Assessment of Magnetic Techniques for Understanding Complex Mixtures of Magnetite and Hematite: The Inuyama Red Chert

Abstract

Magnetite and hematite mixtures occur widely in nature. Magnetic unmixing of the signals recorded by these minerals can be important for assessing the origin of their respective paleomagnetic remanences and for extracting geological and paleoenvironmental information. However, unmixing magnetic signals from complex magnetite and hematite mixtures is difficult because of the weak magnetization and high coercivity of hematite. We assess here the relative effectiveness of first-order reversal curve (FORC) and extended FORC-type diagrams, FORC-principal component analysis (PCA), isothermal remanent magnetization (IRM) curve decomposition, and PCA of remanent hysteretic curves for unmixing magnetic components in samples from the magnetically complex Inuyama red chert, Japan. We also further characterize the domain state and coercivity distributions of both magnetite and hematite with FORC-PCA and IRM acquisition analysis in the red chert. We show that IRM curve decomposition can provide valuable component-specific information linked to coercivity, while FORC-PCA enables effective magnetic domain state identification. PCA of remanent hysteretic curves provides useful information about the most significant factors influencing remanence variations and subtle coercivity changes. To identify components in complex magnetite and hematite mixtures, we recommend PCA analysis of remanent hysteretic curves combined with FORC analysis of representative samples to identify domain states and coercivity distributions.