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UTIG Seminar Series: Fellowship Talks

UTIG Seminar Series: Fellowship Talks

Celebration of the Life of Wann Langston, Jr.

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April 2013 June 2013

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© 2017 Jackson School of Geosciences,
The University of Texas at Austin

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Start:
May 3, 2013 at 10:30 am

End:
May 3, 2013 at 11:30 am

Location:
PRC, 10100 Burnet Road, Bldg 196, Rm 1.603, Austin, TX 78759

Contact:
Charles Jackson, charles@ig.utexas.edu, 512-471-0401

URL:
Event Link

Talk 1: "Syn-rift Volcanism and Seafloor-Spreading in the Northern Gulf of Mexico: New Constraints from Marine Seismic Refraction Data" (Drew Eddy)

Abstract:

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.

Talk 2: "Thermodynamic State of Hydrate-bearing Sediment Around the World" (Dylan Meyer)

Abstract:

In situ salinities, calculated from Archie-derived water saturations, in gas hydrate-bearing sediments at ODP Site 1249 and NGHP Site 01-10, located at Hydrate Ridge and the Krishna-Godavari Basin, respectively, show that these hydrate systems are near the three-phase boundary. Chloride concentrations from ODP Site U1328 near Vancouver Island show that this system is not near the three-phase boundary. Massive volumes of gas hydrate have been identified at these sites as well as submarine sediments along continental margins around the world. The stability of these hydrate systems is controlled by the in situ pressure, temperature, and salinity. We determined the in situ water saturation through the incorporation of Logging-While-Drilling data into an iterative application of Archie’s Law. The in situ salinities were calculated through a volumetric relationship between water saturation and the core-derived salinities. The salinity required for three-phase equilibrium was determined using a classic thermodynamic model for gas hydrate. We examined the in situ salinities of hydrate-bearing sediments around the world to gain understanding into the connection between thermodynamic state and the possibility of hydrate dissociation as a result of fluctuating in situ conditions. The in situ salinities at the study sites indicate that Sites 1249 and 01-10 would be more sensitive to changing in situ conditions than Site U1328 and therefore more prone to mass dissociation.

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10:30 am - UTIG Seminar Series: Fellowship Talks

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3:00 pm - Celebration of the Life of Wann Langston, Jr.