Rheic Ocean ophiolitic remnants in southern Iberia questioned by SHRIMP U‐Pb zircon ages on the Beja‐Acebuches amphibolites

Abstract

The Rheic Ocean was a major oceanic domain between Avalonia and Gondwana in Ordovician‐Silurian times. Most of the Paleozoic plate reconstructions assume that the Rheic Ocean suture lies within southern Iberia, coinciding with the contact between the South Portuguese Zone and the Ossa‐Morena Zone. This paper reports four Sensitive High Resolution Ion Micro‐Probe (SHRIMP) U‐Pb zircon ages from mid‐ocean ridge basalt (MORB)‐featured rocks of the Beja‐Acebuches Amphibolite unit, which crops out along the boundary between the Ossa‐Morena and the South Portuguese Zone, and is considered its most conspicuous suture unit. The obtained ages range from 332 ± 3 to 340 ± 4 Ma, corresponding to the crystallization of the mafic protoliths. These Early Carboniferous ages for the Beja‐Acebuches amphibolites imply that this unit can no longer be viewed as an ophiolite belonging to the Rheic Ocean suture, since this oceanic domain was presumably closed in Devonian times. Tectonic reconstructions joining in a single suture line the Beja‐Acebuches Amphibolite unit in southern Iberia to either the Devonian Lizard ophiolite in southern England or the root zone of the Devonian/Ordovician ophiolitic units in northwest Iberia must be therefore reconsidered because of the age difference. We interpret the Beja‐Acebuches Amphibolite unit to represent a narrow and very ephemeral realm of oceanic‐like crust that opened in Early Carboniferous times, after total consumption of the Rheic Ocean. We suggest that a mantle plume underneath southern Iberia in Early Carboniferous times is the most plausible large‐scale geodynamic scenario for the formation of these MORB‐featured rocks.

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

“…A proximal provenance is also supported by several features of the age spectra (Fig. 8), such as: (1) the abundance of Cryogenian to Ediacaran zircon ages, which are very abundant in basement metapelites (Pereira et al, 2012a(Pereira et al, , 2012bBraid et al, 2011;Talavera et al, 2012;Shaw et al, 2014;Pérez-Cáceres et al, 2017); (2) the coincidence of the Paleozoic zircon population with magmatic events in the surrounding areas (Fernández-Suárez et al, 2000;Jesus et al, 2007;Azor et al, 2008;Rosa et al, 2009) and the detrital record of the upper Paleozoic basement rocks (Braid et al, 2011;Dinis et al, 2012;Pereira et al, 2012b;Pérez-Cáceres et al, 2017).…”

The significance of Late Devonian ophiolites in the Variscan orogen: a record from the Vosges Klippen Belt

“…The second group is represented by the Brévenne Séries in the French Massif Central which preserve Late Devonian subduction-related magmatic rocks (Pin and Paquette 1997;Leloix et al 1999) and by Devonian deep marine sediments and arc to back-arc magmatic rocks of the Vrbno and Drahany Facies in Moravia (Patočka and Valenta 1996;Hladil et al 1999;Janoušek et al 2006). The Beja-Acebuches Ophiolite Complex indicating opening of a basin at 400-370 Ma in SW Iberia (Ribeiro et al 2010) could also be associated with the group of Late Devonian ophiolites, though this interpretation is still debated (Azor et al 2008;Pin et al 2008). This group of ophiolites is generally related to the existence of small backarc domains during Devonian times.…”

The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

“…It deforms the BejaAcebuches amphibolites, interpreted as a suture (Quesada et al 1994;Azor et al 2008;Pin et al 2008), has reverse and sinistral components Orozco 1988, 1991), and is displaced by Late Carboniferous sinistral wrench faults (Simancas 1983).…”