Hydrothermalismes anté-Hercynien en Sud-Ibérie : apport de la géochimie isotopique du plomb.

International audienceLead isotope study has been performed on massive sulphide deposits of Ossa-Morena and Aracena Belt (South Iberia). Results suggest the existence of at least two ancient hydrothermal events. The first one, Upper Brioverian in age (not, vert, similar600-570 Ma), gave birth to Maria-Luisa and Puebla de la Reina massive sulphide deposits; it thus confirms the existence of a Cadomian orogen in South Iberia. Isotopic compositions indicate a local contribution of mantle-derived material (Maria Luisa mine), confirming the presence of ancient oceanic crust in Aracena Belt. This mineralising event seems to extend till the Armorican Massif. The second episode, Eo-Hercynian in age (not, vert, similar400-350 Ma) has allowed genesis of massive sulphide deposits of la Nava Paredon and Aguas Blancas, and could be coeval with the emplacement of South-Iberian massive sulphide ore deposits in the neighbouring South-Portuguese Zone. A more continental crustal source for later ore deposits could explain the much more important metal accumulation in this zone

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

International audienceThe 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

Structural evolution of the southernmost segment of the West European Variscides : the South portuguese Zone (SW Iberia).

The South Portuguese Zone (SPZ) represents the southernmost unit of the Iberian Massif. It is mainly composed of three structural domains, from north to south, the Beja–Acebuches Ophiolitic Complex (BAOC), The Pulo do Lobo Antiform (PLA) and the Iberian Pyrite Belt (IPB). This study proposes a structural analysis of the Spanish part of the SPZ that allows us to point out two main kinds of deformation; one accommodated by early top-to-the-south and following sinistral strike-slip tectonics in the northern part of the SPZ and the other by top-to-the-south thrusting in a wide southern branch. This transition, underlining the strain partitioning, is analysed by lattice preferred orientation of quartz using the texture goniometry method. It shows that the deformation is accommodated in the PLA at low to middle temperature by basal and prismatic left angle bracketaright-pointing angle bracket slip. Quartz textures suggest increasing thermal conditions of deformation from thrust to strike-slip tectonics. Our work within the IPB allows us to present a sequence of deformation showing a primary south-verging ductile thrusting and coeval crustal thickening in response to the thin-skinned tectonics. The progressive deformation generated backthrusts while it turns shallower southward. These features are summarised in an interpretative cross-section of the SPZ that underlines the main structural style of deformation, the fore-mentioned southward propagating thin-skinned thrusts

Syn- to late tectonic stockwork emplacement within the Spanish section of the Iberian Pyrite Belt : structural, textural and mineralogical constraints from the Tharsis-La Zarza area.

In deformed massive sulfide deposits, it is commonly difficult to distinguish between primary stockwork mineralization and remobilized sulfides that occupy late cleavages and deformation structures, and the mechanism of formation of the deformation veins is not always clear. An analysis of sulfide vein networks associated with two massive sulfide deposits of the Iberian Pyrite Belt is presented as an example of this complexity. Variscan deformation has affected the massive sulfide-related stockworks at La Zarza and Tharsis and led to the formation of sulfide-bearing deformation veins. The primary feeder stockwork has a complex mineralogical composition with pyrite-rich veins rimmed by narrow Co-As assemblages (e.g., cobaltite and arsenopyrite). Interstitial galena, chalcopyrite, and sphalerite minerals are also observed. The vein set developed during deformation was emplaced within cleavage and shear planes characteristic of the regional south-verging tectonics. Away from massive sulfides, the characteristic minerals of the syntectonic veins are pyrite and quartz. However, deformation veins developed in contact with primary feeder veins and massive sulfide have Co-As–rich rims and base metal sulfides similar to the primary feeder veins. The development of the complex vein paragenesis within the stockwork zones is explained in terms of regional-scale deformation models