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Mantle–crust interactions during Variscan subduction in the Eastern Alps (Nonsberg–Ulten zone): geochronology and new petrological constraints |
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| Authors: | Simone Tumiati Martin Thni Paolo Nimis Silvana Martin Volkmar Mair |
| Institution: | a Dipartimento di Mineralogia e Petrologia, Università degli Studi di Padova, Corso Garibaldi 37, 35137, Padova, Italy b Institut für Geologie, University of Vienna, Althanstraße 14/UZA2-Geozentrum, 1090, Vienna, Austria c Dipartimento di Scienze Chimiche-Fisiche-Naturali, Università dell’Insubria, via Lucini 3, 22100, Como, Italy d Amt für Baustoffprüfung, Provinz Bozen – Provincia di Bolzano, via V. d'Ega 48, 39053, Cardano (BZ), Italy |
| Abstract: | We have analyzed the Sm–Nd and Rb–Sr whole-rock and mineral isotope systematics of garnet peridotites and associated eclogites and migmatitic gneisses from the Nonsberg–Ulten zone of the Eastern Alps. The garnet peridotites include coarse-grained varieties, characterized by well-preserved to slightly modified mantle geochemical signatures, and finer-grained varieties enriched in amphibole and LILE. Hydration of some of the most strongly deformed, fine-grained peridotites by crustal fluids caused isotopic disequilibrium between the peridotite minerals, preventing accurate age determinations. The coarse-grained peridotites, the eclogites and the country migmatitic gneisses yield garnet–whole-rock and garnet–clinopyroxene Sm–Nd ages that indicate for all rock types an isotopic homogenization event at ca. 330 Ma. The similar ages suggest that all rock types shared a common history since the incorporation of the peridotites in the crust, and constrain the garnet-facies metamorphism of the peridotites, as well as partial melting of the crust, to an episode of crustal subduction at the end of the Variscan orogenic cycle. |
| Keywords: | garnet peridotites migmatites Sm–Nd geochronology subduction metasomatism Ulten zone |
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