title: Botanical and geological significance of potassium-argon dates from the juan fernandez islands.
abstract: Potassium-argon dating of five basalts from the three main islands of the Juan Fernández (or Robinson Crusoe) Islands of Chile in the southeastern Pacific gives ages of 1.01 +/- 0.12 and 2.44 +/- 0.14 million years for Masafuera, 3.79 +/- 0.20 and 4.23 +/- 0.16 for Masatierra, and 5.8 +/- 2.1 for Santa Clara. These ages are much younger than that of the underlying oceanic plate and are consistent with the origin of the island-seamount chain from a mantle hot spot beneath the eastward moving Nazca plate. The young age for the archipelago suggests that speciation within endemic genera has occurred within the past 4 to 5 million years. Endemic genera of apparently more ancient origins, such as Lactoris and Thyrsopteris, have apparently dispersed to the islands and survive refugially.
authors.forename: T F
authors.initials: TF
authors.lastname: Stuessy
authors.forename: K A
authors.initials: KA
authors.lastname: Foland
authors.forename: J F
authors.initials: JF
authors.lastname: Sutter
authors.forename: R W
authors.initials: RW
authors.lastname: Sanders
authors.forename: M S
authors.initials: MS
authors.lastname: O