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Isolating components of magnetic anisotropy for more reliable anisotropy corrections in paleomagnetism

Applicant Biedermann Andrea Regina
Number 167608
Funding scheme Advanced Postdoc.Mobility
Research institution Institute for Rock Magnetism University of Minnesota
Institution of higher education Institution abroad - IACH
Main discipline Geophysics
Start/End 01.11.2016 - 30.04.2018
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All Disciplines (2)

Discipline
Geophysics
Mineralogy

Keywords (7)

magnetite; magnetic fabric; paleomagnetism; NRM deflection; hematite; magnetic mineralogy; anisotropy corrections

Lay Summary (German)

Lead
Ein Ziel von paläomagnetischen Studien ist, anhand der Magnetisierungsrichtung in Gesteinen die Bewegung der Kontinentalplatten seit das Gestein magnetisiert wurde zu bestimmen. Die Richtung des Erdmagnetfelds variiert mit der geographischen Breite: am Äquator ist es ca. horizontal, an den Polen ungefähr vertikal. Eine grundlegende Annahme vieler paläomagnetischer Untersuchungen ist, dass die Magnetisierung im Gestein parallel zum Magnetfeld ist. In verformten Gesteinen sind die magnetischen Eigenschaften aber richtungsabhängig, und ihre Magnetisierung ist nicht parallel zur Magnetfeldrichtung, sondern näher an der bevorzugten Magnetisierungsrichtung. Z.B. in Sedimenten liegt diese oft horizontal, und es scheint dass die Erdplatte näher am Äquator lag, als tatsächlich der Fall war. Für eine zuverlässige Rekonstruktion der Plattenbewegungen ist es deshalb wichtig, für diesen Effekt zu korrigieren.
Lay summary

Ziele des Forschungsprojekts

Für diese Korrektur brauchen wir folgende Informationen:

- Welches Mineral die Magnetisierung trägt

- Die richtungsabhängigen Eigenschaften genau dieses Minerals

Ersteres wird in allen paläomagnetischen Studien bestimmt. Letzteres ist komplizierter, da Gesteine viele verschiedene Mineralien enthalten und jedes in seiner Weise zur Richtungsabhängigkeit der magnetischen Eigenschaften beiträgt, zumal wir oft nicht an dem Mineral interessiert sind, das am stärksten magnetisch ist. Ziel dieses Projekts ist es, Methoden (weiter) zu entwickeln, die uns erlauben, die Eigenschaften genau desjenigen Minerals zu isolieren, das auch für die Magnetisierung verantwortlich ist.

Wissenschaftlicher und gesellschaftlicher Kontext

Die Resultate sind nützlich für künftige paläomagnetische Untersuchungen, oder die Interpretation magnetischer Anomalien.

Direct link to Lay Summary Last update: 17.06.2016

Responsible applicant and co-applicants

Publications

Publication
Anisotropy of (partial) isothermal remanent magnetization: DC-field-dependence and additivity
Biedermann Andrea R, Jackson Mike, Bilardello Dario, Feinberg Joshua M (2019), Anisotropy of (partial) isothermal remanent magnetization: DC-field-dependence and additivity, in Geophysical Journal International.
Grain-size-dependent remanence anisotropy and its implications for paleodirections and paleointensities – Proposing a new approach to anisotropy corrections
Biedermann Andrea R., Bilardello Dario, Jackson Mike, Tauxe Lisa, Feinberg Joshua M. (2019), Grain-size-dependent remanence anisotropy and its implications for paleodirections and paleointensities – Proposing a new approach to anisotropy corrections, in Earth and Planetary Science Letters, 512, 111-123.
Influence of static alternating field demagnetization on anisotropy of magnetic susceptibility: Experiments and implications
Biedermann A.R., Jackson M., Bilardello D., Feinberg J.M., Brown M.C., McEnroe S.A. (2017), Influence of static alternating field demagnetization on anisotropy of magnetic susceptibility: Experiments and implications, in Geochemistry, Geophysics, Geosystems.
Towards a holistic understanding of complex magnetic fabrics
Biedermann A.R. (2017), Towards a holistic understanding of complex magnetic fabrics, University of Minnesota Press, Minneapolis, USA.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
EGU General Assembly 2019 Talk given at a conference Towards a more detailed understanding of magnetic anisotropy of ferromagnetic grains 07.04.2019 Vienna, Austria Biedermann Andrea Regina;
Joint group seminar CENIEH/University of Burgos magnetism groups Individual talk Complex remanence anisotropies and implications for anisotropy corrections in paleomagnetic studies 11.01.2019 Burgos, Spain Biedermann Andrea Regina;
EGU General Assembly Poster Coercivity-dependence of remanence anisotropy: Implications for anisotropy corrections in paleomagnetic studies 10.04.2018 Vienna, Austria Biedermann Andrea Regina;
Institute for Rock Magnetism Lab Meeting, University of Minnesota Individual talk Coercivity-dependence of AARMs and ApARMs; implications for anisotropy corrections in paleomagnetic and paleointensity studies 01.02.2018 Minneapolis, United States of America Biedermann Andrea Regina;
AGU Fall Meeting Poster Anisotropy of anhysteretic remanent magnetization (AARM) and its dependence on experimental parameters: Implications for fabric interpretation and paleomagnetic corrections 14.12.2017 New Orleans, United States of America Biedermann Andrea Regina;
GSA Annual Meeting Talk given at a conference  Isolating components of complex magnetic fabrics to enhance the anisotropy correction of paleomagnetic directions and intensities 24.10.2017 Seattle, United States of America Biedermann Andrea Regina;
International Conference on Rock Magnetism Poster Influence of alternating field demagnetization on susceptibility and anisotropy of susceptibility 14.07.2017 Utrecht, Netherlands Biedermann Andrea Regina;
Institute for Rock Magnetism Lab Meeting, University of Minnesota Individual talk Variation of AMS parameters during alternating field demagnetization 21.06.2017 Minneapolis, USA, United States of America Biedermann Andrea Regina;
EGU General Assembly Talk given at a conference Variation of magnetic anisotropy with coercivity in rocks with multiple remanence carriers, as shown by anisotropy of remanence experiments 23.04.2017 Vienna, Austria Biedermann Andrea Regina;
Hard rock lunch seminar, Department of Earth Sciences, University of Minnesota Individual talk Magnetic anisotropy – measurement techniques, models, and geologic applications 27.02.2017 Minneapolis, United States of America Biedermann Andrea Regina;


Abstract

Paleomagnetic studies define a rock’s magnetic history to make paleogeographic reconstructions. The magnetization in a rock can be used to estimate the intensity and direction of the geomagnetic field at the time it was acquired. However, rock deformation or compaction during lithification can lead to a statistical alignment of the ferromagnetic grains’ easy magnetization axes/planes, thus causing deflection of the natural remanent magnetization (NRM). In this case, neither the paleofield direction nor its intensity are recorded accurately. If not accounted for, NRM deflection can cause major problems for paleogeographic reconstructions or the construction of apparent polar wander paths from paleomagnetic studies. Several correction techniques have been developed, but all have weaknesses and no established procedure exists to date. We propose that it is necessary to (1) determine which mineral is responsible for the remanent magnetization in a rock and (2) isolate the component of anisotropy related to this mineral for a correction. We will conduct a combined rock, paleomagnetic and magnetic fabric study on samples containing both magnetite and hematite and develop a best-practice protocol for isolating the anisotropy due to the remanence carrier, which can then be used to correct for NRM deflection. This will benefit not only the paleomagnetism and archeomagnetism communities, but also exploration scientists who model magnetic anomalies, and also face the problem that magnetization can be tilted away from the magnetic field direction.
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