Strain localization and fluid pathways in mylonite: inferences from in situ deformation of a water-bearing quartz analogue (norcamphor)

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• 作者：Bauer ; P. ; Palm ; S. ; Handy ; M.R.
• 关键词：brittle&ndash ; viscous transition ; fluid pathways ; mylonite ; shear zone ; strain localization ; quartz analogue
• 刊名：Tectonophysics
• 出版年：2000
• 出版时间：May 15, 2000
• 年：2000
• 卷：320
• 期：2
• 页码：141-165
• 全文大小：1.35 M

文摘

Simple shearing of polycrystalline norcamphor containing 10–15vol % water, at near-atmospheric pore fluid pressure and a range of constant temperatures (3–35°C) and shear strain rates (5×10⁻⁵–4×10⁻⁴s⁻¹), induces localization of both strain and fluid flow. Prior to deformation, the water is located at grain triple junctions and pockets along grain boundaries. It forms an average dihedral angle of 46° with the surrounding norcamphor grains. During initial shearing (γ≤1), grain boundaries oriented subparallel to the principal shortening direction dilate and fill with water. At 1<γ<2, these open grain boundaries interconnect to form water-filled dilatant shear surfaces at low angles (10–15°) to the shear zone boundary. These surfaces resemble shear bands or C′ surfaces in mylonitic rock and, depending on the temperature, accommodate displacement by cataclasis (T<15°C) or dislocation creep (T>15°C). The tips of the shear surfaces propagate alternately by intracrystalline plasticity and subcritical fracturing, concomitant with dynamic recrystallization in the rest of the sample. The episodic interconnection of dilatant shear surfaces is associated with short-term increases in displacement rate parallel to the surfaces. These surfaces coalesce to form a high-strain, fluid-filled network subparallel to the experimental shear zone. However, this network never spans the entire length of the shear zone at any given time, even after shearing to γ