ABSTRACT

This Small Grant for Exploratory Research (SGER) is co-sponsored by the Office of International Science and Engineering, and the Petrology and Geochemistry program of the Division of Earth Sciences. The study will address the recent geochemical variations of magmas and volcanic gases in Oldoinyo Lengai, the only currently active carbonatite volcano in the world. Its eruptive activity is dominated by effusive eruptions that emit very low viscosity and low temperature (~540°C) lava flows. Since September 2007, Oldoinyo Lengai has entered a new episode of volcanic activity that is characterized by violent explosions. Such explosive episodes occur only about every 50 years. The project is a full collaboration with Tanzanian scientists that have been able to obtain samples from these eruptions. The composition of these samples is quite different from the lavas usually discharged during the effusive periods of the volcano: it contains approximately 20% SiO2.

The results from this SGER will be compared to those of a prior eruption episode that took place between July 2005 and May 2006, when the team collected volcanic gases emanating from Oldoinyo Lengai that were not severely air contaminated. Gases are chemically and isotopically indistinguishable from upper mantle, mid-ocean-ridge gases, despite the fact that lavas are very different from mid-ocean-ridge basalts (MORB) and occur in a setting far removed from oceanic ridges. The current activity of the volcano will provide the first opportunity to test a number of hypotheses about this particular system. For instance, it is proposed to test if the world's only active carbonatite volcano is now transitioning to erupting higher-silica magmas, and if this transition is accompanied by an increase in SO2 flux from mantle-derived melts and characterized by highly explosive eruptions, and if such transition is caused by gas emissions that are characteristic of upper mantle chemical and isotopic compositions.

Oldoinyo Lengai is a major tourist attraction in Tanzania as it is located close to Ngorongoro Crater, the Serengeti wildlife reserve and lake Natron. Several Massai villages are located on the base of the volcano. Hundreds of tourists climb the crater each year many of them camp in the crater of the active volcano. By characterizing and better understanding the explosive activity of the volcano, hazards to tourists and the local population can be better assessed and pre-cursor activity may be better understood as is currently the case. The proposal will also support a graduate student and further strengthen collaboration of the P.I. with Tanzanian scientists based at the University of Dar Es Salaam.

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