Volcanic Geology of Carnley Volcano, Auckland Islands

Camley Harbour, at the southem end of the Auckland Islands (l66°E, 50°51'S), is a dissected Miocene shield volcano formed on basement continental crust of the Campbell Plateau. Subaerial, marine, and glacial erosion excavated a section through ftows and pyroclastics of the volcanic pile to expose a swarm of dikes and sills which intersect the lowest lava flows, underlying Middle Miocene sediments and basement granite of Cretaceous age.A coarse-grained, crudely layered biotite gabbro intruding the volcanic succession is exposed at McClure Head and Circular Head and probably represents a partially unroofed magma chamber.

Thick sequences of lava which vary from laterally extensive to thin discontinuous ftows are exposed on the slopes of Adams Island and on the F1eming Plateau. Basalt and hawaiite are predominant with minor evolved mugearites, benmoreites, trachyte, and rhyolites restricted to localised centres of eruption.All rocks are more or less porphyritic with phenocrysts of olivine, clinopyroxene, plagioclase, and Fe-Ti oxides.Olivine and clinopyroxene are dominant in the basalts and hawaiites, whereas plagioclase and Fe-Ti oxides become more abundant in the evolved rocks.The dikes and sills are identical petrographically to the ftows and are regarded as intrusive equivalents.

The scale and tectonic setting of this intraplate, mildly alkaline to transitional, tholeiitic volcanic shield invites comparison with the Paleocene–Eocene central complexes of northwest Britain (Skye, Mull, Ardnamurchan) where a greater time span has all but stripped the effusive cover rocks, unroofing the contents of subvolcanic magma chambers.