Widespread Permian granite magmatism in Lower Austroalpine units: significance for Permian rifting in the Eastern Alps
- PDF / 5,217,982 Bytes
- 25 Pages / 595.276 x 790.866 pts Page_size
- 10 Downloads / 206 Views
Swiss Journal of Geosciences
Open Access
ORIGINAL PAPER
Widespread Permian granite magmatism in Lower Austroalpine units: significance for Permian rifting in the Eastern Alps Sihua Yuan1,2 , Franz Neubauer2* , Yongjiang Liu3,4 , Johann Genser2 , Boran Liu2 , Shengyao Yu3,4 , Ruihong Chang2 and Qingbin Guan3,4
Abstract The Grobgneis complex, located in the eastern Austroalpine unit of the Eastern Alps, exposes large volumes of preAlpine porphyric metagranites, sometimes associated with small gabbroic bodies. To better understand tectonic setting of the metagranites, we carried out detailed geochronological and geochemical investigations on the major part of the porphyric metagranites. LA–ICP–MS zircon U–Pb dating of three metagranites sampled from the Grobgneis complex provides the first reliable evidence for large volumes of Permian plutonism within the pre-Alpine basement of the Lower Austroalpine units. Concordant zircons from three samples yield ages at 272.2 ± 1.2 Ma, 268.6 ± 2.3 Ma and 267.6 ± 2.9 Ma interpreted to date the emplacement of the granite suite. In combination with published ages for other Permian Alpine magmatic bodies, the new U–Pb ages provide evidence of a temporally restricted period of plutonism (“Grobgneis”) in the Raabalpen basement Complex during the Middle Permian. Comparing the investigated basement with that of the West Carpathian basement, we argue that widespread Permian granite magmatism occurred in the Lower Austroalpine units. They belong to the high-K calc-alkaline to shoshonitic S-type series on the base of geochemical data. Zircon Hf isotopic compositions of the Grobgneis metagranites show εHf(t) values of − 4.37 to − 0.6, with TDM2 model ages of 1.31–1.55 Ga, indicating that their protoliths were derived by the recycling of older continental crust. We suggest that the Permian granitic and gabbroic rocks are considered as rifted-related rocks in the Lower Austroalpine units and are contemporaneous with cover sediments. Keywords: Grobgneis, Lower Austroalpine nappes, Continental rifting, Post-Variscan granitoids, Permian event 1 Introduction As long discussed for the Eastern and Southern Alps and testified by deposition of thick Permian sedimentary succession, Permian extension occurred in the aftermath of the Variscan orogeny (Krainer 1993 and references therein; Decarlis et al. 2013). The ongoing subsidence did leave only a short time after the Late Carboniferous (Pennsylvanian) Variscan orogeny, in the order of a few Editorial handling: Paola Manzotti. *Correspondence: [email protected] 2 Department of Geology and Geography, Paris-Lodron-University of Salzburg, 5020 Salzburg, Austria Full list of author information is available at the end of the article
million years, for denudation of the uplifting Variscan orogen. In the sedimentary level, thick Permian sedimentary deposits were deposited in the eastern part of the Southern Alps, which also include thick Permian acidic volcanics (Bozen quartz porphyry), Permian reefs and lagoonal evaporites deposited at
Data Loading...
