Constraints on the motions of South American and African Shields during the Proterozoic: I. 40Ar/39Ar and paleomagnetic correlations between Venezuela and Liberia

Abstract

The Encrucijada pluton of Venezuela and amphibolites near Harper, Liberia, are located on opposite sides of the Liberian Pan-African mobile belt, when South America is restored in a fit described in the literature with respect to Africa. Both units yield stable, bipolar, high-temperature magnetizations that, on the basis of thermal demagnetization data, 40Ar/39Ar hornblende and biotite radiometric results, and Rb-Sr whole-rock and biotite radiometric results, appear to be indistinguishable in age at 1.9 to 2.0 Ga. With South America in this reconstruction, the corresponding paleomagnetic poles suggest that ∼1,000 km of right-lateral strike-slip motion has occurred between the West African and Guayana Shields, probably along the Liberian Pan-African Belt. Furthermore, the Encrucijada and Harper poles are distinct from the 1.9- to 2.0-Ga paleomagnetic poles from the Kalahari Shield and tentatively suggest that relative motion has occurred between the Kalahari Shield and the West African and Guayana Shields since that time.