Taenite in Fast-Cooled Meteorites Thermally Stable Over Billion-years Timescale
Abstract
Meteorites, in particular iron and stony-iron meteorites, have received much attention in the paleomagnetic community in the last decades, mainly due to their potential to reliably record ancient magnetic fields. These materials, therefore, became a pivotal source of information about the magnetic and thermal evolution of planetesimals formed in the early solar system. The cloudy zone (CZ) forms within meteoritic metal as a nanometric-sized intergrowth of Ni-rich taenite or tetrataenite islands embedded in a paramagnetic matrix. The CZ has recently been recognized as the most promising magnetic phase to have possibly recorded magnetic activity of the parent body, mostly due to the presence of tetrataenite, commonly reported as "the" ideal paleomagnetic recorder due to its high coercivity and resistance to remagnetization. The formation of tetrataenite, nevertheless, is sensitively dependent on the cooling rate of meteoritic metal; some fast-cooled meteorites are believed to have a CZ predominantly comprised of small (< 40 nm) taenite islands, as a consequence of the rapid cooling that prevented both the formation of tetrataenite as well as the growth of bigger islands. Taenite, in contrast with tetrataenite, is generally considered as a poor paleomagnetic recorder, mostly based on its soft magnetic behavior observed in bulk (μm- to cm-) scale. In this work, however, we show through an extensive, systematic series of micromagnetic simulations that nm-sized taenite is thermally stable over billion-years timescale, which implies that taenite-bearing meteorites, in addition to slowly-cooled tetrataenite-bearing ones, are expected to be reliable sources of paleomagnetic information of planetesimals. Additionally, we find a narrow range of island sizes (~14 to ~30 nm) for which taenite forms stable single-domain (SD) structures, which suggests that slowly-cooled iron meteorites - in which taenite undergoes a phase transition to form tetrataenite - would likely retain a previous natural remanent magnetization in this size range, while larger grains might possibly record a new (chemical) remanent magnetization when tetrataenite forms.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMGP32B0348D