MANTLE XENOLITH MICROSTRUCTURES, TI-IN-QUARTZ IN MYLONITES, AND NON-STEADY STATE RECRYSTALLIZED GRAIN SIZE: ONGOING STRUCTURE PROJECTS AT CCNY

2016 ◽  
Author(s):  
Steven Kidder ◽  
◽  
Emily J. Lubicich ◽  
Hamid Soleymani ◽  
Ashfaq Khan ◽  
...  
Keyword(s):  
Grain Size ◽  
Steady State ◽  
Mantle Xenolith ◽  
Recrystallized Grain Size ◽  
Ti In Quartz

scholarly journals Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan

Solid Earth ◽  
2013 ◽  
Vol 4 (1) ◽  
pp. 1-21 ◽  
Author(s):  
S. Kidder ◽  
J.-P. Avouac ◽  
Y.-C. Chan
Keyword(s):  
Grain Size ◽  
Fluid Pressure ◽  
Geothermal Gradient ◽  
Greenschist Facies ◽  
Stability Field ◽  
Lithostatic Pressure ◽  
Vein Quartz ◽  
Pressure Term ◽  
Recrystallized Grain Size ◽  
Ti In Quartz

Abstract. The accuracy, reliability and best practises of Ti-in-quartz thermobarometry (TitaniQ) in greenschist facies rocks have not been established. To address these issues, we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from the Hsüehshan range, Taiwan. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~100–200 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10–20 μm) has a further restricted Ti concentration peaking at 0.8–2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Unlike previously documented examples, Ti concentration in the quartzite is inversely correlated with blue cathodoluminescence. Deformation was associated with a minimum grain boundary diffusivity of Ti on the order of 10−22m2 s−1. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250–350 °C and 300–410 °C, respectively, with lithostatic pressure of 3–4 kbar (assuming a geothermal gradient of 25° km−1), and with hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure and these temperatures, the Thomas et al. (2010) calibration yields Ti concentrations within error of concentrations measured by SIMS. If fluid pressure is instead used, predicted temperatures are ~30–40 °C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 °C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted.

The effect of cooling during deformation on recrystallized grain-size piezometry

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 531-535 ◽  
Author(s):  
Hamid Soleymani ◽  
Steven Kidder ◽  
Greg Hirth ◽  
Gordana Garapić
Keyword(s):  
Grain Size ◽  
Steady State ◽  
Traditional Approach ◽  
Shear Zones ◽  
Temperature Deformation ◽  
Shear Strain Rate ◽  
Size Distributions ◽  
Final Stress ◽  
Grain Size Distributions ◽  
Recrystallized Grain Size

Abstract Most exposed middle- and lower-crustal shear zones experienced deformation while cooling. We investigated the effect of the strengthening associated with such cooling on differential stress estimates based on recrystallized grain size. Typical geologic ratios of temperature change per strain unit were applied in Griggs Rig (high pressure-temperature deformation apparatus) general shear experiments on quartzite with cooling rates of 2–10 °C/h from 900 °C to 800 °C, and a shear strain rate of ∼2 × 10−5 s−1. Comparisons between these “cooling-ramp” experiments and control experiments at constant temperatures of 800 °C and 900 °C indicated that recrystallized grain size did not keep pace with evolving stress. Mean recrystallized grain sizes of the cooling-ramp experiments were twice as large as expected from the final stresses of the experiments. The traditional approach to piezometry involves a routine assumption of a steady-state microstructure, and this would underestimate the final stress during the cooling-ramp experiments by ∼40%. Recrystallized grain size in the cooling-ramp experiments is a better indicator of the average stress of the experiments (shear strains ≥3). Due to the temperature sensitivity of recrystallization processes and rock strength, the results may underrepresent the effect of cooling in natural samples. Cooling-ramp experiments produced wider and more skewed grain-size distributions than control experiments, suggesting that analyses of grain-size distributions might be used to quantify the degree to which grain size departs from steady-state values due to cooling, and thereby provide more accurate constraints on final stress.

scholarly journals Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan

2012 ◽  
Vol 4 (1) ◽  
pp. 663-706 ◽  
Author(s):  
S. Kidder ◽  
J.-P. Avouac ◽  
Y.-C. Chan
Keyword(s):  
Grain Size ◽  
Best Practices ◽  
Fluid Pressure ◽  
Greenschist Facies ◽  
Stability Field ◽  
Lithostatic Pressure ◽  
Vein Quartz ◽  
Pressure Term ◽  
Recrystallized Grain Size ◽  
Ti In Quartz

Abstract. The accuracy, reliability and best practices of Ti-in-quartz thermobarometry ("TitaniQ") in greenschist facies rocks have not been established. To address these issues we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from Taiwan's Hsüehshan range. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~300 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10–20 μm) has a further restricted Ti concentration peaking at 0.8–2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250–350 °C and 300–410 °C respectively, lithostatic pressure ~5 kbar, and hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure, Ti concentrations predicted by the Thomas et al. (2010) TitaniQ calibration are within error of Ti concentrations measured by SIMS. If fluid pressure is used, predicted temperatures are ~30–40 °C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 °C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted.

A Criterion for Conventional Dynamic Recrystallization: Application to Magnesium Alloys

2007 ◽  
Vol 550 ◽  
pp. 369-374
Author(s):  
Matthew R. Barnett ◽  
Aiden G. Beer
Keyword(s):  
Grain Size ◽  
Steady State ◽  
Dynamic Recrystallization ◽  
Magnesium Alloys ◽  
High Temperatures ◽  
Working Conditions ◽  
Analytical Approximation ◽  
Hot Working ◽  
Strain Rates ◽  
Recrystallized Grain Size

An analytical approximation for the steady state dynamic recrystallized grain size is combined with a simple nucleation criterion to assess the propensity for dynamic recrystallization. In line with observation, the criterion predicts dynamic recrystallization in 99.9995% pure Al but not in material 99.5% pure. It also agrees with the observation that zone refined ferrite can display dynamic recrystallization at high temperatures and low strain rates but not at lower hot working temperatures. The criterion is applied here to common wrought magnesium alloys to argue that conventional dynamic recrystallization is expected under "normal" hot working conditions.

scholarly journals Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy

2021 ◽  
Author(s):  
Mo Ji ◽  
Martin Strangwood ◽  
Claire Davis
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Avrami Exponent ◽  
Model Alloy ◽  
Size Distributions ◽  
Recrystallization Kinetics ◽  
Grain Size Distributions ◽  
Recrystallized Grain Size ◽  
Nb Addition

AbstractThe effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.

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