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Lunar Volcanism: Volcanoes in a Vacuum Main Information Sources

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Lunar Volcanism: Volcanoes in a Vacuum Main Information Sources Main Information Sources Lunar Volcanism: • Apollo • Galileo Volcanoes in a Vacuum • Clementine • Prospector GLY 424/524 February 13, 2002 Mare Basalts • Found only on near side • Found only within impact basins • Required thin, weak crust and Earth’s tidal forces to pull the magma out Apollo 11 Landing Site Apollo 11: Mare Tranquilitatus • Objective: sample relatively old mare surface • Results – Basalts high in Fe, Ti – ~3.7 Ga • Interpretations & Conclusions – Anhydrous (but NOT avesicular!) – Maria are very old – Maria are volcanic 1 Apollo 11: Approach Apollo 11 Landing site Moltke crater, lower right Apollo 11 Boulder field West Crater Apollo 12: Oceanus Procellarum Apollo 12 Landing Site • Objectives – Sample relatively young mare – Sample ray from Copernicus crater • Results – Maria basalts ~3.15 - 3.35 Ga – Granites? • Interpretations & Conclusions – “young” maria are old – Copernicus ~0.9 Ga (or 1.1 or 2.1Ga…) 2 Apollo 12 Apollo 12 Landing site Landing site Near Surveyor crater Apollo 14: Fra Mauro • Objective: Sample Imbrium ejecta • Results – lots of breccias – 3.9 - 4.0 Ga • Interpretations & Conclusions – Fra Mauro = Imbrium ejecta – Trace-element enriched rocks abundant Apollo 14: Fra Mauro Apollo 14 Landing site Cone Crater, lower right 3 Apollo 15: Hadley-Apennine • Objectives – Sample rings of Imbrian basin – Sample Hadley Rille – Sample Mare Imbrium • Results – Mare basalts ~3.2 Ga – Mare breccias ~3.9 - 4.1 Ga • Interpretations & Conclusions – Mare not produced by impact – Highlands have complex composition Apollo 15 Landing Site Apollo 15 Apollo 15 4 Hadley Rille Hadley Rille Apollo 16: Descartes & Caley Apollo 16 Landing Site Formations • Objectives – Sample highland plains – Measure highland heat flow – Land in highlands • Results – Impact breccias 3.8 - 4.2 Ga • Interpretations & Conclusions – Highland plains = ponded impact melt – Highlands are anorthositic Apollo 16 landing site Apollo 16 Bright crater is South Ray Landing Site Descartes crater (degraded crater at base of photo) 5 Apollo 17: Taurus-Littrow • Objectives – Serenitatis massifs – Flat valley plains between mountains & dark mantling (volcanic?) • Results – Variety of breccias – Apollo-11 type basalts ~3.7 Ga – Volcanic glass ~3.5 Ga • Interpretations & Conclusions – No young volcanism – No anorthosites! Apollo 17 Landing Site Apollo 17 Landing Site Apollo 17 Landing Site 6 Apollo 17 • Orange soil • Microscopic glass beads • Pyroclastic eruptions on the Moon? Lunar Mineralogy • Major phases – Plagioclase [CaAl2Si2O8] – Pyroxene [(Ca,Mg,Fe)2Si2O6 – Olivine [(Mg,Fe)2SiO4] – Ilmenite [FeTiO3] • Minor phases – Iron, troilite – Silica – K-spar Lunar Mineralogy: New Mare Basalts minerals • Armalcolite (Mg,Fe)(Ti,Zr)2O5 • Older, high-Ti group – 3.5 - 3.8 Ga • Tranquillityite Fe8(Zr,Y)2Ti3Si3O24 – 9 - 13 wt% TiO2 • Pyroxferroite CaFe6(SiO3)7 – Apollos 11, 17 • Younger, low-Ti group – 3.1 - 3.4 Ga – 1 - 5 wt% TiO2 – Apollos 12, 15 7 Mare Basalts Mare Basalts • Must be at least 2 different sources • Near-surface separation of • Low-Ti – Ol, il, armalcolite, Fe, and/or chromite – Derived from ol+px source • Low-Ti – Depths ~200 - 500 km – Addition/subtraction of olivine • High-Ti • High-Ti – Derived from ol+px+il cumulates – Addition/subtraction of Fe-Ti oxides – <150 km depth Plutonic Rocks Mare Basalts • Ferroan anorthosites • Runny (viscosity of motor oil at room temp) – Primordial lunar crust • Formed in reduced environment – Bulk composition of lunar crust – No magnetite – Less dense than bulk lunar composition – Oxygen, water could not have formed orange – Narrow compositional range (An95-97) glass – Positive Europium anomalies • Almost all show negative Europium – Otherwise low REE components anomaly • Mg-norites – Probably formed from mafic parent magmas • Mg-gabbronorite Magma Ocean Plutonic Rocks: Granite? • Outer ~100 - 150 km of Moon molten • Apollo 12--first discovery during Early Heavy Bombardment • “Trivial” abundances – Heat source = heat of accretion • Found as fragments of interstitial glass from • Olivine sank mare basalts • Plagioclase floated – Shock-heating – Created global highlands crust – Extreme crystal fractionation – Europium can substitute for calcium in plagioclase 8 Plutonic Rocks: KREEP • High abundances of: – Potassium – Rare-Earth Elements – Phosphorus – And other incompatibles • Widely distributed – Last 2% residue from magma ocean? 9.
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