Lunar ilmenite

Table 3.1) concentration. The ordinate position of the solar wind composition is arbitrary. The vertical dashed lines illustrate roughly the magnitude of typical in situ contributions at He, the horizontal tick is for 4He, whereas the upward extension is for 3He trapped gases at lower concentrations would be difficult to identify. Solar wind composition from Table 3.2, lunar ilmenites from Eberhardt et al., 1972 and Pesyanoe from Marti, 1969. All the patterns shown here are of the solar type (cf. Figure 3.2 for the planetary type). 

The lower 3He/4He ratios in the magnetic separates may also be due to the predominance of SEPs, which have a lower 3He/4He ratio < 2.5 x 10 4 (Benkart et al., 1988). Recent studies of lunar ilmenite grains by Nichols, Hohenberg, and Olinger (1994) seem to favor this interpretation they found that the majority of the ilmenite grains were enriched in SEP. 

Nichols, R. H., Jr., Hohenberg, C. M., Olinger, C. T. (1994) Implanted solar helium, neon, and argon in individual lunar ilmenite grains Surface effects and temporal variation in the solar wind composition. Geochim. Cosmochim. Acta, 58, 1031-42. 

Wieler, R., Baur, H. (1994) Krypton and xenon from the solar wind and solar energetic particles in two lunar ilmenites of different antiquity. Meteoritics, 29, 570-80. 

Benkert J.-P., Baur H., Signer P., and Wieler R. (1993) He, Ne, and Ar from solar wind and solar energetic particles in lunar ilmenites and pyroxenes. J. Geophys. Res. 98, 13147-13162. 

Spectra for 22 natural ilmenite samples from different deposits show that ilmenite itself is normally deposited with a composition close to the stoichiometry FeTi03 [108]. The weathering products which occur particularly in beach sands contain Fe ions, but are ill defined and of uncertain composition. The degree of weathering can be measured in any given sample from the MSssbauer spectrum. The spectra of lunar ilmenite at various temperatures is discussed on p. 294. 

Fig. 8. Isotopic compositions of nitrogen and neon released from a lunar ilmenite separate subjected to stepwise etching by hydrofluoric acid. Close to grain surfaces, on the right of the plot, isotopically heavy nitrogen is associated with neon whose Ne/ Ne ratio equals that observed directly in the solar wind, whereas at greater depths within the grains, lighter nitrogen is associated with isotopically heavier neon, attributed by Wieler et al (1986) to solar energetic particles. From Mathew et al (1998).

Internal 87Rb-87Sr isochrons were particularly useful in unraveling the history of the Moon and Mars. As an example, consider mare basalts from the Sea of Tranquility collected by Apollo 11. These lunar basalts consist primarily of calcium-rich (anorthitic) plagioclase and low-calcium pyroxene, along with ilmenite, crystobalite, and other minor phases. Strontium is concentrated in the calcium sites in plagioclase and is excluded from most other phases, resulting in a variation of a factor of several hundred in the strontium... 

Samarium-neodymium evolution diagram for lunar mare basalt 75075. Data points for the total rock, plagiodase, ilmenite, and pyroxene form a precise linear array, the slope of which gives a crystallization age of 3.70 0.07 Ga for this rock (7= 6.54 x 10 12 yr 1). The insert shows the deviations from the best-fit line in parts in 104. After Lugmair et al. (1975a). 

Two scenarios for the crystallization of the lunar magma ocean, involving different amounts of melt. In both models, olivine and orthopyroxene cumulates sink and plagiodase floats, but the thickness of the plagiodase-rich crust is greater for a completely melted Moon. Ilmenite crystallizes late in both models, but mixing of dense, ilmenite-rich rocks with early magnesium-rich cumulates could result from convection. After Ryder (1991). 

He, Ne, and Kr Ilmenite from lunar soil 71501 by the CSSE method (Benkert et ah, 1993 Wieler and Baur, 1994 see also Section 2.8). The soil trapped its solar gases in the last... 

Pavicevic, M., Ramdohr, P., El Goresy, A. Electron microprobe investigations of the oxi-dationstates of iron and titanium in ilmenite in apollo 11, apollo 12, and apollo 14 cristallin rocks. Proc. 3. Lunar Science Conf. Suppl. 3 (Geochim. et Cosmochim. 

Altliough plagioclase, unlike calcium-rich pyroxene, ilmenite, or zircon, does not readily incorporate uranium or thorium, isotopic compositions of lead in plagioclase are of particular interest. Plagioclase is a dominant mineral phase in the lunar crust and a major constituent of mare basalts that can incorporate lead into cation sites normally occupied by potassium, sodium, or calcium and thereby play an important role in the U-Th-Pb isotopic systematics. 

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