A Synthetic Reality Check for the RESET Paleointensity Method Using Preheated Galapagos Lavas

Thellier-series experiments (TSEs) with partial thermoremanent magnetization (pTRM) checks are considered the most reliable paleointensity technique even though thermal alteration can escape detection by pTRM checks (Coe, 1967) and TSEs are strictly valid only on samples containing uniaxial single-domain (SD) ferromagnetic grains with the equivalence of blocking and unblocking temperatures. The recently developed RESET (Repeated thEllier-Series-ExperimenT) paleointensity method (Wang and Kent, 2021) is designed to detect the entirety of thermal alteration and also to correct for non-SD effects by repeating the original TSE on a laboratory-applied total thermoremanence (tTRM), which allows accurate paleointensities to be estimated from thermochemically stable non-SD samples. Here, we show RESET paleointensity results on preheated non-SD magnetite-bearing Galapagos lavas that were previously used for non-SD corrected paleointensity experiments (Wang and Kent, 2013). After the original round of TSEs in 2010, we gave a tTRM to each specimen in 15.0 T and conducted the repeated round of TSEs in April 2011. In August 2015, we conducted thermal demagnetization immediately after imparting another tTRM to each specimen also in 15.0 T. The 15-T tTRM imparted in 2011 was used as a target paleointensity value for the RESET, which is based on the above measurements in 2011 and 2015. Our corrected Arai linearity (CAL) checks indicated that the preheated Galapagos lavas were thermally stable. The RESET paleointensity results from 20 specimens range from 13.1 to 16.2 T, with an average of 14.5 T. Specimen GA84.8c, which yields the highest CAL check value of 0.9976, provides a perfect paleointensity estimation of 15.0 T (Fig. 1). Our data show that the RESET method can effectively yield accurate paleointensity results from thermally stable non-SD igneous samples. Reports of aging experiments imply that the TRM of non-SD samples are described as fragile (Tauxe et al., 2021), but if a laboratory-aging procedure is carried out on the laboratory-applied tTRM and introduces similar fragile effects as the natural aging process to the NRM, it is possible for the RESET method to neutralize such fragile aging effects and yield accurate paleointensity estimate for thermally stable non-SD igneous samples.