Volcanic geology and physical volcanology of Mount Morning, Antarctica

Abstract

Mount Morning is 70 km south of Ross Island and is part of the Cenozoic McMurdo Volcanic Group, which includes the presently active Erebus volcano. Few previous studies have investigated the mountain. The main exposures occur on two ridges on the northwest of the mountain, the field area is a roughly 3x5 km area on the northern part of the Riviera Ridge. The exposed geology indicates two main episodes of volcanic activity; Miocene trachytes and trachyandesites and Quaternary basanites and phonolites. This project is focused primarily on the Quaternary basanites and the objectives were:

• Describe the physical volcanology. • Map and describe the surface geology and petrology and characterise the geochemistry of the rocks. • Develop models for the origin and evolution of the magmas represented by the rocks. • Characterise mantle xenoliths found in the area.

The Quaternary eruptives are represented by eroded scoria cone remnants, dikes, and lava domes and flows. Breccia pipes mark eroded vent areas. Four scoria cones have been mapped and sampled in detail and these are interpreted to have formed by hawaiian and strombolian style activity. They contain distinctive agglutinate beds which have formed lava flows as lapilli and spatter horizons have accumulated on the flanks of cones close to source. The dominant rock-type is strongly porphyritic olivine and clinopyroxene basanite formed by crystal fractionation of olivine, clinopyroxene, opaque oxides, and minor amphibole, apatite and feldspar A dike within one of the scoria cones contains a spectacular suite of abundant, large xenoliths. Ultramafic mantle xenoliths include peridotite and pyroxenites, crustal xenoliths are granulite and granite. The presence of these xenoliths indicates that some basanites are very primitive.