Mars: The Tharsis Region and Shield Volcanoes GLY 424/524 March 4, 2002 Shield Volcanoes: Terrestrial Martian Volcanic Provinces • Basaltic • Shallow flank slopes (<11°) – 7 - 11° proximally – 4° distally • Summit calderas or caldera complexes • Hot-spots beneath ocean crust – Hawaii, Galapagos – Hot-spots beneath continental crust rarely produce shield volcanoes Tharsis Volcanoes Shield Volcanoes: Mars • Huge – Each one ~100x the volume of Hawaii – Why? • Tharsis – Olympus, Arsia, Pavonis, Ascraeus • Elysium Mons 1 Tharsis: Source • Mantle plume • Huge & long-lived • Antipodal to large impact? Olympus Mons • 27 km above m.p.r. • Basal diameter = 600 km • Basal scarp ~3-6 km tall – Locally draped by flows – Unique – Origin unknown • Summit caldera – Nested – 66 x 83 km Olympus Calderas on Shield Volcanoes Mons • Typically nested Caldera – Multpile episodes of magma “withdrawl” • Flank eruptions • Inflation and drainback – Relative ages determined by cross-cutting relations – No general temporal/spatial trend • Magma chamber – About same size as caldera width – About same depth as caldera width 2 Olympus Mons Caldera Ascraeus Mons Caldera Olympus Mons Flows MOC wide-angle • Tens of thousands lava flows drape flanks High-res here • Channel-fed & tube-fed • 102 - 103 km long • Similar in morphology to basaltic lava flows on Hawaii Olympus Mons Flows Mauna Loa, Hawaii Landsat image: phh = black; aa = red 3 Olympus Mons Olympus Mons Aureole lava flows Olympus Mons Aureole • As long as 600 km • Characterized by – Ridges – Troughs – Fractures – Graben Olympus Mons Aureole Aureole Formation • Sub-glacial eruption (table mountain) • Outwash flood deposits • Subaqueous eruption (seamount) • Landslide/debris aprons – Most folks believe this last one, but the VO image MOC wide-angle image question is far from answered Fov ~120 km MOC Narrow angle 4 Pavonis Mons • “Middle” volcano • Simple caldera Arsia Mons Elysium Mons Elysium Mons • Avg. flank slopes ~10° – Steeper than typical shield – Evolved composition? – Role of volatiles? • Dissolved water • Groundwater, groundice • Smaller than Tharsis uplift • Large channels on flank 5 Elysium Mons Elysium Mons • See MOC releases here • www.msss.com/mars_images/moc/7_10_98 _elysium_rel/ • 9 km tall • 240 km across Ages • Tharsis & Elysium mostly Hesperian • Tharsis began forming in Noachian • VERY young lava flows have been found in Elysium region (<10 Ma old) • Elysium region still active? 6.