The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

By A. Biggin, Geert H. M. A. Strik, Cor G. Langereis. 2009

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We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm2which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a ‘Proterozoic dipole low’ period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth’s history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

Subfields: Atmospheric Science, Geophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/b66925106e15c7da7cc8648eefd69c665a8f2f40

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Citations in the corpus

Modelling the palaeo-evolution of the geodynamo (2009, methodology): “11b) are presented together with virtual dipole moment values (VDM) from the IAGA palaeointensity database (Perrin & Schnepp 2004; Biggin et al. 2009).”
The Magnetic Field of Planet Earth (2010, background): “…to 3.2 Ga so far; Tarduno et al. 2007) are also ongoing (e.g. Smirnov and Tarduno 2004; Biggin et al. 2008a, 2008b), particularly in view of improving the existing paleointensity IAGA (International Association of Geomagnetism and Aeronomy) data basis (Perrin and Schnepp 2004; Biggin et al. 2009).”
PADM2M: a penalized maximum likelihood model of the 0–2 Ma palaeomagnetic axial dipole moment (2011, methodology): “PADM2Mp is a preliminary time-varying, 0–2 Ma PADM model created using the P0 subset of nine globally distributed RPI data sets (see Table 1), together with the PINT08 and Geomagia50 API data sets.”