We constrain the timing and kinematics of normal faulting on Sifnos, Cyclades, Greece. Penetrative top-to-the-NE kinematic indicators associated with a shallow dipping foliation occur in the deepest tectonic unit (Greenschist Unit). Combined P–T analysis and Rb–Sr dating indicates that this deformation was under way by 29.4 ± 3.4 Ma at P–T conditions of c. 16 kbar and c. 550 °C, and continued to operate at least until 22.8 ± 0.2 Ma at P–T conditions of c. 8 kbar and c. 400 °C. The later top-to-the-south directed Sifnos Detachment developed at the top of the Greenschist Unit and cuts the top-to-the-NE structures. Zircon fission-track ages suggest that deformation on the Sifnos Detachment was largely terminated by about 13–10 Ma. Subsequent extension was accommodated by high-angle normal faults. Regionally the top-to-the-south detachment phase on Sifnos correlates with top-to-the-south extensional faulting on nearby Serifos, which started there at c. 15–13 Ma. Top-to-the-south extensional shearing on Ios to the SE commenced earlier at c. 19–18 Ma, suggesting that top-to-the-south extension propagated westward from Ios to Sifnos and Serifos, or that extension was partitioned into different top-to-the-south detachment systems that operated at different times. Collectively these top-to-the-south detachments are named here the South Cycladic Detachment System, which played a key role in the opening of the Cretan Sea forearc basin.