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



• 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



• 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…



• 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



IW-2 at 1450 °C: log(fO2) = -11.24 (O’Neill & Pownceby 1993)

-11.24

l o g ( k m o

l )


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)



• 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


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()



• 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



Results at 10-6 bar

Zn speciation of gases and sublimates



Results at 10-6 bar

ratio of transported to sublimated metals

Gas dominant

Solids dominant



ResultsP-T conditions of equal amounts of gasesand sublimates



• 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


Metal speciation

major findings

renggli c. lunar volcanic gas

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