Renggli C. lunar volcanic gas
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Transcript of Renggli C. lunar volcanic gas
7/17/2019 Renggli C. lunar volcanic gas
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A new model for volcanicgas compositions in lunarfire fountain eruptions
C.J. Renggli, P.L. King, R.W. Henley
Research School of Earth Science Funded by the
Australian ResearchCouncil
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• Pyroclastic deposits on the moon (“dark mantle deposits”)extend up to 350 km from the vents
• Coatings on lunar glass beads are rich in “volatiles” andmetals
•Deposition from a gas phase
• Zn, Pb, Ga, Cu, Ni, Fe (primarily sulfides)
G.J. Taylor, Clanton et al. 1978, McKay et al. 1973 & 1992
1C.J. Renggli, P.L. King, R.W. Henley
How are the metals transported and deposited
5 μm
1 mmThin section SEM images of glass bead surfaces
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• Gas + melt drops interact
•
Gas species sublimate ontobeads and form coatings
• 400-500 bar, ~10km below surface
• Exsolution and bubble nucleation
• + 1 =
2
McKay et al. 1973, 1992
Saal et al. 2008
Rutherford & Papale 2009
Fegley 1991C.J. Renggli, P.L. King, R.W. Henley
Gas species
CO, CS2, CS,
COS, S2, HCl
Zn, PbS, Pb, GaCl,
CuCl, Cu, Ni, NiS…
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• Degassing during eruption
• 2-5 °C/sec cooling rate
• 1450 °C initial melt temperature
• Species diffusing as H2O, Cl-, F- and S2-
Saal et al. 2008
3
Gas
species
Lost gas
(mol %)
H 9.9
O 78.6Cl 0.05
S 10.8
F 0.6
C ?C.J. Renggli, P.L. King, R.W. Henley
Calculation of volatile contents
following Saal et al. 2008
Composition of out-gased volatiles:
Apollo 17 glass beads
Diffusion profiles
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IW-2 at 1450 °C: log(fO2) = -11.24 (O’Neill & Pownceby 1993)
-11.24
l o g ( k m o
l )
4C.J. Renggli, P.L. King, R.W. Henley
Calculation of C content in the C-O-H-S-Cl-F gas system
O2(g)
CO(g)
2
-15
-10
-5
0
0 20 40 60 80
C (kmol)
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• Gibbs free energy minimisationof a 49 component system, 6
elements• Temperature 1500 – 500 °C
• Pressure 1 – 10-9 bar
• Ideal gas behaviour
Lunar gas
(mol %)
H 5.4
O 42.7
C 45.3
Cl 0.06
S 5.9
F 0.7
5C.J. Renggli, P.L. King, R.W. Henley
Model input conditions
400 bar
1450 °C
10-9 bar
T << 0 °C
0.1 bar
1450 °C
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Results at 10-6 bar
gas speciation2() → () + 2()
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• Gibbs free energy minimisation of 149 component system, 12chemical elements
• Zn, Pb, Ga, Cu, Ni, Fe
• Metals are unsaturated in the gas phase and have equalconcentrations for comparability (0.001 mol%)
• Sulfides, chlorides, oxides, fluorides and pure metals
•
Solids and gases7C.J. Renggli, P.L. King, R.W. Henley
Model input conditions
G.J. Taylor, Clanton et al. 1978, McKay et al. 1973 & 1992
5 μm
1 mmThin section SEM images of glass bead surfaces
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Results at 10-6 bar
Zn speciation of gases and sublimates
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Results at 10-6 bar
ratio of transported to sublimated metals
Gas dominant
Solids dominant
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ResultsP-T conditions of equal amounts of gasesand sublimates
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• Efficient metal transport into near-vacuum
conditions
• Zn is enriched in the gas phase compared to Ni
and Cu by >104 and >102 respectively
• Formation of chloride (Ga, Cu, Ni) and sulfide
(Pb) gases can increase the metal transport by
several orders of magnitude
• Sublimates are predominantly sulfides (Zn, Pb,
Ga, Ni) and pure metals (Cu, Ni)
• Experiments and analytical re-investigation of
coatings on Apollo 17 & Apollo 15 samples
may shed light on eruption dynamics and
metal contents
11C.J. Renggli, P.L. King, R.W. Henley
Metal speciation
major findings