Abstract

Paleomagnetic data from Pliocene sedimentary strata in the south Wanganui basin, New Zealand, document clockwise tectonic rotation west of and increasing toward the main zone of deformation (axial tectonic belt) associated with the Australia-Pacific plate boundary zone in the North Island of New Zealand. Measured rotation with respect to the Australian plate increases from 1.4° ± 3.9° 80 km west of the axial tectonic belt to 6.5° ± 2.0° and 13.2° ± 3.1° at 45 km and 20 km west of the axial tectonic belt, respectively. These measurements indicate that (1) deformation associated with plate convergence occurs across a wide region up to 270 km west of the Hikurangi Trench, and (2) in the past 2.5 m.y. at least 30 km of transcurrent motion and 10 km of shortening at the plate boundary have been accommodated within the south Wanganui basin by distributed shear west of the plate boundary zone proper. The data support a model suggesting that the Wanganui basin is a lithospheric flexure basin driven by high friction at the plate interface. This strain in the south Wanganui basin and inferred high friction across the plate interface at the basin's eastern margin have occurred since 2.5 Ma.

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