Computer Science
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24.1095n&link_type=abstract
In Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z p 1095-1096 (SEE N94-20636 05-91
Computer Science
Carbonaceous Chondrites, Chondrites, Lunar Composition, Lunar Evolution, Lunar Geology, Lunar Mantle, Lunar Rocks, Lunar Soil, Meteoritic Composition, Neodymium Isotopes, Petrology, Samarium Isotopes, Anomalies, Basalt, Ilmenite, Kreep
Scientific paper
Small anomalies in the isotopic abundance of Nd-142 have been measured for two A17 high-Ti basalts, ilmenite basalt 12056, olivine-pigeonite basalt 12039, feldspathic basalt 12038, and two KREEP basalts. These anomalies correlate with Sm-147/Nd-144 for the basalt source regions as calculated from initial Nd-143/Nd-144 ratios in the basalts, and are interpreted to be from decay of Sm-146 (t1/2 = 103 Ma) in distinct lunar mantle reservoirs. A three-stage model for evolution of Nd-143/Nd-144 and Nd-142/Nd-144 yields reservoir Sm-147/Nd-144 ratios which, with the Nd-142/Nd-144 ratios in the basalts, form a 'mantle isochron' giving a lunar mantle formation interval of 94+2230 Ma (2c(rho)). Calculated reservoir Sm/Nd ratios are in the range expected from some earlier models of basalt petrogenesis. The isochron value of Nd-142/Nd-144 at Sm-147/Nd-144CHUR = 0.1967 is within error limits of the average Nd-142/Nd-144 measured for an L6 chondrite, an H5 chondrite, and the Orgueil carbonaceous chondrite. Evolution of Nd-143 and Nd-142 for high-Ti basalt 70135 was modeled precisely, starting from chondritic relative REE and Nd-isotopic abundances and using the initial (Sm-146/Sm-144)0 ratio inferred from a previous study of angrite LEW86010 as the initial solar system value of this parameter. We infer that the initial Sm/Nd ratio in precursor lunar materials was very nearly chondritic (within approximately 8 percent) prior to lunar differentiation.
Bansal B. M.
Nyquist Larry E.
Shih Chia-You
Wiesmann Henry
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