Records of geomagnetic reversals from volcanic islands of French Polynesia: 1. Paleomagnetic study of a polarity transition in a lava sequence from the Island of Huahine

Abstract

We report the behavior of the earth's magnetic field for a transition recorded in lavas at the volcanic island of Huahine in French Polynesia, south‐central Pacific Ocean. Detailed intermediate fields are observed that record an apparent N‐N excursion. The available K‐Ar ages indicate that most volcanic rocks of the southern part of Huahine erupted at a time close to the Kaena subchron. Gaps in the paleomagnetic sampling or a hiatus in the volcanic activity during the Kaena event may have led to the partial record of a complete polarity transition, missing the fully reversed state. Nevertheless, numerous flows have recorded intermediate fields that somewhat constrain reversal models. The low intensities of magnetization associated with the intermediate directions suggest that the transitional field has mainly low intensities. The beginning of the transition shows inclination steepening, consistent with a zonal model of geomagnetic field reversal based on an axial quadrupole. Large deviations from a north‐south planar distribution of the intermediate directions show that non axisymmetrical nondipolar fields are important in the middle of the transition.