Pliocene and Pleistocene stratigraphy and tectonics, Ohara Depression and Wakarara Range, North Island, New Zealand

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Abstract
The Ohara Depression ‐ Wakarara region is situated at the arcward margin of the forearc basin near Hawke's Bay on the North Island of New Zealand. Deformation of late Pliocene and Pleistocene sediments in approximately the last 2.5 Ma is a product of oblique convergence of the Australian and Pacific plates. The region lies directly to the east of Mesozoic greywacke of the axial ranges of the North Island, and deformation reflects the interaction of this rigid backstop with the inboard part of the forearc. Deformation has resulted in the differential movement of several relatively rigid basement blocks. A veneer of late Neogene and Quaternary sediments on these blocks records the timing and style of deformation. An important observation derived from the Quaternary tectonic record is that strain is partitioned between two northeast‐trending domains that parallel the margin. The western domain that abuts the axial ranges is a domain of strike‐slip faulting. Directly east of the strike‐slip domain, and separated from it by the Mohaka Fault, is a contractional domain. The Ohara Depression has developed within the strike‐slip domain, and the Wakarara Range is a consequence of block uplift along a reverse fault within the contractional domain. The two domains developed contemporaneously and together accommodate what is probably a single transpressive domain at depth. Two episodes of uplift and fault activity are recorded in the region. The first episode occurred in the late Pliocene and is separated from the later episode by a period of tectonic quiescence. The later period of deformation began in the early Pleistocene and is still continuing; the greatest amount of uplift and folding, recorded by synorogenic conglomerates in excess of 200 m thick, occurred in the mid Pleistocene.