Remagnetization of Variscan massifs and reconstruction of the Triassic paleosurface in Europe

Basement rocks (such as e.g. granites and rhyolithes) of European Variscan massifs often show Permo-Triassic remagnetization [e.g. Edel & Schneider, 1995, Geophys. J. Int., 122, 858-876; Edel et al., 1997, C.R.AS. Paris, Earth Planet. Sci., 325, 479-486] resulting in underestimated age determinations. These rejuvenated ages are attributed to an alteration of the primary paleomagnetic signal recently carried by the neo-formation of secondary hematite [Preeden et al., 2009, Geophys. Res. Abstr. EGU, 11, 365,]. Hematite forms under oxic conditions. Thus, one may deduce that the remagnetization of Paleozoic crystalline rocks occurs once the basement rocks are exposed at the Permo-Triassic (paleo)surface. Permo-Triassic remagnetizations are ubiquitous, affecting many emerged Paleozoic rocks in Europe and suggesting a major weathering event under oxic conditions. Previously published paleomagnetic ages [Ricordel et al., 2007, Palaeo3, 251, 268-282] showed a relationship between remagnetization and the development of pink-reddish facies associated to the albitized underlying rocks of the Morvan Massif (France). Parcerisa et al. [2009, Int. J. Earth Sci., doi: 10.1007/s00531-008-0405-1] performed further petrographic analyses and proposed a geochemical model for the genesis of this type of alteration. The extent of the altered zone (> 100 m in depth) points to a sodium enriched groundwater environment [Thiry et al., 2009, Geophs Res. Abstr. EGU, 11, 4103]. The Na+ enrichment is likely related to the Triassic environment characterized by widespread salt deposits, such as leaching of salt, marine aerosols, periodic/episodic contribution of seawater or evaporative solutions. Demonstrating that the albitized facies are of supergenic origin and bound to the Triassic paleosurface deeply renews the ideas about the evolution of basement areas. The recognition of the Triassic paleosurface on widespread basements in Europe will provide spatio-temporal benchmarks to constrain the ablation of these massifs since the Triassic. This will be a major contribution to the geodynamic modelling of these areas. To deepen our understanding of this paleoalteration phenomenon on a supra-regional scale, we aim to acquire more tie points for this Paleozoic surface, which was preserved in the crystalline basement of Europe throughout the Mesozoic and Cenozoic epoch. Therefore we will present results on paleomagnetic investigations as well as petrographic analyses of the profiles through albitized granite and porphyry from the Sudetes in SW-Poland and the Catalonian Mountains in NE-Spain.