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Martian Paterae: Tyrrhena andHadriaca
GLY 424/524
March 6, 2002
TyrrhenaPatera
Martian Volcanic Provinces
TyrrhenaPatera
HadriacaPatera
AmphitritesPatera
ApollinarisPatera
AlbaPatera
Martian Paterae• Shallowly sloping flanks (<2°)• Summit caldera/caldera complex
• Flanks dissected by radial channels– Channels different sizes on different volcanoes
– Channels different orientations on differentvolcanoes
• Originally proposed to be shield volcanoesbuilt from fluid basalts (Mariner 9)
• Now generally believed to be composed ofpyroclastic deposits
Martian Paterae
• Circum-Hellas– Tyrrhena Patera
– Hadriaca Patera
– Peneus Patera
– Amphitrites Patera
• Alba Patera (Tharsis)
• Apollinaris Patera (Elysium)
TyrrhenaPatera
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Hadriaca Patera
ApollinarisPatera
AlbaPatera
Amphitrite 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, friablematerial comprising shield materials
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Koko Crater, HawaiiHighland 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
MOLA: Western HesperiaRegion
TyrrhenaPatera
Hellasbasin
HesperiaPlanum
Highland Paterae: Evidence forPyroclastics
• No evidence for primary flow features onshields– No lava flow margins
– No lava channels, collapsed tubes
• Evidence for aeolian erosion of shieldmaterials– Lots of dunes
– Erosional fabric aligned with strongest seasonalwinds
Highland Paterae: Evidence forPyroclastics
• Channels--probably groundwater
• Hawaiian sapping channels originate on ashbeds overlying lava flows
• Small-scale textures on channel floors
Highland Paterae: PyroclasticFlows
• Models suggest eruption plumes on Marscan’t go as high as plumes on Earth (why?)
• Tyrrhena Patera & Apollinaris Pateradeposits too far (~500 km) from vent to beemplaced by airfall
• Thermal models suggest viability ofwelding pyroclastic flows to createobserved layers in shield materials
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Tyrrhena Patera Lava Flow Field
• More flow lobes identified (23 vs. 29 todate)
• Underlying slopes <1°– Explains downflow widening trends?
[Peitersen and Crown, 2000; 2001]
• More channeled flows than observed in VOimages– Velocities = 10 - 50 m s-1
– Effusion rates ~102 - 104 m3 s-1
Tyrrhena Patera Lava Flow Field
• Largest flow field in southern hemisphere(~1000 x 250 km)
• Young– Shield materials ~Noachian/Hesperian
– Lava flows ~Hesperian/Amazonian
• Transition from early explosive to latereffusive
• A global transition?