Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites

Rivera Banuchi, Victoria B.; Liu, Winnie; Yee, Nathan; Legett, IV, Carey; Glotch, Timothy D.; Chemtob, Steven M.

doi:10.1029/2021je007150

Title: Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites

Abstract

Clay minerals detected with orbital and in situ instruments in ancient Martian terrains constrain Mars' climate and aqueous alteration history. Early in its history, Mars experienced an atmospheric redox change and iron-bearing clay minerals may preserve the effects of that transition. Ferrous smectites, the thermodynamically predicted product of chemical weathering of basalts under anoxic conditions, may have undergone oxidation by exposure to chemical oxidants in the atmosphere or regolith, or by direct photooxidation at the surface. To assess these potential oxidation pathways, ferrous trioctahedral smectites of varying initial iron content were synthesized and subjected to oxidation by ultraviolet (UV) irradiation. Experimental UV irradiation under an anoxic atmosphere equivalent to approximately 7 years of flux on the Martian surface caused partial oxidation of smectite-bound Fe (Fe³⁺/ΣFe = 16–18%) and octahedral sheet contraction. Metal-OH vibrational bands in visible/near infrared (VNIR) reflectance spectra of oxidized smectites changed in band depth and asymmetry with higher iron content. X-ray diffraction patterns of UV irradiated samples indicate the formation of a mixed di- and trioctahedral smectite or a secondary nontronite phase, possibly on the surfaces of higher iron content smectites. Furthermore, these experiments suggest that UV irradiation is able to oxidize structurally bound iron in smectitesmore »« less

Authors:

^[1]; Liu, Winnie ^[2]; Yee, Nathan ^[2];

^[3];

^[4];

^[5]

Temple Univ., Philadelphia, PA (United States); Stony Brook Univ., NY (United States)
Rutgers Univ., Piscataway, NJ (United States)
Stony Brook Univ., NY (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Stony Brook Univ., NY (United States)
Temple Univ., Philadelphia, PA (United States)

Publication Date:: Mon May 02 00:00:00 EDT 2022

Research Org.:: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:: USDOE Office of Science (SC)

OSTI Identifier:: 1869620

Report Number(s):: LA-UR-21-31320
Journal ID: ISSN 2169-9097

Grant/Contract Number:: 89233218CNA000001

Resource Type:: Accepted Manuscript

Journal Name:: Journal of Geophysical Research. Planets

Additional Journal Information:: Journal Volume: 127; Journal Issue: 5; Journal ID: ISSN 2169-9097

Publisher:: American Geophysical Union

Country of Publication:: United States

Language:: English

Subject:: 58 GEOSCIENCES; Planetary Sciences

Citation Formats


                    Rivera Banuchi, Victoria B., Liu, Winnie, Yee, Nathan, Legett, IV, Carey, Glotch, Timothy D., and Chemtob, Steven M. Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites.  United States: N. p., 2022. 
Web.  doi:10.1029/2021je007150.

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                    Rivera Banuchi, Victoria B., Liu, Winnie, Yee, Nathan, Legett, IV, Carey, Glotch, Timothy D., & Chemtob, Steven M. Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites.  United States.  https://doi.org/10.1029/2021je007150

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                    Rivera Banuchi, Victoria B., Liu, Winnie, Yee, Nathan, Legett, IV, Carey, Glotch, Timothy D., and Chemtob, Steven M. Mon .  
"Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites".  United States.  https://doi.org/10.1029/2021je007150.  https://www.osti.gov/servlets/purl/1869620.

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@article{osti_1869620,

  title        = {Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites},

  author       = {Rivera Banuchi, Victoria B. and Liu, Winnie and Yee, Nathan and Legett, IV, Carey and Glotch, Timothy D. and Chemtob, Steven M.},

  abstractNote = {Clay minerals detected with orbital and in situ instruments in ancient Martian terrains constrain Mars' climate and aqueous alteration history. Early in its history, Mars experienced an atmospheric redox change and iron-bearing clay minerals may preserve the effects of that transition. Ferrous smectites, the thermodynamically predicted product of chemical weathering of basalts under anoxic conditions, may have undergone oxidation by exposure to chemical oxidants in the atmosphere or regolith, or by direct photooxidation at the surface. To assess these potential oxidation pathways, ferrous trioctahedral smectites of varying initial iron content were synthesized and subjected to oxidation by ultraviolet (UV) irradiation. Experimental UV irradiation under an anoxic atmosphere equivalent to approximately 7 years of flux on the Martian surface caused partial oxidation of smectite-bound Fe (Fe3+/ΣFe = 16–18%) and octahedral sheet contraction. Metal-OH vibrational bands in visible/near infrared (VNIR) reflectance spectra of oxidized smectites changed in band depth and asymmetry with higher iron content. X-ray diffraction patterns of UV irradiated samples indicate the formation of a mixed di- and trioctahedral smectite or a secondary nontronite phase, possibly on the surfaces of higher iron content smectites. Furthermore, these experiments suggest that UV irradiation is able to oxidize structurally bound iron in smectites without the presence of other chemical oxidants. Photooxidation may have influenced the mineralogy, both syndepositionally and postdepositionally, of Martian alteration assemblages formed near the surface and this process needs not be limited to one part of their formation history.},

  doi          = {10.1029/2021je007150},

  journal      = {Journal of Geophysical Research. Planets},

  number       = 5,

  volume       = 127,

  place        = {United States},

  year         = {Mon May 02 00:00:00 EDT 2022},

  month        = {Mon May 02 00:00:00 EDT 2022}

}

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Works referenced in this record:

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