Titanomagnetite is one of the most common magnetic minerals on Earth and is the main paleomagnetic recorder in most extrusive and intrusive volcanic rocks. Researchers at the Institute for Rock Magnetism (IRM), including Julie Bowles (now a tenure-track Asst. Professor at UW-Milwaukee), Mike Jackson, and Peter Solheid recently published a paper in Nature showing that metal ions (Fe, Ti, Mg, etc.) in titanomagnetite can adjust their crystallographic arrangement (their 'cation ordering') at moderate temperatures (300-500°C). This ordering dramatically affects the mineral's Curie temperature, and hence its paleomagnetic interpretation. Bowles and Solheid recently traveled to Soufriere Hills Volcano on the island of Montserrat in the Caribbean Sea to collect samples from recent pyroclastic flow deposits, where cooling rates are well constrained, in order to better understand the thermal-dependence of this ordering process.
Photo above shows fumaroles emitting steam and sulfur at Soufriere Hills Volcano in Montserrat.
Picture at right shows Adam Stinton collecting oriented paleomagnetic cores from andesite blocks embedded within a pyroclastic flow at Montserrat.
Pictured at left is Peter Solheid, a Senior Staff Scientist at the IRM, standing in front of the restless Soufriere Hills Volcano in Montserrat.
Image to the right shows abandoned apartment buildings in the former capitol city of Plymouth, which was destroyed by a pyroclastic flow in 1997. The roofs of the buildings here collapsed under the weight of several meters of volcaniclastic debris.