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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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TyrrhenaPatera

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100 km

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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?

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20 km

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