Role of Late Cretaceous volcanic-sedimentary melanges, specifically the Aladağ melange, E Turkey, in the rift-drift-subduction-accretion-emplacement history of the Tethyan Inner Tauride ocean

The Aladağ melange is located between Mesozoic Tauride carbonate platform units and the Late Cretaceous Pozantı-Karsantı ophiolite and its metamorphic sole. The melange comprises a lower, mainly sedimentary unit, composed of variably disrupted thrust sheets of deep-sea sediments, with a localized matrix of mass-flow and turbidity current deposits. The upper, volcanic-sedimentary melange comprises highly disrupted basalt-pelagic carbonate-radiolarite units, rarely associated with gravity-flow deposits. Tholeiitic to alkaline basalts in the melange range from N-MORB, to E-MORB and to OIB, and are dated as Middle Jurassic to Early Cretaceous using Radiolaria from interbedded pelagic sediments. Comparisons with accretionary melanges throughout southern Turkey and elsewhere indicate a similar geochemical pattern of variable ‘enrichment’, commonly coupled with a subduction influence (e.g. negative Nb, Ta anomalies). Geochemically, the subduction-influenced basalts are consistent with an oceanic island arc origin. However, the geological setting of Triassic basalts within some of the melanges (e.g. Mersin) is indicative of a rifted continental margin setting. The Mesozoic basalts within the Turkish melanges considered here erupted along the distal, outer northern margin of the Tauride continent, followed by Late Cretaceous subduction-accretion and supra-subduction zone ophiolite emplacement. Regional to global chemical comparisons suggest that the subduction influence could represent geochemical subduction inheritance rather than contemporaneous subduction.