The early evolution of SW Europe Variscides started by opening of the Rheic ocean at ∼500 Ma, splitting Avalonia from Armorica/Iberia. Subduction on the SE side of Rheic generated the Paleotethys back‐arc basin (430–390 Ma, splitting Armorica from Iberia), with development of Porto‐Tomar‐Ferreira do Alentejo (PTFA) dextral transform defining the boundary between continental Armorica and Finisterra microplate to the W. Obduction of Paleotethys was followed by Armorica/Iberia collision and emplacement of NW Iberian Allochthonous Units at 390–370 Ma, whereas toward the west of PTFA, there was antithetic ophiolite obduction (Beja‐Acebuches and Rheic ophiolites plus Finisterra continental slices) on top of Ossa‐Morena Zone, with simultaneous development of eclogites and orogenic magmatism under a flake–double wedge tectonic regime. Continued convergence (<370 Ma) proceeded by intracontinental deformation, with progressive tightening of the Ibero‐Armorican Arc through dextral transpression on the Cantabrian Indentor, from Iberia to Armorica. The proposed model is discussed at the light of the driving mechanism of “soft plate tectonics.”

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The Almade n district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury, nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman times, with peak production during the Renaissance and between 1939± 1945. The district is hosted by a Paleozoic synclinorium overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales and quartzites. Diatremes, alkaline lavas of dierent composition, and late tholeiitic diabases account for the Ordovician to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits of Almade n can be classi®ed into two main types: type 1, early stratiform type ores characterized by cinnabar deposition on the lower Silurian quartzites (Criadero quartzite; e.g. the Almade n and El Entredicho deposits), and type 2, late discordant orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the`frailesca rocks') of alkaline basaltic composition. In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type 2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepcio n) to Upper Devonian (e.g. Corchuelo).

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