Evolution of pantellerite-trachyte-phonolite volcanoes by fractional crystallization of basanite magma in a continental rift setting,Marie Byrd Land,Antarctica |
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| Authors: | Wesley E LeMasurier Sung Hi Choi Y Kawachi Samuel B Mukasa N W Rogers |
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| Institution: | (1) Institute of Arctic and Alpine Research, University of Colorado at Boulder, Boulder, CO 80309-0450, USA;(2) Department of Geology and Earth Environmental Sciences, Chungnam National University, 79 Daehangno, Yuseong-gu, Daejeon, 305-764, South Korea;(3) University of Otago, Dunedin, New Zealand;(4) Department of Geological Sciences, University of Michigan, Ann Arbor, MI, USA;(5) Department of Earth Sciences, Open University, Milton Keynes, UK;(6) Present address: College of Engineering and Physical Sciences, University of New Hampshire, Durham, NH 03824–3591, USA |
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| Abstract: | The Marie Byrd Land province includes 18 large (up to 1,800 km3) central volcanoes distributed across an active volcano-tectonic dome. The typical volcano structure consists of a basal
1,000–5,000 m of basanite surmounted by trachyte and subordinate intermediate rocks, plus phonolite, or pantellerite, or comendite.
The volumes of felsic sections are large (~30–700 km3), but these rocks probably make up <10% of volcanic rock in the province. This paper describes pantellerite volcanoes in
the Ames and Flood Ranges, which include a large and varied suite of these iron-rich, silica-poor rhyolites. Isotopic and
trace element data, maintenance of isotopic equilibrium throughout the basalt-felsic range, and the results of modeling, all
exclude significant crustal contamination and point to fractional crystallization as the process that controls magmatic evolution.
The most unusual feature of these volcanoes is the apparent need to derive pantellerites from basanite, the long interval
of fractionation at the base of the lithosphere and crust, involving kaersutite as the key phase in developing pantellerite,
and a plumbing system that permitted coeval eruption of pantellerite and phonolite from the same edifice. Peralkalinity most
likely developed in upper crustal reservoirs during the final 4–5% of magmatic history, by fractionating a high proportion
of plagioclase under low pH2O. Mantle plume activity appears to drive doming and volcanism. This, a stationary plate, and continental lithospheric structure
seem to provide an optimal environment for the evolution of a diverse, large volume suite of felsic rocks by fractional crystallization. |
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