The evolution of the European Crust – U-Pb, Pb, Hf, and O isotope systematics of de-trital zircon, rutile and K-feldspar from the sediments of major European rivers

Large river systems drain large continental areas that span different geotectonic do-mains. It is commonly believed that river sediments reflect the composition of the underlying continental crust, making them useful for studying its evolution. The dating of magmatic, met-amorphic, or detrital zircon, combined with the use of O and Lu-Hf isotopes, helps to assess crustal growth and the evolution of the continental crust. However, detrital zircon U-Pb age distributions can be biased, leading to potential representation problems. As a result, the inter-pretation of global zircon U-Pb age data and, by extension, the crustal record, has led to on-going discussions and often contradictory conclusions. In this study, we investigated fluvial sands from 15 major rivers in Europe, which drain much of the western part of the continent. We demonstrate that detrital zircon from European rivers qualitatively reflects major geological events mainly at a continental scale, not a river scale. The Variscan Orogeny, the largest epi-sode of crustal reworking in Europe, is represented by 370–270 Ma detrital zircons in all riv-ers. Other important age clusters include the Alpidic (40–25 Ma), post-Alpidic (10–0.2 Ma), Caledonian (490–400 Ma), and Avalonian-Cadomian (650–540 Ma). Detrital zircons of 1170–930 Ma and 1700–1400 Ma are notable in Scandinavia, while 2900–2500 Ma and ca. 1850 Ma zircons are prominent in Eastern Europe. We found that any attempt to quantify crustal growth using detrital zircon should be ap-proached with caution. We demonstrate that the detrital zircon record is not representative of the drainage area on a quantitative level. This is primarily due to recycling and the variable zircon fertility of source rocks, which significantly affect the record in Europe, and probably globally. Using O and Lu-Hf isotopes in detrital zircon, we found that crustal formation peaked in the Neo- and Meso-Proterozoic but this may be also biased due to regions influenced by post-collisional tectonics. To complement the zircon data, we analysed other heavy minerals that are less prone to recycling (such as titanite and apatite) and those which are found in rocks with low zircon fertility (e.g., metamorphic and mafic rocks, such as titanite and rutile). We found that the U-Pb record of detrital rutile is similarly influenced by recycling, but in the case of the Variscan Orogen, it records earlier events than zircon. Titanite, a mineral that is mostly first-cycle, best reflects the Alpidic Orogeny, an event that is nearly invisible in the detrital zircon and rutile records. Dating detrital apatite in combination with trace element analysis, is a useful tool for distinguishing between different geological processes, especially within the Variscan Orogeny.