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Salt-bearing fumarole deposits in the summit crater of Oldoinyo Lengai, Northern Tanzania: interactions between natrocarbonatite lava and meteoric water

Genge, M.J.; Balme, M. and Jones, A.P. (2001). Salt-bearing fumarole deposits in the summit crater of Oldoinyo Lengai, Northern Tanzania: interactions between natrocarbonatite lava and meteoric water. Journal of Volcanology and Geothermal Research, 106(1-2) pp. 111–122.

URL: http://www.sciencedirect.com/science/journal/03770...
DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1016/S0377-0273(00)00251-1
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Abstract

Oldoinyo Lengai in the Northern Tanzania rift is the only active nephelinite–carbonatite stratovolcano. We report the discovery of thermonatrite, aphthitalite, halite and sylvite fumarole deposits on recent natrocarbonatite lava flows erupted in the summit crater during the wet season. These salt deposits occur as delicate, concave fringes or tubes that line the cooling cracks in the lava flows and consist of intergrowths of euhedral crystals. The presence of a dark altered zone, depleted in halides and alkalies, adjacent to cooling cracks and observations of steam fumaroles emanating from the fractures suggest that the salts are formed by sublimation from saturated vapours generated by the extrusion of lavas over meteoric water. The crystallisation sequence recorded in the salts suggests that mixing between meteoric steam and magmatic CO2 and H2S occurs at high temperatures resulting in the sublimation of carbonates and sulphates. At lower temperatures the vapours are dominated by meteoric steam and sublimate halides. The high solubility of the fumarole salts within meteoric water and their formation only during the wet season implies that these are ephemeral deposits that are unlikely to be preserved in the geological record.

Item Type: Journal Article
ISSN: 0377-0273
Keywords: fumarole deposits; Oldoinyo Lengai crater; natrocarbonatite lava
Academic Unit/Department: Science > Environment, Earth and Ecosystems
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 5496
Depositing User: Matthew Balme
Date Deposited: 05 Oct 2006
Last Modified: 02 Dec 2010 19:54
URI: http://oro.open.ac.uk/id/eprint/5496
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