The five islands that comprise the Crozet Archipelago, are emplaced on a shallow plateau on the eastern flank of the southwest Indian Ocean ridge. Associated magnetic anomalies indicate that the plateau formed ca. 50 million years ago.
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| TAAF Stamp depicting Île aux Pingouins |
The two larger eastern islands, Île de l'Est and Île de la Possession are separated from the smaller western Île aux Cochons, Île des Pingouins and Îlots des Apôtres (a series of 14 small islands and steep rocks; maximum size 1.2 sq. km, 290 m alt.) by the Indivat Basin.
All the islands are clearly volcanic in origin. The oldest ages for Île de l'Est and Île de la Possession are respectively, 8.8 and 8.1 million years, but there is basalt of undoubtedly older age.
There is little evidence for extensive glaciation and it is generally assumed that organisms survived glacial maxima.
The earlier geological history of the Crozet Islands is complex and contentious. Given the limitation of the evidence, it is possible to state that Crozet Islands were available for colonization by certain insects at least 9 million years ago.
(Section on Geological history paraphrased from information kindly supplied by Prof. Douglas Craig, Department of Biological Science, University of Alberta, Canada)
