Neotethyan Ankara Melange, central Turkey in its Triassic-Eocene regional tectonic setting including accretionary melanges, magmatic arcs and continental units

Abstract

The classic Neotethyan Ankara Melange formed within the Triassic-Eocene İzmir-Ankara-Erzincan ocean (‘N Neotethys’), bordered in central Anatolia by the Kırşehir and Tauride-Anatolide continental units to the south and by the discontinuous Sakarya continent to the northwest. Farther north, the separate Intra-Pontide ocean probably remained partly open until the early Cenozoic. The Neotethyan Ankara Melange developed via phases of intra-oceanic accretion (mainly pre-Aptian), initial continental accretion (i.e. Coniacian (?)), arc magmatism (Upper Cretaceous) and continent-continent collision (Maastrichtian-Early Eocene). Variably dismembered ophiolitic rocks of Early-Middle Jurassic age within the Ankara Melange formed by supra-subduction zone (SSZ) spreading above a generally northward-dipping subduction zone. Volcanic-sedimentary lithologies of Triassic-Cretaceous age represent fragments of oceanic crust including variably sized oceanic seamounts. The oceanic volcanics and sediments accreted from the downgoing plate, whereas the ophiolites represent fragments of the overriding plate. The main driver of accretion in the Ankara area was collision of a large Upper Jurassic-Lower Cretaceous oceanic seamount (probably plume related) and its capping carbonate platform, with Middle-Late Jurassic fore-arc oceanic lithosphere. Intra-oceanic arc and proximal-distal fore-arc basin units developed above the accretionary complex and within remnant Neotethyan ocean to the north during the Upper Cretaceous. After docking with the Sakarya continent, the Ankara Melange was transgressed by continental margin fore-arc and syn-collisional foreland basin sediments (Campanian-Early Eocene). Comparisons with Neotethyan melanges across Anatolia to the Caucasus indicate exceptional development in the type Ankara area.