Insights on lightning-induced remanent magnetization from high-current impulse experiments

Lightning strikes can induce strong and complex remanent magnetization in rocks,potentially overprinting their natural paleomagnetic record. To investigate themechanisms and outcomes of lightning-induced remanent magnetization (LIRM), weconducted controlled high-current impulse experiments on mafic and ultramaficrocks using the lightning generator of the High Energy Laboratory at the Universityof São Paulo. Peak currents up to ~80 kA with waveform reversals were applied tocylindrical specimens from Trindade Island basalts, Vista Alegre tholeiites, Planaltoda Serra alkaline basalts, and Quatipuru peridotites. Magnetic susceptibility,hysteresis, FORC diagrams, and Lowrie–Fuller tests were measured before and afterthe experiments. Results show that lightning-like currents increase remanentmagnetization in most lithologies, with some specimens exhibiting >400%enhancement, and REM ratios (NRM/SIRM) rising above 0.1, consistent with naturalfulgurites and lodestones. Importantly, waveform polarity reversals producedopposite magnetization directions between nearby and more distant specimens,resulting in the coexistence of two components of remanence within tens ofcentimeters of distance from the striking point. Quatipuru peridotites, which arepredominantly paramagnetic, exhibited distinct behavior, including susceptibilitydecreases and an enhanced frequency-dependent response, suggesting theformation of superparamagnetic grains. These findings demonstrate that lightningdischarges can significantly modify the magnetic properties of rocks. Lightning-induced changes provide diagnostic signatures, amplifying their remanence inorders of magnitude while generating complex directional patterns, whichcomplicate paleomagnetic interpretations.