Abstract The Biga Peninsula in northwestern Turkey hosts a large number of high- and low-sulfidation epithermal gold-silver-(copper) and associated copper-gold porphyry deposits and prospects, associated with voluminous, Eocene-Miocene calc-alkaline volcanism and plutonism. In this area, 50 to 20 Ma intermediate to felsic volcanic and volcaniclastic strata overlie metamorphosed basement rocks of the Camlica Group. The volcanic sequence is variably altered over an area covering several hundreds of square kilometers, including argillic, advanced argillic, and massive to vuggy residual quartz alteration, the latter present at the tops of many of the higher elevation peaks in the area. Moderate- and high-angle normal and oblique faults are common in the area and influenced the distribution of mineralization. While gold mineralization associated with these high-sulfidation epithermal systems and flanking low-sulfidation epithermal systems has long been recognized, the existence of porphyry roots to these systems was not fully appreciated until the discovery of the Halilaga porphyry in 2008. In the southern part of the TV Tower property, low relief areas consist of schist and serpentinite intruded by the Kuşçayir pluton, a composite, ~40 Ma intrusion that averages granodiorite in composition. Intermediate volcanic and volcaniclastic rocks are exposed in the highest elevation areas. The northern edge of the pluton, at low to intermediate elevations, consists of at least six intrusions of similar age and composition that differ primarily in degree of porphyritic texture and phenocryst quartz content. The intrusions are parsed into pre- syn- and late mineralization phases with respect to hydrothermal alteration and mineralization related to at least two Au-Cu porphyry centers, Valley and Hilltop. The porphyry systems occur below and are to some degree overprinted by high-sulfidation alteration and mineralization. The porphyry/high-sulfidation system was subjected to weathering and oxidation, giving rise to a supergene copper enrichment blanket that lies near the transition from the high sulfidation into the porphyry environment. Alteration associated with the porphyry systems includes chlorite-magnetite-actinolite, K-feldspar-biotite-quartz-magnetite-hematite (“potassic”), and, at higher elevations, overprinting quartz-muscovite (“phyllic”) alteration. Quartz stockwork veining is ubiquitous in the phyllic and potassic assemblages, and includes quartz-K-feldspar “A” veins, quartz sulfide “B” veins, pyrite-quartz “D” veins, and quartz-magnetite “M” veins. Copper mineral assemblages range from bornite-chalcopyrite to chalcopyrite-pyrite, and chalcopyrite-chalcocite or chalcocite-covellite-digenite in the supergene zones. High-sulfidation epithermal mineralization is dominantly oxidized, and consists of residual vuggy and massive quartz, alunite, pyrophyllite, and iron oxides. New U-Pb dates for the Kuşçayir pluton and Hilltop and Valley intrusions range from 38 to 40 Ma, consistent with other Cu-Au porphyry systems in the region, whereas most dated high-sulfidation epithermal deposits in the region formed at roughly 29 Ma, coeval with an Oligocene suite of intrusions. It is possible that the epithermal-porphyry relationship at Karaayi is one of overprinting of two unrelated hydrothermal systems.

Abstract Epithermal Au-(Ag) and porphyry Cu-Au-(Mo) mineralization of the Biga Peninsula in northwestern Turkey occurs in a district comprised of NE- to ENE-trending metamorphic horst blocks separated by half-graben volcano-sedimentary basins. These developed as a result of rollback of the northward-subducting African slab during the Eocene, Oligocene, and Miocene. We propose that epithermal and porphyry systems occupy distinct, favorable positions within the overall extensional architecture and fault/fracture array. High- and low-sulfidation epithermal alteration systems, along with related quartz veins, preferentially occupy half-graben basins and border faults. These epithermal systems are found above a core complex detachment fault system, forming major strata-bound silicified zones fed by steeply dipping extensional faults and associated fractures above inferred intrusions. At greater depths and higher pressure and temperature conditions, porphyry-style alteration systems are spatially associated with porphyritic stocks that occur in close association with plutonic bodies. These plutons have intruded the footwall of ductile to brittle extensional faults and spatially and temporally link to metamorphic core complex exhumation. Episodic changes in the tectonic stress resulted in pulses of crustal extension that favored porphyry-type and high-sulfidation-style mineralization during mid to late stages of Eocene and Oligocene extensional tectonic phases. On the other hand, the early stages of each extensional phase promoted higher structural permeability, enabling the development of vein systems and low-sulfidation epithermal-style mineralization. Postemplacement crustal extension resulted in “domino-style” block rotations and half-graben formation throughout the Miocene and Pliocene. Since the early Pliocene, the westward propagation of the North Anatolian fault has resulted in dextral transtension in the Biga Peninsula and, as a result, postmineralization structural dismemberment of deposits and alteration systems is common.

Abstract The Aegean region experienced back-are extension related to the Hellenic subduction system at least from the latest Oligocene to the present. We document Tertiary extension-related kinematics in the north Aegean, in the eastern Rhodope–Thrace of Bulgaria–Greece and the Biga Peninsula of NW Turkey. A regionally consistent NNE–SSW- to NE–SW-oriented kinematic direction, delineated in both areas by stretching lineations and associated ductile–brittle shear fabrics in exhumed metamorphic domes beneath detachments, suggests that they were kinematically coupled during the Tertiary extension. This kinematic framework, combined with regional geochronological data and the stratigraphic record in hanging-wall supradetachment basins, defines an extensional history that includes syn- and post-orogenic episodes from Paleocene to Miocene times. Paleocene–early Eocene synorogenic extension in the Kemer micaschists of the northern Biga Peninsula and in the Kesebir–Kardamos dome in Rhodope–Thrace accommodated gravitationally induced hinterland-directed exhumation of the orogenic stack, coeval with the closure of the Vardar Ocean. Then, following collision within the region, it was succeeded by latest Oligocene–Early Miocene extension as recorded in the Kazdaǧ Massif in the southern Biga Peninsula, which overlaps the Aegean back-arc post-orogenic extension, widely recognized in the central Aegean and southern Greek Rhodope. The protracted record of extension is interpreted to reflect progressive exhumation of the orogenic wedge along the Eurasian plate margin. Southward migration of extension and magmatism across the study areas accounts for sequential shift and roll-back of the subduction boundary at that margin, from the latest Cretaceous in the Rhodope to its present position at the Hellenic trench. The results allow recognition of the investigated areas as an important extensional domain in the north Aegean region, which underwent Tertiary syn- and post-orogenic extension.

ABSTRACT The Intra-Pontide suture is the boundary between the İstanbul Zone and the Sakarya Continent in northwest Turkey. Our new paleontological and stratigraphic data show that the subduction of the Intra-Pontide Ocean was still going on between the late Cretaceous and the early Tertiary. This is in contrast to the recently reported Santonian closure of the Intra-Pontide Ocean. We have gathered much of the earlier published stratigraphic, paleontological, and radiogenic data on both the metamorphic units and the unmetamorphosed sedimentary basins along and near the Intra-Pontide suture. Our analysis shows two successive accretionary prisms were formed along the western and the central segments of the suture zone: (1) an Upper Cretaceous blueschist-eclogite facies metamorphic prism in the Biga Peninsula, and (2) an Upper Jurassic–Lower Cretaceous greenschist-epidote amphibolite facies metamorphic prism between the Armutlu Peninsula and Almacik Mountains. However, in the eastern third segment, Middle Jurassic and Middle to Upper Cretaceous high-pressure–low temperature (HP-LT) and low-pressure–low temperature (LP-LT) subduction-accretion complexes cover a large area, creating the Central Pontide Supercomplex. Between the late Cretaceous and late Paleocene, when the Rhodope-Pontide arc was evolving, an Upper Cretaceous–Paleocene forearc basin (the Kocaeli Basin) consisting of Upper Santonian–Campanian volcanogenics and overlying Upper Campanian–Selandian pelagic limestones also formed over the İstanbul Zone, which formed the hinterland. The paleontological data suggest that collision between the İstanbul Zone and the Sakarya Continent must have occurred later than the early Ypresian. An Upper Cuisian molasse covers all the older units, suggesting a possible medial Cuisian closure (ca. 51 Ma). This closure age can also be correlated with the similar, previously published fission-track uplift ages along the Intra-Pontide suture. Following the medial Cuisian closure of the Intra-Pontide Ocean, a wedge-shaped transtensional intramontane basin, the Thrace molasse basin, opened while the westerly escaping fragments of the Intra-Pontide suture tore off a piece of the Strandja system during the medial Eocene–Oligocene interval.