HR: 1330h
AN: P22A-0062    [PDF]
TI: THEMIS Observations of Aram Chaos: Evidence for an Ice-Covered Lake
AU: * Glotch, T D
EM: tglotch@asu.edu
AF: Arizona State University, Department of Geological Sciences Box 6305, Tempe, AZ 85282-6305
AU: Christensen, P R
EM: phil.christensen@asu.edu
AF: Arizona State University, Department of Geological Sciences Box 6305, Tempe, AZ 85282-6305
AB: Aram Chaos is a large 280 km diameter crater centered at 2.5 N, 338.5 E. Similar to other nearby craters, it has been filled with a large amount of material since its formation. The interior deposits of this crater, however, differ substantially in two ways from those of other craters in the area; 1) Aram Chaos contains the second-largest deposit of gray hematite on Mars, with an areal coverage of ~5000 km$^{2}$. 2) The sedimentary units in the interior of the crater are capped by a light-toned caprock that has a much higher thermal inertia than the underlying sedimentary units. The association of Aram Chaos with the outflow channels, its obvious basin morphology, the presence of friable interior layered deposits, and the presence of gray, crystalline is indicative of past surface and/or subsurface liquid water in the region. Aram Chaos was divided into twelve distinct units that were mapped based on their geomorphological, thermophysical, and compositional properties, primarily using THEMIS, but including TES, MOLA, and MOC data sets,. In at least three locations, stratigraphic relationships indicate that the layered materials in the interior of the crater were deposited after the formation of the chaotic terrain. There are three possibilities for the origin of these deposits; 1) volcanic, 2) aeolian, and 3) fluvial. A volcanic origin for these layers is unlikely, given the poor spectral match between magnetite-derived hematite and the martian hematite spectrum. If the deposits are simply aeolian in nature, then the presence of a distinct hematite rich layer in the middle of these sediments must be explained. Instead, we propose a model in which the layers were deposited in a lake fed by subsurface water flow. The lake was most likely ice-capped because liquid water would probably not have existed on the surface for a long period of time during the Hesperian when the layered materials are inferred to have been deposited. After the initial catastrophic release of subsurface water that formed the chaotic terrain, subsurface water continued to flow at lower rates to the inner basin in Aram Chaos, which would have been the area of least hydrologic head. The water filled the center of Aram Chaos, carrying sediment, and continually raising the ice cap. For a brief period of time, an Fe-rich fluid interacted with the subsurface water to deposit an Fe-oxide rich layer that was subsequently altered to gray hematite.
DE: 5415 Erosion and weathering
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting