A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite Belt genesis

Abstract

[1] The South Portuguese Zone (SPZ) constitutes the southernmost segment of the Variscan Iberian Massif. It is bounded to the north by the Beja-Acebuches Ophiolitic Complex and related accretionary wedge. To the south lie the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis within the Spanish side of the SPZ supports continuous south propagating deformation, evolving from early synmetamorphic thrusting in the internal zone to thin-skinned tectonics in the southern external domain. The accretion of the SPZ to the Ossa Morena Zone is also witnessed by the presence of various mélanges, observed throughout the investigated area. Part of the mélanges observed in the IPB are related to the volcanics and mineralizations setting. A key point to understand the IPB mineralizations genesis is to constrain the volcanogenic model. One underestimated feature is the large amount of submarine calc-alkaline ignimbritic facies, implying the presence of caldera structures within the province. Such correlation between caldera environment and ore deposits strongly suggests that the IPB developed in a continental arc. Our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south. Southward, this episode is immediately followed by the development of the accretionary prism, while farther south, a second subduction zone responsible for the arc setting of the IPB initiates. Subsequent Visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the SPZ.

The Variscan Belt

“…This subduction zone is clearly documented in the South-Iberia transect during the Late Devonian-Early Carboniferous (e.g. Onézime et al, 2003;Simancas et al, 2003). The IBERSEIS deep seismic profile gives evidence for such subduction tectonics, and illustrates the detachment of the deformed upper crust above the lower crust.…”

“…3.27), associated with pyrrhotite-chalcopyrite deposits, is particularly evocative of the South Iberian Pyrite Belt (e.g. Onézime et al, 2003). Felsic magmatism also occurred in the Central Jebilet Basin, in the form of early quartz-keratophyre flows and younger, calc-alkaline granophyric sills and dykes, broadly coeval with or slightly younger than the mafic magmas, as suggested by acid-basic magmatic breccias (magma mixing).…”

The multistage crystallization of zircon in calc-alkaline granitoids: U–Pb age constraints on the timing of Variscan tectonic activity in SW Iberia

“…The South Portuguese Zone includes: (1) the Pulo do Lobo Zone, which has been interpreted to be an accretionary prism (Eden 1991;Silva et al 1990;Quesada et al 1994;Onézime et al 2003;Braid et al 2010Braid et al , 2011 (2) the Iberian Pyrite Belt with upper Devonian to lower Carboniferous sedimentary and volcanic rocks (Dunning et al 2002;Rosa et al 2008); and (3) the Carboniferous Culm series turbidites (Oliveira 1990;Oliveira and Quesada 1998;Pereira et al 2013a).…”

“…In SW Iberia, Carboniferous deformation, metamorphism, emplacement of voluminous magmatism and development of marine basins were consequence of collision between Gondwana and Laurussia that followed the closure of the Rheic Ocean (Onézime et al 2003;Braid et al 2010;Pereira et al 2012a;Gladney et al 2014).…”

Ambient Noise Recorded by a Dense Broadband Seismic Deployment in Western Iberia

“…The dominant geologic feature of western Iberia is the central Iberian massif (CIM), a block of Variscan origin (Dias and Ribeiro, 1995;Simancas et al, 2001Simancas et al, , 2003Onézime et al, 2003;García-Navarro and Fernández, 2004). The Iberian massif is bordered to the west and to the south by the Ceno-Mesozoic Lusitanian and Algarve basins, respectively, both associated with rifting of the Atlantic (e.g., Cloetingh et al, 2002;Casas-Sainz and de Vicente, 2009).…”