KOMATIITES AS AN ANALOG TO UNDERSTAND LARGE VOLCANIC FLOW FIELDS IN THE SOLAR SYSTEM

Komatiites are ultramafic volcanic rocks with >18 weight % MgO. First discovered in the continental shield of Africa in the late 1960s, komatiites are considered to be the extrusive equivalent of peridotites; i.e., the metamorphosed remnants of Archean and Proterozoic high Mg, low Si, high temperature and low viscosity lava flows. Komatiites have been of interest on Earth because they host Fe-Ni-Cu-PGE magmatic ore deposits (including ~25% of the Earth’s Ni reserve), but they have been of interest in planetary geology because of an inferred similarity to extraterrestrial lava flows. Indeed, lunar mare basalts have compositions suggesting a rheological similarity to komatiitic basalts, and the chemistries of Adirondack-class basalts in Gusev crater on Mars are equivalent to high-Mg basalts on Earth. Finally, NASA’s Galileo spacecraft detected potentially ultramafic eruptions on Jupiter’s moon Io in the late 1990s, perhaps a result of intense tidal heating. Thus komatiites are a useful analog to understand the compositions and emplacement styles of extraterrestrial lavas. In particular, the unique temperatures and rheologies of komatiites has been linked to turbulent flow emplacement and thermo-mechanical erosion of substrate by the lavas, possibly a mechanism for the formation of lava tubes and channels. Ever more sophisticated mathematical and fluid dynamic models have demonstrated the complexity and difficulty in large-scale thermal erosion unless large eruption volumes or long eruption durations occurred. Ongoing field work in terrestrial lava channels (this author working with Christopher Hamilton) demonstrates the complex interplay of constructional and erosional processes, and on Mars various roles of volcanic vs. fluvial erosion and tectonic vs. volcanic controls on channel formation. We will discuss these complexities and insights that are gained from modeling komatiites.