Paleomagnetic results from the Waipapa Terrane, Northland Peninsula, North Island, New Zealand: TEctonic implications from widespread remagnetizations

Abstract

Paleomagnetic samples were collected from a wide variety of rock types of the Waipapa terrane, which is exposed along the eastern coast of the Northland peninsula. Twelve sites yield stable magnetic directions, which fail both a fold and regional attitude test at the 99% confidence level, and indicate that widespread remagnetization has occurred over a large (<200 km) area. Rock magnetic experiments suggest that the mechanism for remagnetization was through the formation of fine‐grained magnetite and hematite and was probably controlled by local variation in fluid migration. The mean in situ direction for the 12 sites is I = −70.2°, D=14.4° (α95=7.1°, kappa=38.6), which is significantly different from the predicted axial dipole field directions at the 95% confidence level. The age of the remagnetization is unclear. In an effort to date the remagnetization, a synthetic apparent polar wander (APW) path was constructed for New Zealand using Australian data, and the apparent south pole from the remagnetized Waipapa sites (latitude=69.7°S, longitude= 150.7°E, α95=11.2°) was compared to this APW path. Using this method, the age of the remagnetization is constrained to be between ≈12 and 58 Ma. A major change in the tectonic regime occurred at ≈25 Ma, which is evidenced by obduction of the Northland allochthon and initiation of arc volcanism and subduction. Fluid migration and/or elevated temperatures driven by the initiation of subduction and arc volcanism, along with the obduction of the Northland allochthon seem likely mechanisms for the remagnetization.