Luca Collanega, Christopher Aiden-Lee Jackson , Rebecca E. Bell, Alexander James Coleman, Antje Lenhart, Anna Breda

Pre-existing intra-basement structures can have a strong influence on the evolution of rift basins. Although 3D geometric relationships provide some insight into how intra-basement structures determine the broad geometry and spatial development (e.g. strike and dip) of rift-related faults, little is known about the impact of the former on the detailed kinematics (i.e. nucleation and tip propagation) of the latter. Understanding the kinematic as well as geometric relationship between intra-basement structures and rift-related fault networks is important, with the extension direction in many rifted provinces typically thought to lie normal to fault strike. We here investigate this problem using a borehole-constrained, 3D seismic reflection dataset from the Taranaki Basin, offshore New Zealand. Excellent imaging of intra-basement structures and a relatively weakly-deformed, stratigraphically simple sedimentary cover allow us to: (i) identify a range of interaction styles between intra-basement structures and overlying, Plio-Pleistocene rift-related normal faults; and (ii) examine the cover fault kinematics associated with each interaction style. Some of the normal faults parallel and are physically connected to intra-basement reflections, which are interpreted as mylonitic thrusts related to Mesozoic subduction and basement terrane accretion. These geometric relationships indicate pre-existing, intra-basement fabrics locally controlled the position and attitude of Plio-Pleistocene rift-related normal faults. However, through detailed 3D kinematic analysis of selected normal faults, we show that: (i) normal faults only nucleated above intra-basement structures that experienced Late Miocene compressional reactivation; (ii) thrusts and folds resulting from Late Miocene reactivation and upward propagation of intra-basement structures acted as nucleation sites for Plio-Pleistocene rift-related faults; and (iii) despite playing an important role during rifting, intra-basement structures do not appear to have been significantly extensionally reactivated. Our analysis shows how km-wide, intra-basement structures can have a temporally and spatially far-reaching influence over the nucleation and development of newly formed normal faults, principally due to local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre-existing, intra-basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as simply spatial or geometric relationship between structures developed at multiple structural levels.