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Victoria University Antarctic Research Expedition Science and Logistics Reports 1985-86: VUWAE 30

Background

Background

Previous studies of granitoids in South Victoria Land have been mainly of a reconnaissance nature and associated with regional mapping (Gunn and Warren, 1962; Findlay, 1983). These studies outlined the gross distribution of granitoids and developed preliminary subdivision of the rocks into several plutonic suites. However granitoid nomenclature is still a problem in South Victoria Land for two reasons.

Firstly the early subdivision into red and grey granites has been carried over to the Irizar Granite and Larsen Granodiorite subdivision. Attempts have been made to lump together granitoids hundreds of kilometers apart. This was brought about by a tendency in the past to attempt to "correlate" various granitoids and was probably the result of early mapping carried out by geologists more versed in stratigraphy than igneous petrology. Granitoids should be mapped and named on a pluton basis, with several plutons comprising a batholith. The names Irizar and Larsen should be restricted to the plutons at the type localities.

Secondly the geological structure and outcrop distribution in South Victoria Land is such that many granitoid boundaries are not well defined because of ice and snow cover. Many granitoid plutons appear to grade in physical appearance and chemical composition from centres to margins. Margins in turn grade into high grade metamorphic rocks and in these areas delineating boundaries becomes very subjective indeed.

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Plate 1. Numerous xenoliths in the contaminated marginal phase of the Vida Granite.

Plate 1. Numerous xenoliths in the contaminated marginal phase of the Vida Granite.

Plate 2. Angular blocks of gneiss in coarse-grained Harker Granite.

Plate 2. Angular blocks of gneiss in coarse-grained Harker Granite.

Plate 3. Sampling Vida Granite above Victoria Upper Glacier.

Plate 3. Sampling Vida Granite above Victoria Upper Glacier.

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What is now required is for the granitoids to be mapped on a more detailed individual pluton basis and their geochemical and physical characteristics defined. Since many of the granitoids are derived from melting of basement, and may give rise to some of the numerous dykes it is also important that the geochemistry of these be studied too. In a regional study. Palmer (in prep.) has analysed 120 granitoids from South Victoria Land. It is hoped to assign many of these granitoids into the S- and I-type classification of Chappell and White (1974) now in common use.