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

Abstract

The 40Ar/39Ar ages for 35 volcanic rocks and 14C ages for two charcoal samples from the Madeira Archipelago and Ampère 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-W oriented Madeira rift arm and the N-S oriented Desertas rift arm. Average growth rates for the submarine (5500 km3/Ma) and subaerial (100-150 km3/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, Ampère (31 Ma), Corral Patch and Ormond (65-67 Ma [Féraud 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°36′N/ 24°33′W.