building combined subsolidus-suprasolidus phase diagrams
TRANSCRIPT
Dave Pattison, University of Calgary
Building combined subsolidus-suprasolidus phase diagrams(with implications for how you think about the behaviour of H2O in phase diagrams)
All assemblages +Bt+Qtz+Pl+Ilm+Mt, except where indicated by “-Qtz”, “-Bt”, “-Ilm”.H₂O present below wet solidus;H₂O absent above wet solidus.
MsChlGrt Ms GrtSt
MsGrtSil
MsSil
MsGrtLSil
MsGrtKyL
MsGrtKy
MsChl
KfsGrtLSil
MsLSil
MsCrdCrdKfs
CrdKfsL
GrtCrdKfsL
GrtCrdKfsL (-Bt)
KfsGrtLSil (-Bt)
KfsGrtRtLSil (-Ilm)
MsChlGrtRt (-Ilm)
MsGrtRt (-Ilm) MsGrtKyRt
(-Ilm)
MsChlGrtSt
MsGrtStAnd
MsGrtStSil
MsGrtStRt (-Ilm)
Average Buchan metapelite MnNCKFMASHTO; Fe3+/FeTotal = 0.15HP98 ds 5.5; 2005 a-X models
MsGrtStKy
MsChlRt
MsChlRtEp
MsChlEp
CrdKfsOpxL (-Bt)
GrtCrdOpxKfsL (-Bt)
KfsLSil
MsGrtStMsChlGrt
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Temperature [°C]
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Pres
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MnNCKFMASHTO Fe3+/Fetotal = 0.15
Pattison & Goldsmith (submitted, J Geol Soc)
All assemblages +Bt+Qtz+Pl+Ilm+Mt, except where indicated by “-Qtz”, “-Bt”, “-Ilm”.H₂O present below wet solidus;H₂O absent above wet solidus.
MsChlGrt Ms GrtSt
MsGrtSil
MsSil
MsGrtLSil
MsGrtKyL
MsGrtKy
MsChl
KfsGrtLSil
MsLSil
MsCrdCrdKfs
CrdKfsL
GrtCrdKfsL
GrtCrdKfsL (-Bt)
KfsGrtLSil (-Bt)
KfsGrtRtLSil (-Ilm)
MsChlGrtRt (-Ilm)
MsGrtRt (-Ilm) MsGrtKyRt
(-Ilm)
MsChlGrtSt
MsGrtStAnd
MsGrtStSil
MsGrtStRt (-Ilm)
Average Buchan metapelite MnNCKFMASHTO; Fe3+/FeTotal = 0.15HP98 ds 5.5; 2005 a-X models
MsGrtStKy
MsChlRt
MsChlRtEp
MsChlEp
CrdKfsOpxL (-Bt)
GrtCrdOpxKfsL (-Bt)
KfsLSil
MsGrtStMsChlGrt
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Temperature [°C]
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Pres
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[Bar
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Subsolidus Suprasolidus
Excess H2O Fixed H2O
Pl + Qtz + Ms + H2O ±… = L
Pl + Qtz + Kfs + H2O ±… = L
MnNCKFMASHTO Fe3+/Fetotal = 0.15
Pattison & Goldsmith (submitted, J Geol Soc)
Rationale: low grade mineral assemblages have a lot of hydrous minerals like clays, chlorite, muscovite. These get consumed in prograde dehydration reactions to produce 1) less hydrous minerals like garnet, cordierite, etc., and 2) free H2O fluid that escapes the rock. Exceptions (i.e., prograde H2O-consuming reactions) occur but are relatively rare.
Excess H2O = enough H2O to ensure the lowest grade, most hydrous mineral assemblages on the phase diagram are stable (usually those in the low-T, high-P corner of the phase diagram). In practice, this means adding enough H2O to saturate the entire phase diagram (have free H2O present as a phase everywhere on the phase diagram). Adding more H2O than needed to saturate the entire phase diagram makes no difference to the calculated phase equilibria, but having too little may result in incorrect phase equilibria –even if they don’t look obviously incorrect! You must check the phase diagram to be sure that H2O is present as a phase in every predicted subsolidus mineral assemblage.
Upshot: you do not use the measured H2O content or LOI (loss on ignition) of a subsolidus rock (e.g., a garnet-kyanite schist) to calculate a subsolidus phase diagram that extends to P-T conditions below those of the rock: the lower grade phase equilibria will be wrong once H2O is no longer present as a free fluid phase.
Example input file in Theriak-Domino (using HP ds5.5) for the illustrated subsolidus phase diagram:
SI(091.5798)TI(1.3637)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)H(80)O(?)
Subsolidus phase diagram – excess H2O
Excess H
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Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(80)O(?)
22/11/2020 14:23:59 CPU-Time (hhh:mm:sec): 001:58:45.796
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=80(Mainly) subsolidus phase diagram calculated with excess H2O (H2O = 40, same as H = 80)
Pl + Qtz + Ms + H2O ±… = L
Pl + Qtz + Kfs + H2O ±… = L
Pattison (unpublished)
and liquid (melt)
Increasing amt of H2O needed to saturate low grade hydrous mineral assemblages
Moles of H2O contained in solid or melt phases - excess H2O (H2O = 40, same as H = 80)
Pattison (unpublished)
Abundant H2O-bearing melt(not realistic)
Moles of H2O contained in solid or melt phases - not enough H2O to saturate (H2O = 12.5, same as H = 25)
and liquid (melt)
Maxed out H2O in solids (12.5) – no free H2O phase
Strange low grade mineral assemblages involving Grt, St, Ky!
Domain of H2O present as phase
Maxed out H2O in solids and melt (12.5) – no free H2O phase, but still too much melt
Pattison (unpublished)
450 500 550 600 650 700Temperature [C]
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Pres
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Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(80)O(?)
22/11/2020 14:23:59 CPU-Time (hhh:mm:sec): 001:58:45.796
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
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7 8
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1922
2324
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5859
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6871 73
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=80
These suprasolidus reactions assume excess H2O! They do not correspond to natural reactions (except inunusual situations).
Therefore, delete all reactions above the wet solidus.
Pl + Qtz + Ms + H2O ±… = L
Pl + Qtz + Kfs + H2O ±… = L
(Mainly) subsolidus phase diagram calculated with excess H2O (H2O = 40, same as H = 80)
Pattison (unpublished)
Subsolidus phase diagram calculated with excess H2O (cleaned up but unlabelled, with some less relevant reactions removed )
450 500 550 600 650 700
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Temperature [°C]
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Suprasolidusdomain
Same details as forcompleted diagram
Rationale: in suprasolidus rocks above the wet solidus, all hydrous fluid is consumed by H2O-consuming melting reactions.
Because the porosity of high grade rocks is likely to be near-zero, so is the volume of free H2O fluid contained in the pores, meaning that imperceptible volumes of melt are produced at the wet solidus. That is why “excess H2O” above the wet solidus is not realistic, unless externally-derived fluid infiltration occurs when the rocks are at P-T conditions above the wet solidus.
In dehydration reactions above the wet solidus (e.g., Ms- or Bt-consuming suprasolidus reactions), the H2O released is dissolved into the melt phase, hence the term dehydration-melting reactions. Thus, in contrast to subsolidus reactions in which the H2O released in dehydration reactions escapes the rock, the H2O content of suprasolidus rocks is retained in the rock (in the melt phase) – that is, unless some of the melt escapes (next talk!).
Upshot: use a fixed H2O content for suprasolidus phase equilibria.
Complication: melt has a variable H2O content (higher H2O content at higher P, lower H2O content at lower P).Therefore, more than one fixed-H2O suprasolidus phase diagrams may need to be calculated, as explained below.
Suprasolidus phase diagram – fixed H2O
Pl + Qtz + Ms-or-Kfs + H2O ±… = L
All assemblages +Bt+Qtz+Pl+Ilm+Mt, except where indicated by “-Qtz”, “-Bt”, “-Ilm”.H₂O present below wet solidus;H₂O absent above wet solidus.
MsChlGrt Ms GrtSt
MsGrtSil
MsSil
MsGrtLSil
MsGrtKyL
MsGrtKy
MsChl
KfsGrtLSil
MsLSil
MsCrdCrdKfs
CrdKfsL
GrtCrdKfsL
GrtCrdKfsL (-Bt)
KfsGrtLSil (-Bt)
KfsGrtRtLSil (-Ilm)
MsChlGrtRt (-Ilm)
MsGrtRt (-Ilm) MsGrtKyRt
(-Ilm)
MsChlGrtSt
MsGrtStAnd
MsGrtStSil
MsGrtStRt (-Ilm)
Average Buchan metapelite MnNCKFMASHTO; Fe3+/FeTotal = 0.15HP98 ds 5.5; 2005 a-X models
MsGrtStKy
MsChlRt
MsChlRtEp
MsChlEp
CrdKfsOpxL (-Bt)
GrtCrdOpxKfsL (-Bt)
KfsLSil
MsGrtStMsChlGrt
450 500 550 600 650 700
Temperature [°C]
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Pres
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[Bar
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MnNCKFMASHTO Fe3+/Fetotal = 0.15
Dehydration-meltingreactions
Pl + Qtz + Ms + H2O ±… = L
Pl + Qtz + Kfs + H2O ±… = L
Suprasolidus domain
Pattison (unpublished)
Fixed H2O suprasolidus phase diagram - Step 1.
Obtain the H2O content of the rock (contained in hydrous phases like muscovite and biotite) just below the wet solidus, i.e., modes x H-content (easy in T-D and Perplex, less so in Thermocalc?). Use this as a fixed value for the H2O content (or, in T-D, the H-content) of the rock. Typically one chooses a point on the solidus ~ in the middle of the pressure range of the diagram (in the example shown here, 3.6 kbar).
Example input file in Theriak-Domino (using HP ds5.5) for the illustrated phase diagram:
SI(091.5798)TI(1.3637)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)H(16)O(?)
Note that the bulk composition is identical to the bulk composition for the subsolidus phase diagram except for the reduced H2O (H) content.
Fixed (non-excess) H
450 500 550 600 650 700Temperature [C]
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essu
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ar]
Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(80)O(?)
22/11/2020 14:23:59 CPU-Time (hhh:mm:sec): 001:58:45.796
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
1
2
7 8
13
14
17
18
1922
2324
46
47
54
55
5859
60
61 64
65
6667
6871 73
74
75
76
77
78
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81 82
83
89
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9192
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101 102
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106 107108
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115116
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=80
Determine H2O content of rock on wet solidus (contained in hydrous phases like Ms, Bt):
P = 3.6 kbarT = 653 ⁰CH2O = 8 (H = 16)
This choice is not unique; other points on the solidus could have been chosen (more discussion below)
(Mainly) subsolidus phase diagram calculated with excess H2O (H2O = 40, same as H = 80)
Pattison (unpublished)
600 650 700 750 800 850Temperature [C]
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Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(16)O(?)
22/11/2020 12:44:21 CPU-Time (hhh:mm:sec): 001:30:56.312
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=16Suprasolidus phase diagram calculated with fixed (non-excess) H2O (H2O = 8, same as H = 16)
Note:
+ L (suprasolidus)
+ H2O phase (subsolidus)
no H2O phase (subsolidus)
Pattison (unpublished)
600 650 700 750 800 850Temperature [C]
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Pres
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[Bar
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Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(16)O(?)
22/11/2020 12:44:21 CPU-Time (hhh:mm:sec): 001:30:56.312
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=16Suprasolidus phase diagram calculated with fixed (non-excess) H2O (H2O = 8, same as H = 16)
For this reduced-H2O bulk composition, these subsolidusreactions do not involve a free H2O phase, and so they do not correspond to natural reactions (in a prograde sense at least).
Therefore, delete all reactions below the wet solidus.
Pattison (unpublished)
450 500 550 600 650 700
Temperature [°C]
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Suprasolidus phase diagram (cleaned up but unlabelled)
Subsolidusdomain
Subsolidus phase diagram (cleaned up but unlabelled)
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Suprasolidusdomain
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Combined subsolidus-suprasolidus phase diagram (unlabelled)
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600 650 700 750 800 850Temperature [C]
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Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(16)O(?)
22/11/2020 12:44:21 CPU-Time (hhh:mm:sec): 001:30:56.312
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
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ds 5.5 Avg Buchan Fe3/FeT=0.15 H=16
Note:
+ L (suprasolidus)
+ H2O (subsolidus)
no H2O (subsolidus)
Notice the blue line in the suprasolidus field – it is an H2O-consuming reactionabove the wet solidus(i.e., it is an artifact of the modelling, due to the progressively lower H2Ocontent of the melt)
This results in too much meltbeing generated at low P, which has a knock-on effect on the lower-P phase equilibria!
Suprasolidus phase diagram calculated with fixed (non-excess) H2O (H2O = 8, same as H = 16)
Complication
Fixed H2O suprasolidus phase diagram - Step 2.
Calculate another suprasolidus phase diagram, but with a fixed H2O content for a low pressure (e.g., 1.8 kbar).
Example input file in Theriak-Domino (using HP ds5.5) for the illustrated phase diagram:
SI(091.5798)TI(1.3637)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)H(6)O(?)
Notice again that the bulk composition is identical to the bulk composition for the other phase diagrams except for the further-reduced H2O (H) content.
Fixed (non-excess) H
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Temperature [C]
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[Bar
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Bulk(1)= H(6)O(?)FE(09.1486)F3(1.6145)SI(091.5798)AL(42.8147)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)
26/04/2021 14:59:06 CPU-Time (hhh:mm:sec): 000:33:21.1
Fe3/(FeTot) = 0.150domino vers ion: 01.08.09 (08.07.14, s rc10e1rdatabase: ds55hp1.txtH2O: HHP98PLC1: s i te mixing+margulesWM02V: s i te mixing+margulesGTT01: s i te mixing+margulesBI05: s i te mixing+margulesCHL: s i te mixing+margulesILMTERN: s i te mixingMT00: s i te mixing+margulesOPX: s i te mixing+margulesEP98: s i te mixing+margulesCRD: s i te mixingST: s i te mixing+margulesCTD: s i te mixing+margulesLIQtc2: external+margules
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+ L (suprasolidus)
+ H2O (subsolidus)
no H2O (subsolidus)
Notice the different phase equilibria involving Bt going to Opx between phase diagrams calculated for H2O=8 vs. H2O=3
Suprasolidus phase diagram calculated with fixed (non-excess) H2O (H2O = 3, same as H = 6)
Note:
Bt Opx
Pattison (unpublished)
600 650 700 750 800 850Temperature [C]
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[Bar
]
Bulk(1)= SI(091.5798)AL(42.8147)FE(09.1486)F3(1.6145)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)H(16)O(?)
22/11/2020 12:44:21 CPU-Time (hhh:mm:sec): 001:30:56.312
domino version: 01.08.09 (08.07.14, src10e1rf)database: ds55hp1.txtH2O: HHP98PLC1: site mixing+margulesWM02V: site mixing+margulesGTT01: site mixing+margulesBI05: site mixing+margulesCHL: site mixing+margulesILMTERN: site mixingMT00: site mixing+margulesOPX: site mixing+margulesEP98: site mixing+margulesCRD: site mixingST: site mixing+margulesCTD: site mixing+margulesLIQtc2: external+margules
1
2
34
5
7
8
14
15
1617
19
20
21
24
25
26
31
32
4243
44 45
46
47
4849
5051
52
53
54
58
59
60
61
6265 66
67
68
69
71 72
74
75
76
77
78
79
80
81
82
83
84
8586
87
88
89
9091
92
93
94
95
97
98
102
103
111
ds 5.5 Avg Buchan Fe3/FeT=0.15 H=16
Not
+ L (suprasolidus)
+ H2O (subsolidus)
no H2O (subsolidus)
+L
+L
+L
Suprasolidus phase diagram calculated with fixed (non-excess) H2O (H2O = 8, same as H = 16)
Bt Opx
Notice the different phase equilibria involving Bt going to Opx between phase diagrams calculated for H2O=8 vs. H2O=3
Pattison (unpublished)
600 650 700 750 800 850
Temperature [C]
1000
2000
3000
4000
5000
6000
7000
8000
Pres
sure
[Bar
]
Bulk(1)= H(6)O(?)FE(09.1486)F3(1.6145)SI(091.5798)AL(42.8147)MG(7.0338)MN(0.1416)CA(1.8735)NA(5.7763)K(8.6406)TI(1.3637)
26/04/2021 14:59:06 CPU-Time (hhh:mm:sec): 000:33:21.1
Fe3/(FeTot) = 0.150domino vers ion: 01.08.09 (08.07.14, s rc10e1rdatabase: ds55hp1.txtH2O: HHP98PLC1: s i te mixing+margulesWM02V: s i te mixing+margulesGTT01: s i te mixing+margulesBI05: s i te mixing+margulesCHL: s i te mixing+margulesILMTERN: s i te mixingMT00: s i te mixing+margulesOPX: s i te mixing+margulesEP98: s i te mixing+margulesCRD: s i te mixingST: s i te mixing+margulesCTD: s i te mixing+margulesLIQtc2: external+margules
1
2
3
4
6
7
810
11
12
13
17
18
33
34
36
40
41
42
43
45
46
47
52
53 54
56
57
58
59
60
63
65
66 67
69 70
Position of solidus for three different assumed values of molar H2O (excess, 8 and 3)
Not
Pattison (unpublished)
Yes, if focusing just (mainly) on the P-T conditions of that rock. But you need to be very careful if using the resultant phase diagram to make petrological inferences at higher and especially lower P-T conditions because of the H2O matter! Plus, good to compare thermodynamically-computed H-content of rock, based on the predicted hydrous phases, with the measured H2O/LOI content.
Can I use the measured H2O content of a suprasolidus rock as the value of the fixed H2O content for the phase diagram? (Or, use LOI - loss on ignition - if the rock isn’t too altered?)
All assemblages +Bt+Qtz+Pl+Ilm+Mt, except where indicated by “-Qtz”, “-Bt”, “-Ilm”.H₂O present below wet solidus;H₂O absent above wet solidus.
MsChlGrt Ms GrtSt
MsGrtSil
MsSil
MsGrtLSil
MsGrtKyL
MsGrtKy
MsChl
KfsGrtLSil
MsLSil
MsCrdCrdKfs
CrdKfsL
GrtCrdKfsL
GrtCrdKfsL (-Bt)
KfsGrtLSil (-Bt)
KfsGrtRtLSil (-Ilm)
MsChlGrtRt (-Ilm)
MsGrtRt (-Ilm) MsGrtKyRt
(-Ilm)
MsChlGrtSt
MsGrtStAnd
MsGrtStSil
MsGrtStRt (-Ilm)
Average Buchan metapelite MnNCKFMASHTO; Fe3+/FeTotal = 0.15HP98 ds 5.5; 2005 a-X models
MsGrtStKy
MsChlRt
MsChlRtEp
MsChlEp
CrdKfsOpxL (-Bt)
GrtCrdOpxKfsL (-Bt)
KfsLSil
MsGrtStMsChlGrt
450 500 550 600 650 700
Temperature [°C]
1000
2000
3000
4000
5000
6000
7000
8000
Pres
sure
[Bar
]
750 800
MnNCKFMASHTO Fe3+/Fetotal = 0.15
The final result: a combined subsolidus-suprasolidus phase diagram
Pattison (unpublished)
Pattison & Goldsmith (submitted, J Geol Soc)