Newly determined mid-late Cretaceous 40Ar/39Ar ages on megacrystic kaersutite from lamprophyre dikes in central and north Westland (New Zealand) are presented. These ages (88 Ma, 86 Ma and 68 Ma) indicate that the intrusion of mafic dikes was not necessarily restricted to the previously established narrow age range of 80-92 Ma. The younger (~68-70 Ma) lamprophyre and trachyte dikes imply that tensional stresses in the Western Province were either renewed at this time, or that extension and related magmatism was continuous during opening of the Tasman Sea. Extension-related magmatism in the region did not only precede Tasman Sea initiation (starting at ~83 Ma, lasting to ~53 Ma) but may have sporadically continued for up to 15 Myr after continental breakup.