A recrystallized grain size piezometer for experimentally deformed feldspar aggregates

Post, Alice; Tullis, Jan

doi:10.1016/s0040-1951(98)00260-1

Cited by 81 publications

(39 citation statements)

References 35 publications

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“…The albite piezometer calibrated by Post and Tullis [1999] predicts stresses that fall well below the brittle-failure criteria (0.1 -2.5 MPa). The Post and Tullis piezometer must be extrapolated to considerably lower stress than where it was calibrated and the recrystallization processes involved (low-temperature migration recrystallization, i.e., "bulging" recrystallization) are different than those exhibited by the SWIR samples.…”

Section: Comparison Of Predicted and Natural Deformation Mechanismsmentioning

confidence: 92%

Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust

Mehl¹

2008

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We evaluate the applicability of plagioclase and gabbro flow laws by comparing predicted and observed deformation mechanisms in gabbroic shear zones. Gabbros and layered gabbro mylonites were collected from the Southwest Indian Ridge (SWIR), ODP Hole 735B. Deformation temperatures are constrained by two-pyroxene thermometry, stress is estimated from grain size, and deformation mechanisms are analyzed by microstructure and the presence or absence of a lattice preferred orientation (LPO). Our analyses indicate that mylonite layers deformed at a strain rate in the range of 10 . Plagioclase in pure plagioclase mylonite layers exhibit strong LPOs indicating they deform by dislocation creep. Plagioclase grain size in mixed plagioclase-pyroxene mylonite layers is finer than in pure plagioclase layers, and depends on the size and proportion of pyroxenes. Progressive mixing of pyroxene and plagioclase within gabbro mylonite layers is accompanied by weakening of the LPO indicating that phase mixing promotes a transition to diffusion creep processes that involve grain boundary sliding. Our results indicate that experimental flow laws are accurate at geologic strain rates, although the strain rate for diffusion creep of fine-grained gabbro may be underestimated. At the conditions estimated for the SWIR crust, our calculations suggest that strain localization leads to a factor of two to four decrease in lower crustal viscosity. Even so, the viscosity of lower gabbroic crust is predicted to be similar to that of dry upper mantle.

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Section: Comparison Of Predicted and Natural Deformation Mechanismsmentioning

confidence: 92%

Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust

Mehl¹

2008

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“…The differential stress estimated for these samples using the Twiss (1977) piezometer is~80 MPa. However, because the Twiss (1977) piezometer may overestimate the differential stress when recrystallization occurs by subgrain rotation (e.g., Post and Tullis 1999), the value of 80 MPa should be considered a maximum value estimated by grain size piezometry. In summary, the combination of rheological constraints and recrystallized grain size piezometry indicates that the differential stress at the transition between regimes 2 and 3 in the Ruby Gap duplex is between~60 and 100 MPa.…”

Section: Differential Stressmentioning

confidence: 99%

An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks

2001

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We use the remarkable similarity between microstructures preserved in naturally and experimentally deformed quartzites as a basis to evaluate quartzite flow laws and their application to natural conditions. The precision of this analysis is relatively high because of the well-constrained deformation history of naturally deformed rocks from the Ruby Gap duplex, Central Australia. The external state variables during deformation in the duplex are well constrained by a combination of thermochronological, microstructural and structural observations. Using a flow law with the form _ e Af m H 2 O s n exp ÀQ=RT , our analysis indicates that values of log (A)=±11.20.6 MPa ±n /s and Q=135 15 kJ/mol provide the best description of the combined natural and experimental constraints with values of m=1 and n=4. Motivated by the results of our analysis, we also evaluated the influence of water fugacity on strain rate determined in the laboratory. In this case, we concur with a previously published suggestion that the measured effect of water fugacity (_ e G f 2 H 2 O ) is likely a manifestation of a change in deformation process with increasing stress. The results of this study provide further support for the application of quartzite flow laws to understand deformation conditions in the Earth, and emphasize the important insights that can be gained by analyzing deformation microstructures in naturally deformed rocks.

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“…Optical observation shows that deformation fabrics of quartz and feldspar in the banded granitic gneiss and felsic mylonite in the Red River-Ailaoshan ductile shear zone are typical MT dislocation creep, and hence the temperature for ductile deformation and mylonitization should be in the range of 400-500℃. Based on the relation between flow stress and grain size resulted from dynamic recrystallization of quartz and feldspar in the felsic mylonite [55,67,[69][70][71] the flow stress of the Red River ductile shear zone has been inferred to be 10-50 MPa. The deformation conditions inferred above (temperature and flow stress of feldspar and quartz) [64][65][66][67][68] indicate that the ductile shear zone should have occurred at middle crust during early sinistral strike-slip shear deformation of the Red River deformation zone.…”

Section: Rock Deformation In the Exhumed Middle Crust Ductile Shear Zmentioning

confidence: 99%

Water contents and deformation mechanism in ductile shear zone of middle crust along the Red River fault in southwestern China

Zhou

Yang

2008

Sci. China Ser. D-Earth Sci.

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Using Fourier transform infrared spectroscopy (FTIR), we measured water contents of quartz and feldspar for four thin sections of felsic mylonite and two thin sections of banded granitic gneiss collected from a ductile shear zone of middle crust along the Red Rivers-Ailaoshan active fault. The absorbance spectra and peak position suggest that water in quartz and feldspar of granitic gneiss and felsic mylonite occurs mainly as hydroxyl in crystal defect, but also contains inclusion water and grain boundary water. The water contents of minerals were calculated based on the absorbance spectra. Water content of feldspar in granitic gneiss is 0.05 wt%-0.15 wt%, and that of quartz 0.03 wt%-0.09 wt%. Water content of feldspar ribbon and quartz ribbon in felsic mylonite is 0.095 wt%-0.32 wt%, and those of fine-grained feldspar and quartz are 0.004 wt%-0.052 wt%. These data show that the water content of weakly deformed feldspar and quartz ribbons is much higher than that of strongly deformed fine-grained feldspar and quartz. This suggests that strong shear deformation leads to breakage of the structures of constitutional water, inclusion and grain boundary water in feldspar and quartz, and most of water in minerals of mylonite is released to the upper layer in the crust.hydroxyl in crystal defect, grain boundary and inclusion water, fourier transform infrared spectrum, ductile shear zone, deformation mechanism

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A recrystallized grain size piezometer for experimentally deformed feldspar aggregates

Cited by 81 publications

References 35 publications

Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust

Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust

An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks

Water contents and deformation mechanism in ductile shear zone of middle crust along the Red River fault in southwestern China

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