Status of Basement Terranes in Orogens: Insights From the Cadomian Domain of the North Armorican Variscides, Western France

Abstract

Most of mountain belts worldwide contain remnants of older orogenic systems commonly referred to as fragments, blocks, inliers, slivers, ribbons or terranes. These basement rocks, named as "terranes" in the present work, can behave as strong material or be variably affected by younger tectono-metamorphic events. In the latter case, and when displaying a cold and anomalously thick lithosphere, they form cratonic nuclei (e.g., Wang et al., 2014). Cadomian basement terranes (750-540 Ma) are currently disseminated in the Variscan belt (360-300 Ma) of Central and Western Europe (Figure 1). Most of them display a polyorogenic structural pattern resulting from superimposed Cadomian/Variscan deformations. One exception is the Cadomian domain in Northern Armorica (North Armorican Cadomian-floored domain [NAD] in Figure 1) which is generally thought to have escaped Carboniferous compressional events (

Ordovician sedimentation and basin development in the North Armorican Massif, NW France: Field evidence from the northern Cotentin Peninsula

“…1c). Together, these accommodate around 30% of crustal shortening (Le Gall et al 2021). The amount of dextral shearing on the North and South Armorican Shear Zones is disputed.…”

Katian volcanism in Central Armorican Domain (France) and Central Iberian Zone (Portugal): a single monogenetic basaltic field?

“…These magmatic episodes were linked to a large fragmentation event of the northern Gondwana margin, resulting in the formation of terrane assemblages separated by marine areas (Crowley et al 2000). The ATA (Armorican Terrane Assemblage), also known as Armorican microplate (Matte 2001;Fernández-Suárez et al 2002;Robardet 2003), was one of these continental archipelagoes, comprising a Gondwana-derived Cadomian block in its northern part (Le Gall et al 2021). Despite the fact that the Ordovician paleogeography is nowadays relatively well constrained on a global scale, especially since the works of Fortey and Cocks (2003), Franke et al (2017) and Cocks and Torsvik (2021), the regional features of such terrane assemblages (including domain arrangement, geoenvironment, sedimentary and volcanic features), are still little known.…”