ABSTRACT The Bursa mineral district in northwest Anatolia (Turkey) is an emerging prospective area for porphyry Cu-Mo (Au-Re) mineralization along the Western Tethyan Eocene magmatic belt that links the Balkan to Lesser Caucasus regions along the southern Black Sea coast. Field observations as well as time constraints on mineralized magmas of the Bursa district are limited. Additionally, the tectonic setting of Eocene magmatism in northwest Turkey is controversial and includes either Neotethyan slab roll-back or break-off scenario. We show that the Bursa mineral district consists of porphyry Cu-Mo, skarn Cu, and rare epithermal Au-Ag deposits, prospects, and occurrences on the footwall of the Eskişehir fault, south of the İzmir-Ankara-Erzincan suture zone. The porphyry prospects are hosted within porphyritic dioritic, granodioritic, and granitic rocks that were altered by potassic and phyllic assemblages and quartz-sulfide vein stockwork zones. Our new CA-TIMS and LA-ICP-MS U-Pb and 40 Ar/ 39 Ar ages indicate that porphyry mineralization of the Bursa district formed between 51 and 46 Ma and thus before the porphyry and epithermal Cu-Au mineralization of the Biga (~43–39 Ma) and Rhodope districts (~35–31 Ma) and the Serbo-Macedonian belt (~36–22 Ma). Therefore, we interpret that Eocene magmatism and associated Cu-Au-Mo mineralization migrated westward along the western part of the Western Tethyan Eocene magmatic belt. This migration, which is specific to the Eocene period, represents a second-order and diachronous response to the first-order southward magmatic front migration and roll-back initiation of the Hellenic slab beneath the Balkan-Aegean-western Anatolian region since the Late Cretaceous.

The volcanic basement of the Ecuadorian Western Cordillera (Pallatanga Formation and San Juan unit) is made up of mafic and ultramafic rocks that once formed an oceanic plateau. Radiometric ages from these rocks overlap with a hornblende 40 Ar/ 39 Ar plateau age of 88 ± 1.6 Ma obtained for oceanic plateau basement rocks of the Piñon Formation in coastal Ecuador, and with ca. 92–88 Ma ages reported for oceanic plateau sequences in the Caribbean and western Colombia. These results suggest that the oceanic plateau rocks of the Western Cordillera and flat forearc in Ecuador are derived from the Late Cretaceous Caribbean-Colombia oceanic plateau. Intraoceanic island-arc sequences (Rio Cala Group) overlie the plateau in the Western Cordillera and yield crystallization ages that range between ca. 85 and 72 Ma. The geochemistry and radiometric ages of island-arc lavas from the Rio Cala Group, combined with the age range and geochemistry of their turbiditic, volcaniclastic products, indicate that the arc was initiated by westward subduction beneath the Caribbean Plateau. They are coeval with island-arc rocks of coastal Ecuador (Las Orquideas, San Lorenzo, and Cayo Formations) and Colombia (Ricaurte Arc). These island-arc units may be related to the Late Cretaceous Great Arc of the Caribbean. Paleomagnetic analyses of volcanic rocks of the Piñon and San Lorenzo Formations of the southern external forearc show that they erupted at equatorial or low southern latitudes. The initial collision between South America and the Caribbean-Colombia oceanic plateau caused rock uplift and exhumation (>1 km/m.y.) within the continental margin during the Late Cretaceous (ca. 75–65 Ma). Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc ceased during the Maastrichtian because the collision event blocked the subduction zone below the oceanic plateau. Paleomagnetic data from basement and sedimentary cover rocks in the coastal forearc reveal 20°–50° of clockwise rotation during the Campanian, which was synchronous with the collision of the oceanic plateau and arc sequence with South America. East-dipping subduction beneath the accreted oceanic plateau formed the latest Maastrichtian to early Paleogene (ca. 60 Ma) Silante volcanic arc, which was deposited in a terrestrial environment. Subsequently, Paleocene to Eocene volcanic rocks of the Macuchi unit were deposited, and these probably represent a continuation of the Silante arc. This submarine volcanism was coeval with the deposition of siliciclastic rocks of the Angamarca Group, which were mainly derived from the emerging Eastern Cordillera.