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Online resource 1
for:
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The ~AD 1250 effusive eruption of El Metate shield volcano
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(Michoacán, Mexico): Magma source, crustal storage, eruptive
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dynamics, and lava rheology
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Magdalena Oryaëlle Chevrel*, Marie-Noëlle Guilbaud and Claus Siebe
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Departamento de Vulcanología, Instituto de Geofísica, Universidad Nacional Autónoma de
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México, Coyoacán, México D.F., México
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*e-mail:[email protected]
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METHODS FOR THERMO-BAROMETRY AND
HYGROMETRY CALCULATIONS
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1. Olivine-liquid thermometer:
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In order to constrain the temperature of olivine crystallisation we chose the olivineliquid thermometer based on the Fe–Mg exchange between olivine and the liquid from which
olivine crystallized. We used the equation 22 from Putirka (2008), which is a modification of
the Beattie (1993) thermometer, in order to correct the systematic temperature overestimation:
𝑇 = {15294.6 + 1318.8𝑃(𝐺𝑃𝑎) + 2.4834[𝑃(𝐺𝑃𝑎)]2 }
𝑜𝑙⁄𝑙𝑖𝑞
𝑙𝑖𝑞
𝐿 )]
÷ {8.048 + 2.8352 ln 𝐷𝑀𝑔
+ 2.097 ln[1.5(𝐶𝑀𝑁
+ 2.575 ln[3(𝑋𝑆𝑖𝑂
)]
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− 1.41𝑁𝐹 + 0.222𝐻2 𝑂𝑙𝑖𝑞 + 0.5𝑃(𝐺𝑃𝑎)}
Where:
⁄
𝑜𝑙 𝑙𝑖𝑞
𝑙𝑖𝑞
𝑂𝑙
𝐷𝑀𝑔
= 𝑋𝑀𝑔
⁄𝑋𝑀𝑔
𝑙𝑖𝑞
𝑙𝑖𝑞
𝑙𝑖𝑞
𝑙𝑖𝑞
𝑙𝑖𝑞
𝑙𝑖𝑞
𝐿
𝐶𝑀𝑁
= 𝑋𝐹𝑒𝑂
+ 𝑋𝑀𝑛𝑂
+ 𝑋𝑀𝑔𝑂
+ 𝑋𝐶𝑎𝑂
+ 𝑋𝐶𝑜𝑂
+ 𝑋𝑁𝑖𝑂
𝐿
𝐿
𝑁𝐹 = 7⁄2 ln(1 − 𝑋𝐴𝑙𝑂
) + 7 ln(1 − 𝑋𝑇𝑖𝑂
)
1.5
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When using the olivine-liquid thermometer we took the pressure values suggested by
Hasenaka and Carmichael (1987) and Hasenaka et al. (1994) who showeded that most shield
lavas from the MGVF plot between the 8-kbar dry liquidus boundary defined by Baker and
Eggler (1987) and the 1-bar plagioclase-saturated liquidus boundaries of Grove et al. (1982)
on the olivine-augite-quartz diagram. Based on this we took 8 kbar as a maximum pressure
limit for olivine crystallization.
Considering that olivine is the first mineral to crystallize, we assumed that the
composition of the olivine core is in equilibrium with a liquid having the composition of the
bulk rock. Equilibrium was tested considering the constant Fe-Mg exchange coefficient
between olivine and the liquid: KD(Fe-Mg)ol-liq = 0.3 ±0.03 that is independent of T and
composition. We used a graphical method by plotting the olivine Mg# versus liquid Mg# on
the Rhodes’ diagram (Dungan et al. 1978; Rhodes et al. 1979a; Fig A1). The olivine-liquid
pairs falling outside of this interval were disregarded. We noted that the migration of the
points toward an iron-rich olivine composition indicates differentiation processes of the melt
as olivine crystallizes. Olivine rims are found in equilibrium with a recalculated melt
composition (equals to the bulk rock composition minus the composition of olivine core
according to their proportion is the samples). We then took a lower pressure (5 kbar) to
estimate the lower temperature of olivine crystallisation.
The error associated with this thermometer is estimated to be ± 43 ºC.
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Fig. A1: Rhodes’ diagram: test for olivine–liquid equilibrium. Continuous line represents the constant KD(FeMg)ol-liq = 0.3 and the dashed lines represent the interval: ± 0.03.
 14285/14286 (F1):
Ten olivine core analyses (Fo83) in equilibrium with the bulk rock composition (KD = 0.290
±0.017) yield 1176 ºC (3ºC of stdev) at 8 kbar.
Five olivine rims (Fo75) are found to be in equilibrium with a residual liquid after 6 % of
olivine and 0.5 % of Fe-Ti oxide crystallization at KD = 0.288±0.008 yield T= 1065ºC at 5
kbar.
 1205 (F4b)
Ten olivine core analyses (Fo82) are found in equilibrium with the bulk rock composition (KD
= 0.283 ±0.023) and yield 1135 ºC (3ºC of stdev) at 8 kbar.
Eight olivine rim analyses (Fo78) in equilibrium with a residual liquid after 2 % of olivine
crystallization (KD = 0.292±0.020) yield T= 1084ºC at 5 kbar.
2. Two pyroxenes thermo-barometer:
Since Opx and Cpx are both present in all rocks, we used the two-pyroxene thermobarometer proposed by Brey and Köhler (1990) and recalibrated by Putirka (2008) that is
based on the partitioning of enstatite + ferrosilite (= Fm2Si2O6 = EnFs; FmO = FeO + MgO +
MnO) between clinopyroxene and orthopyroxene. We used Eq. 37 from Putirka (2008) that is
restricted to Cpx with Mg#>0.75 to estimate the temperature:
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𝑋 𝑐𝑝𝑥
𝑐𝑝𝑥
𝑜𝑝𝑥
𝑐𝑝𝑥 )
= 13.4 − 3.4 ln ( 𝐸𝑛𝐹𝑠
+ 23.85(𝑋𝑀𝑛
)
𝑜𝑝𝑥 ) + 5.59 ln(𝑋𝑀𝑔 ) − 8.8(𝑀𝑔#
𝑇(°𝐶)
𝑋𝐸𝑛𝐹𝑠
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𝑜𝑝𝑥
𝑐𝑝𝑥
+ 6.48(𝑋𝐹𝑚𝐴𝑙
) − 2.38(𝑋𝐷𝑖
) − 0.044𝑃(𝑘𝑏𝑎𝑟)
2 𝑆𝑖𝑂6
The output of this equation is then used as input into Eq. 39 to calculate the pressure:
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑃(𝑘𝑏𝑎𝑟) = −94.25 + 0.045𝑇(°𝐶) + 187.7(𝑋𝐴𝑙(𝑉𝐼)
) + 246.8(𝑋𝐹𝑚𝐴𝑙
) − 212.5(𝑋𝐸𝑛
)
2 𝑆𝑖𝑂6
1.66
𝑜𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
+ 127.5(𝑎𝐸𝑛
)−
− 69.4(𝑋𝐸𝑛𝐹𝑠
) − 133.9(𝑎𝐷𝑖
)
𝐾𝑓
where:
𝑜𝑝𝑥
𝑎𝐸𝑛
=
𝑜𝑝𝑥
0.5𝑋𝑀𝑔
𝑜𝑝𝑥
0.5𝑋𝑀𝑔
( 𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥 ) (
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥
𝑜𝑝𝑥 )
𝑋𝐶𝑎 + 0.5𝑋𝑀𝑔
+ 0.5𝑋𝐹𝑒
0.5𝑋𝐹𝑒
+ 𝑋𝐶𝑟
+ 0.5𝑋𝑀𝑔
2+ + 𝑋𝑀𝑛 + 𝑋𝑁𝑎
2+ + 𝑋𝐹𝑒 3+ + 𝑋𝐴𝑙(𝑉𝐼) + 𝑋𝑇𝑖
and
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑐𝑝𝑥
𝑎𝐷𝑖
= (𝑋𝐶𝑎
)⁄(𝑋𝐶𝑎
+ 0.5𝑋𝑀𝑔
+ 0.5𝑋𝐹𝑒 2+ + 𝑋𝑀𝑛
+ 𝑋𝑁𝑎
)
We performed several iterations by solving simultaneously the two equations, which is
accomplished by using the output of one equation as an input for the other, to find the best
solutions for both equations.
As with the other systems, we tested for equilibrium using the Mg-Fe exchange
partition coefficient: KD (Fe-Mg)cpx-opx =(XFecpx / XMgcpx)/( XFeopx / XMgopx) =1.090 ± 0.14. We
excluded the clinopyroxene–orthopyroxene pairs that lie beyond the area delimited by the
dashed lines (Fig. A3). The precision is estimated to be ± 38 ºC and ±2.8 kbar.
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Fig. A3: Test for equilibrium of cpx-opx pairs.
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14285 (F1): In this sample we did not find pyroxene phenocrysts. Five pairs of opx-cpx
microlites where encountered in equilibrium and yielded 1074ºC and 3.5 kbar.
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Six pairs of opx-cpx microlites forming olivine reaction rims indicate 1100ºC and a pressure
near surface (negative value of P).
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1205 (F4b): Nine cpx-opx pairs (both phenocrysts and microphenocrysts) were found to be in
equilibrium and indicate 987 ºC and 4.2 kbar.
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14282 (F4): Sixteen cpx-opx pairs (both phenocrysts and microphenocrysts) were found to be
in equilibrium and indicate an average T=989 ºC and P=4.1 kbar.
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14268 (F5): Sixteen cpx-opx pairs (both phenocrysts and microphenocrysts) were found to be
in equilibrium and indicate an average T=971 ºC and P= 2.1 kbar.
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14298 (F6): Six cpx-opx microphenocryst pairs indicate 946 °C and 0.63 kbar.
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14309 (F7): Only one microlite cpx-opx pair was found in equilibrium and resulted in 894 °C
and 0 kbar.
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1210 (F11): The average value of 7 combinations of microlite cpx-opx pairs found at the rim
of the hornblende crystal indicates T=979 ºC and P= 0.9 kbar.
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14308 (F12): Only one pair of pyroxene phenocrysts was in equilibrium and yielded T=938
ºC and P= 0 kbar. Four pairs of microlites forming the hornblende reaction rim indicate
T=966 ºC and P= 1.16 kbar.
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3. Amphibole thermo-barometer and hygrometer:
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We used the thermo-barometer of Ridolfi et al. (2010). This model was chosen
because it is applicable to amphibole-bearing calc-alkaline products of subduction-related
settings. It is based on empirical formulations which work independently with different
compositional components (i.e. Si*, AlT, Mg*, [6]Al*) of a single amphibole crystal.
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The thermometer is related to the silica index (Si*) defined as:
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𝑇 = −151.487𝑆𝑖 ∗ + 2041
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where
[4]
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[6]
[6]
𝐴𝑙
𝐴𝑙
𝑇𝑖 𝐹𝑒 3+ 𝐹𝑒 2+ 𝑀𝑔 𝐵𝐶𝑎 𝐵𝑁𝑎 𝐴𝑁𝑎
[4]
𝑆𝑖 = 𝑆𝑖 +
− 2 𝑇𝑖 −
−
+
+
+
+
+
−
15
2
1.8
9
3.3
26
5
1.3
15
𝐴
[ ]
+
2.3
∗
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The accuracy of the thermometer is estimated to be of ±22°C.
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The water content of the melt in equilibrium with the amphibole when it crystallizes can be
retrieved using the octahedral aluminum index [6]Al* via:
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𝐻2 𝑂𝑚𝑒𝑙𝑡 = 5.215 𝐴𝑙 ∗ + 12.28
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[6]
where
[4]
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[6]
∗
𝐴𝑙 =
[6]
[6]
𝐴𝑙 𝑆𝑖 + 𝑇𝑖 𝐶𝐹𝑒 2+ 𝑀𝑔 𝐵𝐶𝑎 + 𝐴[ ] 𝐴𝑁𝑎
𝐹𝑒#
𝐴𝑙 +
−
−
−
+
+
− 1.56𝐾 −
13.9
5
3
1.7
1.2
2.7
1.6
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Uncertainty of H2O wt. % is between 0.8 and 1 wt. %.
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Finally, the confining pressure can be calculated from the following barometric equation:
𝑃 = 19.209𝑒 (1.438𝐴𝑙𝑇 )
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Maximum error of the pressure is estimated to be 0.4 kbar.
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14268 (F5): Six hornblendes were analyzed for a total of 23 points, no obvious correlation
was found between the core and the rim of the grains. The PT conditions range from 983 °C,
and 4.7 kbars to 933 °C and 2.7 kbar for a water content between 5.1 and 6.4 wt. % H2O.
Average values are: T=946 ºC (stdev 11ºC); P=3.1 kbar (stdev 0.4 kabr) and 5.5 wt. % H2O
(0.3 stdev).
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14298 (F6): Five hornblendes were analyzed for a total of 12 points. No obvious variation in
P-T was found between the core and the rim of the grains. The P-T conditions range from 980
°C and 4.1 kbar to 950 °C and 2.6 kbar for a water content between 4.9 and 6.4 wt. % H2O.
Average values are: T=972 ºC (stdev 11ºC); P=3.2 kbar (stdev 0.4 kabr) and 5.5 wt. % H2O
(0.5 stdev).
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14309 (F7): Five hornblendes were analyzed for a total of 14 points. No obvious variation in
P-T was found between the core and the rim of the grains. The P-T conditions range from 981
°C and 3.6 kbar to 946 °C and 2.6 kbar for a water content between 5.1 and 6.1 wt. % H2O.
Average values are: T=967 ºC (stdev 11ºC); P=3.2 kbar (stdev 0.3 kabr) and 5.6 wt. % H2O
(0.3 stdev).
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1210 (F11): Six hornblendes were analyzed for a total of 17 points. The PT conditions range
from 940 °C and 4 kbar to 910 °C and 2.4 kbar for a water content between 5.3 and 7.3 wt. %
H2O. Analyses of the rims seem to indicate lower P and T conditions. Average values are:
T=921 ºC (stdev 9ºC); P=2.7 kbar (stdev 0.4 kbar) and 5.7 wt. % H2O (0.5 stdev).
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14308 (F12): Three hornblendes were analyzed for a total of 23 points including one transect
through an amphibole grain. The PT conditions range from 985 °C and 3.2 kbar to 930 °C and
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2.4 kbar for a water content between 5 and 7 wt. % H2O. Average values are: T=953 ºC (stdev
10ºC); P=3.1 kbar (stdev 0.3 kbar) and 6.1 wt. % H2O (0.5 stdev).
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Small variations are observed through the grain and a slight pressure drop at the rim:
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Fig. A4: Estimated PT conditions through an amphibole grain from samples 14308 (F12).
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The average and standard deviation of all the analyzed grains point toward 949 ± 20°C, 3 ±
0.4 kbar, and 6 ± 0.5 %H2Omelt.
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4. Plagioclase-liquid hygrometer:
We used the recent calibration from Waters and Lange (2015) that is based on the
crystal-liquid exchange reaction between the anorthite (CaAl2Si2O8) and albite (NaAlSi3O8)
components and uses thermodynamic data. Calculatations were performed using the
spreadsheet given in the data repository of “American Mineralogist”. The standard error
estimate on the hygrometer model is 0.35 wt% H2O.
In the case of the samples containing olivine (14285 and 1205) we bracket the
minimum water content by that plagioclase crystalized shortly after olivine and therefore use
a reclaculated liquid composition equals to the bulk rock composition to which we have
subsatrcted the olvine composition according to their percentage.
We first assume the PT conditions previously obtained for olivine core crystallisation
(1176 ºC for 14285 and 1144 ºC for 1205, both at 8 kbar).
Then for olivine rim crystallisation at (1065 ºC for 14285 and 1081 ºC for 1205, both
at 5 kbar).
For the sample 14282 from F4, that lacks olivine, we used the PT conditions from the
two-pyroxene theremo-barometer (989 ºC and 4.1 kbar).
In the case of hornblende-bearing lavas (F5, F6, F7, F11, and F12), we assume that
plagioclase phenocrysts crystallised first and hence are in equilibrium with a liquid having the
bulk rock composition. We used here the average PT conditions obtained previously using
the amphibole thermo-barometer.
Note that the obtained water content represents therefore a minimum value.
Also, note that the changes in pressure affect the water content by less than the errors
associated with the method.
 14285 (F1):
Four core plagioclase crystals were analyzed (An73), and results indicate water contents
ranging between 1.9 +/- 0.08 wt. % H2O at 1176 ºC and 8 kbar and 3.5 +/- 0.08 wt. % H2O at
1065 ºC and 5 kbar.
 1205 (F4b):
Five plagioclase cores were analysed (An71) and results indicate water contents between 1.9
+/- 0.02 wt. % H2O at 1135 ºC and 8 kbar and 2.6 +/- 0.02 wt. % H2O at 1081 ºC and 5 kbar.
 14282 (F4):
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One plagioclase phenocryst and 6 microlites were analysed (An60), and results indicate water
contents of 3.6 +/- 0.07 wt. % H2O, at 989 ºC and 4.1 kbar.
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Six plagioclase cores were analyzed (An64) and results indicate water contents of 5.1 +/-0.03
wt. % H2O at 946ºC and 3.1 kbar.
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 14298 (F6):
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Four plagioclase cores were analyzed (An63) and results indicate water contents 4.7 +/-0.1 wt.
% H2O at 972ºC and 3.2 kbar.
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 14309 (F7):
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Three plagioclase cores were analyzed (An74) and results indicate water contents 4.45 +/-0.08
wt. % H2O at 967ºC and 3.2 kbar.
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 1210 (F11):
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Six plagioclase cores were analyzed (An70) and results indicate water contents 5.5 +/-0.07 wt.
% H2O at 922ºC and 2.7 kbar.
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 14308 (F12):
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Three plagioclase cores were analyzed (An64) and results indicate water contents 4.8 +/-0.04
wt. % H2O at 953ºC and 3.1 kbar.
 14268 (F5):
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References:
Baker RB, Eggler DH (1987) Compositions of anhydrous and hydrous melts coexisting
with plagioclase, augite, and olivine or low-Ca pyroxene from 1 atm to 8 kbar: Application to
the Aleutian volcanic center of Atka. Am Mineral 72:12-28
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Beattie P (1993) Olivine-melt and orthopyroxene-melt equilibria. Contrib Mineral
Petrol 115:103-111
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Brey GP, Köhler T (1990) Geothermobarometry in four-phase lherzolites II. New
thermobarometers, and practical assessment of existing thermobarometers. J Petrol 31:13531378
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Dungan MA, Long PE, Rhodes JM (1978) Magma mixing at mid-ocean ridges:
evidence from legs 45 and 45- DSDP. Geophys Res Lett 5:423-425
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Grove TL, Gerlach DC, Sando TW (1982) Origin of calc-alkaline series lavas at
Medicine Lake Volcano by fractionation, assimilation and mixing. Contrib Mineral Petrol
80:160-182
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Hasenaka T, Carmichael ISE (1987). The cinder cones of Michoacán-Guanajuato,
central Mexico: Petrology and chemistry. J Petrol 28:241–269
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Hasenaka T, Ban M, Delgado-Granados H (1994) Contrasting volcanism in the
Michoacán-Guanajuato volcanic field, central Mexico: shield volcanoes vs. cinder cones.
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Putirka KD (2008) Thermometers and barometers for volcanic systems. Rev Mineral
Geochem 69: 61-120
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Rhodes JM, Dungan MA, Blanchard DP, Long PE (1979a) Magma mixing at mid-ocean
ridges: evidence form basalts drilled near 22°N on the mid-Atlantic ridge. Tectonophysic
55:35-61
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Ridolfi F, Renzulli A, Pueriniet M (2010) Stability and chemical equilibrium of
amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and
application to subduction-related volcanoes. Contrib Mineral Petrol 160:45–66
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Waters LE, Lange RA (2015) An updated calibration of the plagioclase-liquid
hygrometer-thermometer applicable to basalts through rhyolites. Am Min 100:2172-2184
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