Late Variscan tectonic orogenic collapse as a trigger for Sn-W mineralizing systems. U-Pb ore geochronology across the Martinamor gneissic dome (Salamanca, Spain)

Abstract

Regional tectonothermal evolution is a primary factor for many mineral deposits formation. Late orogenic gravitational collapse has been widely recognized across different orogens, including the Variscan belt. The Martinamor gneissic dome is a well constrained structure related to the late-Variscan orogenic collapse in the Iberian Massif. We have investigated Sn-W mineralization spatially related to the Martinamor dome by LA-ICP-MS U-Pb dating of cassiterite and wolframite, revealing a wide mineralization timespan of 40 Myr. Our results show: a) an early (338.1 ± 5.8 Ma), minor mineralization phase, (W-dominated), potentially related to Variscan compressive phases; b) a second, major stage which lasted from 324.1 ± 5.9 to 300.7 ± 5.4 Ma, which includes Sn-bearing pegmatites and Sn-W veins formed under the syn-collisional extensional collapse. Structural evidence highlights the role of extensional detachments in channeling mineralizing fluids and creating suitable traps under ductile and ductile–brittle conditions; it also explains the temporal and spatial distribution of the Sn-W vein-type mineralizations in the zone.

Comparisons with other Variscan deposits in the Iberian Massif and European counterparts suggest a regional metallogenic cycle linked to late-Variscan extensional collapse, heat advection, and crustal partial melting processes. These findings underscore the Martinamor dome as a unique structure recording a protracted Variscan tectono-magmatic-metallogenic event, with implications for understanding Sn-W deposit formation in orogenic settings.