Lunar polymict breccia 14321: a compositional study of its principal components

Lunar polymict breccia 14321: a compositional study of its principal components

Qeochimica etCoemochimics Acta, 1975, Vol.39,pp.247to 260. PergmonPress.Printedin Northern &eland Lunar polymict breccia 14321: a astir components A...

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Qeochimica etCoemochimics Acta, 1975, Vol.39,pp.247to 260. PergmonPress.Printedin Northern &eland

Lunar polymict breccia 14321: a astir components A. R. DUNCAN,*

S. M. MCKAY,

study of its principal

J. W. STOESER, M. M. LINDSTROM,

D. J. LXNDSTROM,

J. S. FBUCHTER and G. G. GOLES Center for Volcanology, University of Oregon, Eugene, Oregon 97403, U.S.A.

AbsttacdForty-nine sub-samples of the polymict breccia 14321,184 have been excavated from the rock and analysed by instrumental activation analysis tsohniques, specially modified to allow examination of small samples. Two distinct types of microbreccia claste were analysed. A maze-type basalt of unusual composition is present as several discrete clasts. Mixing models for the elastic components of the breccia illustrate that at least three stages of assembly may be distinguished on compositional grounds. The first was at a site such that EXEEP-rich materials dominated the elastic rocks formed, although a variety of lithio fragments were apparently present. The second assembly stage may have been primarily that of comminution and mixing of the more primitive materials, with addition of mare-type basalt clasts. The third stage saw addition of clasts of 14321-type basalt. In the 6nal assembly stage the light matrix was apparently formed entirely by mutual abrasion of the pre-existing clasts, resulting in little or no change in bulk composition.

concern of our lunar studies has been the examination of elastic mrtterials with the aim of beginning to decipher the complex history of impact excs,vation and brecciation, dispersal, mixing and reassembly into soils or breocias which these rn&~~~s record. In sample 14321,184 we were fortunate to have a brecuia which embodied a diverse ilrray of clasts, which was coherent enough so that good thin sections could be prepared from neighboring slices of the parent rook, and yet was friable enough so that we could extract s number of documented sub-samples with little or no contamination from other components of the breccia. Consequently, we now have much information on the history of this rock and on the different materials available for ~co~oration t~oughout its assembly history.

A MAJOR

SAMPIXNUPROCEDURES Sample 14321,184 was allocated to US as a consortium sample and was received as seven separate fragments weighing a total of approximately 76 g. The parent rock is a polymict breccia with 8 complex constructional history, and the identity of the various igneous and c&&c materials and their textural ~latio~llips could only be partially determined by microscopic examination of the fragment surfaces. Preliminary study of thin sections cut from adjacent portions of rock 14321 made it possible to provide petrographic characterization of the igneous and clastio materials which comprise the breccia as a whole (GRIEVE et al., 1976), and to categorize clast types in addition to those which were observed in hand-specimen. Unfortunately, it was not possible to match speoif?c clasts between thin sections and the fragment surfaces which were to be sampled because of the way in which the thin sections were prepared. The sub-samples removed from 14321,184 are of five different types; these are described below and illustrated in Fig. 1. Two different generations of miorobreceia cleats were sampled. * Present address: Department C. P., S. Africa.

of Geochemistry, University of Cape Town, Rondebosch, 247

,

A. R. DUNC~W et al.

248

The younger generation of sampled microbrecciaa (designated microbreccia-3) is the most common clast type in 14321,184 8nd appears as 8 medium-grey microbreccia with clast sizes up to several cm in greatest dimension. The older generation of microbrecci8s (designated microbreccia-2) occurs aa dark-colored cleats within microbreccia-3 clasts (see Fig. 1). These dark clasts are often rounded, generally have diameters of 8bout 1-2 mm, and occasionally have 8 core of 8 lithic or mineral fragment. The pale-grey matrix material (designated light matrix), which is texturally the youngest material in fragments of 14321,184, has an extremely inhomogeneous distribution. In some portions of the sample it comprises nearly 40 per cent of the exposed surface, whereas in other portions many cm2 of the surface showed no light matrix. It apparently consists of co mminuted mineral and lithic fragments with a few fragments of microbreccia up to O-6mm diameter. Basalt clasts were readily identified by their mineralogy and texture and were easily sampled. In addition to these four types of lithic material some of the larger fragments of plagioclaae and pyroxene present in the light matrix and in microhreccia-3 were also srtmpled. All sub-sampling of 14321,184 was performed in a clean-air work station, using stainless steel, tungsten and tantalum carbide tools. A photographic record of sub-sample locations was made and all sub-samples were fully documented. Owing to the variety of clast sizes present in 14321, our sub-samples range from 3 mg to several grams in mass. Some of the smaller clasts were removed from the rock in their entirety, whereas only portions were removed from many of the larger claets. In a few cases very small sub-samples of visually similar clasts were combined into composite samples. We believe we removed discrete materials from 14321 with little or no contamination from adjacent matrix or claats, snd this belief is generally supported by the compositional similarity between samples within each classification (see Tables l-3). Other 14321 clrtst types which have been recognized in thin section by GRIEVE et al. (1975), such &Bmicrobreccia-1, norite and microgranite, could not be identified with certainty in the fragments of 14321,184, and becense of their small size they clearly would have been impossible Table 1. Basaltic clasts Sample * wt. (mg)

Au%) Na K Be, La Ce Sm Eu Tb Yb Lu Th Hf Ta Fe(%) Ti(%) SC V Cr Mn co

1-B 149.33

1-F 19.12

1-G 31.59

12-A 78.65

17-A 111.69

37 24.89

45 86.95

46 6.21

6.33 3990 1100 19.0 56 10.8 I.34 2.34 6.5 1.15 2.3 7.7 1.2 12.7 1.21 54.6 92 3200 1710 34.3

7.31 4610 1460 22.2 70 13.5 1.41 2.29 7.0 1.19 3.4 8.4 1.2 12.5 1.42 54.8 94 2090 1710 29.3

7.73 4050 1300 20.1 68 10.9 1.39 2.11 6.5 1.20 5.2 7.6 12.6 1.28 52.8 124 2870 1680 32.8

6.83 4130 1130 20.3 66 11.6 1.38 2.49 6.6 1.70 1.7 8.0 1.4 12.9 1.21 55.4 92 3060 1730 32.0

6.39 3915 970 19.9 67 10.8 1.36 2.37 7-2 1.20 1.5 7.7 1.4 13.0 1.35 54.6 104 3300 1870 32.5

6.44 3020 9.6 39 5.9 1.00 1.10 4.5 0.78 3.0 4.6 12.5 1.54 49.0 126 3530 1850 30.8

6.06 3840 1490 19.8 59 10.0 1.36 2.00 7.0 1.25 2.5 7.5 1.3 12.7 1.34 55.7 97 3000 1800 33.6

7.33 4810 1260 25.0 99 14.5 2.11 9-o 1.51 11.8 13.0 1.74 59.4 2040 1750 27,3

* Samples are sub-samples of 14321,184 unless otherwise specified.

Lunar polymict

breccia 14321:

a compositional

study of its principal components

249

to extract even if identified. Our sub-samples represent what appear to be the most common types of materials comprising the breccia.

USAGEOF THE TERM ‘KREEP’ The term KREEP as originally defined and used (HUBBARD et al., 1971; MEYER et al., 1971) referred to a series of glass fragments, glass matrix breccias and annealed cataclastic breccias which had very similar major element compositions (low Fe, moderate Al, basaltic) and a distinctive enrichment in certain minor and trace elements (e.g. U, Th, K, Rb, Be, REE, P) relative to other lunar materials. Subsequent usage (e.g. HU~BARII et al., 1973) has applied the term KREEP to samples which, although showing similar compositional characteristics to the original KREEP, do so to quite different degrees relative to other lunar materials. We feel that grouping alI such materials as ‘KREEP’, in spite of their compositional diversity, will seriously devalue the usefulness of this term. Accordingly, throughout this paper we will use the term ‘KREEP-rich’ aa an adjective denoting relative enrichment in what can be termed the ‘KREEP characteristic’ or large-ion-lithophilic elements. Also, it is now very clear that there is no single rock type to which this term may be applied as an unambiguous label (DRARE et al., 1973), but it is still useful to call attention to compositional characteristics. ANALYTICAL

TECHNIQUES

A total of 49 sub-samples have been analysed by ‘instrumental neutron activation analysis (INAA) for 25 major, minor and trace elements. The INAA procedures of GORDON et al. (1968) were followed with the modifications described in GOLES et al. (1971) and LINDSTROMet d. (1972). In addition to these procedures, there was a separate experiment to determine Ti, Al, V and Mn from short-lived radioisotopes using the method described by Scwarrr et al. (1970). from breccia 14321

47-A 110.96

47-B 24.28

48-A 101.53

48-B 48.15

51 42.18

52 32.48

14321, 235-4 8.79

Representative c/o Error

6.41 3970 1740 230 18.6 66 10.8 1.38 2.13 6.1 1.10 2.3 8.1 I.2 12.8 1.34 56.4 105 2850 1800 31.4

6.82 4230 980 23.2 89 12.9 1.56 3.59 7.6 1.30 2.6 10.0 1.5 14.0 1.45 61.0 96 2730 1830 31.0

6.10 3570 1060 235 19.6 67 10.8 1.39 2.06 6.7 1.14 1.6 8.1 1.3 12.9 1.25 55.9 100 3030 1800 33.1

6.32 4500 1350 25.0 93 13.6 1.59 2.52 8.3 1.60 4.1 10.1 1.4 13.4 1.35 58.2 87 2920 1900 33.3

6.54 4120 2380 270 18.9 81 11.0 1.36 1.62 6.4 1.15 2.1 8.1 0.9 13.4 1.22 56.2 102 3240 1900 33.4

6.54 3960 1030 270 19.2 87 10.3 1.56 2.90 7.3 1.30 1.7 8.2 1.4 13.0 1.26 59.2 101 3030 1970 34.7

7.25 3940 2170 22.9 81 13.6 1.66 2.43 7.0 1.37 3.2 8.7 12.5 1.75 61.9 2430 1730 29.7

2 2 10 30 2 4 2 3 5 3 2 10 3 8 2 4 2 5 2 4 2

Abundances

are in ppm unless otherwise specified.

250

A. R.

DTJNCAN et aE. Table 2. Microbreccia

3

Sample*

-w%) Na K CS Ba La Cl3 Nd Sm Eu Tb Yb Lu Th Hf Zr z%) Tit%) SC v Cl. Mn co

14-A 59.90

16-A 52.71

19-A 65.19

30 28.99

33 15.94

8.89 6010 4300 0.54 1070 88.6 260 125 42.2 3.42 9.6 30.5 4.30 19.0 29.5 720 6.0 8.3 0.95 20.3 39 1280 870 39.0

8.40 6320 4800 0.30 1110 94.9 270 147 47.1 3.34 9.7 32-3 4.40 20.3 34.7 970 6.6 8.9 1.01 20.1 -

8.02 6050 3800 0.42 730 77.7 211 124 37.6 2.70 ‘7.6 25.5 3.50 15.4 24.1 820 6.0 9.6 1.24 29.6 56 1620 1220 37.9

8.77 5590 3320

4880 3360

* Samples

1280 1050 45.9

are clasts from 14321,184

760 78.1 220 34.9 2.93 7.2 23.5 3.60 18.4 25.6 860 4.1 8.3 1.07 21.1 39 1150 1030 32.5

580 26.8 82 14.3 2.05 2.7 8.5 1.48 6.9 10.2 1.8 6.5 0.81 17.4 960 890 20.5

34 42.48 7.76 -

1140 268 -

35-A 73wl

35-B 67.00

35-c 66.75

8.56 6780 3800

6050 5000

7.93 6170 7930

1110 101 276 -

-

-

1340 87.8 271 -

1220 96.2 757 -

41.1 4.57 35.0 4.87 35.0

39.7 3.20 9.0 31.9 4.90 25.2 35.3

3.18 8.9 33.0 4.51 23.3 32.3 1010 4.9 8.9 1.06 20.4 32

46.3 3.44 9.3 33.3 4.79 24.7 35.2 1080 5.2 8.5 1.08 19.3 -

1330 6.7 9.9 25.3 -

1110 5.4 8.7 0.93 19.4 -

1120 1100 38.2

990 1030 41.2

1260 36.4

1000 1075 39.3

unless otherwise specified.

COMPOSITIOXAL

COMPARISONS

Basal ts

We present analytical data for 15 basaltic sub-samples from 14321,184 and 14321,235 in Table 1. Fourteen of the 15 basalt samples are similar in composition and, bearing in mind the size of the samples analyzed (9-150 mg), we do not propose to sub-divide them on a compositional basis. It is not certain how many discrete basalt clasts in 14321 are represented by this main group of sub-samples, because our block of 14321 evidently broke up into a number of pieces while being sawed, and we are not sure of the relationships among basalt clasts that existed prior to that fragmentation. However, it is clear from our documented sampling that at least 3 discrete basalt clasts of this compositional type were present in 14321,184, with one of these possibly being a single’ large clast weighing approximately 20 g. These basalt samples are compositionally quite distinct from other lunar basalts so far analysed, and for convenience of discussion will hereafter be referred to as ‘l&321-type basalt.’ This 14321-type basalt is characterized by greater abundances of Al, alkalies and REE ; and lesser abundances of Fe, Ti and Mn than those in the Apollo 11, Apollo 12, Apollo 15, Apollo 17 and Luna 16 basal&. Its Na, Ba and REE abundances are rather similar to those in the high-K group of Apollo 11

Lunar polymict breccia 14321: a compositional study of its principal components

251

clasts from breccia 14321

35-D 98.15

40 98.63

41 14.53

43 86.19

7.90 6020 -

7.67 5740 4460 1.1 850 56.2 173 88 25.2 2.13 6.3 18.5 2.65 13.8 21.8 630 3.7 8.0 0.70 17.4 37 1450 900 37.2

8.60 6230 3920 -

7.93 6430 3620 1.2 1120 101 303 135 44.5 3.24 11.1 33.0 4.52 23-3 34.2 1100 6.1 8.9 1.15 20.6 29 2580 1100 35.5

1110 92.7 260 37.0 3.10 8.5 30.6 4.50 20.7 31.2 820 5.1 9.1 I.08 21.8 35 1140 1130 37.7

1110 92.7 275 162 43.0 3.34 9.2 32.2 4.83 21.4 54.9 1610 5.9 8.8 1.26 22.1 37 1260 1180 33.7

50 15.21

53 39.80

7.82 8.20 6960 6660 11500 4370 2.0 1430 1080 83.9 79.9 213 250 120 97 34.8 42.3 3.13 3.02 7.9 9.6 29.5 29.0 3.29 3.50 19.1 21.3 30.6 27.9 840 790 5.0 5.2 7.1 8.5 1.11 0.89 20.7 16.4 22 1380 950 1100 1000 34.5 34.7

14321, 236-l 23.07

14321, 235-2 12-61

Represen-

8.67 6670 4790 -

8.67 6650 5260 -

1090 101 256 -

1130 102 273 37.6 3.32 8.8 31.8 4x56 23.2 32.4 1070 5.1 8.0 0.97 17.8 920 950 34.7

2 2 10 6-30 5 2 3 10 2 3 4 3 2 5 2 5 4 2 5 2 8 2 5 2

49.0 3.63 9.4 32.5 4.82 24.3 34.1 920 5.6 8.4 1.12 19.7 32 1000 1020 37.3

tative

O/OError

Abundancesare in ppm unlessotherwisespecified. basslts, but it has markedly lower Fe, Ti and K abundances, and higher Al &bundances than do the high-K basalts. The 14321-type basalt has major element composition similar to some other Apollo 14 basalts (14053, 14072) but has almost twice their concentrations of KREEP-characteristic elements. This distinctive basalt type has been found as olasts in four separate portions of 14321: data for clasts from 14321,184 and 14321,235 are reported here; TAYLOR et al. (1972) and WXNKE et al. (1972) report data from essentially identical basalt clasts in 14321,8& and 14321,223, respectively. No basalts having these major and trace element characteristics have yet been reported either from other Apollo 14 breccias or from other Apollo sites. The closest comparisons for major element compositions are the Mare-l glasses from Apollo 15 soils (REID et al., 1972) and Fecunditatis A glasses from Luna 16 regolith (JAKES et al., 1972), but in both cases these glasses contain significantly less Na,O and K,O than does 14321-type basalt, suggesting that they are more comparable to 14072 and 14053 basalts. In spite of the relative scarcity of 14321-type basalt, it is clear from its low concentrations of meteoritic trace elements (MORGANet al., 1976) that the basalt represents a definite magma type, and is not merely a surficial impact melt (cf. 14310). We conclude that 14321type basalts are unlikely to be widespread in the equatorial portions of the near side of the Moon.

252

A. R. DUNCAN et al. Table 3. Miscellaneouselastic Microbreccia 2

Light matrix

Sample* 15 78.53

-w%n) .-. Na K

cs Ba La Ce Nd Sm Eu Tb Yb LU Th Hf Zr Ts Fe(%) Ti(%) SC V Cr Mn co

36 7.68

39 14.15

42 Il.54

8.07 lO*OO 6.42 8.66 7090 6560 6130 4180 5870 7970 3220 1250 1.29 2.6 1140 1110 800 85.5 112.0 97.1
49 2.94 14.20 11600 3500 600 60.7 197 27.2 7.07 7.1 18.8 3.00 14.4 21.7 850 2.8 4.5 11.4 580 520 15.0

9-A 78.28

9-B 38.80

10-X 95.01

13 27.00

7.02 6.55 7.80 7.46 4430 5300 4630 5180 1450 1990 2560 590 560 600 27.3 58.2 35.6 51.0 83 172 119 138 55 16.8 23.7 14.7 26.4 1.55 2.23 1.74 1.96 3.1 5.5 3.7 4.6 9.3 185 10.5 15.8 1.60 1.85 2.30 2.82 12.2 6.2 9.2 3.6 18.0 12.3 18.1 9.8 1.9 3.4 2.6 12.0 10.1 11.7 10.0 1.36 1.37 1.41 1.25 34.9 44.7 38.9 52.8 104 69 85 86 2920 1630 2800 2160 1660 1560 1600 1480 33.2 “8.1 50.1 33.4

* Samples are sub-samples of 14321,184 unless otherwise specified.

Clmtic

materials

The elastic materials which we have been able to sample meaningfully from breccia 14321 are microbreccia-2, microbreccia-3 and the late-stage light matrix. Compositional data for these materials are presented in Tables 2 and 3, and their compositional relationships are expressed visually in a pair of Fe-alkali-La ternary diagrams (Figs. 2a and 2b). Fe, alkalies and La were chosen as the apex constituents of these ternary diagrams because variations in abundances of these elements serve as an effective discriminant between the different igneous and elastic materials comprising breccia 14321. Microbreccia-2 materials are the oldest elastic material that we have sampled from breccia 14321. All the microbreccia-2 clasts that were examined in thin section consist of a dark-colored matrix material of CREEP-rich composition (GRIEVE et aE., 1975), together with a few small mineral fragments, and are often cored by lithic fragments or large fragments of a single mineral such as plagioclase or olivine. Their petrographic variability is clearly reflected in the compositional variability shown in Table 3. This compositional variability is related to the types

Lunar polymict brcccis 14321: a compositional study of its principal components

253

materials from breccia 14321 Light matrix

24-A 61.66

7.19 4880

49.8 155 22.0 2.08 4.9 13.5 2.35 10.0 16.4 2.6 10.8 1.27 37.9 73 1950 1500 23.5

24-B 64.70

38 29.15

44 30.90

7.10 6.40 668 4800 3960 4890 2300 2620 2360

Composite dusts

54 18.52

14321, 235-3 20.84

14321, 286 1276.70

6.95 7.42 5050 4800 4940 2530 2800 470 640 470 620 710 49.0 51.5 33-7 53.7 41.3 49.2 152 132 103 129 136 157 77 23.1 25.0 17.3 24.8 24.3 26.7 1.83 2.07 1.58 2.06 2.19 2.17 3.9 3.4 5.8 4.6 5.1 17.0 16.3 11.9 18.6 14.0 16.5 2.70 2.40 1.96 2.72 2.19 2.60 10.6 6.5 11.3 8.8 10.9 16.4 17.3 13.0 21.5 15.5 18.0 376 990 470 2.6 3.3 2.0 2.9 2.5 2.8 11.3 10.2 13.2 10.5 11.5 11.0 l-13 1.47 1.04 1.13 1.11 49.0 34.5 37.5 38.7 36.0 38.6 78 73 86 57 84 1930 1980 2760 1990 2250 1880 1870 1500 1660 1600 1450 41.7 33.6 31.5 30.4 35.3 316

14321, 184 Dust-l 94.54

14321, 184 RepresentDust-3 ative 81.69 o/0error

7.27 4740 4800 2620 1050 480 49.5 46.5 164 120 86 76 22.0 22.7 2.21 1.94 16.1 14.5 2.25 2.26 11.2 23.3 17.6 680 640 3.3 3.2 10.6 105 1.14 39.1 39.8 70 2130 2120 1440 34.2 335

2 2 10 5-10 5-10 2 3 10 2 3 4 3 2 5 3 5-15 4 2 5 2 8 2 6 2

and proportions of lit&c and mineral fragments present in the individual subsamples Two of the samples, 14321,184-15 and -42, are distinguished by high K (8000 and 6000 ppm, respectively) and high REE contents (see Table 3). These two KR$EEP-rich microbreccias contsin higher abundances of many KREEP characteristic elements than do the previously reported materials of this type (MEYER et al., 1971). It is very probable that these clasts are cored by norite or noritic microbreccia-1. The limited compositional data for 14321,184-39 indicate that this sample of microbreccia-2 is dominated by a basaltic fragment, probably similar in composition to the Apollo 12 type of mare basalts. Examination of 14321,184-49 revealed abundant fragments of plagioclase, and indeed the composition of this sample indicates that it is dominated by an anorthositic component. Sample 14321,184-36 is very similar in composition to many of the clasts of microbreccia-3 which are discussed below. Microbreccia-3 samples are generally less variable in composition than are microbreccia-2 samples (Table 2) and are dominated by a KREEP-rich component.

254

A. R. DTJWXX et al.

Fig.

Fe

20

Fig. 2b

Fe

Other

Lunar

Materials

Alk

Fig. 2. Fe-alkali-La diagrams for components of 14321 and for other lunar materials. Note particularly that the light matrix samples are compositionally intermediate between the basalts and the bulk of microbreccia-3 samples, and that many microbreccia-2 and -3 samples are obviously KREEP-rich. 11-I and 1 l-2 are average analyses for the two groups of Apollo 11 basalta, 12-1 and 12-2 are average analyses for the two groups of Apollo 12 basalts.

The comparatively small degree of compositional variability shown by the bulk of these samples apparently reflects more efficient mixing and comminution of preexisting materials, or less variable source materials, than was the case for the formation of microbreccia-2. Most of the samples of microbreccia-3 are compositionally very similar to samples of the dark microbreccia from rock 12013. Quantitative estimates of the proportion of KREEP-rich component in microbreccia-3 will be discussed in a later section, but in general it is around 70 per cent. The light matrix material, which is the youngest textural element in breccia 14321, is intermediate in composition between the basalt fragments and the most common group of microbreccia-3 compositions (Table 3 and Fig. 2). Quantitative arguments for postulating that this material was produced by mutual abrasion of

255

Lunar polymict breech 14321: a compositional study of its principal components

the major clast types in 14321 (mainly basalt and microbreccia-3) will be discussed in a later section. Mrxr~o MODELS FOR CYSTIC MATEEIALS Estimates of the proportions of the major types of igneous and meteoritic materials in the lunar soils have been made by calculating compositional mixing models et al., 1972; SCHONFELD and MEYER, 1972). (e.g. GOLESet al., 1971; LINDSTROM This technique for interpreting the composition of a soil in terms of a set of analysed components can be extended to the study of ahy elastic system whose composition is determined by a physical mixture of components. We present here the results of such calculated mixing models for a suite of elastic materials (both microbreccia-3 and light matrix) from breccia 1432 1. Examination of thin sections of breccia 14321 and a preliminary study of the compositional data for sub-samples {Table l-3) suggest that there are four major types of ‘prilmary’ components which together comprise the bulk of elastic materials in this rock. These four types are mare-type basalts, IiREEP-rich material, anorthosite and anorthositic gabbro and a meteoritic component. Within each component-type there are a number of individual and average compositions from which to choose a representative analysis and this range of choices necessitated calculation of about 200 mixing models to derive the set of 22 best mixing models presented in Tables 4 and 5. The models presented are those which gave the lowest residuals (sum of squares of differences between observed and calculated Ta,ble 4. Calculated mixing models for microbreccia-3 samples 14::51,184--14A OSS. Calc. _...~ -.-- (Fe?& &, Cr Mn CO

a(%) Na K L& Ce Sm &I

Yb Lu

8.3

8.2

20.3 1.0 1280 870

20.5 1.0 1170 1040

39.0 8.9 6010 4300 886 260 42.2 3.4 30.5 4.3

Basalts 14053* 14070* * Auorthosite KREEP 14321,184-15 14321,184-42 14321,184.36 Average CC-1

38.8 8.8 6200 6130 87,s 246 42.4 2.9 27.9 3.8 4.2 7.7 51-8 33.3 3.0

14321,184-16A C&k. Obs.

8-9 20-l 1.0 X280 1050

45.9 8.4 6320 4800 94.9 270 47.1 3.3 32.3 4.4

8.6 20.6 1.0 1170 1080

45.8 8.3 6540 6350 95-o 270 45.8 3.0 29.7 4.1

14321,184-30 Obs. Calc.

8.3 21-l 1.1 1150 1170

32.5 8.8 5590 3320 78.1 214 34.9 2.9 235 3.6

14321,184-50 Obs. Calo.

14321,184-41 Obs. C&.

8.3

8.5

8.5

8.8

8.7

22-o 1.0 1300 1100

20.7 1.1 1380 1100

22.6 I.0 1350 1100

22.1 1.3 1260 1180

22.4 1.1 1250 1120

34.1 9.5 5650 4060 76.0 226 367 2.3 22.4 3.2

Mixing coefihients 1.7 15.3 2.9 14.6 46.5 44‘4 66-9 4.5

* Data from COXPSTON etal. (1972), TAYLOR etal. (1972).

3.3

34.5 36.6 7.8 8.1 5660 6080 10600 7040 79.9 86.5 209 229 42.3 41.4 3.1 3-O 29.5 28.8 3.3 3.9 -

33.7 8.5 6230 3920 92.7 270 43.0 3.3 32.2 4.8

33.8 8.4 6370 5830 93.2 268 44.9 2.9 28.6 4.0 -

8.0 3.2 87.5 -

7.4 3.4 31-7 55.3 -

1.3

2.2

Fe% So Ti% Cr Mn

Co Al% Nrt K 1L8

Ce

Sm

Eu Yb Lu

256

A. R. DTJNCAPI‘ et al.

Table 4. (cuwtinwd). 14321,184-36~ Obs. talc. 9-l 21.7 1‘I 1140 1130 37.7 7.9 6020 92.7 248 37.0 3.1 30.6 4*5

8.4 22.2 1.0 1250 1080 38.7 8.1 6310 -

14063 14072 Anorthosite KREEP 14321,184-15 14321,184-42 1432X,184-36 Average CC- 1

4.5 -

Fe(%) .

F&g) CF Mn

CO

W%) Na H La

Ce

sm Eu Yb Lu l&s&&

89.7 240 43.4 3.2 30.2 4.0

14321,184-f9A C&k!. Obe. 9.6 29.6 1*2 1620 1220 37.9 8.0 6050 3800 77-1 211 37.6 2.7 26.5 3.5

14321,184-35A Ubs. Calc.

9.9 30.0 1.3 1550 1340 38.0 8.1 5830 4140 77.5 230 37.4 2-4 23.2 3.3 Mixing 28.1 -

14321,235-l Ohs. Calc.

8.5 8.3 19-I I-1 990 1030 41.2 40.9 8.6 8.7 6640 6780 5970 3800 101 97.9 276 284 46.3 47.2 2.9 3.4 33.3 29.7 4.5. 4.8 coeffioients -

8.4 19.7 1.2 1000 1020 37.2 8.7 6670 4790 101 274 49.0 3.5 32.5 4.8

8.4 20.2 1.2 1050 1060 37.2 8.7 6790 5610 102 302 49.2 2.9 30.0 4.9

14321,184-35c Calo. Ohs. 8.7 19-2 0.9 1000 1080 39.3 7.9 6170 7930 96.2 265 3=2 31.9 4.9

8.3 20-7 1.0 1190 1030 39-9 8.1 6470 7690 93.6 251 3.2 31.4 4.2

-

-

1.9 $I*8 -

2.3 65.9 -

4.7 28+4 62.8 -

4.0 8.0 84.3 -

1.6 96.4 -

1.8

3.7

4.x

3.7

2.0

14321,184.43 Obs. F%(%

&%I Cr Mk co Al(%) Na K La Ce $ k: Yb LU

Bssalts

8.9

20.6 I.2 I.100 35.5 7+9 6430 3620 101 295 44‘5 3.2 33-o 4.5

14053 14072 Anorthosite KREEP 14321,184-15 14321,184.42 14321,194-36 Average CC-1

talc.

AVMB Ohs.

C&k?.

8.9 8.7 8.7 21.7 20‘9 22.0 1.2 1.1 1.1 1290 1240 1140 1030 1120 37.2 37.5 38.0 8.6 8.3 8*5 6800 6220 6400 5270 5100 6660 103 92.2 93.1 303 255 270 49.7 41.8 44.9 2.9 3.2 2.8 29-9 30.7 28.3 4.3 4.4 s 3.9 &fixing co&icients 2-l 6.8 3.8 25.4 81.7 60.7 12.7 3.5 3‘3

Fe% SC Tioj, Cr Mn co AI?& N& K La Ce Sm Eu Yb Lu

Fe% SC Ti% Cr &l.n co Al% Xa K La Ce Sm Eu Yb Lu

257

Luna.r polymict breccia 14321: a compositions study of its principal components

compositions) for the m~mum reasonable set of components and for which all mixing coetXcients are positive in sign. Calcula~d mixing models for 11 separa~ microbreccia-3 clasts, and for an average of ail 15 analysed microbreccia-3 olasts (designated AVMB), are given in Table 4. All of these mixing models contain a KREEP-rich component (14321, 184-15 and/or 14321,184-42), an anorthositic component (15415) and a chondritic component (average CC-l), Of these three components the KREEP-rich one is always dominant in the mixing models, constituting from 66 to 96 per cent of the miorobreccia-3 samples. It was necessary to utilize more than one KRE~P-rich component since the microbrecoia-3 samples have variable K/REE ratios. The two KREEP-ricth compositions we have used as components have markedly different K abundances and KfREE ratios, Sample 14321,184-43 has such a low K/REE ratio that no really satisfactory mixing model could be calculated ; the model given for this sample utilized 14321,184-36 (a KB,EEP-rich microb~~cia-2) as a component since it had the lowest KK/REE ratio of any of our analysed KREEP-rich materials. Most of the ~crobreccia-3 samples require a mare-type basalt as a component, although three of them (14321,184-358, 35C and 14321,235-l) give better calculated mixing models when this ~mponent is excluded. It is no~wo~hy that better mixing models for microbrecoia-3 result from using 14072 and 14053 as the basaltic component than from using AVBAS (the average 14321~type basalt). ~~STROM et al. (1972) concluded that 14072-type basalt is the dominant basaltic component Table 5. Calculated mixing models for light matrix samples 14321,[email protected] Obs. Cak?.

W%)

12.0

52.8 1.4 2920 1660 33.2 7.0 4430 1450 27.3 82.0 147 1.6 9-3 1+

SC

Tit%) Cr Mn CO

Alto/,\ IN& K La Ce Sm EU YIJ Lu

125 52.2 l-3 2730 1720 32.6 6.9 4240 1633 269 87.7 14.2 1.6 9.0 1.5

14321,184-13 Obs. Cale. 10~0 38Q l-3 2160 1480 33*4 7-8 5180 2560 51.0 138 23.7 2.0 158 2.3

10.7 38.9 1.2 2110 1430 33.2 7.9 4890 2820 49.3 144 235 2.2 16.4 2.5

14321,184-24B ObS. C&k.

14321,184~54 14321,18.&34X Ohs. C&x Obs. C81C.

11.0 386 1-l 1880 1920 316 7.1 4800 2360 49.2 142 267 2.2 165 2.6

11.5 37.5 1.1 2230 1650 35.3 7.0 5050 41.3 133 24.3 2.2 X4.0 2.2

11.7 40.7 l-2 2200 1480 34.4 7.4 4960 2900 50.8 149 24.3 2.2 16.9 2-6

11.4 41.3 l-2 2230 lGO0 34.3 7.4 4930 49.8 146 23.9 2.2 16-6 2.5

10.8 37.5 1.3 1950 1940 295 7-2 4880 49.8 142 22.0 2.1 13*5 2.4

11.2 39-3 f-4 2100 lb70 30.6 7.5 4600 48.9 136 22.5 2-l 17.3 2.5

Mixing [email protected] Basalt AVBAS 14053 Anorthositic (AI%) gabbro* Microbreceia-3 AVMB 14321,184-19A 14321,184.33 Average CC- 1 * D&a from 3

FAKITA

53.7 5.0

57.0 -

-

41.3 -

42.3 -

-

-

-

90.0 I.0

9.0

0.7

and SCHMITT(1970), WOOD et GE.(1970).

58.5 0.7

40-8

-

64.1 05

45.4 -

BeYe SC Ti% Cr M.n Co Al% Na K La Ce Sm Eu Yb Lu

A. R. DUND~

258

et d.

Table 5. (cosatiplued). 14321,184-9B Ohs. Cdch IO-1 33.8 1.4 -1630 1560 28.1 7.5 5300 1990 58.2 160 26.4 2.2 18.5 2.8

W%) SC Ti(%) Cr xn co Al(%) Na 11: La Ce Sm EU Yb

Lu

10.3 33.2 1.3 1830 1400 32-o 8.0 5010 3400 60.1 166 27.5 2.4 20.7 2.9

14321,X$4-38 Ohs. Cdc. 13.2 48.9 l-5 2760 1870 31.5 6.4 3960 2300 33.7 96.0 17.3 1.6 11.9 2.0

12.2 49.4 1.3 2600 1670 334 7.0 4460 2010 34.0 106 17.2 1.8 11.3 1.9

14321,184.10A Ohs, C&h. 11.7 44.7 l-2 2800 1600 50.1 6.6 4630 35.6 105 16.8 I.7 IO.5 l-9

12.3 47.2 I.2 2570 1660 50.7 6.8 4520 33.8 105 17.0 1.8 1193 1.8

l4321,235-3 Obs. Calc.

14321,184.44 Calo. Oba

11.3 38.6 1.1 1930 1600 41.7

11.0 38.9 1.2 2150 1460 42.7

10.5 34.5 1.0 1990 1500 30.4

10.0 36.2 1.2 1940 1330 33.1

Fe% SC Ti% Cr Mn co

7.4 4800 2530 49.0 138 23-l 1.8 17.0 2.7

7.5 4950 2840 49.6 145 23.7 2.2 16.5 2.5

4980 2620 53.7 126 24.8 2.1 18.6 2.7

5090 2660 51-3 145 25.4 2.1 16.9 2.4

Al% P;a K La Ce Sm Eu Yb Lu

Mixing ooeEcients Basalt AVBAS 14053 Anorthositic (ANG) ge;bbro Microbreccia-3 AVMB 14321,184-19A 14321,184-33 Average CC- 1

37.4 2.7

81.4 -

59.9 -

18.6 -

76.8 -

-

-

53.5 -

33.5 -

2.8

8.3

19.3 -

41.7 -

3.9

2.0

-

56.2 2.0 -

the soils, and thus is likely to be the dominant basaltic component in the whole of the exposed Fra Xauro formation at this site. We infer from our mixing models for miorobreccia-3 that ~4072~14053-tie basalt was the do~n~nt bassIt type in the early stages of 14321 assembly, and that 14321~type basalt has only been added to the breccia mixing system at a relatively late stage. Calculated mixing models for 10 samples of the light matrix ma;terial are given in Table 5. As discussed Etbove, the light matrix is the youngest textural element in 14321, and to s, first approximation is intermediate in composition between fn almost all csses good mixing models 1432f-type basalt and mic~breccia-3. can be calculated using AVBAS, AV&f$I and anorthositic galbbro (ANG) as components, a fact which strongly suggests that the light matrix has been formed by mutual abrasion of the major clast types in 14321. Basalt (AVBAS) is nearly always the dominant component as would be expected from the friable nature of 14321~type basalt relative to microbreccia-3. In most cases the mixing models suggest that addition of a meteoritic component, other than that included in microbreccia-3, has not occurred during the formation of the matrix. This observation indicates that the matrix material is very unlikely to be pre-existing lunar regolith similar to that sampled by the Apollo missions. For two of the samples it w&s found that 14053 gave more ~tisfac~~ models than did AVBAS, and for sample 14321,184-44 in

Lunar polymict breccia 14321: a compositional study of its principal components

it was necessary to use specific microbreccia-3 average microbreccia-3 (AVMB).

components,

259

rather than the

CoNcLusIoNs

We have shown that carefully controlled sampling of materials from a suitable breccia, followed by detailed analyses of the sub-samples, can provide useful information not only on the assembly history of the breccia itself but also on changes in availability of various fragmental materials at the sites where the breccia was assembled. Breccia 14321 began to be assembled at a site and time such that KREEP-rich materials, diluted by minor amounts of a variety of lithic fragments, predominated in the early mixtures (microbreccias-1 and 2). Subsequent stages of assembly took place at a site and time such that mare-type basalt similar to that which appears to be common in Fra Mauro soils was added in significant amounts (microbreccia-3). During the latest stage or stages of assembly, clasts of the compositionally unusual 1432?-type basalt were added. We do not know whether these contrasts primarily reflect changes in the location of the sites where assembly of the components of this rock was in progress, or changes in the availability of raw materials. The proportions of KREEP-rich materials incorporated decreased relative to those of mare basalts as the assembly of this rock progressed. If this trend is related to changes in assembly sites, one would not expect it to be generally observed in breccias from this region of the lunar surface. If it is related instead to a large-scale change in the relative area of mare basalts exposed in this region, it might well be generally observed in such breccias. Further studies on carefully selected specimens in an attempt to assess which of these two possibilities is the more probable are clearly called for. Additional discussion and interpretation concerning data from this paper and from GRIEVEet al. (1975) are given in DUNCANet al. (1975). Acknowledg?nents-We gratefully acknowledge the assistance of LADRENDown who developed additional computer programs for our data reduction and SHELHIYSALESwho typed drafts of the manuscript. This work was supported by NASA grant NGL 38-003-024. REFERENCES COX~PSTON W., VERNONM. M., BERRY H., RUDOWSKIR., GRAY C. M. and WARE N. (1972) Age and petrogenesisof Apollo 14 basalts. In Lzr.narScience-III, (editor C. Watkins), p. 151. Lunar Sci. Inst. Contrib. 88. DR.M. J., STOESERJ. W. and GOLESG. G. (1973) A unified approach to a fragmental problem: petrological and geochemical studies of lithic fragments from Apollo 15 soils. Earth Pla7,et. Sci. Lett. 20, 425-439. DC-NCANA. R., GRIEVER. A. and WEILL D. F. (1975) The life and times of Big Bertha: lunar brecoia 14321. Geochim. Cosmochim. Acta 89, 265-273. GOLESG. G., DUNCANA. R., LINSXTROM D. J., MARTINRI. R., BEYERR. L., OSAWAM., RANDLE Ii., MEEK L. T., STEIXFJORN T. L. and MCKAY S. M. (1971) Analyses of Apollo 12 specimens: composit.ionalvariations, differentiation processes and lunar soil mixing models. Proc. 2nd Lunar Conf., Geochim. Cosmmhin~ Acta Suppl. 2, p. 1063. M.I.T. Press. GORDONG. E., RANDLEIi., GOLESG. G., CORLISS J. B., BEESONM. H. and O~LEY S. S. (1966) Instrumental act,iration analysis of standard rocks with high-resolution y-ray detectors. GeocXnz. Cosmochim. Acta 32, 369-396.

260

A. R. DUNCAN et al.

GRIEVE R. A., MCKAY G. A., SXITH H. D. and WEILL D. F. (1975) Lunar polymict breccia 14321: a petrographic study. Geochim. Cosmochim. Acta. 39, 229-245. HUBBARD N. J., MEYERC. JR., GAST P. W. and WIESMANN H. (1971) The composition and derivation of Apollo 12 soils. Earth. Planet. Sci. Lett. 10, 341-350. HUBB~D N. J., RHODES J. M., GAST P. W., BONSAI B. M., SHIH C. Y., WIESX&&;NH. and NYQUIST L. E. (1973) Lunar rock types: the role of plagioclase in non-mare and highlund rock types. Proc. 4th Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 4, Vol. 2, pp. 12971312. Pergamon Press. JAKE&P., W.QZNERJ., RIDLEY W. I., REID -4. M., HARMONR. S., BRETT R. and BROWN R. W. Petrology of a portion of the Mare Fecunditatis regolith. Earth Planet. Sci. Lett. 13, 257-271. LINDSTRO~X M. M., DUNCAN A. R., FRUCHTERJ. S., MCKAY S. M., STOESERJ. W., GOLES G. G. and LINDSTROMD. J. (1972) Compositional characteristics of some Apollo 14 elastic matf:,ials. Proc. 3rd Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 3, pp. 1201-1214. M.I.T. Press. MEYER C., BRETT R., HUBBARD N. J., MORRISOND. A., MCKAY D. S., AITKEN F. Ii., TSKEDA H. and SCHONIPELD E. (1971) Mineralogy, chemistry and origin of the KREEP component in soil samples from the Ocean of Storms. Proc. 2nd Lunar Sci. Conf. Geochim. Cosmochim. Acta Suppl. 2, p. 393. M.I.T. Press. MORGAN J. W., GANAPATEY R., KR~~HENB~?HL V. and ANDER~ E. (1975) Meteoritic trace elements in lunar rock 14321,184. Geochim. Cosmochim. Acta 39, 261-264. REID A. M., WARNER J., RIDLEY W. I. and BROWN R. W. (1972) Major element composition of glasses in three Apollo 15 soils. Meteor&x 7, 395-415. SCHWTT R. A., LINN T. A. and WAKITA H. (1970) The determinations of fourteen common elements in rocks via sequential instrumental activation analysis. Radiochim. Acta 13, 200. SCHON~LD E. and MEYER C. (1972) Component abundance and age of the lunar soils by a least-squares mixing model. Proc. 3rd Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 3, pp. 1397-1420. M.I.T. Press. TAYLOR S. R., KAYE M., MUIR P., NANCE W., RUDOWSKI R. and Wm N. (1972) Composition of the lunar uplands: I. Chemistry of Apollo 14 samples from Fra Mauro. Proc. 3rd Lunar Sci. Conf., Geochim. Cosmochim. Acta Suppl. 3, pp. 1231-1249. M.I.T. Press. WHNKE H., BADDENHAWEN H., BALACESCUA., TESCHKEF., SPETTELB., DRAIBUS G., QUIJANO M., KRUSE H., WLOTZXAF. and BEGEMANNF. (1972) Multi-element analyses of lunar samples. In Lunar Science-III (editor C. Watkins), p. 779. Lunar Sci. Inst. Contrib. 88. WXITA H. and SCHMITT R. A. (1970) Lunar anorthosites: rare earth and other elemental abundances. Science 170,969. WOOD J. A., DICKEY J. S., MARTIN U. B. and POWELL B. M. (1970) Lunar anorthosites and a geophysical model of the moon. Proc. Apollo 11 Lunar Sci. Conf., Geochk Cosmochim. Acta Suppl. 1, p. 965. Pergamon Press.