|Friday, May 3, 2013, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
|Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
|Harm Van Avendonk and Peter Flemings, UTIG
Click for a Live Broadcast.
The Gulf of Mexico (GOM) is a small ocean basin with real rifted margins that formed by continental extension and seafloor-spreading during the Jurassic to early Cretaceous. The lack of good, deeply-penetrating geophysical data in the GOM has precluded prior reconstructions of the timing and location of the transition from rifting to seafloor-spreading, as well as the degree to which magmatism influenced these geological processes. Four marine wide-angle seismic refraction profiles were acquired in the northern GOM from the shelf to deep water as part of the Fall 2010 Gulf of Mexico Basin Opening project (GUMBO). I present data and seismic velocity structures of two GUMBO profiles. On both lines, ocean-bottom seismometers at 10-12 km spacing recorded 150-m spaced airgun shots. I use travel times from long-offset re?ections and refractions to image seismic velocities in the sediments, crystalline crust, and upper mantle using a tomographic inversion. GUMBO Line 3 images a buried volcanic rift margin that extends offshore Alabama and past the Florida Escarpment towards the central GOM. I interpret high velocities (>5.0 km/s) in the sediment layer landward of the Florida Escarpment as a Lower Cretaceous carbonate platform. Seaward of the Florida Escarpment, crystalline crust thins from 23 km to 7 km across a narrow, ~100 km-wide necking zone. Beneath this zone, a deep, localized region of anomalously high seismic velocities at the base of crystalline crust (>7.5 km/s) far exceed velocities in the continental lower crust of the eastern US. I interpret this as potential under-plating and/or infiltration from asthenospheric melts, common at volcanic rifts. At the seaward end of GUMBO Line 3 I find high crustal velocities (6.0-7.5 km/s), a consistent crustal thickness (~7 km), and minor lateral velocity variations that strongly suggest mafic ocean crust produced by normal seafloor-spreading. GUMBO Line 2 extends from offshore Louisiana southward across the Sigsbee Escarpment. The velocity model here images a massive sediment package with noticeable lateral heterogeneities that can be attributed to salt tectonics. GUMBO Line 2 crust thins slightly from north to south, and varies greatly in both thickness (3-10 km) and seismic velocity (6.0-8.0 km/s). I interpret GUMBO Line 2 as a rifted margin that experienced moderate syn-rift volcanism. The crust in the continent-ocean transition zone transitions seaward to ocean crust formed by slow seafloor-spreading. These findings substantially increase the amount of ocean crust traditionally interpreted beneath the GOM, and may thus impact heat flow models for the basin, an important aspect of GOM hydrocarbon maturation. I further suggest that the effects of heat and asthenospheric melt were more impactful and prolonged in the northeastern GOM than in the west.