Contrasting boron behavior in the Moon and the Earth

Details Contrasting boron behavior in the Moon and the Earth Contrasting boron behavior in the Moon and the Earth

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.531s&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 531-532

Other

Abundance, Boron, Earth Crust, Gadolinium, Lunar Rocks, Petrology, Crystallization, Ion Probes, Kreep, Metamorphism (Geology), Particle Tracks

Scientific paper

Boron abundances have been determined, along with Sm and Gd, using prompt gamma activation analysis, in 56 lunar rocks. Analyses for other elements (from the same generic samples) were available in the literature. In lunar rocks B is unequivocally an incompatible element and belongs to the group referred to as KREEP. The abundance of B in what has been called ur-KREEP is 34 ppm, and the abundance of B in any lunar rock is a simple linear function of the proportion of such material present in the rock by crystallization or melting processes. This may be illustrated by a plot of log Gd/B vs. arithmetic B, which is tightly grouped. Alpha-track imaging was used to search for sites where B and Li are concentrated within lunar thin sections. The results can only say that these elements occur as fine-grained interstitial material, which does not have a simple petrographic interpretation. Ion probe analysis is under way to try to resolve this paradox. The contrasting behavior of B in the Earth is shown by a similar plot of terretrial igneous, sedimentary, and metamorphic rocks. In these rocks Gd abundances are mostly lower (1-15 ppm), but water-mediated processes may enrich B abundances up to 10x those on the Moon, so that Gd/B ratios decrease significantly. Gadolinium behaves incompatibly by solid/liquid fractionation in most terretrial crystallization or melting processes, but the case for B is more varied, and in arc volcanics a B enrichment may develop during anatexis of subducted oceanic crust by fluid/liquid fractionation.

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