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Structure and Early Evolution of the Northwestern Gulf of Mexico: New Constraints from Marine Seismic Refraction Data

Van Avendonk, Harm J.; Eddy, Drew R.; Christeson, Gail; Norton, Ian; Karner, Garry; Johnson, Chris; Kneller, Erik; Snedden, John W.

Tectonic reconstructions of the Gulf of Mexico show that this small ocean basin formed by continental rifting and seafloor spreading between North America and the Yucatan Block during the Jurassic to early Cretaceous. However, the timing and location of the transition from rifting to seafloor-spreading and the degree to which these geological processes were accompanied by magmatism are not yet well known in the Gulf of Mexico owing to a lack of good, deeply-penetrating geophysical data. In the Fall of 2010 we acquired four marine seismic refraction profiles in the northern Gulf of Mexico from the shelf to deep water as part of the Gulf of Mexico Basin Opening (GUMBO) project to illuminate the deep structure of this region. We here present the data and resulting seismic velocity images of two GUMBO profiles in the northwestern Gulf of Mexico. GUMBO Line 1 extends ~330 km offshore south Texas from Matagorda Island across Alaminos Canyon to the central Gulf. GUMBO Line 2 extends ~400 km from the shelf offshore western Louisiana across the Sigsbee Escarpment. We deployed ocean-bottom seismometers (OBSs) along these seismic lines with a spacing of 10 km to record in-line airgun shots over distances up to 100 km. We used traveltimes of seismic reflections and refractions from the sediments, crystalline crust and upper mantle to image the seismic velocity structure along GUMBO Line 1 and Line 2. On average, seismic velocities increase with depth from 2 km/s near the seafloor to 5 km/s near the interpreted base of salt, but on both profiles we observe a large amount of lateral heterogeneity in the sediments due to salt tectonics. The deeper seismic velocity structure along GUMBO Line 1 also exhibits a large amount of lateral heterogeneity (4.5 km/s to 7 km/s) that may be consistent with thin, ultraslow-spreading (oceanic) crust alternating with emplacement of exhumed mantle lithosphere. If the basement here is indeed oceanic, the prominent magnetic anomaly along the Texas coast may be the expression of synrift volcanism during the early opening of the Gulf of Mexico. In comparison, offshore Louisiana GUMBO Line 2 has thicker crust with higher seismic velocities, and lateral variations in crustal structure are less pronounced than on GUMBO Line 1. Therefore, early seafloor spreading in the Gulf of Mexico may have been accompanied by more robust magmatism in the central and eastern portion of the basin compared to the west.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013