Triassic Paleomagnetism of Northern South America

Abstract

Reconnaissance sampling of three radiometrically dated Late Triassic igneous units in northern South America provides new data on Triassic paleomagnetism and a new estimate of the position of the Triassic pole for South America. The new poles compare favorably with other Triassic poles from South America. Poles in Venezuela for Guacamayas Group (195 m.y.) and Bolivar dikes (199 m.y.), combined with the mean pole for the Las Cabras lavas (204 m.y.) of Argentina, give a mean pole for the South America Triassic at 72°S, 91°W, ^agr95 = 15°. Bullard et al. showed that isobaths of the continental margins of Africa and South America have a minimum misfit for a rotation of 57.6° about a pole at 42.5°N, 29.9°W (500 fm isobath). Triassic paleomagnetic poles for Africa, when rotated about that same best-fit pole, merge with the Triassic poles for South America. A mean-composite pole for African and South American poles together is at 72°S, 106°W, ^agr95 = 10°, N = 5. A dipole geomagnetic field is indicated over the South American and African landmasses during Triassic time.