Minimizing and quantifying mis-indexing in electron backscatter diffraction (EBSD) determinations of antigorite crystal directions

摘要

Antigorite is common in hydrated mantle domains and commonly shows strong alignment either due to deformation or growth in a preferred orientation. The alignment of antigorite imparts a strong anisotropy to the host rock affecting physical properties. A quantitative analysis of how antigorite affects these properties requires a reliable measurement of the crystallographic preferred orientation of antigorite, and EBSD analysis is the most widely used technique. Potential problems include (i) mis-indexing, which can add significant uncertainties to the results; and (ii) sample preparation, which may affect the measured CPO in particular for automated mapping. Combining results derived from X-ray goniometry, EBSD and U-stage techniques with FIB-TEM analysis leads to the following conclusions concerning these two issues. (i) There is a significant issue with mis-indexing a- and b-axes due to rotational similarities about the c-axis. Similar problems may also affect the c-axes measurements but this is less significant than the a- and b-axes when data are filtered using lower MAD values. Filtering using MAD values of <0.7 degrees can significantly change the resulting CPO. (ii) Sample preparation can also affect the measured CPO: sections prepared parallel to the foliation show only minor differences with MAD values of <2.0 degrees. Mis-indexing problems can be minimized by using an MAD value of <0.7 degrees and analysing thin sections cut parallel to the foliation. (C) 2016 Published by Elsevier Ltd.