Oriented thin sections were prepared from samples selected based on their texture and mineralogy. Samples analyzed by EBSD were polished for an additional hour on 0.02 m colloidal silica beyond the polishing done for microprobe analysis. Microprobe samples were C coated. EBSD samples were Au-Pd coated and then polished for an additional minute to remove most of the coating, leaving enough gold along cracks and grain boundaries to mitigate sample charging in the SEM. 1.2. Grain Size Analysis Mean grain size was measured by line intercept method for plagioclase in the gabbronorite and olivine in the harzburgite. At least 100 grains were measured parallel to foliation. Because the grains are roughly equant, a geometric correction factor of 1.5 has been applied to the mean intercept lengths to obtain the average grain size (Underwood, 1970). The arithmetic mean was calculated to be consistent with Van der Wal (1993). However, since the grain size distributions are approximately log-normal, the geometric mean may be a more accurate measure of the average grain size. Both are given in Figure DR3. 1.3. Thermometry 1.3.1. Pyroxene Thermometry Equilibrium temperatures were calculated for clinopyroxene/orthopyroxene pairs in the recrystallized rims of clinopyroxene porphyroclasts. The measured grains are equant with an average grain size of 220 m. Oxide weight percents were measured using the JEOL JXA-733 Superprobe (Massachusetts Institute of Technology), with a 10 m spot size, 10 nA beam current and an accelerating voltage of 15 kV (Table DR1). Using Ca-QUILF (Andersen et al., 1993; Lindsley and Frost, 1992), temperatures were calculated for 6 clinopyroxene/orthopyroxene pairs (Table DR1).

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