U–Pb and Pb–Pb zircon dating of the older orthogneiss suite in the Silvretta nappe, eastern Alps: Cadomian magmatism in the upper Austro-Alpine realm

Timing of Palaeozoic magmatism in the Maggia and Sambuco nappes and paleogeographic implications (Central Lepontine Alps)

“…500 Ma old A-type alkaline granites attributed to continental rifting, recorded in the Briançonnais domain (Guillot et al 1991; and in the Silvretta nappe (Austroalpine domain; Müller et al 1995). A complete collisional sequence is documented in the Aar massif, with early HP metamorphism affecting a gabbro protolith formed at 478 ± 5 Ma, Barrovian metamorphism and decompression partial melting at ca.…”

“…an oceanic plagiogranite in the Silvretta Austroalpine nappe dated at 532 ± 30 Ma (Müller et al 1995); 2. a calc-alkaline gabbro-tonalite series in the same nappe dated at 523 ± 3 and 524 ± 5 Ma, respectively ) and a calc-alkaline granite dated at 533 ± 4 Ma (Müller et al 1995); 3. a 518 ± 11 Ma-old fractionated island-arc(?) gabbro from the mafic-ultramafic association of LoderioBiasca , intercalated between the Simano and Leventina Lower Penninic nappes, i.e.…”

The Schwarzhorn Amphibolite (Eastern Rätikon, Austria): an Early Cambrian intrusion in the Lower Austroalpine basement

“…The reported intrusion ages of older orthogneisses (Table 6) indicate two phases of increased magmatic activity in the Late Proterozoic and Early Cambrian, related to a complex active margin setting on the northern margin of Gondwana (von Quadt 1992;Kounov et al 2012;von Raumer et al 2003von Raumer et al , 2013. The first evidence of island arc magmatism is given by the 609±3 Ma metadiorite and a 568±6 Ma calc-alkaline orthogneiss (Schaltegger et al 1997;Müller et al 1995). Between 535 Ma and 520 Ma, oceanic plagiogranites infer the evolution of either back-arc or fore-arc basins but also contemporary island arc magmatism, as indicated by tholeiitic island arc basalts, calc-alkaline intermediate rocks and an S-type granitoid (Müller et al 1995(Müller et al , 1996Poller 1997;Schaltegger et al 1997).…”

“…The first evidence of island arc magmatism is given by the 609±3 Ma metadiorite and a 568±6 Ma calc-alkaline orthogneiss (Schaltegger et al 1997;Müller et al 1995). Between 535 Ma and 520 Ma, oceanic plagiogranites infer the evolution of either back-arc or fore-arc basins but also contemporary island arc magmatism, as indicated by tholeiitic island arc basalts, calc-alkaline intermediate rocks and an S-type granitoid (Müller et al 1995(Müller et al , 1996Poller 1997;Schaltegger et al 1997). This is in accordance with the geochemical characteristics of the Schwarzhorn Amphibolite which suggest a supra-subduction zone setting, and in this context most probably in an island arc setting.…”

“…An early stage of an active margin setting is attributed to a 590 Ma N-MORB-type basite, which is followed by more abundant volcanic arc basalts of early Cambrian age (Schulz et al 2004). Similarly, the Silvretta Nappe was divided into the Neoproterozoic to Lower Cambrian "older orthogneiss" and the Ordovician "younger orthogneiss" (Maggetti & Flisch 1993;Poller 1997;Müller et al 1994Müller et al , 1995Müller et al , 1996. Thus, the protolithic age of 529+9/-8 Ma of the Schwarzhorn Amphibolite would correspond to rock units regarded as "older orthogneisses" or "gneiss-amphibolite complexes".…”