Research Journal of Environmental and Earth Sciences 4(1): 41-47, 2012
ISSN: 2041-0492
© Maxwell Scientific Organization, 2012
Submitted: May 09, 2011
Accepted: June 28, 2011
Published: January 01, 2012
Estimation of Temperature, Pressure and Oxygen Fugacity of the Cal-Alkaline
Basin-Type Granitoids in the Winneba Area, Ghana
1
Nyarko Saah Esther, 2D.K. Asiedu, 1Dampare Samuel, 1Osae Shiloh,
2
Sakyi Patrick and 1Hanson John
1
Department of Chemistry, Ghana Atomic Energy Commission,
P.O. Box LG 80, Legon, Ghana
2
Department of Earth Science, University of Ghana, P.O. Box LG 80 Legon, Ghana.
Abstract: In Ghana, the granitoids rocks are in two different groups, thus the basin type granitoid and the belt
type granitoids. These granitoids have been studied petrographycally mineralogically and geochemically,
especially the belt-type granitoids since it is the major host of gold occurrences in Ghana, however there are
little studies on the petrogenesis and emplacement conditions of this important rock. In this paper we present
the lacking knowledge on the emplacement conditions (temperature, pressure and the oxygen fugacity) of the
basin-type granitoids in the winneba area of Ghana.The calc-alkaline basin-type granitoids in the Winneba area
is composed of quartz+ plagioclase +potash feldspar+ alkali feldspar+ Biotite+ Hornblende +amphibole+
titanite. The plagioclase composition ranges from Ab58 An1.7 Or0.45 to Ab98 An41 Or41 and mainly in the field of
albite and oligoclase. The amphiboles however have a compositional range of Mg/(Mg +Fe) ranging from 0.52
to 0.62 and a Si content of 7.1 to 7.4 atom per formula unit (afu). Their end-member compositions in the
classification diagram are controlled by Magnesio-Hornblend, tschermakitic-Hornblend, and tschemakite
substitution types. Scanning Electron Microscope (SEM) analyses of coexisting hornblende and plagioclase
(hornblende-plagioclase thermometry), Al content in hornblende (aluminum-in-hornblende barometry) and the
assemblage titanite-magnetite-quartz were used to constrain the P, T and fO2 during the crystallization of the
parent magmas. The estimated temperature indicated an average temperature of crystallization of 677ºC
reflecting late crystallization from highly oxidized magma (log fO2 -20 bars).The rocks were emplaced at an
average pressure of 2.2 kbars corresponding to approximately 8 km depth of below the crust.
Key words: Amphibole, barometry, crystallization, hornblende, magma, plagioclase, thermometry
INTRODUCTION
these granitoids, mainly, mineralogical since they
intruded the gold hosting rocks (Birimian rock). However
this work seeks to add to the existing knowledge on the
birimian granitoids.
The aluminum in hornblende barometer, hornblendeplagioclase thermometer and estimation of fO2, are
parameters used to calculate pressure, temperature and
oxygen fugacity, respectively. The recent application of
Al (IV) and Al (tot) in hornblende, as both a
geothermometer and geobarometer, respectively, provides
new information on the likely temperatures and pressures
that exited during the emplacement of the granitic magma
within the crust.
Hornblende and plagioclase are commonly coexisting
minerals in calc-alkaline igneous rocks, so they are
usually used for thermometry Based on hornblende solidsolution models and well constrained natural and
experimental systems, two hornblende-plagioclase
geothermometers (thermometer A and B) were calculated
by Holland and Blundy (1994) and Masoudi and Jamshidi (2008).
Winneba is found in the Central Region of Ghana and
is the principal town in the district linked by first class
motor road to Accra in the east and Saltpond in the west.
(Layton, 1958).
The area falls within the Birimian terrene. The terrene
is believed to have been accreted onto the Archean
continental crust around 2.1 Ga (Taylor et al., 1992)
during the Eburnean orogeny. The terrene comprises of
metasedimentary and metavolcanic rocks with the former
forming a sedimentary basin and the later, a volcanic belt.
The volcanic belts are typically 15-40 km wide and
between 60 and 90 km apart. The sedimentary basin show
extensive isoclinals folding. (Leube et al., 1990; Leube
and Hirdes, 1986). The birimian sedimentary basin is
characterized by extensive intrusive activities consisting
of granites and pegmaties, contacts between granitiods
and metasediments are irregular, with rafts and relict
structures of metasediments persisting into the granitoids.
Several geochemical studies have been carried out on
Corresponding Author: Nyarko Saah Esther, Department of Chemistry, Ghana Atomic Energy Commission, P.O. Box LG 80,
Legon, Ghana, Tel.: +233 244167190
41
Res. J. Environ. Earth Sci., 4(1): 41-47, 2012
Fig. 1: Geological map of study area after Layton (1958)
( aplites and pegmatites, quartz reefs, series of granites
veins quartz , migmatites and the Western gneiss),then,
the Post Birimian (Basic intrusive- Dykes now
amphibolites, Epidiorites dykes Takwanian), underlain by
the Birimian supergroup (Metamorphosed porphyritic and
vesicular lavas, quartz Biotite and hornblende schist;
hornblend schist, coarse amphibolites, actinolites schites,
quartz schist. Gondites, manganiferous phyllite, epidosites
and granulites, Mica schist finely laminated. (Ahmed
et al., 1977; Layton, 1958). The granites in the area forms
part of the acid intrusion in the Birimian. The junction
between the granites and the surrounding rocks is a sharp
one, though a slight veining of the coarse amphibolites
with which it is in contact on the western part of the area
exist. The granites as describe by Layton (1958) are
porphyroblastic microcline-biotite adamellite. The
Western and northern margins of the granite are relatively
fine grained and non-porphyroblastic, while the margin at
the east show similar characteristics but microcline
granite may occur. (Layton, 1958).
Apart from linearly arranged Biotite-rich ghosts,
there are larger inclusions of hornblende schists pften
contorted, finely schistose and cut by irregular feldspar
veining. Typically, the porphyroblastic granite of the
Winneba area is grey in colour and medium to coarse
grained in hand specimen. They contain minerals such as
Biotite, microcline, amphibole, feldspar (plagioclase is
more abundant than other feldspars). Apatite, sphene, and
rare magnetite are also occasionally seen as accessory
minerals. (Ahmed et al., 1977; Layton, 1958).
Thermometer A is based on the edenite-tremolite
reaction (edenite+4 quartz ÷ tremolite + albite), which is
applicable to quartz-bearing igneous rocks: and
thermometer B is based on the edenite-richterite reaction
(edenite + albite ÷ richterite + anorthite), which is
applicable not only to quartz-bearing but also quartz-free
igneous rocks. According to Anderson (1996).
thermometer B (edenite-richterite) is preferable based on
comparison to other igneous thermometers. In this study
we analyze for the major element composition of feldspar,
plagioclase, biotite and amphilbole minerals in the
granitoids, and using thermometer B, estimated for the
temperature and pressure of the granitoids during
emplacement and further calculated for the oxygen
fugacity. Equilibration temperatures for hornblende plagioclase assemblages were calculated based on
iteration using Anderson and Smith (1995) pressure at
various thermometrs.
The study area: The geological formation of the area
falls under the precambian birimian terrain in Ghana. The
geology of the area is as shown in Fig. 1. The rocks of the
area may be classified as follows from older to younger in
ascending succession.
Tertiary to Recent (Lagoonal deposite, alluvium,
gravels , salt beds, beach and raised beach sands,
laterites, Boulder beds, beded and laminated sands, clay
of uncertain age), the Togo Series (Quartzites, purple +
white facies, breccias, sericite phyllite near base) which
is in unconformity with Tarkwaian and the Acids intrusive
42
Res. J. Environ. Earth Sci., 4(1): 41-47, 2012
Or
1.0
Siderophyllite
Annite
Peraluminous
0.8
Fe2 /mg+Fe2
+
0.6
Biotite
Lepidomelane
+
Meroxene
0.4
Calc-alkaline
0.2
Abl
Phlogopite
And
Olig
Phlogopite 1.2
Lab
1.4
1.6
1.8 Eastonite
Altot (a.p.f.u)
Ab
An
Fig. 5: Biotite chemistry plotted in the Al vs. Fe2+/ (Fe2+ + Mg)
diagram of TrÅger.,(1982)
Fig. 2: Plagioclase chemistry in the Or- Ab- An diagram of
Deer et al. (1966)
MgO
Or
Sanidine
C
P
A
Anorthoclase
Oligoclase
FeOtot
Andesine
Labradorite Bytownite Anorthite
Ab
Fig. 6: Biotite composition diagram showing the classification
of magmas after Abdel-Rahman (1994)
An
Fig. 3: Alkali- feldspar chemistry in the Or- Ab- An diagram of
Deer et al. (1966)
Actionlite
Act Hbl
Magnesio- Hbl
Mg/(Mg+Fe)
Ghana. Sampling was carried out in September- October
2008. These samples were obtained from the outcropped
granitiods along the beach and near the John Boscoss
School in the Winneba Township.
Sampling was problematic though, since there were
few fresh unweathered outcrops of granitiods due to the
extended settlement to the areas where there were
outcrops. However there were relatively fresh once to
sample. The weathered surface were broken off to reveal
fresh surface before sampling, in addition extra care was
taken in order not to sample pegmatites which were in
abundant and so similar to the granitiods due to their
unusual smaller grain size.
Tremolite Tr Hb
Tsch Hbl
1.0
Tschermakite
0.0
8.0
7.5
7.0
6.5
6.0
A12O3
5.5
TSI
Analytical method:
Scanning electron microscope: Prior to analysis by
Scanning Electron Microscope (SEM), the thin section
were washed with deionized water in an ultrasonic bath
and coated with carbon film to eliminate electrostatic
charge-up on the sample surface.
Mineral analyses were performed at the Institute for
the Earth’s Interior, Okayama University, Misasa, Japan.
Fig. 4: Diagram showing the classification of amphibole
according to the nomenclature of Leake et al. (1997)
MATERIALS AND METHODS
Sampling: This study was conducted in the Winneba
Township about 52 km from Accra the capital town of
43
Res. J. Environ. Earth Sci., 4(1): 41-47, 2012
Table 1: Representative SEM plagioclase mineral analyses from the studied basin type granitoids
Oxide
W-01
W-02
W-03
W-05
W-06
W-07
SiO2
60.89
57.73
61.28
68.06
66.09
65.42
23.97
23.45
23.92
19.38
19.77
20.29
Al2O3
CaO
4.99
9.84
5.01
0.58
0.41
1.1
9.41
7.76
9.30
11.01
12.92
12.13
Na2O
0.21
0.13
0.17
0.15
0.09
0.17
K2O
Total
99.47
98.91
99.68
99.18
99.28
99.11
Number of Ions calculated on 8 oxygen basis
Si
2.725
2.584
2.742
3.046
2.958
2.928
Al
1.264
1.237
1.262
1.022
1.043
1.070
Ca
0.239
0.472
0.240
0.028
0.020
0.053
Na
0.817
0.673
0.807
0.955
1.121
1.053
K
0.012
0.007
0.010
0.009
0.005
0.010
Molecular Ratio
Ab
76.47
58.42
76.35
96.33
97.84
94.49
An
22.41
40.94
22.73
2.804
1.716
4.731
Or
1.123
0.644
0.918
0.864
0.448
0.871
Table 2: Representative SEM amphibole mineral analyses from the studied basin type granitoids
Wt %
W-01
W-02
W-03
W-04
W-06
W-07
48.65
48.86
49.27
49.9
49.97
48.91
SiO2
0.91
1.42
1.24
0.65
0.61
1.26
TiO2
7.3
7.17
7.13
6.69
6.59
7.28
Al2O3
FeO
16.29
14.65
15.25
15.48
14.77
15.23
MnO
0.35
0.32
0.19
0.33
0.26
0.29
MgO
12.31
12.91
12.63
12.66
13.4
12.51
CaO
11.06
10.88
11.03
11.15
11.06
10.99
1.98
2.34
2.11
1.97
2.22
2.16
Na2O
0.92
0.92
0.99
0.82
0.89
0.95
K2O
Number of Ions calculated on 23 oxygen basis
Si
7.073
7.103
7.163
7.255
7.265
7.111
Ti
0.099
0.155
0.136
0.071
0.067
0.138
Al
1.251
1.229
1.222
1.146
1.129
1.247
Fe
1.981
1.781
1.854
1.882
1.796
1.852
Mn
0.043
0.039
0.023
0.041
0.032
0.036
Mg
2.668
2.798
2.737
2.744
2.904
2.711
Ca
1.723
1.695
1.718
1.737
1.723
1.712
Na
0.558
0.660
0.595
0.555
0.626
0.609
K
0.171
0.171
0.184
0.152
0.165
0.176
2
0.611
0.596
0.593
0.618
0.594
Mg/(Mg+Fe )0.574
Table 3: Representative SEM biotite mineral analyses from the studied basin type granitoids
Wt %
W-1
W-2
W-3
W-4
W-5
W-6
38.6
39.3
38.4
41.9
40.6
36.2
SiO2
TiO2
1.27
2.30
2.21
2.44
2.16
1.88
17.7
16.4
16.8
17.1
16.5
17.7
Al2O3
Cr2O3
0.00
0.01
0.00
0.03
0.00
0.00
FeO
25.7
22.3
24.4
19.9
22.3
27.2
MnO
0.15
0.24
0.14
0.25
0.19
0.27
MgO
9.89
8.38
7.69
7.61
7.84
8.63
CaO
0.36
0.33
0.29
0.68
0.35
0.96
0.18
0.29
0.26
1.20
0.56
0.31
Na2O
K2O
6.02
9.87
9.54
8.80
9.19
6.08
0.00
0.32
0.16
0.00
0.04
0.36
P2O5
Total
99.9
99.8
99.8
99.9
99.8
99.6
Number of Ions on the basis of 11 oxygens
Si
2.81
2.86
2.79
3.05
2.95
2.64
Ti
0.07
0.13
0.12
0.13
0.12
0.10
Al
1.52
1.41
1.44
1.47
1.42
1.52
Cr
0.00
0.00
0.00
0.00
0.00
0.00
Fe
1.57
1.36
1.49
1.21
1.36
1.66
Mn
0.01
0.02
0.01
0.02
0.01
0.02
Mg
1.07
0.91
0.83
0.83
0.85
0.94
Ca
0.03
0.03
0.02
0.05
0.03
0.08
0.03
0.04
0.04
0.17
0.08
0.04
Na2
0.56
0.92
0.89
0.82
0.85
0.57
K2
P
0.00
0.02
0.01
0.00
0.00
0.02
Total
7.66
7.68
7.64
7.74
7.67
7.57
Fe/Mg+Fe 0.59
0.60
0.64
0.60
0.62
0.64
ASI
2.48
1.43
1.52
1.41
1.48
2.22
44
W-08
64.06
20.79
1.11
12.4
0.4
98.76
W-09
63.42
22.25
1.07
11.7
0.97
99.41
W-10
58.91
25.39
5.82
8.8
0.29
99.21
2.867
1.097
0.053
1.076
0.023
2.838
1.174
0.051
1.015
0.055
2.636
1.339
0.279
0.764
0.017
3.490
4.620
1.982
0.490
4.573
4.936
72.09
26.35
1.563
W-08
49.45
0.85
6.83
15.41
0.27
12.89
10.92
2.06
0.94
W-09
46.5
1.47
6.59
17.9
0.61
11.19
12.17
2.24
1.24
WG-10
50.59
0.36
6.41
14.78
0.28
13.51
10.91
2.15
0.78
7.189
0.093
1.17
1.874
0.033
2.794
1.701
0.581
0.174
0.599
6.76
0.161
1.129
2.176
0.075
2.425
1.896
0.631
0.23
0.527
7.355
0.039
1.098
1.797
0.034
2.928
1.699
0.606
0.145
0.620
W-7
39.3
4.01
16.3
0.00
21.7
0.31
7.57
2.01
0.11
8.47
0.15
99.9
W-8
39.2
1.78
17.2
0.01
23.0
0.21
8.37
0.27
0.26
9.39
0.24
99.9
W-9
39.9
1.96
17.0
0.00
21.2
0.21
8.96
0.27
0.23
9.85
0.16
99.8
W-10
39.5
2.10
17.2
0.00
21.7
0.16
8.83
0.19
0.24
9.50
0.31
99.7
2.86
0.22
1.40
0.00
1.32
0.02
0.82
0.16
0.02
0.79
0.01
7.61
0.62
1.46
2.85
0.10
1.48
0.00
1.40
0.01
0.91
0.02
0.04
0.87
0.02
7.69
0.61
1.59
2.91
0.11
1.46
0.00
1.29
0.01
0.97
0.02
0.03
0.92
0.01
7.73
0.57
1.51
2.87
0.12
1.48
0.00
1.32
0.01
0.96
0.02
0.03
0.88
0.02
7.70
0.58
1.59
Res. J. Environ. Earth Sci., 4(1): 41-47, 2012
Table. 4: Result of geothermobarometry and oxygen fugacity for the basin type granitoids studied compared to other geothermobarometry
Sample ID Plag Ab
Amph Al(T) T-HB(ed-tr) (ºC) T-HB(ed-ri) (ºC) T-BH (ºC)
Pschmidt (kb)
P-A&S (Kbar) LogfO2
WG-01
0.76
1.241
668.7
684.4
667.8
2.90
2.82
-17.33
WG-02
0.58
1.217
706.9
776.5
709.1
2.78
1.37
-14.49
WG-03
0.76
1.207
649.4
675.0
657.3
2.74
2.74
-17.65
WG-04
0.96
1.133
606.2
494.4
608.6
2.38
1.63
-25.32
WG-06
0.98
1.112
617.0
482.8
611.3
2.28
1.32
-25.94
WG-07
0.94
1.237
628.5
549.2
629.9
2.88
2.86
-22.64
WG-08
0.93
1.157
627.8
545.9
624.7
2.50
2.39
-22.79
WG-09A
0.90
1.149
763.6
613.3
675.3
2.46
2.66
-19.92
WG-09B
0.72
1.078
637.8
676.9
643.0
2.12
2.11
-17.58
Back-Scattered Electron (BSE) images and major element
compositions of all mounted grains were obtained using
a HITACHI S-3100H Scanning Electron Microscope
coupled with an EMAX-7000 Energy Dispersive X-ray
Spectrometer, which operated at an accelerating voltage
of 20 kV and 0.3 nA beam current. Correction for the
major element compositions was done by the standardless ZAF correction method of the EMAX-7000 program
(HORIBA Ltd., Ver. 1.32). Analytical points on the
mounted grains were pre-recorded using a Visual Stage
system that was developed to support the probe analyses
using the SEM-EDX and SIMS with extremely high
spatial resolution.
Chemical compositions and structural formulae of
feldspars, amphibole, biotite, are listed in Table 1-3.
The structural formula for the mineral chemistry was
calculated on the basis of 8, 11, 23, and 4 oxygen for
feldspar (K-feldspar and plagioclase), Biotite, amphibole,
respectively.
to 0.62 and a Si content of 7.1 to 7.4 atom per formula
unit (afu).
Their end-member compositions in the classification
diagram (Fig. 4) are controlled by Magnesio-Hornblen,
tschermakitic-Hornblend, and tschemakite substitution
types.
Biotite: Biotite has relatively high Al and moderate Fe
contents (Djouka-Fonkwe et al., 2008) and Microprobe
analyses of the biotite from the basin type granitoids
Table 3. indicate compositions of meroxenes and
lepidomelanes (Fig. 5), following the classification of
Troger (1982) with an intermediate Al content. The most
important feature of biotites is that they are Mg-rich
(Helmy et al., 2004). The range of molar Fe2/ (Fe2+Mg) of
the biotite composition is high (57-64) and the alumina
saturation index (ASI = Al/Ca+Na+K,) is moderate
(1. 4- 2.5) and reflects some extend of alumina activity in
the crystallizing magma (Zen, 1988).
The progressive increase of the total Al contents and
the Fe2+/ (Fe2+ + Mg) ratios in biotite (Fig. 5) are
consistent with a compositional trend of Biotite in
continental-collision related granites (Lalonde and
Bernard, 1993). It indicates contribution of crustal
material (metasediments) during the petrogenesis of the
basin type granitoids magmas, either by assimilation or
anatexis (Shabbani and Lalon-de, 2003 and references
therein). The biotite compositions systematically range
from the calc-alkaline to the peraluminous granitic of the
discriminative trend defined by Abdel-Rahman (1994)
among the different granitoid suites (Fig. 6).
RESULTS AND DISCUSSION
Mineral chemistry:
feldspars: Representative analyses of plagioclase and
their calculated formulae are given in Table 1. The
plagioclase composition ranges from Ab58 An1.7 Or0.45 to
Ab98 An41 Or41. In the Deer et al. (1966) classification
diagram for plagioclase and alkali feldspar (Fig. 2 and 3)
the rocks plotted mainly in the albite and oligoclase field
with only one in the Andesine filed and also mainly along
the albite- oligoclase boundary with only one along the
Andesine- orthoclase boundary respectively.
The range of the plagioclase composition is necessary
for the Al content in hornblende to be solely a function of
pressure (Hollister et al., 1987).
Temperature and pressure: Hornblende and plagioclase
are both used to estimate temperature and pressure of
granitic rocks respectively. The Al content provides
information on the likely temperatures and pressures that
exited during the emplacement of the granitic magma
within the crust and apparently the depth of emplacement
of plutonic rocks.
There are several empirical Al-in-hornblende
barometers that have been used to determine solidus
pressures in calc-alkaline plutons (Hammarstrom and Zen,
1986; Hollister et al., 1987; Johnson and Rutherford,
1989). The most recent barometer (Anderson, and Smith.
Amphibole: Amphibole compositions of the granitoids
were determined and representative analyses together
with their chemical formulae are given in Table 2.
Amphiboles in the granitoids are of igneous origin, as
their Si values do not exceed the 7.50 a.p.f.u. (atoms per
formula unit) of the limit for igneous amphiboles (Leake,
1971; Leake et al., 1997). Amphiboles have a
compositional range of Mg/ (Mg+Fe) ranging from 0.52
45
Res. J. Environ. Earth Sci., 4(1): 41-47, 2012
hornblende (Fig. 4) and Fe2+ biotite in the rocks suggest
relatively oxidized magma.
According to Wones (1989), the assemblages of
titanite + magnetite + quartz in granitic rocks permit an
estimation of relative oxygen fugacity. The LogfO2
estimated bases on Wones (1989) equilibrium expression
of LogfO2= -30930/T+14.98+0.142 (P-1)/T (where, T is
temperature in Kelvin and P is pressure in bars) gave
logfO2 in the limit between -17.6 to -25.9 which shows
that the calc-alkaline, peraluminous, and K-rich magma
crystallized in low oxygen fugacity (fO2) .
1995) was chosen in this study because of the smaller
margin of error and the correction of effect of temperature
and pressure in the equation:
P (±0.6) kbar = 4.76 Al -3.01-{[T(/C)-675]/85}*
{0.530Al+0.005294[T(/C)-675]}
where, P is in kbar, T in ºC and Al is the total Al content
of hornblende in atoms per formula unit.
For estimation of temperature in rocks, Blundy and
Holland (1990) first proposed a very simple, empirical
thermometer on the basis of the edenite-tremolite
reaction; which could be applied only to quartz-bearing,
intermediate to felsic igneous rocks with plagioclase
An<0.92 and Si in hornblende<7. 8 atoms pfu.
In this study, Holland and Blundy (1994)
thermometer for the calculation of temperature is used and
compared with other thermometers. Table 4 shows the
types of thermometers and barometers applied for the
estimation of the temperature and pressure. From the
analyzed rocks, the calc-alkaline basin type granitoids,
crystallized at a temperature range of 776-482ºC
indicating a late crystallization.
The emplacement pressure was estimated at 1.3±0.62.9±0.6 kbars. The pressure was converted to depths by
using an average crustal density of 2.65 g/cm3 and
average pressure of 2.2±0.6 kbars. The average depth of
emplacement of granitoids is approximately 8 km.
C
C
C
C
C
CONCLUSION
The application of Al in hornblend barometry of
Anderson and Smith (1995) indicated a minimum
pressure of ~2.12±0.6 kbars and a maximum of 2.9±0.6
kbars for the basin-type intrusion.
The average pressure of the magma corresponded to
approximately 8km depth of emplacement using an
average crustal density of Temperature estimates based on
the hornblendeplagioclase geothermometer of Blundy and
Holland (1990) is 482-776ºC which probably reflect latestage crystallization from a highly oxidized magmas (log
fO2 25.9 to 17.6).
ACKNOWLEDGMENT
We also acknowledge the logistics, field assistance
and laboratory assistance of Mr. Samuel Ganyaglo and
Mr. Opata and the entire staff of the Department of
Nuclear Engineering and mathematical science of the
institute of Ghana Nuclear Research center.
T-HB(ed-tr) refers to Holland and Blundy Hbld-Plag
thermometry calibration reaction
edenite + 4 quartz = tremolite + albite
T-HB(ed-ri) refers to Holland and Blundy Hbld-Plag
thermometry calibration reaction
edenite + albite = richterite + anorthite
T-BH refers to Blundy and Holland Hbld-Plag
thermometry calibration reaction
edenite + 4 quartz = tremolite + albite
P-Sch refers to Schmidt (1992) Al-in Hornblende
barometer
P-A and S refers to Anderson and Smith (1995) Al-in
Hornblende barometer
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