Experimental Investigation of CO2 Solubility in Martian BasaltsWith Varied Oxidation State and Applications to Martian Atmospheric Evolution
3-11
0 1 2
-10
-9
-8
-7
-6
Pressure (GPa)
golfO
2
Martian Mantle
WI
1+WI
2+WI
3+WI CO Stable2
Graphite Stable
Introduction
B. D. Stanley1, M. T. Mounier1,2, and M. M. Hirschmann1
1 Dept. of Geology and Geophysics, University of Minnesota, 2 Dept. of Earth and Planetary Sciences, Northwestern University ([email protected])
FTIR Analysis
Data Conclusions
Acknowledgements
Experiments
melt
graphite
Pt
4 mm
melt
2 mm
Pt-Fe doped
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Pre
ssur
e (G
Pa)
160015001400Temperature (°C)
Oxidized Pt-Fe Reduced Pt-Fe Graphite Saturated
The NASA Mars Fundamental Research Program funds this experi-mental program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Dept. of Geology and Geo-physics, University of Minnesota. Parts of this work were carried out in the Institute of Technology Characterization Facility, UMN, which receives partial support from National Science Foundation through the National Nanotechnology Infrastructure Network program. Mössbauer analyses were conducted at the Institute for Rock Mag-netism, UMN, which receives partial support from the NSF through the Instrumentation and Facilities program.
Evidence for stable liquid water on the Martian surface early in its history requires the exis-tence of a thicker greenhouse atmosphere than currently present. Models of Martian atmo-spheric evolution include volcanic outgassing as a major input, however calculations of its impact use studies of CO2 solubilities in basalts of terrestrial composition to determine total CO2 released over the course of Martian history. This work investigates the solubility of CO2 in basalts of Martian composition at varying oxygen fugacity (fO2) and conditions of pos-sible partial melt generation in the mantle in order to construct more realistic models of the evolution of the Martian atmosphere.
Oxybarometry of SNC meteorites suggests that the oxygen fugacity of much of the Martian mantle is reducing (iron-wustite, IW, ±1) and so carbon is likely stored as graphite in a reduced Martian mantle (After [1]).
Experiments were performed using a 0.5” piston-cylinder apparatus under hot, piston-in conditions. Two capsule designs were used:
1) 2 mm Pt-Fe doped capsule2) 4 mm Pt graphite double capsule
Experimental conditions were 1400 to 1625°C, and 1.0 to 2.5 GPa.
Mössbauer Analysis
Velocity (mm/s)
B254Humphreyno CO2
room temperature
1.00
0.98
0.96Tran
smis
sion
(a.u
.)
12840-4-8-12
1.00
0.99
0.98
Tran
smis
sion
(a.u
.)
Velocity (mm/s)12840-4-8-12
OxidizedHumphreyno CO2
room temperature
Velocity (mm/s)
1.00
0.98
0.97
Tran
smis
sion
(a.u
.)
12840-4-8-12
0.99
ReducedHumphreyno CO2
room temperature
Starting material:82% Fe3+, 18% Fe2+
Experimental glass:82% Fe3+, 18% Fe2+
Starting material:100% Fe2+
CO2 concentration =44.01× Id ρ ε*
C1graphite
+ O2gas
↔ CO2gas
⇒ KI =fCO2fO2
CO2gas
+ O12−
melt↔ CO3
2−
melt⇒ KII =
XCO 3
2−
melt
XO2−
melt fCO2
where XO2−
melt = 1 − XCO 3
2−
melt
XCO 3
2−
melt =KIKIIfO2
1+ KIKIIfO2at constant T and P
CalculationsHolloway et al. [4] showed that the solubility of CO2 in graphite saturated melts is only related to fO2.
-18.6
-18.5
-18.4
-18.3
-18.2
-18.1
-18.0
lnK
II
600580560540520
1/Temperature (x10-6 K-1)
0 = -13.5 ± 13.9 kJ mol-1Δ
-19.0
-18.5
-18.0
-17.5
-17.0
-16.5
lnK
II
3.02.52.01.51.00.5
Pressure (GPa)
lnKII0 = -15.7 ± 0.30 = 18.8 ± 1.5 cm3 mol-1Δ
lnKII = lnKII0 −
ΔV0
RT
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ (P − P0 ) −
ΔH0
R
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
1
T−
1
T0
⎛
⎝ ⎜
⎞
⎠ ⎟
Experimental CO2 solubilities were used to fit lnKII [5] allowing calculation of at any P-T-fO2 conditions.
XCO3
2 −melt
References
Oxide ExperimentalHumphrey1 Humphrey2
SiO2 46.91 46.96 49.16TiO2 0.53 0.56 2.29Al2O3 10.52 10.93 13.33FeOT 19.87 19.23 11.23MnO 0.38 0.42 -MgO 10.79 10.65 10.41CaO 7.99 8.02 10.93Na2O 2.40 2.56 2.15K2O 0.11 0.10 0.51P2O5 0.52 0.57 -Total 100.0 100.0 100.0
Hawaiian Tholeiite3
Compositions are calculated Cr-free and normalized.
Experimental Humphrey1- Electron microprobe analysis of experimental glass;
Humphrey 2- [2]; Hawaiian Tholeiite3- [3]
Starting Material
• CO2 solubility in synthetic Humphrey basalt does not depend on the oxidation state of the iron, thereby confirming the assertion of Brooker [11] that Fe2+ and Fe3+ have similar influence on CO2 solubility in mafic silicate melts.
• CO2 solubility in graphite-saturated experi-ments is lower, as predicted by Holloway [4].
• Modeled cumulative CO2 outgassed from volcanic outgassing fails to produce a strong CO2 greenhouse by the end of the late Noa-chian calling into question whether a graph-ite-saturated Martian mantle can ventilate enough CO2 to create the required early strong greenhouse.
4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Time (Ga)
0.001
0.01
0.1
1
10
Cum
ulat
ive
CO
2 Out
gass
ed (b
ar)
IW
IW+1
IW+1
IW
[10]
[10] [9]
[8]
Gusev basalt source region Y-980459 source region
Strong Greenhouse
Graphite-saturated
0.001
0.01
0.1
1
Cal
cula
ted
CO
2 so
lubi
lity
(wt.%
)
-1.0 -0.5 0.0 0.5 1.0
)
1320°C, 1.0 GPa Gusev basalt source region [7]
1540°C, 1.2 GPa Y-980459 source region [6]
Graphite-saturated
Δ
1000
800
600
400
200
Inte
grat
ed A
bsor
banc
e (c
m-1
)
2.001.751.501.251.000.750.500.250
Loaded CO2 (wt.%)
= 83778 ± 1045 L mol-1 cm-2 ε*
Coefficient values ± 95% Confidencea = 12.95 ± 0.56b = 553.0 ± 6.9
1.25
1.00
0.75
0.50
0.25
0
Abs
orba
nce
4000 3500 3000 2500 2000 1500
Wavenumber (cm-1)
CO32-
OH-
Oxidized HumphreyPt-Fe doped capsule1400ºC, 2.0 GPa, 30 min.
2.5
2.0
1.5
1.0
0.5
0
CO
2 S
olub
ility
(wt.%
)
160015001400Temperature (°C)
2.0 GPa
0.01
0.1
1
10
3.02.01.00Pressure (GPa)
1500°C
Oxidized Humphrey Reduced Humphrey Graphite Saturated Humphrey Hawaiian Tholeiite [3]
CO
2S
olub
ility
(wt.%
)
[1] Hirschmann M. M., and Withers A. C. (2008) EPSL, 270, 147-155. [2] Gellert R. et a l. (2006) JGR Planets, 111 , E02S05. [3] Pan V. et a l. (1991) Geochim Cosmochim Ac, 55, 1587-1595. [4] Holloway J. R. et al. (1992) Eur J Mineral, 4, 105-114. [5] Fine G., and Stolper E. M. (1986) EPSL, 76, 263-278. [6] Musselwhite D. S. et al. (2006) Meteorit Planet Sci, 41, 1271-1290. [7] Monders A. G. et a l. (2007) Meteorit Planet Sci, 42, 131-148. [8] Carr M. H. (1999) JGR Planets, 104, 21897-21909. [9] Manning C. V. et al. (2006) Icarus, 180, 38-59. [10] Pepin R. O . (1994) Icarus, 111, 289-304. [11] Brooker R. A. e t al. (2001) Chem Geol, 174, 225-239.
