Imaging the subsurface from central peaks of impact craters C. Quantin (1), J. Flahaut (1), H. Clenet (1), P. Allemand (1), P. Thomas (1), (1)Laboratoire de Géologie de Lyon, Terre, Planètes, Environnements, UCBL/ENS Lyon, CNRS UMR 5276 , Villeurbanne cedex France (cathy.quantin@univ-lyon1.fr ). Abstract Based on the analysis of 31 central peaks of impact craters in the vicinity of Valles Marineris, we study the composition of the subsurface at different locations and different depths. Based on coupled CRISM and HiRISE data, we determine the composition and the nature of the rocks exhumed by the 31 impacts craters. The results allow to image the first 20 km of the subsurface in the vicinity of Valles Marineris and reveal a major crustal discontinuity. 1. Introduction Despite recent efforts from space exploration to sound the Martian subsurface with RADARs, the structure of the Martian underground is still unknown. Major geological contacts or discontinuities inside the Martian crust have not been revealed. Another way to sound the subsurface is to analyze the central peaks of impact craters that have been exhumed from depth at the time of impact. The last Martian mission, MRO (Mars Reconnaissance Orbiter), did a real effort in targeting the central peaks of impact craters with both its high resolution instruments: CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) and HiRiSE (High Resolution Imaging Science Experiment). We analyze the composition and the nature of the rocks exhumed from depth on 31 impacts craters in the vicinity of Valles Marineris. The stratigraphic uplift forming the central peak depends on the size of the impact and would represent around 1/10 of the final diameter [1]. The studied impacts have emplaced over a large range of elevation from +6000 m to - 2000 m (MOLA absolute elevation) and the impacts have a diameter of between10 km and 150 km. These large ranges of values give a remarkable sampling of the subsurface that allowed us to image the first 20 km of the subsurface. 2. Dataset and method 49 HiRiSE images and 30 CRISM observations are processed. We integrate these data as well as derived products from these data to a Geographic Information System (GIS). Our GIS also includes data with a global coverage such as a MOLA elevation map, THEMIS infrared mosaics, geological maps, TES global map and OMEGA mineralogical maps. CTX images were also included to provide a context for HiRiSE data. CRISM is the hyperspectral imager onboard MRO that measures the reflectance at visible and near-infrared wavelengths [2]. Targeted MRO/CRISM images collect 544 wavelengths from 0.36 to 3.9 μm in ~10-12 km wide swaths at 18-36 m/pixel resolution. The data are processed with CAT (CRISM Analysis Tool) [3]. The CRISM data are first corrected from the atmosphere effect using a ratio with a CRISM scene of Olympus Mons, scaled to the same column density of CO 2 . Then, the data are filtered in order to remove the spectral spikes and the spatial stripes. The cleaned data cubes are then geo-projected. Spectral parameters typical of certain minerals are computed and mapped [4]. Our GIS allows us to collect relevant information for the 31 impact craters: their diameter, their geographic position and the elevation of the central peak, from MOLA data. We are so able to define the pre-impact elevation of the rocks exposed in the central peaks of the studied craters. 3. Results Our analyses of both mineralogy from 35 CRISM hyperspectral data cubes and rock nature from 50 HiRISE pictures allow us to distinguish two kind of material exhumed in the central peak (see figure 1). EPSC Abstracts Vol. 6, EPSC-DPS2011-801, 2011 EPSC-DPS Joint Meeting 2011 c  Author(s) 2011