Grain-size-dependent remanence anisotropy and its implications for paleodirections and paleointensities - Proposing a new approach to anisotropy corrections

TitleGrain-size-dependent remanence anisotropy and its implications for paleodirections and paleointensities - Proposing a new approach to anisotropy corrections
Publication TypeJournal Article
Year of Publication2019
AuthorsBiedermann A.R, Bilardella D., Jackson M., Tauxe L, Feinberg JM
JournalEarth and Planetary Science Letters
Volume512
Pagination111-123
Date Published2019/04
Type of ArticleArticle
ISBN Number0012-821X
Accession NumberWOS:000462106300012
Keywordsanisotropy correction; Bushveld Complex; field intensity variations; Geochemistry & Geophysics; magnetic-anisotropy; paleodirection; Paleointensity; paleomagnetism; partial anhysteretic remanence; reconstruction; remanence anisotropy; susceptibility; temperature
Abstract

Paleomagnetic data provide information on the evolution of the Earth's magnetic field, and are used to reconstruct plate motions. One fundamental assumption underlying these interpretations is that the magnetization of a rock reliably records the direction and intensity of the magnetizing field, i.e. that the magnetization is parallel to the field direction, and the intensity of magnetization is proportional to the field strength. Preferred alignment or anisotropic distribution of magnetic grains can affect both the direction and the intensity of magnetization. Therefore, correction techniques, employing the anisotropy of magnetic susceptibility (AMS), thermal remanence (ATRM), or anhysteretic remanence (AARM) are used to account for these effects. We find that AARM within the same rock can vary dramatically with coercivity/grain size, so that anisotropy corrections can also depend on how AARM was measured. A consequence of the dependence of AARM on coercivity is that although a specimen may have been magnetized in a single direction, different grain size fractions may record magnetizations in different orientations. These directional variations, as revealed during progressive alternating field (AF) demagnetization, could erroneously be interpreted as changes in field or reorientation of the rock unit, when in reality they are related to grain-size-dependent remanence anisotropy. Similarly, intensity variations caused by grain-size-dependent anisotropy may bias paleointensity estimates. These observations have important consequences for studies on the evolution of the Earth's magnetic field, magnetic overprinting, and paleogeographic reconstructions. (C) 2019 Elsevier B.V. All rights reserved.

DOI10.1016/j.epsl.2019.01.051
Short TitleEarth Planet. Sci. Lett.
Student Publication: 
No
Research Topics: