Contributions to the volcanic geology of the Black Island, Brown Peninsula, and Cape Bird areas, Mcmurdo sound, Antarctica

Abstract

Abstract In the three areas studied, the McMurdo volcanics have been subdivided into four formations: Melania (oldest, and predominantly basaltic); Aurora Trachyte; Nubian Basalt; and the Trachyte Hill Formation. Tentative correlations have been made among the three areas. In addition to these four divisions, maps are presented showing the lavas subdivided on the basis of their petrography (particularly phenocryst contents). Five broad petrographic types are recognised: Olivine-augite basalts; plagioclase basalts; hornblende basalts; pyroxene trachytes, and hornblende trachytes. Black Island and Brown Peninsula are believed to have been originally stratovolcanoes, similar to the present form of Mt Bird. In each area, this early conebuilding phase (Melania Formation) is predominantly olivine-augite basalt, although locally trachyte and trachybasalt are recognised. This phase was followed, after a period of prolonged quiescence, by the Aurora Trachyte Formation, comprising extensive viscous flows of pyroxen...