Changes of the geomagnetic field vector obtained from lava sequences on the island of Vulcano (Aeolian Islands, Sicily)

Abstract

A combined geochronologic ( K Ar ) and palaeomagnetic study has been conducted on five volcanic sections (70 flows) on the island of Vulcano. The sections span the interval from 15 ± 2 to 135 ± 4 ka, with large hiatuses. Rock magnetic investigations indicate that the natural remanent magnetisation (NRM) is carried by titanomagnetites in the four oldest sections, with a contribution from high coercivity magnetic minerals in the youngest section. Palaeomagnetic directions obtained by thermal demagnetisation document a large magnetic excursion, at around 110 ka, with virtual geomagnetic poles (VGPs) that lie over eastern Siberia. These directions may represent a volcanic record of the termination of the Blake event. Only about 15% of the samples (from 19 flows) proved suitable for palaeointensity (Thellier and Thellier) determinations. These measurements indicate that the geomagnetic field has varied at Vulcano between 16 and 53 μT in the explored time interval. When combined with previous results obtained at Mt. Etna for the period from 140 to 60 ka (Tric et al., 1994, Phys. Earth Planet. Inter., 85: 113–129), these results document a broad low at around 115 ka. The palaeointensity values from Vulcano and Etna are consistent with global values, suggesting the presence of a dominant dipole-field contribution. These values, on the other hand, are significantly smaller than those recently obtained from La Réunion in the southern hemisphere. This suggests that large, long-lived, non-dipolar components of the geomagnetic field may be present at La Réunion in the interval from 130 to 90 ka. These observations are consistent with the fact that the VGP angular dispersion, calculated from non-excursional data, is significantly smaller at Vulcano than at La Réunion.