Secular variation of the Late Archean–Early Proterozoic geodynamo

Смирнов, А. В.; Tarduno, J. A.

doi:10.1029/2004gl020333

Cited by 51 publications

(46 citation statements)

References 22 publications

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“…The simulation with very small inner core, such as Earth is believed to have had one billion or more years ago, has an extraordinarily high O/E ratio, which also suggests a low Precambrian reversal rate. We note that currently available data do not indicate that the average field intensity was unusually high from 1 to 2.5 Ga [Macouin et al, 2003;Smirnov et al, 2003;Dunlop and Yu, 2004], but may indicate smaller contributions of even harmonics to the field around 2.5 Ga than from 0 -5 Ma [Smirnov and Tarduno, 2004]. Thus, symmetry of the timeaveraged field may prove to be a more robust predictor of reversal frequency than intensity.…”

mentioning

confidence: 66%

Symmetry and stability of the geomagnetic field

Coe¹,

Glatzmaier²

2006

Geophysical Research Letters

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Computer simulations of the geodynamo reveal a strong inverse correlation between stability and equatorial symmetry of the simulated field. This result is consistent with the paleomagnetically inferred degree of symmetry of Earth's magnetic field during the past 150 Ma, which reversed polarity more frequently when it was more symmetrical. A geodynamo simulation with solid inner core much smaller than it is today produced an exceptionally antisymmetric field, raising the possibility that reversals may have been much less common in the distant geologic past than more recently. Paleomagnetic evidence suggests that this might well be true.

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confidence: 66%

Symmetry and stability of the geomagnetic field

Coe¹,

Glatzmaier²

2006

Geophysical Research Letters

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“…Longer timescale variations in geomagnetic behaviour (Macouin et al, 2004;Coe and Glatzmaier, 2006;Biggin et al, 2008) may well be associated with the growth of the inner core which affects the geodynamo both by changing the geometry of the spherical shell it operates in and by providing a highly efficient power source (Gubbins et al, 2003;Labrosse, 2003) for its operation. Smirnov and Tarduno (2004) studied geomagnetic palaeosecular variation (PSV) in the late Archaean and early Proterozoic and reported that it was similar to that observed in the last 5 Myr with a suggestion of more dipole dominance. Very recently, Biggin et al (2008) reanalysed PSV in this period (2446-2823 Ma) with a much larger Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.…”

Section: Introductionmentioning

confidence: 78%

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

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 ZAm 2 which 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.

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“…The first sample (NR1) represents a ∼2.45 Ga Matachewan mafic dike (Smirnov and Tarduno, 2004). Over 95% of the oxide minerals present were relatively large (several hundreds of microns to >1 mm) grains, containing one or several subordinate sets of trellis type lamellae (e.g., Haggerty, 1991).…”

Section: Natural Rock (Nr) Samplesmentioning

confidence: 99%

Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

Смирнов

2009

Earth Planet Sp

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Magnetic measurements at cryogenic temperatures (<300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio (R LT ) between a lowtemperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in a 2.5 T field (field cooling, FC) and in a zero field environment (zero field cooling, ZFC). Synthetic magnetite samples ranged in mean grain size from 0.15 to 100 μm, representing nearly single-domain (SD), pseudosingledomain (PSD), and multidomain (MD) magnetic states. The R LT ratio monotonically increases from 0.58 to 1.12 with the decreasing mean grain size, being close to unity for PSD grains (0.15-5 μm) and smaller than unity for MD magnetite (12-100 μm). The R LT ratio of 1.27 is observed for acicular magnetite characterized by nearly SD behavior. These observations indicate that within the range of ∼0.15 to ∼5 μm, the low-temperature SIRM may be higher than that expected from "normal" magnetic domain wall displacement. Such a behavior can be caused by the presence of a SD-like component in the magnetization of these grains, which origin, however, is uncertain. The natural rocks containing nearly stoichiometric magnetite manifest a dependence of the R LT ratio on magnetic domain state identical to that observed from synthetic magnetites. Therefore, the comparison of FC SIRM and ZFC SIRM at very low temperatures may allow a crude estimate of magnetic domain state in some magnetite-bearing rocks, such as shallow mafic intrusions or some marine sediments.

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Secular variation of the Late Archean–Early Proterozoic geodynamo

Cited by 51 publications

References 22 publications

Symmetry and stability of the geomagnetic field

Symmetry and stability of the geomagnetic field

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

Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

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