Reexamining the relationship between Apollinaris Patera and the basalts of the Gusev crater plains, Mars

A possible source of the Gusev crater basalts analyzed by the Spirit rover is Apollinaris Patera. We test this hypothesis by identifying and analyzing potential lava flow paths using Thermal Emission Imaging System, Mars Orbiter Camera, High Resolution Imaging Science Experiment, and Mars Orbiter Laser Altimeter data sets together with published geologic mapping. Image interpretation reveals three possible flow paths from Apollinaris onto Gusev crater floor via a breach in Gusev's northwest rim; an unnamed crater that must have postdated any potential flow along the paths currently blocks the breach. After correcting for the unnamed crater, topographic profiles constructed along possible flow paths demonstrate that elevation along each path increases from ∼80 to 430 m. For two of the pathways, this elevation change indicates that lavas could not have traversed through them. The third profile, though, is less conclusive as the topography may reflect a broad flexural arch. However, on the basis of two of the topographic profiles together with the lack of obvious lava flow structures that indicate flow south through the breach, we propose that Apollinaris was not the direct source of the Gusev basalts. Instead, we argue that it seems more likely that the Gusev basalts were sourced from below the crater itself. The similar ages (as derived from crater counts) of Apollinaris's south flank and the Gusev plains lavas, however, suggest that the two volcanic regions may be part of a common magmatic feature.