Reconstructing the Variscan Terranes in the Alpine Basement: Facts and Arguments for an Alpidic Orocline

Abstract

The existence of pieces of the Variscan belt in the Alpine basement has been acknowledged for a long time but the correlation of these massifs to the litho-tectonic domains established in Western Europa outside the Alpine chain is still disputed. Due to their ubiquitous character, the abundant late Variscan migmatites and granites are useless to reconstruct the Variscan architecture in the Alpine basement. Ophiolitic sutures, high- and low-grade metamorphic units, and foreland basins provide a preliminary reconstruction of the Variscan orogen exposed in the Alpine basement. The longitudinal extension of the Armorican and Saxo-Thuringian microcontinents between Laurussia and Gondwana is proposed independently of the Intra-alpine and Galatian terranes. The litho-tectonic units of the Corsica-Sardinia segment are correlated to the Moldanubian, Armorican and Saxo-Thuringian Domains. In the Alpine Helvetic and Penninic Domains, the Chamrousse ophiolites are ascribed to the Tepla-Le Conquet suture, whereas the Lepontine, and Stubach ophiolites represent the Rheic suture. The south-directed nappe stack of the South Alpine Domain is similar to the Moldanubian French Massif Central. In the Austroalpine nappe stack, the Ritting ophiolites separate Saxo-Thuringia and Armorica continental blocks. Disentangling the Variscan belt in the Alpine basement suggests a concave-to-the-East arcuate structure called here the Variscan Alpidic orocline.

Carboniferous-Permian tectono-metamorphic evolution of the Pelvoux Massif (External Crystalline Massif, Western Alps), with discussion on flow kinematics of the Eastern-Variscan Shear Zone

“…A similar D1/M1 event is documented in the SW Belledonne area with the wellpreserved low angle S1, holding a E-W trending L1 stretching lineation, interpreted as due to an eastward nappe stacking event responsible for crustal thickening coeval with the barrovian metamorphism (M1) (Fernandez et al, 2002;Fréville et al, 2018). In SW Belledonne massif, the peak of M1 metamorphism is dated on monazite (LA-ICP-MS) and zircon (SIMS) at around 337 ± 7 Ma and 338 ± 5 Ma respectively (Fig.…”

“…0.5-0.6 GPa, 600 °C, recorded in staurolite-bearing micaschists and up to ca. 0.8 GPa, 680 °C for the migmatitic gneiss in lowest unit (Guillot and Ménot, 1999;Fernandez et al, 2002;Fréville et al, 2018). The M1 metamorphism is coeval with a D1 deformation characterized by the development of a westward dipping foliation S1 and E-W stretching L1 lineation interpreted as an eastward nappe stacking event (Fréville et al, 2018).…”

“…1). In spite of several geodynamic interpretations Faure et al, 2014;Faure and Ferrière, 2022;Fernandez et al, 2002;Oliot et al, 2015;Rossi et al, 2009;Von Raumer et al, 2013), the timing of the main tectono-metamorphic events in the ECMs, and the correlations between these massifs remain poorly constrained mainly because of a strong imprint by late-orogenic transpressional tectonics during Carboniferous time and intense partial melting and plutonism in the mid-lower crust at that time. Widespread Carboniferous crustal partial melting in response to thermal relaxation (i.e.…”

Deformation, crustal melting and magmatism in the crustal-scale East-Variscan Shear Zone (Aiguilles-Rouges and Mont-Blanc massifs, Western Alps)

“…1A for instance) (e.g. Ballèvre et al, 2018;Simonetti et al, 2020;Martinez-Catalan et al, 2021;Faure and Ferrière, 2022).…”

Thermal evolution of a Variscan syn-orogenic intracontinental basin (Servoz basin, Western Alps): RSCM geothermometry and geochronology

“…Dobmeier et al, 1999), which prevents correlations with preserved basins in other Variscan massifs. Recently, it has been proposed that the ECMs belong to the Saxothuringian zone of the Variscan belt, rather than to the Moldanubian zone (Faure & Ferrière, 2022). Therefore, additional data on the early Variscan history of the ECMs are required to constrain their paleogeographic position in the Variscan belt and their geodynamic timing and thermal evolution.…”