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Potassium-argon dating of five basalts from the three main islands of the Juan Ferna??ndez (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.
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Botanical and geological significance of potassium-argon dates from the Juan Ferna??ndez Islands