CompuServe Messages

Doug & Wayne: Re: further notes on ultramafic lavas — komatiites are olivine-rich rocks distinguished by low silica content (v. "undersaturated" in the parlance of petrology). Strictly by the definition of low-silica content, carbonatites can be termed ultramafic but as the name suggests, their composition is quite different from other lavas. (Komatiites, for example, are composed of rather common olivine & pyroxene – just in much higher proportion than a normal run-of-the-mill basalt.) As you may be aware, Doug, there are modern examples of volcanos in the world currently erupting carbonate (!) lavas. Mostly these are along the East African Rift zone, I believe actually in Rwanda & Burundi (scene of so much current human grief). There have been a couple of articles in _Science_ magazine in the last 3 or 4 years showing photos of molten calcite lava flows. Interestingly, I do not recall that these eruptions are/were particularly gas-rich and violent. Compared to a Pinatubo or a St. Helens, in contrast their eruptive style (at least recently) has been v. quiescent. Scott M.