PALEOMAGNETISM OF JURASSIC AND LOWER CRETACEOUS ROCKS IN THE WESTERN FLANK OF THE PERIJA RANGE; CONSTRAINTS FOR JURASSIC PALEOGEOGRAPHY AND ROTATIONS
The comparison of these directions with middle Jurassic and lower Cretaceous directions calculated for a nearby site in the craton (4N72W) documents different magnitude of clockwise rotation. For La Quinta Formation the magnitude is 41.7° ± 16.3, while for the Rio Negro Formation is 28,2° ± 16.4. Comparison of the Jurassic mean direction with the reported in the eastern flank of the PR for only Jurassic rocks (Gose et al. 2003; D= 48.1 I=26.8; clockwise rotation 44.7°±14.2° N=1) indicate similar magnitude of rotations but different inclination values. Comparison between Jurassic directions of the PR with the Jurassic directions from the Santa Marta massif (Bayona et al. 2010; D= 20.4 I=-18.2; clockwise rotation 17°± 12.8°), indicate a higher magnitude of clockwise rotation for the PR, but different inclinations; the Santa Marta massif inclinations are negative, whereas in the PR are positive. The difference in magnitude of inclination for both middle Jurassic units could be explained as a result of magnetization at different paleolatitudinal position of those blocks.
More sites in Jurassic and lower Cretaceous rocks are needed in the northern segment of the PR to document whether the scale of vertical-axis rotation is regional or is associated to local structures, and better constrain the paleogeographic position of the PR for Jurassic and early Cretaceous time.