On the Rhodopean protoliths and their Middle Jurassic to Early Cretaceous evolution. A review

Abstract

The Rhodope Massif represents a large high-grade metamorphic complex situated in the Balkan Peninsula, straddling the border between Bulgaria and Greece. Geological studies carried out during the last thirty years clearly established that the complex is composed of three major lithotectonic units characterized by differing protolith ages and Alpine thermotectonic evolution. The Rhodope Massif consists of Upper and Lower terranes representing continental fragments composed mainly of pre-Mesozoic magmatic rocks and covered by Early Mesozoic sedimentary sequences. These two entities are separated by an Intermediate Terrane comprising a Jurassic magmatic arc and its host rocks tectonically intercalated with Jurassic ophiolitic fragments together with the Early Mesozoic sediments. Detailed analyses of the previously published geochronological data revealed that the three main tectonic terranes were juxtaposed in the Late Jurassic–Early Cretaceous during the continental collision and northward subduction of the Lower and Intermediate terranes. These rocks experienced Middle Jurassic to Early Cretaceous high-pressure metamorphism, followed by high-temperature one accompanied by anatexis. At that time, the Upper Terrane was metamorphosed and deformed only partially. Being part of the European margin, this terrane represented an upper continental plate during the subduction, and therefore is not considered as a part of the Alpine Rhodope metamorphic complex. It is important to note that, although most of the present-day fabric and major tectonic zones in the Rhodope metamorphic complex are younger than Early Cretaceous, and therefore they postdate the geological evolution discussed in this study, they often reactivate the old boundaries between the main terranes and units.