FROM PERI-GONDWANA TO PRESENT DAY EUROPE: CRUSTAL EVOLUTION OF THE BALKAN AS A CASE STUDY FOR THE CONTINENT

The Balkan continental crust is mostly comprised of Cadomian/Avalonian terranes, that were involved in multiple orogenic events during the Phanerozoic. These terranes allow us to trace the crustal evolutionary history of Europe along the Ordovician (syn-Caledonian), Variscan and Alpine orogenies in a relatively small geographic area. We collected igneous rocks of various ages from the Serbo-Macedonian (SMM) and Rhodope massifs in Northern Greece, as well as sediments rich in heavy minerals from the mouths of the large rivers draining the terranes to the Aegean Sea (Strymon, Nestos and Evros Rivers). Zircon U-Pb ages from igneous rocks of the SMM and Rhodope portray the episodic crustal evolution of these terranes with phases of magmatism in the Neoproterozoic (598 Ma), Ordovician (460 Ma), Carboniferous (300 Ma), Triassic (250 Ma), Paleocene (65 Ma), and Miocene (ca. 23 Ma). Hf-in zircon shows the evolution of the igneous signature from negative εHf_(t) values in the Ordovician towards positive values in the Eocene, fitting the evolution trend of external ogorenic belts towards more juvenile values. In some contrast, zircons from the river sediments show the same episodic age peaks (with the addition of a 150 Ma Jurassic peak), while their εHf_(t) values indicate a crustal recycling trend bound by evolution lines of Hf-T_DM = 0.6-1.6 Ga. Rutiles in the river samples record mostly the final orogenic phase during Alpine orogeny (35 Ma), with only few grains preserving Triassic and Jurassic ages. This crustal evolutionary trend in the river zircons reflects, in our view, the ongoing recycling of the Cadomian/Avalonian basement of the SMM and Rhodope that served as the initial crustal ingredients, and few outcrops of it have survived. Some extent of crustal addition on this evolving Cadomian/Avalonian substrate brings about the shallow rise in εHf_(t) values we observe in the igneous basement rocks. We suggest that this mode of crustal evolution, involving the repeated reworking of Neoproterozoic peri-Gondwana crust alongside variable igneous mantle-like additions is the mode by which much of the European continental crust has evolved since the late Neoproterozoic.