Lithology, U[sbnd]Pb zircon geochronology, and geochemistry of the Austroalpine Sieggraben Complex

Author(s): Marián Putiš, Jiří Sláma, Qiu Li Li, Ondrej Nemec, Martin Ondrejka, Xian Hua Li, Friedrich Koller, Lukáš Ackerman, Ladislav Strnad, Peter Ružička
Abstract: The Sieggraben Complex (SC) in Eastern Austria provides comprehensive information on the pre-Permian, Permian, and Alpine (Cretaceous) evolutional stages of the crustal and mantle sections included into the Austroalpine basement HP/UHP belt. The SC in the Sieggraben–Schwarzenbach area consists of three, top-to-bottom tectono-stratigraphic units: (1) the Paragneiss unit, (2) the Marble–Eclogite unit, which contains MORB and OIB types of mafic rocks, and (3) the Micaschist–Calcschist unit. The N-MORB type mafic rocks yield a U[sbnd]Pb age of 369.7 ± 2.0 Ma, have ε_Nd(370) = +8.5 to +7.4 and TDM_(2st) of 0.42–0.50 Ga, while the E-MORB types (U[sbnd]Pb ages around 400 Ma) show ε_Nd(400) = +9.4 to +5.6 and TDM_(2st) of 0.37–0.67 Ga, both indicating rather juvenile mantle sources during the formation of the inferred oceanic Devonian basin. The rocks of these units revealed Cambrian, Proterozoic, and Archean zircon sources. The ages of 285.8 ± 9.2 and 265.7 ± 2.1 Ma from eclogite and amphibolite, respectively, and 265.5 ± 1.4 Ma from paragneiss indicate an important Permian metamorphic overprint. Permian granitic dykes dated from ∼265 to 260 Ma, exceptionally at 273 and 253 Ma, crosscut the lithological units. A clinopyroxenite dyke, which crosscuts harzburgite of the underlying mantle fragment, yielded a magmatic age of 253.3 ± 2.9 Ma. Overall, these ages suggest a strong Permian extension, overheating, and melting of the crustal and mantle rocks. The eclogite ages from ∼100 Ma, but mainly between 92 and 90 Ma, constrain the Late Cretaceous metamorphic event terminated by an 88.4 ± 0.8 Ma pegmatite intrusion in the Paragneiss unit. The Permian and Cretaceous metamorphic events often caused resetting of the relatively older zircon ages, together with a decrease of zircon ε_Hf(t) values, and an increase of whole-rock ⁸⁷Sr/⁸⁶Sr values. A Carboniferous metamorphic age of ∼340 Ma was rarely detected. The SC finally represents a part of an early Late Cretaceous intra-continental subduction zone, which formed within a strongly-thinned crystalline basement due to the Devonian and Permian extensions. A similar Cretaceous suture zone with HP amphibolite, dated at ∼130–100 Ma by white mica Ar[sbnd]Ar ages (100–90 Ma exhumation), has been described around the Lubeník line between the Gemeric and Veporic tectonic units of the Inner Western Carpathians in the framework of the Cenozoic AL–CA–PA (Alpine–Carpathian–Pannonian) microplate.
Organisation(s): Department of Lithospheric Research
External organisation(s): Comenius University Bratislava, Czech Academy of Sciences, Chinese Academy of Sciences (CAS), Charles University Prague
Journal: Lithos
Volume: 482-483
ISSN: 0024-4937
DOI: https://doi.org/10.1016/j.lithos.2024.107739
Publication date: 10-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 105120 Petrology, 105105 Geochemistry
Keywords
ASJC Scopus subject areas: Geology, Geochemistry and Petrology
Portal url: https://ucrisportal.univie.ac.at/en/publications/09a72b58-4665-4caa-92f2-6445be51bd80

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