The Time-Averaged Field Investigations Project: A Synthesis

The Time-Averaged Field Investigations (TAFI) project is a multi-institutional effort to study the behavior of Earth's magnetic field over the past 5 Ma. Paleomagnetic directions from over 800 lava flows and dikes at 15 globally distributed locations have been obtained. Radiometric and paleointensity measurements have been performed on suitable specimens from individual flows. The new data significantly improve geographical coverage of the paleofield, particularly in the southern hemisphere and at high latitudes. We have integrated data collected under the TAFI project with the highest quality paleosecular variation (PSV) data available from the IAGA PSVRL, Global Paleomagnetic Database, and with regional compilations of published PSV data for Hawaii, Mexico, the South Pacific, Reunion, and the western United States. The data are compatible with a geocentric axial dipole average field, but also permit small but persistent axial quadrupole (g_2O) and axial octupole (g_3O) terms. We report on latitudinal variations in PSV diagnostics from the TAFI data. Where sufficient data are available regionally we compare statistical distributions of paleodirections with those predicted by PSV models.