Early Carboniferous magmatism and metamorphism in the Schladming Complex, Eastern Alps: Constrain on the subduction of Rheic Ocean
Authors: Huang Qianwen , Liu Yongjiang , Neubauer Franz , Genser Johann , Yuan Sihua , Chang Ruihong , Guan Qingbin , Yu Shengyao 
Published: March 2022

&lt;p&gt;The Schladming-Seckau system as one part of Middle Austroalpine Unit experienced the Variscan event and overprinted by the Alpine orogeny, which is a key to reveal the tectonic evolution history of Easterrn Alps (Neubauer and Frisch, 1992). Recently, Cambrian-Ordovician magmatism and Permian-Triassic magmatism were reported in the Schladming Complex (Huang et al., 2021), they are related to the subduction of Proto-Tethys Ocean and opening of Meliata back-arc basin, respectively. Here, we present the whole-rock geochemistry, zircon U-Pb and Hf isotopic analysis of paragneiss and granitic rocks in the Sch&amp;#246;der Valley to constrain the relationship between Schladming Complex and Variscan orogeny.&lt;/p&gt;&lt;p&gt;The biotite-plagioclase gneiss, hornblende-gneiss, mica-schists formed the main body of the Schladming Complex (Neubauer et al., 2018). The zircon age data of biotite-plagioclase gneiss show the peak age of 603 Ma and 487 Ma with dominated metamorphic age of 355 Ma, indicating the rocks mainly sourced from the Neoproterozoic and Ordovician rocks and suffered the strong Carboniferous metamorphism. Similar to the biotite-plagioclase gneiss, two Ordovician granitic gneisses (485Ma &amp;#8211; 483 Ma) also comprise significance metamorphic age of 355 Ma. Their primitive mantle-normalized multiple elements patterns exhibit strong depleted in Nb, Ta, Ti, Zr, and Hf, showing a typical subduction-related features.&lt;/p&gt;&lt;p&gt;Not only the metamorphism shows the Carboniferous subduction event, but also two granites prove the existence of Carboniferous magmatism. These two granites have crystallization age of 353 Ma and 355 Ma, respectively. The zircon &amp;#949;Hf(t) scatter between -1.29 and 6.04, suggesting the magma of granite derived from deplete mantle and mixed with the continent materials. Their geochemical data display subduction-related characteristics that depleted in HFSE (eg. Nb, Ta, Ti, Zr, and Hf) and enriched in LILE (eg. Ba, Th, K). The Carboniferous metamorphism and magmatism together showing the subduction of Rheic Ocean before Variscan orogeny in the Eastern Alps.&lt;/p&gt;&lt;p&gt;Acknowledgement: The study is financially supported by NSFC (91755212).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Huang, Q.W., Liu, Y.J., Genser, J., Neubauer, F., Chang, R.H., Yuan, S.H., Guan, Q.B., Yu, S.Y., 2021. Permian-Triassic A-type and I-type granites in the Schladming Complex, Austroalpine Unit: Constraints on subduction of Paleo-Tethys Ocean in the Eastern Alps, In: Li, S., Santosh, M. (Eds.), The 2021 Annual Convention of the International Association for Gondwana Research (IAGR) and the 18th International Symposium on Gondwana to Asia. Gondwana Research, China, Qingdao, pp. 21-22.&lt;/p&gt;&lt;p&gt;Neubauer, F., Frisch, W., 1992. Pre-Mesozoic geology of the Middle and Upper Austro-Alpine metamorphic basement east of the Tauern Window. 17-36.&lt;/p&gt;&lt;p&gt;Neubauer, F., Genser, J., Heberer, B., Etzel, A., Olive, S., 2018. Field Trip Post&amp;#8208;EX&amp;#8208;1 Transect across the Eastern Alps, XXI International Congress of the Carpathian Balkan Geological Association Salzburg, Austria, pp. 137-222.&lt;/p&gt;