VOLCANIC ROCKS FROM FOCA-KARABURUN AND AYVALIK-LESVOS GRABENS (WESTERN ANATOLIA) AND THEIR PETROGENIC-GEODYNAMIC SIGNIFICANCE (FOCA-KARABURUN VE AYVALIK-MIDILLI GRABENLERINDEKI (BATI ANADOLU) VOLKANIK KAYALAR VE ONLARIN PETROJENETIK-JEODINAMIK ÖNEMLERI)

The Foça-Karaburun and Ayvalık-Lesvos grabens (western coast of Anatolia, Turkey) are two important NW−SE-trending extensional areas generated in response to the Early Miocene−Holocene extension of the Western Anatolian region, related to the opening of the ‘unconventional’ back-arc basin of the Aegean Sea. The abundance of geo-structural evidence and the occurrence of volcanic rocks representing all the stages of the Aegean-Western Anatolia volcanism render the Foça-Karaburun and Ayvalık-Lesvos Grabens key localities to exemplify the petrogenetic and geodynamic evolution of the area. In this context, the Foça-Karaburun and Ayvalık-Lesvos grabens, possibly formerly a single graben, formed along an original NE−SW-trending extension, later dissected by E−W-trending transtensional faults, are investigated to constrain the petrogenetic and geodynamic evolution of the whole Aegean region. Calcalkaline and shoshonitic volcanic rocks with scattered ultrapotassic-shoshonitic or lamproitic lavas and dykes represent the orogenic phase of the magmatic activity, while the younger K- and Na-rich alkaline basaltic rocks are the result of later magmatism characterized by an intraplate geochemical signature reflecting progressively decreasing subduction rates. While the tectonic lineaments and the structures of the study area allow the reconstruction of the tectonic evolution of Western Anatolia and Aegean Sea, the volcanic rocks from the different stages of Neogene volcanism within the two studied grabens and surrounding areas permit a precise record of the geochemical evolution of the magma sources.