Does melt underplate the continents?
Fyfe [1992] argues that ponded magma may travel long distances (hundreds of kilometers?) along the Moho. Heat would be transferred laterally away from the arc to cause lower crustal metamorphism and secondary volcanism in distant places. There is some seismological evidence for past underplating beneath hot spots [Caress et al. 1995] and oceanic arcs [Suyehiro et al., 1996]: sub-Moho material with seismic velocities characteristic of basalt or a mix of peridotite and basalt. Deep electromagnetic sounding [Gough, 1981] also provides some evidence for deep layers of melt: regional lower-crustal high electrical resistivities. However, while some case can be made for the existence of underplating, little can be said about the particulars (i.e. thickness of melt layers, etc.). Does the lower crust melt? The temperature of a basaltic melt is typically much higher than the melting point of granitic (or granodioritic) crustal rock, particularly if the rock contains significant water. Some melt
