Inert gases in twelve particles and one “dust” sample from Luna 16

F~ARTll AND PLANETARY SCll;NCE LETTERS 13 (1972) 400-406. NORTH-HOLLAND PUBLISHING COMPANY

INERT

GASES

ONE "DUST"

IN TWELVE SAMPLE

PARTICLES FROM

LUNA

AND 16

D. H E Y M A N N , A. Y A N I V * and S. L A K A T O S Departments of Geology and Space Science, Rice Unil,ersity, Houston, Texas, USA Received 14 November 1971 Revised version received 29 November 1971

The inert gases were measured mass-spectrometrically in 12 fragments and 1 ~'dust" sample from Luna 16. The fragments were classified petrologically by microscopic inspection. The major petrologic types were breccias and basalts. The former were much richer in trapped gases than the latter, and were apparently formed by the welding of local fines. However, there was no clear-cut difference in gas content of either breccias or basalts between zone A (top) and zone G (bottom)./he 4lte/2°Ne ratio of the breccias (average 49) was systematically smaller than that of the basalts (average 78), probably because of He-Ne fractionation during or after the formation of the breccias. We suggest that the 4He/2 °Ne ratios of bulk fines in general may reflect the proportions of basNtic and breccia (plus cindery glasses) fragments in the fines. Substantial variations of 4He/~He were found, which could not be explained with the presence of variable proportions of cosmogenic 3Hec. Either the solar-wind value has changed in time, or the fragments with the small ratios were exposed to solar flares rich in 3He and/or 4He. Exposure ages of four fragments are several hundred million years. The "°Ar/~6Ar slopes of breccias and basalts are identical: 0.65.

1. Introduction Twelve particles, four from zone A and eight from zone G, were studied with the microscope for the purpose of classification. As no thin sections were made, the classification is wholly based on their external appearance. Six particles, two from zone A and four from zone G, were classified as breccias, A number of these breccias were quite friable: small portions of them tended to b r e ~ off during the handling under the microscope. Three particles, two from zone A and one from zone G, were classified as basalts; one particle from zone A and one from zone G were classified as a gabbro, following Vinogradov's [1 ] terminology. All of these particles were probably fragments from larger rocks. Particle G-32-1 appeared to be glassy throughout; i.e., a cinder. The " d u s t " sample consisted o f rock * On leave of absence from the Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv, Israel.

fragments, mineral fragments, and glasses ranging in size from 4 0 - 1 5 0 ~ m ; all told about 40 particles. No a t t e m p t was made to separate the " d u s t " sample into groups of similar petrology for the inert gas analysis, but six particles were ground to a fine powder, part of which was used for major element analysis (see below). The remainder of the powder, or untreated fragments, and the dust sample were analyzed for rare gases. The experimental techniques have been published elsewhere [2]. The results are shown in table 1.

2. Detailed description of the particles Microscopic observations of samples at 40× magnification. Only longest and shortest dimensions are given. A-30-1. Basalt. Size: 1100 × 825 ~tm. Dark brownish gray, fine- to very fine-grained, subangular fragment containing a few vesicles. Individual minerals were not recognizable.

401

D . H e y m a n n e t al,, l n e r t gases in L u n a 16 s a m p l e s

Table 1 Inert gas contents (units 10-s cm 3 STP/g). Sample

Type

Weight

3He

4He

A-30-2 A-34-2 G-42-1 G-42-2 G-42-3 G-42-4

Br Br Br Br Br B

535 400 2250 1800 1405 645

1 510 4930 3950 4850 2980 1 790

3 510000 12 800000 7200000 12 900000 5830000 5440000

A-30-1 A-34-1 G-32-2 G-30-1 G-30-2 G-32-! G-49

Bs Bs Bs Ga Ga Gl Du

805 405 825 680 710 600 435

210 201 373 260

2540

523 000 111 000 2 3 2 000 260 000 541 000 3 8 3 000 7820000

6700

18000000

B u l k [ l I Du

488 220

20Ne 91 900 249000 143000 215000 124000 112000

2 ~Ne

22Ne

36Ar

38Ar

4°Ar

a4Kr

281 679 425 606 357 333

7 110 18 800 11 300 16 700 9060 8680

53 700 58 700 46 100 48 500 49000 41 300

10 000 10900 8520 9050 9200 7 740

47 100 54 700 44700 53 800 45 300 44 800

22 20 18 19 20 16

18 47

447

97

1 220 1 350 1 230 370 1 420 2 920 27 300

228 285 341 329 549 5 180

5 910

1.5

32 400

9.0

54000

10300

53000

5 850. 1 520 4 450 2 500 6 780 8 630 112000

358

425 205 554 673 8520

340000

900

27000

28

66 40

169

81

6 5 4 3

680 180 300 990

7 660

-

I

32Xe

3.5

3.4 2.4

2.4 2.9 2.8 -

0.9

22

1.4

8.5

Br = breccia, Bs = basalt, Ga = gabbro, GI = glass, Du = "dust". Weights are given in ~g. The errors of absolute amounts are z5%, except for numbers printed in italics. For the latter the errors are in the 10 20% range, principally because of large blank corrections, small peakheights, or both. A-30-2. B r e c c i a . Size: 1200 X 1 0 0 0 / l m . Dark brown, subangular fragment. Minute p y r o x e n e and feldspar grains were observed. A b o u t onetenth of surface area was covered with b r o w n glass. A-34-1. B a s a l t . Size: 875 × 6 7 5 / l m . Dark b r o w n , fineto very fine-grained, subangular fragment with vesicles. One mineral grain in the glassy matrix was a pale-brown p y r o x e n e . A-34-2. B r e c c i a • Size: 1440 X 6 6 0 / l m . Dark brownish gray, friable, s u b r o u n d e d fragment. Specks o f white feldspar and a few dark b r o w n glass spherules were observed. A-30-1. G a b b r o . Size: 1025 X 800/~m. Coherent, subangular to angular crystalline rock fragment. It consisted of light- to m e d i u m - b r o w n pyroxene ( 6 0 - 6 5 % ) and white feldspar ( 3 0 - 3 5 % ) , together with yellow-green olivine ( ? ) ( " 5%) and ilmenite (2- 4%).

G-30-2.

Size: 975 X 8 0 0 / J m . Coherent, subangular crystalline rock fragment consisting of b r o w n p y r o x e n e ( 7 5 - 8 0 % ) and white feldspar ( 2 0 - 2 5 % ) together w i t h ilmenite ( l - 2 % ) .

sional fragment, one side was rounded, opposite side angular. Minute mineral grains embedded in the brown glass were observed. G-32-2. B a s a l t . Size: 1260 × 1000 ~zm. Brown, very fine-grained angular fragment. Individual mineral grains were not distinguishable. G-42-1 • B r e c c i a . Size: 3630 X 1700/~m. Brownish gray, subrounded, friable fragment. One side had brown-glass coating. Two rock fragments (400 to 600 ~m each) were observed; they consisted of light-brown p y r o x e n e partially surrounded by white feldspar. G-42-2. B r e c c i a . Size: 2775 × 1220/am. Brownish gray, subrounded, friable fragment. Grains of p y r o x e n e , feldspar as well as glass spherules were distinguishable. G-42-3.

Gabbro.

G-32-1. G l a s s . Size: 950 X 8 7 5 / 2 m . Nearly equidimen-

G-42-4.

Size: 1960 × 8 9 0 / l m . Brownish gray, subrounded, friable fragment with vesicular dark-brown glass coating on one side. Specks of white feldspar were observed.

Breccia.

Size: 1300 × 1 3 0 0 # m . Brownish gray, equidimensional, subrounded fragment. A b o u t 60% o f it consisted o f brown glass, 40% was light b r o w n p y r o x e n e and white feldspar.

Breccia.

402 G-49.

D.Heymann et al.. inert gases in Luna 16 samples " D u s t " . Grain size: 40--150 ~m. Sample con-

sisted essentially of individual grains of pyroxene, feldspar, glass spherules, and their small aggregates covered by particles ( < 20/Ira) of mostly brown glass.

3. Discussion Judging from the absolute amounts of trapped He, Ne, Ar, Kr, and Xe (table 1) the particles can be clearly separated into two groups, which coincide with the two major petrologic types: basalts or gabbro and breccias. Particles in the first group (including the glassy cinder) contain about 1 - 5 X 10-3 cm 3 STP/g of trapped 4He, those in the second (including the "dust" sample) contain about 3 - 1 3 × 10-~ cm 3 STP/g. The same separation into two distinct groups is also shown by the other trapped gases as represented by 2°Ne, 36Ar, 84Kr, and 132Xe. The trapped gas contents of the breccias are somewhat smaller, or nearly equal to those of the Luna 16 bulk fines as reported by Vinogradov [1]; the agreement is particularly good for 36Ar and S4Kr. However, the gas contents of the breccias are always much greater than those that have been reported for basaltic lithic fragments of similar size (~1 mm) in the Apollo l l , 12, and 14 fines [ 2 - 4 ] . These observations seem to suggest that the breccias represent essentially welded fines, presumably of local

origin. However, it is also possible that the fines themselves contain a large proportion of breccia fragments in a//size ranges, so that the bulk gas content of the former is dominated by the average gas content of the latter. Which of the two explanations is more nearly correct cannot be firmly settled with the data at hand. Vinogradov [ 1] has reported that the particles in the +450/Jm fraction are always very rich in breccia fragments, cinders, and slags ( ~ 6 0 - 8 0 % ) , but this is also the fraction of the fines which contains only a small percentage of the trapped gases in the Apollo 11, 12, and 14 samples, hence presumably also in the Luna 16 fines. Little is known about the particle distribution for sizes less than 250 #m. Elemental ratios such as 4He/2°Ne show a number of interesting trends (table 2). The breccias have distinctly smaller 4He/2 ONe ratios (range 3 8 - 6 0 ; average 49) than the basaltic fragments (range 5 2 - 1 0 0 ; average 78). A similar relationship may exist among the Apollo 11 samples. Funkhouser et al. [5] have reported a range of 4He/2°Ne ratios in Apollo 11 breccias of 47--76 (average of seven = 60). Regrettably there are only few fines in the Apollo 11 collection to which these values can be compared. The most widely studied fines, 10084, have a bulk 4He/2°Ne ratio of about 100 [21. The bulk 4He/2°Ne ratio in 12070 is only about 50 [3]. In an earlier paper we have suggested that the 12070 fines contain principally unheated and moder-

Table 2 Isotopic and elemental ratios. Sample

4He/3He

~°Ne/~2Ne 2~Ne/22Ne

36Ar/3sAt

4°Ar/36At

4He/2°Ne

2°Ne/36Ar

36Ar/S4Kr 84Kr/~32Xe

A-30-2 A-34-2 G-42-1 G-42-2 G-42-3 G-42-4

2 320 2 600 1 820 2 670 2 800 3 030

12.9 13.24 12.7 12.9 13.7 12.9

0.040 0.036 0.038 0.036 0.039 0.038

5.36 5.37 5.41 5.36 5.32 5.34

0.88 0.93 0.97 1.11 0.92 1.08

38 51 50 60 47 49

1.71 4.24 3.10 4.40 2.50 2.70

2 500 2 900 2 600 2 600 2 800 2 600

6.1 6.1 7.4 8.0 6.9 5.5

A-30-1 A-34-1 G-32-2 G-30-1 G-30-2 G-32-1 G-49

2 450 552 622 l 000 l 100 l 740 3 360

13.2 9.02 10.5 12.24 12.22 12.8 13.12

0.040 0.281 0.227 0.138 0.119 0.059 0.042

5.33 4.73 3.41 4.51 4.31 5.32 5.27

5.49 3.84 4.30 10.9 5.40 2.02 1.19

89 73 52 100 80 44 76

4.80 1.13 3.62 6.82 4.77 2.96 4.10

1 600 1 950 3 000

-

Bulk [1]

2 670

12.80

0.0332

5.26

0.98

53

6.3

2 500

2.6

6.4

403

D.Heymann et aL, Inert grasses in Luna 16 samples

Table 3

Sample

Basalts/ breccias + cinders

Bulk 4He/20 Ne

TiO 2 [wt %1

FeO [wt (/~I

Apollo ll; 10084 Apollo 12; 12070 Luna 16;zone A Luna 16;zoneG

0.7 0.2 0.4 0.2

-100 -50 -50 -50

7.42 3.1 3.39 3.30

15.98 [8] 17.3 [81 16.80 [1] 19.6(/ ll]

[61 [61 [71 [71

[2] [31 [l] [1]

[81 [8] [ll [1]

We have adopted the basalt/breccia + cinders ratio of 0.7 from the coarse fines 10085 to represent the "fine" fines 10084. ately heated materials, but we did not identify these constituents. The present Luna 16 results seem to suggest that the "moderately" heated materials might be breccias, cinders, and slags, which are abundant in 12070. Hence, it might be instructive to correlate the ratios of basaltic to breccia (plus glassy cinders) fragments with the bulk 4He/2°Ne ratios. This we have done in table 3. One would expect that fines rich in basaltic fragments have the largest 4He/2°Ne ratio, and table 3 bears this out. However, table 3 shows also that there is a clear-cut correlation between 4He/2°Ne and Ti content. Eberhardt et al. [9] were the first to show that ilmenite fragments in 10084 have much larger 4He/2°Ne ratios (about 200) than the value of 100 in the bulk sample. Kirsten et al. [10] found relatively large mean 4He/ 2°Ne ratios in Ti-rich fragments and ilmenites in individual grains (larger than 200/~m) of the 12070 fines. Plagioclase nearly always shows the largest values [3, 10]. Studies of inert-gas relationships in individual minerals are of great value, because of the possibility of correlating the 4He/2°Ne and other ratios to measured diffusion coefficients when these become available. Studies of such relationships in particles of different petrologic type are important in their own right because they often bear on the process of formation, in this case of the breccias. We think now that the formation of gas-rich lunar breccias from equally gas-rich fines was nearly always attended by a H e - N e fractionation, i.e., loss of He relative to Ne, either because of the rapid diffusion of the light inert gases He, Ne, and Ar out of a gascloud, or because of 4He losses when the already consolidated breccia cooled to ambient temperatures (see [11]). Both the 36Ar/84Kr (mean 2500) and 84Kr/132Xe (mean 6.6) ratios in the Luna 16 fragments are significantly larger than the corresponding values in Apollo

11 fines 10084 (2300 resp. 4.7), although we have seen that the 4He/2°Ne ratios in the former are smaller. (The 2°Ne/a6Ar ratios show no definite trend; this ratio nearly always shows the greatest fluctuation of the four elemental ratios. We do not know why this is so.) A "reversal" of this kind has been reported for the Apollo 12 fines 12070 and for feldspathic fragments [3], and was tentatively explained in terms of moderate, strong, or very strong reheating, coupled with periodic near-quantitative loss of He and Ne by impact heating of the regolith. This suggestion cannot explain the "reversal" in the Luna 16 breccias, because these fragments cannot have suffered nearquantitative He and Ne loss during or after their formation. We think therefore that the Luna 16 breccias were formed from parent materials that already had relatively large 36Ar/84Kr and 84Kr/132Xe ratios. The isotopic ratios in table 2 are grossly similar to the corresponding ones in Apollo 11, 12, and 14 fines. Because of the large 4He contents (table 1), the presence of radiogenic 4He from in situ decay of U and Th cannot have changed the 4He/3He ratio detectably. In five particles (A-34-1, G-30-1, G-30-2, G-32-2, and G-32-1) there is a clear-cut change in the 4He/3He, 21Ne/22Ne, and 36Ar/38Ar ratios from the bulk values [ 1], indicating the presence of cosmogenic gases. However, a substantial variation of 4He/3He ratios is seen to occur among the remaining particles without the concomitant variations of the 2 i Ne/22Ne and 36Ar/3SAr ratios. In fact, the 4He/3He ratio changes from a low of 1820 (G-42-1) to a high of 3360 (G-49), while the z ~Ne/22Ne ratio varies from 0.046 to 0.042, and the 36Ar/38Ar ratio from 5.27 to 5.41 (the variations of the latter two ratios are random, not systematic as would be expected from the presence of cosmogenic gases; furthermore, the variations are much too small).

404

D.Heyrnann et al., Inert gases in Luna 16 samples

That the 4He/3He variation in these particles is probably not due to substantial loss of He, coupled with isotopic fractionation is seen from particles G-42-1 and G-49. The first particle has a 4He/3He ratio of 1820 and a 4He/~°Ne ratio of 50. The corresponding values in the second particle are 3360 and 76 respectively, This trend is opposite to what one would expect from fractionation by gas loss. Particle G-42-1 is of special interest because it is a clear-cut case of a 4He/3He ratio well below the value of the bulk fines that cannot be explained by the presence of cosmogenic gases. Geiss et al. [12] have reported fluctuations in the solar-wind 4He/3He ratios from their foil experiments and have suggested that the average 4He/3He ratio in the solar wind itself could have been significantly higher in the past than it is now. If this is the case then the trapped gas in G-42-1 represents relatively recent solar wind. However, since G-42-1 is a breccia, it is also conceivable that its parent materials were exposed to solar wind implantation sometime in the past when the solar wind 4He/3He ratio was temporarily below 2000. Another explanation, which we cannot exclude, is that G-42-1 was exposed to intense solar flares so that directly implanted 3He (or 3H) from the flares resulted in an apparently small (4He/3Hr)tr ratio, Six particles contain detectable amounts of cosmogenie gases. In order to calculate production ratios for 3Hec, 21Nee and 38Arc, the major element composition (O, Mg, A1, Si, Ca, and Ti) must be known (Fe, although a major element contributes so little to 38Arc in comparison to Ca and Ti that it was neglected). For

A-34-1 we have used the average basalt composition from [1]. For G-42-1 and G-32-2 we have used the composition as determined by microprobe analysis on glass beads which we have made by melting small aliquots ( 2 0 0 - 2 5 0 / a g ) of the powdered particles. The analyses were carried out at the Smithsonian Astrophysical Observatory through the kind assistance of Dr. J.A. Wood. Judging from the analysis of three samples of 10084 which were treated in the same manner, the errors for the significant target elements were + 10% or less. For G-30-1 and G-30-2 we have used the composition as estimated from the petrology determined by microscopic inspection. For the glassy particle G-32-1 we had no data on its composition, hence no exposure ages were calculated. In table 4 we show the calculated cosmogenic gases and the corresponding exposure ages. For reasons explained above, the choice of (4He/3He)tr = 2670 [1] is somewhat arbitrary, but for cases such as A-34-1 and G-32-2, where the meadured 4He/3He ratio is well below 1000, the calculated 3Hec is only about 10% smaller for (4He/3He)tr = 1800. For G-30-I and G-30-2 the decrease in 3Hec would be about 40%. 21Nec was calculated with two values of (21Ne/2ONe)tr. In case (a) we adopted 2.7 X 10-3, the value of the Apollo 11 fines [2]; in case (b) 2.4 X 10-3, the value of Apollo 14 fines [4]. It is seen that the choice makes relatively little difference except for G-42-1.38Arc was calculated with (36Ar/38Ar)tr = 5.33. The production rates of the cosmogenic isotopes 3He, 2 ~Ne, and 3BAr were calculated with the equations shown in table 4 [13], and the chemical data of table 1. The equation for

Table 4 Cosmogenic gases. Sample

A-34-1 G-42-1 G-30-1 G-30-2 G-32-2 G-32-1

q-tee

160 1270 160 290 290 80

2iNe c (a)

2~Nec (b)

38Arc

43 -21 48 84 16

44 82 22 50 85 19

37 -14 71 124

3Hec

2,Nec

Exposure ages [106 years]

21Nec

38Arc

3He

21Ne (a)

21Ne (b)

3SAr

3.7 15 7.6 6.0 3.5 5.0

1.2 1.2 1.6 0.68 0.68 -

154 1150 147 282 264

279

286 456 141 360 454

264

135 345 443

3Hec = 1.00 [0.01179 O + 0.5721 × 10-8 cm 3 STP g" my"1 (27rgeometry); ~Nec = 0.00347 [2.2 Mg + 1.35 AI + Si + 0.17 Ca + 0.017 (Fe + Ni + Ti)] X 10 8 cm 3 STP g-~ (2n geometry); 38Alc = 0.000597 [28.5 Ca + Fe + Ni + 2.5 Ti] × 10-8 cm 3 STP g-~ my-j (2rr geometry).

72 366 795

D.Heymann et aL, Inert gases in Luna 16 samples

aSAr was adjusted for the production from Ca to bring the expression in line with the results of Bogard et al. [14]. The 4°Ar/36Ar ratio ranges from 0.88 to 10.9. A least square fit of all the samples yields: 4°At = (0.88 -+ 0.10) 36At + (0.49 -+ 0.07) X 10.4 cm 3 STP/g. However, least square fits for the breccias and the basalts separately yield: Breccias: 4°Ar = (0.65 -+ 0.07) 36At + (l.6 +- 0.2) X 10-4 cm 3 STP/g; Basalts: 4°Ar = (0.65 + 0.09) 36Ar + (0.47 -+ 0.10) X 10-4 cm 3 STP/g. Hence the breccias and the basaltic plot along straight lines (4°Ar vs 36Ar) with identical slopes, but the lines are separated by 1.1 × 10-4 cm 3 STP/g of 4°At. That breccia fragments of different gas contents fall along one curve can be explained by assuming that they were formed from identical parent fines, but that the median grain size varies from fragment-tofragment, i.e., that the most gas-rich breccias contain a larger proportion of very fine "dust". That grain size fractions from Apollo 11 and 14 fines fall along a straight-line 4°Ar-36Ar correlation has been previously demonstrated [15,4]. The increased 4°Ar intercept of the breccias does not appear to be due to systematically larger K contents of the breccias. Perhaps a°Ar was trapped from an ambient gasphase during the formation of the breccia (see also [11 ]).

4. Summary 1. On the basis of their trapped gas contents, twelve fragments and a "dust" sample from Luna 16 fall clearly into two groups: breccias (including a glassy cinder) and basalts (including the dust sample). The former contain about an order of magnitude more trapped gas than the latter. 2. There seems to be no clear-cut systematic difference in gas contents between breccias (or basalts)

405

in levels A (top) and G (bottom), but with the limited statistics this conclusion cannot be firm. 3. The breccias appear to be welded fines of local origin. 4. The breccias have distinctly lower 4He/2°Ne ratios (average 49) than the basaltic fragments (average 78). Apparently the formation of breccias is attended by a H e - N e fractionation. 5. Both the 36Ar/S4Kr (average 2500) and ~4Kr/ 132Xe (average 6.6) ratios in the Luna 16 particles are significantly greater than the corresponding values in 10084, but are similar to the values in 12070. 6. One breccia fragment, G-42-1, has a 4He/3He ratio of 1820, much smaller than the value of 2670 in bulk fines. It contains little if any cosmogenic 3Hec. 7. Exposure ages of five particles are typically a few hundred million years. 8. Breccias and basaltic fragments show identical 36Ar-4°Ar slopes, but the former contain about 1 X 10-4 cm 3 STP of volume-correlated 4°Ar which apparently was trapped from a gasphase when the breccias formed.

Acknowledgments We thank Dr. J.A. Wood for his help in the microprobe analysis at the Smithsonian Astrophysical Observatory. Dr. B.N. Powell has assisted with the mounting and polishing of the samples prior to their microprobe analysis. Mr. J.R. Walton has helped with the inert gas analysis. Supported by NASA grant NGL 44006-127.

References

[ 11 A.P. Vinogradov, Preliminary data on lunar ground brought to Earth by automatic probe "Luna-16", Proc. Apollo 12 Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 2, Vol. 1 (1971) 1. I2] D. Heymann and A. Yaniv, Inert gases in the tines from the Sea of Tranquillity, Proc. Apollo 11 Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 1, Vol. 2 (1971) 1247. [3] D. Heymann and A. Yaniv, Inert gases from Apollo ll and Apollo 12 fines: Reversals in the trends of relative element abundances, Earth Planet. Sci. Letters 10 ( 1971) 387. [4] D. Heymann and A. Yaniv, unpublished data from Apollo 14 fines.

406

D.Heymann et al., Inert gases in Luna 16 samples

[5] J.G. Funkhouser, O.A. Schaeffer, D.D. Bogard and J. Z~ihringer, Gas analysis of the lunar surface, Proc. Apollo 11 Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 1, Vol. 2 (1970) 1111. The breccias in question were considerably larger than our Luna 16 breccias. [6] U.B. Marvin, J.A. Wood, G.T. Taylor, J.B. Reid, Jr., B.N. Powell, J.S. Dickey, Jr. and J.F. Bower, Relative proportions and probable sources of rock fragments in the Apollo 12 soil samples, Proc. Apollo 12 Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 2, Vol. 2 (1971) 679. [71 J.A. Wood, J.B. Reid, Jr., J.G. Taylor and U.B. Marvin, Petrological character of the Luna 16 sample from Mare Fecunditatis, Meteoritics 6 (1971) 181. [8] C. Frondel, C. Klein, Jr. and J. Ito, Mineralogical and chemical data on Apollo 12 lunar fines, Proc. Apollo 12 Lunar Sci. Conf., Geochim. Cosmochim Acta, Suppl. 2, Vol. 1 (1971) 719. [9] P. Eberhardt, J. Geiss, H. Graf, N. Gr6gler, U. Kr~ihenbiihl, H. Schwaller, J. Schwarzmiiller and A. Stettler, Trapped solar wind noble gases, exposure age and K/Atage in Apollo 11 lunar fine material, Proc. Apollo 11 Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 1, Vol. 2 (1970) 1037. [ 10] T. Kirsten, J. Steinbrunn and J. Zahringer, Location and

[11]

[12]

[13]

[ 14]

[15]

variation of trapped rare gases in Apollo 12 lunar samples, Proc. Apollo 12 Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, Vol. 2 (1971) 1651. D. Heymann and A. Yaniv, Breccia 10065: Release of inert gases by vacuum crushing at room temperature, Proc. Apollo 12 Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, Vol. 2 (1971) 1681. J. Geiss, P. Eberhardt, F. B/ihler, J. Meister and P. Signer, Apollo 11 and 12 solar wind composition experiments: fluxes of He and Ne isotopes, J. Geophys. Res. 75 (1970) 5972. A. Yaniv, G.J. Taylor, S, Allen and D. Heymann, Stable rare gas isotopes produced by solar flares in single particles of Apollo 11 and Apollo 12 fines, Proc. Apollo 12 Lunar Sci. Cont., Geochim. Cosmochim. Acta, Suppl. 2, Vol. 2 (1971) 1705. D.D. Bogard, J.G. Funkhouser, O.A. Schaeffer and J. Z~thringer, Noble gas abundances in lunar material Cosmic ray spallation products and radiation ages fi-om the Sea of Tranquillity and the Ocean of Storms, J. Geophys. Res. 76 (1971) 2757. D. Heymann and A. Yaniv, 4°At anomaly in lunar samples from Apollo 11, Proc. Apollo 11 Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 1, Vol. 2 (1970) 1261.