A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia

Abstract

Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean, Associated allochthonous terranes in the hanging-and foot-walls of the suture derive from the former margins.whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana, The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical. petrological. structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia-Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots. ResumeUne suture sans racines et la perte des racines d'une cha'ine montagneuse : la cha'ine varisque du Nord-Ouest de I'Iberie. Des ophiolites d'ages differents affieurent dans le Nord-Ouest de l'Iberie dans une suture sans racines. temoin de l'ocean * Corresponding author.E-mail address: jrmc @usal.es (J.R. Martfnez Catahin).RhMque. Les terrains allochtones sur et sous la suture derivent de ses deux rnarges, tandis que I' autochtone relatif appartient a la marge passive du Nord de Gondwana. On peut deduire l'evolution des plaques dans cetle partie de la region circum-Atlantique it partir des dounees stratigraphiques, petrologiques, structurales, metarnorphiques et geochronologiques. Celte evolution inc1ut le developpernent d'un rift continental et l'ouverture de l'ocean Rhe'ique pendant le Carnbro-Ordovicien ainsi que sa ferrneture au Devonien rnoyen a superieur. On decrit aussi I' evolution de la convergence et collision varisque entre Laurussia et Gondwana, du debut jusqu'aux demiers stades d'un effondrernent associe a la perte des racines orogeniques.Keywords: Oceanic suture; Rheic Ocean; Variscan evolution; N\V IberiaMots des : Suture oceanique ; Ocean Rhelque ; Evolution varisque ; Nord-Ouest de l'Iberie IntrodnctionThe North-West (NW) of the Iberian Massif is located at the hinge zone of the Ibero-Armorican Arc ( Fig. 1) and preserves relicts of oceanic domains that once separated the Paleozoic continents [50,51]. A suture occurring in the hanging-wall of a large thrust system is rootless, which makes its interpretation difficult. However, the excellent exposure of the ophiolitic and associated allochthonous terranes permits the establishment of a sequence of emplacement, crosscutting relationships, and metamorphic gradients.In the absence of continental-scale strike-slip shear zones and faults, the Galician-northeru Portugal section is retrodeformable, permitting qualitative palinspastic reconstructions of the Gondwana-Laurussia conver gence. These characteristics make of NW Iberia a key site to uuravel the history of the Paleozoic plate evolution of the circum-Atlantic region, and specially that of the Rheic Ocean. This contrib...

The onset of the assembly of Pangaea in NW Iberia: Constraints on the kinematics of continental subduction

“…The supercontinent Pangaea assembled from the collision between Gondwana and Laurussia, following the closure of the Rheic Ocean dur ing the Upper Paleozoic (Matte, 1986;Scotese, 1997;Stampfli and Borer, 2002;Martinez Catalan et al, 2009 (Martinez Catalan et al, 1996). There is a lack of consistent indicators of along-strike components during the subduction, so ideas about the early relative plate movement between the two main land masses involved in the assembly of Pangaea are highly speculative (e.g.…”

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

“…Distribution of continental blocks based on Stampfli and Kozur (2006), Golonka (2007) and Sibuet et al (2012). within the Variscan Belt (e.g., Arenas and Martínez Catalán, 2003;García-Navarro and Fernández, 2004;Martínez Catalán et al, 2009). Several authors have suggested that after the main phase of Variscan deformation, there was a period of delamination and crustal collapse with an associated increased heat flow responsible for renewed igneous activity in central and NW , which was probably promoted by orocline bending (Gutiérrez-Alonso et al, 2008, 2011, 2012Weil et al, 2010Weil et al, , 2013Pastor-Galán et al, 2013).…”

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

“…1 and 2). This suture is rootless and problems exist for a clear correlation with the other suture zones described in the belt, although it is generally accepted that all of them correspond to a unique, more or less complex, oceanic domain, the Rheic Ocean (Simancas et al, 2005;Martínez Catalán et al, 2009). The allochthonous complexes show a late Variscan synformal structure and they are considered to be large klippens composed of several terranes, stacked in a huge and structurally intricated nappe pile (Fig.…”