The Red Planet: A Survey of Mars


basalt — a common type of fine-grained, volcanic rock, composed primarily of the minerals pyroxene and plagioclase.

caldera — a roughly circular depression near the summit of a volcano.

graben — a topographic valley, created by motions along faults at the edges of the valley (see Fig. 2a).

olivine — a common mineral in igneous (volcanic) rocks, containing magnesium, iron, silicon, and oxygen.

plagioclase — a common mineral in igneous rocks, containing calcium, sodium, aluminum, silicon, and oxygen.

plate tectonics — The surface of the Earth is broken into 12 main regions, or plates. Each plate moves over the Earth's surface independent of the other plates at speeds of a few centimeters per year. Most volcanic and tectonic activity on Earth is concentrated at the boundaries between these plates. Plate tectonics apparently has not occurred on Mars, although other processes related to mantle convection (slide #14) have been important on Mars.

pyroxene — a common mineral in igneous rocks, containing calcium, magnesium, iron, silicon, and oxygen.

superposition — when one geologic unit lies on top of another unit, the upper unit has the younger age.

tectonic — deformation of a planet's surface in the form of faulting and folding of rock layers.

thermal expansion — When heated, most objects expand in size. This increases the volume occupied by a given mass of material, decreasing its density and causing it to be buoyant relative to material of the same composition but lower temperature ("hot air rises"). Such differences in density provide the driving force for convective flow within planets.

volcanic — formed by the eruption of molten rock (called lava or magma) onto the surface of a planet.

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