Paleomagnetism of the Chiapas Massif, southern Mexico: Evidence for rotation of the Maya Block and implications for the opening of the Gulf of Mexico
We have analyzed 180 oriented samples of the batholithic complex and overlying red beds of the Chiapas Massif in southern Mexico for a paleomagnetic study. Both stepwise alternating-field and thermal demagnetization procedures revealed dual-polarity characteristic magnetizations above 10-30 mT or 200-400 °C in about 60% of the samples demagnetized. Three distinct and ancient paleomagnetic directions have been identified. Late Permian intrusions (256 ± 10 Ma) yield nearly equatorial southern hemisphere paleolatitudes and a paleopole (13.4°S,176.1°E; 12 sites, K = 15.4, A95 = 11.4°) rotated ∼75°, counterclockwise, with respect to the North American reference pole. A selected set of Late Triassic(?)-Jurassic red beds of the Todos Santos Formation yields a paleopole at 22.6°N, 170.6°E (4 sites, K = 56.8, A95 = 12.3°), which implies ∼60° counterclockwise rotation, and a near equatorial northern hemisphere paleolatitude. Middle-Late Jurassic dikes and granites yield a paleopole at 77.4°N, 97.4°E (6 sites, K = 269.2, A95 = 4.1°) near the Mid-Jurassic segment of the North American apparent polar wander path. These data are consistent with a pre-rift configuration in which the Maya Block is rotated to a position off the coast of Texas and Louisiana in the present-day area of the Gulf of Mexico. A further implication is that by Oxfordian times, Chiapas (and by inference the Maya Block) was essentially in its current position with respect to cratonic North America.