Abstract: The pre-Jurassic metamorphic rocks of the Biga Peninsula can be evaluated as three maintectonostratigraphic units, which show significant differences from each other in terms of degree of metamorphism,deformation characteristics and tectonic settings. These are: 1) Kazdağ Unit, 2) Kalabak Unit, and 3) KarakayaUnit. The Kazdağ Unit forms the high-grade metamorphic core rocks of the Kazdağ Massif on the visible base of theBiga Peninsula. The Kalabak Unit and the Karakaya Unit are located on this high-grade metamorphic basement ascomposite tectonic slices and form the lower-grade metamorphic outer envelopes.The Kalabak Unit, which is the main subject of this paper, consists of the Dedetepe Formation, the SazakFormation, the Torasan Formation, and Devonian Çamlık metagranodiorite, which cuts all these units. In additionto lithological, stratigraphic and structural similarities of these metamorphic rocks, which are the outer envelopeof the metamorphic core in the Kazdağ Massif and also outcrop in other metamorphic massifs of the region suchas Çamlıca, Karabiga and Karadağ, their U-Pb zircon ages also show that they can be correlated with each other.According to the results obtained from U-Pb zircon dating, the maximum sedimentation ages of the protoliths for themetasedimentary rocks of the Kalabak Unit are in the range of 557-582 Ma. The crystallization age of the protolithfor the metabasites, which has primary relationship to these metasedimentary rocks, is 577 Ma. In addition, protolithcrystallization age of the eclogites, which are tectonic slices in these metasedimentary rocks, is 565 Ma. In additionto similar protolith ages, the fingerprint of a tectonothermal event at about 300-340 Ma is important in terms ofexpressing a common geological history for all samples.Formation environment and age of the metavolcanic rocks of the Kalabak Unit represent consistent andsignificant geotectonic environments. The Dedetepe Formation, which is at the bottom, represents a subductionmélange, the Sazak Formation represents an active continental margin and the Torasan Formation represents acoeval sedimentary sequence. These geotectonic environments developed during the late Precambrian-earlyPaleozoic period while the Proto-Tethys oceanic crust subducted to the south, under the Gondwanaland continent.These oldest rocks of the Sakarya Zone, together with the rocks they were spatially associated with during youngerperiods, were affected by repetitive deformations which resulted in their present position.