Thermally induced inversion of Al-substituted titanomagnetite in basalts: Evidence for partial self-reversal

Abstract

We report properties of laboratory-induced thermoremanence combined with detailed rock magnetic experiments on basaltic samples which contain aluminum-substituted titanomagnetite (Fe2.24Ti0.64 Al0.12O4). Prior to Thellier-Coe paleointensity experiments, specimens were first demagnetized using an alternating field with a peak field of 90 mT and were then imparted an anhysteretic remanent magnetization (ARM) to represent a natural remanent magnetization (NRM). Results show that the partial thermal remanent magnetization (pTRM) gain and ARM remaining are linearly correlated up to 300°C. Between 300 and 460°C, specimens acquire thermoremanence with a direction antiparallel to the external field direction, leading to intensity decreases. This coincides with the onset of the mineral transformation from Al-titanomagnetite to a magnetic phase with higher Tc. Our results support that phase interaction with distinct Tc, values in partiall oxidized titanomagnetite can produce partial self-reversal thermoremanence in rocks. Copyright 2006 by the American Geophysical Union.