Late Cenozoic extension of the Alpine collisional orogen, northeastern Greece: Origin of the north Aegean basin

Abstract

The Rhodope metamorphic core complex, exposed beneath the Strymon Valley detachment in northeastern Greece, comprises a platform carbonate sequence >5000 m thick intruded by Tertiary calc-alkaline plutons. The final thickening of the north Aegean Alpine collisional orogen in Paleogene time and its Neogene-Quaternary extensional dismemberment in the backarc of the Hellenic subduction zone produced structures within and above the Rhodope core complex that are related here to four successive deformations. In early–middle Eocene time (D1), the Falakron marble series was subducted northeastward beneath the Serbo-Macedonian–West Thracian gneiss complex, a heterogeneous ophiolite-bearing high-grade metamorphic terrane that was accreted to southeastern Europe in Cretaceous time. The orogen began to extend on a northeast-southwest axis in earliest Miocene time, evidenced in the Rhodope core complex by the emplacement of the Symvolon granodiorite ca. 21 Ma within a northwest-trending midcrustal coaxial rupture of the Falakron slab (D2). The Strymon Valley detachment system succeeded the D2 Symvolon rupture and related structures, facilitating unroofing of the core complex and a transition from ductile to brittle deformation ca. 16–3.5 Ma (D3). The Serbo-Macedonian gneiss complex, the island of Thasos, and a supradetachment basin were translated relatively southwestward as much as 80 km in the D3 hanging wall. Balanced reconstructions of D2 and D3 displacements predicate two new hypotheses concerning the Cenozoic tectonic evolution of northeastern Greece. First, the southwest-vergent Thasos detachment and northeast-vergent low-angle normal faults in the Olympos region may both have rooted in the coaxial Symvolon rupture zone to form a bivergent early Miocene extensional system. Second, the Olympos and Falakron carbonate platforms may be correlative remnants of the subducted eastern margin of the Apulian microcontinent, implying that the “Vardar zone,” the putative Alpine suture, is a rootless ophiolite belt, and that segments of the Alpine suture are actually exposed over a zone as wide as 200 km, including the Rhodope province. Cumulative D2 and D3 stretching of greater than or equal to 100% created the north Aegean basin. The North Anatolian fault, which accommodates the westward escape of Anatolia from the Pontide suture, propagated into the north Aegean region in late Pliocene time. Its offshore continuation, the North Aegean Trough, transfers dextral strike-slip displacement into extension to the north, principally expressed in northern Greece by the Thermaikos, Strymon, and Drama half grabens (D4).