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N. G. Barlow, C. B. Perez (U. Central Fl.), J. Koroshetz (U. Fl.)
A study of martian impact craters with fluidized ejecta morphologies has revealed that the area south of the Valles Marineris canyon system may contain a large near-surface volatile reservoir. The area is located in the Solis Planum region (20S-30S, 50W-90W). An analysis of craters displaying the single lobe (SL) ejecta morphology found that the onset diameter for these craters is between 3 km and 5 km, compared to the 5 km to 6 km onset diameters found for this morphology throughout most of the martian equatorial region (i.e., within 30 degrees north and south of the equator). This is the largest area of smaller-than-normal onset diameters found in our study of the equatorial region. In addition, analysis of the distribution of multiple lobe (ML) ejecta morphologies also indicates a higher than normal abundance of craters with this morphology in the Solis Planum region. A global study by Barlow and Bradley (Icarus, v. 87, pp. 156-179, 1990) found a strong correlation among latitude, diameter, and ejecta morphology, which is consistent with the proposed distribution of subsurface volatiles based on geothermal and hydrologic models. Acording to the Barlow and Bradley model, SL morphologies result from impact into ice while ML morphologies result from excavation into liquid-rich reservoirs. Our current study suggests that the ice-rich layer producing the SL morphology lies closer to the surface (<300 to 500 m) in the Solis Planum region than elsewhere in the equatorial region (~520-572 m) and that an underlying liquid reservoir, which produces the ML morphologies, has been present since the region formed in the Hesperian. Topographic maps of the area suggest a slight depression in this region (relative elevation <6-7 km) compared to the surrounding terrain (>7 km). We propose that the uplift of the Tharsis Bulge to the west of this region warped the area and tilted a pre-existing groundwater table. The tilting of the groundwater table caused the volatiles to accumulate in the slight depression where today the smaller onset diameters and abundance of ML morphologies are found.
The author(s) of this abstract have provided an email address for comments about the abstract: ngb@physics.ucf.edu