Influence of source materials and fractionating assemblage on magmatism along the aegean arc, and implications for crustal growth

Volcanic products from Methana, Santorini and Nisyros show mineralogical and geochemical characteristics that can be linked to their differentiation at different crustal levels, and varying sources of subducted sediments. The products from Methana, in the western part of the arc, where the overriding plate is thicker, are affected by amphibole fractionation and crustal contamination. Santorini volcano, in the central part of the arc, is located on an extensively thinned section of the overriding plate; it shows high Y-contents, a-typical for average continental crust. Crustal contamination is minor, similar to Nisyros volcano. Products of the latter, easternmost volcanic centre have been variably affected by amphibole fractionation. Its sub-arc magma source is different from the central and western part of the arc, reflecting sedimentary input from the Nile. Amphibole fractionation, caused by crystallization at greater depths, seems necessary to lower Y-contents and yield volcanic products that resemble average continental crust in this respect. In detail, however, none of the magmatic products of the Aegean Arc displays MREE-HREE patterns or levels of compatible elements that are an exact match for average continental crust. Garnet stability and mixing processes appear crucial to obtain the REE and compatible element characteristics of continental crust.