Paleomagnetism and 40Ar/39Ar ages from la Palma in the Canary Islands

The structure of the time-averaged geomagnetic field has been known forcenturies to be approximately dipolar. Significant departures of the time-averagedfield from that of an axial geocentric dipole, however, have been reportedfor decades. The data on which time-averaged field models are based must beof the highest quality in order to document subtle long-term features. Wepresent here new paleomagnetic data and 40Ar/39Ar ages for the island of La Palma, The Canary Islands.Paleomagnetic samples were obtained from 28 lava flows. Of these, 21 met ourminimum acceptance criteria for use in time-averaged field models. The 40Ar/39Ar age determinationswere successfully carried out on samples from eight of the flows. Our isotopicages and paleomagnetic polarities are consistent with the currently acceptedgeomagnetic reversal timescales. The reversed data in the updated databaseare antipodal to the normal data within the uncertainties, and the time-averageddirection is indistinguishable from that expected from a geocentric axialdipole. © Copyright 2000 by the American Geophysical Union.