VOLCANICS OF BLACK ISLAND AND BROWN PENINSULA

The object of the volcanics project was to map end collect rocks of the McMurdo Volcanic Series on Black Island end Brown Peninsula, and to compare their age with the surrounding Moraine. It was undertaken during the first half of the VUWAE9 expedition from November 16th to December 18th 1964, end all personnel contributed. A brief examination of the volcanoes of the Koettlitz region was later made during the second half of the expedition to assist the main study.

The first area visited was Black Island, and it soon became evident that there were a number of different types of volcano of which two could be readily identified in the field. These were designated 'trachyte' and 'basalt', pending later petrographic examination. The former was light to medium grey in colour, sometimes porphyritic and sometimes non-porphyritic. Both had a characteristic yellow weathering which was thought to be a possible source of the 'loess' dust [gap — reason: illegible] in the area. The basalt could be divided into two groups: Firstly, an earlier dark coloured porphyritic olivine basalt which underlaid the trachyte, and probably formed a large volcano similar to Mount Discovery before the major glaciations. Secondly, there was a much younger basalt, with small phenocrysts and usually red in colour. Cones of this type were considered to be later than both the trachytes and most of the glaciations. The volcanic rocks of Brown Peninsula were very similar with the addition of a [unclear: tuff] deposit. This was very widespread on the Peninsula, and was thought to have come from a number of vents on the Peninsula.

On return to New Zealand thin sections were made of the key slides end from this further sub-divisions of the rocks have been possible from their mineral content, and this can be applied to the field evidence when compiling the final map. A particularly interesting feature is the appearance of calcite in the tuff from a particular event on Brown Peninsula. This could be the first indication of carbonatite lavas in the region, and the rocks concerned will be studied in detail to examine this possibility.

J. W. Cole.