Geology and petrology of the Campbell—Aviator Divide, Northern Victoria Land, Antarctica

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Abstract
Three major rock units are present on the ridge system between the Campbell and Aviator Glaciers: (1) Upper Tertiary to Quaternary alkaline volcanic rocks, all included in the McMurdo Volcanic Group; (2) Jurassic flows and sills (the Ferrar Group) with interbedded sediments (the Beacon Group); and (3) a Basement Complex, consisting mainly of ?Precambrian schist and hornfels intruded by Paleozoic granite plutons. The post-Paleozoic sediments and volcanic rocks are described in this paper. The McMurdo Volcanic Group consists of a linear belt of volcanoes, ranging in size between single flows or small cones and large central volcanoes similar to Mt Erebus. Two distinct magma suites are recognised; the smaller flows, cones, and mounds are dominantly olivine basalt, but the larger volcanoes are composed of more alkaline differentiates, ranging from trachybasalt to trachyandesite and trachyte, with minor trachytoid phonolite and alkaline ignimbrite. There is abundant evidence for recent volcanism throughout the Campbell-Aviator Divide, and magma composition appears to be quite independent of age. Both the Beacon and Ferrar Groups rest unconformably on the Kukri Peneplain which separates them from the older Basement Complex. The Beacon Group consists mainly of quartzose and arkosic sandstone, with minor conglomerate, mudstone, and volcanic-derived sediment. The mineralogy indicates that the Group was derived directly from the underlying granites and metasediments. Flows and sills of tholeiitic basalt and dolerite comprise the Ferrar Group, which is invariably intimately involved with Beacon sediments. The dominant mineral assemblage is clinopyroxene-plagioclase, with only minor pigeonite, hypersthene, and olivine, and in northern Victoria land the Ferrar rocks appear to be less oversaturated than elsewhere in Antarctica. Pollen samples from Beacon mudstone interbedded with Ferrar lavas at Section Peak, a few miles to the west, indicate an upper Triassic-lower Jurassic age for volcanism and sedimentation.

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