Rosa de Boer: Untangling the complex magnetization of Archean dykes using Micromagnetic Tomography
Channel: Institute for Rock Magnetism
Date: 2021-06-01

12th Institute for Rock Magnetism Conference 

Lightning Talk

Title: Untangling the complex magnetization of Archean dykes using Micromagnetic Tomography

Authors: Rosa A. de Boer (1), Claire I.O. Nichols (2), Roger R. Fu (3) & Lennart V. de Groot (1)

Institutions:
(1)Paleomagnetic Laboratory Fort Hoofddijk, Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
(2)Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
(3)Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA

Abstract:
The direction and intensity of the past geomagnetic field is recorded in rocks containing magnetic minerals. These remanent magnetizations are the primary source of information on the behavior of the ancient Earth magnetic field. Some of the oldest rocks containing a signal of the past geomagnetic field are found at Isua, Greenland and were formed during the early Archean. Obtaining reliable paleointensities and paleodirections from these rocks is paramount for our understanding of the Archean magnetic field, especially since samples of such an age that contain a primary magnetic signal are rare.

Paleoarchean dyke samples from Isua, Greenland demonstrate complex magnetic behavior because they contain a mixture of magnetic minerals, which have been affected by a low to medium grade metamorphic overprint, resulting in several magnetic generations. Studying these magnetic generations by means of analyzing individual grains can now be done by Micromagnetic Tomography (MMT, de Groot et al., 2018; 2021). MMT is a new, non-destructive technique that combines the results of scanning magnetometry with spatial and volumetric data of the magnetic recorders within the samples. Through a mathematical inversion the magnetic moment of each individual recorder is determined, in contrast to traditional bulk analysis.

Preliminary results show multiple iron-oxide populations within the dyke samples and various shapes in the magnetic flux signal. Flux analyses of the different populations with alternating field demagnetization steps could further unravel the complex magnetization of the samples. Application of MMT might unlock information on the early geomagnetic field that was previously unobtainable.