16 Nov 2023
 | 16 Nov 2023
Status: this preprint is open for discussion.

Along-strike variation of volcanic addition controlling post breakup sedimentary infill: Pelotas margin, Austral South Atlantic

Marlise Colling Cassel, Nick Kusznir, Gianreto Manatschal, and Daniel Sauter

Abstract. We investigate the lateral variability of breakup volcanic addition along-strike of the Pelotas segment of the Austral South Atlantic rifted margin and its control on post-rift accommodation space and sediment deposition. Our analysis of regional seismic reflection profiles shows that magmatic addition on the Pelotas margin varies substantially along strike from extremely magma-rich to magma-normal within a distance of ~300 km. Using 2D flexural backstripping we determine the post-rift accommodation space above top volcanics. In the north, where SDRs are thickest, the Torres High shows SDRs up to ~ 20 km thick and post-breakup water-loaded accommodation space is ~2 km. In contrast, in the south where magmatic addition is normal and SDRs are thinner, post-breakup water-loaded accommodation space is ~ 3–4 km. We show that post-breakup accommodation space correlates inversely with SDR thickness, being less for magma-rich margins and more for magma normal/intermediate margins. The Rio Grande Cone, with large sediment thickness, is underlain by small SDR thicknesses allowing large post-breakup accommodation space. A relationship is observed between the amount of volcanic material and the TWTT of first volcanics; first volcanics are observed at 1.25s TWTT for the highly magmatic Torres High profile while, in contrast, for the normally magmatic profiles in the south, first volcanics are observed at 4.2s TWTT or deeper. The observed inverse relationship between post-breakup accommodation space and SDR thickness is consistent with predictions by a simple isostatic model of continental lithosphere thinning and decompression melting during breakup.

Marlise Colling Cassel et al.

Status: open (until 03 Jan 2024)

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Marlise Colling Cassel et al.

Marlise Colling Cassel et al.


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Short summary
The Atlantic Ocean results from the break-up of the palaeocontinent Gondwana. Since then, the Brazilian and African margins record a thick volcanic layers and received a large contribution of sediments recording this process. We show the influence of early volcanics on the sediments deposited later by analysing the Pelotas Margin, south of Brazil. The volume of volcanic layers is not homogeneous along this sector, promoting variation in the space available to accommodate later sediments.