Melting minerals found to be source of Tanzanian volcano’s carbon-based lavas

May 7th, 2009 - 2:09 pm ICT by ANI  

Washington, May 7 (ANI): Scientists studying the world’s most unusual volcano in Tanzania have discovered the reason behind its unique carbon-based lavas, attributing them to an extremely small degree of partial melting of typical minerals in the earth’s upper mantle.

Although carbon-based lavas, known as carbonatites, are found throughout history, the Oldoinyo Lengai volcano, located in the East African Rift in northern Tanzania, is the only place on Earth where they are actively erupting.

The lava expelled from the volcano is highly unusual in that it contains almost no silica and greater than 50 percent carbonate minerals.

Typically, lavas contain high levels of silica, which increases their melting point to above 900 degree Celsius.

The lavas of Oldoinyo Lengai volcano erupt as a liquid at approximately 540 degrees C. This low silica content gives rise to the extremely fluid lavas, which resembles motor oil when they flow.

“Since the volcano was under magma pressure during the eruption, we were able to collect pristine samples of the volcanic gases, with minimal air contamination,” said Tobias Fischer, volcanologist at the University of New Mexico.

The pristine samples collected during a 2005 eruption offered the scientists a deeper look at the processes taking place in the earth’s upper mantle.

The geochemical analyses revealed that magma from the upper mantle below both the oceans and continents is a uniform and well-mixed reservoir of “typical” volcanic gases such as carbon dioxide, nitrogen, argon and helium.

The lava expelled from the volcano is highly unusual in that it contains almost no silica and greater than 50 percent carbonate minerals.

Typically, lavas contain high levels of silica, which increases their melting point to above 900 degrees C.

The lavas of Oldoinyo Lengai volcano are comprised of carbonatites, which erupts as a liquid at approximately 540 degrees C.

This low silica content gives rise to the extremely fluid lavas, which resembles motor oil when they flow.

“These finding are significant because it shows that these extremely bizarre lavas and their parent magmas, nephelinites, were produced by melting of a typical upper mantle mineral assemblage without an extreme carbon content in the magma source,” said geochemist Bernard Marty at the Centre de Recherches Petrographiques et Geochimiques in Nancy, France.

“Rather, in order to make carbonatite lavas, all you need is a very low melt fraction of 0.3 percent or less,” he added. (ANI)

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