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The Ordovician orogeny in the Alpine basement: constraints from geochronology and geochemistry in the Aar Massif (Central Alps)

Abrecht, Jürgen
Corfu, Fernando
Published in Schweizerische mineralogische und petrographische Mitteilungen. 2003, vol. 83, p. 183-195
Abstract A sequence of magmatic and metasedimentary rocks from the Susten pass area (Aar Massif, Central Alps of Switzerland) provides evidence of an orogenic cycle of Ordovician age overprinted by the Variscan orogeny. Several stages of this evolution have been dated by U-Pb on zircon, titanite and monazite, complementing previously published U- Pb zircon data from the same area. A gabbro, with epsNd values of +4 to +7 was formed at 478 ± 5 Ma and was then affected by a HP metamorphic stage. A subsequent HT metamorphic event was succeeded by partial melting during decompression at about 450 Ma. Titanite in calcsilicate marble and monazite in metapelite formed at 319 ± 3 Ma and 317.5 ± 2 Ma, respectively. This Variscan metamorphism probably reached amphibolite facies conditions and considerably changed the whole-rock chemical and isotopic compositions of the amphibolites, but it left the U-Pb systems in zircon virtually unaffected. The association of mafic and ultramafic rocks together with sediments could be generated in both convergent and divergent settings. The metamorphic overprints blurred the original geochemical and isotopic characteristics too much to permit a specific geodynamic interpretation. The studied rock association is suggested to be part of an ancient active or passive margin sequence of the peri-Gondwanan Hun terrane.
Keywords Ordovician orogenyAlpine basementGeochronologyU-PbAar Massif
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Research group Isotope Geochemistry, Geochronology and Thermochronology
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SCHALTEGGER, Urs, ABRECHT, Jürgen, CORFU, Fernando. The Ordovician orogeny in the Alpine basement: constraints from geochronology and geochemistry in the Aar Massif (Central Alps). In: Schweizerische mineralogische und petrographische Mitteilungen, 2003, vol. 83, p. 183-195. https://archive-ouverte.unige.ch/unige:28437

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Deposited on : 2013-06-10

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