Mathematics – Logic
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p21a08j&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P21A-08
Mathematics
Logic
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5410 Composition, 5480 Volcanism (8450), 6200 Planetology: Solar System Objects (New Field), 6250 Moon (1221)
Scientific paper
Recent orbital remote-sensing missions have provided new compositional information about the global distribution of basalt types on the Moon. Previous work suggested a wide distribution of basalts of intermediate Ti content, which are rare in the lunar sample collections, and the occurrence of other basalts that are compositionally or mineralogically dissimilar to the returned samples and lunar basaltic meteorites. Measurement of thorium concentrations by Lunar Prospector's gamma-ray spectrometer reveal some basalt flows in the Procellarum region to have elevated thorium concentrations relative to most of the sampled basalts. Clementine UVVIS derived FeO estimates suggest that these basalts, with ~20 wt% FeO, do not derive their thorium enrichment from contamination by KREEP-rich Imbrium ejecta, re-excavated from beneath basalts by young craters such as Kepler and Aristarchus. Enrichment in thorium may result from assimilation of crustal rocks prior to eruption or from KREEP enrichment in mantle source regions. Distinguishing between these possibilities is needed to determine whether any cause-effect relationships exist between the enrichment of heat-producing Th, U, and K in the Procellarum KREEP Terrane and features such as the lack of anorthositic crust in the region, relaxation of topography across the Procellarum basin, and extended volcanism that occurred there. To investigate these basalts, we integrate Lunar Prospector gamma-ray data (resampled to 0.5 degree resolution), Clementine spectral reflectance (using modified algorithms to derive FeO and TiO2 concentrations), Lunar Orbiter images, and photogeologic maps. Results to date suggest significant enrichment of thorium in Eratosthenian basalts of Western Procellarum at levels of ~3-5 ppm, similar to concentrations measured in some Apollo 11 high-K basalts from Mare Tranquillitatis and in rare incompatible-element-rich basaltic glasses from Apollo 14 and Apollo 15 samples. It is unclear at present whether thorium enrichment correlates with age (as determined by crater counts) or with basalt classifications according to spectral characteristics.
Gillis Jeffery J.
Jolliff Brad L.
Lawrence D. Jr. J.
Maurice Sylestre
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