Crustal evolution of peri-Gondwana crust into present day Europe: The Serbo-Macedonian and Rhodope massifs as a case study

Abstract

The continental crust of Europe west of the Trans-European Suture Zone (TESZ), is mostly a collage of Peri-Gondwana Cadomian and Avalonian terranes that were formed on the late Neoproterozoic active margins of the supercontinent, rifted from it during consecutive opening of oceanic basins, and variably involved in Ordovician, Carboniferous (Variscan), and Cretaceous-Eocene (Alpine) orogenies. While in many localities it is possible to study isolated portions of the European geologic history, few sites can hold evidence for the entire record in a relatively small area. The Balkan terranes of the Serbo-Macedonian (SMM) and the Rhodope massifs, which contain Neoproterozoic Cadomian remnant basement, and were involved in multiple Phanerozoic phases of magmatism and metamorphism, provide an ideal locality in which we can study the entire crustal evolutionary history of Europe (west of the TESZ). Here we present new zircon U-Pb-Hf and rutile UPb data from basement rocks of the SMM and Rhodope as well as of beach placers from mouths of the large rivers draining the Balkan towards the Aegean Sea (Strymon, Nestos and Evros Rivers). Basement igneous rocks of the SMM and Circum-Rhodope were dated to the late Neoproterozoic (588 Ma), middle Ordovician (ca. 460 Ma), Carboniferous (300 Ma), Permo-Triassic (254 Ma), Paleocene (65 Ma) and Miocene (ca. 23 Ma), demonstrating the episodic nature of crustal evolution in this terrane assemblage. Hf-in zircon shows these intrusions evolve from negative εHf(t) values in the Ordovician towards positive values in the Paleocene. Zircons in beach placer samples also show distinct age peaks that follow the pulses of igneous activity in the source terranes, with the addition of Jurassic (ca. 150 Ma) zircons. The UPb system in rutiles from the beach placer samples was mostly reset, and records the final metamorphic phase during Alpine orogeny (35 Ma), with some rutiles preserving Eo-Alpine (80 Ma) ages. In contrast to the igneous samples, detrital zircons from the beach placer samples follow a trend bound by evolution lines leading to Hf-TDM model ages between 0.6 and 1.6 Ga. As a whole since the late Neoproterozoic the Balkan crust was the subject of repeated reworking in a series of magmatic/orogenic events. Some extent of juvenile igneous addition on this evolving Cadomian substrate brings about the shallow rise in εHf(t) values we observe in the igneous basement rocks. The end result observed in the Balkan is of a continental crust comprising a Neoproterozoic peri-Gondwana Cadomian core, reworked in multiple episodes of Phanerozoic orogenies, and augmented to some extent by variable mantle derived input. We argue that this mode of crustal origin and evolution is also applicable to many peri-Gondwana terranes of Western Europe.