Geochemical and Palaeontological Insights into Middle Triassic Intra-Pontide Ocean Island Fragments: Elmadağ Olistostrome, Central Anatolia

Abstract

The Late Cretaceous closure of the Neotethyan Intra-Pontide Ocean generated m & eacute;langes in front of southward-advancing nappes. These include the Elmadag Olistostrome, which consists of blocks embedded in a Coniacian (Upper Cretaceous) siliciclastic to calcareous-siliciclastic matrix. This olistostrome locally contains basaltic blocks alternating with platform lime-stones. Benthic foraminifera from these limestones yielded Anisian ages in two localities east/southeast of Ankara (Central Anatolia). At the Ta degreesönü locality, the Anisian to lower Ladinian basalt-limestone succession is overlain by an upper Ladinian sequence of volcanogenic clastic rocks, chert, and detrital limestone. At all localities, the basalts display alkaline composi-tions with typical OIB-like trace element signatures. High abundances of incompatible elements, coupled with high Nb/Zr, Zr/Y, and Nb/Y ratios, indicate a contribution from enriched/recycled components in their petrogenesis. Geological and geochemical evidence suggests that the basalt-limestone assemblage represents fragments of Anisian ocean islands in the Intra-Pontide Ocean. These islands were accreted to the southern Pontide margin during the late Ladinian. Following the clo-sure of the Intra-Pontide Ocean during the Late Cretaceous, the Elmadag Olistostrome was emplaced onto the Middle Trias-sic basement and the Jurassic-Cretaceous carbonate cover of the Sakarya Continent, as well as on the Izmir-Ankara-Erzincan ophiolitic m & eacute;lange.