An Ordovician magmatic and metamorphic event in the pre-Mesozoic basement of the Central Alps (Aar Massif and Gotthard Nappe)

Article Article scientifique Article An Ordovician magmatic and metamorphic event in the pre-Mesozoic basement of the Central Alps (Aar Massif and Gotthard Nappe) eng 2025-10-15 2025 author Noroña Muñoz Eliana Maribel 984312 Services communs du département des sciences de la terre (DETCO) author Ulianov Alexey 735099 author Spikings Richard Alan 550467 Services communs du département des sciences de la terre (DETCO) author Gerdes Axel author Berger Alfons author Abrecht Jürgen author Wiederkehr Michael 599960 author Schaltegger Urs 0000-0003-4404-8607 134356 Services communs du département des sciences de la terre (DETCO) 1-32 19 10.1186/s00015-025-00492-9 1661-8726 https://link.springer.com/10.1186/s00015-025-00492-9 <p>Large areas of both the external Helvetic Aar Massif and the internal Helvetic Gotthard Nappe in the pre-Mesozoic basement of the European Alps are composed of felsic gneiss, augen-gneiss and metagranite, traditionally called “orthogneiss”. Based on the scarce existing geochronology, they have been tentatively associated with an active continental margin of late Ordovician age. New zircon LA-ICP-MS U–Pb age determinations confirm the late Ordovician age for the Gärsthorn Gneiss Complex of the southern Aar Massif and the Streifengneis Complex of the Gotthard Nappe, yielding a range of mean ages for individual samples from 441 to 454 Ma. The chemical characteristics of this slightly peraluminous gneiss association, the ubiquitous presence of inherited Proterozoic to Cambrian cores in zircon, and the widely variable Hf isotopic composition of inherited cores as well as of Ordovician growth zones point to a siliciclastic metasedimentary protolith. Our conceptual model involves the accumulation of Gondwana-derived detritus in a massively overthickened fore-arc wedge during the early Ordovician. This latter was molten during the late Ordovician, a cryptic mafic underplating during slab rollback and extension possibly triggering the anatexis. The existence of oscillatory-zoned high-uranium zircon rims around the Ordovician growth zones yielding a Mississippian-age (~ 308–315 Ma) points to renewed melting of these rocks during the Variscan Orogeny and metamorphism.</p> Pre-Mesozoic basement of the Alps Aar Massif Gotthard Nappe Anatectic granite U–Pb geochronology Zircon Trace elements Hf isotopes Active margin Dewey 550 Federal Office of Topography swisstopo 42 Département des sciences de la Terre 154 false 663 Isotope Geochemistry, Geochronology and Thermochronology Swiss journal of geosciences 118 1 68905746-5fb5-4d37-a417-daa0f4dfbd3e Article (Published version) Public Article_scientifique_from_crossref.pdf 15174894 application/pdf CC BY-4.0 8b82bb7543837c8e819db7a86473c71d39310e3c036b09a8d4c041ff6950ef7b openAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

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An Ordovician magmatic and metamorphic event in the pre-Mesozoic basement of the Central Alps (Aar Massif and Gotthard Nappe)	Swiss journal of geosciences			2025	11	19

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NoroÃ±a MuÃ±oz, Eliana

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