The Agulhas Plateau: Structure, Formation and Environmental Impact of a Large Igneous Province


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Nicole.Parsiegla [ at ] awi.de

Abstract

The Agulhas Plateau (AP) is an oceanic plateau in the Indian Ocean south of the African continent. We investigated its structure and evolution using seismic refraction, seismic reflection and potential field data. Our P-wave velocity-depth model of the AP along profile AWI-20050200 shows 20 km thick oceanic crust on average with velocities well above 7 km/s in the lower 10 km of the plateau. Velocity and density structure strengthen the hypothesis for an evolution as a Large Igneous Province (LIP). Like other LIPs, such as the Ontong Java Plateau, the AP consists of three major structural units: an extruded cover, an intruded middle crust and a lower crustal body. Plate-tectonic reconstructions suggest a coeval formation of the AP together with Maud Rise and Northeast Georgia Rise. Between these three parts a triple junction was situated which caused the fragmentation. Using the structural information from this seismic refraction profile and another crossing one, we could estimate the total volume of material accreted to the plateau to about 4 x 106 km³. We differentiated between intruded and extruded parts of igneous material and used the extruded basaltic volumes for estimation of carbon dioxide and sulphur dioxide emission. The volume of this extruded layer with velocities between 3 and 5 km/s and a thickness of 1.8 km on average was estimated to be about 4 x 105 km³. In this layer, volcanic flows could be identified in coincident seismic reflection data. Our calculations lead to implications on the possible impact of the AP formation to the Cretaceous environment. We conclude that the emitted carbon dioxide volume was too small to have a direct impact on the climate, but feedback mechanisms possibly enhanced the effect. Sulphur dioxide has not such a long resistance time in the atmosphere as carbon dioxide, therefore had a small impact on the climate, but probably a more important one on the ocean environment by increasing the acidity of the surrounding water masses. Due to heat generation during the AP formation, solved oxygen from the ocean could have been released into the atmosphere, leading to anoxic conditions in the ocean. In summary, we gained new information about the structure and evolution of the AP, which are essential to estimate the influence of its formation on environmental conditions during its formation in the Cretaceous.



Item Type
Conference (Talk)
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Not peer-reviewed
Publication Status
Published
Event Details
AGU Fall Meeting, 10. - 14.12.2007, San Francisco..
Eprint ID
17946
Cite as
Parsiegla, N. , Gohl, K. and Uenzelmann-Neben, G. (2007): The Agulhas Plateau: Structure, Formation and Environmental Impact of a Large Igneous Province , AGU Fall Meeting, 10. - 14.12.2007, San Francisco. .


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