Mathematics – Logic
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..345w&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Mathematics
Logic
Scientific paper
Location Ariadnes Colles and the chaotic terrains Atlantis Chaos, Gorgonum Chaos and a further, unnamed chaotic terrain centred at 37°S, 164.4°W form individual provinces of hummocky terrain located at the deepest parts of Eridania Basin, the putative source region of Ma'adim Vallis [1,2,3,4]. The location was recently proposed as a MSL landing site [5]. Previous studies The individual knobs within Ariadnes Colles range between flat-topped mesas of up to 10 km in width and 200 m of relief down to small cone-shaped hills of only a few hundred meters in width [2] (Fig.1). Although classified as chaotic terrain, this area differs significantly from the chaotic terrains found elsewhere on Mars. The hills consist of a light-toned, indurated material [3, 5] covered by dark rock [1]. Howard and Moore [3] noted that the smaller knobs exhibit a more rounded top, are lower in elevation and are found close to the borders of the knob field, whereas the more mesa-like hills are concentrated towards its centre. They also noted that the light-toned hill tops are dissected by linear features they interpreted as joints. The mineralogy of this region is very diverse. Preliminary results based on CRISM data are consistent with the presence of phyllosilicates, sulphates and/or hydrated silica and pyroxene [5]. New obserations Our investigations using HRSC imagery confirm this overall pattern. The smaller hills consist exclusively of light-toned material and are covered only partly by a thin veneer of dust (Fig. 2). Their bases are angular or irregularly shaped and their tops are rounded to peaked, but never exhibit a mesa-like flat top. In contrast, the much larger mesas are always built up by basaltic material, which is superimposed on the bright knobs. Figure 3 shows a HiRISE image of one of the lighttoned knobs. It can be clearly seen that the light-toned material rises from beneath the inter-knob lava which covered it prior to erosion. It has been eroded and forms a scarp near the foot of the hill. On other knobs, the basaltic material can be found on higher elevations or even at the top. Directly beneath it, the hill exhibits a bright layer that follows the topography with a constant thickness. This layer appears to be harder than the remainder of the light-toned material. Below it, the hills consist of bulk, massive, indurated material. Both the outer layer and the bulk light-toned material are heavily dissected by joints. These joints are partly oriented in a rectangular pattern, but in many cases the exposed outer side of the crust shows a polygonal pattern. Discussion The formation process of the material forming the knobs is poorly constrained. The location of the features below the high stand of a lake proposed by [1] and their light colour are consistent with a formation as an evaporite in a standing body of water, as proposed by [3], who suggested halite as a possible material. The possible detection of sulphate absorbtion features by [5] supports the interpretation of an evaporitic origin.. The development of the individual knobs appears to follow a regional tectonic framework, as suggested by the angular outer boundaries of the individual hills [3]. The observation of a highly jointed, light toned layer superimposed on the bright material in the centre of the knobs that rises from below the basaltic cover between the hills suggests that the hills were not formed by differential displacement along faults and subsequent erosion along these zones of weakness, but by local uplift caused by internal deformation of the light-toned material. Combining these observations, our leading hypothesis is the formation of the lighttoned material by evaporation, followed by uplift of the hills by salt-tectonic movement. Future work We will test this hypothesis and investigate possible alternative processes using spectral data from OMEGA and CRISM flanked by geologic mapping and age determinations based on HRSC and HiRISE imagery. Acknowledgement We thank the HRSC Team and the German Space Agency DLR for financial support of this study. References [1] Irwin, R. P. et al. (2004) JGR, 109, E12. [2] Capitan, R. D. (2007) LPSC XXXVIII, #1338. [3] Howard, A. D. and Moore, J. M. (2004) GeoRL, 31,1, DOI 10.1029/2003GL018925. [4] Williams, L. H. et al. (2008), LPSC XXXIX, #1994. [5] Dobrea, E. N. (2007), 2nd MSL Landing Site Workshop, 23-24.08.2007.
Gasselt S. V.
Gerhard Neukum
Wendt Lorenz
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