Potential field data along the Texas portion of the Gulf of Mexico indicate a large-amplitude coast-parallel magnetic maximum and a smaller Bouguer gravity high. Models constrained by seismic-refraction data indicate that these maxima manifest a deeply buried volcanic rifted passive margin or other magnetic high in the outer transitional crust. Buried 12–15 km, the source is 220 km wide, similar to the Vøring Plateau in Norway and the U.S. East Coast. This margin, which formed during the opening of the Gulf of Mexico, differs in origin from the transform boundary of the northeast Mexico margin (Tehuantepec transform), and we infer a Jurassic triple junction related to the Borderland rift system, which is traceable as far as southeast California.

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