Achondrites eucrites

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... 

Fig. 4. Abundances of chemical elements in lunar rock 12018 vs. the abundances in the basaltic achondrite (eucrite) Juvinas. Data for Juvinas from Wanke et al.121 and Mason17 ...

The basaltic achondrites (eucrites as well as howardites) show the greatest similarity to the lunar mare basalts (Fig. 4). We will come back to this relation later on. 

Two approaches were used to determine the half-life of lutetium-176. These were analysis of lutetium-bearing minerals with known ages and direct counting. Variable results range from 2 to 7 X 10 ° years and a calculation from the slope of a Lu/Hf isochron formed by ten achondrites (eucrites) with an age of 4.55 x 10 years gave a value of (3.53 0.14) x 10 years. This value accords with a recent estimate of 3.8 x 10 years. 

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. 

It was soon discovered that there were other solar system objects that were older and had more primitive strontium than the basaltic achondrites. Table 8.3 compares the (87Sr/86Sr)o value determined for BABI with those from some other important samples from the early solar system. If Allende, Angra dos Reis, and the basaltic achondrites formed directly from the solar nebula, then the time intervals shown in the right-hand column of Table 8.3 are valid. Note that the uncertainties on these time intervals, a few million years, are much smaller than the uncertainty in the eucrite isochron shown in Figure 8.9 ( 260 Myr). However, the validity of the time intervals determined from the initial ratios depends completely on the validity of the idea that they all formed directly from the bulk material of the solar nebula. 

Differentiated (planetary) Achondrites Angrites Aubrites Brachinites HED meteorites Eucrites Howardites Diogenites Ureilites Stony-irons Pallasites... 

Goodrich C. A. and Righter K. (2000) Petrology of unique achondrite Queen Alexandra Range 93148 a piece of the pallasite (howardite-eucrite-diogenite ) parent body Meteorit. Planet. Sci. 35, 521—535. 

Palme H., Baddenhausen H., Blum K., Cendales M., Dreibus G., Hofmeister H., Kruse H., Palme C., Spettel B., Vilcsek E., and Wanke H. (1978) New data on lunar samples and achondrites and a comparison of the least fractionated samples from the Earth, the Moon and the eucrite parent body. Proc. 9th Lunar. Sci. Conf. 25—57. 

Eugster O. and Michel T. (1995) Common asteroid break-up events of eucrites, diogenites and howardites, and cosmic-ray production rates for noble gases in achondrites. Geochim. Cosmochim. Acta 59, 177-199. 

Heymann D., Mazor E., and Anders E. (1968) Ages of calcium-rich achondrites I. Eucrites. Geochim. Cosmochim. Acta 32, 1241-1268. 

This is approximately equivalent to the Mn-Cr closure age for Chervony Kut, the noncumulate eucrite with the highest individual Mn/ Mn initial ratio. Other achondrites, including a palla-site and the unusual basaltic achondrite Acapulco, have Mn-Cr ages 8-10Myr after the HED differentiation event. These timescales are consistent with the notion that a variety of differentiated meteorites sample various depths in asteroids of various sizes during this early epoch following accretion. 

Hohenberg et al. (1981) studied Xe in different mineral fractions of the Angra dos Reis achondrite and were able to derive separately the isotopic composition of the cosmogenic Xe produced by Ba and rare earth elements. The respective entry in Table 4 is for a chondritic value of (La + Ce + Nd)/Ba = 0.52. The value for meteorites given by Kim and Marti (1992) is modified from earlier data on chondrites and eucrites. 

Figure 9. Exposure age distributions of HED meteorites (howardites, eucrites, diogenites) and aubrites or enstatite achondrites. The HED data are from the compilation by Welten et al. (1997), with only the (shielding corrected) Kr-Kr ages being displayed for the eucrites. Included are 4 new diogenite ages from Welten et al. (2001b). In addition, the -3 Myr age of the howardite Kapoeta has been added (Caffee and Nishiizumi 2001). For data sources of aubrites see text. Note the different abscissa scales between the lowermost panel and the others.

The chemical analysis of ALHA 81005 in Table 18.10 and the data contained in the report by Hill et al. (1991) define a field for lunar meteorites and lunar basalt in Fig. 18.25 in terms of the Fe/Mn, K/La, and Fe/Sc ratios. Data point 1 in that diagram identifies ALHA 81005 and point 2 is the Calkalong lunar meteorite. The locations of these data points within the cluster of lunar rocks (open circles) that were collected on the Moon by the Apollo astronauts leaves no doubt that ALHA 81005 and Calkalong are rocks from the Moon. The diagram also contains a field defined by HED achondrites (howardites, eucrites. 

Fig. 18.25 Lunar basalt (open circles) collected by the Apollo astronauts and lunar meteorites (solid circles) collected in Antarctica occupy a well-defined area in coordinates of their Fe/ Mn, K/La, and (Fe/Sc) x 0.01 ratios. The achondrites of the HED (Howardite, Eucrite, Diogenite) groups (crosses) lie in a separate field. The SNC (solid triangles) meteorites (Shergottites, Nakhlites, Chassignites) originated from Mars. The sample numbered 1 is ALHA 81005 and 2 is Calkalong which was recovered in the Australian desert. The Fe/Sc ratio was reduced by a factor or 0.01 in order to prevent the data points from crowding into the Fe/Sc corner of the triangle (Data for ALHA 81005 from Korotev et al. 1983 and for the other samples from Hill et al. 1991)...

Among the fractionated meteorites, such as the eucrites, the lanthanides show some variation. These meteorites, the basaltic achondrites, are basalts, originating as lavas on small asteroidal bodies (Basaltic Volcanism Study Project 1981, p. 214). The eucrites form one important class. Since the asteroid 4 Vesta, 555km in diameter, has a basaltic-like surface from spectral reflectance data, it is a prime candidate for the source of such meteorites, although considerable dynamical problems remain (Gehrels 1979). 

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