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 (Fe2.24Ti0.64Al0.12O4). 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 partially oxidized titanomagnetite can produce partial self‐reversal thermoremanence in rocks.