Preliminary results of the radiolarian-chert hosted manganese deposit within the Vezirler ophiolitic mélange (Kula-Manisa, western Turkey): constraints on the origin, paleo-redox conditions, and depositional environments

In Turkey, Late Cretaceous ophiolitic complexes and mélange assemblages of the İzmir-Ankara-Erzincan Suture Zone, part of the northern branch of the Neotethys Ocean are rich in Mn-oxide deposits. These deposits are related to the red-violet radiolarian-chert blocks within the mélange units. Of these, the Vezirler Mélange, consisting of pelagic limestone, pillow basalt, radiolarite blocks, and highly altered serpentinite are distributed in the northern part of the Kula (Manisa) region, western Turkey. Here, the Mn-oxide deposit occurs as interlayers and, to a lesser degree in sharp contact with the radiolarian-chert-basalt-mudstone associations, and are highly folded and fractured. Based on XRD and petrographic studies, mineral paragenesis of the Mn-ores consists predominantly of braunite, pyrolusite, pysilomelane, quartz, and calcite. Geochemically, Mn-ores have high Ba (mean 10,854 ppm) and Sr (mean 4491 ppm) and low contents of Co (< 250 ppm), Zn (< 150 ppm), and Ni (< 500 ppm). High Mn/Fe (> 7) and low Co/Ni (< 1), Co/Zn (< 2), Y/Ho (< 41) ratios and low ΣREE (< 100) indicate that Kula Mn-ores formed in a submarine hydrothermal system. Redox-sensitive element ratios [V/(V + Ni) = 0.13–0.46, Ni/Co = 1.74–4.59)] and positive Mn*_sn (0.22–0.92) indicate that the Kula Mn-ores formed in an oxic depositional environment. Furthermore, a low La_n/Nd_n (1.19–3.04), La_sn/Nd_sn (< 1.36); moderate La_sn/Ce_sn and Al/(Al + Fe) ratios; weak negative Ce/Ce* anomaly (0.58); low Ce_anom values (< − 0.32); and high Sr concentrations (up to 20,178 ppm) indicate that the Kula manganese deposit formed in a high-salinity and oxygenated marine sedimentary environment with as part of a distal hydrothermal system. Radiolarians from different blocks within the Late Cretaceous mélange complexes hosting the Mn-oxide deposits along İzmir-Ankara-Erzincan Suture Zone in northern Turkey yielded a wide range of ages, Middle Triassic to Late Cretaceous. Hence, the Mn-oxides could have formed at any time during that interval, when oceanic crust was generated in different tectonic settings of the İzmir-Ankara Ocean. The ophiolite was then emplaced southward onto the Menderes Platform prior to the middle Eocene.