The Earth’s mantle has long been considered non-magnetic, due to high temperatures at depth.
An international team of scientists used ID18 to study the iron oxide hematite (Fe2O3), a strongly magnetic mineral, at temperatures and pressures found down to the Earth’s lower mantle. Their study, published in Nature, provides evidence that hematite retains magnetic properties at the depth of the transition zone between the upper and lower mantle at certain temperatures and could therefore be a source of magnetic anomalies there.
Scientists have traditionally considered the Earth’s mantle to be non-magnetic due to its elevated temperatures being too high to retain any magnetism in the constituting minerals. However, satellite and aeromagnetic data provide evidence for magnetic anomalies in the mantle, particularly around cooler areas such as subduction zones (tectonic plate boundaries where one plate is forced underneath another). The source of the anomalies remains largely unknown, but iron oxides are considered a likely source due to their high critical temperatures. Of these, hematite (Fe2O3) is the dominant iron oxide at depths of around 300 – 600 km below the Earth’s surface – a transition zone between the upper and the lower mantle.