Life cycle of the Cabo Verde Archipelago : Growth and denudation of seamounts and islands
The Cabo Verde Archipelago in the Atlantic Ocean exhibits seamounts and islands in different stages of evolution. Mature islands are well-eroded, exposing early stages of volcanism. However, little is known about the submarine realm of the archipelago. To gain a better understanding of the geological and geodynamic evolution of the archipelago, data and observations from seamounts and islands were combined and different phases of magmatic-tectonic evolution investigated. The thesis provides the first geochronological data for the Cabo Verde Seamounts. A pillow lava from the extinct Nova Holanda (Senghor) Seamount in the NE yields a 40Ar-39Ar weighted mean age of 14.872 ± 0.027 Ma (2sigma). Lava samples from the phonolitic Cadamosto Seamount (SW) were 40Ar-39Ar dated, revealing young eruption ages with a combined weighted mean age of 21.14 ± 0.62 ka (2sigma). This volcanic eruption period can be linked to rapid crustal unloading due to sea level lowstands in the Last Glacial Maximum. Combined with petrological observations a long-lived magmatic plumbing system below Cadamosto is revealed. The evolution of the mature Maio Island was investigated. Uplifted mid-ocean ridge basalts exposed on Maio and overlying deep-sea sedimentary sequences contain Early Cretaceous fossil assemblages and record information on the young Atlantic Ocean. Based on field observations, 40Ar-39Ar geochronology and structural geology the Miocene evolution of Maio was refined, confirming a period of intense igneous growth between ~16 and 8.7 Ma. Extensive polymict conglomerates below Late Miocene lavas are re-interpreted as landslide deposits, confining an erosional period to between 8.7 to 6.7 Ma. A Pleistocene large-scale fossil dune located in the E of Maio records recent uplift and changes in the paleo-environmental conditions. The thesis provides important insights to different phases of the magmatic-tectonic evolution of the archipelago and ocean island evolution worldwide.