ABSTRACT: The results achieved from the gological studies that hava been carried out on the Tertiary aged rock units cropping out in the vicinity of the town of Ayvalık in Balıkesir province are presented and the genetic interpretations of the igneous rocks in terms of plate tectonics are made. In the area under investigation, firs plu= tonic intrusion was the Koiak pluton intruded during Eocene-Oligocene time which was sueeeded by the monzonitic dikes of Maden Adası. Volcanİsm shows five different volcanic periods from late Oligocène to pliocene gi« vîg rise to produce different volcanic materials. Petrochemical analyses carried out on the formations such as Alîbey volcanics (late Oligocène), Hallaçlar formation (Late Oligocene-Early Miocene), Dedetepe formation (Early Miocene), Yuntdağ Völemks (Middle-Late Miocene) and Dededağ volcanics (Early Pliocene) indicated that these volcanics are essentially calcalkaline and partly shoshonitîc showing continental crustal origin,