Thomas Brian Phillips, Ken McCaffrey

The make-up of continental crust reflects its past tectonic history, containing a multitude of different lithological units and pre-existing structures that vary in strength with crustal properties typically varying across short distances. These variations exist across a range of scales and exert a great control over multiple aspects of rift physiography, including rift structural style, fault spacing and density, and the geometry of individual faults. We examine rift physiography across the Great South Basin, New Zealand, and show how variations in upper crustal lithology between basement terranes and the abundance and nature of pre-existing structures within these distinct areas influences the rift structural style from the rift to individual fault scale. We first characterise basement terranes beneath the Great South Basin, such as the sedimentary Murihiku Terrane or the dominantly granitic Median Batholith, and assess the pre-existing structures present within each. Secondly, we quantitatively analyse how extension was accommodated within each of these terranes by examining the structural style and calculating the fault density and beta-factor across a series of transects. In addition, we also examine fault behaviour at the boundaries between terranes, and the role of homogeneous granitic bodies in resisting extension and ‘anchoring’ sections of the rift. We compare the results of our study to examples from recently-published numerical modelling. However, we also highlight how local, small-scale complexities within rift systems can influence rift geometry at a scale below that typically analysed in modelling studies, emphasising the need for multi-scale analysis.