Mineralogy and Petrology of the Apollo 12 Lunar Sample

Details Mineralogy and Petrology of the Apollo 12 Lunar Sample Mineralogy and Petrology of the Apollo 12 Lunar Sample

May 1971

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1971saosr.333.....w&link_type=abstract

SAO Special Report #333 (1971)

Mathematics

Logic

18

Scientific paper

We sectioned, examined, and classified 499 coarse (>0.6 mm) particles from five of the Apollo 12 soil samples: 12070, collected on the rim of Surveyor Crater; 12032 and 12037, from the rim of Bench Crater; 12033, from a light-colored layer in a trench dug in the rim of Head Crater; and 12001, collected between craters. Samples 12070 and 12001 appear to be well-gardened soils, random mixtures of debris fragments, most of which derive from bedrock near at hand. The particles consist largely of mare basalts or degradation products thereof (microbreccia, cindery glasses of composition equivalent to the bulk soil), samples of the volcanic flows of Eratosthenian age that cover this portion of Oceanus Procellarum. Textures and mineral compositions of virtually all the basalt fragments we examined point to their formation in one or more relatively thin (~ 10 m) lava flows. All the soils contain about 10% of particles that are noritic in composition (low Ca pyroxenes and calcic plagioclase in nearly equal amounts), but most of these have the textures of thermally recrystallized microbreccias. Many of the Apollo 11 anorthosites (a type that was not found in the Apollo 12 soil) have similar textures; we suggest that primary igneous anorthosites and norites were brecciated and recrystalized in an early, hot regolith. Soils 12032 and 12033 contain major amounts of a component alien to the local soil (as represented by 12070 and 12001) in the form of twisted, ropy particles of brownish glass. These are noritic in composition, but apparently derive from a different source than the crystalline norites in the soil. We believe the latter came from small terra exposures in the vicinity of the Apollo 12 site and from beneath the local mare basalt, while the ropy glasses are ejecta from the Crater Copernicus, samples of a Copernican ray that crosses the Apollo 12 site. Petrological characteristics of the lunar rocks and geophysical (gravity, topography) properties of the lunar surface are consistent with a structural model in which Oceanus Procellarum and the non-mascon maria are underlain by ~25 km of norite (with a thin covering of basalt), the mascon maria by lunar mantle material (covered by >1 km of basalt), and the highlands by ~25 km of anorthosite. Most of this structure appears to have developed during crystallization and differentiation of an early lunar surface magma system; the mare basalts were erupted in a later episode of igneous activity, probably owing to decay of long-lived radioactivity at depth in the Moon. We found several unusual particles among the 499 studied: A rhyolite or micrographic granite rich in K and Fe; an agglomeration of glassy spherules of composition unmatched by any other known lunar material (high in normative ilmenite and mafics, low in plagioclase); and a meteorite, more similar to Type II carbonaceous chondrites than to any other known meteorite class.

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