Abstract
Thirteen sites from a probably Lower Cretaceous tholeiitic dike swarm in Rio Grande do Norte (approx. 5.5ºS, 36.8ºW) have been sampled (128 samples). After the alternating field cleaning, their mean direction is D = 186.6º, I = + 20.6º with α95 = 14.0, K = 12.9, N = 10. This yields a pole at 80.6ºS, 274.8ºE with A95 = 9.5 and K = 26.8, which for South America is nearer to the Upper Cretaceous poles than to the Lower Cretaceous poles. This may reflect an uncertainty in determination of the age of the dikes: although some existing radiometric determinations indicate ages of about 130 m.y., some authors attribute a younger age (Upper Cretaceous or Tertiary) to the dikes. Rock magnetic investigations showed that the magnetic phase in the tholeiitic rocks is mainly magnetite and maghemite with poor titanium content.
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