Schematic of the back-arc system of the southern Lau basin showing the change in subduction influence from north to south, substantially modified from Martinez et al. (2007). In the north (panel (a)), the ELSC is about 100 km from the Tofua arc. The melting regime for the back-arc is just slightly influenced by the slab flux that dominates the geochemical signals at the volcanic front of the arc. In the south (panel (b)), the VFR is only 45 km from the arc, and the back-arc melting system is strongly influenced by the subduction component. More water is added to the spreading center melting regime, causing higher extents of melting and greater crustal thickness at the same time as an increased flux of water and other elements from the slab. In general, back-arc magmas are a mixture of melts produced by decompression melting as at normal ridges in the half of the melting regime distal to the arc (the “dry side”), and melts produced by hydrous flux melting in the proximal side of the melting regime (the “wet side”) (Langmuir et al. 2006).
Media Type: Illustration
Investigator: Charles Langmuir