Tyrrhena Terra: tens of phyllosilicate-bearing crater ejecta on Mars

Details Tyrrhena Terra: tens of phyllosilicate-bearing crater ejecta on Mars Tyrrhena Terra: tens of phyllosilicate-bearing crater ejecta on Mars

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p12a..03l&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P12A-03

Mathematics

Logic

[1060] Geochemistry / Planetary Geochemistry, [3617] Mineralogy And Petrology / Alteration And Weathering Processes, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Terrains formed during the Phyllosian period of Mars (Bibring et al., 2006) distinguish themselves by the presence of rocks altered by liquid water. Was this alteration driven by an active hydrologic cycle at surface, or in subsurface by hydrothermal systems or in a warm and wet crust? Here we present the study of one of those terrains: the region of Tyrrhena Terra, between Isidis Planitia and Hellas Planitia. Most of the region is composed of Noachian highlands, dissected by numerous valley networks, and highly cratered. Some lower plains present wrinkle-ridges. OMEGA (Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activité, onboard Mars Express) and CRISM (Compact Reconnaissance Imaging Spectrometer for Mars, onboard Mars Reconnaissance Orbiter) have identified tens of hydrated minerals-bearing outcrops in the region. The detection of absorption bands at 1.9 µm and 2.3 µm indicates the presence of Fe/Mg rich phyllosilicates. The quasi-totality of the detected outcrops is linked to craters of the region: either their ejecta blankets, or their flanks, or their central up-lifts. The other outcrops correspond to hills and scarps. Those craters seem randomly located in the region, but with less occurrences on the wrinkle-ridged plains. Their sizes vary from 37 km to less than 1 km. The largest of them (generally diameter > 5 km) are surrounded by lobate ejecta blankets. The difference between the phyllosilicate-bearing craters and the others of the region could either come from the difference in the ejecta and crater material, or from the state of the surface of the craters (dust or sand cover, different composition at the surface). The presence of phyllosilicates associated to craters could come from: 1. the exhumation by the impacts of buried pre-altered rocks; 2. the alteration in the ejecta by volatiles released by the impact; 3. the alteration through post-impact processes such as hydrothermal systems. Detailed study of the location of the phyllosilicate-bearing outcrops with CRISM and HiRISE (High Resolution Imaging Science Experiment, onboard Mars Reconnaissance Orbiter) help the understanding of the origin of the alteration, and hence of the time when alteration was possible on Mars.

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