Mineral magnetism of dusty olivine: A credible recorder of pre-accretionary remanence

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2011-12, Vol.12 (12), p.n/a
• Main Authors: Lappe, Sophie-Charlotte L. L., Church, Nathan S., Kasama, Takeshi, da Silva Fanta, Alice Bastos, Bromiley, Geoff, Dunin-Borkowski, Rafal E., Feinberg, Joshua M., Russell, Sara, Harrison, Richard J.
• Format: Article
• Language: English
• Subjects: chondrules; dusty olivine; electron holography; first-order reversal curves; Holography; Magnetic fields; Magnetic properties; Magnetism; Meteors & meteorites; Mineralogy; Minerals; Petrology; Rocks; transmission electron microscopy
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2011GC003811

The magnetic properties of olivine‐hosted Fe‐Ni particles have been studied to assess the potential of “dusty olivine” to retain a pre‐accretionary remanence in chondritic meteorites. Both body‐centered (bcc) and face‐centered cubic (fcc) Fe‐Ni phases were formed by reduction of a terrestrial olivine precursor. The presence of Ni complicates the magnetic properties during heating and cooling due to the fcc‐bcc martensitic transition. First‐order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non‐interacting single‐domain (SD) particles, and a “butterfly” structure extending to 250 mT, attributed to single‐vortex (SV) states. SD and SV states were imaged directly using electron holography. The location of the SD/SV boundary is broadly consistent with theoretical predictions. A method to measure the volume of individual SD particles using electron holography is presented. Combining the volume information with constraints on coercivity, we calculate the thermal relaxation characteristics of the particles and demonstrate that the high‐coercivity component of remanance would remain stable for 4.6 Ga, even at temperatures approaching the Curie temperature of pure Fe. The high coercivity of the particles, together with the chemical protection offered by the surrounding olivine, is likely to make them resistant to shock remagnetization, isothermal remagnetization and terrestrial weathering, making dusty olivine a credible recorder of pre‐accretionary magnetic fields. Key Points Dusty olivine is a credible carrier of pre‐accretionary remanence Remanence is carried by both single‐domain and single‐vortex states Remanence blocks immediately below Tc and remains stable for 4.6 Ga at any T