Mostra temporanea chiusa venerdì 31 maggio.

Vi informiamo che venerdì 31 maggio la nostra mostra temporanea “Caldera – all’ombra del supervulcano” rimarrà chiusa e pertanto non sarà accessibile al pubblico.


New U-Pb zircon and bistratigraphic data of the Tyros Unit, eastern Crete

Gernold Zulauf, Joachim Blau, Wolfgang Dörr, Thomas Klein, Jochen Krahl, Evelyn Kustatscher, Rainer Petschick & Bas van de Schootbrugge

We investigated volcanic and sedimentary rocks of the Toplou Beds, which constitute the uppermost part of the Tyros Unit of eastern Crete. U-Pb TIMS analyses of zircons, separated from a metarhyolite of the lower Toplou Beds, yielded concordant ages at 361.2 ± 1.2, 307.4 ± 1.2 and 228 ± 1.7 Ma. The youngest age is interpreted to refl ect the timing of melt emplacement in Carnian times. The older ages are inherited from zircons, which belong to the crystalline basement through which the rhyolite melt was ascending. At higher stratigraphic levels we found fern fragments inside black slates, which are intercalated with Carnian metasandstones and metaconglomerates. The fern fragments resemble most closely the genus Phlebopteris, which is typical for the Triassic to Early Jurassic of Europe. Findings of the foraminifera Gandinella falsofriedli inside dolomite of the uppermost part of the Toplou Beds suggest a Norian/Rhaetian age. As the basal parts of the Tripolitza Nappe yielded Ladinian and Carnian ages, the Tyros Unit cannot continue upwards into the Tripolitza Platform. The misfi t in ages and the inversion in metamorphic grade of Tyros and Tripolitza rocks suggest a thrust contact between both units. The Triassic records inside the Tyros Unit can be explained by subduction and collision following the closure of the Palaeotethys. Subduction underneath the Cimmerian ribbon continent is documented by metaandesite in the basal parts of the Tyros Unit (Chamezi Beds), which rest unconformably on top of Carboniferous/Permian crystalline basement. The andesites and shallow marine clastics are interpreted to have been deposited in a fore-arc position. Redeposited neritic carbonates in the form of pebbles in Lower Triassic and Anisian conglomerates of the Chamezi and Tripokefala beds, respectively, suggest uplift and erosion of pre-existing carbonate platforms. This phase of uplift and erosion is attributed to collision of Pelagonia with the Cimmerian ribbon continent following the closure of the Palaeotethys. Uplift and erosion were still active in Ladinian times explaining the lack of Ladinian fossils inside the Tyros Unit. The shallow-marine and terrestrial conditions during Carnian sedimentation of the Toplou Beds can be well correlated with the conditions during deposition of the Cassianer/Raibler Beds of the Southern Alps.

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