Publication Date:
2022-05-25
Description:
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Volcanology and Geothermal Research 177 (2008): 589-605, doi:10.1016/j.jvolgeores.2007.11.025.
Description:
Mount Erebus, Antarctica, is a large (3794 m) alkaline open-conduit stratovolcano that
hosts a vigorously convecting and persistently degassing lake of anorthoclase phonolite magma.
The composition of the lake was investigated by analyzing glass and mineral compositions in
lava bombs erupted between 1972 and 2004. Matrix glass, titanomagnetite, olivine,
clinopyroxene, and fluor-apatite compositions are invariant and show that the magmatic
temperature (~1000°C) and oxygen fugacity (ΔlogFMQ = -0.9) have been stable. Large
temperature variations at the lake surface (ca. 400 - 500°C) are not reflected in mineral
compositions. Anorthoclase phenocrysts up to 10 cm in length feature a restricted compositional
range (An10.3-22.9Ab62.8-68.1Or11.4-27.2) with complex textural and compositional zoning.
Anorthoclase textures and compositions indicate crystallization occurs at low degrees of
effective undercooling. We propose shallow water exsolution causes crystallization to occur and
shallow convection repeats this process multiple times, yielding extremely large anorthoclase
crystals. Minor variations in eruptive activity from 1972 to 2004 are decoupled from magma
compositions. The variations probably relate to changes in conduit geometry within the volcano
and/or variable input of CO2-rich volatiles into the upper-level magma chamber from deeper in
the system.
Eleven bulk samples of phonolite lava from the summit plateau that range in age from 0 ±
4 ka to 17 ± 8 ka were analyzed for major and trace elements. Small compositional variations
are controlled by anorthoclase content. The lavas are indistinguishable from modern bulk lava
bomb compositions and demonstrate that Erebus volcano has been erupting lava and tephra from
the summit region with the same bulk composition for ~17 ka.
Description:
The work at Erebus volcano and the continued operation of the Mount Erebus Volcano
Observatory is supported by grants (OPP-0229305, ANT-0538414) from the Office of Polar
Programs, National Science Foundation.
Keywords:
Erebus volcano
;
Phonolite
;
Lava bombs
;
Mineralogy
;
Geochemistry
;
Antarctica
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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