The Cambrian-Early Ordovician Rift Stage in the Gondwanan Units of the Iberian Massif

Abstract

A rifting stage initiated the Variscan cycle in NW Gondwana, lasted from Terreneuvian to Early Ordovician times and culminated in opening of the Rheic Ocean. The result of lithospheric stretching was the development of a horst-and-graben structure in the upper crust and formation of basins with sharp variations in thickness and facies of the sedimentary infill. Emplacement of large volumes of igneous rocks, both plutonic and volcanic, accompanied this stage in three different intervals: (i) Early Igneous Event (Terreneuvian), exclusively composed of felsic peraluminous rocks associated with the formation of core complexes in the mid-upper crust; (ii) Main Igneous Event (Cambrian Series 2 to Furongian), displaying bimodal character; and iii) Late Event (Tremadocian-Floian), with mixed characteristics of the other two events and abundant peralkaline rocks. The rifting axis was initially located close to the Cadomian suture that fringed the Ossa Morena Zone. For about 60 m.y. the rifting processes initially propagated "ziplike" along the axis and then widened cratonward to affect inner parts of Gondwana, such as the Central Iberian Zone. The rift/drift transition was diachronous, starting in Iberia (Ossa Morena Zone) in the Furongian.

Updated stratigraphic framework and biota of the Ediacaran and Terreneuvian in the Alcudia-Toledo Mountains of the Central Iberian Zone, Spain

“…Phase, which affected the Central Iberian and Ossa-Morena Zones of the Iberian Massif and the Anti-Atlas of Morocco (Álvaro & Vizcaïno, 2018;Sánchez García et al, 2019) and is associated with the onset of: (i) a variable stratigraphic hiatus represented by angular discordance and paraconformable discontinuities overlain by Furongian breccias and conglomerates, punctuated, in the Ossa-Morena Zone, by the Venta del Ciervo tuff (~ 489 Ma; López-Guijarro et al, 2008); and (ii) the intrusion and extrusion of large Furongian granitoiddominant and volcanic/volcaniclastic bodies with calcalkaline affinity, such as the Ollo de Sapo and Urra formations. Although some authors have interpreted these igneous rocks as related to both subduction (e.g., Castro et al, 2002;Díez Montes et al, 2010;Montero et al, 2017;García-Arias et al, 2018) and an intermediate magmatism associated with migmatites that extended subduction processes until at least ca.…”

“…Although some authors have interpreted these igneous rocks as related to both subduction (e.g., Castro et al, 2002;Díez Montes et al, 2010;Montero et al, 2017;García-Arias et al, 2018) and an intermediate magmatism associated with migmatites that extended subduction processes until at least ca. 465 Ma (Pereira et al, 2018), the Toledanian Phase has been recently reinterpreted as a break-up unconformity (for a summary, see Sánchez-García et al, 2019) representing the sharp transition from rift to drift conditions that led to the subsequent opening of the Rheic Ocean (Linnemann et al, 2007;von Raumer & Stampfli, 2008;Nance et al, 2010Nance et al, , 2012.…”

The enigmatic curvature of Central Iberia and its puzzling kinematics

“…Oliveira et al, 2019a;2019b); and (3) the Baixo Alentejo Flysch, which is located to the southwest and is a syn-orogenic composite turbiditic sequence with ages from ~330 to ~310 Ma (Oliveira et al, 2019b). The boundary between the South Portuguese and Ossa Morena zones is a sinistral shear zone (so-called Beja-Acebuches, Quesada and Dallmeyer., 1994;Pérez-Cáceres et al, 2016) that contains a strongly deformed amphibolitic belt with oceanic affinity (Munha et al, 1986;Munha, 1989;Quesada et al, 2019).…”

“…This belt potentially represents dismembered relics of the Rheic ocean and/or a subsidiary seaway that opened during a Variscan transtension event in SW Iberia (e.g. Pérez-Cáceres et al, 2015;Quesada et al, 2019).…”

“…3). However, the Early Paleozoic basin architecture in Iberia and their local deformation events require further research (Sánchez-García et al, 2019).…”