Botanical and Geological Significance of Potassium-Argon Dates from the Juan Fernández 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.

Los peces litorales del archipiélago de Juan Fernández (Chile): endemismo y relaciones ictiogeográficas

“…Aún cuando existen opiniones sobre la posible edad de las islas del archipiélago de Juan Fernández, aproximadamente 2,5 a 6,0 millones de años (Newman y Foster, 1983;Stuessy et al 1984), resulta muy complejo señalar las posibles causas de la presencia en ellas de un grupo tan diverso de especies. Algunas que deben poseer larvas leptocéfalas (aún desconocidas), pueden haber sido transportadas a grandes distancias desde el Pacífico Occidental, como podría ser el caso de Muraenichthys y Gymnothorax.…”

Speciation and Biogeography of <I>Erigeron</I> (Asteraceae) in the Juan Fernández Archipelago, Chile, based on AFLPs and SSRs

“…The utility of these islands for interpretation of evolutionary and biogeographic events derives from their east-west orientation from the major source area (southern South America), their considerable isolation from the mainland (667 km) as well as distance between the islands (181 km), and the known geological ages (ca. four my for Robinson Crusoe and one to two my for Alejandro Selkirk; Stuessy et al 1984). This setting suggests that there is a much higher probability of a propagule first arriving and establishing on Robinson Crusoe Island, being older and closer to the continent, than on Alejandro Selkirk Island.…”

Taxonomy and biogeography of the coastal fishes of Juan Fernández Archipelago and Desventuradas Islands, Chile

“…(González-Ferrán 1987:50) whereas Juan Fernández Islands range between 1-4 m.y.a. (Stuessy et al 1984). The Desventuradas are the eastern outcrop of the "Easter hot line" that is connected by submarine seamouts to Easter Island and Salas y Gómez Island.…”