Geomagnetic Paleointensity Around 30 Ma Estimated From Afro‐Arabian Large Igneous Province

Abstract

AbstractWe conducted a geomagnetic paleointensity study of lava flows at ∼30 Ma distributed in the Lima‐Limo section of the Afro‐Arabian Large Igneous Province. The Tsunakawa‐Shaw method, which has built‐in low‐temperature demagnetization and double heating procedures, was applied to 120 specimens from 45 lava flows, successfully obtaining paleointensities from 75 specimens within 34 lava flows. We measured hysteresis loops and thermomagnetic curves to examine the influence of magnetic properties on the paleointensities but found no relationship between the paleointensities and the ratios of the hysteresis parameters. We calculated 27 flow‐level paleointensity means after excluding specimens that possibly contain titanomaghemite based on thermomagnetic curves. We observed cyclic changes of paleointensity in the lowest reversed magnetozone, which may reflect paleosecular variations. To estimate a representative virtual axial dipole moment (V(A)DM) at ∼30 Ma, we applied a flow‐level selection criterion depending on the specimen numbers. Eleven flow‐level means passed the criterion, which gave an averaged VADM of 4.2 ± 2.1 × 1022 Am2. This is similar to five averaged VADMs reported previously in the Late Cretaceous and the Cenozoic using the Tsunakawa‐Shaw method. We combined our data with available data between 25 and 35 Ma. We concluded that the mode of 4.4 × 1022 Am2 from 32 flow‐level means is representative of this period. This is close to two previously reported long‐term representative VADMs since the Jurassic.