Modelling impact volcanism for the Ontong Java Plateau (OJP)
Department of Geology, University College Dublin, Ireland
We have conducted new hydrocode simulations to test whether impact volcanism is a viable process to explain the origin of the OJP, currently recognised as the largest oceanic LIP on Earth. Having previously established that the thermal and physical state of the target lithosphere is critical to melt production (Jones et al., 2002), we used the dry lherzolite melting parameterization of Katz (2001), and a hot geotherm appropriate for 10-20 Ma oceanic crust at the onset of the OJP at 120 Ma (Coffin et al., 2003). We used an iron projectile of diameter 30 km and velocity 20 km/s with vertical incidence. If the same projectile struck continental lithosphere, it would produce a large impact crater ~300 km across with 10-20 km uplift similar to the largest impact crater preserved on Earth (Vredefort). In our simulation, the effect of changing the target to hot oceanic lithosphere is very dramatic, and produces massive melting predominantly as a giant sub-horizontal disc with a diameter in excess of 1000 km down to ~200 km depth in the upper mantle within ~10 minutes, although most of the initial melt is shallower than ~100 km. The total volume of mostly ultramafic melt, is ~ 3 x 106 km3, ranging from superheated liquid (100% melt, > 500 degrees above solidus) within 100 km of ground zero, to varying degrees of partial melt with depth and distance. It would take up to tens of thousands of years to solidify. This total volume of melt is equivalent to approximately 3 times as much, or ~107 km3 of basalt if it were distributed as a conventional 20% partial melt of the mantle. We conjecture that much of this melt would be buoyant and erupt rapidly, followed by an extended second period of additional melting likely to extend to greater depths, as envisaged by Abbott, Glikson, Rogers, Ingle, Coffin etc. modelling. In our view these results are sufficiently similar to OJP to warrant serious multidisciplinary investigation, as suggested by Coffin & Ingle (2003), including mantle convection modelling. We have established that it is theoretically possible, and with a much smaller projectile than envisaged by Coffin & Ingle (2003; 50 km projectile).
Coffin M. F. and Ingle S. P. (2003) IUGG abs JSV03.