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DOI	10.1016/j.tecto.2021.228736
	Shear deformation of nano- and micro-crystalline olivine at seismic slip rates
	Thieme M.; Pozzi G.; Demouchy S.; De Paola N.; Barou F.; Koizumi S.; Bowen L.
发表日期	2021
ISSN	00401951
卷号	802
英文摘要	Several thermally activated mechanisms have been proposed to explain the dynamic weakening of faults at fast, seismic slip rates v > 0.1 m s−1. Nevertheless, direct constraints from microstructural observations on the operation of such weakening mechanisms are still lacking for most rock forming minerals. This includes olivine, a very refractory mineral relevant for seismic activity occurring in peridotite massifs. Here, we report mechanical data and microstructures of olivine aggregates deformed in a rotary shear apparatus at slip rates from 10−2 m s−1 to 1 m s−1. A number of 34 shear deformation experiments were performed under axial stresses of 20 MPa and at room temperature. Samples are composed of either synthetic iron-free nanocrystalline forsterite powder (initial grain size = 0.07 μm) or natural iron-bearing olivine powder from San Carlos or San Bernardino (Fo91, Arizona, USA; initial grain size = 70 ± 2 μm). Shear deformation lasts from a few seconds up to 5 min and ends after 0.03 to 3 m of slip. Independently of the initial grain size or composition, friction coefficients decrease from peak values of 0.8 to values below 0.4, after only 0.1 m of slip. The recovered samples were characterized by scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. For all samples, before the onset of dynamic weakening, the deformation localizes in a principal shear zone, well-marked in the natural olivine aggregates by a rapid decrease of grain size down to <1.7 μm. Variations in texture, fractured grains and the formation of a fine-grained matrix support cataclastic flow at an early stage of deformation, responsible for the foremost grain size reduction. The samples display well-defined zones with partially sintered microstructure, and shape preferred orientation. The initial texture of the cold-pressed starting material is rapidly reduced to a near random distribution after only 0.03 m of slip. All crystal preferred orientations (CPO) remain weak, with a J-index ≲2. Based on the microstructures, the dominant deformation mechanism may be enhanced effective diffusion (by surface and grain boundary diffusion) causing mechanical weakening and a viscous behavior, which is then temperature-dependent under sub-solidus conditions. We find no microstructural evidence for frictional melting, flash heating or thermal decomposition. Our results advocate that dynamic weakening of faults is independent of initial grain size, and can be achieved after displacements as low as 0.1 m without production of frictionally induced-melt. © 2021 Elsevier B.V.
关键词	Experimental deformation Friction High-velocity torsion Olivine Shear zone
英文关键词	Aggregates; Crystal orientation; Decomposition; Friction; Grain boundaries; Grain size and shape; High resolution transmission electron microscopy; Iron; Nanocrystalline materials; Nanocrystals; Olivine; Scanning electron microscopy; Seismology; Shear deformation; Textures; Crystal preferred orientations; Dominant deformation mechanism; Electron back scatter diffraction; Grain-boundary diffusion; Micro-structural observations; Nanocrystalline forsterite; Shape preferred orientations; Thermally activated mechanisms; Fault slips; crystallinity; deformation; experimental study; grain size; olivine; preferred orientation; seismicity; shear zone; slip rate; thermal decomposition
语种	英语
来源期刊	Tectonophysics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/208079
作者单位	Geosciences Montpellier, CNRS and Université de Montpellier, UMR 5243, Montpellier, 34095, France; Department of Earth Sciences, Rock Mechanics Laboratory, Durham University, Durham, DH1 3LE, United Kingdom; Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Tokyo, Japan; Department of Physics, Durham University, Durham, DH1 3LE, United Kingdom
推荐引用方式 GB/T 7714	Thieme M.,Pozzi G.,Demouchy S.,et al. Shear deformation of nano- and micro-crystalline olivine at seismic slip rates[J],2021,802.
APA	Thieme M..,Pozzi G..,Demouchy S..,De Paola N..,Barou F..,...&Bowen L..(2021).Shear deformation of nano- and micro-crystalline olivine at seismic slip rates.Tectonophysics,802.
MLA	Thieme M.,et al."Shear deformation of nano- and micro-crystalline olivine at seismic slip rates".Tectonophysics 802(2021).