Correlation of the nappe stack in the Ibero-Armorican arc across the Bay of Biscay: a joint French–Spanish project

Abstract

A correlation between allochthonous units exposed in the NW Iberian Massif and the southern Armorican Massif is carried out based on lithological associations, structural position, age and geochemistry of protoliths and tectonometamorphic evolution. The units on both sides of the Bay of Biscay are grouped into Upper, Middle and Lower allochthons, whereas an underlying allochthonous thrust sheet identified in both massifs is referred to as the Parautochthon. The Lower Allochthon represents a fragment of the outermost edge of Gondwana that underwent continental subduction shortly after the closure of a Palaeozoic ocean which, in turn, is represented by the Middle Allochthon. The latter consists of supra-subduction ophiolites and metasedimentary sequences alternating with basic, mid-ocean ridge basalt (MORB)-type volcanics, with inheritances suggesting the proximity of a continental domain. Seafloor spreading began at the Cambro-Ordovician boundary and oceanic crust was still formed during the Late Devonian, covering the lifetime of the Rheic Ocean, which is possibly represented by the Middle Allochthon. The opening of the oceanic domain was related to pulling apart the peri-Gondwanan continental magmatic arc, which is represented by the Upper Allochthon.

The transition from Pangea amalgamation to fragmentation: Constraints from detrital zircon geochronology on West Iberia paleogeography and sediment sources

“…2) played an important role in accommodating the oblique convergence between Laurussia and Gondwana (Ribeiro et al, 1990;Dias and Ribeiro, 1993;Shelley and Bossière, 2000;Simancas et al, 2005;Martínez Catalán et al, 2007;Ribeiro et al, 2007). Other authors, however, consider that these shear zones represent large strike-slip faults that crosscut the original boundaries between the Variscan geotectonic zones (Martínez Catalán, 2011;Ballèvre et al, 2014;Martínez Catalán et al, 2014;Gutiérrez-Alonso et al, 2015). Regardless of their specific roles during Variscan and post-Variscan deformation, they have a dextral sense of movement and are associated with the formation of the Pennsylvanian Buçaco (along the Porto-Tomar Shear Zone; Flores et al, 2010) and Santa Susana (along the Santa Susana Shear Zone; Machado et al, 2012) pull-apart basins (Fig.…”

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

“…The WEVB is classically divided into a number of zones based on the differences in the early Paleozoic stratigraphy as well as structural style, metamorphism, and magmatism (Lotze, 1945;Julivert, 1971;Franke, 1989;Martínez Catalán et al, 1997Ballèvre et al, 2014). These zones broadly correspond to increasing distance from the Gondwanan margin toward the Rheic Ocean (Fig.…”

Pre-Cadomian to late-Variscan odyssey of the eastern Massif Central, France: Formation of the West European crust in a nutshell

“…480 Ma age peak. This event resulted in the opening of the Rheic Ocean and probably other smaller oceanic domains (e.g., Galicia-Massif Central Ocean(s)), and the drift of the Avalonian continental ribbon away from the main Gondwana supercontinent (e.g., Gerdes and Zeh, 2006;Linnemann et al, 2008;Nance et al, 2010;Ballèvre et al, 2014). Finally, the closure of these oceans from the Devonian to the Carboniferous led to the formation of the supercontinent Pangea during the Variscan orogeny (e.g., Kroner and Romer, 2013;Matte, 2001, Nance et al, 2010, as is partly recorded by the ca.…”