THE CONTRIBUTION OF SATELLITE IMAGES FOR TRACING AND MAPPING OF VOLCANIC FEATURES: APPLICATION ON THE MIOCENE POLYCHNITOS IGNIMBRITE, NORTHEASTERN MEDITERRENEAN BASIN

Digital processing of satellite SPOT-PAN data has been used for mapping and illustrating specific characteristics of the Miocene Polychnitos ignimbrite, an important pyroclastic formation occupying the 1/6 of central-eastern Lesbos island. Miocene volcanism on Lesbos, which lies in the northeastern Aegean just off the coast of Asia Minor, was the result of regional extension of the Aegean-Anatolian microplate. The volcanic succession comprises of shoshonites ranging from basalt to rhyolite, both underlain and overlain by calcalkaline volcanic rocks (Pe-Piper, 1993). The character of volcanism was particularly explosive giving rise to two pyroclastics formations, the Sigri pyroclastics to the west and the Polychnitos ignimbrite to the east. Three vector layers with photolineaments have resulted from digital processing. The first vector layer displays the extent of the ignimbrite and six terraces probably representing the ignimbrite cooling units. It also displays the interface of the Polychnitos ignimbrite with marbles, peridotite and lower lava units. The second vector layer comprises the flow lines of the ignimbrite whilst the third one displays the lineaments of the basement peridotite, which near its borders show continuity within the ignimbrite. Three rose diagrams have been constructed on the basis of the second and third vector layers. The first rose diagram shows the flow lines in the ignimbrite to display a primary northwesterly and a secondary N-S direction, which is interpreted to result from the initial channeling of the pyroclastic flow between the peridotite and the Lower Lava which probably represented topographic highs of the paleorelief. This channeling was locally enhanced by NE and NW equivalent lineaments in the peridotite (second and third rose diagrams). North of the peridotite the ignimbrite has flowed mainly towards the east and arrived New Kidoniae and to the northwest towards Paleos and the islet of Barbalia. Both these directions are depicted from the rose diagrams of the lineaments in the basement peridotite. A vent area in the proximity of the Kalloni Gulf Graben is suggested.