Unraveling the geological history of the South Atlantic margin: Records of West Gondwana Breakup from South Brazil and Uruguay margin

Abstract

Continental Flood Basalts, Seaward Dipping Reflectors (SDRs), and oceanic plateaus or seamounts often occur in close geographic proximity. In South America, the Paraná-Etendeka Continental Flood Basalts are followed by SDR-related magmatism, and even after the formation of oceanic crust, anomalous magmatism persists in the region, as seen in the Walvis Ridge and Rio Grande Rise. This study investigates volcanic and sedimentary rocks from offshore wells in the Pelotas and Punta del Este basin margins, revealing the offshore extension of the Paraná Basin. Our data demonstrate geochemical and isotopic affinities between margin volcanic rocks and the Paraná-Etendeka Large Igneous Province. The basalts from the margin display OIB- and E-MORB-like geochemical and isotopic compositions consistent with EMI and EMII mantle sources. However, these isotopic signatures may have been modified by assimilation of continental crust or subcontinental lithospheric mantle. The presence of zircon xenocrysts support this interpretation, and suggests that volcanic rocks from the margin were emplaced above the continental crust with magmatic assimilation of rocks from Dom Feliciano Belt. The Rio Grande Rise also exhibits an EMI-like isotopic fingerprint similar to the Walvis Ridge, indicating a possible shared origin during the Cretaceous. However, this isotopic content may also result from magmatic assimilation of continental crust slivers or subcontinentallithospheric mantle. These findings highlight the role of a persistent thermal anomaly throughout the magmatic evolution of the South Atlantic.