An attempt to determine the absolute geomagnetic field intensity in Southwestern Iceland during the Gauss-Matuyama reversal

A Goguitchaichvili, M Prevot*, J Thompson, N Roberts

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We have measured the variation in the intensity of the geomagnetic field during the Gauss-Matuyama (N4-R3) polarity reversal by application of the Thelliers' method to specimens of lava flows from Hvalfjordur district in Western Iceland (Reynivallahals Mts.). Eleven lava flows all show very similar directions corresponding to an equatorial VGP (Plat = 2.9 degrees N, Plong = 81.9 degrees E, A(95) = 4.2, K = 119). Twenty-nine specimens from nine of the flows were pre-selected for palaeointensity determination on the basis that specimens from the same drill cores showed a single component of magnetisation upon thermal or AF demagnetisation,, and possessed low magnetic viscosity and reversible susceptibility curves upon heating at 600-650 degrees C. Observation that the directional data obtained in the course of the palaeointensity experiments occasionally showed substantial non-linearity indicates that a significant chemical remanent magnetization (CRM) can be acquired in the direction of the laboratory field during heating at T. For each double heating step we calculated the ratio of CRM(T) to the magnitude of the natural remanent magnetization (NRM(T)) in the direction of characteristic remanence (obtained independently from another specimen from the same core). When this ratio exceeded 15%, the paleointensity data was rejected. In addition, specimens for which the quality factor was less than 5 were rejected. Twelve reliable palaeointensity values were obtained from specimens representing five lava flows. The results confirm that the palaeointensity was substantially reduced during the N4-R3 reversal. The range of mean palaeointensity values obtained for the five flows is 8.8 to 20.5 and the overall mean is 14.8 +/- 4.6 mu T. This corresponds to an equivalent VDM of 3.81 +/- 1.19 (10(22) A m(2)). A comparison of all Thellier palaeointensity data from the R3 magnetozone in the Rayinivallahals Mts. area reveals a progressive although irregular increase in the palaeointensity between the Gauss-Matuyama and Matuyama-RCunion reversals. This trend is opposite to that expected from the saw tooth model of palaeointensity variations. (C) 1999 Elsevier Science B.V. All rights reserved.

Original languageEnglish
Pages (from-to)53-66
Number of pages14
JournalPhysics of the Earth and Planetary Interiors
Issue number1
Publication statusPublished - Aug 1999

Keywords / Materials (for Non-textual outputs)

  • geomagnetic field
  • Iceland
  • Gauss-Matuyama reversal


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