Recent investigations of the 0-5 geomagnetic field recorded by lava flows
Johnson, Catherine L.
Constable, Catherine G.
Barendregt, René W.
Brown, Laurie L.
Opdyke, Neil D.
We present a synthesis of paleomagnetic directional data collected from 873 lava flows at 17 different locations under the collaborative Time Averaged geomagnetic Field Initiative (TAFI). The data range from 05 Ma in age, and provide new high quality data with improved spatial coverage. Data quality at each site is measured using k, the best estimate of the Fisherian precision parameter, and its influence on inclination anomaly and VGP dispersion is evaluated by systematically excluding data with successively higher values of k. When combined with regional compilations from NW USA, SW USA, Japan, New Zealand, Hawaii, Mexico, S. Pacific and the Indian Ocean, a data set of 2283 pairs of declination and inclination data, with k>100, and VGP latitudes greater than 45 is obtained. This is a more than 7fold increase over similar quality data in the existing Global Paleomagnetic Database (GPMDB). The new data set spans 78 S to 53 N, and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the timeaveraged field (TAF) and paleosecular variation (PSV) for the Brunhes and Matuyama epochs, and for the 0–5 Myr interval combined. PSV, as measured by dispersion of virtual geomagnetic poles, shows less latitudinal variation than predicted by current statistical PSV models. Variation of inclination anomaly with latitude is assessed using 2parameter zonal TAF models – these have axial quadrupole contributions of 2% – 4% of the axial dipole term, and axial octupole contributions of 3% – 5%. Approximately 2% of the octupole signature is likely the result of bias incurred by averaging unit vectors. The new data set provides significant improvement over previous compilations, and can contribute to a new generation of global paleomagnetic field models.
Sherpa Romeo green journal (pre or post print only)
Paleomagnetic directional data , Lava flows , Time-Averaged Field Investigations (TAFI) , Geomagnetic field , 0-5 Ma