Quartz EBSD data from the Simplon Shear Zone, central Alps

Published: 14-12-2020| Version 1 | DOI: 10.17632/whp6ppzd98.1
Contributors:
Tarryn Cawood,
John Platt

Description

This dataset contains microstructural data for dynamically recrystallized quartz in deformed granites, as collected by electron backscatter diffraction (EBSD). The data is from two transects through the exhumed footwall of the normal-sense Simplon Shear Zone, central Alps, both of which extend from low-temperature mylonites adjacent to the hangingwall, to high-temperature mylonites further into the footwall.

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Crystallographic orientation measurements were obtained for domains of dynamically recrystallized quartz by electron backscatter diffraction (EBSD), using a JEOL-7001F scanning electron microscope operated at low vacuum, equipped with a Hikari EBSD detector and EDAX OIM software, at the University of Southern California Core Center of Excellence in Nano Imaging. Probe-polished thin sections were further polished in colloidal silica, and analyzed at 20-25 kV accelerating voltage, 15-17 mm working distance, 70° specimen tilt, and a step size of 0.75-8 μm. Data were reduced and cleaned using EDAX OIM software. Cleaning was done using grain CL standardization, neighbor orientation correlation, and a correction for Dauphine twinning (with a pseudosymmetry of 60 degrees). Each population of quartz grains was then filtered to exclude non-quartz phases (based on indexing quality), to exclude grain sizes less than 3 x the step size (which may be artifacts), and to only include the single, targeted grain size population (this was done visually, excluding large relict grains, and any grains that clearly belonged to a separate grain size population, as observed in grain size histograms). Area-weighted grain sizes were determined in the EDAX OIM software. Number-weighted grain sizes were calculated with the GrainSizeTools script (Lopez-Sanchez, M.A., 2018. GrainSizeTools: a Python script for grain size analysis and paleopiezometry based on grain size. The Journal of Open Source Software. Doi: 10.21105/joss.00863, available at: https://sourceforge.net/projects/grainsizetools/). C-axis pole figures were generated in the EDAX OIM software, and opening angles were manually measured.