Open Access

Palaeosecular variation for 0.1-21 Ka from the Okataina Volcanic Centre, New Zealand

Earth, Planets and Space200961:BF03352901

https://doi.org/10.1186/BF03352901

Received: 27 September 2007

Accepted: 30 March 2008

Published: 23 January 2009

Abstract

Studies of palaeodirections and palaeointensities were carried out on mainly rhyolitic lavas and pyroclastics from the Okataina Volcanic Centre, New Zealand, which has erupted during the past 32 kyr. Of the 17 sites studied, 14, spanning the period 0.1-21 Ka yielded good mean palaeodirections, while three carried unstable natural remanent magnetizations. Of 49 specimens from 7 sites, on which Thellier palaeointensity experiments were carried out, 21 specimens gave successful results, yielding 3 site mean palaeointensities for 1886 AD, 5 Ka, and 7.5 Ka. When the new palaeodirections, together with previously reported archaeo and volcanic data, were compared with sedimentary records from New Zealand and eastern Australia for the last 10 kyr, good agreement was obtained in inclination but discrepancies were observed in declination. The new 7.5 Ka and 5 Ka palaeointensities are moderately high and relatively low, respectively, and are concordant with the global trend. The mean palaeointensity obtained for 1886 AD is, 11% higher than the IGRF1900. The difference is scarcely significant, but might indicate a small bias toward high values. Although the sedimentary directional curves show excellent agreement with the prediction from CALS7K, the fit of the palaeointensity data to model values was relatively poor over the wider Pacific region. Further reliable palaeointensity data are needed to solve the discrepancy.

Key words

Palaeosecular variation Okataina rhyolite lava palaeointensity Thellier method