Micromechanisms of shear zone propagation at the brittle–viscous transition

Fußeis, Florian; Handy, Mark R.

doi:10.1016/j.jsg.2008.06.005

Cited by 75 publications

(61 citation statements)

References 62 publications

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“…Depending on the dislocation density and on the magnitude and orientation of the stress field the crack can split up into arrays of individual cracks as shown in inset of Figure 6b. The importance of cleavages and textural properties in controlling the brittle behavior of rocks was already recognized for dolomite [73], calcite [74], and feldspar [75]. The presence of exposed cleavage surfaces suggests that the initiation of weakening is also controlled by the amount of energy which can be converted into surface energy during brittle failure along cleavage planes.…”

Section: The Effect Of Rock Texture On the Mechanism Of Flash Heatingmentioning

confidence: 98%

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

et al. 2016

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Abstract:Earthquakes are the result of slip along faults and are due to the decrease of rock frictional strength (dynamic weakening) with increasing slip and slip rate. Friction experiments simulating the abrupt accelerations (>>10 m/s 2 ), slip rates (~1 m/s), and normal stresses (>>10 MPa) expected at the passage of the earthquake rupture along the front of fault patches, measured large fault dynamic weakening for slip rates larger than a critical velocity of 0.01-0.1 m/s. The dynamic weakening corresponds to a decrease of the friction coefficient (defined as the ratio of shear stress vs. normal stress) up to 40%-50% after few millimetres of slip (flash weakening), almost independently of rock type. The microstructural evolution of the sliding interfaces with slip may yield hints on the microphysical processes responsible for flash weakening. At the microscopic scale, the frictional strength results from the interaction of micro-to nano-scale surface irregularities (asperities) which deform during fault sliding. During flash weakening, the visco-plastic and brittle work on the asperities results in abrupt frictional heating (flash heating) and grain size reduction associated with mechano-chemical reactions (e.g., decarbonation in CO 2 -bearing minerals such as calcite and dolomite; dehydration in water-bearing minerals such as clays, serpentine, etc.) and phase transitions (e.g., flash melting in silicate-bearing rocks). However, flash weakening is also associated with grain size reduction down to the nanoscale. Using focused ion beam scanning and transmission electron microscopy, we studied the micro-physical mechanisms associated with flash heating and nanograin formation in carbonate-bearing fault rocks. Experiments were conducted on pre-cut Carrara marble (99.9% calcite) cylinders using a rotary shear apparatus at conditions relevant to seismic rupture propagation. Flash heating and weakening in calcite-bearing rocks is associated with a shock-like stress release due to the migration of fast-moving dislocations and the conversion of their kinetic energy into heat. From a review of the current natural and experimental observations we speculate that this mechanism tested for calcite-bearing rocks, is a general mechanism operating during flash weakening (e.g., also precursory to flash melting in the case of silicate-bearing rocks) for all fault rock types undergoing fast slip acceleration due to the passage of the seismic rupture front.

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Section: The Effect Of Rock Texture On the Mechanism Of Flash Heatingmentioning

confidence: 98%

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

et al. 2016

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“…In these thin-sections, a set of T-fractures of Petit (1987) or 'transgranular fractures' of Fusseis and Handy (2008) are identified, which are at steep angles, 69°-86°, to the Y-planes (Fig. 14a, b).…”

Section: Studies Of Brittle and Brittle-ductile Deformationmentioning

confidence: 99%

Higher Himalayan Shear Zone, Zanskar Indian Himalaya: microstructural studies and extrusion mechanism by a combination of simple shear and channel flow

Mukherjee

Koyi

2009

Int J Earth Sci (Geol Rundsch)

134

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Thin-section studies of the Zanskar Shear Zone (ZSZ) rocks reveal a top-to-SW and subsequent primary and secondary top-to-NE ductile shearing; brittle-ductile and brittle extensions; top-to-SW brittle shear, steep normal faulting and fracturing. In the proposed two-phase model of ductile extrusion of the Higher Himalayan Shear Zone (HHSZ), a top-to-SW simple shearing during 22-18 Ma was followed by a combination of top-to-SW simple shear and channel flow at 18-16 Ma. The second phase simulates a thin ZSZ characterized by a top-to-NE shearing. The channel flow component ceased around 16 Ma, the extruding HHSZ entered the brittle regime but the topto-SW shearing continued until perturbed by faults and fractures. Variation in the extrusion parameters led to variable thickness of the ZSZ. Shear strain after the extrusion is presumably maximum at the boundaries of the HHSZ and falls towards the base of the ZSZ, which crudely matches with the existing data. The other predictions: (1) spatially uniform shear strain after the first stage, (2) fastest extrusion rate at the base of the ZSZ, and (3) a lack of continuation of the ZSZ along the Himalayan trend are not possible to validate due to paucity of suitable data. Nonparabolic shear fabrics of the ZSZ indicate their heterogeneous deformation.

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“…Handy and Stünitz, 2002;Pennacchioni and Mancktelow, 2007;Fusseis and Handy, 2008). Shear zones and style of strain accommodation and localization processes in granitoids have been described by different authors (Ramsay and Graham, 1970;Burg andLaurent, 1985, 1986;Gapais et al, 1987;Goncalves et al, 2016, and references therein).…”

Section: Introductionmentioning

confidence: 97%

“…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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Micromechanisms of shear zone propagation at the brittle–viscous transition

Cited by 75 publications

References 62 publications

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

Higher Himalayan Shear Zone, Zanskar Indian Himalaya: microstructural studies and extrusion mechanism by a combination of simple shear and channel flow

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

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