Flow laws and fabric transitions in wet quartzite

Tokle, Leif; Hirth, Greg; Behr, W. M.

doi:10.1016/j.epsl.2018.10.017

Cited by 93 publications

(178 citation statements)

References 52 publications

Supporting

Mentioning

152

Contrasting

Order By: Relevance

“…Thus, we interpret the apparent low‐temperature microstructure of the fine‐grained recrystallized quartz to instead be the result of high stress and strain rate deformation at the same P‐T conditions of 700°C and 0.8 GPa suggested by Menegon et al () for the long‐term viscous creep in the mylonites. This reinforces that care should be taken when qualitatively attributing deformation temperatures to microstructures due to the accompanying trade‐off between strain rate, water content, and stress (Hirth & Tullis, ; Piazolo et al, ; Tokle et al, ).…”

Section: Discussionmentioning

confidence: 69%

“…The rheology of quartz‐bearing pseudotachylyte shear zones in Nusfjord east was modeled using a mixed flow law that considers a 10% volume fraction of quartz deforming by dislocation creep (flow laws from Hirth et al, and Tokle et al, ) and a 90% volume fraction of anorthite‐diopside aggregate deforming by wet diffusion creep (flow law from Dimanov & Dresen, ), based on the typical proportions of quartz in and around the mylonitized pseudotachylytes (see section ).…”

Section: Resultsmentioning

confidence: 99%

“…Flow laws calculated for mylonitized pseudotachylyte‐bearing shear zones at 700°C (error bars show the uncertainty relating to the predicted temperature range of 650°C–750°C added to the empirical uncertainty of the experimental flow laws). Shown are dislocation creep of quartz (Hirth et al, ; Tokle et al, ), wet diffusion creep of the anorthite‐diopside matrix (Dimanov & Dresen, ), and a composite flow law for 10% quartz and 90% anorthite‐diopside matrix. Dashed grey line shows differential stress calculated from quartz piezometry and resultant strain rate from mixed flow law.…”

Section: Resultsmentioning

confidence: 99%

“…The dislocation creep flow laws for quartz of Hirth et al () and Tokle et al () were used to calculate and compare possible strain rates for quartz, based on the deformation microstructures characterized in section . For the recrystallized pseudotachylyte matrix, the wet diffusion creep flow law for an anorthite‐diopside aggregate (Dimanov & Dresen, ) was chosen as appropriate due to the fine grain size and lack of crystal preferred orientation (CPO) in Nusfjord pseudotachylytes, as suggested by Menegon et al ().…”

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Transient High Strain Rate During Localized Viscous Creep in the Dry Lower Continental Crust (Lofoten, Norway)

Campbell

Menegon

2019

JGR Solid Earth

View full text Add to dashboard Cite

Understanding the ability of the lower crust to support transient changes in stresses and strain rates during the earthquake cycle requires a detailed investigation of the deformation mechanisms and rheology of deep crustal fault rocks. Here, we show that lower crustal pseudotachylyte-bearing shear zones are able to accommodate short-term episodes of high strain rate and high stress deformation by accelerated viscous creep, followed by a reduction in stresses to some ambient deformation condition. Quartz microstructure within pseudotachylyte-bearing shear zones in otherwise undeformed granulites from Lofoten, Norway, indicates that dynamic recrystallization occurred during viscous creep under rapid strain rates and high stresses of~10 −9 s −1 and~100 MPa, respectively. Lower stress microstructures (i.e., foam textures) are also recorded in the shear zones, indicating spatial and temporal variations of stress and strain rate during deformation cycles. Both the high and lower stress quartz recrystallization took place under granulite facies conditions of 650°C-750°C and 0.7-0.8 GPa and represented a record of highly localized viscous creep within the lower crust. This implies that lower crustal pseudotachylytes are potentially able to form extremely localized weak zones within strong lower crust, enabling a deep mechanical response to perturbations in stress and strain rate such as those experienced during the seismic cycle, for example, seismogenic loading followed by subsequent postseismic relaxation.Plain Language Summary Detailed investigation of the strength and deformation style of fault rocks sourced from the Earth's lower crust is important to understand how the lower crust reacts to shortterm variations in stress and strain rate, which can occur, for example, between earthquakes. Here, we show that solidified pseudotachylytes (initially melts produced due to frictional heating along the fault plane during an earthquake) occurring at depths of 25-30 km in the lower crust can accommodate deformation at particularly high strain rates and high stresses via solid-state creep. We look at pseudotachylytes formed in lower crustal shear zones that are now exhumed in Lofoten, Norway. Deformation microstructures in quartz within these pseudotachylytes have recorded rapid strain rates and high stresses. These microstructures are occasionally transformed into lower stress versions, indicating that during the deformation the stress and strain rate varied through both time and space. Both stages, however, record the same deformation temperatures and pressures, indicating that these are snapshots of ongoing deformation within the lower crust. We conclude that, when the lower crust is strong, pseudotachylytes will form important weak zones that accommodate deformation even during rapid variations in the deformation conditions, for example, as occurs during the postseismic period immediately after an earthquake.

show abstract

Section: Discussionmentioning

confidence: 69%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Transient High Strain Rate During Localized Viscous Creep in the Dry Lower Continental Crust (Lofoten, Norway)

Campbell

Menegon

2019

JGR Solid Earth

View full text Add to dashboard Cite

show abstract

“…Put simply, the data suggest a change in DRX kinetics as CPO evolves and different slip systems become dominant. This observation is particularly interesting given the recent finding of (at least) two dislocation creep regimes for quartz-one dominated by basal-<a> fabrics and the other by prism-<a> fabrics-depending on the rate-limiting deformation process (Tokle et al, 2019).…”

Section: Crystal Orientationmentioning

confidence: 92%

Rates of Dynamic Recrystallization in Geologic Materials

Cross

Skemer

2019

JGR Solid Earth

View full text Add to dashboard Cite

Grain size reduction via dynamic recrystallization (DRX) is intimately related to the softening of crystalline materials under an applied stress, and plays a role in numerous geodynamic processes that involve strain‐weakening feedbacks. Despite its importance, few studies have provided empirical constraints on the rates of DRX and grain size reduction. Here we examine DRX rates using the Johnson‐Mehl‐Avrami‐Kolmogorov theory for phase transformation kinetics. Our analysis uses a compilation of published and newly‐derived DRX data from experimental studies on a wide range of geologic and engineering materials. We find that DRX rates are strongly dependent on the homologous temperature at which deformation occurs, with DRX occurring over a broad range of shear strains (0.01 < γ < 200), and more rapidly with increasing homologous temperature. Moreover, the experimental data can be described by a single fit to a modified form of the Avrami equation that incorporates homologous temperature dependence, implying that, to first order, DRX rates are largely material independent. We also examine the influence of stress, deformation work rate, crystal orientation, and initial grain size on DRX rates and compare DRX data from experimental and natural conditions. Overall, we show that microstructures can evolve over long transient intervals, and provide a framework for determining DRX kinetics from empirical data, which can ultimately be incorporated into geodynamic models of grain size evolution in the Earth.

show abstract