Pseudotachylytes Generated During Seismic Faulting and Eclogitization of the Deep Crust

Austrheim, Håkon; Boundy, T. M.

doi:10.1126/science.265.5168.82

Cited by 258 publications

(183 citation statements)

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“…It is conceivable that cavitation may contribute to an enhanced permeability and fluid flow localized in shear zones that is frequently observed [Rutter and Brodie, 1985]. Unstable ductile failure in mylonite shear zones at the base of the seismogenic upper crust has been suggested as a possible source mechanism for earthquakes [Hobbs and Ord, 1988] and pseudotachylytes at great depth [Austrheim and Boundy, 1994;Hobbs et al, 1986;White, 1996;Renshaw and Schulson, 2004]. Failure is often attributed to shear heating and/or dehydration reactions and possibly transient fluid pressure pulses.…”

Section: Introductionmentioning

confidence: 99%

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Rybacki¹,

Wirth²,

Dresen³

2010

J. Geophys. Res.

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[1] We performed high-strain torsion experiments on fine-grained (≈4 mm) anorthite aggregates in a Paterson-type gas deformation apparatus. The dense hydrous (≈0.1 wt% H 2 O) samples contain < 3 vol% Si-enriched residual glass located at triple junctions. Specimens were twisted at constant rate to a maximum shear strain of about 5 at experimental conditions of 100-400 MPa confining pressure, temperatures of 950°C-1200°C, and shear strain rates of ≈2 × 10 −5 , 5 × 10 −5 , and 2 × 10 −4 s −1 . Resulting maximum shear stresses at the sample periphery were in the range of ≈2-80 MPa. The samples showed strain hardening at slow deformation rate and strain weakening at fast strain rate, respectively. Fitting the stress strain rate data to a power law yields linear viscous behavior. Microstructural analysis shows locally enhanced dislocation density, suggesting diffusion-assisted and/or dislocation-assisted grain boundary sliding as the dominant deformation mechanism. Deformed samples exhibit abundant cavities, nucleated mostly at grain triple junctions and at grain boundaries in response to cooperative grain boundary sliding. At shear strains ≥ 2, growth and coalescence of the cavities form an anastomozing network of regularly spaced strings oriented at about 30°to the direction of maximum compressive stress and ∼15°to the shear plane. Strain is localized along these shear bands associated with a shape-preferred orientation of high-aspect ratio feldspar grains and with segregation of initial pore fluids (residual glass) into the bands. More than one third of the samples were deformed to terminal failure that occurred suddenly at shear strains of ≈3-5. The experiments indicate that cavitation damage may facilitate fluid flow and deep seismicity in highly strained shear zones.Citation: Rybacki, E., R. Wirth, and G. Dresen (2010), Superplasticity and ductile fracture of synthetic feldspar deformed to large strain,

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Section: Introductionmentioning

confidence: 99%

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Rybacki¹,

Wirth²,

Dresen³

2010

J. Geophys. Res.

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“…Guermani and Pennacchioni, 1998;Pennacchioni and Mancktelow 2007); most of these studies consider deformation at shallow to intermediate crustal depths (Fusseis and Handy, 2008;Mazzoli et al, 2009;, although case studies under conditions of upper amphibolite to granulite (White, 1996;Pennacchioni and Cesare, 1997;Pittarello et al, 2013;Altenberger et al, 2013) and eclogite facies (Austrheim and Boundy, 1994;Austrheim, 2013, and references therein) were also investigated.…”

Section: Introductionmentioning

confidence: 99%

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

Molli

Menegon

Malasoma³

2017

Solid Earth

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Abstract. The switching in deformation mode (from distributed to localized) and mechanisms (viscous versus frictional) represent a relevant issue in the frame of crustal deformation, being also connected with the concept of the brittle-"ductile" transition and seismogenesis. In a subduction environment, switching in deformation mode and mechanisms and scale of localization may be inferred along the subduction interface, in a transition zone between the highly coupled (seismogenic zone) and decoupled deeper aseismic domain (stable slip). However, the role of brittle precursors in nucleating crystal-plastic shear zones has received more and more consideration being now recognized as fundamental in some cases for the localization of deformation and shear zone development, thus representing a case in which switching deformation mechanisms and scale and style of localization (deformation mode) interact and relate to each other. This contribution analyses an example of a millimetrescale shear zone localized by brittle precursor formed within a host granitic protomylonite. The studied structures, developed in ambient pressure-temperature (P -T ) conditions of low-grade blueschist facies (temperature T of ca. 300 • C and pressure P ≥ 0.70 GPa) during involvement of Corsican continental crust in the Alpine subduction. We used a multidisciplinary approach by combining detailed microstructural and petrographic analyses, crystallographic preferred orientation by electron backscatter diffraction (EBSD), and palaeopiezometric studies on a selected sample to support an evolutionary model and deformation path for subducted continental crust. We infer that the studied structures, possibly formed by transient instability associated with fluctuations of pore fluid pressure and episodic strain rate variations, may be considered as a small-scale example of fault behaviour associated with a cycle of interseismic creep and coseismic rupture or a new analogue for episodic tremors and slow-slip structures. Our case study represents, therefore, a fossil example of association of fault structures related to stick-slip strain accommodation during subduction of continental crust.

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“…These unusual fault rocks, regarded as earthquake fossils [Andersen and Austrheim, 2006;Lin, 2008], hold important clues on the physical processes of seismic slip [e.g., Austrheim and Boundy, 1994;Di Toro et al, 2005;Ueda et al, 2008;Del Gaudio et al, 2009;Janssen et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of fault pseudotachylytes in granites

Ferré¹,

Geissman²,

Zechmeister³

2012

J. Geophys. Res.

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[1] We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.

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Pseudotachylytes Generated During Seismic Faulting and Eclogitization of the Deep Crust

Cited by 258 publications

References 20 publications

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

Magnetic properties of fault pseudotachylytes in granites

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