Don’t miss our talks on siderophiles in brecciated lunar meteorites ( )and lunar cumulate impact melts ( ) on !

abstract # 2013abstract #2061 Thursday afternoon

spherules (n=3)glasses & vitrophyres (n=3)regolith nuggets (n=3)

very fine-grained intergranular melt (n=2)proto-poikilitic melt (n=5)

medium cumulate melt (n=8)

Fig. 7 Compositions of metal particles compared to metal particles in endogenous lunar rocks.Dunite 72415 and 72417 metal particles after [ ] and [10], confidence class for pristinity (CCP) - 9 ;

spinel troctolite 67435 after [13] - CCP ; “feldspathic lherzolite”(an olivine gabbro norite) 67667 [14] - CCP 7 (confidently pristine [11]); troctolite clast in73235 [14] - CCP ; n ield for Apollo 17 basalts after [17]; metal particle in the olivine cumulate ofNWA 733 after [18]; green line represents the “cosmic trend” of Ni:Co concentrations of 20:1 in chondrites; green f

Shi r 1614 (confidently pristine [after 11]) troctolite 76535 taenite after

[12], CCP - 9 [11], note that this rock also contains high-Co kamacite; 8 (confidently pristine [11])

4 (doubtful pristinity [11]) orite 78527 after [16] - CCP 4 [14]; fields indicate compositional ranges of

kamacite in equilibrated H, L and LL chondrites after [6, 19]. Orange lines encircle data from the same clasts.

ş

troctolite clast in 60035 after [15] - CCP 6 (pristine with caution [14]);

All Shi r 161 data normalized to 100 wt%.ş

LL

L

H

Apollo 17marebasalts

feldspathiclherzolite

67667

spinel troctolite67435

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20 25

Ni (wt%)

Co

(w

t%)

30 35 40 45 50 55 60

3.5

4.0

troctolite clast73235,136

olivinecumulateNWA 733troctolite

60035

norite 78527

dunite 72415 & 72417 [4-10]

100 mμ100 mμ

AcknowledgmentsA. J. Irving (University of Washington) for the samples, D. A. Kring (LPI Houston) foranalytical support, P. Carpenter & A. Foreman (Washington University St. Louis) forEMPA support and preliminary data, R. Zeigler (Nasa-JSC Houston) for preliminary data.We appreciate funding from NASA grant NNX11AJ66G.

INTRODUCTION

Iron-Nickel(-Cobalt) Metal in Lunar Rocks RevisitedAxel Wittmann and Randy Korotev

Iron-Nickel(-Cobalt) Metal in Lunar Rocks Revisited

Iron-nickel metal particles have long been used asproxies for meteoritic contamination or to supportthe pristine character of lunar rocks [1-4].

In Shi r 161 (Figs. 1 A-C), a lunar feldspathicregolith breccia, low bulk-rock siderophile traceelement concentrations of 88 ppm Ni and 2.6 ppbIr indicate minor meteoritic contamination [5].

Our survey of metal and sulfide particles in Shi r161, and their petrologic contexts probes intoconstraints for their origins.

ş

ş

About 60 metal and 30 sulfide particles wereanalyzed with the

in a 550mm thin section ofShi r 161.

JEOL JXA-8200 ElectronMicroprobe at Washington University

(Fig. 1 B-C) lunar meteorite2

ş Care was taken to correct for theinterference of the Fe k-ß X-ray peak with te Cok-a X-ray peak.

SAMPLES & METHODS

Sulfides and Phosphides

Metal Particles

Troilite is most common. Concentrations of P are typically <0.03 wt% and Ni concentrations range from<0.06 wt% to a few wt%. Three pentlandite particles have compositions comparable to lunar and terrestrial pentlandite [8-9]. PossibleFe-phosphide (P up to 9.45 wt%, Ni up to 15.4 wt%, poor totals) was only found in association with troilite and FeNi-metal in a rim on acrystallized spherule.

Most metal particles are <10 m in size and are intergrown with troilite.The Ni and Co concentrations of these particles (normalized to 100 wt%) are shown in comparison with metal particle compositions inpresumably endogeneous lunar rocks (Fig. 7) and in lunar impactites (Fig. 8).

–

– μ

PETROGRAPHY

10 mμ10 mμ

A

B

A C

SUMMARY

�

�

�

�

Metal particles in Shi r 161 spherules and vitrophyres mostly resemble “meteoritic” and mare basalt compositions.

Very fine- to finely crystallized melt clasts contain metal particles that have variable abundances of Ni and Cobut their ratios mostly follow the chondritic trend.

Cumulate (impact) melt particles tend to have very high Ni concentrations, but their compositions in singleclasts can be quite variable.

Comparison with metal particle compositions in some “pristine” lunar rocks suggests some of their compositions areindistinguishable from such that crystallized in larger volumes of impact melt.

ş

ş

ş

in Shi r 161

in Shi r 161

(>~100 m thick?)

REFERENCES

Fig. 8 Ni versus Co in Shi r 161 metal particles compared to metal particle compositions in lunar polymict rocks.

green line represents the “cosmic trend” of Ni:Co concentrations of20:1 in chondrites; range lines encircle data from the same clasts.

ş Field for metal particles in granulite79215 after [20]; “high cobalt and structures in Apollo 15 soils” after [21]; fields for Apollo 11 and Apollo 17 basalts and Apollo polymict rocks (”rangeof metal compositions in polymict rocks”) after [4]; “meteoritic” field after [1];

o

α γmost

All Shi r 161 data normalized to 100 wt%.ş

“meteoritic”

Apollopolymictrocksgranulite

79215

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20 25

Ni (wt%)

Co

(w

t%)

30 35 40 45 50 55 60

3.5

4.0

high Ni metal particlesin Apollo 15 soils

pristinetroctolite76535 fine cumulate melt (n=4)

Fig. 3

A B C-

Note that the plane polarized lightimages (A) in Figs. 3-6 have thesame scale.

Cumulate clast #54.Well-equilibrated assemblage of subhedralolivine (Fo ) and plagioclase (An ),

and intercumulus poikilitic pyroxene(En , Wo and En , Wo ). The two-

pyroxene thermometer of [7] yields anequilibration temperature of 890±20°C.

-PPL micrograph; and BSE imagesof troilite and metal particle (39.7 wt% Niand 2.1 wt% Co). Five other metal particlesin this clast have 37.5-56.4 wt% Ni and0.5-2.1 wt% Co.

77-79 95-97

78 3 86 45

Fig. 1

A-B-

C-

Shi r 161sample material.

The sliced upmeteorite; Thinsection planepolarized light (PPL)image; Back-scattered electron(BSE) image of thethin section withoutlines of clasts.

ş

500 mμ500 mμ 10 mμ10 mμ

100 mμ100 mμ

500 mμ500 mμ

500 mμ500 mμ

500 mμ500 mμ

Fig. 5

A- B-C-

D-

Proto-poikilitic impact melt clast #8.Optically discontinuous, proto-poikilitic olivine(Fo ) and pyroxene

(An ).

PPL micrograph; Cross-polarized lightmicrograph; BSE image ;

BSE image of troilite and metal particleassemblage (33.4 wt% Ni and 1.5wt% Co).Three other metal particles in this clast have35.4-40 wt% Ni and 1.5-1.6 wt% Co.

63-70

95-98

(En , Wo ) embed

euhedral to subhedral plagioclase

(rotated by ~45°)

44-61 7-36

500 mμ500 mμB

10 mμ10 mμ

Fig. 6

A- B- C-

Intergranular-felty impact melt clast #43.Very fine-grained anhedral olivine (Fo ) and skeletal pyroxene

(An ).

PPL micrograph; BSE image; BSE image of troilite andmetal particle (53.7 wt% Ni and 3.6wt% Co). Another metal particlein this clast has 51.7wt% Ni and 2.6 wt% Co.

78-83

95-98(En , Wo ) are intergrown with granular plagioclase78-81 3

500 mμ500 mμ 500 mμ500 mμ500 mμ500 mμ

Fig. 4

A- B- C-

D-

Intergranular clast #26 showsanhedral olivine (Fo ) enclosed in

poikilitic, twinned pigeonite (

) and zoned augite (En

Fs Wo ) that is interstitial to

subhedral plagioclase (An ).

PPL micrograph; BSE image;Cathodoluminescence false color image;

BSE image of troilite and pentlandite(arrow: 33 wt% Fe, 33.7 wt% S, 28.2 wt%Ni, 5.2 wt% Co).Another pentlandite particle (

and a metal particle (44.2 wt% Ni, 2 wt%Co) were found in this clast.

46-52

39-

47 18-27 30-37

95-97

En Fs Wo

to En Fs Wo

34.7 wt%Fe, 33.8 wt% S, 27.8 wt% Ni, 3.1 wt% Co)

56 38 6

47 38 15

Fig. 2

A- B-.

BSE image;EMPA data for spottraverse X-Y.Note kamacite Ni(6.8±0.2 wt%) andCo (0 )concentrations aretypical for L-chondrites [6].

.82±0.07 wt%

Kamacite-tetrataenite nugget

23

54

5

1725

107

116

16

10

34

38

88

18

38

26

46

115

148

27

43

159

36

63

4

50

118

126

135

156

74

2

6

7

1312

15

19

20

28

58

95

136

3381

12311

3

17

10

4

6

15

5

7

2 8

1

9

13

1

3

4

5

6

7

8

9

10

12

11a+b

1330

37

44

51

52

5359

77

102

1

31

14

39

78

105

160

161

162

polymict lithic breccia vitrophyresVLT basalt? crystallized meltsmonomineralic cumulatesglasses hornfelses

spherules

Two of the particles are 60 and 40μm nuggets . The rest are ~5–20μm size troilite.

metal-sulfide(Fig. 2 A-B)

in , and mostly intergrown withØ

Host materials for the FeNi and FeS particlesare clasts of cumulates (Fig. 3), finely crystallizedimpact melts (Figs. 4-6), and glassy impact melts.The Fes-FeNi particles occur on grain boundariesof plagioclase, pyroxene and olivine crystals, andin the glassy mesostasis. Associations withchromite or ilmenite are rare (~3 % of FeS-FeNigrains).

100 mμ100 mμ 50 mμ50 mμ

B C DA

A B

C

C D

5 mm

A B

C

spherules (n=3)glasses & vitrophyres (n=3)regolith nuggets (n=3)

very fine-grainedintergranular melt (n=2)proto-poikilitic melt (n=5)

medium cumulate melt (n=8)Dhofar 287 regolith particles [22]fine cumulate melt (n=4)

0 10 20 30 40 50Distance [μm]

0

1

2

3

4

5

6

7

8

50

55

Ni

or

or

[wt%

]C

oS

YX

B

10 mμ10 mμ

X

Y

A

Department of Earth & Planetary Sciences, Washington University in St. Louis,One Brookings Drive, St. Louis, Missouri, wittmann@levee.wustl.edu

Photo byG. Hup &P. Mani

é

[1] Goldstein J. I & Yakowitz H. (1971) , 177-191. [2] Smith J. V. & Steele I. M.(1976) , 1059-1116. [3] Warren P. H. & Wasson J. T. (1979) , 583-610.[4] Ryder G. et al. (1980) , 471-479. [5] Korotev R. L. (2012) , 1365-1402.[6] Kallemeyn G. W. et al. (1989) , 2747-2767. [7] Lindsley D. H. & Anderson D. J. (1983)

88, A887–A906. [8] Nazarov M. A. et al. (1980) , 800-802. [9]Anthony J. W. et al. (1990) , MSA, Chantilly, VA., 588 pp. [10] DymekR. F. et al. (1975) , 301-341. [11] Warren P. H. (1993) , 360-376. [12]Gooley R. et al. (1974) , 1329-1339. [13] Prinz M. et al. (1973) 179, 74-76. [14]Warren P. H. & Wasson J. T. (1979) , 583-610. [15]

Nehru C. E. et al. (1978) , 773-788. [17] Papike J. et al. (1991) , Cambridge University Press & LPI, p.121-181.[18] Jolliff B. L. et al. (2003) , 7857-4879. [19] Rubin A. E. (1990) GCA 54, 1217-1232.[20] Bickel C. E. et al. (1976) , 1793-1819. [21] Axon H. J. & Goldstein J. I. (1973)

, 173-180. [22] Demidova S. I. (2003) , 501-514.

Proc. LSC 2Am. Min. 61 Proc. LPSC 10

Proc. LPSC 11 MAPS 47GCA 53

J. Geophys. Res. LPSC XIHandbook of Mineralogy

Proc. LSC 6 Am. Min. 78GCA 38 Science

Proc. LPSC 10Proc. LPSC 9

Lunar SourcebookGCA 67Proc. LSC 7

EPSL 18 MAPS 38

nd

th

th

th

th

th

th

Warner R. D. et al. (1980), 377-394. [16]Proc. Conf. Lunar Highlands Crust