Sources and processes in arc magmatism: the crucial role of water (An inaugural lecture to the Society)
Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium. E-mail: Marlina.Elburg@ugent.be
Abstract
Arc magmatism distinguishes itself from magmatism in other tectonic settings by the crucial role that water plays in its petrogenesis. Water influences the geochemistry of the sub-arc mantle, by transferring fluid-soluble elements from the slab into the mantle. Water probably also carries the oxidised signature from the slab into the mantle wedge. The ubiquitous negative Ti-anomaly in arc magmas may reflect an increase of the compatibility of titanium in the solid residue during partial melting in water-bearing peridotite. Finally, water also has a strong influence on the identity of minerals involved in crystal fractionation processes, and gives rise to the low-Fe (calc-alkaline) fractionation trend by lowering the temperature at which the silicates start crystallising, without influencing the crystallisation temperature of iron-oxides.