Computer Science
Scientific paper
Oct 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..50...41h&link_type=abstract
Earth and Planetary Science Letters, Volume 50, Issue 1, p. 41-58.
Computer Science
11
Scientific paper
Ion and electron microprobe analyses of twenty-one Cr-Al-spinel harzburgite xenoliths from southern African kimberlites show two chemical groups. Orthopyroxenes from ``fertile'' harzburgites have higher CaO (mean of 11, 0.95 wt.%), Al2O3 (3.05 wt.%), Cr2O3 (0.85 wt.%) and Li (0.8 ppmw) than those from ``barren'' harzburgites (mean of 10, CaO 0.24 wt.%, Al2O3 1.10 wt.%, Cr2O3 0.35 wt.%, Li 0.3 ppmw). Olivines from all harzburgites have similar chemistry except that mean values of Li and Na are higher for barren than fertile harzburgites (Li 0.9 vs. 0.4 ppmw; Na2O 16 vs. 7 ppmw). Orthopyroxenes from fertile harzburgites are chemically distinct from those in garne lherzolites from southern Africa and spinel lherzolites from southwest U.S.A., but orthopyroxenes from barren harzburgites are indistinguishable from those in many coarse garnet lherzolites.
Chromium, Ca, Ni, Na and Li in coexisting olivines and orthopyroxenes from the above rock types show complex patterns, which for Ca, Cr and Ni can be related to pressure and temperature. Temperatures from an empirically calibrated thermometer based on Ni-Mg exchange between olivine and orthopyroxene, measured modes of harzburgites (fertile, mean of 10: ol 68, opx 31, spinel-silicate intergrowth <0.5 barren, mean of 8: ol 76, opx 23, spinel and spinel-silicate intergrowth 1), and high-pressure experimental studies suggest (a) that harzburgites are residues of partial melting, (b) that barren harzburgites were melted to a greater extent at a higher temperature (though probably at a similar depth) than fertile harzburgites, and (c) that incomplete reequilibration during retrograde metamorphism has led to development of complex inter- and intragranular textures, probably in the range ~700-900°C.
Barry Dawson J.
Hervig Richard L.
Smith Joseph V.
Steele Ian M.
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