The 40Ar/39Ar age dating of the Madeira Archipelago and hotspot track (eastern North Atlantic)

The 40Ar/39Ar ages for 35 volcanic rocks and C-14 ages for two charcoal samples from the Madeira Archipelago and Ampere Seamount (eastern North Atlantic) are presented. The volcanic evolution of Madeira can be divided into a voluminous shield stage (>4.6-0.7 Ma) and a subsequent low-volume posterosional stage (<0.7-0 Ma). Volcanism during the shield stage originated from a two-armed rift system, composed of the E-Woriented Madeira rift arm and the N-S oriented Desertas rift arm. Average growth rates for the submarine (5500 km(3)/Ma) and subaerial (100-150 km(3)/Ma) shield stages on Madeira are among the lowest found for ocean island volcanoes. It is proposed that Madeira represents the present location of a >70 Myr old hotspot which formed Porto Santo Island (11.1-14.3 Ma), Seine, Ampere (31 Ma), Corral Patch and Ormond (65-67 Ma [Feraud et al., 1982, 1986]) Seamounts, and the Serra de Monchique (70-72 Ma [McIntyre and Berger, 1982]) complex in southern Portugal. Age and spatial relationships result in a calculated absolute African plate motion above the hotspot of 1.2 cm/yr around a rotation pole located at 43 degrees 360'N/24 degrees 330'W.