The relationship between exsolution and magnetic properties in hemo-ilmenite: Insights from Mössbauer spectroscopy with implications for planetary magnetic anomalies

Abstract

Remanence properties of ilmenites with exsolved hematite have recently been the object of much study, because their high natural remanent magnetization (NRM) is greater than predicted for these two minerals. X-ray diffraction (XRD) and Mössbauer spectroscopy in conjunction with electron microprobe and NRM measurements were used to explore the possibility that single domain (SD) hematite lamellae in the ilmenite host could explain the observed remanence, and to determine if magnetite is present. XRD results show the presence of ilmenite and hematite. Mössbauer data show that only species assigned to hematite, ilmenite, and a small amount of tetrahedral Fe3+ are present. Magnetic properties at high and low T also indicate that the only magnetic minerals are ilmenite and hematite. Magnetic data suggest that ultra-fine hematite lamellae are magnetically ordered, and their resultant remanent magnetic anomalies may contribute significantly to magnetism on terrestrial planets, even those without present-day magnetic fields. Copyright 2004 by the American Geophysical Union.