Tectono-magmatic evolution of the Weinsberg Composite Pluton (Bohemian Massif): AMS constraints on incremental emplacement during late-Variscan stress transition

This integrated structural study combining field mapping, anisotropy of magnetic susceptibility (AMS), petrological analysis, and gravity modelling of the Weinsberg Composite Pluton (WCP) provides new insights into magma emplacement mechanisms during post-collisional plutonism in the high-grade Moldanubian Zone of the Central European Variscides. The results indicate that pluton emplacement was strongly controlled by evolving tectonic stress regimes during the Variscan post-collisional evolution. New structural and AMS data, together with P-T modelling and published geochronological constraints, suggest that granitoid crystallisation proceeded in multiple stages under changing regional stress fields. The WCP records a transition from regional N–S compression (∼335–325 Ma) to NW–SE transtension (∼325–300 Ma), expressed in both internal fabric evolution and structural relationships. These evolving stress regimes controlled magma ascent pathways and emplacement depths, with younger intrusions emplaced at progressively shallower crustal levels. This progressive evolution resulted in a complex structural overprint during the final stages of pluton assembly and cooling. Gravity modelling further constrains the subsurface geometry of the pluton, revealing an asymmetrical root zone and deeper structural features related to the Variscan tectonic reorganisation. Overall, the WCP preserves evidence of incremental magma emplacement over ∼30 Myr (∼332–300 Ma). The evolution of the Weinsberg Composite Pluton can be subdivided into three principal tecto-magmatic stages: (a) early post-collisional phase (∼332–327 Ma), characterised by the emplacement of the oldest Weinsberg-type granitoids (WTG I); (b) middle post-collisional phase (∼326–318 Ma), dominated by the emplacement of the volumetrically dominant WTG II in the central part of the pluton, followed by intrusion of the younger WTG III into a partially crystalline granitic mush; and (c) late post-collisional phase (∼318–300 Ma), marked by emplacement of smaller intrusive bodies, including the Mauthausen granite (∼318 Ma) and Freistadt granodiorite (∼302 Ma), into already largely solidified plutonic units.