THE PALEOZOIC VOLCANO-PLUTONIC ASSOCIATION OF NORTH DOBROGEA, ROMANIA: A REMNANT OF A CONTINENTAL MARGIN MAGMATIC ARC IN THE VARISCAN BELT OF EUROPE

Part of the Variscan belt fringing the southern margin of the East European Craton, the pre-Triassic basement of the North Dobrogea, Romania, is inferred to comprise telescoped fragments of an accretionary wedge and parts of a continental margin magmatic arc, with an associated retro-arc foreland basin. The Palaeozoic basement of the North Dobrogea is thought to have evolved from an Early Devonian passive margin setting to a Late Devonian-Early Carboniferous Andean type system, that continued subducting until collision in the Early Permian, with a general subduction direction to the S-SW. In the Late Permian, rifting accompanied by alkali volcanism is explained as a consequence of the extensional collapse of the Variscan orogen, overthickenned by thrusting and granite intrusion. During Late Devonian - Middle Carboniferous, partial melting of the upper crust in North Dobrogea is followed by emplacement of important S type granitic plutons. Since Late Carboniferous, continuous subduction with high convergence rates resulted in partial melting of the upper mantle, as well as in backarc compression and initiation of a southward propagating imbricate thrust system. Accumulated in piggyback basins on top of the thrust system, Late Carboniferous - Early Permian syntectonic continental sediments record evolution from terrigenous fanglomerates to fluvial red beds, topped by a volcano-sedimentary succession representing products of a calc-alkaline, rhyolitic volcanism. This subaerial, dominantly explosive acid volcanism emplaced large amounts of pyroclastic flows and minor air-fall tuffs. Small plutons ranging from gabbros and diorites to tonalities and granites, emplaced in the Palaeozoic formations of western North Dobrogea as shallow, I-type intrusives with cross-cutting contacts, are interpreted as the exhumed roots of the Variscan volcano-plutonic arc. The transition from the Early Permian syn-collisional calc-alkaline magmatism to the Late Permian alkaline magmatism reflects the changing stress regime from compression to transtension and was explained as result of slab roll-back. A comparison with the tectonic evolution of the Western European Variscides and the Uralides is presented.