Mathematics – Logic
Scientific paper
Feb 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004e%26psl.219....1b&link_type=abstract
Earth and Planetary Science Letters, Volume 219, Issue 1-2, p. 1-12.
Mathematics
Logic
19
Martian Meteorites, Shock, High Pressure, Aluminum, (Na-Ca)-Hexaluminosilicate
Scientific paper
A (Ca,Na)-hexaluminosilicate, whose Ca end member was previously synthesized in numerous high-pressure experiments, has been identified by Raman spectroscopy in heavily shocked Martian meteorites. This mineral has a structural formula close to (CaxNa1-x)Al3+xSi3-xO11 and is similar to the calcium aluminum silicate phase previously synthesized in high-pressure experiments performed on anorthite and rocks of basaltic composition. This new mineral occurs in shock melt pockets in two distinct settings and is intimately intergrown with SiO2-stishovite. The first setting, encountered in Zagami, consists of idiomorphic equant crystals overgrown by acicular stishovite that crystallized from a melt of labradorite composition. The second setting contains the (Na,Ca)-hexaluminosilicate phase intergrown with stishovite and hollandite and was formed during partial melting at high pressures. The mineralogical association (Na,Ca)-hexaluminosilicate+stishovite was observed in shock melt pockets, which have distinct bulk compositions in seven Martian shergottites. This new mineral represents, after majorite, the second natural occurrence of a silicate mineral with silicon in both four and six coordination. The assemblage stishovite+(Na,Ca)-hexaluminosilicate sets constraints on the pressure and temperature conditions that prevailed during shock in some of the studied meteorites. The (Na,Ca)-hexaluminosilicate mineral is a potential carrier of Al and Na during subduction of oceanic crust in the lower mantle of the Earth.
Beck Pierre
Daniel Isabelle
El Goresy Ahmed
Gautron Laurent
Gillet Philippe
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