A field like today's? The strength of the geomagnetic field 1.1 billion years ago

Sprain, Courtney J.; Swanson‐Hysell, Nicholas L.; Fairchild, Luke M.; Gaastra, Kevin

doi:10.1093/gji/ggy074

Cited by 25 publications

(15 citation statements)

References 78 publications

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“…By increasing the QPI cutoff from 3 to 4 a pivotal set of intensities by Thomas (1993) are removed at 1.3 Ga, which results in a relatively flat or possibly slowly decreasing moment over Precambrian time. The time averaged Precambrian dipole moment (combined VDM and VADM) is in the range 58 − 62 ZAm 2 in Table 3, slightly higher than the estimate by Sprain et al (2018). The other striking observation from Figures 12-14 is the number and length of time gaps in the data.…”

Section: Pint Paleointensity Databasementioning

confidence: 70%

“…As discussed by Smirnov et al (2016) and Sprain et al (2018), examples of this effect may include the Keweenawan rocks dated at 1.1 Ga, which exhibit anomalously high paleointensities and puzzling asymmetries between the normal and reversed polarity sections (Pesonen and Halls, 1983). These asymmetries could be created by rapid changes in paleolatitude or paleo-secular variation (e.g., Swanson-Hysell et al, 2009;Sprain et al, 2018). The Keweenawan intensities of Pesonen and Halls (1983) are also 2-3 times higher than the Tudor Gabbros (Yu and Dunlop, 2001), Abitibi dykes (Macouin et al, 2003), and central Arizona diabase sheets (Donadini et al, 2011), all of which were emplaced within about 50 Myr of the Keweenawan.…”

Section: Pint Paleointensity Databasementioning

confidence: 92%

“…It is well known that multidomain components can produce concave-up demagnetization curves (Arai plots) (e.g., Shcherbakova et al, 2000;Chauvin et al, 2005;Biggin et al, 2007;Tauxe and Yamazaki, 2015;Smirnov et al, 2016;Sprain et al, 2018), which could result in an over estimate of the primary intensity if not heated sufficiently. As discussed by Smirnov et al (2016) and Sprain et al (2018), examples of this effect may include the Keweenawan rocks dated at 1.1 Ga, which exhibit anomalously high paleointensities and puzzling asymmetries between the normal and reversed polarity sections (Pesonen and Halls, 1983). These asymmetries could be created by rapid changes in paleolatitude or paleo-secular variation (e.g., Swanson-Hysell et al, 2009;Sprain et al, 2018).…”

Section: Pint Paleointensity Databasementioning

confidence: 99%

“…Biggin et al (2015) found a paleointensity peak between 1.0 and 1.5 Ga that could be a signature of ICN. Recently the primary signature of some of the underlying data has been questioned and revised (e.g., Smirnov et al, 2016;Sprain et al, 2018). Simultaneously, recent upward revisions of the thermal conductivity of iron have decreased estimates of the age of the inner core to Neoproterozoic time (e.g., Driscoll and Bercovici, 2014;Davies, 2015;Nimmo, 2015), although significant uncertainty remains.…”

Section: Introductionmentioning

confidence: 99%

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Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Driscoll

Wilson

2018

Front. Earth Sci.

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The paleomagnetic record is central to our understanding of the history of the Earth. The orientation and intensity of magnetic minerals preserved in ancient rocks indicate the geodynamo has been alive since at least the Archean and possibly the Hadean. A paleomagnetic signature of the initial solidification of the inner core, arguably the singular most important event in core history, however, has remained elusive. In pursuit of this signature we investigate the assumption that the field is a geocentric axial dipole (GAD) over long time scales. We study a suite of numerical dynamo simulations from a paleomagnetic perspective to explore how long the field should be time-averaged to obtain stable paleomagnetic pole directions and intensities. We find that running averages over 20 − 40 kyr are needed to obtain stable paleomagnetic poles with α 95 < 10 • , and over 40 − 120 kyr for α 95 < 5 • , depending on the variability of the field. We find that models with higher heat flux and more frequent polarity reversals require longer time averages, and that obtaining stable intensities requires longer time averaging than obtaining stable directions. Running averages of local field intensity and inclination produce reliable estimates of the underlying dipole moment when reversal frequency is low. However, when heat flux and reversal frequency are increased we find that local observations tend to underestimate virtual dipole moment (VDM) by up to 50% and overestimate virtual axial dipole moment (VADM) by up to 150%. A latitudinal dependence is found where VDM underestimates the true dipole moment more at low latitudes, while VADM overestimates the true axial dipole moment more at high latitudes. The cause for these observed intensity biases appears to be a contamination of the time averaged field by non-GAD terms, which grows with reversal frequency. We derive a scaling law connecting reversal frequency and site paleolatitude to paleointensity bias (ratio of observed to the true value). Finally we apply this adjustment to the PINT paleointensity record. These biases produce little change to the overall trend of a relatively flat but scattered intensity over the last 3.5 Ga. A more careful intensity adjustment applied during periods when the reversal frequency is known could reveal previously obscured features in the paleointensity record.

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Section: Pint Paleointensity Databasementioning

confidence: 70%

Section: Pint Paleointensity Databasementioning

confidence: 92%

Section: Pint Paleointensity Databasementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Driscoll

Wilson

2018

Front. Earth Sci.

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“…However, while the main and final stages of MCR have been represented by several highquality paleomagnetic datasets (Swanson-Hysell et al, 2009, 2014Tauxe and Kodama, 2009;Kulakov et al, 2013cKulakov et al, , 2014Fairchild et al, 2017), the paleomagnetic data for the precursor stage remain limited. In contrast to the numerous paleomagnetic directional data, very few paleointens ity determinations have been retrieved from the MCR rocks to date (Pesonen and Halls, 1983;McArdle et al, 2004;Kulakov et al, 2013a;Sprain et al, 2018). However, even some of these data have been recently shown to be biased due to the presence of non-ideal (i.e.…”

Section: Goals and Questions Addressed In This Workmentioning

confidence: 99%

Probing the Precambrian Geodynamo: Analysis of the Geomagnetic Field Behavior and Calibration of Pseudo-Thellier Paleointensity Method for Mesoproterozoic Rocks

Foucher¹

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Mesoproterozoic geomagnetic field strength from Nova Guarita mafic dykes (Amazon Craton)

et al. 2023

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Palaeointensity data from the Precambrian are key to understanding the timing of the Earth’s Inner Core Nucleation (ICN). Due to the scarcity of data, the ICN timing is still poorly constrained and is thought to have occurred between 2500 to 500 Ma. Numerical dynamo simulation models predict an increase in entropy, a stronger driving force for convection that could affect the field strength and show an anomaly in the palaeointensity record at ICN. We present new estimates of the geomagnetic field intensity (palaeointensity) from the Mid-Mesoproterozoic (1406 ± 1424 Ma) Nova Guarita dyke swarm, in the northern Mato Grosso State (SW Amazon Craton, Brazil). To obtain palaeointensity estimates, we used the non-heating Preisach method, with palaeointensity criteria at the specimen, and site level. Five sites provided accepted palaeointensity results, yielding virtual dipole moment (VDM) estimate of 65 ± 12 ZAm2 at 1416 ± 13 Ma, 53 ± 4 ZAm2 at 1418 ± 3 Ma, 12 ± 2 and 8 ± 2 ZAm2 at 1418 ± 5 Ma, and 71 ± 16 ZAm2 at 1424 ± 16 Ma, thus an average estimate of 43 ± 30 ZAm2 for ∼1410 Ma. The estimate is similar to the average VDM data (∼50 ZAm2), calculated for the period from 1600 to 1000 Ma. This average represents only a snapshot of the Earth’s magnetic field strength. While the new data are too limited in time to contribute directly to the question of ICN, they nevertheless contribute to constraints useful for assessing numerical simulations of the Mesoproterozoic geodynamo.

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A field like today's? The strength of the geomagnetic field 1.1 billion years ago

Cited by 25 publications

References 78 publications

Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Probing the Precambrian Geodynamo: Analysis of the Geomagnetic Field Behavior and Calibration of Pseudo-Thellier Paleointensity Method for Mesoproterozoic Rocks

Mesoproterozoic geomagnetic field strength from Nova Guarita mafic dykes (Amazon Craton)

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