JURASSIC OPENING OF THE GULF OF MEXICO AND THE APPARENT CENOZOIC SEGMENTATION OF THE MAYA BLOCK

Models of the Jurassic opening of the Gulf of Mexico (GOM) are based on geophysical data, paleomagnetic data from the Chiapas Massif of southern Mexico, and external constraints imposed by global plate reconstructions. These models invoke either a one- or two-stage Euler pole rotation of the Maya Block, with oceanic crust forming along with a ~36° counterclockwise (CCW) rotation about a pole located at ~23°N/84°W. However, this rotation does not honor paleomagnetic data that indicate >70-CCW rotation of the Chiapas Massif (east part of the Maya Block) about a pole 24.5°N/84.7°W as it is translated along the west margin of the GOM. Second, this model projects ocean crust below the Cenozoic cover of the Veracruz Basin of southern Mexico, an interpretation unsupported by reported geologic or geophysical data. In contrast, honoring paleomagnetic data from the Chiapas Massif places the prerift massif north of the Marathon uplift of southwest Texas-equally untenable. An ongoing investigation sponsored by PEMEX Exploración y Producción of the Neogene depositional systems along the west and south margins of the GOM introduces insight that may help to reconcile the disparity between geologic and paleomagnetic observations. In particular, postextensional depositional trends define a curvilinear Jurassic slope margin that extends along most of the western GOM coast. Also, the distribution of related block faulting and Mesozoic growth strata suggest NNW/SSE-directed extension along this trend, all of which are consistent with a NNW-trending transform margin. If we restore the modern margin of the Yucatan Platform to the updip limit of Jurassic salt of south Texas, these observations fit a 45°-CCW rotation of the Maya Block about a pole located at 28°N/76.5°W, which still does not honor the available paleomagnetic data. Therefore, we propose a Cenozoic segmentation of the Maya Block where the massif rotates 20° CCW about a pole located at 16.4°N/92.5°W. This second rotation is consistent with 70 km of sinsitral offset and ENE-directed compression documented in the Neogene fold-and-thrust belt of the Sierra Chiapas of southeast Mexico. Taken together, these two rotations restore the Massif to a position southwest of the Marathon Uplift and the observed magnetic pole location to within 5° of the expected paleopole.