Mathematics – Logic
Scientific paper
May 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991sci...252..827s&link_type=abstract
Science (ISSN 0036-8075), vol. 252, May 10, 1991, p. 827-830. INSU-supported research.
Mathematics
Logic
24
Earth Mantle, Petrology, Pyroxenes, Seismology, Solid Solutions, Mineralogy, Rocks
Scientific paper
The seismologically delineated transition zone, at depths between 400 and 670 kilometers, is a fundamental discontinuity in the earth that separates the upper mantle from the lower mantle. Xenoliths from within or close to the transition zone are dominated by pyropic garnet and associated pyroxene or mineralogically heterogeneous garnet lherzolite. These xenoliths show evidence for the high-pressure (90 to 120 kilobars) transformation of pyroxene to a solid solution of pyroxene in garnet (majorite) and silicon in octahedral coordination; low-pressure (less than 80 kilobars) exsolution of clinopyroxene or orthopyroxene from the original majorite is preserved. Although mineral modes and rock proportions below the transition zone and the relative amount of eclogite present cannot be accurately asessed from the xenoliths, it is likely that both majorite and beta-spinel help produce the observed seismic gradient of the transition zone.
Field Stephen
Haggerty Stephen E.
Sautter Violaine
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