Abstract

An ophiolitic suture zone and associated active continental margin sequences of mid-Jurassic age are found in northern Turkey exposed in inliers surrounded by an extensive Upper Cretaceous to Eocene volcanic blanket. The pre–Late Jurassic rocks of the eastern Black Sea Mountains (eastern Pontide tectonic zone) consist of two distinct lithologic associations: a “continental” assemblage represents a Permian to Early Jurassic north-facing magmatic arc, whereas an “oceanic” assemblage, including a locally metamorphosed ophiolite suite overlain by deep-sea sediments, is believed to represent the vestiges of an oceanic realm that existed north of the arc during the ?Permian to Jurassic interval. During the mid-Jurassic, the oceanic assemblage underwent penetrative deformation and was overthrust by the continental assemblage. The latter has not been penetratively deformed except for a wide zone of intense cataclasis along its basal thrust. The southern part of the continental assemblage was affected by east-west gravity faulting and basaltic and some trachytic volcanism during the Early Jurassic. We interpret the Permian to mid-Jurassic geological record of the eastern Pontides as the expression of the progressive contraction of a Permian-Jurassic ocean with a south-dipping subduction zone. Its closure resulted in the overthrusting of the continental assemblage onto the oceanic assemblage. Regional considerations suggest that the suture forms a part of an orogenic belt stretching from the mid-Jurassic South Rhodope Orogen through the early to mid-Mesozoic orogenic zones of the peri-Black Sea regions, northern Iran, Afghanistan, central Tibet, and China. This orogenic belt resulted from the closure of Permian-Triassic Paleo-Tethys. The oceanic assemblage we describe is believed to be a part of the floor of this ocean, whereas the continental assemblage is viewed as a part of a previously defined Cimmerian continent.

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