Kenneth A. Hoffman

University of Wisconsin–Madison

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Brad S. Singer

University of Wisconsin–Madison

Pierre Camps

Géosciences Montpellier

Claire Carvallo

Institut de minéralogie, de physique des matériaux et de cosmochimie

Yongxin Pan

Chinese Academy of Sciences

Rixiang Zhu

Institute of Geology and Geophysics

Hervé Guillou

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

Ajoy K. Baksi

Louisiana State University

Ruiping Shi

East China Normal University

Elisabeth Schnepp

Montanuniversität Leoben

Lars N. Hansen

University of Minnesota

Cooperative Institutions

Centre National de la Recherche Scientifique

Chinese Academy of Sciences

Institute of Geology and Geophysics

University of Chinese Academy of Sciences

California Polytechnic State University

Université de Montpellier

United States Geological Survey

University of Minnesota

University of California, Santa Barbara

Géosciences Montpellier

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Polarity transition records and the acquisition of remanence: A cautionary note

Geophysical Research Letters (1986)

Kenneth A. Hoffman Steven B. Slade

Simulations of natural smoothing of paleomagnetic reversal records suggest that illustrative features of actual field behavior may be made undiscernible even when relatively short integration times are associated with the acquisition of magnetic remanence. The results of this exercise further caution against the sole use of logs of component behavior (i.e. declination, inclination and intensity) for analysis, since time‐averaging of the complete vector field not only smooths, but also can significantly alter the component paleomagnetic waveforms.

Polarity (international relations)

Smoothing

Natural remanent magnetization

Secular Variation

Component (thermodynamics)

10.1029/gl013i005p00483

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Citations (35)

Magnetic Source Separation in Earth's Outer Core

Science (2008)

Kenneth A. Hoffman Brad S. Singer

We present evidence that the source of Earth's axial dipole field is largely independent from the sources responsible for the rest of the geomagnetic field, the so-called nonaxial dipole (NAD) field. Support for this claim comes from correlations between the structure of the historic field and the behavior of the paleomagnetic field recorded in precisely dated lavas at those times when the axial dipole was especially weak or nearly absent. It is argued that a "stratification" of magnetic sources exists in the fluid core such that the axial dipole is the only observed field component that is nearly immune from the influence exerted by the lowermost mantle. It follows that subsequent work on spherical harmonic-based field descriptions may now incorporate an understanding of a dichotomy of spatial-temporal dynamo processes.

Outer core

Geomagnetic pole

Stratification (seeds)

Geomagnetic reversal

10.1126/science.1159777

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Citations (29)

Stability of mantle control over dynamo flux since the mid-Cenozoic

Physics of The Earth and Planetary Interiors (2008)

Kenneth A. Hoffman Brad S. Singer Pierre Camps Lars N. Hansen Katie Johnson

Core–mantle boundary

Geomagnetic reversal

Geomagnetic pole

Outer core

10.1016/j.pepi.2008.07.012

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Citations (15)

Transitional field configurations and geomagnetic reversal

Nature (1978)

Kenneth A. Hoffman M. Fuller

Geomagnetic reversal

Polarity (international relations)

Polarity reversal

Geomagnetic pole

Geomagnetic secular variation

10.1038/273715a0

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Citations (76)

Precise ages of the Réunion event and Huckleberry Ridge excursion: Episodic clustering of geomagnetic instabilities and the dynamics of flow within the outer core

Earth and Planetary Science Letters (2014)

Brad S. Singer Brian R. Jicha Daniel J. Condon Alexandra S. Macho Kenneth A. Hoffman

Excursion

Magnetostratigraphy

Clockwise

10.1016/j.epsl.2014.08.011

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Citations (42)

Paleointensity study of Early Miocene lavas from Pingzhuang, Inner Mongolia, China

Geophysical Research Letters (2002)

Ruiping Shi Ruilin Zhu Yongxin Pan Guanghai Shi Kenneth A. Hoffman

A paleomagnetic and geochronologic investigation has been conducted on 17 lava flows from Inner Mongolia, north China. Radiometric K‐Ar dating experiments give an age between 23 and 22 Ma for these volcanic units. Rock magnetic measurements of thermomagnetic curves and hysteresis loops show the primary carrier of remanence to be pseudo‐single domain titanomagnetite. Stepwise thermal demagnetization isolated a well‐defined direction of characteristic remanent magnetization (ChRM) in all studied lava flows with a mean direction of D/I = 359.8°/62.2° (α 95 = 3.8°). Fifty samples from 11 lavas were pre‐selected on the basis of thermomagnetic analyses to carry out Thellier‐Thellier paleointensity experiments with systematic partial thermoremanent magnetization (pTRM) checks. Twenty‐three samples from 7 lavas yield reliable paleointensity estimates with a mean virtual dipole moment (VDM) of (3.9 ± 0.9) × 10 22 Am 2 , about half the strength of the modern‐day field.

Thermomagnetic convection

Thermoremanent magnetization

Magnetic mineralogy

Rock magnetism

Natural remanent magnetization

Radiometric dating

10.1029/2002gl015990

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Citations (14)

On the age and morphology of the reunion event

Geophysical Research Letters (2000)

Ajoy K. Baksi Kenneth A. Hoffman

Data pertinent to the age of the normal polarity Reunion “Event” (or subchron), and whether it is a split feature, are critically examined. New 40 Ar/ 39 Ar age determinations on lavas from two sequences on Reunion Island, along with available potassium‐argon (K‐Ar), 40 Ar/ 39 Ar and astrochronological analyses, indicate an age of 2.15–2.13 Ma. Although the possibility cannot be completely ruled out, at present there is no convincing evidence supporting the contention of a short duration of normal polarity some 70–90 kyr later.

Polarity (international relations)

K–Ar dating

Morphology

Feature (linguistics)

10.1029/2000gl008536

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Citations (34)

Banach Spaces and Algebras: Spectral Theory . Edgar Raymond Lorch. Oxford University Press, New York, 1962. xii + 158 pp. $5.50.

Science (1962)

Kenneth A. Hoffman

10.1126/science.138.3537.132.a

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