Analysis of an Updated Paleointensity Database (Q<sub>PI</sub>‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic

Kulakov, E.; Sprain, Courtney J.; Doubrovine, Pavel V.; Смирнов, А. В.; Paterson, Greig A.; Hawkins, Louise; Fairchild, Luke M.; Piispa, E. J.; Biggin, Andrew J.

doi:10.1029/2018jb017287

Cited by 55 publications

(61 citation statements)

References 88 publications

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“…This implies that, regardless of how frequently AD/NAD undergoes brief collapse, the field recovers to spend most of its time in a similarly dipole dominated state. Intervals of stable average AD dominance also apparently coincided with significant variations in long-term average field intensity [31][32][33] . This further suggests that the magnitude of the AD and NAD field are correlated on long-timescales such that the degree of AD dominance remains approximately constant.…”

Section: Resultsmentioning

confidence: 82%

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

et al. 2020

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A defining characteristic of the recent geomagnetic field is its dominant axial dipole which provides its navigational utility and dictates the shape of the magnetosphere. Going back through time, much less is known about the degree of axial dipole dominance. Here we use a substantial and diverse set of 3D numerical dynamo simulations and recent observation-based field models to derive a power law relationship between the angular dispersion of virtual geomagnetic poles at the equator and the median axial dipole dominance measured at Earth’s surface. Applying this relation to published estimates of equatorial angular dispersion implies that geomagnetic axial dipole dominance averaged over 107–109 years has remained moderately high and stable through large parts of geological time. This provides an observational constraint to future studies of the geodynamo and palaeomagnetosphere. It also provides some reassurance as to the reliability of palaeogeographical reconstructions provided by palaeomagnetism.

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Section: Resultsmentioning

confidence: 82%

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

et al. 2020

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“…This supports previous assertions that the time‐averaged field of the past 10 million years is not a perfect geocentric axial dipole but one with a more complex mean field morphology. Field strength compilations (e.g., Biggin et al., 2015; Bono et al., 2019; Kulakov et al., 2019; Hawkins et al., 2019; Shcherbakova et al., 2017; Smirnov et al., 2016) demonstrated that earlier times record different VDM distributions from the past 10 million years. It is suspected that for other intervals further back in geologic time, VGP dispersion and other estimates of PSV behavior are different than seen for this most recent interval (e.g., Biggin, Strik, et al., 2008; Biggin, van Hinsbergen, et al., 2008, 2009; de Oliveira et al., 2018; Doubrovine et al., 2019; Smirnov et al., 2011; Tarduno et al., 2002).…”

Section: Resultsmentioning

confidence: 99%

Covariant Giant Gaussian Process Models With Improved Reproduction of Palaeosecular Variation

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et al. 2020

Geochem Geophys Geosyst

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A commonly used family of statistical magnetic field models is based on a giant Gaussian process (GGP), which assumes each Gauss coefficient can be realized from an independent normal distribution. GGP models are capable of generating suites of plausible Gauss coefficients, allowing for palaeomagnetic data to be tested against the expected distribution arising from a time‐averaged geomagnetic field. However, existing GGP models do not simultaneously reproduce the distribution of field strength and palaeosecular variation estimates reported for the past 10 million years and tend to underpredict virtual geomagnetic pole (VGP) dispersion at high latitudes unless trade‐offs are made to the fit at lower latitudes. Here we introduce a new family of GGP models, BB18 and BB18.Z3 (the latter includes non‐zero‐mean zonal terms for spherical harmonic degrees 2 and 3). Our models are distinct from prior GGP models by simultaneously treating the axial dipole variance separately from higher degree terms, applying an odd‐even variance structure, and incorporating a covariance between certain Gauss coefficients. Covariance between Gauss coefficients, a property both expected from dynamo theory and observed in numerical dynamo simulations, has not previously been included in GGP models. Introducing covariance between certain Gauss coefficients inferred from an ensemble of “Earth‐like” dynamo simulations and predicted by theory yields a reduced misfit to VGP dispersion, allowing for GGP models which generate improved reproductions of the distribution of field strengths and palaeosecular variation observed for the last 10 million years.

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“…We then compared our API determinations with the subsets from Kulakov et al. (2019), which were analyzed using a suite of 10 paleointensity quality criteria (Q PI ). Subsets I‐III yield for the late Cretaceous interval (65–84 Ma) a median dipole strength around 34 ZAm 2 , that is, twice lower than our mean dipole strength of 58.9 ± 6.9 ZAm 2 derived from Tuoyun volcanics and baked sediments for the time interval 60–70 Ma.…”

Section: Discussionmentioning

confidence: 99%

Paleomagnetism of Paleocene‐Maastrichtian (60–70 Ma) Lava Flows From Tian Shan (Central Asia): Directional Analysis and Paleointensities

et al. 2020

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The Tuoyun volcanics from the Tian Shan range (Central Asia) give an opportunity to investigate the variability of the Earth's magnetic field during the Cretaceous and Early Paleogene. In the paper we focus on Maastrichtian-Paleocene basalts and report new paleomagnetic results from 70 lava flows (respectively 45 directional groups) sampled near Tuoyun village (75.33°E; 40.18°N) from three distinct sections. Combined with previous results, our new data set yields a virtual geomagnetic pole at φ S ¼ 180.2°E, ϑ S ¼ 49.5°N with an angular standard deviation S ¼ 20:8 ∘ j 23:1 ∘ 18:8 ∘ (for N ¼ 93 directional groups). The mean inclination I s ¼ 36.2°is indicative of an emplacement of the Tuoyun volcanics at a paleolatitude around 20°N, consistent with the high dispersion k ¼ 14.6 of the directions. Such an inclination value is 10-15°l ower than the predictions from the apparent polar wander paths for stable Europe and East Asia. This observation can be partly explained by crustal shortening within the East Asian plate during the India-Asia convergence, but also needs to invoke a local field anomaly in Central Asia as previously proposed. Our absolute paleointensity experiments conducted on two lava flows and two baked sedimentary layers yield a mean virtual dipole moment of 58.9 ± 6.9 ZA•m 2 , consistent with the values at 60-70 Ma in the global paleointensity database. Compared to relative paleointensity results during the Cretaceous Normal Superchron and during the Plio-Pleistocene, the relative variability in intensity-supposed to be a proxy for the geodynamo's activity-estimated here at 31 ± 5% (N ¼ 15) from pseudo-Thellier experiments possibly corroborates a correlation between geomagnetic reversal frequency and paleosecular variation rate during the past 120 Myr. An open question is whether the changes in the frequency of reversals correlate with the gradual temporal changes of the magnetic field during stable periods, referred to as paleosecular variation (PSV). An increase of PSV rate with reversal frequency has often been proposed (e.g., Biggin et al., 2008). Identifying such a correlation however depends on our ability to accurately quantify PSV through geological time. This is

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Analysis of an Updated Paleointensity Database (Q_PI‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic

Cited by 55 publications

References 88 publications

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

Covariant Giant Gaussian Process Models With Improved Reproduction of Palaeosecular Variation

Paleomagnetism of Paleocene‐Maastrichtian (60–70 Ma) Lava Flows From Tian Shan (Central Asia): Directional Analysis and Paleointensities

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Analysis of an Updated Paleointensity Database (QPI‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic

Cited by 55 publications

References 88 publications

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time

Covariant Giant Gaussian Process Models With Improved Reproduction of Palaeosecular Variation

Paleomagnetism of Paleocene‐Maastrichtian (60–70 Ma) Lava Flows From Tian Shan (Central Asia): Directional Analysis and Paleointensities

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Analysis of an Updated Paleointensity Database (Q_PI‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic