COMPARING OLIVINE DEFORMATION CONDITIONS FOR NORTH CAROLINA BLUE RIDGE DUNITE DEPOSITS USING EBSD-BASED PALEOPIEZOMETRY AND SLIP-SYSTEM ANALYSIS
This study explores olivine analyses from dunite deposits NE of Buck Creek (Deposit #9 – D9, Mincey Mine - MM, Moore’s Knob - MK, Webster-Addie - WA, Dark Ridge - DR), with a revised approach to determine recrystallized grain size for paleopiezometry using EBSD data. We adapted published MATLAB/MTEX code (for quartz) that uses grain orientation spread to separate recrystallized and relict grains and calculate statistical grain-size data for olivine. Median recrystallized grain size was used in 3 different paleopiezometers. Recrystallized grain size/stress estimates for BC samples using thin section and EBSD methods are similar; the EBSD method is more quantitative and includes significantly more data points. Median grain sizes vary from 75-150 μm, corresponding to stresses of 32-56 MPa. Crystallographic Preferred Orientation (CPO) plots and Inverse Pole figures from EBSD data indicate C- or E-type fabrics - (100) or (001) slip for D9, WA, and DR deposits and A-type fabrics – (010) slip for MM and MK deposits.
Recrystallized grain size/stress estimates for BC samples overlap with those determine for the 5 deposits in this study; however, the slip systems active during deformation are distinctly different for BC (B-type) vs. the other deposits (C/E- or A-type), suggesting different tectonic settings for deformation of the different deposits.