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Meteorite Minerals vs. the Earth's Mantle Minerals
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- Subject: Meteorite Minerals vs. the Earth's Mantle Minerals
- From: Steven Excell <excell@concentric.net>
- Date: Sat, 3 Jan 1998 23:03:36 -0800
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Sorry, I've been remiss in posting this, but finally got around to it.
The journal Science has an exceptional two-page overview of the similarities in meteorite and asteroid minerals with those found in the Earth's upper, transitional and lower mantle zones. The author, Dieter Stoffler (Museum of Natural History, Homboldt Universitat, Berlin, Deutschland) uses an analogous shocked chondrite host (olivine, orthopyroxene, clinopyroxene, plagioclase and troilite) with a shock melt vein (majorite, ringwoodite, perovskite, troilite and glass) that contains inclusions (ringwoodite, wadsleyite, perovskite, clinoenstatite and plagioclase glass) from the shocked host. Stoffler then shows a cut-away view of the Earth's mantle and shows where each mineral occurs within the mantle's zones.
The commonality is that the high-pressure-phase assemblages deep within the Earth's mantle are not unlike the shock-induced, high-pressure assemblages found in asteroids and meteorites. Since the protoplanetary Earth accreted from solar system debris, both should have started with the much the same basic minerals and elements. Yet, over geologic time, each underwent differing processes. At 600+ km of depth within the Earth's mantle one can find perovskite that formed at over 23 GPa of pressure -- and immense amount of pressure that can only occur on the Earth's surface in research labs where diamond anvils are used to artificially create these crushing conditions. Because perovskite and other mantle minerals are also found in meteorites, the nature of the huge impacts -- and the huge pressures created --can be understood by studying terrestrial mantle rocks.
The article, which can be found in most university libraries, is cited as:
Stoffler, Dieter. "Minerals in the Deep Earth: A Message from the Asteroid Belt." Science. Vol. 278, pp. 1576-1577. November 28, 1997.
Stoffler's article is worth reading for most meteoritephiles and worth saving for those who study meteorite thin sections.
Steve
excell@cris.com