Foreland Magmatism during the Arabia–Eurasia Collision: Pliocene–Quaternary Activity of the Karacadağ Volcanic Complex, SW Turkey

Abstract

Pliocene to Quaternary magmatism in the Karacadag Volcanic Complex in SE Turkey occurred in the foreland region of the Arabia–Eurasia collision and can be divided into two phases. The earlier Karacadag phase formed a north–south-trending volcanic ridge that erupted three groups of lavas. The same range of mantle sources contributed to the younger Ovabag phase lavas, which were erupted from monogenetic cones to the east of the Karacadag fissure. As at several other intraplate localities across the northern Arabian Plate this magmatism represents mixtures of melt from shallow, isotopically enriched mantle and from deeper, more depleted mantle. The deep source is similar to the depleted mantle invoked for other northern Arabian intraplate volcanic fields but at Karacadag this source contained phlogopite. This source could be located in the shallow convecting mantle or may represent a metasomatic layer in the base of the lithosphere. There is no evidence for a contribution from the Afar mantle plume, as has been proposed elsewhere in northern Arabia. Melting during the Karacadag and Ovabag phases could have resulted from a combination of upwelling beneath weak or thinned lithosphere and restricted local extension of that weakened lithosphere as it collided with Eurasia. Tension associated with the collision focused magma of the Karacadag phase into the elongate shield volcano of Mt. Karacadag. The northern end of the fissure accommodated more extensive differentiation of magma, with isolated cases of crustal contamination, consistent with greater stress in the lithosphere closest to the collision. Most magma batches of the Karacadag and Ovabag phases differentiated by fractional crystallization at ∼5 MPa, near the boundary between the upper and lower crust. Magma batches dominated by melt from garnet lherzolite show evidence for restricted amounts of differentiation at ∼22·5 MPa, which is close to the base of the lithospheric mantle.