Deep crustal structure in the eastern Gulf of Mexico

We use air gun data recorded by ocean bottom seismometers to constrain the velocity structure along Gulf of Mexico Basin Opening Line 4, a profile extending from the northwestern Florida peninsula across the Florida Escarpment to the central Gulf of Mexico. Moderately thinned continental crust with a Moho depth of 32-33km, average sediment thickness of 6km, and an average crustal thickness of 27km is interpreted on the northeast end of the profile offshore Florida. Thinned and intruded continental crust is identified over a horizontal distance of 225km where the crustal layer thins from 25km to 6-7km; mean seismic velocities of the crust in this region increase from 6.55km/s to 6.95km/s from northeast to southwest and are evidence for increased magmatic input as rifting developed. Oceanic crust with an average thickness of 5.6-5.7km is observed over a distance of 175km on the southwest end of the profile, with an extinct spreading ridge with an axial valley morphology imaged on a coincident seismic reflection profile. Anomalously high upper oceanic crust velocities of 6.0-6.7km/s are interpreted as massive basalt flows and could reflect increased temperatures during emplacement. Integrating well, seismic reflection and our seismic refraction data allow us to estimate a full-spreading rate of 2.2cm/yr for seafloor spreading along the profile; this indicates that oceanic crust was emplaced at a slow-spreading center.