Experimental investigation of Apollo 16 “Rusty Rock” alteration by a lunar fumarolic gas

Renggli, Christian J.; Klemme, Stephan

doi:10.1002/essoar.10503055.2

Cited by 1 publication

(3 citation statements)

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“…Concentrations of volatiles in mare basalts may also be lowered by degassing. Renggli et al (2017) showed with lunar gas phase modeling that at 1200 ºC, 10 -6 bar and at IW-2, the predominant gas species are S2, CO, and H2 -with Zn, Cl, and F speciation of Zn o (g), HCl, and HF, respectively (Renggli et al, 2017;Renggli and Klemme, 2021). At higher pressures (1 bar) the dominant S-speciation changes to S2 becoming subordinate relative to H2S and COS. As such, the amount of degassing expected from our elements of interest is S > Cl > F > Zn, in agreement with the trend of Ustunisik et al (2015).…”

Section: Discussionmentioning

confidence: 95%

“…If degassing occurred under vacuum conditions at the surface via a fracture network, then where M1,2 are the masses of the light and heavy isotopologues, respectively. For lunar gas compositions, COS and H2S are the expected dominant phases for S (Renggli et al, 2017;Renggli and Klemme, 2021). Under ideal degassing into a vacuum, the fractionation of these S-bearing isotopologues yields 1000lnMelt-H2S, Melt-COS = 28 and 16‰, respectively, enriching the melt in 34 S. In contrast, equilibrium fractionation between these vapor species and silicate melt has the opposite effect, with COS and H2S being 34 S-rich relative to the melt, depleting the melt in 34 S (Marini et al, 2011;Richet et al, 1977).…”

Section: Isotopic Systematics Of Lunar Volcanismmentioning

confidence: 99%

“…In the case of "Rusty Rock" 66095, which represents the 'end-member' of low  66 Zn (-15‰) and high  37 ClSBC and  37 ClWSC values (~15‰) resulting from vapor condensation (Day et al, 2017;Shearer et al, 2014), these isotope values may reflect specific conditions such as orders of magnitude higher Cl2 values when compared to pyroclastic gases (Renggli and Klemme, 2021).…”

Section: The S Zn and CL Isotope Composition Of Mare Basaltsmentioning

confidence: 99%

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The Zn, S, and Cl isotope compositions of mare basalts: Implications for the effects of eruption style and pressure on volatile element stable isotope fractionation on the Moon

Gargano

Dottin

Hopkins

et al. 2022

American Mineralogist

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We compare the stable isotope compositions of Zn, S, and Cl for Apollo mare basalts to better constrain the sources and timescales of lunar volatile loss. Mare basalts have broadly elevated yet limited ranges in δ66Zn, δ34S, and δ37ClSBC+WSC values of 1.27 ± 0.71, 0.55 ± 0.18, and 4.1 ± 4.0‰, respectively, compared to the silicate Earth at 0.15, –1.28, and 0‰, respectively. We find that the Zn, S, and Cl isotope compositions are similar between the low- and high-Ti mare basalts, providing evidence of a geochemical signature in the mare basalt source region that is inherited from lunar formation and magma ocean crystallization. The uniformity of these compositions implies mixing following mantle overturn, as well as minimal changes associated with subsequent mare magmatism. Degassing of mare magmas and lavas did not contribute to the large variations in Zn, S, and Cl isotope compositions found in some lunar materials (i.e., 15‰ in δ66Zn, 60‰ in δ34S, and 30‰ in δ37Cl). This reflects magma sources that experienced minimal volatile loss due to high confining pressures that generally exceeded their equilibrium saturation pressures. Alternatively, these data indicate effective isotopic fractionation factors were near unity. Our observations of S isotope compositions in mare basalts contrast to those for picritic glasses (Saal and Hauri 2021), which vary widely in S isotope compositions from –14.0 to 1.3‰, explained by extensive degassing of picritic magmas under high-P/PSat values (>0.9) during pyroclastic eruptions. The difference in the isotope compositions of picritic glass beads and mare basalts may result from differences in effusive (mare) and explosive (picritic) eruption styles, wherein the high-gas contents necessary for magma fragmentation would result in large effective isotopic fractionation factors during degassing of picritic magmas. Additionally, in highly vesiculated basalts, the δ34S and δ37Cl values of apatite grains are higher and more variable than the corresponding bulk-rock values. The large isotopic range in the vesiculated samples is explained by late-stage low-pressure “vacuum” degassing (P/PSat ~ 0) of mare lavas wherein vesicle formation and apatite crystallization took place post-eruption. Bulk-rock mare basalts were seemingly unaffected by vacuum degassing. Degassing of mare lavas only became important in the final stages of crystallization recorded in apatite—potentially facilitated by cracks/fractures in the crystallizing flow. We conclude that samples with wide-ranging volatile element isotope compositions are likely explained by localized processes, which do not represent the bulk Moon.

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Section: Discussionmentioning

confidence: 95%