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Seismic Refraction Profiles Indicate a History of Syn-Rift Volcanism and Seafloor-Spreading in the Northeastern Gulf of Mexico

Eddy, Drew; Christeson, Gail; van Avendonk, Harm; Norton, Ian; Karner, Garry; Johnson, Chris; Kneller, Erik; Snedden, John

We present analyses of marine seismic refraction data in the northeastern Gulf of Mexico that provide unprecedented constraints on regional crustal structure. Two >500 km-long profiles collected during the 2010 GUMBO cruise (Gulf of Mexico Basin Opening) cross the shelf offshore Alabama through the De Soto Canyon towards the central Gulf of Mexico (GUMBO 3) and northwest of Tampa across the Florida Platform and Florida Escarpment (GUMBO 4). On both lines, ocean-bottom seismometers at 12 km spacing recorded 150 m spaced airgun shots over >100 km offsets. We use travel-times from these long-offset reflections and refractions to image seismic velocities in the sediments, crystalline crust, and upper mantle using a tomographic inversion. Velocities >5.0 km/s are observed in the sediment layer adjacent to the Florida Escarpment, which we interpret to represent a Lower Cretaceous carbonate platform. We show that crystalline crust thins significantly across the continental shelf and Florida Escarpment from ~25 km to ~7 km in the deep-water eastern Gulf of Mexico. Multi-channel seismic reflection data coincident to GUMBO 3 displays seaward-dipping reflectors (SDRs) within this zone of crustal thinning. Additionally, localized areas of anomalously high seismic velocities (>7.5 km/s) are found beneath thick crystalline crust at the landward end of GUMBO 3. These seismic velocities exceed those of continental lower crust in the eastern US. On the other hand, the seismic velocity structure is similar to that observed at volcanic rifted margins, where underplating and/or infiltration of asthenospheric melts have modified the lower crust. We image high crustal seismic velocities (6.0-7.5 km/s) and minor lateral velocity variations at the seaward ends of GUMBO 3 and GUMBO 4, along with 6-8 km crustal thicknesses; we interpret these regions as mafic ocean crust produced by normal seafloor-spreading. Ocean crust at GUMBO 3 is imaged as thicker (8 km), with slower upper crustal velocities (~6.0 km/s) and faster lower crustal velocities (>7.5 km/s) in comparison to GUMBO 4, where the ocean crust is thinner (6 km) with lower overall crustal velocities (6.0-7.0 km/s). We suggest that thicker ocean crust with higher velocities on GUMBO 3 compared to GUMBO 4 may be explained by elevated syn-rift mantle temperatures in the vicinity of the De Soto Canyon and South Georgia Rift Basin during rifting and continental breakup.


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