Geochronology, stratigraphy and geochemistry of Cambro-Ordovician, Silurian and Devonian volcanic rocks of the Saxothuringian Zone in NE Bavaria (Germany)—new constraints for Gondwana break up and ocean–island magmatism

Höhn, Stefan; Koglin, Nikola; Klopf, Lisa; Schüssler, Ulrich; Tragelehn, Harald; Frimmel, Hartwig E.; Zeh, Armin; Brätz, Helene

doi:10.1007/s00531-017-1497-2

Cited by 10 publications

(1 citation statement)

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“…The Cambro‐Ordovician protolith ages of the Saxon granulites overlap with U–Pb zircon ages in the range 500–470 Ma obtained throughout the Variscan belt for a late stage of rift magmatism in the northern Gondwana margin (e.g. Díez Fernández, Pereira, & Foster, 2015; Höhn et al., 2018; Kryza & Fanning, 2007; Kusbach et al., 2015; Tichomirowa, Sergeev, Berger, & Leonhardt, 2012). Another age population of the Saxon granulites dated by Sagawe et al.…”

Section: Previous Geochronologymentioning

confidence: 51%

Geochronological and petrological constraints from the evolution in the Saxon Granulite Massif, Germany, on the Variscan continental collision orogeny

Rötzler

Timmerman

2020

Journal Metamorphic Geology

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Controversy over the plate tectonic affinity and evolution of the Saxon granulites in a two‐ or multi‐plate setting during inter‐ or intracontinental collision makes the Saxon Granulite Massif a key area for the understanding of the Palaeozoic Variscan orogeny. The massif is a large dome structure in which tectonic slivers of metapelite and metaophiolite units occur along a shear zone separating a diapir‐like body of high‐P granulite below from low‐P metasedimentary rocks above. Each of the upper structural units records a different metamorphic evolution until its assembly with the exhuming granulite body. New age and petrologic data suggest that the metaophiolites developed from early Cambrian protoliths during high‐P amphibolite facies metamorphism in the mid‐ to late‐Devonian and thermal overprinting by the exhuming hot granulite body in the early Carboniferous. A correlation of new Ar–Ar biotite ages with published P–T–t data for the granulites implies that exhumation and cooling of the granulite body occurred at average rates of ~8 mm/year and ~80°C/Ma, with a drop in exhumation rate from ~20 to ~2.5 mm/year and a slight rise in cooling rate between early and late stages of exhumation. A time lag of c. 2 Ma between cooling through the closure temperatures for argon diffusion in hornblende and biotite indicates a cooling rate of 90°C/Ma when all units had assembled into the massif. A two‐plate model of the Variscan orogeny in which the above evolution is related to a short‐lived intra‐Gondwana subduction zone conflicts with the oceanic affinity of the metaophiolites and the timescale of c. 50 Ma for the metamorphism. Alternative models focusing on the internal Variscan belt assume distinctly different material paths through the lower or upper crust for strikingly similar granulite massifs. An earlier proposed model of bilateral subduction below the internal Variscan belt may solve this problem.

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