Oscillating brittle and viscous behavior through the earthquake cycle in the Red River Shear Zone: Monitoring flips between reaction and textural softening and hardening

Wintsch, Robert P.; Yeh, Meng Wan

doi:10.1016/j.tecto.2012.09.019

Cited by 71 publications

(36 citation statements)

References 98 publications

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“…The observed decrease in strength is mainly due to switches in deformation mechanisms and changes in mineral phases accommodating deformation. Phase transformations thus appear as one of the key mechanisms for reaction softening and/or deviation from steady state behavior [ Stünitz and Tullis , ; Gueydan et al , ; Oliot et al , ; Goncalves et al , ; Okudaira et al , ], especially at the brittle‐ductile transition where sufficient permeability and income of acidic meteoric water may lead to substantial increase in the white mica content [ Wintsch et al ., ; Wintsch and Yeh , ]. On the other hand, as demonstrated in this work it is also the crystal plastic and brittle processes in combination with precipitation/neocrystallization that lead to efficient phase mixing and formation of relatively weak matrix bands.…”

Section: Discussionmentioning

confidence: 99%

Major softening at brittle‐ductile transition due to interplay between chemical and deformation processes: An insight from evolution of shear bands in the South Armorican Shear Zone

2016

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The formation of S‐C/C′ fabrics in the South Armorican Shear Zone has been evaluated by detailed microstructural study where the focus was given to initiation and early evolution of the C/C′ fabric shear bands. Our observations suggest that the S‐C/C′ fabrics formed at distinct temperature conditions indicating >550°C for the S fabric and 300–350°C at 100–400 MPa for the C/C′ fabric shear bands. The evolving microstructure within shear bands documents switches in deformation mechanisms related to positive feedbacks between deformation and chemical processes and imposes mechanical constraints on the evolution of the brittle‐ductile transition in the continental transform fault domains. Three stages of shear band evolution have been identified. Stage I corresponds to initiation of shear bands via formation of microcracks with possible yielding differential stress of up to 250 MPa. Stage II is associated with subgrain rotation recrystallization and dislocation creep of quartz and coeval dissolution‐precipitation creep of microcline. Recrystallized quartz grains show continual increase in size and decrease in stress and strain rates from 94 MPa to 17–26 MPa and 3.8 × 10−12 s−1–8 × 10−14 s−1 associated with deformation partitioning into weaker microcline layer and shear band widening. The quartz mechanical data allowed us to set some constrains for coeval dissolution‐precipitation of microcline which at our estimated pressure‐temperature conditions suggests creep at 17–26 MPa differential stress and 3.8 × 10−13 s−1 strain rate. Stage III is characterized by localized slip along white mica bands accommodated by dislocation creep at strain rate 3.8 × 10−12 s−1 and stress 9.36 MPa. Our mechanical data point to dynamic evolution of the studied brittle‐ductile transition characterized by major weakening to strengths ~10 MPa. Such nonsteady state evolution may be common in crustal shear zones especially when phase transformations are involved.

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Section: Discussionmentioning

confidence: 99%

Major softening at brittle‐ductile transition due to interplay between chemical and deformation processes: An insight from evolution of shear bands in the South Armorican Shear Zone

2016

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“…The Picacho Mountains represents the northwest end of the greater Catalina MCC, which Figure 1. Fluid-rock interaction in a detachment system associated with the formation of a metamorphic core complex (modified after Gottardi et al, 2013;Wintsch & Yeh, 2013). includes the Rincon, Tortolita, and Santa Catalina Mountains (Figure 2; Coney, 1980;Davis, 1980;Richard et al, 1999;Spencer et al, 2012). At the southern end of the Picacho Mountains lies the prominent landmark Picacho Peak (Figure 2), an andesitic early Miocene volcanic center (Brooks, 1986;Richard et al, 1999;Shafiqullah et al, 1976;Spencer et al, 2012).…”

Section: Picacho Mountains Metamorphic Core Complexmentioning

confidence: 99%

“…Fluid–rock interaction in a detachment system associated with the formation of a metamorphic core complex (modified after Gottardi et al, ; Wintsch & Yeh, ).…”

Section: Introductionmentioning

confidence: 99%

Fluid–Rock Interaction and Strain Localization in the Picacho Mountains Detachment Shear Zone, Arizona, USA

et al. 2018

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The Picacho Mountains (SE Arizona, USA) are composed of a variety of Paleogene, Late Cretaceous, and Proterozoic granite and gneisses that were deformed and exhumed along the gently south to southwest dipping detachment shear zone associated with the Picacho metamorphic core complex. The detachment shear zone is divided into three sections that record a progressive deformation gradient, from protomylonites to ultramylonites, and breccia. New thermochronological data from mylonite across the footwall of the detachment shear zone associated with the Picacho metamorphic core complex suggest that the footwall was exhumed through about ~300°C between 22 and 18 Ma by progressive incisement of the footwall of the detachment shear zone. Combined geochronological and oxygen and hydrogen stable isotope data of metamorphic silicate minerals reveal that mylonite recrystallization occurred in the presence of a deep‐seated metamorphic/magmatic fluid, and experienced a late stage meteoric overprint during the development and exhumation of the detachment shear zone. Quartz‐biotite and quartz‐hornblende geothermometry from the base to the top of the detachment shear zone yield equilibrium temperatures ranging from 630 to 415°C, respectively. This temperature trend is attributed to an insulating effect caused by rapid slip and juxtaposition of cool hanging wall on top of a hot footwall. It is suggested that rapid cooling of the top of the detachment shear zone caused strain to migrate toward lower structural level by incisement of the footwall of the shear zone. Progressive strain front migration into the ductile footwall produced hydromechanical anisotropies parallel to the detachment shear zone, effectively saturating the footwall with magmatic/metamorphic fluids and preventing downward flow of meteoric fluids. The combined microstructural, geochronological, and stable isotope results presented in this study provide insight on the dynamic feedback between deformation and fluid flow during the evolution of a detachment shear zone.

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“…The presence of phyllosilicate-rich lithologies, including phyllonites and certain gouges and foliated cataclasites, in fault zones is thought to dramatically impact fault zone rheology (Wintsch et al, 1995;Jefferies et al, 2006aJefferies et al, , 2006bHoldsworth et al, 2011;Rutter et al, 2013;Wintsch et al, 2013). Phyllosilicates (e.g.…”

Section: Introductionmentioning

confidence: 99%

Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India

Wallis

Lloyd

Phillips

et al. 2015

Journal of Structural Geology

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a b s t r a c tPhyllosilicate-rich fault rocks are common in large-scale fault zones and can dramatically impact fault rheology. Experimental evidence suggests that multi-mechanism frictional-viscous flow (FVF) may operate in such lithologies, potentially significantly weakening mature fault cores. We report microstructures indicative of FVF in exhumed phyllonites of the Karakoram Fault Zone (KFZ), NW India. These include interconnected muscovite foliae, lack of quartz/feldspar crystal preferred orientations, and sutured grains and overgrowths indicative of fluid-assisted diffusive mass transfer. FVF microphysical modelling, using microstructural observations from the natural fault rock and experimentally-derived friction and diffusion coefficients, predicts low peak shear strengths of <20 MPa within the frictionalviscous transition zone. Chlorite geothermometry indicates that synkinematic chlorites grew at 351 ± 34 C (c. 10 km depth) during FVF, immediately above the transition to quartz crystal plasticity. The deformation processes and interpreted low shear strength of the exhumed KFZ fault rocks provide analogues for processes operating currently at depth in active faults of similar scale. If similar lithologies are present at depth, then the Quaternary seismic characteristics of the KFZ support faults with phyllonitic cores being able to accommodate large seismic ruptures. The results also provide rare rheological constraints for mechanical models of the India-Asia collision zone.

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Oscillating brittle and viscous behavior through the earthquake cycle in the Red River Shear Zone: Monitoring flips between reaction and textural softening and hardening

Cited by 71 publications

References 98 publications

Major softening at brittle‐ductile transition due to interplay between chemical and deformation processes: An insight from evolution of shear bands in the South Armorican Shear Zone

Major softening at brittle‐ductile transition due to interplay between chemical and deformation processes: An insight from evolution of shear bands in the South Armorican Shear Zone

Fluid–Rock Interaction and Strain Localization in the Picacho Mountains Detachment Shear Zone, Arizona, USA

Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India

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