Two-thirds of the island consists of intensely folded flysch, capped with Aptian age fossils, tuff and greywacke in the Cumberland Bay Series.
In the west are basalt flows, pillowed spilite, prehnite and trachyandesite, as well as shale with radiolarite fossils.
[1] Uranium-lead dating of zircon and muscovite grains from the southern Andes and South Georgia (gathered from the peraluminous Darwin granite suite and undersea Tobifera Formation rhyolite) indicates that the rocks formed during the middle Jurassic.
The fragmentation of the Gondwana supercontinent is preserved in an ophiolite in the Rocas Verdes marginal basin—part of the Larsen Harbour complex on South Georgia.
Feldspar phenocrysts formed in cracks within the Beagle granite pluton, likely related to the tectonism affecting the high-grade metamorphic rocks of the Cordillera Darwin in Tierra del Fuego.