Tunc, Ismail Onur2025-01-272025-01-2720241300-0985https://doi.org/10.55730/1300-0985.1914https://search.trdizin.gov.tr/tr/yayin/detay/1240164https://hdl.handle.net/20.500.12428/27521The pre-Liassic basement of the Biga Peninsula, located in the westernmost part of the Sakarya Zone, consists of metamorphic assemblages that were considered to represent different continental basements in the north and south, and the suture (ophiolitic/ melange) zone(s) between them. The cetmi melange, defined as between these continental fragments (the Kazdag Massif in the south and the camlica Massif in the north) was evaluated as a subduction accretionary melange of the Intra-Pontide Ocean and it was assumed that a suture passed through this part of the peninsula. This study was carried out on the most widely distributed outcrops of the cetmi melange(?) on the northwest flank of the Kazdag Massif. These units, which are named the orenli metamorphics, are represented by a succession of low-grade metamorphic volcanic-volcaniclastic rocks and alternating metasedimentary rocks and recrystallized limestones. The tectonostratigraphically lowermost levels of the orenli metamorphics are a blocky -chaotic assemblage, whereas the uppermost levels are a regular metavolcanic-metapelite succession, which passes upward into the Late Triassic recrystallized limestones, and is cut by very low-grade metamorphic diabase dykes of 165.81 +/- 1.55 Ma age. Furthermore, metavolcanic rocks of this succession show a calc-alkaline association of Basalt-Andesite-Dacite-Rhyolite (BADR) pattern in the chemical classification diagram, which is the signature volcanic rock suite of convergent margins. In addition, all the metavolcanic rock samples show a significant enrichment in terms of incompatible elements and LIL elements and negative Nb and Ti anomalies on the MORB normalized multielement spider diagram, which indicates that these rocks characterize high -K calc-alkaline volcanism at the active continental margins. Field relationships, zircon U-Pb geochronology, and geochemical data support that these units, outcropping in the study area, represent a Triassic active continental margin, most probably a fore -arc setting, related to the Paleo-Tethyan subduction, but not the subduction melange of the Intra-Pontide Ocean.eninfo:eu-repo/semantics/openAccessSakarya zoneBiga peninsulaNorthwest AnatoliaPaleo-Tethyan active continental marginorenli metamorphicsArticle33310.55730/1300-0985.1914N/AWOS:0011964217000052-s2.0-851903828191240164Q2