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Volcanology of Mars

The Case for Basalt

Compelling arguments can be made for the interpretation of at least the vast majority of Martian volcanism as being basaltic in nature.

Olympus Mons - a Martian shield volcano. Click image for closer view.

Nearly all of the volcanic landforms on Mars have clear basaltic analogs on Earth. The shields are quite similar in morphology (if not in size) to the basaltic shields of Earth (Carr and Greeley, 1980). The small cones and buttes are also consistent with basaltic landforms found on Earth (Hodges and Moore, 1994).

The absence of plate tectonics on Mars results in the absence of the belts of silicic composite stratovolcanoes found here on Earth. Instead, Mars exhibits hot-spot volcanism resulting in the development of shield volcanoes similar to the basaltic landforms found on Earth (Hodges and Moore, 1994).

Lava flows in the Elysium region. Click image for closer view.

Volcanic regions on Mars exhibit immense numbers of lava flows that exhibit structures and evidence of low viscosity that are consistent with basaltic flows. The effect of gravity in flow rheology is such that the lower Martian gravity would cause flows to be thicker than they would be on Earth. Therefore the thin, highly fluid appearance of these flows is especially indicative of low-viscosity material such as basalt (Francis, 1993).

Studies of Mars' moment of inertia can provide estimates of the distribution of iron between the core and mantle of Mars. Preliminary studies indicate a 16 to 27 percent FeO composition of the Martian mantle, as opposed to the 8 to 11 percent for the Earth. Higher iron content in the mantle should lead to lower viscosity lavas (McGetchin and Smyth, 1978).

Analysis of the soil samples collected by the Viking landers in 1976 indicate iron-rich clays consistent with weathering of basaltic rocks (Francis, 1993).

The discovery of meteorites (the SNC's) on Earth that apparently have a Martian origin provides first-hand evidence of the nature of Martian volcanism. These include actual basaltic samples. Analysis of the FeO content of the Shergotty meteorite shows a concentration of 18 percent, in agreement with the predictions mentioned above (Dodd, 1986; Francis, 1993).

Martian meteorite. Johnson Space Center Image. Click image for closer view.

Content assembled by Brian H. Day, Margaret McCrary, and Bill Frye.
Curator: Brian H. Day.
Responsible NASA Official: Donald James

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