Other
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24.1089n&link_type=abstract
In Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z p 1089-1090 (SEE N94-20636 05-91
Other
Anorthosite, Breccia, Crystallization, Lunar Composition, Lunar Crust, Lunar Geology, Lunar Rocks, Lunar Soil, Metamorphism (Geology), Meteoritic Composition, Minerals, Recrystallization, Chromites, Degassing, Feldspars, Igneous Rocks, Ilmenite, Iron, Olivine, Phosphates, Pyroxenes, Sulfides, Troilite
Scientific paper
Noritic anorthosite clasts from breccia 67016 have bulk compositions similar to that of the upper crust of the Moon and petrogenetic affinities with pristine ferroan anorthosites. Rb-Sr and Sm-Nd isotopic compositions of mineral separates from one of these clasts suggest very old (greater than or = 4.4 Ga) ages, but interpretation of these data is complicated by the multi-stage history of the clasts which involved magmatic crystallization, brecciation, subsolidus recrystallization, and sulfide metasomatism. These clasts record some of the earliest events on the Moon, including early crust formation, accretionary bombardment, and degassing of the lunar interior. Modal analyses of these clasts show they are now composed of about 70 percent plagioclase, 28 percent pyroxene, 2 percent troilite, and minor amounts of ilmenite and chromite. No metallic iron, phosphates, or other trace phases were observed. Olivine is very rare, occurring only as relicts within secondary troilite+pyroxene intergrowths which may reflect reaction of olivine with sulfurous vapors. PIXE proton microprobe analyses of the sulfides show that the metasomatism was accompanied by enrichments of Cu, Zn, Ni, Se, and Sb. The clasts have been only mildly shocked since the observed texture was established. Major and minor element mineral compositions are very homogeneous and strikingly similar to those of pristine ferroan anorthosites. Pyroxene compositions indicate equilibration temperatures of 850-900 C. Except for the sulfide and chalcophile element metasomatism, these clasts appear to be essentially monomict and probably represent a noritic member of the ferroan anorthosite suite. Their low Ni contents and Ni/Co ratios are consistent with the interpretation of these clasts as igneous rocks which have escaped mixing with meteoritic material.
Alibert Chantai
McCulloch Malcolm T.
Norman Douglas M.
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