Martian Paterae: Tyrrhena and Hadriaca Tyrrhena Patera GLY 424/524 March 6, 2002 Martian Volcanic Provinces Martian Paterae • Shallowly sloping flanks (<2°) • Summit caldera/caldera complex Alba Patera • Flanks dissected by radial channels – Channels different sizes on different volcanoes Apollinaris – Channels different orientations on different Patera Tyrrhena Patera volcanoes Hadriaca Patera • Originally proposed to be shield volcanoes built from fluid basalts (Mariner 9) Amphitrites Patera • Now generally believed to be composed of pyroclastic deposits Martian Paterae Tyrrhena Patera • Circum-Hellas – Tyrrhena Patera – Hadriaca Patera – Peneus Patera – Amphitrites Patera • Alba Patera (Tharsis) • Apollinaris Patera (Elysium) 1 Hadriaca Patera Apollinaris Patera Alba Amphitrite Patera Patera Crater ~300 km Patera Channels • Probably fluvial – Groundwater? (sapping) – Runoff? (rain) • Source – Magmatic degassing? – Earlier, warmer, wetter period of Mars? • Both consistent with fine-grained, friable material comprising shield materials 2 Koko Crater, Hawaii Highland vs. Lowland Paterae • Lowland Paterae – Apollinaris, Alba – Probably mostly lava flows • Highland Paterae – Hadriaca, Tyrrhena, Amphitrites, Peneus – Probably fine-grained, friable shield materials – Pyroclastic fall or flows Highland Paterae: Evidence for MOLA: Western Hesperia Pyroclastics Region • No evidence for primary flow features on Hesperia Planum shields – No lava flow margins – No lava channels, collapsed tubes Hellas Tyrrhena basin Patera • Evidence for aeolian erosion of shield materials – Lots of dunes – Erosional fabric aligned with strongest seasonal winds Highland Paterae: Evidence for Highland Paterae: Pyroclastic Pyroclastics Flows • Channels--probably groundwater • Models suggest eruption plumes on Mars • Hawaiian sapping channels originate on ash can’t go as high as plumes on Earth (why?) beds overlying lava flows • Tyrrhena Patera & Apollinaris Patera • Small-scale textures on channel floors deposits too far (~500 km) from vent to be emplaced by airfall • Thermal models suggest viability of welding pyroclastic flows to create observed layers in shield materials 3 Tyrrhena Patera 4 100 km 5 Tyrrhena Patera Lava Flow Field Tyrrhena Patera Lava Flow Field • More flow lobes identified (23 vs. 29 to • Largest flow field in southern hemisphere date) (~1000 x 250 km) • Underlying slopes <1° • Young – Explains downflow widening trends? – Shield materials ~Noachian/Hesperian [Peitersen and Crown, 2000; 2001] – Lava flows ~Hesperian/Amazonian • More channeled flows than observed in VO • Transition from early explosive to later images effusive – Velocities = 10 - 50 m s-1 • A global transition? – Effusion rates ~102 - 104 m3 s-1 6 N 20 km 7.