Palaeomagnetism of Mesozoic igneous rocks from the Maranha~o Basin, Brazil, and the time of opening of the South Atlantic

Details Palaeomagnetism of Mesozoic igneous rocks from the Maranha~o Basin, Brazil, and the time of opening of the South Atlantic Palaeomagnetism of Mesozoic igneous rocks from the Maranha~o Basin, Brazil, and the time of opening of the South Atlantic

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979e%26psl..42..427s&link_type=abstract

Earth and Planetary Science Letters, Volume 42, Issue 3, p. 427-436.

Mathematics

Probability

4

Scientific paper

From Middle-Upper Jurassic volcanics at the western margin of the Maranha~o Basin (6.4°S, 47.4°W) 15 sites (121 samples) have a mean magnetization direction D = 3.9°, I = -17.9° with α95 = 9.3°, k = 17.9 after AF cleaning (all sites have normal polarity). This yields a pole (named SAJ2) at 85.3°N, 82.5°E (A95 = 6.9°) which is near to the other known Middle Jurassic South American pole. For 21 sites (190 samples) from Lower Cretaceous basalt intrusions from the eastern part of the Maranha~o Basin (6.5°S, 42°W) the mean direction is D = 174.7°, I = +6.0° with α95 = 2.8°, k = 122 (all sites have reversed polarity) yielding a pole (SAK9) at 83.6°N, 261°E (A95 = 1.9°) in agreement with other Lower Cretaceous pole positions for South America. Comparing Mesozoic pole positions for South America and Africa in the pre-drift configuration after Bullard et al. [13] one finds a significant difference (with more than 95% probability) for the Lower Cretaceous and Middle Jurassic poles and also a probable difference for the mean Triassic poles indicating a small but probably stationary separation of the two continents from the predrift position in the Mesozoic until Lower Cretaceous time which may be due to an early rifting event.

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