Morphology and origin of an evaporitic dome in the eastern Tithonium Chasma, Mars Davide Baioni n , Forese Carlo Wezel Planetary Geology Research Group, Institute of Earth Science, University of Urbino, Campus Scientifico Sogesta, 61029 Urbino (PU), Italy article info Article history: Received 20 June 2009 Received in revised form 16 January 2010 Accepted 20 January 2010 Available online 2 February 2010 Keywords: Evaporitic dome Mars Karst landforms Planetary geology Tithonium Chasma abstract A 3.4 km-high, dome-shaped upland in eastern Tithonium Chasma (TC) coincides with areas containing abundant surface signatures of the sulphate mineral kiersite, as identified by the OMEGA image spectrometer. The dome has surface features on its summit, flanks, and at its base that were apparently formed by liquid water released from melting ice. These features include a variety of karst landforms as well as erosive and depositional landforms. The surface of the dome has few impact craters, which suggests a relatively young age for the dome. Rock layers in the dome are laterally continuous but are visibly deformed in some places. The mineralogical and structural characteristics of the dome suggest that it was emplaced as a diapir, similar to many salt diapirs on Earth. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction The Tithonium Chasma (TC) is the northern trench of the western troughs of the Valles Marineris (VM) structure (Fig. 1), a rift system that belongs to the Tharsis radial pattern of fractures (Carr, 1981). Located next to the Martian equator, TC extends about 850 km in an east–west direction and has an elongated shape. Deposits indicated by OMEGA data to consist of magnesium sulphate (Bibring et al., 2006) are present at both ends of TC (Popa, 2006; Popa et al., 2007a). A dome-shaped upland consisting of this material rises from the Chasma floor at the eastern end of TC and is the topic of this paper. Previous work examining this structure showed its similarity with terrestrial structures (Baioni and Wezel, 2008) and the existence of karst landforms and processes (Baioni et al., 2009). These kind of structures, known as interior layered deposits (ILDs), occur throughout the chasms of the Valles Marineris and were first recognized in Mariner 9 images (Sharp, 1973; Mc Cauley, 1978; Lucchitta et al., 1994). In all these canyons the layered deposits tend to form light-toned, rounded mounds or flat-topped mesas toward the centre of the canyons and separated from the canyon walls by an irregular depression or moat. The ILDs also typically have an albedo and erosive style very different from the wall rocks (Carr, 2006). Multiple hypotheses for the origin and mechanism of formation of the ILDs have been proposed (Komatsu et al., 1993; Lucchitta et al., 1994; Weiz and Parker, 2000; Malin and Edgett, 2000; Chapman and Tanaka, 2001; Hauber et al., 2006; Rossi et al., 2008), most authors suggest that these are younger than the present troughs that they have found. It has been argued that they could be deposits forming within ancestral basins (Fueten et al., 2008; Fueten et al., 2009) or that they could be older exhumed deposits (Catling et al., 2006; Malin and Edgett, 2000), but still the origin of the ILDs remain among the most puzzling and controversial of the canyons’ features. The goal of this work was to determine the nature and origin of the elevated structure in eastern TC. To this end, a morphological analysis of the newly available Mars reconnaissance orbiter (MRO) high resolution imaging science experiment (HiRISE) images was performed with the aim of describing surface features and landforms, and, where possible, morphogenetic processes. The morphological features of the structure were investigated through an integrated analysis of HiRISE, high resolution stereo camera (HRSC), Mars orbiter camera (MOC), and thermal emission imaging system (THEMIS) data. The morphometric characteristics of the structure were measured using a topographic map (50 m contour intervals) built from HRSC and Mars orbiter laser altimeter (MOLA) data. 2. Study area setting The TC canyon (Fig. 1b) cuts through the surrounding Hesperian plateau (Scott and Tanaka, 1986) and has a depth of about À 2,600 m relative to the average Martian MOLA radius ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/pss Planetary and Space Science 0032-0633/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pss.2010.01.009 n Corresponding author. Tel./fax: + 39 722 304295. E-mail address: dvbgeo@uniurb.it (D. Baioni). Planetary and Space Science 58 (2010) 847–857