Physics
Scientific paper
Nov 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986jgr....9112375m&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 91, Nov. 10, 1986, p. 12375-12387.
Physics
75
Earth Mantle, Geochemistry, Mineralogy, Petrology, Planetary Evolution, Abundance, Basalt, Lunar Rocks, Osmium Isotopes, Spinel
Scientific paper
Fourteen spinel lherzolites, for which extensive trace-element data are available, may be divided into three groups depending upon the percentage loss of basaltic partial melt; averages are slightly depleted, -7 percent melt (Ca/Sa greater than 0.09); moderately depleted, -13 percent (0.09 greater than Ca/Si greater than 0.06); and strongly depleted, -20 percent (0.06 greater than Ca/Si). Re abundances of the groups are correlated with percent depletion, and the intercept of 0.0071 x Cl chondrite corresponding to undepleted mantle is identical to that independently derived from (Os-187)/(Os-186) in osmiridium of known age. The distribution of Re in mafic and ultramafic rocks is apparently closely related to S and Se abundances. Lherzolite data suggest that the abundances of highly siderophile elements (Os, Re, Ir, Pd, Au) and chalcogenic elements (S, Se, Te) in a primary basaltic melt are significantly higher than those of average oceanic ridge basalts, but may be similar to those of trace-element-rich Indian Ocean ridge basalts. The estimated S content (1000 ppm) of a primary basaltic melt is compatible with experimentally measured S solubilities at high temperature and pressure. On the basis of lherzolite depletion and using published trace-element data for spinel lherzolites and ocean-ridge basalts, estimated abundances in ppb in pristine upper mantle are Os, 3.1; Re, 0.26; Ir, 3.4; Pd, 4.5; Au, 1.01; S, 200,000; Se, 57. The trace-element pattern closely resembles that of the CM2 chondrites, but not of the CO3, CV3 or H chondrites. The pattern is a reasonable match, except for Au, with Apollo-17 lunar breccias that contain a 'group 2' ancient meteoritic component, suggesting that rather similar objects bombarded earth and moon during the first 600 Myr of their history.
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