Abstract

Rapidly changing ore deposit types in the Late Cretaceous and early Tertiary in the Southeastern Anatolian orogenic belt in east-central Turkey, from Baskil on the south to Divrigi on the north, broadly reflect shifting tectonic environments in an evolving collisional orogen, a part of the extensive Tethyan orogen. Late Cretaceous (~83–79 Ma) subduction-related arc magmatism in the Baskil arc was followed by extension that exhumed the metamorphic basement, unroofed the obducted ophiolites, and filled basins with Maastrichtian to Paleocene subaerial and submarine sedimentary rocks. Calc-alkaline (Divrigi pluton, ~76–73 Ma) and alkaline igneous rocks (Hasançelebi and Keban districts, ~76–74 Ma) accompanied post-Baskil arc extension. In the early to middle Eocene, shallow and locally voluminous intrusions of intermediate composition (Çöpler, Kabatas, Bizmisen-Calti, Dedeyazi-Polat, Karamadazi, and Horoz), localized mainly along major strike-slip faults, formed during closure of the Neotethyan Ocean. These intrusions are dated between ~50 and 44 Ma, peaking at 48 Ma.

Geochemical data from a suite of igneous rock samples across the transect reflect temporally based changes from arc-type to late orogenic environments, as demonstrated by Late Cretaceous rocks in the Baskil area on the south and the more deeply eroded Late Cretaceous plutons in the Divrigi area on the north (Divrigi). These magmatic products were followed in the Eocene by calc-alkaline magmatism related to either incipient slab-rupture or crustal-scale faults that cut from northeast (Çöpler, Kabatas, Bizmisen-Calti, and Polat-Cavuslu) to southwest (Karamadazi and Horoz) obliquely across the transect. The multielement patterns for the Late Cretaceous magmatic rocks resemble the patterns for magmas generated in enriched source regions compared to primitive mantle and mid-oceanic-ridge basalt. Locally, at Divrigi-Hasançelebi and Keban, the geochemical characteristics are suggestive of the influx of low field strength elements into the mantle source regions from a subducted slab, and an arc to postcollisional to late-orogenic setting for their generation. Eocene magmatic rocks display similar geochemical characteristics regardless of the geographic setting and associated hydrothermal system. Their characteristics favor a subduction zone enrichment that was inherited either from an older event, or from an older slab, or from a mantle wedge contaminated by a contemporaneous subduction component.

40Ar/39Ar and U/Pb geochronology on biotite, zircon, K-feldspar, hornblende, and sericite from a suite of magmatic rocks and alteration zones defines three magmatic-related metallogenic events in the Southeastern Anatolian orogenic belt between 78 and 44 Ma. The oldest metallogenic event between ~78 to 74 Ma is related to arc-type calc-alkaline magmatic rocks (83–79 Ma) intruded into the Bitlis-Poturge and Malatya-Keban metamorphics and overlying Komurhan-Ispendere ophiolites of Tauride platform. Uneconomic porphyry-type Cu-Au systems formed at Topalkem-Baskil (Elazig) and Ispendere-Sisman (Malatya). A second metallogenic event, between ~74 and 69 Ma, is contemporaneous with postcollisional exhumation and extension-related magmatism. During this event, calc-alkaline followed by alkaline magmatism (76–73 Ma) was accompanied by formation of iron oxide copper-gold (IOCG) systems at ~74 to 73 Ma at Divrigi (Sivas). Alkaline magmatism at ~76 to 74 Ma is associated with IOCG systems at Hasancelebi (Malatya) and porphyry Cu-Mo and Pb-Zn veins at Keban (Elazig). The youngest metallogenic event between ~50 and 40 Ma is represented by porphyry Cu-Au deposits associated with calc-alkaline intrusive complexes at Çöpler and Kabatas and Fe skarns at Karamadazi, Horoz, Dedeyazi, and Bizmisen-Calti.

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