Geochronology of Mount Morning, Antarctica: two-phase evolution of a long-lived trachyte-basanite-phonolite eruptive center |
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| Authors: | Adam P Martin Alan F Cooper W James Dunlap |
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| Institution: | (1) Department of Geology, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand;(2) Department of Geology and Geophysics, The University of Minnesota, Minneapolis, MN 55455, USA |
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| Abstract: | Mount Morning is a Cenozoic, alkaline eruptive center in the south-west Ross Sea, Antarctica. New ages on 17 Mount Morning
volcanic rocks (combined with 34 existing ages) allows division of Mount Morning volcanism into two phases, erupted between
at least 18.7 Ma and 11.4 Ma, and 6.13 and 0.02 Ma. The position of Mount Morning on the active West Antarctic Rift System
within the stationary Antarctic plate is a key factor in the eruptive center’s longevity. The earliest, mildly alkaline, Phase
I volcanism comprises predominantly trachytic rocks produced by combined assimilation and fractional crystallization processes
over 7.3 m.y. Strongly alkaline Phase II volcanism is dominated by a basanite – phonolite lineage, with the youngest (post
last glacial maximum) activity dominated by small volume primitive basanite eruptions. The evolution from mildly to strongly
alkaline chemistry between phases reflects magma residence time in the crust, the degree of mantle melting, or the degree
of magma—country-rock interaction. Phase I magmatism occurred over a comparable area to the present-day, Phase II shield.
The 5.2 m.y. volcanic hiatus separating Phase I and II coincides with a cycle of eruption and glacial erosion at the nearby
Minna Bluff eruptive center. Mount Morning is the likely source of volcanic detritus in Cape Roberts drill-core (about 24.1
to 18.4 Ma) and in ANDRILL drill-hole 1B (about 13.6 Ma), located 170 km north and 105 km north-east respectively, of Mount
Morning. Based upon the timing of eruptions and high heat-flow, Mount Morning should be considered a dormant volcano. |
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