Abstract
Thellier-type paleointensity experiments associated with partial thermal remanent magnetization checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies have revealed that a substantial portion of paleointensity results with positive checks for historical lava samples largely fails to predict known Earth magnetic field intensity values. To determine the fidelity of paleointensity values, conventional Thellier-type paleointensity experiments were performed on Kilauea lava flows that erupted in 1960. The positive partial thermal remanent magnetization checks for our results range from 30.28 ± 1.38 µT to 52.94 ± 1.89 µT. This strongly indicates that conventional paleointensity checks cannot guarantee the fidelity of paleointensity results, especially when the unblocking temperatures for the newly formed magnetic particles are higher than the treatment temperature. Therefore, in this study, to check for thermal alteration during heating, the temperature dependence of the hysteresis parameter measured at room temperature for the thermally treated samples was also measured. Our new results show that nearly all biased paleointensity values correspond to a ratio of the coercivity of remanence to the magnetic coercivity of > 3 and a chemical alteration index > ~ 10%, which indicates the strong effect of the domain state and thermal alteration on the fidelity of the paleointensity results. Our study provides feasible criteria to further improve the fidelity of paleointensity estimations.
Highlights
Variations in the Earth’s magnetic field intensity at different time scales contain significant information concerning the growth of the Earth’s deep interior (Macouin et al 2004; Tarduno et al 2007; Biggin et al 2015) and the evolution of the geodynamo (Larson and Olson 1991; Olson et al 2013)
We strongly suggest that the domain state and thermal stability of samples be systematically incorporated into the paleointensity studies, except for all conventional criteria
We presented the paleointensities of 1960 Kilauea lava flow samples using the temperature dependence of the hysteresis parameters according to modified Thellier experiments using the IZZI protocol
Summary
Variations in the Earth’s magnetic field intensity at different time scales contain significant information concerning the growth of the Earth’s deep interior (Macouin et al 2004; Tarduno et al 2007; Biggin et al 2015) and the evolution of the geodynamo (Larson and Olson 1991; Olson et al 2013). There are two different types of approaches used to trace temporal variations in the geomagnetic field intensity: relative paleointensity (RPI) determinations (Tauxe 1993) and absolute paleointensity determinations (Thellier 1938; Thellier and Thellier 1959). Modern absolute paleointensity determinations require multiple step heating with systematic alteration (or consistency) checks. Thellier-type double-heating techniques include multiple slight modifications, with each method having advantages and disadvantages The most commonly used technique is the so-called “Coe” protocol (Coe 1967) in which the specimen is first heated to an initial temperature (Ti) in a zero-field to determine the natural remanent magnetization (NRM) lost. Detailed reviews of various Thellier-type techniques have been provided by Valet (2003) and Biggin (2010)
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