Gargazon formation

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The Gargazon formation ( Italian Formazione di Gargazzone ) is an up to 800 m thick formation in the Südalpen within the Etschtaler Vulkanit group . It mainly consists of pyroclastic current deposits .

The formation is named after the municipality of Gargazon south of Merano and was formed in the Permian period at the end of a volcanic period lasting around ten million years.

description

The Gargazon Formation consists of ignimbrites and is up to 800 meters thick. The rock has no grain size grading and is composed especially of rhyodacite lapilli tuffs and crystalline ash . The material was ejected in the lower to middle Permian when a caldera was formed . The formation has been dated to 276.5 ± 1.1 Ma.

While the lower part of the facies is divided into regular plates up to 30 cm wide by almost vertical breaks, the upper part is more uniform and solid. Shortly before the eruption, parts of the magma were probably already partially crystallized, which is why there are a lot of plagioclase , quartz and modified biotite or pyroxe crystals in the rock . The high mass of erupted material (mass of the Gargazon formation) and the high proportion of crystals (40–60%) are typical of eruptions that form a caldera.

Through superficial weathering, the ignimbrites of the Gargazon formation create a holey appearance comparable to gas bubbles.

distribution

The rocks of the Gargazon formation are found particularly on the slopes of the northern Adige Valley , between Merano and Bolzano , although they are more extensive on the east side of the valley than on the west side. There is also a great location north of Lago di Santa Giustina on the south side of Monte Luco . The formation also occurs above the eastern slope of the valley, in the Sarntal and northeast of Trento in the Cembra valley and east of it.

Individual evidence

  1. ↑ M. Avanzini, GM Bargossi, A. Borsato, GB Castiglioni, M. Cucato, C. Morelli, G. Prosser, A. Sapelza: Notes on the geological map of Italy at a scale 1: 50,000, sheet 026 Appiano. Agenzia per la protezione dell 'ambiente e per i servizi tecnici, Servizio Geologico d'Italia, accessed on May 13, 2020 .
  2. ↑ a b c Rainer Brandner, Alfred Gruber, Corrado Morelli, Volkmar Mair: Pulses of Neotethys-Rifting in the Permomesozoic of the Dolomites .
  3. ↑ GM Bargossi, US Klötzli, V. Mair, M. Marocchi, C. Morelli: The Lower Permian Athesian Volcanic Group (AVG) in the Adige valley between Merano and Bolzano: a stratigraphic, petrographic and geochronological outline . ( amazonaws.com [PDF; accessed on May 14, 2020]).
  4. ↑ Corrado Morelli, Marta Marocchi, Alessandro Moretti, Giuseppe Maria Bargossi, Giorgio Gasparotto, Bert de Waele, Urs Klötzli, Volkmar Mair: Volcanic stratigraphy and radiometric age constraints at the northern margin of a mega-caldera system: Athesian Volcanic Group (Southern Alps , Italy) . ( amazonaws.com [PDF; accessed on May 14, 2020]).
  5. ^ Rainer Brandner, Alfred Gruber, Lorenz Keim: Geology of the Western Dolomites: From the birth of Neothetys in the Permian to carbonate platforms, basins and volcanic rocks of the Triassic . In: Geo.Alp Sediment 2007 . Publications of the Institute for Geology and Paleontology of the University of Innsbruck and the Naturmuseum Südtirol, 2004 ISSN 1824-7741 p. 103 PDF
  6. ^ CART (Carta Geologica d'Italia 1: 50,000). Retrieved May 14, 2020 .
  7. ↑ Istituto Superiore per la Protezione e la Ricerca Ambientale - ISPRA (ed.): Note illustrative della Carta geologica d'Italia - 1: 50,000: Foglio 060 Trento . S.EL.CA., Rome 2010 pp. 53-54 PDF