Plate-plume interaction driving microcontinent formation in the South Atlantic: Evidence from the Rio Grande Rise and Valdivia Bank

The Rio Grande Rise is a prominent bathymetric feature in the South Atlantic Ocean. While its formation was influenced by the Tristan–Gough mantle plume and the mid-ocean ridge, the roles of rifting, continental breakup, and its connection to the Valdivia Bank (VB) remain controversial. This study integrates geological, geochemical, and geophysical data with a new plate reconstruction to evaluate if these features include microcontinental fragments and how they formed. Compelling evidence for a continental component in the RGR includes dredged Proterozoic rocks and low Ce/Pb and Nb/U ratios in its volcanic rocks, indicating assimilation of continental crust. Sedimentary records from DSDP Site 516 reveal a history of magmatism and ongoing continental influence until the Late Cretaceous. Seismic and gravity data show transitional crust and extensional features typical of magma-rich rifted margins. We present a new kinematic plate reconstruction illustrating the RGR-VB system's breakup from Gondwanan margins around 100 Ma (Early Cretaceous), evolving through microplate formation and culminating in final separation by 72 Ma (Campanian). This synthesis of evidence demonstrates that the Rio Grande Rise is a microcontinent. These findings challenge purely oceanic plateau interpretations for the Rio Grande Rise and support a hybrid origin involving plume-plate interaction during a distinct microplate stage. This refined model highlights the influence of inherited tectonic structures and plume dynamics in shaping continental fragmentation, offering new insights into microcontinent formation within plume-influenced rifted margins and providing a framework for interpreting similar systems globally.