Pre-Cambrian Metamorphic Rocks of the Sakarya Zone in the Biga Peninsula; Late Ediacaran Gondwanaland Active Continental Margin

The pre-Jurassic metamorphic rocks of the Biga Peninsula can be evaluated as three main tectonostratigraphic units, which show significant differences from each other in terms of degree of metamorphism, deformation characteristics and tectonic settings. These are: 1) Kazdag Unit, 2) Kalabak Unit, and 3) Karakaya Unit. The Kazdag Unit forms the high-grade metamorphic core rocks of the Kazdag Massif on the visible base of the Biga Peninsula. The Kalabak Unit and the Karakaya Unit are located on this high-grade metamorphic basement as composite 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 Sazak Formation, the Torasan Formation, and Devonian camlik metagranodiorite, which cuts all these units. In addition to lithological, stratigraphic and structural similarities of these metamorphic rocks, which are the outer envelope of the metamorphic core in the Kazdag Massif and also outcrop in other metamorphic massifs. of the region such as camhca, Karabiga and Karadag, 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 the metasedimentary rocks of the Kalabak Unit are in the range of 557-582 Ma. The crystallization age of the protolith for the metabasites, which has primary relationship to these metasedimentary rocks, is 577 Ma. In addition, protolith crystallization age of the eclogites, which are tectonic slices in these metasedimentary rocks, is 565 Ma. In addition to similar protolith ages, the fingerprint of a tectonothermal event at about 300-340 Ma is important in terms of expressing a common geological history for all samples. Formation environment and age of the metavolcanic rocks of the Kalabak Unit represent consistent and significant geotectonic environments. The Dedetepe Formation, which is at the bottom, represents a subduction melange, the Sazak Formation represents an active continental margin and the Torasan Formation represents a coeval sedimentary sequence. These geotectonic environments developed during the late Precambrian-early Paleozoic 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 younger periods, were affected by repetitive deformations which resulted in their present position.