Determination of Geomagnetic Field Paleointensity from Red Sea Basalts by the Thellier–Coe Method at Heating in Argon and Air

Abstract—Paleointensity of the geomagnetic field is determined from the natural remanent magnetization of Holocene basalts from the Red Sea rift zone by the Thellier method in the Coe modification with heating in air and argon. It is shown that when basalts are heated in air, titanomagnetite, the carrier of remanent magnetization, undergoes mineralogical changes at temperatures 50–100°C below the maximum blocking temperature, which impedes paleointensity determination. It is established that the Thellier–Coe procedure conducted in argon atmosphere avoids oxidation of titanomagnetite and thus significantly improves the quality of paleointensity determination. When heating is conducted in air, only 50–60% of the natural remanent magnetization can be used to calculate paleointensity, while when in argon, the percentage reaches up to 87% and the quality factor is 1.5–3 times higher. The paleointensity value estimated from heating in argon is 10–20% lower than that estimated from heating in air. The paleointensity of 62 ± 1 µT determined from the Red Sea basalts is about 1.7 times as high as the current field in the region according to the IGRF13 model. The high paleointensity value allows us to attribute the period of formation of the studied basalts to the time of the Levantine Iron Age Anomaly 1.5–0.5 ka BC.