Textural controls on the brittle deformation of dolomite: the transition from brittle faulting to cataclastic flow

Austin, N. J.; Kennedy, Lori A.; Logan, John M.; Rodway, Ray

doi:10.1144/gsl.sp.2005.243.01.06

Cited by 11 publications

(5 citation statements)

References 30 publications

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“…The sharp change in strain-rate due to an increase in velocity results in a sudden change in the state of stress at grain boundaries or pre-existing defects and the nucleation of new dislocations. Most of the strain is accommodated by slip along cleavage planes and newly-formed dislocations migrating through the crystal structure until reaching microstructural obstacles (e.g., cleavage planes, micro-cracks, twins and grain boundaries), producing intragranular micro-fractures along crystallographically controlled weaknesses 52 53 .…”

Section: Discussionmentioning

confidence: 99%

Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes

Spagnuolo

Plümper

Violay

et al. 2015

Sci Rep

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Rupture fronts can cause fault displacement, reaching speeds up to several ms−1 within a few milliseconds, at any distance away from the earthquake nucleation area. In the case of silicate-bearing rocks the abrupt slip acceleration results in melting at asperity contacts causing a large reduction in fault frictional strength (i.e., flash weakening). Flash weakening is also observed in experiments performed in carbonate-bearing rocks but evidence for melting is lacking. To unravel the micro-physical mechanisms associated with flash weakening in carbonates, experiments were conducted on pre-cut Carrara marble cylinders using a rotary shear apparatus at conditions relevant to earthquakes propagation. In the first 5 mm of slip the shear stress was reduced up to 30% and CO2 was released. Focused ion beam, scanning and transmission electron microscopy investigations of the slipping zones reveal the presence of calcite nanograins and amorphous carbon. We interpret the CO2 release, the formation of nanograins and amorphous carbon to be the result of a shock-like stress release associated with the migration of fast-moving dislocations. Amorphous carbon, given its low friction coefficient, is responsible for flash weakening and promotes the propagation of the seismic rupture in carbonate-bearing fault patches.

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Section: Discussionmentioning

confidence: 99%

Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes

Spagnuolo

Plümper

Violay

et al. 2015

Sci Rep

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“…The LSR is a modified version of the triaxial rock press used at Texas A&M University [ Handin et al ., ] and is described in detail in Austin et al . []. The samples used in the deformation experiments are ∼20 × 40 mm, right circular cylinders or cores (Figure ).…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Schematic diagram of the experimental apparatus used in the deformation experiments. (A) Schematic of Large Sample Rig apparatus (LSR) [after Austin et al ., ] showing locations of the external load cell (LC) and displacement transducer (DCDT). (B) Detailed view of the confining pressure vessel housing the sample assembly (Argon gas is used as the confining medium).…”

Section: Experimental Methodsmentioning

confidence: 99%

Energetics of glass fragmentation: Experiments on synthetic and natural glasses

Kolzenburg

Russell

Kennedy

2013

Geochem Geophys Geosyst

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[1] Natural silicate glasses are an essential component of many volcanic rock types including coherent and pyroclastic rocks; they span a wide range of compositions, occur in diverse environments, and form under a variety of pressure-temperature conditions. In subsurface volcanic environments (e.g., conduits and feeders), melts intersect the thermodynamically defined glass transition temperature to form glasses at elevated confining pressures and under differential stresses. We present a series of room temperature experiments designed to explore the fundamental mechanical and fragmentation behavior of natural (obsidian) and synthetic glasses (Pyrex TM ) under confining pressures of 0.1-100 MPa. In each experiment, glass cores are driven to brittle failure under compressive triaxial stress. Analysis of the loaddisplacement response curves is used to quantify the storage of energy in samples prior to failure, the (brittle) release of elastic energy at failure, and the residual energy stored in the post-failure material. We then establish a relationship between the energy density within the sample at failure and the grain-size distributions (D-values) of the experimental products. The relationship between D-values and energy density for compressive fragmentation is significantly different from relationships established by previous workers for decompressive fragmentation. Compressive fragmentation is found to have lower fragmentation efficiency than fragmentation through decompression (i.e., a smaller change in D-value with increasing energy density). We further show that the stress storage capacity of natural glasses can be enhanced (approaching synthetic glasses) through heat treatment.

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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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Textural controls on the brittle deformation of dolomite: the transition from brittle faulting to cataclastic flow

Cited by 11 publications

References 30 publications

Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes

Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes

Energetics of glass fragmentation: Experiments on synthetic and natural glasses

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

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