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Coesite-Sanidine Eclogites from Kimberlite: Products of Mantle Fractionation or Subduction?
Daniel J. Schulze and Herwart Helmstaedt
The Journal of Geology
Vol. 96, No. 4 (Jul., 1988), pp. 435-443
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/30062158
Page Count: 9
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Eclogite xenoliths from kimberlite have long been considered as products of crystallization of basaltic magmas within the upper mantle, and the Ca/(Ca + Mg) and Fe/(Fe + Mg) values of garnets in some suites have been interpreted as representing a fractionation sequence. Many recent studies, however, have concluded that some xenolithic eclogites have originated by subduction of oceanic crust. We show that coesite and/or sanidine occur throughout virtually the entire compositional range of mantle-derived eclogites, although in igneous crystallization models these minerals should be present only in the more "evolved" (i.e., Ca- and Fe-rich) compositions. The distribution of these two minerals constitutes petrographic and major element evidence consistent with an origin for these eclogites through subduction of altered oceanic crust, without subsequent partial melting.
The Journal of Geology © 1988 The University of Chicago Press