NEW EVIDENCE THAT THE MEDUSAE FOSSAE FORMATION ON MARS WAS MORE EXTENSIVE THAN PREVIOUSLY THOUGHT

The Medusae Fossae Formation (MFF) remains one of the more enigmatic deposits identified on Mars. Recent studies have provided support for an ignimbrite origin for MFF, but alternative origins have not yet been totally eliminated. At the 2009 GSA meeting, we reported on recent mapping efforts that reveal evidence that MFF was previously much more areally extensive than is inferred from the boundaries identified through Viking-based geologic mapping. The release of version 11 of the Thermal Emission and Imaging System (THEMIS) global mosaics provides an improved base on which to map out possible outliers of MFF materials. Here we present results from recent mapping of MFF outliers on the new THEMIS daytime infrared mosaic, which has a 100 m spatial resolution posting, supported by evidence of thermophysical variations between layers exposed within the eroded outlier deposits inferred from the co-registered THEMIS nighttime infrared mosaic. New mapping within the MC-23 NW quadrangle of Mars indicates that isolated outliers of MFF, identified during the work reported last year, now appear to be connected, resulting in considerable expansion of the area potentially covered by previous MFF deposits that have subsequently undergone intense aeolian erosion and degradation. The increased area that may have been covered by MFF has important implications for the ignimbrite origin of MFF, particularly with regard to the original volume of the deposits. If MFF is the result of large ignimbrite eruptions, the increased total volume of the deposits implies that the equivalent of 1000 Toba-sized eruptions (the largest explosive eruption identified from terrestrial deposits) would be required to generate the MFF materials.