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

Abstract

[1] 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.

The Vortex State in Geologic Materials: A Micromagnetic Perspective

“…We thus now have the micromagnetic confirmation of the phenomenological model proposed by Pike and Fernandez () for these features. For weakly interacting ensembles of natural SV particles with random packing, these pairs of positive and negative peaks from individual grains will produce a positive ridge along B c , accompanied by a negative trough below it (Lappe et al, , ; Zhao et al, ). Our modeling results, together with observations from such natural SV‐dominated materials, lead to the conclusion that a central ridge is a fundamental feature of the SV FORC fingerprint.…”

Widespread occurrence of silicate‐hosted magnetic mineral inclusions in marine sediments and their contribution to paleomagnetic recording

“…Such contrasting properties produce detectable rock magnetic signatures that enable discrimination between these two important types of magnetic minerals in sediments. For example, FORC diagrams with a SSD component and moderate vertical spread (Figures a, e, and g) are a useful indication of the presence of magnetic mineral inclusions [ Lappe et al ., ; Muxworthy and Evans , ] that contrast with the noninteracting central‐ridge FORC signature observed for biogenic magnetite [e.g., Egli et al ., ; Roberts et al ., ; Chang et al ., ]. However, samples that contain dispersed magnetic nanoparticles in silicates can also give rise to FORC signatures with weak magnetostatic interactions [e.g., Usui et al ., ].…”

Understanding fine magnetic particle systems through use of first-order reversal curve diagrams

“…The magnitude of the major peaks increases, as does their distance from the B i = 0 axis (the nucleation/annihilation field), as the dot size increases further to 67 nm (Figure d). To our knowledge, dusty olivine in chondritic meteorites is the only geological material that has been suggested to contain single vortex‐like states as inferred from FORC diagrams [ Lappe et al ., , ]. Regardless, micromagnetic simulation of an elongated magnetite particle (100 × 80 × 80 nm) just above the stable SD‐PSD threshold is likely to be relevant to geological samples [ Carvallo et al ., ].…”