Bimodal Magmatism
Because intra-oceanic
arc systems involves the subduction of a (generally) older and therefore denser
oceanic crust under younger crust it can be strange to think that felsic
magmas, lavas and associated volcanics can exist in this tectonic setting.
Bimodal magmatism is in fact common in intra-oceanic arc systems. There are
several models that exist to explain the bimodal magmatism observed in
intra-oceanic arc systems. Traditionally thought to be formed from fractional
crystallisation of more mafic magmas (Stern, 2004). Larter
and Leat (2003) suggest that the
presence of silicic magmas represent partial melts of andesitic or basaltic
igneous rocks in the crust. Geochemical and
experimental results support this theory (Leat and Larter, 2003).