Geomagnetic Secular Variation During the Brunhes Epoch in the Indian and Atlantic Ocean Regions

Abstract

Brunhes epoch secular variation in the Indian and Atlantic Ocean regions has been examined using available and unpublished palaeomagnetic results from igneous rocks. Specimens from 401 separate units, all of which have unstable components minimized, are involved. More than half of these data are previously unpublished. The data are classified as fist order when the mean direction for each body is derived from at least four separate specimens, and second order when the number of specimens per body is not considered. Geomagnetic palaeosecular variation models are examined in terms of the latitude dependence of angular dispersion (S) of virtual geomagnetic poles (VGP's).Value of S from second order data, while exhibiting wide 95 per cent confidence intervals, increase with latitude. First order data also yield S values increasing with latitude, and are sufficiently well defined to indicate that S may have increased more rapidly with latitude during the Brunhes Epoch than at present. While the simple diode wobble model for the geomagnetic field is clearly excluded by the results, no distinction can be made between other current models, and the possibility of the existence of a region of attenuated Brunhes epoch non-dipole activity in the westcentral Indian Ocean cannot be excluded.

Palaeomagnetism of the Canary Islands and Madeira

“…All specimens were demagnetized in alternating magnetic fields of 100, 200, and 300Oe, and mean directions of stable remanent magnetism were computed using minimum dispersion computation methods (see Watkins, Hajash & Abranson 1972 for discussion). 2 3 3 3 3 3 3 2 2 3 2 3 3 3 3 3 3 3 3 2 4 4 4 Table 1).…”

Mono Lake or Laschamp geomagnetic event recorded from lava flows in Amsterdam Island (southeastern Indian Ocean)

“…This result is not surprising in so far as the remanence of the lava from Amsterdam is not contaminated by significant spurious components. This was not the case, for example, in a recent study on the volcanic sequence from Possession Island (Camps et al 2001), where the authors concluded that the intermediate directions initially described by Watkins et al (1972) correspond to reversed directions, which had been incompletely cleaned of their present‐day field viscous overprint. Here, we believe that the previously published data for Amsterdam Island (Watkins & Nougier 1973), which were not resampled in the present study are, equally reliable.…”

Paleomagnetism of Young New Zealand Basalts and Longitudinal Distribution of Paleosecular Variation.

“…(Watkins et al, 1972), Crozet Is. (Watkins et al, 1972), Easter Is. (Isaacson and Heinrichs, 1976), France (Doell, 1970), Gulf of Guinea, (Piper and Richardson, 1972) Hawaii Is.…”

“…(Watkins et al, 1972), Comores Is. (Watkins et al, 1972), Crozet Is. (Watkins et al, 1972), Easter Is.…”