Paleointensity results from the late-Archaean Modipe Gabbro of Botswana



[1] Rock-magnetic and Thellier-Thellier-Coe paleointensity results are reported for a new collection of samples from the 2.78 Ga Modipe Gabbro of Botswana. The magnetic properties are very favorable, leading to an unusually high success rate and a well-constrained result of 36–40 µT (95% confidence interval). We discuss the long-standing problem of allowing for the enormous differences between the natural and laboratory cooling rates, and apply a temperature-dependent correction derived from first-order reversal curve (FORC) data. Whereas pure single-domain (SD) corrections often lead to quite large decreases in paleointensity estimates (sometimes exceeding 50%), we find a modest increase of about 10%. The Earth's Magnetic Dipole moment in the late Archaean is thereby estimated to have been ∼6×1022 Am2.