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Highly Silicic Compositions on the Moon

Explore the red spots on the Moon with low FeO and TiO2 concentrations, feldspathic magmas, and silicic areas. Learn about silicate mineralogy and magma evolution revealed by lunar radiometry. Discover the implications of silicic compositions on lunar geology.

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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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