Abstract The classical S–I–A-type granites from the Lachlan Orogen, SE Australia, formed as a tectonic end-member of the accretionary orogenic spectrum, the Paleozoic Tasmanides. The sequence of S- to I- to A-type granite is repeated at least three times. All the granites are syn-extensional, formed in a dominantly back-arc setting behind a single, stepwise-retreating arc system between 530 and 230 Ma. Peralkaline granites are rare. Systematic S–I–A progressions indicate the progressive dilution of an old crustal component as magmatism evolved from arc (S-type) to proximal back-arc (I-type) to distal back-arc (A-type) magmatism. The alkaline and peralkaline A-type Younger granites of Nigeria were generally hotter and drier than the Lachlan A-type granites and were emplaced into an anhydrous Precambrian basement during intermittent intracontinental rifting. This geodynamic environment contrasts with the distal back-arc setting of the Lachlan A-type granites, where magmatism migrated rapidly across the orogen. Tectonic discrimination diagrams are inappropriate for the Lachlan granites, placing them in the wrong settings. Only the peralkaline Narraburra suite of the Lachlan Orogen fits the genuine ‘within-plate’ setting of the Nigerian A-type granites. Such discrimination diagrams require re-evaluation in the light of an improved modern understanding of tectonic processes, particularly the role of extensional tectonism and its geodynamic drivers.

Abstract James Robert Temple Hazell, known to many as Robin Hazell, passed away in March 2017, in Bodmin, Cornwall, aged 89, after a professional life spanning close to 70 years. Robin’s main contributions addressed the exploration for and development of groundwater especially in hard rock areas. Much of this work was undertaken in the country of his first overseas posting, Nigeria, and was primarily spent in the field. He started his career in south and east Nigeria mapping groundwater resources and uncovering links between geology, baseflow and the likelihood of surface water being contaminated. In northern Nigeria he developed conceptual models for how groundwater existed in fractured rocks, and the importance of mineralogy and fractures, and used this knowledge to help site many thousands of successful boreholes. Perhaps Robin’s greatest legacy, however, was his generosity in teaching and mentoring other hydrogeologists. Robin’s last public contribution was his paper at the conference on Groundwater in Fractured Rocks, the subject of this Special Publication.

Abstract: Rollover is the folding of the hanging-wall sedimentary record in response to slip on listric normal faults, and is a common feature of sediment-rich, gravity-driven tectonic provinces. Rollovers have been extensively studied by means of geometrical reconstruction, and numerical and analogue modelling. However, the detailed interaction between the kinematics of bounding listric normal faults and their hanging-wall deformation is not yet fully understood. In this study, we use 3D seismic-reflection data from the Forcados-Yokri area, western Niger Delta, Nigeria, to study the lateral linkage and landwards backstepping history of an array of listric normal faults, particularly focusing on their influence on the development and evolution of hanging-wall rollovers. Five individual, partly overlapping rollover structures have been studied with respect to their relative initiation and decay time, their spatial distribution, and their relationship to the tectonic history of their respective bounding faults. We demonstrate that the studied rollovers are highly dependent on the development of their bounding faults in terms of initiation time, lateral linkage, internal structural development and decay. Fault–rollover interaction is dynamic and changes through time depending on the temporal evolution of listric faults. Four genetic types of fault–rollover interaction were identified in this study: (1) the rotation of a rollover–crestal-collapse system, controlled by a changing lateral bounding-fault orientation during fault growth; (2) a stepwise shift of rollover–crestal-collapse systems associated with rollover abandonment, controlled by the initiation of a new fault in the footwall of an older structure; (3) a gradual shift of successive rollovers controlled by branching main faults; and (4) a general landwards and upwards migration of crestal-collapse faults within a rollover above stationary listric main faults.