Apollo-12 basalts

Nyquist L. E., Shih C. Y., Wooden J. L., Bansal B. M., and Wiesmann H. (1979) The Sr and Nd isotopic record of Apollo 12 basalts implications for lunar geochemical evolution. Proc. Lunar Planet. Set Conf. 10, 77-114. 

Volcanics from the Onverwacht Group, Swaziland and South Africa, comprise the basal part of the Early Precambrian Barberton greenstone belt found both in Swaziland the Transvaal. Data from them gave an age of about 3.54 Ga calculated using an initial [ Nd/ Nd]o ratio of 0.50809 00004 (Hamilton et aL 1979). The strontium and neodymium isotopic record of Apollo-12 basalts from the Moon were examined. Isochrons were derived for an achondrite (eucrite) and another meteorite and gave ages of about 4.58 and 4.562 Ga, respectively, with primordial [ Nd/ Nd]p ratios of 0.50684 0.00008 and 0.506664. An initial [ Sr/ Sr]o ratio was termed ADOR. The isotopic evolution of neodymium in the Earth has been described by means of a model termed CHUR (GHondritic Uniform Reservoir). And the present value of the [ Nd/ Nd] ratio is 0.512638 relative to a [ Nd/ Nd] ratio of 0.7219. The present value of the [ Sm/ Nd] ratio of CHUR is 0.1967, which permits calculation of [ Nd/ Nd] ratio in any past time interval. 

Figure 3 Ages of mare basalts and pyroclastic glasses show no correlation with Ti02. Age data are from previous compilations by BVSP (1981), Ryder and Spudis (1980), Fernandes et al. (2002a), and (for pyroclastic glasses) Shih et al. (2001), plus a lower limit cited for Apollo 17 VLT basalts by Taylor et al. (1991). The Ti02 data are averaged from the compilation of Haskin and Warren (1991). The five major Apollo basalt types are shown with small symbols because each point represents one of many available samples from the given locale, whereas each of the lunar meteorites represents (probably) our only sample from its locale.

Tera F, Wasserburg GJ (1972) U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks. Earth Planet Sci Lett 14 281-304... 

A laser probe study of Apollo 17 basalts [4] illustrates the use of the laser dating to interpret temperature release patterns. The laser 39Ar-40Ar method has been used to study three Apollo 17 basalts 70215, a basalt with a normal well-behaved 39Ar-40Ar release pattern 70017, a basalt with a disturbed 39Ar-40Ar release... 

Russell et al. (1977, 1978b) also measured two Apollo 17 and one Apollo 15 basalt samples and found small variations of 6 Ca of ca. +l%o, but again also spiked the samples after ion exchange separation so the results need to be verified. Russell et al. (1977) measured calcium obtained by lightly leaching an Apollo 15 soil sample and formd it to have 5 Ca of +3.3 0.4. This heavy Ca is inferred to be associated with the grain surfaces and result from solar wind sputtering. 

Provost A. and Bottinga Y. (1974). Rates of solidification of Apollo 11 basalts and hawaiian tholeiite. Earth. Planet. Scl Letters, 15 325-337. 

Donaldson C.H., Usselman T.M., Williams R.J., and Lofgren G.E. (1975) Experimental modeling of the cooling history of Apollo 12 olivine basalts. Proc. Lunar Sci. Conf. 6th,... 

Tera, F. and Wasserburg, G.J., 1972. U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks. Earth Planet. Sci. Lett., 14 281-304. Titterington, D.M. and Halliday, A.N., 1979. On the fitting of parallel isochrons and the method of maximum likelihood. Chem. Geol., 26 183-195. 

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... 

The 147Sm-143Nd system was first used in cosmochemistry by Lugmair et al. (1975a), who published a precise isochron age for an Apollo 17 basalt (Fig. 8.11). The system developed rapidly thereafter. Note that the spread in 147Sm/144Nd in the mineral phases of this basalt is less than 50%, not factors of ten, several hundred, or even a few thousand, as can be seen in other systems. The fact that precise isochron ages can still be obtained is a testament to the care taken in chemical separation of samarium and neodymium and the precision of modem mass spectrometric analysis. 

Lugmair, G. W., Scheinin, N. B. and Marti, K. (1975a) Sm-Nd age and history of Apollo 17 basalt 75075 Evidence for early differentiation of the lunar exterior. Proceedings of the 6th Lunar Science Conference, Geochimica et Cosmochimica Acta Supplement, 6, 1419-1429. 

Lunar surface materials (Apollo and Luna returned samples and lunar meteorites) are classified into three geochemical end members - anorthosite, mare basalt, and KREEP. These components are clearly associated with the various geochemically mapped terrains of different age on the lunar surface. The composition of the lunar interior is inferred from the geochemical characteristics of basalts that formed by mantle melting, and geochemistry provides constraints on the Moon s impact origin and differentiation via a magma ocean. 

Six maimed American Apollo missions have returned 382 kg of rocks and soils from the nearside of the Moon. Three automated Soviet Luna missions have also returned small amounts of soils. Most missions sampled maria only the Apollo 14, 15, and 16 missions sampled highlands materials and basin ejecta as well as basalts. Descriptions and geologic significances of the various Apollo and Luna landing sites were given by Hiesinger and Head (2006). 

Mare basalts include lavas that erupted from fissures and pyroclastic deposits that produced glass beads. Six of the nine missions to the Moon that returned samples included basalts. The mare basalts from different sites have distinctive compositions and are classified based on their Ti02 contents, and to a lesser extent on their potassium contents (Fig. 13.3). A further subdivision is sometimes made, based on A1203 contents. Mare basalts are compositionally more diverse than their terrestrial counterparts. Volcanic glass beads, formed by fire fountains of hot lava erupting into the lunar vacuum, were found at several Apollo sites and eventually were shown to be a constituent of virtually every lunar soil. The glasses are ultramafic in composition and formed at very high temperatures. 

Lunar mare basalts from the various Apollo and Luna missions are classified by their titanium and potassium contents. After Lucey et al. (2006). 

Samples returned by the Apollo and Luna missions can be readily distinguished based on their contents of FeO and thorium. This may seem like an unlikely choice of chemical components for classification, but they nicely discriminate rock types and are easily measured by remote sensing. The FeO and thorium contents of ferroan anorthosites, mare basalts, impact melt breccias, and lunar meteorites are shown by various symbols in Figure 13.4. 

The same ferroan anorthosite-mare basalt-KREEP components also define the compositions of lunar soils. The soils from each site contain different proportions of these end members. For example, Apollo 12 soils are mixtures of mare basalt and KREEP, whereas Apollo 15 soils contain all three components. 

As noted earlier, lunar meteorites are mostly breccias of ferroan anorthosite and related early crustal rocks, although a few mare basalt meteorites are known. The lunar meteorites likely sample the whole Moon. The absence of KREEP-rich breccias so common among Apollo samples collected from the nearside in the lunar meteorite collection implies that KREEP-rich rocks cover only a small area on the Moon. In fact, the lunar highlands meteorites appear to provide a closer match to the average lunar crust than do the Apollo highlands samples (Fig. 13.5), as measured by geochemical mapping (see below). 

The isotopes of thorium include mass numbers 223-234. 232Th has a half-life of 1.39 x 1010 years, See also Radioactivity. It emits an alpha-particle and forms meso-thorium 1 (radium-228), which is also radioactive, having a half-life of 6.7 years, emitting a beta-particle. Since 2 2Th captures slow neutions to form, by a series of nuclear reactions, >>U which is fissionable, thorium can be used as a fuel for nuclear reactors of the breeder type. Thorium occurs in earth minerals, an average content estimated at about 12 ppm. Findings of hc Apollo 11 space flight indicated that thorium concentrations in some lunar rocks are about the same as the concentrations in terrestrial basalts. 

Figure 10.6. Remote-sensed spectra of representative areas on the Moon s surface (from Gaddis et al., 1985). Left telescopic spectral reflectance scaled to unity at 1.02 i.m and offset relative to adjacent spectra right residual absorption features for the same measurements after a straight line continuum extending from 0.73 pm to 1.6 pm has been removed, (a) Highland soil sampled at the Apollo 16 landing site (b) high-Ti mare basalt at the Apollo 17 landing site (c) low-Ti mare basalt at Mare Serenitatis and (d) pyroclastic deposits at Taurus-Littrow.

Fig. 2. Total carbon abundances (by combustion) in basaltic rocks, breccias and bulk fines from Apollo 11, 12, 14 and 15 missions. Horizontal bars indicate different samples...

The Apollo 11 rocks contain large amounts of ilmenite, as can be seen from Tables 2 and 3 (high titanium content). We have plotted the chemical composition of rock sample 12018 in Fig. 3a vs. that of the carbonaceous chondrites (the most primitive of all meteorites), in Fig. 3b vs. the basaltic achondrite (eucrite) Juvinas (a class of meteorites which have undergone magmatic differentiation) and in Fig. 4 vs. the average composition of the Earth s... 

There cannot be any doubt that the lunar maria were formed by large lava flows2The basalts from the various landing sites differ in composition (Table 3), but samples from a single mare site are not uniform either. Fig. 5 plots the concentrations of Al vs. Mg in lunar basalts from Apollo 12. The observed trend can be accounted for by magmatic differentiation processes, with the variations in chemical composition reflecting origin at different depths. 

Apollo 11 brought back two chemically differing groups of basalt high-K and low-K rocks. From age determinations we know that these two rock types solidified more than 200 million years apart. Turner23 found a K-Ar age of 3.55 x 109 yrs for the high-K rocks and 3.82 x 109 yrs for the low-K rocks. 

Fig. 7. Mixing diagram from the two-component model of Wanke et al,6 for the Apollo 12 soils (12037, 12070, 12042, 12033) und breccias (12034, 12073). Note that the element lines and the compositions (position along the x-axis) were calculated via least-squares fit from the data for basaltic rocks, Apollo 12 soils and breccias only. The data for KREEP and the soil sample from the Fra Mauro formation (14) were not used for the computation of the element lines. The position of these samples along the x-axis was calculated via the previously determined element lines. Finally, the distance between the magmatic rocks and KREEP was divided into 100 units...

As we will see in Chap. VI, we now have evidence that the KREEP (norite) component in the Apollo 12 soil represents ejecta from the crater Copernicus. We should note here that the composition of the Apollo 14 soil samples and KREEP is nearly identical. KREEP was later shown to be admixed also with the Apollo 15 and 16 soil samples. The Apollo 15 soil contains all three major components found so far mare basalt, KREEP (norite), and anorthosite12,16 (see Table 5). 

Table 5. Concentrations of mare basalt, KREEP and anorthosite in Apollo 15 soils12). The highest anorthosite concentrations were found for the samples from locations close to the Apennine front...

Figure 10 The tungsten isotopic composition of Apollo 15 basalt 15555 shows no internal variation as a function of TaAV, consistent with its low exposure age (source Lee et al, 2002).

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