Continuous production of nanosized magnetite through low grade burial
Article first published online: 10 AUG 2012
©2012. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Volume 13, Issue 8, August 2012
How to Cite
2012), Continuous production of nanosized magnetite through low grade burial, Geochem. Geophys. Geosyst., 13, Q08Z48, doi:10.1029/2012GC004104., , , and (
- Issue published online: 10 AUG 2012
- Article first published online: 10 AUG 2012
- Manuscript Revised: 20 JUN 2012
- Manuscript Accepted: 20 JUN 2012
- Manuscript Received: 15 FEB 2012
- chemical remanent magnetization;
 Geological processes, such as burial, can lead to remagnetization in rocks due to neoformed magnetic minerals that have passed a critical volume, called blocking volume. In this study, we designed a heating experiment for claystones obtained from the Paris Basin (France), in the 50–130°C temperature range, in order to simulate <4 km burial remagnetization. At a given temperature, remanence increased rapidly within a couple of days and stabilized afterward. There was a positive relation between the experimental temperature and the obtained remanence. Remanence was determined to be carried equally by stable chemical remanent magnetization and unstable thermo-viscous remanent magnetization. By assuming that magnetite formed during the experiment, we interpreted the increase of chemical remanent magnetization and the increase of thermo-viscous remanent magnetization as the continuous growth of the >20 nm and ∼20 nm minerals respectively. This result led us to propose a conceptual model of nucleation-and-growth process of magnetite during low grade burial from ∼2 to ∼4 km depth. Ultrafine magnetite (≤20 nm) was predominant over single domain magnetite (>20 nm) for <4 km depth. Transposed to natural conditions, our heating steps experiment suggested that claystone-type rocks are remagnetized during burial. For temperatures higher than 200°C, the extrapolation of our results indicated that burial remagnetization, due to the chemical remanent magnetization, might be larger than the natural remanent magnetization.