Processes of clastic sedimentation associated with Late Cretaceous ophiolite emplacement in the SW segment of the Antalya Complex (S Turkey)

Abstract

Clastic sediments provide important clues to the timing and processes of ophiolite emplacement, when integrated into the regional temporal and tectonic framework. Four related settings of Late Cretaceous ophiolite-related clastic sediment deposition are exposed in the SW segment of the Antalya Complex, along the western limb of the Isparta Angle, an orocline in SW Turkey. The restored pre-emplacement paleogeography is indicative of a regional-scale Mesozoic carbonate platform, bordered to the east by a Late Triassic volcanic rift that partially infilled with deep-sea sediments, passing eastwards into several Mesozoic carbonate platforms (floored by pre-rift or syn-rift crust) and finally into the South Neotethys. First, emplacement-related sediments unconformably overlie exhumed ultramafic and gabbroic ophiolitic rocks and comprise locally variable mass-flow deposits (up to several-hundred m thick) that are dominated by subaqueous screes and debris-flow deposits. Fossil evidence (benthic and planktic foraminifera, radiolarians and macrofossils) indicates accumulation during the Campanian-Maastrichtian. Much of the coarse talus was derived from weathering and erosion of intrusive ophiolitic rocks (sheeted dykes, gabbro). Petrographic, XRD and whole-rock geochemical analysis of sandstones and igneous clasts indicate additional derivation from basaltic rocks, interpreted as the eroded extrusive layer of the ophiolite. Additional material was derived from Late Triassic-Cretaceous deep-water volcanics and sediments, and also from Late Cretaceous (and older) platform carbonates. The coarse clastics relate to ophiolite emplacement onto the continental margin, rather than forming in an oceanic setting (e.g., rifted ridge or oceanic fracture zone). The emplacement was associated with crustal extension that exposed ultramafic and gabbroic rocks on the seafloor, where they were covered by clastic debris. Secondly, Late Cretaceous calciturbidites and debris-flow deposits depositionally overlie Late Triassic-Late Cretaceous deep-water passive margin sediments. The clastic debris was derived from the emplacing ophiolite and from an adjacent Mesozoic carbonate platform. Thirdly, calciturbidites and debris-flow deposits also depositionally overlie the same carbonate platform. Fourthly, west of the same carbonate platform, ophiolite-derived mass-flow breccias accumulated locally and were then interleaved with previously emplaced ophiolitic plutonic rocks (mainly serpentinite and gabbro), typically at high angles. The four depositional settings relate to ongoing stages of Late Cretaceous ophiolite emplacement in a setting dominated by regional-scale thrusting and strike-slip (i.e., transpression). The latest Cretaceous deformation and related clastic deposition affected part of the northern, active continental margin of the Southern Neotethys, but without reaching more inboard continental crust (regional Tauride platform), a situation that contrasts with more orthogonally emplaced ophiolites.