Volcanological Evolution

 

Prior to the early 1990's, much was known about the geochemical evolution of lavas from Mt. Erebus. Clearly, the stratigraphically oldest lavas were of a primitive basanitic composition, while the current activity is a more chemically evolved tephriphonolite. However, only a few age dates existed for the whole of Mt. Erebus and these were limited to imprecise conventional K/Ar dates. Beginning in 1993, Dr. Philip Kyle and two of his students (Chris Harpel and Richard Esser) began utilizing the more advanced, high precision 40Ar/39Ar dating technique to determine the ages of many of the exposed lava flows on Mt. Erebus. Prior to the use of 40Ar/39Ar geochronology on Mt. Erebus, what little age data existed suggested that the volcano was several million years old, including the young-looking summit area. We now know that the entire volcano is just slightly older than 1 million years old and that the summit is significantly younger than 100,000 years old.

By combining the new geochronologic data with the existing database of geochemical data, we can better confirm an evolutionary model for the development of Mt. Erebus. Below are the summarized results from several researchers working on the evolution of the volcano.

General Background

Mt. Erebus is one of several volcanoes in the McMurdo Volcanic Group which itself consists of Late Cenozoic intraplate alkaline volcanoes.

cross-section of crust below Mt. Erebus
Cross-section of the crust and upper mantle below Ross Island, Antarctica. A "hot spot" or mantle plume is theorized as the mechanism to account for the origin of Mt. Erebus and Ross Island.

Below are six cartoons showing the proposed volcanic evolution of Mt. Erebus. All of the time spans (ka =1000 years) are based on 40Ar/39Ar geochronology of lava flows exposed on the summit and flanks of the volcano.

cross-section of crust below Mt. Erebus ~1300-700 ka: proto-Erebus shield and cone building phase. 
-basanite/tephrite shield (1300-1050 ka) 
-phonotephrite cone (1050-700 ka)
cross-section of crust below Mt. Erebus ~700-350 ka: Subsidence of proto-Erebus summit produces Fang Ridge escarpment (~700 ka?). Continued eruption of flank phonotephrites and tephriphonolites.
cross-section of crust below Mt. Erebus ~350-250 ka: Activity shifts from proto-Erebus tephriphonolite to anorthoclase-phyric tephriphonolite characteristic of modern-Erebus
cross-section of crust below Mt. Erebus ~250-90 ka: Anorthoclase-phyric tephriphonolite continues to build the bulk of the modern-Erebus.
cross-section of crust below Mt. Erebus ~90-70 ka: Subsidence of modern-Erebus summit produces present day caldera.
cross-section of crust below Mt. Erebus ~70 ka-present: Summit and flank anorthoclase tephriphonolite and phonolite flows continue. Present pyroclastic cone at summit probably built over last 1000 years.