The Rio Grande Rise – a detached microcontinent or a large igneous province?

Tabea.Altenbernd [ at ]


The Rio Grande Rise (RGR) is a prominent plateau in the South Atlantic consisting of a western (WRGR) and eastern (ERGR) part. It formed during the evolution of the South Atlantic together with the Walvis Ridge under the influence of the Tristan-Gough Mantle Plume at the mid-Atlantic spreading ridge. While recently several deep seismic profiles across the Walvis Ridge unraveled its crustal structure, such experiments are missing across the RGR. Therefore, there is an ongoing debate about the composition of the RGR: a detached microcontinent or a large igneous province (LIP) formed in the Cretaceous in the central South Atlantic. Existing gravity models support depending on the chosen density and crustal thickness either hypothesis. In spring 2019, the ERGR and WRGR were examined by a scientific cruise to acquire solid information on their crustal fabric and evolution of the plateau by geophysical and petrological experiment. For the geophysical part of the cruise we will provide constraints for the following questions: What crustal types are present in the RGR? Are there indications for a microcontinent within the plateau? Do we see differences between the ERGR and WRGR? Does the crust differ from the crustal structure of the Walvis Ridge? We will present P-wave velocity models derived from two wide-angle seismic profiles crossing the WRGR and ERGR in an NNE-SSW direction. The WRGR is in its central part underlain by an up to 30 km thick crust, while the crust below the ERGR is in its maximum only half as thick. The lowermost crustal layer below both ERGR and WRGR is 10 to 13 km thick and characterized by P-wave velocities of 7-7.4 km/s. The examined crust shows a similar velocity-depth structure as oceanic LIPs. We did not find any indications for the presence of a microcontinent. In contrast, our findings point to a volcanic origin of the RGR.

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Conference (Poster)
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AGU Fall Meeting 2019, 09 Dec 2019 - 13 Dec 2019, San Francisco, USA.
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Altenbernd, T. , Jokat, W. and Geissler, W. (2019): The Rio Grande Rise – a detached microcontinent or a large igneous province? , AGU Fall Meeting 2019, San Francisco, USA, 9 December 2019 - 13 December 2019 .

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