Reactivation of pre-existing intra-basement structures can influence the evolution of rift basins, yet the detailed kinematic relationship between these structures and overlying rift-related faults remains poorly understood. 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: (a) identify a range of interaction styles between intra-basement structures and overlying, Plio-Pleistocene rift-related normal faults; and (b) 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 reverse faults formed during Mesozoic subduction and basement terrane accretion. These geometric relationships indicate pre-existing intra-basement structures 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: (a) normal faults only nucleated above intra-basement structures that experienced late Miocene compressional reactivation, (b) despite playing an important role during subsequent rifting, intra-basement structures have not been significantly extensionally reactivated, and (c) preferential nucleation and propagation of normal faults within late Miocene reverse faults and folds appears to be the key genetic relationship between contractionally reactivated intra-basement structures and rift-related normal faults. Our analysis shows that km-scale, intra-basement structures can control the nucleation and development of newly formed, rift-related nor-mal faults, most likely due to a 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 660 | EAGE COLLANEGA Et AL.

No abstract

Complex patterns of normal faults with multiple orientations and/or highly curved shapes have been traditionally explained by successive tectonic phases of 2-dimensional deformation. Alternatively, multiple fault sets have been proposed to develop simultaneously and in orthorhombic symmetry during a single phase of 3-dimensional deformation. We use analogue models of normal faults to demonstrate that, without the influence of pre-existing structures, 3D extension is preferentially accommodated by the alternate, rather than simultaneous, development of faults with different trends. By means of stress-driven interactions, 3D deformation can be partitioned into coupled systems of normal faults, which display geometries commonly observed in tectonic settings affected by interacting plate boundaries. Under radial extension, deformation is accommodated by major curvilinear grabens coupled with minor perpendicular faults, resulting in the triple junctions of grabens observed in Afar. On the other hand, the alternate development of perpendicular faults accommodates synchronous bi-directional and mutually perpendicular extension, giving the same fault pattern observed in the Barents Sea rift-shear margin.

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.

16Discrete structures (e.g. faults) or pervasive fabrics (e.g. foliation), which may occur in pre-