Striped domains of coarse-grained magnetite observed by X-ray photoemission electron microscopy as a source of the high remanence of granites in the Vredefort dome

Researchers have identified striped domains of coarse-grained magnetite, observed through advanced microscopy techniques, as the source of the high remanence in granites from the Vredefort Dome. This discovery challenges traditional understanding, as such magnetite is typically associated with weak coercivity and remanence. The study used X-ray magnetic circular dichroism (XMCD) analysis and X-ray absorption spectroscopy (XAS), conducted at the SPring-8 synchrotron facility, to investigate a shocked Vredefort granite specimen. The presence of hematite lamellae on partially oxidized magnetite indicated striped domains that intensified remanence and coercivity. Unlike natural lodestones formed by lightning strikes, which showed no magnetic domain structures despite containing maghemite, the Vredefort granites' intense remanent magnetization is attributed to post-impact hydrothermal activity, suggesting a unique mechanism for magnetic hardening.

Kubo, H., Nakamura, N., Kotsugi, M., Ohkochi, T., Terada, K., & Fukuda, K. (2015). Striped domains of coarse-grained magnetite observed by X-ray photoemission electron microscopy as a source of the high remanence of granites in the Vredefort dome. Frontiers in Earth Science, 3. https://doi.org/10.3389/feart.2015.00031