This PhD investigates the tectonics, sedimentation and magmatism of the Canterbury Basin. Unlike the emergent part of Zealandia continent, the offshore Canterbury Basin has not been deformed by Cenozoic plate boundary movements and represents a rare opportunity to conduct detailed analysis of the mid- Cretaceous rifting (~110 Ma to ~85 Ma) and the Late Cretaceous to Paleogene drift sequences. The results help improve understanding of the regional processes that led to the breakup of eastern Gondwana and the far-field effects of Cenozoic plate boundary deformation. The Canterbury Basin initiated in the mid-Cretaceous (~110 Ma) as a rift system. Syn- rift sedimentation was characterised by under-filled depocenters, where early syn-rift sedimentation was dominated by short drainage systems sourced from within the basin to produce alluvial fans along fault scarps inter-fingered with axial braided river or lake deposits. The predominance of local drainage systems coupled with a low supply of sediment into the Canterbury Basin during the Late Cretaceous may partly account for the under-filling of rift depocenters. Post rift latest Cretaceous and Paleogene, pelagic sediments draped and buried most of the earlier-formed horsts, with complete burial being achieved ~60 Myr after the onset of faulting. Despite filling of the rift structures, many of the geomorphological features of the contemporary Canterbury Basin were also present in the Late Cretaceous including, the Chatham Rise and the topographic hinterland west of the basin. The timing of the Cretaceous- Paleogene marine transgression and the degree of preservation of rift structures in the Canterbury Basin, differs from that in northern Zealandia (e.g., Taranaki Basin). These differences may reflect the relative tectonic quiescence in the offshore Canterbury Basin post ~85 Ma and the ongoing influence of subduction beneath northern Zealandia in the Late Cretaceous and Eocene. A total of 346 faults were analysed, with maximum displacements ranging from <0.1 to 2.8 seconds two way time. Results of the structural interpretation of the rifting show that the Canterbury Basin was stretched in three directions forming three sets of synchronous normal faults. The parallelism the three sets of rift faults and future spreading centres suggests that the multi-directional extension in the Canterbury Basin records the early stages of Gondwana breakup. The plate tectonic forces responsible for Gondwana breakup probably commenced soon after the cessation of subduction (e.g., < 5 Myr), and ~20 Myr before breakup. With the onset of breakup extension was focused along the spreading centres and multi-directional stretching of Zealandia ceased or continued at much diminished rates. The geometries of rift fill in seismic reflection lines has been quantified using the ratio of syn-rift strata thickness to syn-rift fault throw (here referred to as the Sediment Fill Ratio - SFR). Measurements from seven sedimentary basins globally (including the Canterbury Basin), permits recognition of four types of rift basins: (1) starved (SFR≤0.2), (2) under-filled (0.2<SFR≤0.9), (3) balanced-filled (0.9<SFR≤1.1), and (4) over-filled (SFR>1.1). The degree of syn-rift basin fill at the cessation of faulting varies with fault size across the same basin and between different rift basins for the same fault size. Small faults are more often characterized by balanced or over-filled geometries because they have low displacement rates and are located in the hangingwall of larger faults (e.g., >1 seconds TwT throw) where sedimentation rates are locally high. Rift systems dominated by large faults, such as the Canterbury Basin, tend to be under-filled, and require sediment supply from outside the rift system to become over-filled. The offshore Canterbury Basin provides a new perspective on Early Oligocene erosion that occurred between 29 and 32 Ma throughout the basin. Seismic reflection data permits mapping of erosive channels that incised the shelf and slope of the Canterbury Basin during the Early Oligocene. Similar channels are inferred onshore and offer an explanation for thickness variations of Oligocene limestones at a time when the rates of deformation were inferred to be low. Channelisation initiated due to a sea-level fall associated with uplift west of the Canterbury Basin that potentially reflects the onset of Cenozoic plate boundary deformation. The drainage system set-up during the Early Oligocene displays similar trends to the present day hydrographic pattern, which suggests that the first-order topographic elements of the eastern South Island may be 30 Myr in age or older. Seismic reflection data in the offshore Canterbury Basin has enabled us to identify 185 buried magmatic structures, some of which were previously unknown, ranging in age from mid-Cretaceous to Pleistocene. Buried volcanic edifices of <1 to 20 km diameter have been mapped and are grouped into five geomorphological and chronological categories. 1. Monogenetic to polygenetic volcanoes up to 5 km diameter within the Cretaceous syn-rift succession. 2. Large volcanic complexes with diameters >10 km within the post-breakup Late Cretaceous succession. 3. Monogenetic to polygenetic volcanoes of Paleocene to Middle Miocene age. 4. Large Miocene composite volcanoes of >10 km diameter formed in association with present-day Banks and Otago peninsulas. 5. Eruptive centers along the Chatham Rise that erupted during the Late Neogene. The continuous volcanic activity of the Canterbury Basin from the Late Cretaceous rifting to the Late Neogene was accompanied by widespread sill intrusion but did not resolve batholiths or plutons which, if present, are at depths of >10 km depth. This study increases the total known surface area of volcanoes in the Canterbury Basin by 300%, and suggests that across Zealandia, more volcanoes can be expected to exist of varying ages.