The active North Mernoo Fault Zone (NMFZ) is the youngest of three discrete phases of basement-involved extensional faulting to deform the northwestern corner of the continental Chatham Rise since the Cretaceous. The first two phases, inferred to be of Late Cretaceous and Eocene age, respectively, were both part of widespread extensional systems that developed over most of the Chatham Rise region. The third phase, the Late Miocene to Recent NMFZ, developed on the northwestern corner of the rise as a consequence of the interaction between the Chatham Rise plateau and the southern end of the Hikurangi subduction zone. A study of seismic reflection data from the northwestern Chatham Rise has revealed: (1) the detailed structure that relates to each phase of normal faulting; (2) the patterns of fault reactivation during successive episodes of extension; and (3) the significant structural control that older deformational fabrics have had on the development of the NMFZ.During the Late Cretaceous phase of extension, two major fault-bounded half-grabens together with other smaller basins developed beneath the upper continental slope. These E-W-trending, S-dipping faults are inferred to have accommodated about 2-7 km of horizontal extension across a 30 km wide region. The early Cenozoic extensional system reactivated some Cretaceous half-graben structures but mainly formed new faults with similar geometry in crust north of the Cretaceous structures. The early Cenozoic faults are inferred to have accommodated about 1-4 km of horizontal extension across a 60-km-wide region. The late Cenozoic NMFZ also reactivated some of the Cretaceous normal faults and almost all of the major early Cenozoic normal faults in this region. In addition, many new extensional structures developed and produced an E-W- to WNW-ESE-trending, southward dipping, domino-style array of faults up to 100 km in width. Although the density of faults in the NMFZ is greater than that of the two previous extensional systems to include this region, the total horizontal extension since late Early Pliocene times is estimated to be no more than 3 km.The common reactivation of old normal faults during the late Cenozoic development of the NMFZ indicates a significant level of structural inheritance from the previous episodes of extension to effect the region. Furthermore, the parallelism between the newly developed faults and the older two extensional systems suggests that the normal faults could be reactivating structures in the Torlesse terrane basement, which in turn relate to an early, Mesozoic phase (> 100 Ma) of accretionary tectonics. The kinematics of active extension within the NMFZ is, therefore, likely to be influenced by the pre-existing structural discontinuities that resulted from a history of poly-phase deformation.