Palaeozoic-Early Tertiary Tethyan Evolution of Mélanges, Rift and Passive Margin Units in the Karaburun Peninsula (western Turkey) and Chios Island (Greece)
Authors: Robertson Alastair H. F. , Pickett Elizabeth A. 
Published: April 2008

Abstract

Similar Palaeozoic-Lower Tertiary units in the northern Karaburun Peninsula (western Turkey) and the adjacent island of Chios (Greece) provide insights into the tectonic evolution of the Tethyan Ocean near the junction between the Taurides/Anatolides and Hellenides. The northwest Karaburun Peninsula is dominated by a highly sheared mélange (
c.
τ 2 km thick) with Silurian-Carboniferous blocks (up to hundreds of metres in size) of neritic and pelagic limestone, black ribbon chert, shale, extrusives and volcanogenic sediments. The blocks are set in a matrix of siliciclastic turbidites, pelagic carbonates and channelized conglomerates. Northern Chios is similarly composed of mélange (
c.
3–4 km thick) with limestone blocks dated as Silurian-Carboniferous, black ribbon chert, shale and volcanics within predominantly siliciclastic sediments, including local conglomerates.

Both mélanges are unconformably overlain by Lower Triassic basinal successions (with sheared basal contacts), including terrigenous clastics, pelagic carbonate, radiolarite, lava and volcanogenic sediments, interpreted as rift successions. In both areas, successions shallow upwards into extensive Mesozoic carbonate platform facies, similar to those widely developed in the Taurides and Hellenides. On the Karaburun Peninsula, deposition was punctuated by emergence and localized deltaic siliciclastic deposition in latest Triassic-earliest Jurassic time. The Karaburun carbonate platform later emerged, eroded, then subsided in Campanian-Maastrichtian time; it then collapsed in the Maastrichtian-earliest Tertiary and was overlain by another mélange (Bornova Mélange), with blocks of both local platform-derived and accreted Mesozoic oceanic lithologies, and was finally thrust imbricated during continental collision. On Chios, a Lower Jurassic carbonate platform succession is overthrust by an exotic Carboniferous-Lower Jurassic mixed shallow-water carbonate and siliciclastic unit.
Most tectonic hypotheses for the mélange are problematic. They include formation as Palaeozoic basinal ‘olistostromes’, as an ideal Late Palaeozoic subduction-accretion complex basin, as an Early Triassic rift, or as entirely tectonic mélange. The mélange are seen here as the end-product of a combination of Late Palaeozoic southward(?) subduction-accretion (culminating in trench-microcontinent collision?), Early Triassic rifting and latest Cretaceous-Early Tertiary subduction/collision. Regional comparisons suggest that initial mélange formation took place in Late Carboniferous-Early Permian time. Subsequent Early Triassic rifting was associated with siliciclastic, calcareous and radiolarian deposition, and andesitic volcanism. The Triassic rift was overlain by a subsiding passive margin adjacent to a northerly Neotethyan oceanic basin from Middle Triassic-Late Cretaceous. This ocean closed in the Late Cretaceous-Early Tertiary, resulting in collapse of the passive margin, subduction-accretion and further mélange formation in a foredeep. Continental collision resulted in further deformation of the Palaeozoic mélange, thrust imbrication of the Mesozoic platform and shearing at its base.