South Atlantic Transect Site Survey Data in Support of IODP Expeditions 390 and 393
Abstract
IODP South Atlantic Transect Expeditions 390 and 393 comprise a multidisciplinary drilling project along a crustal age transect at ~31°S across the South Atlantic. Site survey data in support of these expeditions were acquired in 2016 during the CREST (Crustal Reflectivity Experiment Southern Transect) project, and include seismic reflection, seismic refraction, bathymetry, backscatter, gravity, and magnetics data. The centerpiece of the program is a ~1500 km continuous seismic reflection flowline profile from the Mid-Atlantic Ridge to the Rio Grande Rise, covering seafloor that ranges in age from 0 to 71 Ma. The study also includes five coincident seismic reflection/refraction profiles in ridge-parallel orientations. Spreading half-rates in the study region vary from a slow-spreading rate of 13.5 mm/yr to an intermediate spreading rate of 31 mm/yr. Our interpretations of the CREST magnetic data show that the planned IODP Expeditions 390 and 393 drill sites are located at crustal ages of 7, 15, 31, 49, and 61 Ma, with corresponding spreading half-rates of 17, 25.5, 24, 19.5, and 13.5 mm/yr.
Along the flowline transect, seismic reflection data image a seismic layer 2A with a mean thickness of 760 m in 0-48 Ma crust, with no systematic change in thickness when compared to crustal age or spreading rate. Sediment accumulates in topographic lows between unsedimented or lightly sedimented basement highs along the transect, suggesting that the crust is never fully sealed by sediment cover. Velocities at the top of layer 2A increase rapidly from ~2.4 km/s at 0 Ma to ~4.2 km/s at 6 Ma, and then undergo a more gradual increase to ~4.9 km/s at 58 Ma. We interpret the velocity trends to indicate that hydrothermal circulation continues to crustal ages of ~58 Ma. Crustal thickness averages 5.6 km at the 7, 15, and 49 Ma drill sites, which is less than the global average of 6.15 km. In contrast, crustal thickness is 7.0 km at the 31 Ma drill site, where bathymetric data reveal a peak in seafloor volcano abundance implying abundant magmatism in this region. Two drill sites are planned in 61 Ma crust, with varying sediment thicknesses of ~180 and ~640 m. Seafloor and crustal structure in this region is rugged and highly-variable, likely because of the slow-spreading rate of 13.5 mm/yr.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T43F0509C
- Keywords:
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- 7218 Lithosphere;
- SEISMOLOGY;
- 7220 Oceanic crust;
- SEISMOLOGY;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8416 Mid-oceanic ridge processes;
- VOLCANOLOGY