Geomagnetic field intensity and inclination records from Hawaii and the Réunion Island: Geomagnetic implications

摘要

We report on new paleointensity and inclination records obtained in Hawaii from 386 samples drilled in 137 subaerial flows of the HSDP2 long basaltic core that we have combined in a composite record with the other Hawaiian results to produce a unique and accurate lava record of absolute geomagnetic field intensity and inclination at Hawaii for the last 405kyr. These data are considered together with published results from La Réunion Island, for about the same time period in order to compare them to model results. In Hawaii, when recognized excursional periods are omitted, the average VADM (VDM) value is about 8.2×(8.4)×10~(22)Am~2 and the inclination is on the average 29.8°, i.e. about 6° shallower than the expected value at this location (GAD value). In the Réunion Island, we selected published results in which both inclination and intensities values are obtained using modern methods and strict criteria. The average VADM (VDM) is 9.4±2.3 (8.7±2.3)10~(22)Am~2 and the average inclination value (when transitional data are ignored) is -44.4±2.4°, about 7° steeper than the GAD value. These results, compared with model intensities predicted by dynamo solutions that incorporate lateral variations in core-mantle boundary heat-flow derived from seismic tomography, are too high for both localities, but they decrease as the amplitude of thermal boundary anomalies increases. With strong boundary heat-flow, the model inclination anomaly at Hawaii fits with the data but at La Réunion, model inclination anomalies have the wrong sign. This comparison indicates that strong boundary heat-flow anomalies give the best fit to the data and that future improvements will be obtained by proportionally increasing both the Rayleigh number and the amplitude of heat-flow variations.