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

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.