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

Solid Earth, vol. 15, pp. 1265–1279

Abstract

We investigate, using observations from seismic reflection data, the lateral variability in breakup extrusive magmatic addition along the 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 back-stripping, we determine the post-rift accommodation space above top volcanics. In the north, where volcanic seaward-dipping reflectors (SDRs) are thickest, the Torres High shows SDRs up to ∼20 km thick, and post-breakup water-loaded accommodation space is much less than in the south, where magmatic addition is normal and SDRs are thinner. 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 two-way travel time (TWTT) of first volcanics: first volcanics are observed between 1.2 and 2.2 s TWTT for the highly magmatic Torres High profile, while, in contrast, for the normally magmatic profiles in the south, first volcanics are observed between 4.2 and 6.5 s TWTT. 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 magmatic addition melting during breakup. The methodology that we use in this paper provides a new approach for investigating the complex magmatic and sedimentary evolution of rifted continental margins.

Authors 4

1. Marlise Colling Cassel Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University (Aachen, Germany)

   RWTH Aachen University (Germany)

2. Nick Kusznir

   University of Liverpool

   Affiliation as printed

   School of Environmental Sciences, Liverpool University, Liverpool, L69 3GP, UK

   University of Liverpool (Liverpool L69 3BX, United Kingdom - United Kingdom)

3. Giänreto Manatschal

   Centre National de la Recherche Scientifique · Institut Terre & Environnement de Strasbourg · Université de Strasbourg

   Affiliation as printed

   Université de Strasbourg, CNRS, ITES UMR 7063, 67084 Strasbourg, France

   ITES - Institut Terre Environnement Strasbourg (5 rue René Descartes, 67084 Strasbourg - France)

4. Daniel Sauter

   Centre National de la Recherche Scientifique · Institut Terre & Environnement de Strasbourg · Université de Strasbourg

   Affiliation as printed

   Université de Strasbourg, CNRS, ITES UMR 7063, 67084 Strasbourg, France

   ITES - Institut Terre Environnement Strasbourg (5 rue René Descartes, 67084 Strasbourg - France)