Late- to post-Variscan tectonics and the kinematic relationship with W–Sn vein-type mineralization: evidence from Late Carboniferous intramontane basins (Porto–Sátão syncline, Variscan Iberian belt)

Abstract

Many studies have constrained that late-Variscan buckling produced the arcuate geometry of the Ibero-Armorican belt. Nonetheless, debate remains on the associated geodynamic framework. Poorly studied Late Carboniferous intramontane basins offer an excellent framework to decipher the timing and kinematics of the late- to post-Variscan tectonics. Understanding the latter also helps constrain the structural emplacement mode of contemporaneous W–Sn–Nb–Ta–Li mineralization. In Iberia, the Porto–Sátão syncline is an example of such a Late Carboniferous intramontane basin. We present a structural analysis of the syncline, its basement and the associated W–Sn deposits. The regional structure is dictated by the Alcudian angular unconformity, caused by Cadomian tectonics (575–555 Ma) and separating tilted Ediacaran and subhorizontal Lower Paleozoic formations. Superimposed Variscan deformation led to F1–F3 folds with steep and gentle plunges, respectively. The late-orogenic D3 fabric is locally affected by post-orogenic F4 kink folds and an S4 crenulation cleavage. W–Sn-bearing vein systems occur along granite-hosted cone sheets, or exploit cross-fold joints associated with the F3 and F4 fold generations, revealing a close kinematic relationship between granite-related mineralization and the late- to post-Variscan deformation style. This structural history is interpreted as a plate-scale geodynamic change from Late Carboniferous north–south (D3) to Early Permian WNW–ESE (D4) convergence.