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 (stan0525@umn.edu)

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.