A Neoarchean paleomagnetic pole from the Kisii Series of western Kenya: Implications for crustal mobility

Abstract

The Kisii Series lavas of western Kenya were the target of a paleomagnetic study. The Kisii Series is a volcano-sedimentary sequence dated to 2531±3Ma (U–Pb) that rests unconformably over the Mesoarchean–Neoarchean Nyanzian and Kavirondian Series. The paleomagnetic study reported in this paper expands on an earlier study by Brock et al. (1972) using modern demagnetization and analysis techniques. In spite of the advanced methods, the results of both our new study and the previous study are statistically indistinguishable. We therefore combine the results of both investigations to arrive at a grand mean pole at 7°S, 166°E (A95=8°). Due to the relatively minor tilt-corrections, a fold test is inconclusive; however, the dual-polarity magnetization passes a reversal test. We argue for a primary remanence on the basis of a comparison to other paleomagnetic data in Kenya and Tanzania and geological information. We examine the relationships between age-equivalent paleomagnetic poles from the Tanzanian, Zimbabwe and Kaapvaal cratons. Based on this limited dataset, we cannot conclude whether or not the observed apparent polar wander was due to true polar wander or modern-style plate tectonics, such as would be implied by the (variable) apparent polar wander path segments. We favor the latter explanation based on the disparate lengths of the Zimbabwe versus Tanzanian apparent polar wander paths during the 2700–2500Ma interval. The Protopangea model is not consistent with paleomagnetic data from these three cratons.