Variations in the Earth’s magnetic field intensity at different time scales bear great information on the growth of Earth’s deep interiors (Macouin et al. 2004; Tarduno et al. 2007; Biggin et al. 2015) and the evolution of geodynamo (Larson and Olson, 1991; Glatzmaier et al. 1999; Olson et al. 2013). There are two different types of approaches to trace the temporal variation of geomagnetic field intensity: relative paleointensity determination (RPI, Tauxe 1993) and absolute paleointensity determinations (Thellier 1938; Thellier and Thellier 1959). Sediments carry depositional or post-depositional remanent magnetization (DRM or pDRM), and are excellent media to records the semi-continuous RPI (Valet et al. 2005; Yamazaki and Oda 2005; Channell et al. 2009; Ziegler et al. 2011). In practice, volcanic rocks are suitable for high resolution spot-readings ancient geomagnetic field intensity determination.
Modern absolute paleointensity determinations require multiple step heatings with systematic alteration (or consistency) checks. The Thellier protocol (Thellier 1938; Thellier and Thellier 1959) was initially proposed to compare the destruction of thermoremanent magnetization (TRM) and acquisition of laboratory-induced partial thermoremanent magnetization (pTRM) at equal temperatures. Thellier-type double heating techniques have been slightly modified, with each method has pros and cons (Thellier 1938; Thellier and Thellier 1959; Coe 1967; Aitken et al. 1988; Yu et al. 2004). The most commonly used technique is the so-called “Coe” protocol (Coe 1967), in which we first heat the specimen to Ti in a zero-field to determine the NRM lost. To determine the pTRM gained, we second heat specimen to Ti in an in-field conditions. Aitken et al. (1988) modified the Coe method (1967) by reversing the order of double heating. The IZZI protocol alternates the Aitken method in odd steps and the Coe method in even steps (Yu et al. 2004). Detailed reviews of various Thellier-type techniques were provided by Valet (2003) and Biggin (2010).
Once the paleointensity determination is carried out, the results are displayed in an Arai plot (Nagata et al. 1963) where the slope of NRM remaining versus pTRM gained is the ratio of ancient to laboratory magnetic field intensity. Only the stable single-domain (SD) particles follow a linear Arai plots, reflecting identical spectrum of unbloking temperature (Tub) and blocking temperature (Tb). Multi-domain (MD) and pseudo-single domain (PSD) grains tend to produce a non-linear (or sometimes zig-zagging) Arai plots (Dunlop and Özdemir 2001; Leonhardt et al. 2015; Paterson et al. 2015). Inequivalent Tub over Tb is responsible for such a non-linearity in an Arai plot. To quantify undemagnetized pTRM for non-uniformly magnetized TRM, the pTRM tail check was introduced (Riisager et al. 2000; Riisager and Riisager 2001; Yu and Dunlop 2003). In addition to the physical origin, a chemical contribution can alter the linearity of an Arai plot. For instance, growing of newly formed magnetic particles by chemical transformations (Yamamoto 2006) can induce thermochemical remanent magnetization (TCRM).
The most convenient (yet the easiest) way to ensure the high fidelity of paleointensity determinations is to check the quality of paleointensity determination using historic rocks whose geomagnetic field intensity is readily known (e.g., IGRF-International Geomagnetic Reference Field). To this end, the reliability of absolute paleointensity determinations was tested using historic lavas from Hawaii, US (Tsunakawa and Shaw 1994; Chauvin et al. 2005; Oishi et al. 2005; Herrero-Bervera and Valet 2009; Morales et al. 2010; Cromwell 2015), Italy (Calvo et al. 2002), Japan (Tsunakawa and Shaw 1994; Yu 2012), Spain (de Groot et al. 2015; Calvo et al. 2016), and western US (Coe et al. 2004).
Among various historic sites, the 1960 historic lavas in Hawaii drew more attention because of its accessibility. However, relatively easier accessibility did not guarantee successful duplication of geomagnetic field intensity information. In fact, the 1960 lava often yielded biased paleointensity determination toward higher/lower values up to 10–20% (Tanaka and Kono 1991; Tsunakawa and Shaw 1994; Tanaka et al. 1995; Valet and Herrero-Bervera 2000; Hill and Shaw 2000; Yamamoto et al. 2003; Herrero-Bervera and Valet 2009; Morales et al. 2010). Origin of heterogeneous or anomalous paleointensity outcome possibly lies on the influence of thermochemical remanent magnetization (TCRM) (Yamamoto et al. 2003), on the presence of local magnetic anomaly (Morales et al. 2010), or alteration and neo-formation of magnetic particles during repeated heatings (Zhao et al. 2014).
The present study was designed to incorporate the temperature dependence of magnetic hysteresis as a potential alteration checker. We aim to determine the exact mechanisms for the biased paleointensity results with positive pTRM checks. This is extremely important for paleointensity determinations for older rocks.