The recrystallized grain size piezometer for quartz: An EBSD-based calibration

We have reanalyzed samples previously used for a quartz recrystallized grain size paleopiezometer, using electron backscatter diffraction (EBSD). Recrystallized and relict grains are separated using their grain orientation spread, which acts as a measure of intragranular lattice distortion and a proxy for dislocation density. For EBSD maps made with a 1 mu m step size, the piezometer relationship is D= 10(3.91 +/- 0.41) . sigma (1.41 +/- 0.21) (for root-mean-square mean diameter values). We also present a sliding resolution piezometer relationship, D = 10(4.22 +/- 0.51) sigma (1.59 +/- 0.26,) that combines 1 mu m step size data at coarser grain sizes with 200 nm step size data at finer grain sizes. The sliding resolution piezometer more accurately estimates stress in fine-grained (< 10 mu m) samples. The two calibrations give results within 10% of each other for recrystallized grain sizes between 10 mu m and 100 mu m. Both piezometers match the original light optical microscopy quartz piezometer within error. Plain Language Summary Constraining stress magnitudes imposed during the high-temperature creep of rocks in the lithosphere is crucial to our understanding of tectonics. Stress magnitudes can be constrained by their inverse relationship with recrystallized grain size: a method known as paleopiezometry. Quantitative microstructural analysis of deformed rocks is now routinely carried out using electron backscatter diffraction (EBSD): a scanning electron microscope technique. We outline a procedure for quantifying mean recrystallized grain size from EBSD data and provide the first EBSD-based paleopiezometer calibration, in this case for quartz. Our empirical piezometer calibration can be used to robustly quantify stress magnitudes driving quartz deformation at the time of recrystallization.