Evolution of the Silvretta Nappe

Maggetti, Marino; Flisch, Markus

doi:10.1007/978-3-642-84640-3_28

Cited by 25 publications

(13 citation statements)

References 14 publications

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“…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".…”

Section: Discussionmentioning

confidence: 99%

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

Nilius¹,

Froitzheim²,

Nagel³

et al. 2016

Geologica Carpathica

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Abstract:The Alpine nappe stack in the Penninic-Austroalpine boundary zone in the Rätikon (Austria) contains a 4×1 km tectonic sliver of meta-diorite, known as the Schwarzhorn Amphibolite. It was deformed and metamorphosed in the amphibolite facies and is unconformably overlain by unmetamorphic Lower Triassic sandstone, indicating pre-Triassic metamorphism. Cataclastic deformation and brecciation of the amphibolite is related to normal faulting and block tilting during Jurassic rifting. Zircon dating of the Schwarzhorn Amphibolite using LA-ICP-MS gave a U-Pb age of 529+9/-8 Ma, interpreted as the crystallization age of the protolith. Geochemical characteristics indicate formation of the magmatic protolith in a supra-subduction zone setting. The Cambrian protolith age identifies the Schwarzhorn Amphibolite as a pre-Variscan element within the Austroalpine basement. Similar calc-alkaline igneous rocks of Late Neoproterozoic to Early Cambrian age are found in the Upper Austroalpine Silvretta Nappe nearby and in several other Variscan basement units of the Alps, interpreted to have formed in a peri-Gondwanan active-margin or island-arc setting.

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Section: Discussionmentioning

confidence: 99%

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

Nilius¹,

Froitzheim²,

Nagel³

et al. 2016

Geologica Carpathica

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“…Eclogite-facies metamorphism (730 C, 2.7 GPa) occurred during Variscan (360±350 Ma) times (Miller and Tho Èni, 1995). Based on geochemical and metamorphic characteristics, the O È tztal-Stubai eclogites are similar to those from the Silvretta basement (Maggetti et al, 1987;Maggetti and Galetti, 1988;Maggetti and Flisch, 1993), for which Panafrican (> 900 Ma) or`C aledonian'' high-pressure, low-pressure metamorphic events (D 1 , 550±650 C, 1.4±1.6 GPa) have been assumed. However, no geochronological data exist so far for eclogite facies events predating Variscan amphibolite facies (D 2 , 600±680 C, 0.55±0.75 GPa).…”

Section: Tectonic Implications and Conclusionmentioning

confidence: 98%

“…in the Koralpe-Saualpe complex (Manby and Thiedig, 1988;Miller et al, 1988;Miller, 1990;Tho Èni and Miller, 1996;Gregurek et al, 1997). Most of these eclogites are related to Eoalpine metamorphic events (Frank et al, 1987;Jagoutz, 1992, 1993;Tho Èni and Miller, 1996), but pre-Alpine ages are known for eclogite facies metamorphism in the western parts of the Austroalpine crystalline basement units (e.g., Maggetti and Flisch, 1993;Miller and Tho Èni, 1995). The presence of eclogite at Hochgro Èssen (Muriden basement complex) is of interest because this area is situated in the northernmost parts of the Austroalpine basement units that have undergone only Alpine greenschist facies overprint, as inferred from surrounding phyllites and gneisses.…”

Section: Introductionmentioning

confidence: 99%

Relics of eclogite facies metamorphism in the Austroalpine basement, Hochgr�ssen (Speik complex), Austria

Faryad

Melcher

Hoinkes

et al. 2002

Mineralogy and Petrology

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Retrograde eclogites and serpentinites from the Hochgro Èssen massif, Styria, are parts of the Speik complex in the Austroalpine basement nappes of the Eastern Alps. They are in tectonic contact with pre-Alpine gneisses, amphibolites, and Permo-Triassic quartz phyllites (Rannach Series). The eclogites are derived from ocean-¯oor basalts with af®nities to mid-ocean ridge and back-arc basin basalts. Fresh eclogites are rare and contain omphacite with a maximum of 39 mol% jadeite content, garnet (Py 15±19 ) and amphibole. Retrograde eclogites consist of amphibole and symplectites of Na-poor clinopyroxene (5±8 mol% Jd) albite AE amphibole. Amphiboles are classi®ed as edenite, pargasite, tschermakite, magnesiohornblende and actinolite. In relatively fresh eclogite, edenite is a common amphibole and texturally coexists with omphacite and garnet. An average temperature of 700 C was obtained for eclogite facies metamorphism using garnet-pyroxene thermometry. A minimum pressure of 1.5 GPa is indicated by the maximum jadeite content in omphacite. Thermobarometric calculations using the TWEEQ program for amphibole in textural equilibrium with omphacite and garnet give pressures of 1.8±2.2 GPa at 700 C. The equilibrium assemblage of Na-poor clinopyroxene, albite, amphibole and zoisite in the symplectites gives a pressure of about 0.6±0.8 GPa at 590±640 C. 40 Ar/ 39 Ar radiometric dating of edenitic amphibole in textural equilibrium with omphacite gave a plateau age of Ã Present address: Federal Institute of Geosciences and Natural Resources, Hannover, Federal Republic of Germany 397.3 AE 7.8 Ma, and probably indicates retrograde cooling through the closure temperature for amphibole ($ 500 C). The age of the high-pressure metamorphism thus must be pre-Variscan and points to one of the earliest metamorphic events in the Austroalpine nappes known to date.

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“…The 451 ± 2 Ma old (Flisch 1987) ''Young Orthogneisses'' of the Silvretta Nappe consist of metamorphised neutral-acidic volcanic and intrusive rocks (Magetti and Flisch 1993). The Magdalensberg Formation of the Stolzalpe Nappe is composed by Middle Ordovician (Havlicek et al 1987) mafic, alkaline rocks.…”

Section: Ca 450 Ma Groupmentioning

confidence: 99%

Multiple provenance of detrital zircons from the Permian–Triassic boundary in the Bükk Mts., Hungary

Zajzon

Szabó²,

Weiszburg

et al. 2009

Int J Earth Sci (Geol Rundsch)

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Detailed zircon analyses were carried out on samples from the Bálvány North section, which contains the Permian-Triassic boundary. A fine-grained sandstone bed within the ''boundary shale'' contains a significant amount of zircon crystals. Pupin morphological, scanning electron microscopy [secondary electron, back-scattered electron, cathodoluminescence (CL)] and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) investigations were done in selected single grains to combine morphological information with radiometric ages, and infer the provenance of zircons. Three populations are distinguished on the basis of Pupin morphology. Their centres of gravity are S17, S2 and P1. The LA-ICP-MS radiometric ages reveal three main age groups and a smaller one, apart from a few scattered old ages. The largest group, comprising ca. 50% of the measured grains, has an age of 470-440 Ma. The two other main groups, which together represent ca. 25% of the measured grains, are around 280 and 600 Ma. The 280 Ma group contains slightly more grains than the 600 Ma group. A small group has an age of 370-340 Ma. In addition, there are some older grains with ages of 850, 969, 1,050 and 2,150 Ma. Based on the zircon morphology no clear separation of the different age groups could be made. Both the 280 Ma and the 470-440 Ma age groups tend to show zircon crystals derived from three types of sources: crustal granites, calcalkaline granitoids and alkali granites and/or their volcanic equivalents. Zircons in the 450 Ma group have a magmatic rim around their altered, relict core, as revealed by CL images. Post-magmatic processes also affected the rim. The age of the core is possibly reset during the formation of the magmatic rim. This suggestion is supported by the LA-ICP-MS data, because no difference was seen between the core and the rim. The different roundness of the zircons, the well-sorted crystals and the at least five different source rocks indicate previous concentration of the grains, before their transportation into the ''boundary shale''. Austroalpine and Southern Alpine rocks could be the sources of the zircon crystals, which fit well into the paleogeographical model of the area, which suggests that the Bükk Mts. was located in the foreground of the Alpine units.

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Evolution of the Silvretta Nappe

Cited by 25 publications

References 14 publications

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

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

Relics of eclogite facies metamorphism in the Austroalpine basement, Hochgr�ssen (Speik complex), Austria

Multiple provenance of detrital zircons from the Permian–Triassic boundary in the Bükk Mts., Hungary

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