Alkaline Martian Magmas And The Gusev Plains

Evidence has accumulated during the Martian Spirit Rover mission that the Gusev Plains are composed of pretty-darn alkaline basaltic lava rocks. Not at all like those crazy-assed nearly-pure andesitic lava rocks that were so common at the 1997 Pathfinder landing site.

Nevertheless, I yearn for the andesite. If I'm not mistaken, andesite implies (or at least suggests) subduction and plate tectonic processes, like on Earth (Andesite is named after the Andes Mountains, where these processes are quite vigorous).

Basalt implies rock derived from the mantle, however. The Gusev Plains are in the ancient Southern Highlands, where no plates have ever thought about moving, whereas the Pathfinder site is close to the transition to the Northern Plains, and who knows whatever might have happened there?

Sedimentary rocks, like where the Opportunity Rover is located, are more provocative.