Dating Gondwanan continental crust at the Rio Grande Rise, South Atlantic

Abstract

Crystalline continental rocks and associated crust-contaminated basaltic rocks were unexpectedly dredged on the crest and at seamounts of the Rio Grande Rise, South Atlantic. Zircon U-Pb ages of one gabbro (ca. 2,200 Ma) and four granitoids (between ca. 1,430-480 Ma) indicate that the breakup of SW Gondwana left behind continental fragments of dominantly African age. These rocks may have been incorporated into the oceanic lithosphere by complex processes including rifting and interaction of the Tristan-Gough mantle plume with hyperextended continental margins. Until ca. 80-70 Ma, the Rio Grande Rise and an old portion of the Walvis Ridge formed a conjugate pair of aseismic ridges, and the Tristan-Gough plume was positioned at the Mid-Atlantic Ridge. The finding of continental rock fragments in one of these conjugate pairs opens new perspectives on the mechanisms of continental break-up, the nature of this conjugate pair, and the geodynamic evolution of rifted Gondwana margins in the South Atlantic.

Late Cretaceous Ridge Reorganization, Microplate Formation, and the Evolution of the Rio Grande Rise – Walvis Ridge Hot Spot Twins, South Atlantic Ocean

“…All of the disparate pieces of this complex apparently formed by hot spot interaction with the MAR at varying eruption volumes, from a massive plateau‐forming eruption that emplaced RGR Massif to smaller eruptions of hot spot magmas to form the other edifices (Galvão & de Castro, 2017; O’Connor & Duncan, 1990; O’Connor & Jokat, 2015a). Although the mantle plume hypothesis is widely accepted, continental granitoid rocks have been recovered from RGR Massif and some investigators posit a continental fragment at its core (Santos et al., 2019), but others interpret these rocks as dropstones, so it is unclear how much credence to give this conclusion. The history of the Cruzeiro do Sul rift that cleaves both RGR Massif and Libra Massif of the southern ERGR is unclear.…”

Expedition 391 Scientific Prospectus: Walvis Ridge Hotspot: drilling Walvis Ridge, Southeast Atlantic Ocean, to test models of ridge-hotspot interaction, isotopic zonation, and the hotspot reference frame

“…It has been proposed that Valdivia Bank and RGR Massif are continental fragments (van der Linden, 1980;Santos et al, 2019). Continental rocks and zircons have been found in other LIPs such as Kerguelen Plateau and Broken Ridge (Frey et al, 2002;Ingle et al, 2002), Iceland (Torsvik et al, 2015), and Mauritius (Torsvik et al, 2013).…”

“…Evidence of continental material has been found in other oceanic plateaus (Kerguelen Plateau: Frey et al, 2002;Ingle et al, 2002;Mauritius: Torsvik et al, 2013;Iceland, Torsvik et al, 2015). Furthermore, the same has been suggested for Rio Grande Rise (Santos et al, 2019), so the idea cannot yet be dismissed. Coring on Valdivia Bank can help test this idea either through direct drilling of continental rocks, observing continental crustal contamination in the geochemistry of the recovered rocks, or finding xenocrystals (e.g., quartz or zircon) or xenoliths of continental crust.…”

Correlação tectono-deposicional entre a margem continental brasileira e a Elevação do Rio Grande

“…E a Cadeia Walvis, do lado leste do Atlântico, teria origem comum, do ponto de vista temporal e espacial. Contudo, amostras de rochas continentais proterozoicas, coletadas pelo Serviço Geológico do Brasil (Companhia de Pesquisa de Recursos Minerais -CPRM), acenderam a discussão sobre a possibilidade de crosta continental associada a pontos quentes (Santos et al, 2019).…”