Pleistocene volcanism on São Tomé, Gulf of Guinea, West Africa

Abstract

New Ar/Ar data for alkaline basaltic rocks on the West African island of São Tomé document a Pleistocene eruptive episode that saw the formation of cinder cones and lava flows between 0.036 ± 0.004 and 0.86 ± 0.02 Ma (2σ). The cinder cones trend north-northeast along the long axis of the island, interpreted as a rift zone. This rift zone appears to be the source of several lava flows that reach the coastline, including one that underlies the airport of São Tomé. Estimates of magma production rates, both from recent lava flows and from consideration of the total edifice history suggest low magma production rates (10−4–10−2 m3/s), compared to other ocean island settings. Assuming a background of low overall volcanic activity, it is expected that any future eruptions would most likely occur along the north-northeast rift, resulting in cinder cone and lava flow emplacements that may impact the densely populated northeast region of the island.