Earthquake swarms commonly occur in upper-crustal hydrothermal-magmatic systems and activate mesh-like fault networks. How these networks develop through space and time along seismic faults is poorly constrained in the geological record. Here, we describe a spatially dense array of small-displacement (< 1.5 m) epidote-rich fault veins (i.e., hybrid extensional-shear veins) within granitoids, occurring at the intersections of subsidiary faults with the exhumed seismogenic Bolfin Fault Zone (Atacama Fault System, northern Chile). Epidote hybrid extensional-shear veining occurred at 3-7 km depth and 200-300 degrees C ambient temperature. At a distance of <= 1 cm to fault veins, the magmatic quartz of the wall rock shows (i) thin (< 10 mu m thick) interlaced deformation lamellae and (ii) systematically crosscutting veinlets healed by quartz and feldspars, and it appears shattered at the vein contact. Clasts of deformed magmatic quartz, with deformation lamellae and healed veinlets, are included in the epidote-rich fault veins. Deformation of the wall-rock quartz is interpreted to record the transient large stress perturbation associated with the propagation of small earthquakes preceding conspicuous epidote mineralization. Conversely, the epidote-rich fault veins record cyclic events of extensional-to-hybrid veining and either aseismic or seismic shearing. The dilation and shearing behavior of the epidote-rich fault veins are interpreted to record the later development of a mature and hydraulically connected fault-fracture system. In this latter stage, the fault-fracture system cyclically ruptured due to fluid pressure fluctuations, possibly correlated with swarm-like earthquake sequences.