The relationship between late-orogenic extension and hydrothermal ore formation: New age constraints from the Central Rhodopes, south Bulgaria

ISSN:0016-7037ISSN:1872-953

Fluid circulation related to post-messinian extension, Thassos Island, North Aegean

International audienceIn the North Aegean Domain, Thassos Island contains a Plio-Pleistocene basin controlled by a large-scale flat-ramp extensional system with a potential décollement located at depth within a marble unit. Numerous mineralizations associated with normal faults of Plio-Pleistocene age are the sign of fluid circulation during extension. Two main generations of fluid flow are recognized, related to Plio-Pleistocene extension. A first circulation under high-temperature conditions (about 100­200°C) resulted in dolomitization of marbles near the base of the Plio-Pleistocene basin. The dolomites are characterized by low d18O values (down to 11 versus Standard Mean Ocean Water). Some cataclastic deformation affected the dolomites. Hydrothermal quartz that crystallized in extension veins above a blind ramp also has low d18O values (about 13). This shows that high-temperature fluids moved up from the décollement level toward the surface. A second downward circulation of continental waters at near-surface temperature is documented by calcite veins in fault zones and at the base of the Plio-Pleistocene basin. These veins have O isotope values relatively constant at about 23­25 and C isotope values intermediate between the high d13C value of the carbonate host rock (about 1­3 versus Peedee Belemnite) and the low d13C value of soil-derived carbon (-10). The calcites associated with the oxidative remobilization of primary sulphide Zn­Pb mineralization of Thassos carbonates have comparable O and C isotope compositions. Hot fluids, within the 100­200°C temperature range, have likely contributed to the weakening of the lower marble unit of Thassos and, thus, to the process of décollement

Pre-Alpine evolution of a segment of the North-Gondwanan margin: Geochronological and geochemical evidence from the central Serbo-Macedonian Massif

The Serbo-Macedonian Massif (SMM) represents a composite crystalline belt within the Eastern European Alpine orogen, outcropping from the Pannonian basin in the north, to the Aegean Sea in the south. The central parts of the massif (i.e. southeastern Serbia, southwestern Bulgaria, eastern Macedonia) consist of the medium- to high-grade Lower Complex, and the low-grade Vlasina Unit. New results of U–Pb LA-ICP-MS analyses, coupled with geochemical analyses of Hf isotopes on magmatic and detrital zircons, and main and trace element concentrations in whole-rock samples suggest that the central SMM and the basement of the adjacent units (i.e. Eastern Veles series and Struma Unit) originated in the central parts of the northern margin of Gondwana. These data provided a basis for a revised tectonic model of the evolution of the SMM from the late Ediacaran to the Early Triassic. The earliest magmatism in the Lower Complex, Vlasina Unit and the basement of Struma Unit is related to the activity along the late Cadomian magmatic arc (562–522 Ma). Subsequent stage of early Palaeozoic igneous activity is associated with the reactivation of subduction below the Lower Complex and the Eastern Veles series during the Early Ordovician (490–478 Ma), emplacement of mafic dykes in the Lower Complex due to aborted rifting in the Middle Ordovician (472–456 Ma), and felsic within-plate magmatism in the early Silurian (439 ± 2 Ma). The third magmatic stage is represented by Carboniferous late to post-collisional granites (328– 304 Ma). These granites intrude the gneisses of the Lower Complex, in which the youngest deformed igneous rocks are of early Silurian age, thus constraining the high-strain deformation and peak metamorphism to the Variscan orogeny. The Permian–Triassic (255–253 Ma) stage of late- to post-collisional and within-plate felsic magmatism is related to the opening of the Mesozoic Tethys