Transition of Mount Etna lavas from a mantle-plume to an island-arc magmatic source

Mount Etna lies near the boundary between two regions that exhibit signific antly different types of volcanism. To the north, volcanism in the Aeolian island arc is thought to be related to subduction of the Ionian lithosphere (1). On Sicily itself, however, no chemical(2,3) or seismological(4) eviden ce of subduction-related volcanism exists, and so it is thought that the vo lcanism-including that on Mount Etna itself-stems from the upwelling of man tle material(5), associated with various surface tectonic processes(1,6). B ut the paucity of geological evidence regarding the primary composition of magma from Mount Etna means that its source characteristics remain controve rsial. Here we characterize the trace-element composition of a series of la vas emitted by Mount Etna over the past 500 kyr and preserved as melt inclu sions inside olivine phenocrysts. We show that the compositional change in primary magmas from Mount Etna reflects a progressive transition from a pre dominantly mantle-plume source to one with a greater contribution from isla nd-arc (subduction-related) basalts. We suggest that this is associated wit h southward migration of the Ionian slab, which is becoming juxtaposed with a mantle plume beneath Sicily. This implies that the volcanism of Mount Et na has become more calc-alkaline, and hence more explosive, during its evol ution.