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Mineral and bulk compositions of three fragments from Luna 16
EARTH AND PLANETARY SCIENCE LETTERS 13 (1972) 323-327. NORTH-HOLLAND PUBLISHING COMPANY
MINERAL
AND BULK COMPOSITIONS
OF THREE
FRAGMENTS
F R O M L U N A 16
I. M. STEELE and J. V. SMITH Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, 6063Z USA Received 8 November 197 l Revised version received 22 November 1971
Electron microprobe analyses of fragment G37 show that it is a mare basalt with high aluminum and low magnesium content. Detailed analyses are given of olivine, pyroxene, ilmenite, utvtispinel and plagioclase. Fragment G46 is a cinder with bulk composition fairly similar to G37. Fragment G51 is entirely composed of plagioclase, An93_96, with low contents of minor elements.
1. Introduction and procedures
2. Results and discussion
From the Luna 16 material (see [ 1] for preliminary description), we have received three fragments: (a) G37, a basalt containing about 50% plagioclase, 30% pyroxene, 15% olivine, 6% ilmenite, 3% ulv6spinel and small amounts of metal and zircon. (b) G51, a cream-colored material entirely composed of plagioclase except for fragments of ilmenite and pyroxene adhering to the sides. (c) G46, a cinder that consists of a complex mixture of minerals and glass, and whose bulk composition is fairly similar to that of G37 : it contains vesicles and its general properties suggest partial melting of a basalt or of regolith. A polished section was prepared o f each fragment, and minerals identified by reflected light microscopy supplemented by electron probe micro-analysis. The sections were not thinned in order to minimize loss of material. In addition to analyses o f individual minerals, bulk analyses of G37 and G46 were obtained by scanning systematically across the exposed area. The bulk analyses were recalculated to 100% to compensate for holes. Since the bulk composition of G46 is quite similar to that of G37, no detailed mineral analyses were made of the former. The electron microprobe technique is similar to that used in earlier lunar studies from Chicago and details are omitted for brevity.
Table 1 compares the bulk microprobe analyses of G37 and G46 with the chemical analysis given for crystalline rocks from Luna 16 by Vinogradov [1]. Considering the statistical and analytical problems of electron microprobe analysis of such small fragments as G37 and G46, it seems reasonable to suppose that G37 and G46 belong to the same general population as that surveyed by Vinogradov. Table 1 Chemical analyses.
P2Os SiO: TiO: A1203 Cr~O 3 MgO FeO MnO CaO Na~O K20
G37 bulk microprobe
G46 bulk microprobe
Luna 16 (Ref. [ 1], table 4, #4)
0.4 42.8 4.3 15.4 0.3 6.4 18.1 0.3 11.2 0.7 0.1
0.5 43.4 3.0 18.8 0.3 6.4 13.6 0.2 12.9 0.7 0.1
43.8 4.9 13.65 0.28 7.05 19.35 0.20 10.4 0.38 0.15
(100.0) * * Recalculated to 100%.
(99.9) *
-
324
LM.Steele, J. V.Smith, Mineral and bulk compositions
Fig. l(a). Reflected light micrograph of fragment G37 demonstrating textural relation between ilmenite and ulvospinel (white), olivine and pyroxene (light gray) and plagioclase (dark gray).
Fig. l(b). Drawing showing position of ilmenite (IL), ulvospinel (USP), olivine ~OL), and zircon (ZR).
Many of the differences are probably consistent with changes in the modal ratio of plagioclase, ferromagnesians and ore minerals, but there may be significant changes in mineral composition undetectable from this comparison. The bulk composition of G37 can be approximated quite well by about 47 + 5% plagioclase, 30 + 5% pyroxene, 14 + 3% olivine, 6 + l% ilmenite and 3 + 1% ulv~3spinel, which proportions are consistent with visual estimates from fig. 1. Noteworthy in the bulk analysis of G37 is the high content of A1203 and low content of MgO with respect to most Apollo 11 and 12 basalts. These result from a relatively high content of plagioclase and a relatively low content of Mg in the pyroxene and olivine. Table 2 shows the analyses of olivines and pyroxenes from G37. The olivine is strongly zoned from 59
LM.Steele, J. V.Smith, Mineral and bulk compositions
Z
e~
Z
Q
d~2dd~ddd
~
~e~
f21.
-6
E
Q
~
~
d
~
Z
~
% Z m
~
~ Q
e-
©
325
1.M.Steele, J. V.Smith, Mineral and bulk compositions
326
•] //
/ En
v
....
-
-
-
-
-
-
-
....... x
-
......
Jf
l-
,,
....
/
, Fs
,,
(mol %) A p o l l o 11 A p o l l o 12 A p o l l o 14 L u n a 16 G 3 7
Fig. 2. Pyroxene compositions for G37 compared with ranges for Apollo 11, 12 and 14 specimens. to 30 tool % Fo w i t h rare zoning to 10% Fo, the m o s t magnesian olivine c o r r e s p o n d i n g closely to the olivine reported by V i n o g r a d o v [ 1 ]. Minor e l e m e n t c o n t e n t s are c o n s i s t e n t with those collected for mare basalts by Smith [2]. The p y r o x e n e is highly z o n e d w i t h c o m p o s i t i o n s
that lie in a band near the center of the Di-Hd-En-Fs quadrilateral (fig. 2). This is consistent with a high temperature of crystallization near the crest of the pyroxene exsolution tunnel• The range of composition is much less than the extreme limits for Apollo 11, 12 and 14 samples outlined in the figure• The mean corn-
Table 3 Electron microprobe analyses of ihnenite and ulv6spinel. lhnenite G37
Ulvospinel G37
1.2
I
I .
.
I
I
1.0
P2Os SiO: TiO 2 AI:O 3 Cr~O 3 MgO FeO MnO CaO
ND 0.43 51.4 0.14 0:37 0.72 45.6 0.4t 0.12
ND 0. l I 50.3 0.17 0.29 0.30 46.6 0.45 0.15
ND 0 00 50.0 0.19 0.32 0.62 45.8 0.43 0.21
ND 0.04 49.7 0.15 0.38 0.81 44.4 0.46 0.33
ND 0.06 39.1 2.95 5.98 1.41 57.3 0.45 0.17
ND 0.03 27.9 3.59 7.98 2.09 53.9 0.46 0.25
Total
99.2
98.4
97.6
96.3
97.4
96.2
0.8 ".
~0.6 /
u•0.4 0.2
Si Ti AI Cr Mg Fe Mn Ca
0.09 7.83 0.03 0.06 0.22 7.72 0.07 0.03
0.02 7.80 0.04 0.05 0.09 8.03 0.08 0.03
0.00 7.80 0.05 0.05 0.19 7.94 0.08 0.05
0.01 7.83 0.04 0.06 0.25 7.77 0.08 0.07
0.01 4.92 0.78 1.05 0.47 10.78 0.09 0.04
0.01 4.72 0.95 1.42 0.70 10.15 0.09 0.06
~.
•
,
,%.
~
I 20
...... x
_
i
_
_
_
I
"~
X ".
\
•
X X~
•
i
,,
"~.
15415
-=->,, i
10
Ab - - - -
X X
•
~
-
0.0
Cations based on 24 oxygens
__
[
X
( m o l %)
Apollo 12 e x o t i c fragments Apollo 12 b a s a l t i c f r a g m e n t s L u n a 16 6 3 7 ",///// L u n a 16 651
Fig. 3. Plagioclase compositions for G37 and G51 compared with ranges for Apollo 12 basaltic and exotic fragments, and for the 15415 rock.
I.M.Steele, J. V.Smith, Mineral and bulk compositions
327
Table 4 Electron microprobe analyses of plagioclase. G51 G37 mol % An mol % Ab mol % Or wt % K wt % Fe wt % Mg
88 8.0 0.6 0.09 0.69 0.20
91 8,0 0.3 0.04 0.56 0.15
89 8.0 0.3 0.04 0.60 0.12
91 7.5 0.2 0.03 0.54 0.14
91 7.0 0.3 0.04 0.44 0.11
91 7.5 0.4 0.05 0.56 0.09
87 10.0 0.4 0.05 0.68 0.10
88 9.0 0.6 0.09 0.57 0.08
range
mean
93-96 5- 3 ND
95 4 ND
-
ND 0.13 0.05
ND = not determined.
position is more Fe-rich than those of Apollo 11 and 12 basalts. Minor elements in the pyroxenes are consistent with those found in Apollo 12 pyroxenes when plotted against FeO content (see, for example, fig. 4 of Keil et al. [3]). Table 3 contains analyses of ilmenite and ulvospinel. The former has a relatively low Mg content varying from 0.3 to 0.8 wt %, consistent with the relatively high Fe content of the coexisting pyroxene and olivine. Similarly the ulv6spinel corresponds fairly well to the iron-rich members of the chromiteulvospinel found for Apollo 12 rocks (e.g. [ 3 - 5 ] ) . The plagioclase from G37 ranges from 87 to 91 tool % An with contents of K, Mg and Fe corresponding to mare basalts [2]. Fig. 3 shows the content of Fe vs. tool % Ab. The data for G37 fall well within the band for Apollo 12 basaltic fragments. The plagioclase from G51, however, fits with the region ascribed to exotic fragments from Apollo 12, material variously described as norite, anorthosite, KREEP, gray-mottled, etc. Also shown is the datum for plagioclase from 15415, the 'Genesis' rock [6]. Both the G51 and 15415 plagioclases have low contents of minor elements, with the former being somewhat more sodic. Until a thin section is made of fragment G51, it will not be known whether it is a single crystal or a rock fragment. In conclusion, these data are consistent with fragment G37 being derived from mare basalt. Fragment G46 is a complex cinder, and fragment G51 consists of plagioclase low in minor elements.
Acknowledgements We thank the Dept. of Materials Research of the University of Illinois and J.B. Woodhouse for use of an electron microprobe during breakdown of the Chicago microprobe. The study was supported by NASA grant NGL 14-001-171.
References [ 1] A.P. Vinogradov, Preliminary data on lunar ground brought to Earth by automatic probe Luna 16, Proc. Second Lunar Sci. Conf. 1 (1971) 1. [2] J.V. Smith, Minor elements in Apollo 11 and Apollo 12 olivine and plagioclase, Proc. Second Lunar Sci. Conf. 1 (1971) 143. [3] K. Keil, M. Prinz and T.E. Bunch, Mineralogy, petrology, and chemistry of some Apollo 12 samples, Proc. Second Lunar Sci. Conf. 1 (1971) 319. [41 E.N. Cameron, Opaque minerals in certain lunar rocks from Apollo 12, Proc. Second Lunar Sci. Conf. 1 (1971) 193. [5] P.R. Simpson and S.H.U. Bowie, Opaque minerals in Apollo 12 samples, Proc. Second Lunar Sci. Conf. 1 (1971) 207. [6] I.M. Steele and J.V. Smith, Mineralogy of Apollo 15415 "Genesis rock": Source of anorthosite on Moon, Nature, in press.
MINERAL
AND BULK COMPOSITIONS
OF THREE
FRAGMENTS
F R O M L U N A 16
I. M. STEELE and J. V. SMITH Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, 6063Z USA Received 8 November 197 l Revised version received 22 November 1971
Electron microprobe analyses of fragment G37 show that it is a mare basalt with high aluminum and low magnesium content. Detailed analyses are given of olivine, pyroxene, ilmenite, utvtispinel and plagioclase. Fragment G46 is a cinder with bulk composition fairly similar to G37. Fragment G51 is entirely composed of plagioclase, An93_96, with low contents of minor elements.
1. Introduction and procedures
2. Results and discussion
From the Luna 16 material (see [ 1] for preliminary description), we have received three fragments: (a) G37, a basalt containing about 50% plagioclase, 30% pyroxene, 15% olivine, 6% ilmenite, 3% ulv6spinel and small amounts of metal and zircon. (b) G51, a cream-colored material entirely composed of plagioclase except for fragments of ilmenite and pyroxene adhering to the sides. (c) G46, a cinder that consists of a complex mixture of minerals and glass, and whose bulk composition is fairly similar to that of G37 : it contains vesicles and its general properties suggest partial melting of a basalt or of regolith. A polished section was prepared o f each fragment, and minerals identified by reflected light microscopy supplemented by electron probe micro-analysis. The sections were not thinned in order to minimize loss of material. In addition to analyses o f individual minerals, bulk analyses of G37 and G46 were obtained by scanning systematically across the exposed area. The bulk analyses were recalculated to 100% to compensate for holes. Since the bulk composition of G46 is quite similar to that of G37, no detailed mineral analyses were made of the former. The electron microprobe technique is similar to that used in earlier lunar studies from Chicago and details are omitted for brevity.
Table 1 compares the bulk microprobe analyses of G37 and G46 with the chemical analysis given for crystalline rocks from Luna 16 by Vinogradov [1]. Considering the statistical and analytical problems of electron microprobe analysis of such small fragments as G37 and G46, it seems reasonable to suppose that G37 and G46 belong to the same general population as that surveyed by Vinogradov. Table 1 Chemical analyses.
P2Os SiO: TiO: A1203 Cr~O 3 MgO FeO MnO CaO Na~O K20
G37 bulk microprobe
G46 bulk microprobe
Luna 16 (Ref. [ 1], table 4, #4)
0.4 42.8 4.3 15.4 0.3 6.4 18.1 0.3 11.2 0.7 0.1
0.5 43.4 3.0 18.8 0.3 6.4 13.6 0.2 12.9 0.7 0.1
43.8 4.9 13.65 0.28 7.05 19.35 0.20 10.4 0.38 0.15
(100.0) * * Recalculated to 100%.
(99.9) *
-
324
LM.Steele, J. V.Smith, Mineral and bulk compositions
Fig. l(a). Reflected light micrograph of fragment G37 demonstrating textural relation between ilmenite and ulvospinel (white), olivine and pyroxene (light gray) and plagioclase (dark gray).
Fig. l(b). Drawing showing position of ilmenite (IL), ulvospinel (USP), olivine ~OL), and zircon (ZR).
Many of the differences are probably consistent with changes in the modal ratio of plagioclase, ferromagnesians and ore minerals, but there may be significant changes in mineral composition undetectable from this comparison. The bulk composition of G37 can be approximated quite well by about 47 + 5% plagioclase, 30 + 5% pyroxene, 14 + 3% olivine, 6 + l% ilmenite and 3 + 1% ulv~3spinel, which proportions are consistent with visual estimates from fig. 1. Noteworthy in the bulk analysis of G37 is the high content of A1203 and low content of MgO with respect to most Apollo 11 and 12 basalts. These result from a relatively high content of plagioclase and a relatively low content of Mg in the pyroxene and olivine. Table 2 shows the analyses of olivines and pyroxenes from G37. The olivine is strongly zoned from 59
LM.Steele, J. V.Smith, Mineral and bulk compositions
Z
e~
Z
Q
d~2dd~ddd
~
~e~
f21.
-6
E
Q
~
~
d
~
Z
~
% Z m
~
~ Q
e-
©
325
1.M.Steele, J. V.Smith, Mineral and bulk compositions
326
•] //
/ En
v
....
-
-
-
-
-
-
-
....... x
-
......
Jf
l-
,,
....
/
, Fs
,,
(mol %) A p o l l o 11 A p o l l o 12 A p o l l o 14 L u n a 16 G 3 7
Fig. 2. Pyroxene compositions for G37 compared with ranges for Apollo 11, 12 and 14 specimens. to 30 tool % Fo w i t h rare zoning to 10% Fo, the m o s t magnesian olivine c o r r e s p o n d i n g closely to the olivine reported by V i n o g r a d o v [ 1 ]. Minor e l e m e n t c o n t e n t s are c o n s i s t e n t with those collected for mare basalts by Smith [2]. The p y r o x e n e is highly z o n e d w i t h c o m p o s i t i o n s
that lie in a band near the center of the Di-Hd-En-Fs quadrilateral (fig. 2). This is consistent with a high temperature of crystallization near the crest of the pyroxene exsolution tunnel• The range of composition is much less than the extreme limits for Apollo 11, 12 and 14 samples outlined in the figure• The mean corn-
Table 3 Electron microprobe analyses of ihnenite and ulv6spinel. lhnenite G37
Ulvospinel G37
1.2
I
I .
.
I
I
1.0
P2Os SiO: TiO 2 AI:O 3 Cr~O 3 MgO FeO MnO CaO
ND 0.43 51.4 0.14 0:37 0.72 45.6 0.4t 0.12
ND 0. l I 50.3 0.17 0.29 0.30 46.6 0.45 0.15
ND 0 00 50.0 0.19 0.32 0.62 45.8 0.43 0.21
ND 0.04 49.7 0.15 0.38 0.81 44.4 0.46 0.33
ND 0.06 39.1 2.95 5.98 1.41 57.3 0.45 0.17
ND 0.03 27.9 3.59 7.98 2.09 53.9 0.46 0.25
Total
99.2
98.4
97.6
96.3
97.4
96.2
0.8 ".
~0.6 /
u•0.4 0.2
Si Ti AI Cr Mg Fe Mn Ca
0.09 7.83 0.03 0.06 0.22 7.72 0.07 0.03
0.02 7.80 0.04 0.05 0.09 8.03 0.08 0.03
0.00 7.80 0.05 0.05 0.19 7.94 0.08 0.05
0.01 7.83 0.04 0.06 0.25 7.77 0.08 0.07
0.01 4.92 0.78 1.05 0.47 10.78 0.09 0.04
0.01 4.72 0.95 1.42 0.70 10.15 0.09 0.06
~.
•
,
,%.
~
I 20
...... x
_
i
_
_
_
I
"~
X ".
\
•
X X~
•
i
,,
"~.
15415
-=->,, i
10
Ab - - - -
X X
•
~
-
0.0
Cations based on 24 oxygens
__
[
X
( m o l %)
Apollo 12 e x o t i c fragments Apollo 12 b a s a l t i c f r a g m e n t s L u n a 16 6 3 7 ",///// L u n a 16 651
Fig. 3. Plagioclase compositions for G37 and G51 compared with ranges for Apollo 12 basaltic and exotic fragments, and for the 15415 rock.
I.M.Steele, J. V.Smith, Mineral and bulk compositions
327
Table 4 Electron microprobe analyses of plagioclase. G51 G37 mol % An mol % Ab mol % Or wt % K wt % Fe wt % Mg
88 8.0 0.6 0.09 0.69 0.20
91 8,0 0.3 0.04 0.56 0.15
89 8.0 0.3 0.04 0.60 0.12
91 7.5 0.2 0.03 0.54 0.14
91 7.0 0.3 0.04 0.44 0.11
91 7.5 0.4 0.05 0.56 0.09
87 10.0 0.4 0.05 0.68 0.10
88 9.0 0.6 0.09 0.57 0.08
range
mean
93-96 5- 3 ND
95 4 ND
-
ND 0.13 0.05
ND = not determined.
position is more Fe-rich than those of Apollo 11 and 12 basalts. Minor elements in the pyroxenes are consistent with those found in Apollo 12 pyroxenes when plotted against FeO content (see, for example, fig. 4 of Keil et al. [3]). Table 3 contains analyses of ilmenite and ulvospinel. The former has a relatively low Mg content varying from 0.3 to 0.8 wt %, consistent with the relatively high Fe content of the coexisting pyroxene and olivine. Similarly the ulv6spinel corresponds fairly well to the iron-rich members of the chromiteulvospinel found for Apollo 12 rocks (e.g. [ 3 - 5 ] ) . The plagioclase from G37 ranges from 87 to 91 tool % An with contents of K, Mg and Fe corresponding to mare basalts [2]. Fig. 3 shows the content of Fe vs. tool % Ab. The data for G37 fall well within the band for Apollo 12 basaltic fragments. The plagioclase from G51, however, fits with the region ascribed to exotic fragments from Apollo 12, material variously described as norite, anorthosite, KREEP, gray-mottled, etc. Also shown is the datum for plagioclase from 15415, the 'Genesis' rock [6]. Both the G51 and 15415 plagioclases have low contents of minor elements, with the former being somewhat more sodic. Until a thin section is made of fragment G51, it will not be known whether it is a single crystal or a rock fragment. In conclusion, these data are consistent with fragment G37 being derived from mare basalt. Fragment G46 is a complex cinder, and fragment G51 consists of plagioclase low in minor elements.
Acknowledgements We thank the Dept. of Materials Research of the University of Illinois and J.B. Woodhouse for use of an electron microprobe during breakdown of the Chicago microprobe. The study was supported by NASA grant NGL 14-001-171.
References [ 1] A.P. Vinogradov, Preliminary data on lunar ground brought to Earth by automatic probe Luna 16, Proc. Second Lunar Sci. Conf. 1 (1971) 1. [2] J.V. Smith, Minor elements in Apollo 11 and Apollo 12 olivine and plagioclase, Proc. Second Lunar Sci. Conf. 1 (1971) 143. [3] K. Keil, M. Prinz and T.E. Bunch, Mineralogy, petrology, and chemistry of some Apollo 12 samples, Proc. Second Lunar Sci. Conf. 1 (1971) 319. [41 E.N. Cameron, Opaque minerals in certain lunar rocks from Apollo 12, Proc. Second Lunar Sci. Conf. 1 (1971) 193. [5] P.R. Simpson and S.H.U. Bowie, Opaque minerals in Apollo 12 samples, Proc. Second Lunar Sci. Conf. 1 (1971) 207. [6] I.M. Steele and J.V. Smith, Mineralogy of Apollo 15415 "Genesis rock": Source of anorthosite on Moon, Nature, in press.