New Io data spur discussion on ultrabasic lavas



In the late 1960s, the Viljoen brothers identified a new class of igneous rock in the ancient (3.5 Ga) Barberton greenstone belt of South Africa. Called komatiites, after the Komati River that flows nearby, these new rocks were soon recognized in Precambrian terrains around the world as the metamorphosed remnants of ancient ultrabasic lava flows and shallow intrusions, the extrusive equivalent of peridotites. Komatiites, although rare in the geologic record, soon became of interest to a wide variety of geologists because of their unique texture, composition, and physical properties, and their genetic association with massive nickel sulfide ore deposits.

With recognition of the inferred high temperature, low viscosity turbulent emplacement, and great thermal erosive potential of these lavas, komatiites became an analog to low-viscosity extraterrestrial lavas, which formed long, sinuous lava channels and flow fields on the Moon,Venus, Mars, and Io. Now, with indications from the Galileo spacecraft and other instruments that active volcanism on Jupiter's moon, lo,may include ultrabasic eruptions, there is renewed interest in understanding the nature of komatiite lavas and what they can tell us about the thermal-compositional-physical dynamics of the early Earth, and perhaps other planets as well.