Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii

Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars

Richard V. Morris, D. W. Ming, T. G. Graff, R. E. Arvidson, James Bell, S. W. Squyres, S. A. Mertzman, J. E. Gruener, D. C. Golden, L. Le, G. A. Robinson

Research output: Contribution to journalArticle

57 Citations (Scopus)

Abstract

Iron-rich spherules (> 90% Fe2O3 from electron microprobe analyses) ∼ 10-100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H2O and/or OH-1. The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al3+ for Fe3+ substitution and structural H2O and/or OH-1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.

Original languageEnglish (US)
Pages (from-to)168-178
Number of pages11
JournalEarth and Planetary Science Letters
Volume240
Issue number1
DOIs
StatePublished - Nov 30 2005
Externally publishedYes

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spherules
spherule
Volcanoes
Temazepam
hematite
tephra
volcanoes
mars
Sulfates
Mars
sulfates
volcano
occurrences
sulfate
acids
Acids
acid
Rocks
Hydrolysis
Sulfate minerals

Keywords

  • Concretions
  • Hematite
  • Mars
  • Mars Exploration Rover
  • Meridiani Planum
  • Spherule
  • Sulfate

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)

Cite this

Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii : Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars. / Morris, Richard V.; Ming, D. W.; Graff, T. G.; Arvidson, R. E.; Bell, James; Squyres, S. W.; Mertzman, S. A.; Gruener, J. E.; Golden, D. C.; Le, L.; Robinson, G. A.

In: Earth and Planetary Science Letters, Vol. 240, No. 1, 30.11.2005, p. 168-178.

Research output: Contribution to journalArticle

Morris, Richard V. ; Ming, D. W. ; Graff, T. G. ; Arvidson, R. E. ; Bell, James ; Squyres, S. W. ; Mertzman, S. A. ; Gruener, J. E. ; Golden, D. C. ; Le, L. ; Robinson, G. A. / Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii : Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars. In: Earth and Planetary Science Letters. 2005 ; Vol. 240, No. 1. pp. 168-178.
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abstract = "Iron-rich spherules (> 90{\%} Fe2O3 from electron microprobe analyses) ∼ 10-100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100{\%} (93-99{\%}) suggest structural H2O and/or OH-1. The transmission M{\"o}ssbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al3+ for Fe3+ substitution and structural H2O and/or OH-1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.",
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AB - Iron-rich spherules (> 90% Fe2O3 from electron microprobe analyses) ∼ 10-100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe/Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H2O and/or OH-1. The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al3+ for Fe3+ substitution and structural H2O and/or OH-1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.

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