Evidence for Relatively Recent Hydrothermal Activity Due to an Impact within the Syrtis Major

Based on detailed morphological and mineralogical analyses, we have identified a relatively fresh impact crater on the northern edge of the Syrtis Major Volcanic Plains (71.8E, 17.0N) with indications of hydrothermal activity. The crater is 40 km in diameter and 2 km depth, and has a well preserved ejecta blanket, terraced walls, a few superposed impact craters and a well developed central peak with a central pit. The maximum age of this impact crater is constrained to the mid/late Hesperian by the formation age of the Syrtis Major Volcanic Plains. CRISM observations were used to identify extensive hydrated silicates outcrops. When combined with altimetry (MOLA) and imaging (Hirise and HRSC) data, these outcrops are associated with the top and rim of the central peak, and the northern part of the crater floor. The mineralogy is dominated by Fe/Mg-phyllosilicates and chlorite, a suite of minerals that frequently results from hydrothermal alteration in terrestrial craters. Lesser abundances of Al-phyllosilicates are also present. Impact shock decomposition analyses indicate that this suite of minerals postdate the impact event. In this study we present the mineralogy of this fresh crater and propose a nominal stratigraphy as evidence for impact triggered hydrothermal activity in a relatively late stage of the evolution of Mars.