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

Abstract

In Turkey, Late Cretaceous ophiolitic complexes and melange assemblages of the Izmir-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 melange units. Of these, the Vezirler Melange, 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 ( 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 Lan/Ndn (1.19–3.04), Lasn/Ndsn (< 1.36); moderate Lasn/Cesn and Al/(Al + Fe) ratios; weak negative Ce/Ce* anomaly (0.58); low Ceanom 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 melange complexes hosting the Mn-oxide deposits along Izmir-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 Izmir-Ankara Ocean. The ophiolite was then emplaced southward onto the Menderes Platform prior to the middle Eocene.