Erstfeld-Gneiskomplex

Représentation et statut

Index

GM-E

Couleur CMYK

(0%,16%,16%,2%)

Couleur RGB

R: 250 G: 190 B: 175

Rang

Formation lithostratigraphique

Usage

Ce terme est en usage.

Status

terme informel

Discussion du statut

Nomenclature

Deutsch

Erstfeld-Gneiskomplex

Français

Complexe gneissique d'Erstfeld

Italiano

Complesso gneissico di Erstfeld

English

Erstfeld Gneiss Complex

Origine du nom

Erstfeld (UR) im Reusstal

Variantes historiques

Erstfeldergneis (Baltzer 1880, Heim 1891, Sauer 1905, Staub 1911), Erstfelder-Gneiszone (Hugi 1934), gneiss d'Erstfeld (Gysin 1952a), Erstfelder-Gneis (Hügi 1955), série d'Erstfeld-Lötschental (Krummenacher 1959), Erstfeld Gneiss Complex (Berger et al. 2017), Erstfeld-Gneiskomplex (Gisler 2018)

Description

Description

Altkristallin des Aarmassivs: helle Biotit-Gneise von sehr variabler Textur (fluidal, plattig-parallel, massig), feinkörnigen Glimmergneis. / Meist helle, oft gebänderte Biotitgneise und -schiefer, Biotit-Sericit-Schiefer, Biotit-Chlorit-Schiefer (Metasedimente) oder granitische Orthogneise, Einschaltungen von Kalksilikat-Marmoren, Marmoren und Amphibolitschollen.

Hiérarchie et succession

Unités hiérarchiquement subordonnées

• Silberberg-Gneis
• Graustock-Gneis
• Grüeni-Gneis

Unités sus-jacentes

• Innertkirchen-Migmatit

Âge

Âge au sommet

• Paléozoïque

Âge à la base

• Précambrien

Géographie

Extension géographique

Nördliches Aarmassiv, von Erstfeld (mit eine maximale Breite von 4 km) bis zu Jungfrau - Lauterbrunnenbreithorn im Westen.

Région-type

Reusstal / Erstfeldertal (UR)

Paléogéographie et tectonique

• Socle polycyclique anté-varisque de l'Helvétique

Paléogéographie

continent européen

Termes génériques

• Aar

Métamorphisme

polycyclique

Faciès métamorphique

• faciès à schistes verts (épizone)
• faciès à amphibolites
• faciès à granulites

Remarque sur le métamorphisme

high-grade metamorphism at least during the Ordovician and Variscan

Références

Révision

Berger Alfons, Mercolli Ivan, Herwegh Marco, Gnos Edwin (2017) : Geological Map of the Aar Massif, Tavetsch and Gotthard Nappes. Geological Special Map 1:100'000, Explanatory Notes 129

p.29: Biotite-plagioclase gneiss with sillimanite, kyanite and garnet as accessory phases represents the dominant rock type of the Erstfeld Gneiss Complex. The structure of this gneiss is very heterogeneous, showing transitions between a centimetre-scale layering of leucocratic and melanocratic bands and containing locally spectacular ptygmatic folds. Larger (up to hundreds of metres) homogeneous leucocratic bodies were even interpreted in the past as separate single intrusions.
These structures result from different degrees of partial melting during anatexis of the same metasedimentary sequence. Heterogeneous polycyclic deformation overprints these originally already complex structures and is responsible for the present-day aspect of these gneisses (ABRECHT 1994 and references therein). Calcsilicate rocks, marble, amphibolite and ultramafic rocks occur as centimetre- to metre-sized inclusions in the biotite-plagioclase gneiss as well as larger coherent intercalations. In particular, in the region of the Sustenpass and in the Erstfeldertal, large sequences of metasedimentary gneiss, marble and calcsilicate rocks occur 
alternating with amphibolite (sometimes with relictic gabbroic textures), garnet amphibolite and ultramafic rocks: the “Silberberg Serie” (LOTZE 1914, SCHALTEGGER 1984, ABRECHT 1994), the “Graustock and Grüeni Gneisses” (LEHMANN 2008) and as exposures in the Gotthard Base Tunnel near Erstfeld (BEKADDOUR 2009). ABRECHT et al.(1991) interpreted this peculiar lithostratigraphic association of the “Silberberg Serie” as an ophiolitic olistostrome deposited in a flyschoid setting.
The relictic primary mineral association found in all rocks of the Erstfeld Gneiss Complex indicate metamorphic conditions at upper amphibolite- to granulite-facies conditions (ABRECHT 1994, LEHMANN, 2008). These mineral assemblages were subsequently overprinted in a complex way at lower metamorphic conditions. This complex polycyclic structural and metamorphic history indicates a multistage evolution of the Erstfeld Zone. This is further supported by isotope ages of different geochronometres, indicating the occurrence of high-grade metamorphism, at least during the Ordovician and Variscan cycles (SCHALTEGGER 1993, Tab. 2). Moreover, LEHMANN (2008) used electron microprobe chemical age dating to date complex-zoned monazites of the “Graustock Gneiss” yielding Variscan metamorphic ages but also age domains with a peak at ~520 Ma and relic cores of > 600 Ma. Similarly, the biotite-plagioclase gneiss and the “Grüeni Gneiss” yielded monazite ages of ~380 Ma and cores of > 500 Ma.

Principales publications

Arbenz P. (1910) : Zur Kenntnis der Bohnerzformation in den Schweizeralpen. Beitr. geol. Karte Schweiz (N.F.) 24/1, 16 Seiten

Matériel et divers