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

Hamid Soleymani, Steven Kidder, Greg Hirth and Gordana Garapic
The effect of cooling during deformation on recrystallized grain-size piezometry
Geology (Boulder) (March 2020) 48 (6): 531-535


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 degrees C/h from 900 degrees C to 800 degrees C, and a shear strain rate of -2X10 (super -5) s (super -1) . Comparisons between these "cooling-ramp" experiments and control experiments at constant temperatures of 800 degrees C and 900 degrees 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 approximately 40%. Recrystallized grain size in the cooling-ramp experiments is a better indicator of the average stress of the experiments (shear strains > or =3). Due to the temperature sensitivity of recrystallization processes and rock strength, the results may under-represent 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.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 6
Title: The effect of cooling during deformation on recrystallized grain-size piezometry
Affiliation: City University of New York, Graduate Center, Department of Earth and Environmental Sciences, New York City, NY, United States
Pages: 531-535
Published: 20200318
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 37
Accession Number: 2020-030421
Categories: Igneous and metamorphic petrologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2020151
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Brown University, USA, United StatesState University of New York-New Paltz, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202020
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