Insights on Lightning‐Induced Remanent Magnetization From High‐Current Impulse Experiments

Abstract Lightning strikes generate intense transient magnetic fields capable of inducing strong and complex remanent magnetizations in rocks, potentially overprinting their original paleomagnetic record. To investigate the mechanisms and outcomes of lightning‐induced remanent magnetization, we conducted controlled high‐current impulse experiments on mafic and ultramafic rocks using the lightning generator of the High Energy Laboratory at the University of São Paulo. Current pulses up to ∼80 kA with waveform reversals were applied on alkaline volcanic rocks from Trindade Island, tholeiitic basalts from Vista Alegre, glimmerites from Planalto da Serra, and basalts from the Quatipuru complex. Rock magnetic experiments performed before and after the high‐current experiments include: magnetic susceptibility, hysteresis, first‐order reversal curve diagrams, and Lowrie–Fuller tests. Lightning‐like currents significantly increase remanent magnetization in most lithologies, with some specimens exhibiting up to a ∼490‐fold increase, and REM ratios (natural remanent magnetization/Saturation Isothermal Remanent Magnetization) rising above 0.1, consistent with natural fulgurites and lodestones. Importantly, waveform polarity reversals produced opposite magnetization directions between nearby and more distant specimens, resulting in the coexistence of two different components of remanence within tens of centimeters of distance from the striking point. Quatipuru basalts, which are predominantly paramagnetic, exhibited a distinct behavior, including susceptibility decreases and an enhanced frequency‐dependent response, suggesting the formation of superparamagnetic grains. In addition to remanence enhancement lightning discharges can also produce opposite‐direction remagnetization in low‐coercivity assemblages, expressed as a characteristic curvature in AF demagnetization paths, therefore providing diagnostic signatures that can help recognize lightning‐affected samples in paleomagnetic studies.