THE EUROPEAN CONTINENTAL CRUST AS RECORDED BY U-PB, LU-HF, AND O ISOTOPES IN DETRITAL ZIRCONS FROM MODERN RIVERS

We present a combined U-Pb, Lu-Hf, and O isotopic study for approximately 3700 detrital zircons from 15 major rivers in Europe. The age distributions are qualitatively representative of the geology of Europe at the continental scale and also reflect the assembly and disintegration of the main supercontinents since the Archean. At the drainage basin scale, qualitative representation is rather limited. The predominant lithology in many basins are sedimentary rocks with drainage systems exclusively tapping source rocks younger than 650 Ma. The detrital age distributions, however, include large numbers of Precambrian grains older than 650 Ma. These characteristics emphasize (i) the strong influence of recycling on the distributions and (II) demonstrate that age distributions are not quantitatively representative. The presence and proportions of age maxima are furthermore strongly dominated by factors such as source rock fertility, the sand generation potential of different source lithologies, recycling, and geomorphological and geographical factors.

Variscan detrital zircons are most prominent in many rivers and mirror the largest episode of crustal reworking in Europe. Other age clusters relate to the Alpine and post-Alpine Cenozoic 40-25 Ma and 10-0.2 Ma, the Caledonian 490-400 Ma, and the Avalonian-Cadomian 650-540 Ma orogenic cycles. Detrital zircons of 1700-1400 Ma and 1170-930 Ma are significant in Scandinavia, and 2500-2900 Ma and ca. 1850 in eastern Europe. Permian post-Variscan ages were only found in the Italian Po and Scandinavian Glomma rivers. In terms of Hf and O isotopes, Permian detrital zircon in the Po river show significant crustal contamination; on the other hand, Permian detrital zircon in the Glomma river show juvenile, mantle-like signatures. The data indicate that the European crust is characterized by strong crustal recycling linked to the succession of predominantly collisional orogens. The notably minor transfer of truly juvenile magmas into the rock record occurred during the Permian post-Variscan and the late Cenozoic post-Alpean post-collisional extensional stages.