Volatiles and Fluids in Subduction Zones

Petrologic evolution of arc magmas

Along-arc variations in felsic tephra compositions differ from those in mafic rocks due to somewhat different source conditions and stronger crustal influences, particularly at Guatemala (collaboration with C2; there is more to come on this topic). We have analyzed several tephras and volcanic systems in detail to understand their volatile release, eruptive and magmatic evolution, and the volcanic hazards. We demonstrate long-term changes in low-pressure magmatic evolution of the Chiltepe magma system in Nicaragua. Where the volcanic arc is displaced at a segment boundary in Nicaragua and El Salvador, with the most mafic volcanism connecting the displaced arc limbs, we show that magmatism at the crossing of the tectonic elements is a mixture of components from both types of magma systems. The visible evidence of such interaction is the presence of high-Mg olivines in dacitic tephras. Masaya, the most productive, and Nejapa-Miraflores, the most mafic, magma systems of the central CAVA switched between different mantle sources within short time intervals of order 102 years; mantle heterogeneities must exist at a small scale (km) beneath these volcanoes.