RHODOPE AND VARDAR - THE METAMORPHIC AND THE OLISTOSTROMIC PAIRED BELTS RELATED TO THE CRETACEOUS SUBDUCTION UNDER EUROPE

The Rhodope massif of Bulgaria and Greece is a complex of Mesozoic syn metamorphic nappes stacked in an Alpine active margin environment. A n ew analysis of the Triassic to Eocene history of the Vardar suture zon e in Greece discloses its Cretaceous setting as a subduction trench. W e present a geological traverse that takes into account these new obse rvations and runs from the Hellenides to the Balkans, i.e. from the Af rican to the Eurasian sides of the Tethys ocean, respectively. The pre sent review first defines the revisited limits of the Rhodope metamorp hic complex. In particular, the lower part of the Serbo-Macedonian mas sif is an extension of the Rhodope units to the west of the Struma riv er. Its upper part is separated as the Frolosh greenschist unit, which underlies tectonic slivers of Carpathic-Balkanic type. Several greens chist units, which locally yield Mesozoic fossils, follow the outer li mits of the Rhodope. Their former attribution to a stratigraphic cover of the Rhodope has been proven false. They are divided into roof gree nschists, which partly represent an extension of the Strandza Jurassic black shales basin, and western greenschists, which mostly derive fro m the Vardar Cretaceous olistostromic assemblage. The Rhodope complex of synmetamorphic nappes includes Continental Units and Mixed Units. T he Continental Units comprise quartzo-feld-spathic gneisses in additio n to thick marble layers. The Mixed Units comprise meta-ophiolites as large bodies or small knockers. They are imbricated, forming an open d ome whose lower, Continental Unit constitutes the Drama window. The up permost Mixed Unit is overlain by remnants of the European prate. The present-day structure results from combined large-scale thrust and exh umation tectonics. Regional inversions of synmetamorphic sense-of-shea r indicate that intermediate parts of the wedge moved upward and forwa rd with respect to both the lower and upper plates. A kinematic model is based on buoyancy-driven decoupling at depth between subducted cont inental crust and the subducting lithosphere. Continuing convergence a llows coeval underthrusting of continental crust at the footwall, deco upling at depth, and upward-forward expulsion of a low-density metamor phic wedge above. The continental crust input and its upward return ma y have lasted for at least the whole of the Early Cretaceous, as indic ated by isotopic ages and the deformation history of the upper plate. A Late Eocene marine transgression divides the ensuing structural and thermal evolution into a follow-up uplift stage and a renewed uplift s tage. Revision of the limits of the Vardar belt in Greece first result ed in separating the Paikon mountain as a tectonic window below the Va rdar nappes. It belongs to the western, Hellenic foreland into which a system of thrust developed downward between 60 and 40 Ma. The eastern limit is a dextral strike-slip fault zone that developed greenschist facies foliations locally dated at 50-40 Ma. Revision of the lithologi cal components discloses the preponderance of Cretaceous volcano-detri tic and olistostromic sequences that include meta-morphite blocks of R hodope origin. Rock units that belong to the Vardar proper (ophiolites , Triassic and Jurassic radiolarites, remnants of an eastern Triassic passive margin) attest for a purely oceanic basin. The Guevgueli arc d ocuments the Jurassic change of the eastern Triassic passive margin in to an active one. This arc magmatic activity ended in the Late Jurassi c and plate convergence was transferred farther northeast to the subdu ction boundary along which the Rhodope metamorphic complex formed. We interpret the Rhodope and the Vardar as paired elements of a Cretaceou s accretionary wedge. They document the tectonic process that exhumed metamorphic material from under the upper plate, and the tectonic-sedi mentary process that fed the trench on the lower plate. The history of the Rhodope-Vardar pair is placed in the light of the history of the Tethys ocean between Africa and Europe. The Cretaceous subduction then appears as the forerunner of the present Hellenic subduction, account ing for several shifts at the expense of the lower plate. The Late Eoc ene shift, at the closure of the Pindos basin, is coeval with the init iation of new uplift and magmatism in the Rhodope, which probably docu ment the final release of the low-density, continental root of the Rho dope from subduction drag.