Computer Science
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.4827s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, p. 4827
Computer Science
8
Lunar Rocks, Potassium Isotopes, Calcium Isotopes, Granite, Lunar Probes, Radioactive Age Determination, Meteoritic Composition, Igneous Rocks
Scientific paper
K-Ca age determinations were undertaken for three lunar granitic samples (14321,1062, 14303,206, and 12013,141). K-Ca isotopic analyses of bulk samples of seven pristine lunar igneous rocks, including four mare basalts (10017, 15555, 14321,1394, and 14305,304,371), one norite (15445,17), one anorthosite (60025), one KREEP basalt (72275,543), and seven meteorites (Juvinas, Pasamonte, Moore County, Stannern, Y75011,84B, Zagami, and Shergotty) were also performed. The K-Ca mineral isochron for lunar granitic clast 14321,1062 yields an age of 4.06 +/- 0.07 Ga for lambda(K-40) = 0.5543/Ga and an initial Ca-40/Ca-44 of 47.141 +/- 0.010 (normalized to Ca-42/Ca-44 = 0.31221). Low precision K-Ca ages of 4.04 +/- 0.64 Ga and 3.76 +/- 0.72 Ga were obtained for lunar granites 14303,206 and 12013,141, respectively, due to their lower K/Ca ratios. Initial Ca-40/Ca-44 values for seven lunar and seven meteoritic bulk samples are similar. Assuming a lunar initial value of Ca-40/Ca-44 as 47.136 +/- 0.002 (2sigma-m) and +/- 0.006 (2sigma-p), a ten- to twenty-fold fractionation for K/Ca enrichment is consistent with a granite genesis model involving a silicate-liquid immiscibility process.
Nyquist Larry E.
Shih Chia-You
Wiesmann Henry
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