Potassium-argon ages, volcanic stratigraphy, and geomagnetic polarity history of the Canary Islands; Lanzarote, Fuerteventura, Gran Canaria, and La Gomera

Abstract

In order to produce a quantitative within and between-island stratigraphic framework for four of the Canary Islands, K-Ar ages and paleomagnetic polarities have heen determined for 51 igneous bodies. The following major conclusions result for the respective islands: 1. On Lanzarote, lava sequences of the Farmara massif in the north and Los Ajaches massif in the south overlap slightly in age and range in age from 6 to 12 m.y. One lava flow at the southern limit of the island is at t=19.0 ± 0.68 m.y. equivalent in age to a similar lava at the northern end of Fuerteventura, immediately to the south. 2. Hornblende and biotite separated from a syenite of the basement complex of Fuerteventura provide ages of 20.8 and 18.4 m.y. respectively. An aegerine-augite separated from an alkali syenite in the basement complex provides a measured age of 38.6 m.y. A low grade metamorphic rock north of the main basement complex provides a K-Ar age of 35.3 m.y. The basement complex therefore precedes t=35 m.y. but is unlikely to predate the Mesozoic sediments of west-central Fuerteventura. Basalts of the Jandia peninsula were extruded between t=17 and 14 m.y., preceding the basalt sequences of the east-central part of Fuerteventura by 3 m.y. or more, and are equivalent in age to the older lavas of the northwest coast of Gran Canaria. 3. Two long-duration volcanic phases are present on Gran Canaria. The older basalts, rhyolites, rhyolitic and trachytic ignimhrites, and phonolites are limited to the period t=16 to 9 m.v. and are separated from an explosive volcanic series and basalts by a quiescent period lasting on the order of 5 m.y., during which carbonate-rich sediments were deposited. 4. On the island of La Gomera, quiescence occurred between t=8.0 and 5.2 m.y., when uplift, tilting, and substantial erosion occurred. The basement complex of this island was intruded in part 12 m.y. ago at about the same time as the oldest outcropping extrusive activity began. These extrusives span up to 4 m.y. Horizontal lavas were extruded onto the eroded basement between t =5.2 and 4.7 m.y. The paleomagnetic data reveal detection of the Jaramillo event on Lanzarote, the Matuyama reversed epoch on Gran Canaria, and an event within the Gauss epoch on Gran Canaria. Polarity data in each island are amenable to use in fine within-and between-island stratigraphic correlation. Although hiatuses up to 5 m.y. long are present in some islands, when all four islands are considered as a whole, volcanism of diverse petrological type has occurred throughout much of the last 20 m.y.