Abstract The Capel and Faust basins (northern Lord Howe Rise) are located in the SW Pacific between Australia, New Zealand and New Caledonia. New seismic, gravity, magnetic and bathymetry data and rock samples have enabled the construction of a three-dimensional geological model providing insights into the crustal architecture and basin stratigraphy. Multiple large depocentres up to 150 km long and 40 km wide, containing over 6 km of sediment, have been identified. These basins probably evolved through two major Early Cretaceous rifting episodes leading to the final break-up of the eastern Gondwanan margin. Pre-break-up plate restorations and potential field data suggest that pre-rift basement is a collage of several discrete terranes, including a Palaeozoic orogen, pre-rift sedimentary basins and rift-precursor igneous rocks. It is likely that a pre-existing NW-trending basement fabric, inherited from the New England Orogen (onshore eastern Australia), had a strong influence on the evolution of basin architecture. This basement fabric was subjected to oblique rifting along an east–west vector in the ?Early Cretaceous to Cenomanian and NE–SW-oriented orthogonal rifting in the ?Cenomanian to Campanian. This has resulted in three structural provinces in the study area: Eastern Flank, Central Belt and Western Flank.

Average orogenic strain rates may be calculated when it is possible to date mica cleavage or syndeformational veins and estimate finite strain. Deformation of accretionary-style thrust sheets in the western Lachlan Orogen occurred by chevron folding and faulting over an eastward propagating décollement. Based on 40 Ar/ 39 Ar dates of white micas, which grew below the closure temperature, this deformation started ca. 457 Ma in the west and ended ca. 378 Ma in the east, with apparent “pulses” of deformation ca. 440, 420, and 388 Ma. The 40 Ar/ 39 Ar data from thrust sheets in the Bendigo structural zone show that deformation progressed from early buckle folding, which started at 457–455 Ma, through to chevron fold lock-up and thrusting at 441–439 Ma. Based on retrodeformation, the total average strain for this thrust sheet is −0.67, such that the bulk shortening across the thrust sheet is 67%. This amount of strain accumulated over a duration of ∼16 m.y. gives a minimum strain rate of 1.3 × 10 −15 s −1 and a maximum strain rate of 5.0 × 10 −15 s −1 , based on fan thickness considerations. The total shortening is between ∼310 km and ∼800 km, which gives a décollement displacement rate between ∼19 mm yr −1 (minimum) and ∼50 mm yr −1 (maximum). If deformation occurred in pulses ca. 457–455 and ca. 441–439 Ma, then the calculated strain rate would be on the order of 1 × 10 −14 s −1 . These strain rates are similar to convergence rates in western Pacific backarc basins and shortening rates in accretionary prisms and turbidite-dominated thrust systems as in Taiwan.

Deformation in accretionary orogens, such as the eastern Australian Tasmanides, is clearly partitioned either as thin-skinned thrusting or thick-skinned faulting, with structural style dependent on the nature and stratal thicknesses of the sequences involved. The thin-skinned thrust systems consist of either detachment-related folds and thrust sheets within attenuated passive margin sequences or thrust sheets of chevron-folded turbidites with leading imbricate-fan geometry that are developed within former submarine fans overlying back-arc basin oceanic lithosphere. Thick-skinned belts consist of major thrust faults that root into the seismic reflection Moho with no apparent common décollement and cause crustal-scale imbrication of former arc, forearc, submarine fan, and accretionary complex elements. The Tasmanides are a composite orogenic system made up of three distinct orogenic belts whose character and structural style have resulted from the deformation of different tectonic components; the former rifted passive margin to make the Delamerian Orogen, a turbidite fan system(s) in a back-arc setting to make the Lachlan Orogen, and an arc-subduction complex that includes some older accreted components to make the New England Orogen. The inboard Delamerian Orogen consists of an external, craton-vergent thrust belt with foreland-style, detachment-related folds and thrusts linked to a high-T/low-P metamorphic complex. The centrally located Lachlan Orogen is made up of three separate thrust systems largely developed in submarine turbidite fans and incorporates a shear-zone-bounded high-T/low-P metamorphic belt. The outermost New England Orogen is constructed from craton-vergent, fore-arc and magmatic arc sequences, subduction complexes, and ophiolite fragments.