EMPLACEMENT AND EROSION BY ARCHEAN KOMATIITE LAVA FLOWS AT KAMBALDA -REVISITED

We have developed a mathematical model to evaluate the now and erosion al potential of submarine, channelized komatiite lavas at Kambalda, We stern Australia. Field data from Kambalda were used to constrain the c hoice of important input parameters, and model results were compared w ith data from field studies and geochemical analyses. Our results sugg est that thermal erosion is strongly dependent upon the nature and beh avior of the substrate. If the substrate is treated as an unconsolidat ed, hydrous sediment that can be fluidized by vaporized seawater, then our model predicts that an initially 10-m-thick basal Kambalda komati ite lava could have produced very high thermo-mechanical erosion rates (similar to 23-10 m/day), crustal thicknesses of similar to 5-20 cm a t distances of similar to 5-35 km from the source, and a high degree o f lava contamination (similar to 3-12%). In contrast, if the substrate is treated as a more consolidated, anhydrous sediment that could not be fluidized, then our model predicts that a Kambalda komatiite flow w ould have had much lower thermal erosion rates (similar to 1.2-0.4 m/d ay) and degrees of contamination (similar to 1-3%), and would have had crustal thicknesses of similar to 5-20 cm at longer flow distances of similar to 30-165 km. Field constraints are generally consistent with our predictions for a non-fluidized substrate. The reentrant embaymen ts at Kambalda are thought to form from either erosion of deep channel s in a flat basaltic seafloor [Huppert et al., 1984], or erosion of a thin (<5 m) sediment with minor undercutting of basalt in pre-existing topography [Lesher et al., 1984]. Our modeling indicates that the for mer was possible for long eruption durations (months), whereas the lat ter was possible for short eruption durations (<2 weeks). As the latte r hypothesis is more consistent with the existing field evidence for t hermal erosion at Kambalda, we believe it is the preferred interpretat ion.