Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter

Abstract

this study presents a review of published geological data, combined with original observations on the tectonics of the simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi-to anchizonal, dextral centovalli strike-slip fault. the structures of the simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. the following main Alpine tectonic phases and structures may be distinguished: pression, du soulèvement du dôme de gneiss du Lépontin et de l'abaissement de la dépression de la Dent blanche (Valpelline).Nous concluons que le poinçon adriatique s'est déplacé selon un chemin ré-gulier de direction NW à WNW, accompagné des déformations de raccourcissement NW-sE, W-E et sW-NE. studer

New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps

“…(Preiswerk et al, 1934). The contrasted tectonic syntheses of Maxelon and Mancktelow (2005) and of Steck (2008) give a measure of the uncertainties that still characterise our present-day understanding of its tectonic structure. During Alpine collision the Lepontine dome suffered severe metamorphic conditions increasing from upper greenschist facies in the north to upper amphibolite in the south (e.g.…”

“…The pre-orogenic evolution of the Alpine realm leads to the creation and differentiation of several paleogeographic domains whose remnants have subsequently been stacked in the orogenic belt during Tertiary collision (Schmid et al, 1996;Steck, 2008). From an internal (Upper) toward an external (Lower) position the following domains are generally distinguished: the Adriatic plate sensu lato in South Alpine and Austroalpine position; the remnants of the Liguro-Piemontese ocean in Upper Penninic level; the nappes and klippes issued from the Briançonnais paleogeographic domain stacked in the Middle Penninic; the remnants of the North Penninic basin and its North margin assembled in the Lower Penninic nappes together with the series originated from the Valais Trough; finally the Helvetic sensu lato domain that is distributed in the Ultrahelvetic and Helvetic nappes and in the external massifs.…”

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

“…Complex fold interference patterns resulting from intense polyphase deformation, and the potential existence of longitudinal discontinuities in the paleogeography, exclude simple correlations between tectonic structures to the west and to the east of a central zone represented by the Sambuco and Maggia gneissic bodies. Consequently there still is no general agreement on the geometry of the nappe stack in the Central Alps (see contrasted interpretations by Berger et al 2005;Grujic and Mancktelow 1996;Maxelon and Mancktelow 2005;Steck 1998Steck , 2008. Berger et al (2005) introduced into the Lepontine Alps the concept of ''tectonic accretion channel'' (TAC) (Engi et al 2001): TAC units are tectonic mélange zones with eclogitic relics interpreted as resulting from intense deformation along plate boundaries during subduction.…”

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

“…As a result, the continuation of the SFZ to the SE was still controversial and different models have been proposed: (1) a continuation of the brittle SL into the E-W striking Centovalli Line (Figure 1a), where clear brittle deformation was described [e.g., Bearth, 1956b;Laubscher, 1971;Schmid and Kissling, 2000;Steck, 2008]; (2) a continuation of the SFZ (both ductile shearing and the brittle detachment) across the Ossola Valley into the Isorno Valley toward the NE (Figure 1a) and into the Toce Dome [Mancktelow, 1985[Mancktelow, , 1990[Mancktelow, , 1992; and (3) no prolongation at all of the SFZ in the SE region but rather an accommodation by back folding (Masera and Vanzone folds) associated with anticlockwise rotation of the hanging wall [Keller et al, 2006].…”

“…[3] The Simplon Fault Zone (SFZ) [Bearth, 1956a;Steck, 1984Steck, , 1987Steck, , 1990Steck, , 2008Mancktelow, 1985Mancktelow, , 1990Mancktelow, , 1992Merle et al, 1986;Mancel and Merle, 1987] in the central Alps and the Brenner Fault Zone [Behrmann, 1988;Selverstone, 1988;Fügenschuh et al, 1997] in the eastern Alps are the most prominent low-angle detachment systems developed in the European Alps. In this paper, we specifically concentrate on the SFZ for several reasons.…”