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Geophysical Monograph Series




The geology of Cape Evans and Cape Royds, Ross Island, Antarctica

S. B. Treves

During the austral summer of 1960–61, several areas around McMurdo Sound were mapped. The study of observations and material collected from Cape Evans and Cape Royds has been essentially completed. Both Cape Evans and Cape Royds are located on the flanks of Mt. Erebus and consist of volcanic rocks. Cape Royds probably consists of three(?) kenyte flows which are partially mantled by volcanic agglomerate and lithic tuff. To the northeast these rocks appear to be covered by a younger, thin flow of olivine basalt. The kenyte flows are distinguished from each other by their thickness and stratigraphic relationships. The youngest flow is approximately 30 ft thick in most places, whereas the other two flows are less than 10 ft thick. The intermediate flow sometimes swells to a thickness of 20 ft. Glassy tops and bottoms also help to identify the flows. The glassy portions exhibit flow structures and are vesicular and strikingly porphyritic. The present surface of areas now occupied by kenyie is very irregular and rough with a relief of as much as 30 ft. This surface probably is fairly representative of the original surface of the youngest flow, as it is glassy in most places. The interior of the flows consists of aphanitic-porphyritic kenyte, which exhibits phenocrysts of anorthoclase as long as three inches. The phenocrysts are rudely aligned in the direction of flow.
The agglomerate and tuff consist of glass shards and fragments of kenyte and basalt. The fragments in the lithic tuff are somewhat rounded and may have been transported a short distance by streams. These rocks probably represent an explosive phase which may be related to vent-clearing that took place prior to the eruption of the olivino basalt, the youngest flow exposed in this area.
Erratics of igneous, sedimentary, and metarnorphic rocks are common at Cape Royds. The rocks exposed along the shore are covered with crusts mid crystals of mirabilite.
Cape Evans consists of two(?) kenyte flows which are similar to those exposed at Cape Royds. The youngest flow here locally swells to thicknesses of 50 ft. To the north, in front of the ice-cored moraine which marks the end of the Barne Glacier and which limits the rock exposures in this area, the kenyte is mantled by a thin but persistent cover of outwash which consists of sand and gravel-sized fragments of kenyte, tuff, agglomerate, basalt, and anorthoclase crystals. Large blocks of lithic tuff, agglomerate, and olivine basalt are common constituents of the moraine, but do not crop out here.

Citation: Treves, S. B. (1962), The geology of Cape Evans and Cape Royds, Ross Island, Antarctica, in Antarctic Research: The Matthew Fontaine Maury Memorial Symposium, Geophys. Monogr. Ser., vol. 7, edited by H. Wexler, M. J. Rubin, and J. E. Caskey Jr., pp. 40–46, AGU, Washington, D. C., doi:10.1029/GM007p0040.

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