1,2,4,- 1Ocean University of China, Key Lab of Submarine Geoscience and Prospecting Techniques, MOE, Institute for Advanced Ocean Study, College of Marine Geosciences, Qingdao, China (liuyongjiang@ouc.edu.cn)
- 2Laboratory for Marine Mineral Resources, Qingdao Marine Science and Technology Center, Qingdao 266237, China
- 3Department of Environment and Biodiversity, Geology and Geomorphology Division, Paris-Lodron-University of Salzburg, Austria
- 4Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, College of Earth Sciences, Guilin University of Technology, China
- 5College of Earth Science, Institute of Disaster Prevention, China
- 6Department of Earth Sciences, The University of Hong Kong
The Austroalpine basement in the eastern Alps underwent Proto-Tethys and Paleo-Tethys tectonic evolution. To restore the tectonic processes of Proto-Paleo-Tethys Ocean in the eastern Alps, we carried out a systematic study by U-Pb zircon geochronology and geochemistry. In the Schladming Complex our study shows that the granodioritic gneisses (539-538 Ma) with A2-type geochemical signature and the fine-grained amphibolite (531 Ma) with E-MORB affinity, represent a bimodal magmatism. A medium-grained amphibolite (495 Ma) exhibits OIB-like geochemical features. The monzonite granitic gneiss (464 Ma) and plagioclase gneiss (487 Ma) have volcanic arc geochemical features. In Speik-Gleinalpe Complex the amphibolites (489-496 Ma), granitic gneiss (491 Ma) and plagiogneiss (472-476 Ma) all have subduction-related geochemical signatures. These all magmatism recorded the subduction and back-arc basin tectonic processes of Proto-Tethys Ocean.
In Schladming Complex we found that the overgrowth rims of zircons of the early Paleozoic biotite-plagioclase gneiss and granitic gneisses give a dominantly metamorphic age of ca. 355 Ma. In addition, the zircons from the samples of Speik-Gleinalpe also yield a metamorphic age of ca. 400 Ma. In the Schladming Complex we also dated two granites with crystallization age of 353-355 Ma, which have subduction-related geochemical characteristics. These Devonian-Carboniferous metamorphism and magmatism together indicate that the Austroalpine basement had been overprinted by the Variscan orogeny.
In the southern and western Saualpe crystalline basement, the three amphibolites yield crystallization ages of 415-418 Ma and have similar geochemical signature of OIB. We suggest that the Late Silurian-earliest Devonian OIB-like magmatism was related to a back-arc extension setting along the northern margin of Gondwana and indicating the opening of the Paleo-Tethys Ocean.
In the Plankogel Complex we found two N-MORB amphibolites exhibit late Permian/Early Triassic protolith ages (254-227 Ma), representing the Paleo-Tethys oceanic crust relics. The manganese quartzites are explained as siliceous deep-sea sediments with a large Permian to Early Triassic (244-282 Ma) volcanic components. We interpret the Plankogel Complex as an ophiolitic complex of Paleo-Tethys suture.
Based on our studies above we restore the tectonic evolution of Proto-Paleo-Tethys Ocean in the eastern Alps: The basement complexes in the eastern Alps had been a part of the active continental margin of Gondwana. With the subduction of the Proto-Tethys oceanic plate to the south, a back-arc rift developed along the northern margin of the Gondwana in the Early Cambrian, resulted in the opening of a back-arc basin (Speik Ocean) and the break-off of the proto-E Alps terranes from Gondwana in the Late Cambrian. In the Early Ordovician the proto-E Alps terranes collided back to the Gondwana with the closure of Speik Ocean. During the Late Silurian-earliest Devonian the Paleo-Tethys Ocean opened as back-arc basin due to southward subduction of Rheic Ocean, resulting in the break-off of the proto-south-Europe marginal terranes from the northern margin of Gondwana. From Late Devonian to Early Carboniferous the break-off terranes drifted northward and accreted to the southern margin of European continent with the consuming and closure of Rheic Ocean. In the Late Permian-Middle Triassic the Paleo-Tethys Ocean was closed after continuing northward subduction.
How to cite: Liu, Y., Neubauer, F., Huang, Q., Guan, Q., Genser, J., Liu, B., Yuan, S., and Chang, R.: Tectonic evolution of Proto-Paleo-Tethys Ocean in the eastern Alps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17318, https://doi.org/10.5194/egusphere-egu26-17318, 2026.
