Electronic Supplement 3 – Polytype quantification

Figure A3.1. Deconvoluted XRD spectrum for sample BG–045a; see Electronic Supplement 2 for details on the methodology. This sample contains so little illite, but considerable chlorite and additional minor quartz and K-feldspar, that it is impossible to identify the polytype-specific illite peaks. The illite peak at 25.5 °2θ is overshadowed by the much larger chlorite peak at 25.1 °2θ. Illite peaks at 27.8 °2θ and 29.8 °2θ are most strongly affected by interference with K-feldspar peaks and are unreliable. Peaks at 23.8 °2θ and 32.1 °2θ are those most likely to yield reliable results. For the medium and fine fractions, these peaks were not identified, thus 2M1 illite is assumed to be absent in these fractions. For the 2–6 µm fraction, one of two peaks on either side of 32.1 °2θ might be illite but could not be clearly identified. Based on comparison with K-feldspar-free sample BG–045b from the same fault, we estimate that this sample might contain some 2M1 illite, though most likely well below 10%. Black curve – original data, blue curves – deconvoluted single peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.

Figure A3.2. Deconvoluted XRD spectrum for sample BG–045b; see Electronic Supplement 2 for details on the methodology. 2–6 µm (top): Four polytype-specific illite peaks could be identified; no peak was found at 32.1 °2θ. When there is no significant interference at this possition, we include the absent peak as 0% 2M1 in the calculation of the mean value for all five peaks. <2 µm (middle): Peak at 25.5 °2θ could not be identifeid due to interference with chlorite and was excluded from the calculation of the mean. <0.2 µm (bottom): Peaks at 25.5 °2θ and 29.8 °2θ could not be identified and were excluded from the calculation of the mean. Note that with such small amounts of 2M1 illite/muscovite in the samples, polytype quantification is not very accurate and the results should be taken as estimates rather than precise values. Black curve – original data, blue curves – deconvoluted single peaks, red curves – illite polytype-sepcific peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.

Figure A3.3. Deconvoluted XRD spectrum for sample BG–115; see Electronic Supplement 2 for details on the methodology. The illite peak at 23.8 °2θ could not be clearly identified and has been excluded from the calculation of the mean. Black curve – original data, blue curves – deconvoluted single peaks, red curves – illite polytype-sepcific peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.

Figure A3.4. Deconvoluted XRD spectrum for sample BG–048; see Electronic Supplement 2 for details on the methodology. Illite peaks at 23.8 °2θ could not be identified and have been excluded from the calculation of the mean. This sample contains very little illite, but a lot of chlorite and traces of both K-feldspar and plagioclase. Illite peaks at 27.8 °2θ and 29.8 °2θ are most strongly affected by interference with feldspar peaks and are unreliable. The peaks at 25.5 °2θ and 32.1 °2θ are more likely to yield reliable results. Since only two peaks could actually be measured, the polytype quantification in this samples should be considered a rough estimate rather than a precise value. Black curve – original data, blue curves – deconvoluted single peaks, red curves – illite polytype-sepcific peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.

Figure A3.5. Deconvoluted XRD spectrum for sample BG–134; see Electronic Supplement 2 for details on the methodology. This is the only sample where interference with other peaks is relatively minor (except for chlorite). All five illite polytype-specific peaks could be identified. Black curve – original data, blue curves – deconvoluted single peaks, red curves – illite polytype-sepcific peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.

Figure A3.6. Deconvoluted XRD spectrum for sample BT; see Electronic Supplement 2 for details on the methodology. This sample contains significant kaolinite, which causes interference on the 2.58Å band. Polytype quantification is therefore somewhat uncertain and the results should be regarded with caution. While all illite peaks could be identified, the 32.1 °2θ peaks in the medium and fine fractions are unusually high. The reason for this is uncertain, but we have excluded these peaks from the calculation of the mean. Black curve – original data, blue curves – deconvoluted single peaks, red curves – illite polytype-sepcific peaks, dashed line – background, green curve – modelled curve (sum of all blue curves), grey vertical lines – positions of polytype-specific illite peaks.