Abstract Protracted magmatism has long been recognized in the exotic South Portuguese Zone of southern Iberia where Early–Late Devonian volcano-sedimentary successions potentially record processes associated with ocean closure and continental collision associated with the formation of Pangaea. Collectively, these rocks represent a bimodal, predominantly submarine volcanic succession with massive sulfides spatially associated with basalts and rhyolites. Volcanic rocks are intruded by the voluminous Sierra Norte Batholith. Although the region hosts some of the world's largest ore deposits, the temporal and genetic relationships between the Iberian Pyrite Belt, the Sierra Norte Batholith and the evolution of the Variscan Orogen remain enigmatic. In an attempt to better understand these complexities, field investigations and targeted geochronology were completed throughout the volcanic and sedimentary rocks of the Iberian Pyrite Belt, and the plutonic rocks of the proximal Sierra Norte Batholith. Our results suggest that the emplacement of the pyrite belt was both pre- and syncollisional, and was initiated primarily by lithospheric delamination related to tectonic escape and crustal thinning of the lower plate. In this scenario, protracted magmatism occurred in both subaerial and subaqueous settings from c. 370 to 338 Ma.

Abstract It has long been recognized that the Late Palaeozoic evolution of SW Iberia preserves a record of terrane accretion, collision and suturing between Laurussia (South Portuguese Zone) and Gondwana (Ossa Morena Zone), which is one of the key events in the development of the Variscan orogen and the amalgamation of Pangea. The suture zone (Pulo do Lobo Zone) is classically considered to be an accretionary complex and is characterized by an assemblage of greenschist facies, polydeformed and imbricated meta-sedimentary rocks, mélanges and mafic complexes. However, recent work has shown some of the metasedimentary rocks and mélange were probaby derived from neither the upper nor the lower plates. Mafic complexes in the mélange have NMORB compositions, highly depleted Sm–Nd isotopic signatures and geochronological data imply that their protoliths probably formed prior to c. 354 Ma. Geochronological data also imply that components of the mafic mélange contain a volumetrically minor amount of ancient continental detritus. The Pulo do Lobo Zone together with the two bounding units (South Portuguese and Ossa Morena zones) were also intruded by c. 360–310 Ma composite plutons and related dykes ranging from gabbro to granite in composition. The oldest phases of these intrusions are syn- to late-tectonic with respect to the deformation. Taken together these recent observations suggest that much of the tectonic evolution of the Pulo do Lobo Zone post-dates the onset of collisional tectonics elsewhere in the Variscan orogen, suggesting that its evolution was dominated by subduction in relatively narrow tracts of oceanic lithosphere. This scenario may be broadly analogous to the complex Cenozoic tectonic evolution of the eastern Mediterranean oceanic tracts relative to the ongoing collision between the African, Eurasian and Arabian plates.

Abstract The Rheic Ocean formed during the Late Cambrian–Early Ordovician when peri-Gondwanan terranes (e.g. Avalonia) drifted from the northern margin of Gondwana, and was consumed during the collision between Laurussia and Gondwana and the amalgamation of Pangaea. Several mafic complexes, from the Acatlán Complex in Mexico to the Bohemian Massif in eastern Europe, have been interpreted to represent vestiges of the Rheic Ocean. Most of these complexes are either Late Cambrian–Early Ordovician or Late Palaeozoic in age. Late Cambrian–Early Ordovician complexes are predominantly rift-related continental tholeiites, derived from an enriched c. 1.0 Ga subcontinental lithospheric mantle, and are associated with crustally-derived felsic volcanic rocks. These complexes are widespread and virtually coeval along the length of the Gondwanan margin. They reflect magmatism that accompanied the early stages of rifting and the formation of the Rheic Ocean, and they remained along the Gondwanan margin to form part of a passive margin succession as Avalonia and other peri-Gondwanan terranes drifted northward. True ophiolitic complexes of this age are rare, a notable exception occurring in NW Iberia where they display ensimatic arc geochemical affinities. These complexes were thrust over, or extruded into, the Gondwanan margin during the Late Devonian–Carboniferous collision between Gondwana and Laurussia (Variscan orogeny). The Late Palaeozoic mafic complexes (Devonian and Carboniferous) preserve many of the lithotectonic and/or chemical characteristics of ophiolites. They are characterized by derivation from an anomalous mantle which displays time-integrated depletion in Nd relative to Sm. Devonian ophiolites pre-date closure of the Rheic Ocean. Although their tectonic setting is controversial, there is a consensus that most of them reflect narrow tracts of oceanic crust that originated along the Laurussian margin, but were thrust over Gondwana during Variscan orogenesis. The relationship of the Carboniferous ophiolites to the Rheic Ocean sensu stricto is unclear, but some of them apparently formed in a strike-slip regimes within a collisional setting directly related to the final stages of the closure of the Rheic Ocean.