Magnetic anomalies of lava fields in the Canary islands. Possible consequences for paleomagnetic records

Abstract

Measurements of the total magnetic field have been performed above the surface of 12 lava flows in the Canary islands of La Palma and Tenerife. Directions can differ by up to 15° and intensity changes reach 20%. The mean-flow directions do not coincide and the mean-flow virtual dipole moments (VDMs) differ by more than 10%. The deviations are linked to topographic features at the surface of the flows and should persist during emplacement of the next overlying flow. Such effects can thus limit the resolution of paleomagnetic records of detailed geomagnetic features and the field intensity variations above the flows (and between the mean-flow values) could explain a significant part of the scatter inherent to many paleointensity studies. Historical field variations have been recorded from the same flows and are in agreement with the European curve for the same period. However, there is also some correlation with the present field which suggest that the underlying magnetized bodies could have affected the paleomagnetic records. Biases induced by the crustal field would increase considerably during periods of reduced field intensity like during reversals and induce erroneous records. Samplings performed over large distances within each lava flow would provide the best way to average out the contribution of the anomalies. In any case, such effects should not be neglected in paleomagnetic studies.