Cenozoic distributed rotational deformation, South Island, New Zealand

[1] New structural and paleomagnetic data from the Marlborough region, New Zealand, provide better constraints on the timing of the formation of the South Island orocline. These data indicate that approximately 100degrees of clockwise bending of the crust has occurred across this part of the plate boundary zone during the Neogene, most of which took place between the early and late Miocene ( circa 25 - 8 Ma), implying that distributed shear has been an important mechanism in the accommodation of Neogene finite strain. A simple kinematic model suggests that this distributed deformation has been accommodated by the rotation of elongate blocks parallel to the main fabric, in response to continuous deformation in the underlying lithospheric mantle beneath. After the introduction of a significant convergent component to the plate motion in the late Miocene, distributed deformation may have ceased to play such a significant role in the central Marlborough fault zone, with motion becoming concentrated on the Marlborough faults themselves. In the northeastern part of Marlborough, however, an extra clockwise rotation of similar to 35degrees has occurred since this time, which might be explained by the reorganization of the crust into more equidimensional blocks where they terminate against the Hikurangi margin.