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1 Department of Geology, Saint Mary's University, Halifax, N.S. B3H 3C3, Canada (e-mail: gpiper{at}smu.ca)
2 Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, PO Box 1006, Dartmouth, N.S. B2Y 4A2, Canada
Late Miocene igneous rocks of Samos, in the southeastern Aegean Sea, comprise monzodiorite and minor granite of the Katavasis complex, trachyte and rhyolite of the Ambelos volcanic centre, and bimodal basalt–rhyolite at basin margins. Six new K–Ar ages, together with existing geochronology and biostratigraphy, show that the Katavasis complex and Ambelos centre date from 10–11 Ma and basalt–rhyolite from 8 Ma, correlating with cooling ages for the Katavasis complex and an unconformity in the basin fill. Monzodiorite, granite, trachyte and basalt all have similar radiogenic isotopes. Monzodiorite and basalt have similar trace element compositions and could result from 5–10% partial melting of enriched garnet lherzolite in the subcontinental lithosphere. Variations in trace elements suggest that trachyte and monzodiorite evolved by fractional crystallization from a parental magma similar to the younger basalt. The Katavasis and Ambelos rocks were synchronous with regional extension and listric faulting, which created opportunities for mid-crustal magma chambers and magma fractionation. Basalt extrusion was synchronous with the onset of north–south strike-slip faulting, which permitted more rapid transfer of magma to the surface. Late Miocene strike-slip faulting propagated from north to south in western Anatolia and the southeastern Aegean Sea, providing pathways for different types of mantle melts.
