Early to Middle Miocene Pacific–Australia plate boundary in New Zealand: an alternative transcurrent-fault system
R. J. MUSGRAVE, 2003. "Early to Middle Miocene Pacific–Australia plate boundary in New Zealand: an alternative transcurrent-fault system", Evolution and Dynamics of the Australian Plate, R.R. Hillis, R.D. Müller
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Only about 15 million years of Pacific-Australia motion is needed to reconstruct the two halves of the Permian Maltal terrane on either side of the Alpine Fault, the current plate boundary. Most Early Miocene and earlier reconstructions of New Zealand ignore the misfit that arises from keeping the Alpine Fault as the plate boundary before 15 Ma. The new reconstruction developed here removes this inconsistency by postulating the operation of a different transcurrent-fault system during the Early to Middle Miocene, running west of the Marlborough Sounds Block and east of the Flordland Block (the Flordland Fault System). Transfer of the the locus of transcurrent motion from the Flordland Fault System to the Alpine Fault was a response to a mid-Miocene change in Pacific-Australia motion, and arose by a process analogous to the Pliocene to present adjustment of the Alpine Fault to the Pliocene change in Pacific-Australia motion. In both cases the change in motion increased convergence on the transcurrent system, and resulted in bending of the active transcurrent fault and propagation of new faults aligned with the new motion vector. Growth of the bends in both the Alpine Fault and the Flordland Fault System can be explained by the contrast between deformation restricted to the Pacific Plate south of the bends, and shared between both plates near the bends. Restoration back to 9.5 Ma reconstructs the elements of the Flordland Fault System as collinear, except for a bend in the Waimea Fault, west of the Marlborough Sounds Block. Bending of the Waimea Fault occurred during the Middle Miocene and is associated with compression in northwest Nelson. Transcurrent motion on the Flordland Fault System allows reconstruction back to between 25 and 20 Ma, when a shift in the position of the Pacific-Australia motion pole initiated significant rates of lateral displacement within New Zealand.