ResearchOnline@JCU This file is part of the following reference: Quentin de Gromard, R. (2011) The Paleozoic tectonometamorphic evolution of the Charters Towers Province, North Queensland, Australia. PhD thesis, James Cook University. Access to this file is available from: http://eprints.jcu.edu.au/22000 The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact ResearchOnline@jcu.edu.au and quote http://eprints.jcu.edu.au/22000
RQ30-matrix Order Mineral/feature identified X-ray maps used Threshold Area Significance of pixels with highest greyscale values (inch 2 % ) values 1 background Inverted sum (Al+Fe+Mg+K+Ti) 253-255 4.29 8.5 Black background 2 Ilmenite Sum (Ti+cumul1) 190-255 0.35 0.7 Minerals containing high Ti 3 Fe oxide Sum (Fe+cumul2) 194-255 0.13 0.3 Minerals contanining high Fe Total remaining iron minerals (TRFe) Min intensity (Fe+cumul3) 23-255 14.41 28.5 Remaining minerals containing Fe 4 Biotite Sum (inverted TRFe+K+cumul3) 216-255 9.64 19.1 Minerals containing high Fe and high K 5 Chlorite Sum (inverted TRFe+Mg+inverted K+cumul4) 157-255 4.52 9.0 Minerals containing high Fe, high Mg and low K 6 Muscovite Sum (K+Al+2*cumul5) 211-255 9.97 19.4 Minerals containing high K and high Al 7 Quartz Sum (inverted Al+cumul6) 210-255 13.46 26.6 Remaining minerals containing no Al 8 Plagioclase Cumul7 128-355 8.33 16.5 Remaining minerals Modal percentage of all minerals normalized to the matrix area Ilmenite 0.7 Fe oxide 0.3 Biotite 20.9 Chlorite 9.8 Muscovite 21.2 Quartz 29.1 Plagioclase 18.0 RQ30-pseudomorph Order Mineral/feature identified X-ray maps used Threshold Area Significance of pixels with highest greyscale values (inch 2 % ) values 1 Background Sum (Al+K+Fe+Mg+Ti) 180-255 1.631 28.5 White background 2 Ilmenite Sum (Fe+Ti+2*cumul1) 149-255 0.034 0.6 Minerals containing high Fe and high Ti 3 Biotite Sum (Fe+K+2*cumul2) 215-255 1.492 26.0 Minerals containing high Fe and high K 4 Chlorite Sum (Fe+Mg+inverted K+cumul3) 190-255 0.384 6.7 Minerals containing high Fe, high Mg and low K 5 Muscovite Sum (K+Al+2*cumul4) 179-255 1.42 24.8 Minerals containing high K and high Al 6 Quartz Sum (inverted Al+cumul 5) 236-255 0.434 7.6 Remaining minerals containing no Al 7 Plagioclase Cumul6 128-255 0.331 5.8 Remaining minerals Modal percentage of all minerals normalized to the pseudomorph area Ilmenite 0.8 Biotite 36.4 Chlorite 9.4 Muscovite 34.7 Quartz 10.6 Plagioclase 8.1 Table 1. Table showing the methodology involved in the production of binary images and the calculation of mineral modes for sample RQ30. Inverted image refers to the inversion of the gray scale values (i.e. 255 minus the original gray scale value). Cumul is a summation of areas of all previously measured minerals resulting in a binary file where the mineral of interest is black. 9
(a) (b) Background Apatite 0.1% Ilmenite 1% Biotite 9.1% Muscovite 22.8% Quartz 10.4% Plagioclase 3.1% Cordierite 53.5% Background Ilmenite 0.8% Garnet 1.2% Biotite 30.4% Muscovite 51.6% Quartz 4.3% Cordierite 1.8% Plagioclase 10% Background (c) Muscovite 42.8% Apatite 0.3% Staurolite 2.5% Ilmenite+Pyrrhotite 2.8% Quartz 22% Biotite 16% Plagioclase 13.6% Figure 7: Binary images showing the modal mineralogy (the mineral of interest is in black) for three isolated areas: (a) the cordierite core, (b) the reaction rim and (c) the matrix. The background corresponds to the area of the map of no interest for mode calculation. Images produced via the routine described in text and in Table 1. Sample IS90. 10
RQ83-matrix Order Mineral/feature identified X-ray maps used Threshold Area Significance of pixels with highest greyscale values (inch 2 % ) values 1 Background Sum (Al+K+Fe+Mg+Ti) 0-1 21.682 36.7 Black background (removed pseudo areas) 2 Ilmenite Sum (Ti+cumul1) 192-255 0.219 0.4 Minerals containing high Ti 3 Fe oxides Sum (Fe+cumul2) 220-255 0.054 0.1 Minerals containing high Fe Total Remaining Iron Minerals (TRFe) Min intensity (Fe+cumul3) 52-255 6.797 11.5 Remaining minerals containing high Fe 4 Chlorite Sum (inverted TRFe+Mg+cumul3) 170-255 6.797 11.5 Minerals containing high Fe and high Mg 5 Muscovite Sum (K+Al+cumul4) 148-255 5,677 9.6 Minerals containing high K and high Al 6 Quartz Sum (inverted Al+Cumul5) 183-255 17.758 30.1 Remaining minerals containing no Al 7 Plagioclase Cumul6 128-255 6.84 11.6 Remaining minerals Modal percentage of all minerals normalized to the matrix area Ilmenite 0.6 Fe oxides 0.1 Chlorite 18.2 Muscovite 15.2 Quartz 47.6 Plagioclase 18.3 RQ83-pseudomorph Order Mineral/feature identified X-ray maps used Threshold Area % Significance of pixels with highest greyscale 1 Background values (inch 2 ) values Sum (Al+K+Fe+Mg+Ti) 0-127 21.682 All pixels containing some Al, K, Fe, Mg and/or Ti Inverted cumul0 128-255 58.0 All pixels containing none of the above elements 3 Ilmenite Sum (Fe+Ti+2*cumul1) 194-255 0.194 0.3 Minerals containing high Fe and high Ti 4 Chlorite Sum (Mg+inverted K+cumul2) 167-255 6.404 11.8 Minerals containing high Mg and low K 5 Muscovite Sum (Al+K+2*cumul3) 210-255 7.567 13.9 Minerals containing high Al and high K 6 Quartz Sum (inverted Al+cumul 4) 183-255 5.45 10.1 Remaining minerals containing no Al 7 Plagioclase Cumul5 128-255 3.228 6.0 Remaining minerals Modal percentage of all minerals normalized to the pseudomorph area Ilmenite 0.7 Chlorite 28.0 Muscovite 33.1 Quartz 24.0 Plagioclase 14.2 Table 2. Table showing the methodology involved in the production of binary images and the calculation of mineral modes for sample RQ83. Inverted image refers to the inversion of the gray scale values (i.e. 255 minus the original gray scale value). Cumul is a summation of areas of all previously measured minerals resulting in a binary file where the mineral of interest is black. 11
Background (a) (b) Ilmenite 0.8% Chlorite 9.4% Muscovite 34.7% Background Ilmenite 0.7% Chlorite 9.8% Muscovite 21.2% Biotite 36.4% Quartz 10.6% Fe-oxide 0.3% Quartz 29.1% Plagioclase 8.1% Biotite 20.9% Plagioclase 18% Figure 8: Binary images showing the modal mineralogy (the mineral of interest is in black) for two isolated areas: (a) the pseudomorph and (b) the matrix. The background corresponds to the area of the map of no interest for mode calculation. Images produced via the routine described in text and in Table 2. Sample RQ30. 12
IS90-matrix Order Mineral/feature Threshold Area Significance of pixels with highest X-ray maps used identified values (inch 2 % ) greyscale values 1 Background Sum (Al+K+Fe+Mg+Ca+CP) 150-255 22.276 43.5 White background 2 Apatite Sum (Ca+cumul1) 180-255 0.074 0.2 Minerals containing high Ca 3 Ilmenite and pyrrhotite Sum (Fe+cumul2) 164-255 0.829 1.6 Minerals containing high Fe 4 Biotite Sum (K+Mg+cumul3) 183-255 4.644 9.0 Minerals containing high K and high Mg 5 Muscovite Sum (K+cumul4) 169-255 12.377 24.2 Remaining minerals containing high K 6 Staurolite Sum (Al+cumul5) 203-255 0.71 1.4 Minerals containing high Al 7 Quartz Sum (inverted Al+cumul6) 227-255 6.38 12.4 Remaining minerals containing no Al 8 Plagioclase Sum (Ca+cumul7) 165-255 3.966 7.7 Remaining minerals containing Ca Modal percentage of all minerals normalized to the matrix area Apatite 0.3 FeS and FeTi oxides 2.8 Biotite 16.0 Muscovite 42.8 Staurolite 2.5 Quartz 22.0 Plagioclase 13.6 IS90-reaction rim Order Mineral/feature Threshold Area Significance of pixels with highest X-ray maps used identified values (inch 2 % ) greyscale values 1 Background Sum (Al+K+Fe+Mg+Ca+CP) 176-255 16.444 53.0 White background 2 Ilmenite Sum (Fe+inverted Al+cumul1) 177-255 0.108 0.4 Minerals containing high Fe and no Al 3 Garnet Sum (Fe+inverted K+cumul2) 227-255 0.177 0.6 Minerals containing high Fe and no K 4 Biotite Sum (K+Mg+cumul3) 181-255 4.443 14.3 Minerals containing high K and high Mg 5 Muscovite Sum (K+cumul4) 161-255 7.513 24.2 Remaining minerals containing high K 6 Quartz Sum (inverted Al+cumul5) 209-255 0.621 2.0 Remaining minerals containing no Al 7 Cordierite Sum (Mg+cumul6) 163-255 0.248 0.8 Remaining minerals containing Mg 8 Plagioclase Sum (Ca+cumul7) 128-255 1.456 4.7 Remaining minerals containing Ca Modal percentage of all minerals normalized to the mantle area Ilmenite 0.8 Garnet 1.2 Biotite 30.4 Muscovite 51.6 Quartz 4.3 Cordierite 1.8 Plagioclase 10.0 IS90-cordierite core Order Mineral/feature Threshold Area Significance of pixels with highest X-ray maps used identified values (inch 2 % ) greyscale values 1 Background Sum (Al+K+Fe+Mg+Ca+CP) 187-255 4.33 30.6 White background 2 Apatite Sum (Ca+cumul1) 158-255 0.011 0.1 Minerals containing high Ca 3 Ilmenite Sum (Fe+cumul2) 198-255 0.107 0.7 Minerals containing high Fe 4 Biotite Sum (K+Mg+cumul3) 212-255 0.898 6.3 Minerals containing high K and high Mg 5 Muscovite Sum (K+cumul4) 152-255 2.235 15.8 Remaining minerals containing high K 6 Quartz Sum (inverted Al+cumul5) 206-255 1.019 7.2 Remaining minerals containing no Al 7 Plagioclase Sum (Ca+cumul6) 203-255 0.303 2.1 Remaining minerals containing Ca 8 Cordierite Sum (Mg+cumul7) 137-255 5.251 37.1 Remaining minerals containing Mg Modal percentage of all minerals normalized to the pseudomorph area Apatite 0.1 Ilmenite 1.0 Biotite 9.1 Muscovite 22.8 Quartz 10.4 Plagioclase 3.1 Cordierite 53.5 Table 3. Table showing the methodology involved in the production of binary images and the calculation of mineral modes for sample IS90. Inverted image refers to the inversion of the gray scale values (i.e. 255 minus the original gray scale value). Cumul is a summation of areas of all previously measured minerals resulting in a binary file where the mineral of interest is black. 13
Background Ilmenite 0.7% (a) Quartz 24% Background (b) Chlorite 28% Plagioclase 14.2% Ilmenites 0.6% Muscovite 15.2% Muscovite 33.1% Fe oxide 0.1% Quartz 47.6% Chlorite 18.2% Plagioclase 18.3% Figure 9: Binary images showing the modal mineralogy (the mineral of interest is in black) for two isolated areas: (a) the pseudomorph and (b) the matrix. The background corresponds to the area of the map of no interest for mode calculation. Images produced via the routine described in text and in Table 3. Sample RQ83. 14
Ilmenite+Pyrrhotite Quartz Biotite Muscovite Plagioclase Cordierite Figure 10: Reconstructed binary images showing the distribution of each mineral over the whole pseudomorph plus matrix area for sample IS90. 15
Ilmenite Biotite Chlorite Muscovite Quartz Plagioclase Figure 11: Reconstructed binary images showing the distribution of each mineral over the whole pseudomorph plus matrix area for sample RQ30. 16
Ilmenite Chlorite Quartz Muscovite Plagioclase Figure 12: Reconstructed binary images showing the distribution of each mineral over the whole pseudomorph plus matrix area for sample RQ83. 17
Cordierite Biotite Muscovite Staurolite cc rr cc rr m cc rr m SiO 2 48.75 48.80 36.62 36.76 36.28 47.29 46.98 46.46 27.67 TiO 2 0.01 0.00 1.25 1.29 1.46 0.24 0.45 0.37 0.57 Al 2 O 3 31.46 32.03 19.62 19.54 19.19 36.85 36.36 36.13 52.90 FeO 6.68 6.47 16.25 16.54 16.76 0.60 0.57 0.53 12.88 MnO 0.47 0.50 0.14 0.14 0.16 0.01 0.01 0.02 0.52 MgO 8.30 8.33 11.67 11.83 11.52 0.45 0.49 0.47 1.83 CaO 0.02 0.02 0.01 0.01 0.01 0.01 Na 2 O 0.84 0.76 0.31 0.33 0.32 1.12 1.19 1.29 K 2 O 0.01 0.00 8.09 8.12 7.97 7.25 7.65 8.04 Total 96.53 96.90 93.95 94.55 93.69 93.82 93.71 93.31 96.38 Si 5.09 5.07 5.50 5.50 5.49 6.23 6.22 6.20 7.78 iv Al 0.91 0.93 2.50 2.50 2.51 1.77 1.78 1.80 0.22 (iv) 6.00 6.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 vi Al 2.97 2.99 0.98 0.94 0.91 3.95 3.89 3.88 17.30 Ti 0.14 0.14 0.17 0.02 0.04 0.04 0.12 Fe 0.58 0.56 2.04 2.07 2.12 0.07 0.06 0.06 3.03 Mn 0.04 0.04 0.12 Mg 1.29 1.29 2.61 2.64 2.60 0.09 0.10 0.09 0.77 1.92 1.90 5.78 5.79 5.80 4.13 4.10 4.07 Ca Na 0.17 0.15 0.09 0.10 0.09 0.29 0.31 0.33 K 1.55 1.55 1.54 1.22 1.29 1.37 0.17 0.16 1.64 1.65 1.64 1.51 1.60 1.70 Total 11.06 11.05 15.42 15.44 15.43 13.64 13.70 13.77 29.34 Table 4. Table showing representative analyses of cordierite, biotite, muscovite and staurolite from sample IS90. cc cordierite core; rr reaction rim; m matrix 18
Biotite Muscovite Chlorite Plagioclase p m p m p m p m c r c r SiO 2 37.13 37.61 48.79 48.76 30.40 27.32 61.33 62.35 62.16 62.27 TiO 2 0.85 1.15 0.16 0.31 0.08 0.08 0.02 0.00 0.06 0.01 Al 2 O 3 19.04 18.27 37.77 37.53 22.21 19.97 24.14 24.26 24.09 24.05 FeO 17.14 16.83 0.76 0.97 20.75 27.37 0.15 0.19 0.18 0.18 MnO 0.15 0.16 0.01 0.00 0.23 0.20 0.02 0.01 MgO 11.21 11.27 0.48 0.58 14.26 12.48 0.01 0.00 CaO 0.17 0.08 0.02 0.08 0.25 0.28 6.24 5.79 5.98 5.64 Na 2 O 0.18 0.07 1.11 1.04 0.02 0.04 8.23 8.20 8.39 8.59 K 2 O 7.81 8.45 6.07 5.49 1.17 0.84 0.06 0.08 0.07 0.08 Cl 0.02 0.02 0.01 Total 93.68 93.90 95.18 94.76 89.36 88.57 100.17 100.87 100.97 100.83 Si 5.61 5.67 6.28 6.29 6.08 5.77 2.72 2.74 2.74 2.74 iv Al 2.39 2.33 1.72 1.71 1.92 2.23 1.26 1.26 1.25 1.25 (iv) 8.00 8.00 8.00 8.00 8.00 8.00 vi Al 1.00 0.93 4.01 3.99 3.31 2.74 Ti 0.10 0.13 0.02 0.03 0.01 0.01 Fe 2.16 2.12 0.08 0.10 3.47 4.83 Mn 0.02 0.02 0.04 0.04 Mg 2.52 2.53 0.09 0.11 4.25 3.93 (vi) 5.80 5.73 4.20 4.24 11.09 11.55 Ca 0.03 0.01 0.00 0.01 0.05 0.06 0.30 0.27 0.28 0.27 Na 0.05 0.02 0.28 0.26 0.01 0.01 0.71 0.70 0.72 0.73 K 1.50 1.63 1.00 0.90 0.30 0.23 Cl (xii) 1.59 1.66 1.28 1.17 0.36 0.31 Total 15.39 15.40 13.48 13.41 19.44 19.86 5.00 4.98 5.00 5.00 An 29.53 28.07 28.26 26.62 Ab 70.47 71.93 71.74 73.38 Table 5. Table showing representative analyses of biotite, muscovite, chlorite and plagioclase from sample RQ30. m matrix, p pseudomorph, c core, r - rim 19
Biotite Muscovite Chlorite m p m p m SiO 2 37.93 53.11 47.45 25.43 25.08 TiO 2 1.06 0.04 0.05 0.06 0.09 Al 2 O 3 18.48 34.19 37.19 23.23 23.42 FeO 16.54 1.12 1.69 23.22 23.74 MnO 0.14 0.02 0.34 0.34 MgO 10.29 0.51 0.44 15.85 15.74 CaO 0.22 0.04 0.06 0.08 0.06 Na 2 O 0.14 0.94 1.51 0.01 0.01 K 2 O 8.33 5.76 6.59 0.03 0.01 Cl 0.02 0.01 0.01 Total 93.15 95.74 94.98 88.26 88.50 Si 5.75 6.75 6.19 5.26 5.19 iv Al 2.25 1.25 1.81 2.74 2.81 (iv) 8.00 8.00 8.00 8.00 8.00 vi Al 1.05 3.87 3.92 2.92 2.90 Ti 0.12 0.00 0.01 0.01 0.01 Fe 2.10 0.12 0.18 4.01 4.11 Mn 0.02 0.06 0.06 Mg 2.33 0.10 0.08 4.88 4.85 (vi) 5.62 4.10 4.19 11.88 11.93 Ca 0.04 0.01 0.01 0.02 0.01 Na 0.04 0.23 0.38 0.00 0.01 K 1.61 0.93 1.10 0.01 0.00 Cl 0.01 (xii) 1.69 1.17 1.49 0.03 0.02 Total 15.31 13.27 13.68 19.91 19.95 Table 6. Table showing representative analyses of biotite, muscovite and chlorite from sample RQ83. m matrix, p - pseudomorph 20
Garnet Plagioclase rr m cc rr m c r c r c r c r c r SiO 2 37.91 37.91 37.88 37.83 63.15 62.68 63.51 63.62 63.58 63.85 TiO 2 0.02 0.02 0.03 0.03 0.04 0.00 0.01 0.00 0.00 0.02 Al 2 O 3 21.01 21.01 21.08 21.05 22.67 22.91 22.57 22.38 22.58 21.95 FeO 29.13 29.13 29.36 29.38 0.10 0.13 0.06 0.11 0.02 0.02 MnO 7.83 7.83 7.64 8.06 0.02 0.01 0.01 0.00 0.00 0.01 MgO 3.10 3.10 3.15 2.87 0.00 0.01 0.00 0.00 0.00 0.00 CaO 1.30 1.30 1.09 1.02 4.13 4.73 4.10 4.02 3.99 3.64 Na 2 O 0.06 0.06 0.02 0.02 8.74 8.30 8.00 8.20 7.73 8.26 K2O 0.02 0.02 0.00 0.00 0.03 0.03 0.06 0.05 0.04 0.04 Total 100.37 100.37 100.24 100.26 98.88 98.79 98.31 98.36 97.93 97.78 Si 3.03 3.03 3.03 3.03 2.81 2.80 2.84 2.84 2.84 2.86 Al 1.98 1.98 1.99 1.99 1.19 1.21 1.19 1.18 1.19 1.16 Ti 0.00 0.00 0.00 0.00 Fe 1.95 1.95 1.96 1.97 Mn 0.53 0.53 0.52 0.55 Mg 0.37 0.37 0.38 0.34 Ca 0.11 0.11 0.09 0.09 0.20 0.23 0.20 0.19 0.19 0.17 Na 0.76 0.72 0.69 0.71 0.67 0.72 Total 7.98 7.98 7.97 7.97 4.97 4.96 4.92 4.93 4.90 4.92 X alm 0.66 0.66 0.67 0.67 X py 0.12 0.12 0.13 0.12 X spess 0.18 0.18 0.18 0.19 X gross 0.04 0.04 0.03 0.03 An 20.75 23.96 22.07 21.31 22.18 19.59 Ab 79.25 76.04 77.93 78.69 77.82 80.41 Table 7. Table showing representative analyses of garnet and plagioclase from sample IS90. cc cordierite core, rr reaction rim, m matrix, c core, r - rim 21
Fe+Mg+Mn+Ti 0.38 0.33 0.28 0.23 0.18 (a) 0.13 3.73 3.78 3.83 3.88 3.93 3.98 4.03 VI Al K 1.65 1.55 1.45 1.35 1.25 1.15 1.05 0.95 (b) 0.85 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Na Fe+Mg+Mn+Ti 5.15 5.05 4.95 4.85 4.75 4.65 4.55 4.45 (c) 4.35 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 VI Al K 1.80 1.70 1.60 1.50 1.40 1.30 (d) 1.20 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 Na 9.20 30 Fe+Mg+Mn+Ti 8.80 8.40 8.00 7.60 (e) 7.20 2.70 2.80 2.90 3.00 3.10 3.20 3.30 3.40 3.50 VI Al An 28 26 24 22 20 18 (f) 16 2.70 2.72 2.74 2.76 2.78 2.80 2.82 2.84 2.86 2.88 Si 0.69 0.20 0.19 0.18 X Mg 0.68 Na 0.17 0.16 (g) 0.67 5.06 5.07 5.08 5.09 5.10 5.11 5.12 Si 0.15 (h) 0.14 5.06 5.07 5.08 5.09 5.10 5.11 5.12 Si Legend RQ30 pseudomorph RQ30 matrix RQ30 pseudomoprh/matrix boudary IS90 cordierite core IS90 reaction rim IS90 matrix RQ83 pseudomorph RQ83 matrix IS104 pseudomorph IS104 matrix 22
Figure 13: Diagrams showing the relationship between VIAl and Fe+Mg+Mn+Ti (a) and Na and K (b) in muscovite. Diagrams showing the relationship between VIAl and Fe+Mg+Mn+Ti (c) and Na and K (d) in biotite. Diagram showing the relationship between VIAl and Fe+Mg+Mn+Ti in chlorite (e). Diagram showing the relationship between Si and An content in plagioclase (f). shaded areas represents plagioclase core analysis, the arrows indicate the transition from plagioclase core (shaded) to rim. Diagram showing the relationship between Si and XMg (g) and Si and Na (h) in cordierite. 23
P (kbar) 7 6 Pattison 92TP a H2 O = 1 Ky Sil Ms Als Kfs 5 4 3 Ky And P Als Chl Crd Bt 0.4 0.3 0.2 0.9 0.8 0.7 0.6 0.5 Mg-Bt Sil Mg-Crd 2 0.1 Sil 1 0 (a) And 400 500 600 700 800 T (ºC) Fe-Bt Als Fe-Crd P (kbar) 7 6 5 Holdaway 71TP a H2 O = 1 Ky Sil Ms Als Kfs 4 3 2 Ky And 0.3 H Als Chl Crd Bt 0.3 0.2 0.9 0.8 0.7 0.6 0.5 0.4 Mg-Bt Sil Mg-Crd 1 0 (b) 0.1 Sil And 400 500 600 700 800 T (ºC) P-T region of reaction (1) (Ms+Qtz+Crd+Als+Bt) assemblages Isopleths of Mg/(Mg+Fe) in Bt in reaction (1) Qtz + H2O in excess; Ms in excess below reaction Ms=Als+Kfs Figure 14: Contours of Mg/(Mg+Fe) in biotite plotted on petrogenetic grids of Pattison et al. (2002) for the Pattison 1999 triple point (a) and the Holdaway 1971 triple point (b). Reaction 1: 2Ms + 3Crd = 2Bt + 8Als + 7Qtz +3n H2O. 24
0.4 700 o C 0.3 Ti (apfu) 0.2 600 o C 500 o C IS90 RQ30 0.1 RQ83 0.4 0 (a) 0.3 0.4 0.5 0.6 0.7 0.8 Mg/(Mg+Fe) 0.3 700 o C Ti (apfu) 0.2 0.1 600 o C 500 o C IS90-matrix IS90-reaction rim RQ30-matrix RQ30-pseudomorph 0 (b) 0.3 0.4 0.5 0.6 0.7 0.8 Mg/(Mg+Fe) Figure 15: Ti-in-biotite thermometer grid of Henry et al. (2005). (a) Ti/XMg plot for all biotite analysis for samples IS90, RQ30 and RQ83. (b) Ti/XMg plot for the average biotite composition from the pseudomorph and from the matrix for samples IS90 and RQ30. 25
(a) (b) (c) Legend: Matrix: Qz + Bt + Ms + Pl Reaction rim: Ms + Bt + Pl Cordierite Idioblastic biotite Deformed biotite Muscovite Quartz Plagioclase Ilmenite Crack Fluid Figure 16: Series of sketches showing the inferred textural and mineralogical evolution of mica rich pseudomorph after cordierite. (a) Cordierite porphyroblast at the onset of pseudomorphing process. Microcracks start to develop from the margin of the cordierite porphyroblast towards the core. Some cracks develop due to the replacement of quartz by plagioclase by fluid infiltration and diffusion. Another series of cracks develop by increase strain rate during exhumation. Both crack types are filled by micas. (b) The process advances until the entire rim of the cordierite porphyroblast is replaced by micas resulting in the reaction rim. Continuous replacement of quartz by plagioclase and increase strain rate contributes to further microcracking of the reaming cordierite. (c) The process continues until the whole cordierite porphyroblast is replaced. 26