Global Secular Variation and Excursions Within the Brunhes – is it Real?

Abstract:

We analyzed 64 high quality magnetic profiles crossing the Central Indian Ridge and the Southeast Indian Ridge between 21°S and 28°S. All profiles cover the entire Anomaly 1 and they do not cross discontinuities, major faults, or significant isolated bathymetric features. When stacked over single ridge segments, correlated variations in the magnetic field become apparent. However, these variations change from one ridge segment to the next and when stacked over the entire ridge, all correlated variations are lost. Therefore we conclude that the correlated variations represent local effects, in this case mainly caused by bathymetry and irregularities of the spreading process which are typically limited to one ridge segment. Since we do not see any anomalies associated to geomagnetic excursions, we carried out forward modelling which shows that any excursion lasting for longer than 10.000 years should become visible in our data, thus putting an upper limit of 10.000 years to the maximum duration of geomagnetic excursions during the Brunhes.