | دانلود رایگان |
We performed high-strain torsion experiments on aggregates of Fo50 olivine to test the influence of imposed boundary conditions on localizing deformation. We deformed both solid and thin-walled cylinders of Fo50 either at constant strain rate or at constant stress. Samples deformed in constant-strain-rate experiments reached a peak stress followed by weakening at a continually decreasing weakening rate. In contrast, samples deformed in constant-stress experiments weakened at an accelerating weakening rate. Localization is manifested in samples deformed at constant stress as irregularities along strain markers, S-C foliations, and torsional buckling of thin-walled cylinders. In contrast, samples deformed at constant strain rate deformed homogeneously. Grain-boundary maps created with electron-backscatter-diffraction data indicate that high-strain regions in constant-stress samples correlate with finer grain sizes and stronger crystallographic fabrics. Since the dominant deformation mechanism is grain-size sensitive, heterogeneous recrystallization leads to strain localization in finer-grained regions. However, variations in strength are not large enough to initiate localization in constant-strain-rate experiments. The magnitude of grain-size heterogeneity remains relatively constant with increasing strain, implying that shear zones are maintained throughout the experiments even as non-localizing regions recrystallize. Based on our results, we propose that deformation driven at constant stress in Earth's lithosphere will easily localize even if structural heterogeneities are not initially present.
⺠We tested how shear zone boundary conditions affect strain localization in olivine. ⺠Samples were deformed in torsion at either constant strain rate or constant stress. ⺠Constant-stress conditions significantly increase the likelihood of localization. ⺠Localization occurs by grain-size reduction coupled with grain-boundary sliding.
Journal: Earth and Planetary Science Letters - Volumes 333â334, 1 June 2012, Pages 134-145