Paleomagnetism of the La Mora Formation: Late Triassic-Late Jurassic paleolatitudinal record for Southern Mexico and its Gondwanan disconnection

A comprehensive paleomagnetic study of the La Mora Formation fluvial sediments, presumably deposited during the Late Triassic-Early Jurassic, over the Mixteca terrane, allows us to document the most likely Early Mesozoic paleoposition of the Acatlán-Oaxaquia block among the mosaic of peri-Gondwanan blocks just before and during Pangea break-up. The oxide microscopy and the rock magnetic studies confirm that the magnetic carrier is titanomagnetite, hematite partially to almost totally replacing titanomagnetite (maghemite), and pigmentary hematite, in varying proportions related to dominant facies along the sedimentary sequence. Paleomagnetic results indicate that chemical remanent magnetization was acquired at during a time-lapse from the last steps of deposition to the burial and weakly deformation stage during the Late Jurassic (ca. 160 Ma). The mean paleolatitudes in flattening, unflattening, and geographic coordinate inclinations are: 7.6°N ± 1.6°, 9.8°N ± 1.7° and 11.1°N ± 1.6°, in comparison to the current latitude that is 18°N. However, a southern paleoposition of the La Mora Formation for the Late Triassic, is indicated from detrital zircon provenance ages from Amazonian craton sources, suggesting that the Acatlán-Oaxaquia block was juxtaposed to the northwestern Gondwana corner (i.e. NW South America), close to 7°S ± 2°. Therefore, we reported ca. 1800 ± 220 km of northward transport of the Acatlán-Oaxaquia block during the Late Triassic to Late Jurassic Pangea break-up. Last, the magnetic anisotropy susceptibility (AMS) indicates a primary origin magnetic fabrics with a slight syn-sedimentary tectonic overprint that agree with the Amazonian westward paleo-fluvial system.