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Highly Silicic Compositions on the Moon

Highly Silicic Compositions on the Moon. Glotch et al. Presented by Mark Popinchalk. The Moon!. Red spots Deep UV w/ respect to NIR, low FeO and TiO 2 concentrations Feldspathic magmas with high silica contents UV/Visible/NIR/GRS directly sensitive to silicic volcanism

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Highly Silicic Compositions on the Moon

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  1. Highly Silicic Compositions on the Moon Glotch et al. Presented by Mark Popinchalk

  2. The Moon! • Red spots • Deep UV w/ respect to NIR, low FeO and TiO2 concentrations • Feldspathic magmas with high silica contents • UV/Visible/NIR/GRS directly sensitive to silicic volcanism • Most silicic areas Anorthite

  3. Diviner Lunar Radiometer Experiment • Lunar Reconnaissance Orbiter • 7.8, 8.25, 8.55 µm • Compared Mid IR spectra shapes; Red Spots vs surrounding mare and highlands • Data covers all Red Spots

  4. Christiansen Function • Directly sensitive to silicate mineralogy • Bulk Si02 • Convoluted with Laboratory Spectra : Concavity, curvature, strong positive slope • Show silicate content • I – slope between 3,4 • c – concavity from 3-5

  5. Most-silicic strong concave up • Concave down, positive I is a mix

  6. Mare and Highlands, negative concave, negative slope • CF • Mare = 8.33 • Highlands = 8.19

  7. Concavity Index on Lunar Orbiter IV image • More Red, more Silicic

  8. Silicon, or Silicoff? • Red Spots with CF shorter than anorthite, positive I and c • Quartz, Si rich glass, alkali feldspars • Hansteen Alpha, Lassel Massif, Gruithusien Domes, rim/ejecta Aristarchus Crater • High Si, evolved lithologies • Helmet Feature, Montes Riphaeus indistinguishable

  9. Theories • Represent both Extrusive and Intrusive igneous processes. • Gruithuisen Domes/Hansteen Alpha • Previously proposed silicic volcanic constructs • Diviner consistent with extrusive volcanic process • Aristarchus/Lassell appear to be silicic lithologies at depth • Craters revealing plutonic or pyroclastic deposits

  10. A), D) Impacts reveal silicic below • B), C) Volcanic formation • D) Nothing

  11. Extrusive Silicic Volcanism • Gruithuisen Domes/Hansteen Alpha • Occurred Late Imbrian epoch • Before mare volcanism • Crystals in Apollo Rocks • Crystallization ages that span 500 million years • Silicate Immiscibility? • Granitic Plutons • Slow crystalizationlate stage magma • Prevent large extrusive features -> revealed

  12. Basaltic Underplating • Hot basaltic magma intrudes into lunar crust • Melting of crust, generate silicic magmas • Buoyant, rise as rhyolite plumes • Thin curst, heat producing elements, basaliticmagmatisim in PKT

  13. Conclusions • 4 distinctly different geologies. • Gruithusien Domes/Hansteen Alpha • Extrusive silicic volancism • Aristarchus/Lassell • Impact craters reveal silicic plutons at depth • Multiple igneous processes over time • With silicic results

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