Wednesday, November 17, 2010

Blocks and Valleys in Southwestern Melas Chasma

This HiRISE image covers a portion of the wallrock and canyon floor in southwestern Melas Chasma.

Along the floor of Melas Chasma is an unusual blocky deposit composed of light-toned blocks in a darker matrix. The high resolution of the HiRISE image reveals layers only a few meters thick in some of the light-toned blocks. The blocks vary in size but most fall between 100-500 meters in diameter.

Although most blocks appear rounded, others have angular edges and can be very elongated. The morphologies of the blocks suggest ductile deformation, such as from a flow or by tectonic disruption after emplacement. Aeolian ripples are interspersed between the blocks in the darker matrix.

Small valleys can be seen along the wallrock to the south. The wallrock is a mixture of two geologic units that differ mainly in their reflectance. The light-toned unit appears to be thinner and only exposed in localized spots. Several of the light-toned deposits are seen only in the valleys, suggesting they were either deposited or are exposed by erosion.

Photo credit: NASA/JPL/University of Arizona

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