The Wechsel Gneiss Complex of Eastern Alps: an Ediacaran to Cambrian continental arc and its Early Proterozoic hinterlan
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Swiss Journal of Geosciences
Open Access
ORIGINAL PAPER
The Wechsel Gneiss Complex of Eastern Alps: an Ediacaran to Cambrian continental arc and its Early Proterozoic hinterland Franz Neubauer1* , Yongjiang Liu2,3 , Ruihong Chang1 , Sihua Yuan1,4 , Shengyao Yu2,3 , Johann Genser1 , Boran Liu1 and Qingbin Guan2,3 Abstract Many metamorphosed basement complexes in the Alps are polymetamorphic and their origin and geological history may only be deciphered by detailed geochronology on the different members including oceanic elements like ophiolites, arc successions, and continental passive margin successions. Here we present a case study on the Lower Austroalpine Variegated Wechsel Gneiss Complex and the overlying low-grade metamorphosed Wechsel Phyllite Unit at the eastern margin of Alps. The Wechsel Gneiss Complexes are known to have been overprinted by Devonian metamorphism, and both units were affected by Late Cretaceous greenschist facies metamorphism. New U–Pb zircon ages reveal evidence for two stages of continental arc-like magmatism at 500–520 Ma and 550–570 Ma in the Variegated Wechsel Gneiss Complex. An age of ca. 510 Ma of detrital zircons in metasedimentary rocks also constrain the maximum age of metasedimentary rocks, which is younger than Middle Cambrian. The overlying Wechsel Phyllite Unit is younger than 450 Ma (Late Ordovician) and seems to have formed by denudation of the underlying Variegated Wechsel Gneiss Complex. We speculate on potential relationships of the continental arc-type magmatism of the Variegated Wechsel Gneiss Complex and potential oceanic lithosphere (Speik complex) of Prototethyan affinity, which is also preserved in the Austroalpine nappe complex. The abundant, nearly uniform 2.1 Ga- and ca. 2.5 Ma-age signature of detrital zircons in metasediments (paragneiss, quartzite) of the Variegated Wechsel Gneiss Complex calls for Lower Proterozoic continental crust in the nearby source showing the close relationship to northern Gondwana prominent in West Africa and Amazonia. Keywords: Subduction, Prototethys, Provenance, Neoproterozoic, Cambrian 1 Introduction As known for a long time, the Austroalpine nappe complex of Eastern Alps and Western Carpathians contains two major basement units, which collided during the Variscan orogeny (e.g., Neubauer and Frisch 1993; Putiš et al. 2009; Vozárová et al. 2012, 2017). These include (1) a nearly unmetamorphic Gondwana-derived fossilrich unit, which represents an Ordovician back-arc and Editorial handling: Othmar Müntener *Correspondence: [email protected] 1 Department of Geography and Geology, Geology Division, Paris-LodronUniversity of Salzburg, Hellbrunnerstraße 34, 5020 Salzburg, Austria Full list of author information is available at the end of the article
a Devonian passive margin (Loeschke and Heinisch 1993; Schönlaub and Heinisch 1993; Neubauer and Sassi 1993); and (2) amphibolite-grade metamorphic units, which were fully affected by Variscan amphibolite-grade metamorphism including Devonian, early Variscan highpressure
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