AbstractIos (an island in the Cycladic archipelago, Greece) was the first recognized Aegean metamorphic core complex. There is a paradoxical absence of an age jump in low‐temperature geochronology transects across the Ios Detachment Fault. This paper explains why this is so, by modelling the conductive response to detachment faulting. We demonstrate that transects across detachment faults consistently record age jumps only at shallow palaeodepths. Conductive relaxation of the perturbed geotherm keeps pace with fault movement, so the hangingwall heats just as fast as the footwall cools. Key variables are the fractional depth to the partial resetting zone, d [0.0.1], and the magnitude and rate of slip on the detachment. At shallow palaeodepths (d < 0.3, 10–50 km slip), significant age jumps occur across the actual fault contact. At deeper levels of exposure, this is no longer the case, and the effects of a ‘stewing zone’ readily become evident.