Geodynamic evolution of an Alpine terrane—the Austroalpine basement to the south of the Tauern Window as a part of the Adriatic Plate (eastern Alps)

Abstract

The Austroalpine basement underwent a multistage Precambrian to Tertiary evolution. Meta-magmatic rocks occur in pre-Early Ordovician and post-Early Ordovician units. Protolith zircon ages and whole-rock trace element data define two magmatic evolution lines. An older trend with Th/Yb typical of subduction-related metamorphism, started by 590 Ma N-MORB-type and 550–530 Ma volcanic arc basalt-type basic suites which mainly involved depleted mantle sources, and was continued by mainly crustal-source 470–450 Ma acid magmatic suites. A presumably younger evolution by tholeiitic MORB-type and 430 Ma alkaline within-plate basalt-type suites is characterized by an intraplate mantle metasomatism and multicomponent sources. These magmatic trends can be related to a Neoproterozoic to Ordovician active margin and a subsequent Palaeo-Tethys passive margin along the north-Gondwanan periphery. During Variscan collision, the Austroalpine basement underwent multiphase deformation and metamorphism. Early deformation involved non-coaxial shearing with formation of sheath folds and calcsilicategneiss bodies in some regions. Syndeformational clockwise P–T paths in lower basement parts passed high-pressure and high-temperature amphibolite-facies stages and are interpreted by a Devonian to Carboniferous crustal stacking. A post-collisional Permian thermal event is documented by pegmatite intrusions, LP-HT assemblages and monazite ages. Ductile overprinting under greenschist-facies conditions during the Cretaceous is indicated by foliated pegmatites and monazite ages in samples with retrogressed garnet. The emplacement of the Oligocene Rieserferner pluton was controlled by sinistral shear zone deformation along the Defereggen–Antholz–Vals line. Shear zone activity ceased at 15 Ma and was superseded by brittle strike-slip movements along NW and SE trending faults.

About a peri-Gondwanan-North African enlarged acceptance of the Caledonian Orogeny

“…In this way it becomes clear that the Ordovician granitic magmas intruded all the future Cadomian terranes. In agreement with von Raumer et al ( , 2003Raumer et al ( , 2009) and Schulz et al (2008) such widespread phenomena should be attributed to an orgenic event. We also mention that Condie et al (2008), observe a significant granitic magmatic pulse around Gondwana at 450 Ma.…”

“…Schulz et al (2008) show that in the Austroalpine domain south of the Tauern window there are many Ordovician 480 to 450 Ma acid plutonic and volcanic rocks, now orthogneisses and metaporphyroids. Their geochemical signatures are more or less influenced by a subduction process and they can by assigned to an active margin setting.…”

The north-subducting Rheic Ocean during the Devonian: consequences for the Rhenohercynian ore sites

“…Amstutz et al (1971) correlated the Middle Devonian massive sulfides and Lahn-Dill-type mineralizations from the southern and eastern Carpathians (Kräutner 1970) with those of the Rhenohercynian domain. Although Gawęda et al (2016) plead for a subduction environment under a globally called "Rhenohercynian Zone" for the western Carpathian Tatra region and its granitoids, their location in the eastern continuation of the Eastern Alps (Adriatic plate, Schulz et al 2008) would not coincide with Kräut-ner's (1970) supposed ore distribution (comp. Handy et al 2010).…”

Beauty and complexity of metamorphism: case studies from the frontal part of the Adria microplate

“…The metapelitic phyllonites of Cima Dura, a lithological horizon bordering the Tauern Window to the south for several tens of kilometers (Bianchi and Dal Piaz 1930;Borsi et al 1973Borsi et al , 1978Sassi et al 1974;Schulz et al 2008), have been interpreted as a huge syndeformational preferential zones of channelized fluid flow and associated retrograde alteration (Mazzoli et al 1993;Butturini et al 1995). Deformational effects and recrystallisation of the Alpine mylonitic metamorphic overprint are well recognised both in the field and in thin section, although not pervasively distributed.…”

“…The geochronological framework of magmatic and metamorphic events, and the lithostratigraphy of the Austroalpine basement of the Eastern Alps have been recently reviewed by Schulz et al (2008), whereas the details of the Austroalpine and Southalpine magmatic activity, from Permian to Cenozoic, and the geodynamic evolution of the region are presented in two companion papers (respectively Bellieni et al 2010, andSpiess et al 2010, this volume).…”