Abstract The Serbo-Macedonian Massif (SMM) is a large, elongate basement complex in the Internal Hellenides, which stretches from Serbia to the Chalkidiki Peninsula in northern Greece. As a result of similarities in lithology and structural grain, the SMM has long been considered part of the adjacent Rhodope Massif. Recent work, however, based on precise geochronological and geochemical data, has revealed that the SMM is not a homogeneous crustal entity but made up of several crustal units, only one of which is related to the Rhodope Massif. One of these units, the Pirgadikia Unit, occurs as a tectonic sliver in a mélange zone bordering the western margin of the SMM that separates it from the adjacent Vardar Zone. The Pirgadikia Unit consists of leucocratic mylonitic para- and orthogneisses. According to trace-element and Sr-isotope data, the orthogneisses originated in a magmatic arc setting. Dating of this unit by the Pb–Pb single-zircon evaporation method yielded Pan-African ages of 555.8 ± 2.6 Ma on a paragneiss collected near the village of Taxiarchis, and two ages of 570.0 ± 7.0 Ma and 587.6 ± 3.4 Ma on orthogneisses from the quayside at Pirgadikia village. The rocks enveloping this Late Precambrian basement complex are gneisses of the Vertiskos Unit. This unit, which is regarded as a distinct terrane, occupies the northwestern part of the Greek SMM and consists of Silurian orthogneisses with a magmatic arc signature and subordinate metasediments. Orthogneisses of the Vertiskos Unit adjacent to the mylonites of the Pirgadikia Unit gave Pb–Pb ages of between 428.2 ± 1.2 Ma and 433.0 ± 2.1 Ma. One of these samples was additionally dated by the conventional U–Pb method. This sample has three concordant zircon grains confirming a Silurian intrusion age and two inherited cores pointing to an older basement into which precursor rocks to the Silurian gneisses were intruded. The upper intercept of a Concordia plot yielded an age of c. 2.5 Ga, which is a common age in the cratons of Gondwana. The Pan-African age of the Pirgadikia Unit and the inherited ages of the Vertiskos Unit support the notion that these units are terranes derived from Gondwana. They were finally accreted to the Hellenic orogen during the closure of one of the branches of the Tethys Ocean. The presence of exotic terranes in the Internal Hellenides contradicts the hypothesis that this part of the Hellenides formed a stable hinterland during the Alpine phase and thus the Hellenides can be considered an accretionary orogen.

The Hellenides constitute an integral part of the Alpine orogenic system in southeast Europe. Despite the recognition of several subparallel zones, which are interpreted as terranes separated by ophiolitic sutures (e.g., Pindos and Vardar sutures), the classical view of an orogen with a foreland fold-and-thrust belt, a central crystalline zone, and a rather undeformed hinterland is still under discussion. This paper concentrates on basement terranes of exotic provenance in two of the internal zones of the Hellenides that support the interpretation of the Hellenides as an accretionary orogen formed by amalgamation of crustal segments during the subduction of Tethyan oceanic basins. The oldest of these terranes, the Florina terrane in the Pelagonian zone, is composed of Neoproterozoic arc-related orthogneisses. Two other exotic terranes occur east of the Vardar zone within the Serbo-Macedonian Massif. The Pirgadikia terrane is a microterrane in the southern Chalkidiki Peninsula that consists of Pan-African mylonitic orthogneisses with volcanic arc–related trace-element geochemistry and Sr isotopic composition. The Vertiskos terrane occupies the northwestern part of the Serbo-Macedonian Massif and is primarily composed of coarse-grained, volcanic arc–related peraluminous orthogneisses of Silurian age. These terranes are exotic in relation to the other parts of the Hellenides. The provenance of the late Proterozoic Pan-African Florina and Pirgadikia terranes is assumed to be Gondwanan, whereas the Silurian Vertiskos terrane may have been part of the so-called Hun ter-rane, which formed at the northern active continental margin of Gondwana in the early Paleozoic.

Abstract The Kassandra mining district in the eastern Chalkidiki Peninsula of northern Greece contains ~12 Moz Au in porphyry and polymetallic carbonate-hosted replacement sulfide orebodies. Zircon U-Pb geochronology defines two distinct magmatic episodes in the late Oligocene (27-25 Ma) and early Miocene (20-19 Ma). Both suites are characterized by high K calc-alkaline magmas with the younger early Miocene porphyritic stocks and dikes having indications of shoshonitic geochemistry. Normalized rare earth element patterns support plagio-clase fractionation among the late Oligocene suite, whereas amphibole or garnet fractionation is more likely for early Miocene porphyries. Carbonate replacement mineralization is hosted in marble contained within the semibrittle Stratoni fault zone. Mineralization varies along the 12-km strike length of the fault zone from Cu-bearing skarn adjacent to the late Oligocene Stratoni granodiorite stock westward into Au-Ag-Pb-Zn-Cu carbonate replacement deposits at Madem Lakkos and Mavres Petres. Piavitsa, at the western end of the exposed fault zone, hosts siliceous Mn-rich replacement bodies associated with crustiform Au-rich quartz-rhodochrosite veins. Structural and alteration relationships suggest that carbonate replacement mineralization is syn- to postemplacement of the late Oligocene Stratoni granodiorite stock at 25.4 ± 0.2 Ma. The Olympias Au-Ag-Pb-Zn carbonate replacement deposit, located north of the Stratoni fault zone, is hosted in marble and associated semibrittle structures. Olympias is broadly similar to the Madem Lakkos and Mavres Petres deposits. Early Miocene Au-Cu mineralization at Skouries is associated with a narrow pipe-shaped multiphase porphyry stock emplaced into the hinge zone of a regional antiform. Late Oligocene and early Miocene magmatism overlaps spatially within the district but defines distinct petrogenetic events separated by about 5 m.y. Carbonate replacement massive sulfide deposition was largely controlled by an extensional structure and receptive host rocks within the fault zone, whereas a major regional fold axis localized the Skouries porphyry system. The change in character of mineralization with time may reflect a combination of factors including preexisting structural control, magmatic-hydrothermal processes, and the availability of reactive host rocks.