In the northern part of Tanzania is one strange volcano named Oldoinyo
Lengai. It has produced carbonatites. Do you have more information
about the composition of the lava from this volcano (petrological,
geochemical-mainly the amount of REE)? Is it true, that in 1960 (or
68?) eruption the lava was outgoing from the crater and its temperature
was about 470C? What is the source of the carbonatites?
Roman Krska
Roman,
You are right. The lava at Oldoinyo Lengai is strange. Most of the
world's volcanoes erupt silicate lavas (mostly silicon and oxygen).
Oldoinyo Lengai erupts carbonate lavas (mostly carbon and oxygen). The
carbonate minerals in the lava are
nyerereite
and
gregoryite
.
Here is a chemical analysis of one flow:
Trace element
concentrations (in ppm) for the same flow are:
I did not find any rare earth element analyses for the carbonatite lava
flows. I don't have the temperature data handy for the 1967 eruption.
Temperatures for lava lakes and lava flows of the 1988 eruption ranged
from 491 to 544C. The carbonatites are from the mantle. They are
probably related to phonolites or nephelinites by liquid
immiscibility.
Steve Mattox, University of North Dakota
Source of information: Effusive natrocarbonatite activity at Oldoinyo
Lengai, June 1988 by Keller, J., and Krafft, M., 1990, Bulletin of
Volcanology, v. 52, p. 629-645.
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