FAULT-CONTROLLED GYPSUM VEIN NETWORKS: INSIGHTS FROM THE ACTIVE GALERA FAULT, SOUTHERN SPAIN

Veins provide insights into the strain conditions under which they formed, the timing and sequence of fracturing, and the nature of the fluids from which their cement precipitated. Intense fracturing within fault zones promotes vein formation, but there are still open questions about the extent of fault control on vein formation, the type of veins and their development. This study analyses the influence of an active strike-slip fault —the Galera Fault, Southern Spain— on the formation, distribution, and evolution of gypsum vein networks hosted in Pliocene and Pleistocene rocks. Field mapping and structural analysis reveal veins are concentrated within the fault damage zone, with their spatial distribution being controlled by fault geometry, kinematics, and the lateral continuity of host lithologies. Structural analysis at 18 sites indicates that vein orientation correlates with tectonic structures. Veins near faults exhibit organized, consistent strikes, while those farther away show more variable orientations. Vein strike is highly sensitive to the local strain defined by the geometry, kinematics, and interactions of faults and subsidiary structures. Additionally, vein length tends to increase near faults. Vein intensity and density are controlled by vein length and orientation, and the thickness of vein-hosting beds. Moreover, veins formed shortly after sediment deposition under minimal lithostatic load, likely driven by fault-related strain. This early formation is supported by microstructures such as cone-in-cone and the rotation of early veins due to tectonic tilting. In conclusion, this research highlights the strong tectonic influence on vein formation, evolution, distribution, and attributes.