In order to contribute to resolution of the possibility that the Kerguelen-Gaussberg Ridge (in the south-central Indian Ocean) is a continental fragment remaining after separation of Gondwanaland, a series of analyses have been made on collections of igneous rock from the island of Kerguelen. Petrographic analyses and measurement of the major- and trace-element concentrations, Sr-isotopic ratios, K-Ar ages, and paleomagnetic properties of intrusive and extrusive bodies have been added to the known volcanic stratigraphy and some previously unpublished geochemical data, to arrive at a preferred origin for the island. It is concluded that Kerguelen is not older than late Oligocene to early Miocene in outcrop, and that it migrated southwest-ward to its present location, away from the southeastern branch of the Mid-Indian ridge system, during the Tertiary crustal-spreading episode.
No evidence is known to suggest that the island is of continental origin. Alkali syenite bodies, some of which are rich in quartz, were intruded into shield basalt in the southwestern part of the island during late Miocene to early Pliocene time, and are late-stage differentiates, similar to those found on other oceanic islands. Even though direct sampling of unexposed parts of the ridge (during the Deep-Sea Drilling Project) may yield lower Tertiary to upper Mesozoic sedimentary and igneous rocks, it is considered unlikely that any of the samples will consist of continental material.