气候变化领域集成服务门户(CCPortal): How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?

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DOI	10.1029/2020JB020323
	How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?
	Cross A.J.; Olree E.; Couvy H.; Skemer P.
发表日期	2020
ISSN	21699313
卷号	125 期号:8
英文摘要	Ultramylonites—intensely deformed rocks with fine grain sizes and well-mixed mineral phases—are thought to be a key component of Earth-like plate tectonics, because coupled phase mixing and grain boundary pinning enable rocks to deform by grain-size-sensitive, self-softening creep mechanisms over long geologic timescales. In isoviscous two-phase composites, “geometric” phase mixing occurs via the sequential formation, attenuation (stretching), and disaggregation of compositional layering. However, the effects of viscosity contrast on the mechanisms and timescales for geometric mixing are poorly understood. Here, we describe a series of high-strain torsion experiments on nonisoviscous calcite-fluorite composites (viscosity contrast, ηca/ηfl ≈ 200) at 500°C, 0.75 GPa confining pressure, and 10−6–10−4 s−1 shear strain rate. At low to intermediate shear strains (γ ≤ 10), polycrystalline domains of the individual phases become sheared and form compositional layering. As layering develops, strain localizes into the weaker phase, fluorite. Strain partitioning impedes mixing by reducing the rate at which the stronger (calcite) layers deform, attenuate, and disaggregate. Even at very large shear strains (γ ≥ 50), grain-scale mixing is limited, and thick compositional layers are preserved. Our experiments (1) demonstrate that viscosity contrasts impede mechanical phase mixing and (2) highlight the relative inefficiency of mechanical mixing. Nevertheless, by employing laboratory flow laws, we show that “ideal” conditions for mechanical phase mixing may be found in the wet middle to lower continental crust and in the dry mantle lithosphere, where quartz-feldspar and olivine-pyroxene viscosity contrasts are minimized, respectively. ©2020. American Geophysical Union. All Rights Reserved.
英文关键词	calcite; geometric mixing; shear zone; strain partitioning; torsion; ultramylonite
语种	英语
来源期刊	Journal of Geophysical Research: Solid Earth
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/187685
作者单位	Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States; Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States
推荐引用方式 GB/T 7714	Cross A.J.,Olree E.,Couvy H.,et al. How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?[J],2020,125(8).
APA	Cross A.J.,Olree E.,Couvy H.,&Skemer P..(2020).How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?.Journal of Geophysical Research: Solid Earth,125(8).
MLA	Cross A.J.,et al."How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?".Journal of Geophysical Research: Solid Earth 125.8(2020).