Geomorphology and Age Constraints of Seamounts in the Cabo Verde Archipelago, and Their Relationship to Island Ages and Geodynamic Evolution

Abstract

Abstract The Cabo Verde Archipelago is related to a mantle plume located close to the rotational pole of the African Plate. It consists of islands and seamounts arranged in a horseshoe‐shaped pattern open to the west, thus forming two volcanic chains, each with a weak east‐west age progression. High‐resolution swath bathymetry of 12 Cabo Verde seamounts is used here to assign each seamount to its pre‐shield, shield or post‐shield evolutionary stage, respectively. The eastern seamounts exhibit degraded and partially eroded morphologies, and are mainly in their post‐shield stage. A new 40Ar‐39Ar date for Senghor Seamount at 14.872 ± 0.027 Ma supports old ages for the eastern seamounts. The western seamounts generally exhibit younger volcanic‐edifice‐construction morphologies, showing fresh effusive and explosive volcanics, including rarely observed deep‐water explosive volcanism in the Charles Darwin Volcanic Field. Furthermore, the two previously unknown seamounts Sodade and Tavares in the westernmost termini of both volcanic chains exhibit pristine volcanic morphologies, in agreement with present‐day volcanism and seismic activity recorded from the western seamounts. The islands and seamounts rest on three submarine platforms to the east, northwest and southwest, respectively. Taken together, the seamount and island data suggest a shift in igneous activity from the eastern to the other platforms at about 8–6 Ma. However, the complex evolution pattern for both volcanic chains includes the simultaneous occurrence of pre‐shield or shield edifices at any time, followed by erosional and rejuvenation stages. The new seamount data still demonstrate ongoing westward submarine‐growth in both volcanic chains.

Keywords

• volcanology
• bathymetry
• geochronology
• ocean islands