aegirine, augite, clinopyroxene, alkali feldspar, kaersutite, nepheline, olivine, plagioclase, quartz and sanidine. Aegirine, aenigmatite, amphibole, augite, clinopyroxene, alkali feldspar, glass, iron oxide-titanium oxide, nepheline, plagioclase and quartz make up the groundmass. The volcanic rocks contain xenoliths consisting of syenite and of rocks from older stages of Mount Morning activity. Spinel peridotite and less commonly clinopyroxenite, dunite, harzburgite, lherzolite, norite, pyroxenite and websterite have been reported as xenoliths. The early volcanic rocks of Mount Morning are comparable to mildly alkaline rocks from Mount Melbourne, while the more alkaline late volcanic rocks resemble these from Mount Erebus. The older rocks define the "Mason Spurr lineage" while the younger ones are referred to as the "Riviera Ridge lineage". Basaltic rocks are concentrated on the lower slopes, while phonolite is mainly found in the upper sector of Mount Morning. The composition changes between the early and late volcanic activity of Mount Morning may be due to alteration in crustal magma processes. Eruption history Mount Morning has been active during the Miocene, Pliocene and Pleistocene. Argon-argon dating and potassium-argon dating have been used to infer the duration of volcanic activity at Mount Morning. Gandalf Ridge has yielded ages of 18.7±0.3-15.5±0.5 million years, Pinnacle Valley 15.2±0.2-13.0±0.3 million years, Mason Spur 12.8±0.4-11.4±0.2 million years, rocks below the summit of 6.13±0.20-~1.00 million years and 4.51±0.31-0.02 million years on other formations. Some of these eruptions may have deposited volcanic ash over the McMurdo Sound area and in the Transantarctic Mountains. Even older activity at Mount Morning may be recorded in volcanic deposits from Cape Roberts which go back to 24.1 million years ago. This is a long lifespan for a volcano by Antarctic standards, and may be due to tectonic factors that kept magma generation focused on Mount Morning for a long time. Loading by glaciers may have influenced volcanic activity at Mount Morning. Volcanic activity has been subdivided into two phases separated by a hiatus, an early phase lasting between 11.4±0.2-18.7±0.3 million years ago and a late phase from 6.13±0.02 million years ago to almost present-day. These phases are also known as the phase I or the Mason Spur Lineage, and as the phase II or the Riviera Ridge Lineage. The early phase produced mildly alkaline volcanic rocks, the late phase which makes up most of the outcrops strongly alkaline rocks. The early phase has produced ignimbrites from a caldera at Mason Spur, an otherwise rare type of