Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates

J. J. Bellucci; M. J. Whitehouse; A. A. Nemchin; J. F. Snape; G. G. Kenny; R. E. Merle; P. A. Bland; G. K. Benedix

doi:10.1016/j.epsl.2019.115977

Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates

J. J. Bellucci^*, M. J. Whitehouse, A. A. Nemchin, J. F. Snape, G. G. Kenny, R. E. Merle, P. A. Bland, G. K. Benedix

^*Corresponding author for this work

Geology and Geochemistry

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ¹⁸O [(¹⁸O/¹⁶O)_sample/(¹⁸O/¹⁶O)_Standard-1] × 10³] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ¹⁷O [δ¹⁷O-1000(1 + δ¹⁸O /1000)^0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ¹⁷O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ³⁷Cl [(³⁷Cl/³⁵Cl)_sample/(³⁷Cl/³⁵Cl)_standard – 1] × 10³] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ¹⁷O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ¹⁷O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.

Original language	English
Article number	115977
Pages (from-to)	1-8
Number of pages	8
Journal	Earth and Planetary Science Letters
Volume	531
Early online date	27 Nov 2019
DOIs	https://doi.org/10.1016/j.epsl.2019.115977
Publication status	Published - 1 Feb 2020

Funding

The authors would like to acknowledge Kerstin Lindén for help preparing the samples. Dr. Ludovic Ferrière and the Natural History Museum Vienna are thanked for loaning the rock chip sample of Tissint used in this study. Dr. Andreas Pack and an anonymous reviewer are thanked for their comments that have improved the quality of this manuscript and Dr. Frédéric Moynier is thanked for editorial handling. Dr. PAB acknowledges support from the Australian Research Council via their Australian Laureate Fellowship scheme. GKB acknowledges support from Curtin University via their Research Fellowship scheme and the Australian Research Council Discovery Grant number DP170102972 . This work was funded by grants from the Knut and Alice Wallenberg Foundation ( 2012.0097 ) and the Swedish Research Council (VR 621-2012-4370 ) to MJW and AAN and VR grant ( 2016-03371 ) to J.J.B. The NordSIMS ion microprobe facility operated as a Swedish-Icelandic infrastructure (VR 2014-06375) during the period of analysis. This is NordSIMS publication #615. Appendix A

Funders	Funder number
Australian Research Council	DP170102972
Curtin University of Technology
Knut och Alice Wallenbergs Stiftelse	2012.0097
Vetenskapsrådet	VR 621-2012-4370, 2016-03371

Keywords

Cl isotopes
Mars
martian atmosphere
martian surface
phosphates
triple oxygen

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title = "Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates",

abstract = "The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ18O [(18O/16O)sample/(18O/16O)Standard-1] × 103] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ17O [δ17O-1000(1 + δ18O /1000)0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ17O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl [(37Cl/35Cl)sample/(37Cl/35Cl)standard – 1] × 103] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.",

keywords = "Cl isotopes, Mars, martian atmosphere, martian surface, phosphates, triple oxygen",

author = "Bellucci, {J. J.} and Whitehouse, {M. J.} and Nemchin, {A. A.} and Snape, {J. F.} and Kenny, {G. G.} and Merle, {R. E.} and Bland, {P. A.} and Benedix, {G. K.}",

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AU - Bellucci, J. J.

AU - Whitehouse, M. J.

AU - Nemchin, A. A.

AU - Snape, J. F.

AU - Kenny, G. G.

AU - Merle, R. E.

AU - Bland, P. A.

AU - Benedix, G. K.

PY - 2020/2/1

Y1 - 2020/2/1

N2 - The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ18O [(18O/16O)sample/(18O/16O)Standard-1] × 103] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ17O [δ17O-1000(1 + δ18O /1000)0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ17O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl [(37Cl/35Cl)sample/(37Cl/35Cl)standard – 1] × 103] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.

AB - The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). The phosphates measured here have a range in δ18O [(18O/16O)sample/(18O/16O)Standard-1] × 103] from +1.0 to +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions taking place on the surface of Mars. Three samples have a Δ17O [δ17O-1000(1 + δ18O /1000)0.528-1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA 7533) have an elevated positive Δ17O outside of analytical uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl [(37Cl/35Cl)sample/(37Cl/35Cl)standard – 1] × 103] and enrichments in halogens not seen in the rest of the sample suite. Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA 7533, which are the explicit result of exchange reactions on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2σ, MSWD = 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.

KW - Cl isotopes

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KW - martian atmosphere

KW - martian surface

KW - phosphates

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Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates

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