Regional Analysis of the new geochemical maps of Mars
surface by Mars Odyssey GRS and it implications on the
Martian interior: Tharsis region

Abstract: The Gamma Ray Spectrometer (GRS) on board Mars Odyssey is the first mission
to provide elemental concentrations of global extent for the surface
throughout the midlatitudes of Mars. Up to the time of release of this
study, there are global concentration maps for Ca, Cl, Fe, H, K, Si and Th
with reasonable confidence. The region of interest of this study comprises
the western part of the Tharsis region and Olympus Mons where the Si map
shows a well defined anomalously low region. This work aims at explaining
the possible reasons for such an anomaly, and weather it can be explained
through statistical considerations or geological ones. Data analysis of that
region using updated software codes on IDL shows the anomaly to be
statistically significant which encourages further geomorphological and
geochemical analysis to deduce the possible reasons for such an anomaly. Fe
is shown to have also a specific trend in the region. On the other hand,
geomorphological considerations suggest the prolonged volcanic history
of the region to be responsible for the observed composition. The extent of
regolith or dust contribution opposed to bedrock one is discussed too.

Recent work by other workers (Newsom et al., 2007) shows the dust in the
heavily mantled regions on Mars to be representative to some extent, to the
underlying bedrock, which facilitates the treatment of the region and gives
some weight to the analysis given concerning the geological history. In
addition, geochemical simulations using publicly available software of model
compositions of the Martian Mantle shows that it is possible to have
compositions in agreement with the GRS estimates for the region under
certain conditions and constraints on the starting composition, depth and
extent of partial melting and degree of fractionation. Volcanic processes
are suggested to explain the low silicon anomaly. While the results are very
encouraging, some questions remain open like the lack of correlation
with the basaltic Martian meteorites.