Gravity and magnetic constraints on the Jurassic opening of the oceanic Gulf of Mexico and the location and tectonic history of the Western Main transform fault along the eastern continental margin of Mexico

Abstract

Although the Gulf of Mexico (GOM) has been the subject of geophysical and geologic studies for several decades, its crustal structures and opening kinematics remain poorly understood largely because of the difficulty in imaging the deeper basinal structure beneath its thick sedimentary and evaporitic layers. We have used gravity and magnetic data combined with seismic reflection and refraction data to better understand the crustal structure and basin opening kinematics. We have focused on the 700-km-long Jurassic continent/ocean transform fault that accommodated counterclockwise rotation of the Yucatan Block along the eastern continental margin of Mexico. We have used recent satellite-derived gravity data to reveal the pattern of spreading ridge-transform segments in the center of the basin. We then derived on a pole of rotation that revealed the kinematics of early opening of the GOM basin and the tectonic control the continent-ocean transform fault, the Western Main Transform fault (WMTF), that defined the continent-ocean boundary (COB) between continental rocks in the eastern Mexico and Jurassic oceanic crust in the western GOM. Regional magnetic anomaly data along with seismic reflection and refraction data were used to further constrain the location of the WMTF. Three 2D gravity models revealed the location of the WMTF approximately 100 km offshore eastern Mexico at its furthest point and extending onshore in southern Mexico. The gravity models found that the contact between continental and oceanic crust is marked by an abrupt increase from 6.5 to 10 km in crustal thickness. To the west of the WMTF, the eastern Mexico margin is underlain by a 60-km-wide zone of stretched continental crust. We also determined a COB for the entire GOM that was consistent with the plate reconstruction, values of crustal thickness based on seismic refraction, and fracture zone azimuths related to the Jurassic spreading system.