FeO-Al2O3-SiO2
The almandine enthalpy is based largely on the reaction alm + 3hem = 3mt + ky +2q determined experimentally by Harlov & Newton (1992). The calculated slope fitted to the iron cordierite breakdown reaction 2alm + 4sill + 5q = 3fcrd in HP90 had a positive slope relative to the earlier experimental brackets on this reaction. However, the more recent experiments of Mukhopadhyay & Holdaway (1994) have confirmed the positive slope for this breakdown reaction. These data for Fe-cordierite are in excellent agreement with the Fe-Mg exchange equilibrium experiments of Perchuk & Lavrenteva (1983) for garnet-cordierite, as shown below.
A model for staurolites involving variable H2O contents (as suggested by Holdaway et al., 1995) was found to be successful at fitting most of the equilibria involving Fe- and Mg-staurolites. However, this model has not been included here because (a) the simpler model of HP90 gave almost indistinguishable PT locations for all equilibria, and (b) the activity models used involve assumptions about site distributions for Fe, Mg, Al, Si and H in natural and synthetic staurolites which are probably not well enough understood (Hawthorne et al., 1993) to make robust activity estimates. Most of the experimental equilibria, other than those of Richardson (1968), involving garnet, staurolite and chloritoid are quite well fited by the data. The recent high-pressure equilibria on chloritoid stability from Vidal et al. (1994) are very well fitted.
230) alm + 3hem = 3mt + ky + 2q (Harlov & Newton, 1992)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 - 23.0 20.0 650 -23.89 -18.71 21.14 0.66 3 (-21.79 <-> -19.75)
0 - 22.5 22.0 700 -20.43 -19.57 0.15 22.65 0.66 cH = -20.69 (sd 0.54)
0 - 26.0 25.5 800 -21.59 -20.73 -0.02 25.48 0.66 within bracket
0 - 29.0 28.0 900 -21.85 -20.12 28.33 0.66 uH = 0.86, d/s = -0.2, h = 0.84
231) alm + 2sill = 3herc + 5q (Bohlen et al., 1986)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 - 3.0 800 6.65 708 24 5 (2.49 <-> 3.98)
0 - 2.9 780 6.19 701 26 cH = 3.48 (sd 0.42) 2
0 - 5.2 865 880 3.61 4.17 -4 861 22 within bracket
0 - 5.5 5.1 880 3.44 4.41 5.48 0.43 uH = 0.39, d/s = -2.8, h = 0.82
0 - 6.9 6.5 940 2.31 3.27 -0.09 6.41 0.43
0 - 8.9 8.5 1020 0.63 1.59 -0.79 7.71 0.43
0 - 8.8 1015 1035 0.67 1.47 50 1085 20
232) alm + 5cor = 3herc + 3sill (Shulters & Bohlen, 1989)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 - 7.2 850 6.73 -58 792 24 6 (4.75 <-> 6.10)
0 - 8.3 7.9 900 5.80 6.91 0.51 8.81 0.34 cH = 4.38 (sd 0.46) 2
0 - 10.6 9.9 1000 3.96 5.88 10.45 0.34 too low but OK
0 - 12.3 11.9 1100 4.15 5.24 12.21 0.35 uH = 0.57, d/s = -1.3, h = 0.24
233) 2alm + 4sill + 5q = 3fcrd (Mukhopadhyay et al., 1991)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 - 2.3 1.9 650 110.62 115.18 -0.05 1.85 0.14 3 (114.71 <-> 116.75)
0 - 2.5 2.1 700 113.45 117.99 2.30 0.14 cH = 115.71 (sd 1.13)
0 - 2.7 2.3 750 116.30 120.83 0.05 2.75 0.14 within bracket
uH = 0.73, d/s = -0.8, h = 0.94
234) 6fst + 25q = 8alm + 46ky + 12H2O (Rao & Johannes, 1979)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 6.0 680 700 998.55 1010.01 683 18 3 (999.59 <-> 1007.87)
0 0 10.0 640 660 993.15 1003.57 654 20 cH = 1000.50 (sd 5.16) 2
0 0 15.0 590 610 1001.23 1010.53 -2 588 24 within bracket
uH = 3.01, d/s = 0.4, h = 0.75
* 6fst + 25q = 8alm + 46ky + 12H2O (Ganguly, 1972)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 7.0 700 1012.49 -21 679 18 ** NOT USED **
0 0 10.0 690 1019.16 654 20 cH = 1000.50 (sd 5.16)
0 0 10.6 14.0 650 1001.66 1022.48 -0.21 10.39 2.40
0 0 15.5 600 650 1009.52 1032.50 -20 580 24
* 2fst + 15q = 4fcrd + 10sill + 4H2O (Richardson, 1968)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 2.0 550 575 578.35 592.31 12 587 8 ** NOT USED **
0 0 4.0 675 596.84 679 8 cH = 598.77 (sd 2.42)
0 0 3.0 650 607.86 633 8
235) 23fctd + 7q = 2fst + 5alm + 19H2O (Rao & Johannes, 1979)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
1.18 0 10.0 560 580 1750.60 1775.69 573 10 2 (1759.19 <-> 1779.14)
1.18 0 14.0 580 1766.25 580 10 cH = 1766.80 (sd 5.92) 2
1.18 0 6.0 560 1772.09 556 10 within bracket
uH = 7.14, d/s = 0.4, h = 0.06
236) 8fctd + 10ky = 2fst + 3q + 4H2O (Rao & Johannes, 1979)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0.41 0 6.0 530 550 404.48 411.12 -22 508 14 3 (399.29 <-> 404.98)
0.41 0 10.0 550 570 398.84 405.31 -6 544 14 cH = 397.04 (sd 2.38) 2
0.41 0 14.0 570 590 396.09 402.50 573 16 too low but OK
uH = 2.04, d/s = -0.5, h = 0.38
237) 3fctd = alm + 2cor + 3H2O (Ganguly, 1969; Vidal et al., 1994)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
-0.49 0 12.0 570 595 281.44 286.62 7 602 8 3 (285.83 <-> 288.42)
-0.49 0 19.0 612 640 285.78 291.29 624 8 cH = 288.07 (sd 0.79) 2
-0.49 0 25.0 627 635 287.04 288.58 632 8 within bracket
-0.49 0 30.0 615 650 284.34 290.95 635 10 uH = 1.10, d/s = -0.2, h = 0.16
238) 3fctd = alm + 2cor + 3H2O (Ganguly, 1969)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 8.0 580 600 284.34 288.56 598 8 3 (286.21 <-> 289.04)
0 0 11.5 605 620 285.58 288.63 617 8 cH = 288.07 (sd 0.79) 2
0 0 15.0 620 640 285.84 289.78 631 8 within bracket
0 0 20.0 650 670 289.10 292.93 -5 645 8 uH = 1.02, d/s = -0.3, h = 0.19
239) 3fctd = 4dsp + alm + H2O (Vidal et al., 1994)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
-0.16 0 30.0 615 635 122.80 124.03 7 642 28 2 (122.82 <-> 124.28)
-0.16 0 33.0 580 615 123.06 125.19 603 30 cH = 124.46 (sd 0.81) 2
too high but OK
uH = 0.61, d/s = 0.8, h = 0.40
* 6fst + 25q = 8alm + 46sill + 12H2O (Richardson, 1968)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 2.0 680 1481.77 560 10 ** NOT USED **
0 0 5.0 675 700 1389.57 1417.82 -49 626 10 cH = 1333.44 (sd 5.68)
240) 6fst + 25q = 8alm + 46sill + 12H2O (Dutrow & Holdaway, 1989)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
7.22 0 3.2 627 647 1324.72 1347.16 635 10 2 (1330.48 <-> 1347.16)
7.22 0 5.0 673 693 1330.48 1351.94 676 10 cH = 1333.44 (sd 5.68) 2
within bracket
uH = 5.97, d/s = 1.4, h = 0.14
* 8fctd + 10sill = 2fst + 3q + 4H2O (Richardson, 1968)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0.41 0 2.0 500 550 330.40 342.42 -24 476 20 ** NOT USED **
0.41 0 5.0 525 550 338.40 343.80 -63 462 22 cH = 324.66 (sd 2.47)
* 5fctd = fcrd + 3herc + 5H2O (Grieve & Fawcett, 1974)
ln_K x(CO2) P(kbar) T(C) H(low) H(high) miss calc 2sd summary
0 0 1.0 525 550 529.32 541.94 -13 512 6 ** NOT USED **
0 0 2.0 550 575 526.71 538.51 -8 542 6 cH = 522.77 (sd 1.44)
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