Evidence for strain induced graphitization across a ductile fault zone

A suite of slate samples collected along a 2 km transect crossing the Lishan Fault in central Taiwan were evaluated to assess the role of ductile strain energy in natural graphitization at greenschist facies metamorphic conditions. Scanning electron microscope (SEM) imaging documents phyllosilicate and quartz replacement textures consistent cleavage development via dissolution-precipitation processes that increase in intensity from east to west. X-ray diffraction data reveal an east-to-west linear decrease in the full-width-at-half-maximum (FWHM) values of the 004 muscovite peaks and shifts towards higher 2θ (lower d) values. Rietveld refinements required two distinct muscovite populations and muscovite microstrain to account for the muscovite peak variability. Except for the westernmost sample, isothermal conditions were verified with calcite-dolomite geothermometry results. Finally, Raman spectroscopic results including D1-FWHM, G-FWHM, Raman band separation (RBS), and a lesser-known vibrational mode B2g-FWHM, showed robust linear trends across the sampling transect. However, the G-FWHM parameter showed a trend opposite of that expected from thermally driven graphitization.