The Kaguya mission detected small but widespread outcrops of nearly pure ferroan anorthosite in and around large impact basins on the Moon. Along with certain lunar rocks, highly feldspathic lunar meteorites such as MIL 090034 (M34), 090036 (M36), and 090070 (M70) may provide samples of this material. We have measured the Ar-40/Ar-39 release patterns and cosmogenic Ar-38 concentrations of several small (<200 microg) samples separated from M34,36, and 70. From petrographic observations concluded that "some of the clasts and grains experienced generations of modifications," a conclusion that we examine in light of our data

Delaney, J.

Ebihara, M.

Herzog, G. F.

Lindsay, F. N.

Nyquist, L. E.

Park, J.

Shih, C.-Y.

Shirai, N.

Swisher, C., III

Turrin, B.

Yamaguchi, A.

NASA Technical Reports Server

Fig.1. Among lunar meteorites, M34, M36, 
and M70 have the largest modal abun-
dances of plagioclase. M34 & 70 differ 
from M36. 
 
Fig. 2. 
Apparent 
Age spectra 
and K/Ca 
ratios  of 
M34, M36 
and M70. 
LATE BOMBARDMENT OF THE LUNAR HIGHLANDS RECORDED IN MIL 090034, MIL 090036 AND 
MIL 090070 LUNAR METEORITES. J. Park
1,4,5
, L.E. Nyquist
2
, C.-Y. Shih
3
, G.F. Herzog
4,5
,
 
A. Yamaguchi
6
, N. 
Shirai
7
, M. Ebihara
7
, F.N. Lindsay
4,5
, J. Delaney
4,5
,
 
B. Turrin
8,5
, C. Swisher III
8,5
. 
1
Lunar Planet. Inst., Houston, TX 
77058, 
2
KR/NASA Johnson Space Center, Houston, TX 77058, 
3
JE-23, ESCG/Jacobs Sverdrup, Houston, TX 
77258-8477 
4
Dept Chem. & Chem. Biol, 
5
Rutgers Univ., Piscataway, NJ 08854, 
6
Antarctic Meteorite Research Cen-
ter, Natl. Inst. Polar Research, Tokyo 190-8518, Japan, 
7
Tokyo Metropolitan Univ., Hachioji, 192-0372, Japan, 
8
Dept. Earth Planet. Sci. 
 
Introduction: The Kaguya mission detected small 
but widespread outcrops of nearly pure ferroan anortho-
site in and around large impact basins on the Moon [1]. 
Yamamoto et al [2] took these observations as evidence 
for a 50-km thick layer of once-molten anorthosite un-
derlying much of the lunar surface (cf. [3]). Along with 
certain lunar rocks, highly feldspathic lunar meteorites 
such as MIL 090034 (M34), 090036 (M36), and 090070 
(M70) may provide samples of this material. We have 
measured the 
40
Ar/
39
Ar re-
lease pat-
terns and 
cosmogenic 
38
Ar concen-
trations of 
several small 
(<200 g) 
samples sep-
arated from 
M34,36, and 
70. From 
petrographic 
observations 
[4] conclud-
ed that “some of the clasts and grains experienced gener-
ations of modifications,” a conclusion that we examine in 
light of our data.  
M34,36,70 are anorthositic regolith breccias [5]. The 
petrology and mineralogy of samples of the breccias al-
located to us were reported by [6]. Fig. 1 and rare earth 
element abundances suggest pairing of M34 and M70, as 
also suggested by [7,8]. Yamaguchi et al. [6] interpreted 
M70 to be a crystalline melt breccia, whereas M34 and 
M36 are fragmental or regolith breccias. Mg-suite frag-
ments, a rare feature in lunar highland meteorites, were 
found in M34[6]. Plagioclase mineral fragments in M70 
were found to have a narrow compositional range, An93-
An98, whereas plagioclase in M34 ranges from An82-
An99, and in M36 from An64-An98. Mg’ (molar 
Mg/(Mg+Fe) for olivines in M34 and M70 are similar to 
those in FAN. Some olivines in M36 have higher Mg’ 
numbers. The range of  Mg’ in olivine and An in plagio-
clase imply a contribution of Mg-suite rocks to M36 as 
well as to M34. Molar Ti/(Ti + Cr) and Fe/(Fe + Mg) in 
some pyroxenes in M34 and M36 are similar to those of 
LT and VLT mare basalts, implying that these pyroxenes 
originated from mare basalts [6]. 
Experimental Methods for Ar-Ar Analyses:  
Samples were separated by handpicking from 68 mg 
of M34,20,1,8; 129 mg of M36,16,4; and 43 mg of 
M70,17,21. Sugary, polycrystalline masses ranging from 
53 to 330 g were hand-picked and the elemental com-
positions confirmed as anorthositic by either EDX or x-
ray fluorescence. The grains selected from M34 included 
darkly colored streaks, possibly impact melt. Samples 
were irradiated for ~80 h with Cd shielding at the USGS 
Triga reactor.  
0.0 0.4 0.8
3
6
2
4
0.0 0.4 0.8
3
6
5
10
3
6
0.0 0.4 0.8
0
2
4
0.0 0.4 0.8
0
4
8
2
 
 A
g
e
 (
G
a
)
 
 
 1
0
0
0

K
/C
a 
21702 M34, 54 g
 
 
 
 21678 M34, 58 g
 
 1
0
0
0

K
/C
a
 
21703 M36, 237 g
 A
g
e
 (
G
a
)
 
39
Ar cumulative
 
 
39
Ar cumulative
 
 
21715 M70, 172 g
3.7 ± 0.2 Ga
3.4 ± 0.2 Ga
3.8 ± 0.1 Ga
3.6 ± 0.3 Ga
 
 
Results: Argon release patterns and ages. Figure 2 
shows our four best Ar age spectra without corrections 
for trapped 
40
Ar. All release patterns are disturbed at low 
fractional 
39
Ar release (<0.2) and relatively flat at high 
ones (>0.6), although with large uncertainties because of 
low K concentrations. For M34, 36, and 70, the respec-
tive weighted mean ages (Ga) calculated for the high-
temperature ages (Ga), which we take to indicate the 
time of the last major re-settting, are 3.4±0.3 (M34, 
n=5), 3.80±0.12 (M36, n=5), and 2.62±0.17 (M70; n=6) 
or 3.5±0.7 (n=4, excluding 2 analyses). These results 
suggest but do not prove lower ages for M34 and M70 
than for M36.  
other highland meteorites
mingled
mare
MIL 090034
MIL 090036
MIL 090070
FAN
Troctolite
Norite
Dho 950
67075
https://ntrs.nasa.gov/search.jsp?R=20130011272 2019-08-31T00:19:53+00:00Z
Fig. 3. 
40
Ar/
36
Ar 
vs. 
39
Ar/
36
Ar 
isochrons for 
M36 (a) and M34 
plus M70 (b). 
Low temperature 
data shown by 
open symbols 
were excluded 
from the regres-
sions. 
Isochrons. Isochrons for 
40
Ar/
36
Ar vs. 
39
Ar/
36
Ar were 
plotted for the high-temperature data after removing a 
small cosmogenic 
36
Ar component (
36
Arc) calculated 
using the relation 
36
Arc = 0.65×
38
Arc. The isochron age 
for M36 is 3.54±0.04 Ga (Fig. 3a), about 2 less than the 
high-temperature weighted average above. For M34 we 
obtain 3.23±0.31 Ga, and for M70 3.05±0.59 Ga (Fig. 
3b). The isochron ages cannot be clearly distinguished 
because of the relatively large uncertainties for the M34 
and M70 ages. Nevertheless, the ages of M34 and M36 
agree only at the limits of uncertainty, a strong hint that 
M34, and problably M70 as well because of its strong 
compostional pairing with M34, experienced a major 
outgassing event more recently than did M36. Incorpora-
tion in the laboratory of 0.5-1.8×10
-8
 cm
3
 STP/g of at-
mospheric 
40
Ar 
[9] would have 
raised the ap-
parent ages of 
some release 
steps, especial-
ly ones with 
low 
39
Ar/
40
Ar 
ratios. Data 
points in the 
lower left-hand 
corner of Fig-
ure 3 probably indicate atmospheric Ar in several frac-
tions of M34 and M70, but not of M36. 
Cosmic-ray exposure. We calculated the concentra-
tion of cosmogenic 
38
Ar from the relation 
38
Arc=(5.35
38
Ar–36Ar)/(5.35-0.65) . Average total 38Arc 
concentrations (cm
3
 STP/g) over total 
37
Ar concentra-
tions (cm
3
 STP/g), a measure of total cosmic-ray expo-
sure in Ca-rich and K- and Cl-poor material, are as fol-
lows: M34 (7.8±2.2)×10
-4
 (n=5); M36, (2.0±0.3)×10
-2
 
(n=5); M70 (7.0±1.3) ×10
-4
 (n=6). Thus, the average 
cosmogenic 
38
Arc concentration is ~25 times larger for 
M36 than for M34 and M70. The difference is even larg-
er if we consider high-temperature 
38
Arc/
37
Ar ratios, from 
which apparent cosmic ray exposure (CRE) ages can be 
calculated (Figure 4). A lower bound on the total dura-
tion of irradiation can be estimted from an upper bound 
 on the production rate of 
38
Arc, P38 = 0.22 × 10
 8
 cm3 
STP/(g-Ma) [9], based on a Ca concentration of ~12 wt% 
in MIL meteorites [10].  The results (Ma) are: 1.3±0.6 
(M34) (n=5); 50±10 (M36) (n=5) and 1.6±0.3 Ma 
(M70)(n=6). (The relative CRE ages in Fig. 4 show indi-
vidual data). The apparent CRE ages for M34 and M70 
are short and agree well within their error limits, suggest-
ing that they were excavated to (or from) the lunar sur-
face at the same time. Also, values of “4-” CRE ages 
for lunar meteorites rarely exceed 5 Ma [11], suggesting 
that M36 was excavated to the lunar surface much earli-
er. 
Discussion and Conclusions: The high-temperature 
Ar/Ar ages of M34, M36, and M70 are much younger 
than the anorthositic protolith from which they were 
formed. The ages fall within the range of ages for impact 
melt clasts from other lunar feldspathic regolith breccias, 
which indicate a broad Ar/Ar age peak between 3.0 and 
3.5 Ga [12]. M34 and M70 are compositionally similar 
to Apollo 16 FANs; M36 to Apollo 16 soils. One large 
Apollo 16 FAN (60015) has a similarly young Ar-Ar age 
[13]. Also, from an Ar/Ar study of 7 ‘rocks’ extracted 
from Apollo regolith sample 63503, [14] inferred a ma-
jor impact event in the Cayley plains ~3.3 Ga ago and 
perhaps a broader bombardment of the Moon at that 
time. Orbital geochemical data (cf. [1,2]), show central-
peak craters in the lunar highlands to be suitable sources 
for highly aluminous M70 and M34, but higher trace 
element abundances in M36 suggests an origin in the 
vicinity of the Procellarum KREEP terrain (PKT). 
References: [1] Ohtake M. et al. (2009) Nature 461, 236–240. 
[2] Yamamoto et al. (2012) GRL 39, L13201-L13207. [3] Korotev 
R.L. et al. (2010) LPS 41, 1440.pdf. [4] Liu Y. et al. (2011) LPS 42, 
1261.pdf. [5] Corrigan C. et al. (2010) Ant. Met. News Lett. 33. [6] 
Yamaguchi A. et al. (2012) Geochem. Soc. Japan, 59, 2P48. [7] 
Zeigler R. et al. (2012) LPS 43, 2377.pdf., [8] Shirai N. et al. (2012) 
LPS 43, 2003.pdf. [9] Eugster O.and Michel Th. (1995) GCA, 59, 
177-199. [10] Shirai et al., per. comm. [11] Herzog G.F. (2004) Trea-
tise Geochem. 1, 347-380. [12] Shuster D.L. et al. (2010) EPSL 290, 
155-165. [13] Park J. et al. (2010) Lunar Science Forum, #59. [14] 
Cohen B.A. et al. (2005) MPS 40, 755-777. 
0
5000
10000
15000
20000
0 20 40 60
39
Ar/ 
36
Ar
4
0
A
r/
 3
6
A
r
MIL090036
Age=3.54 ± 0.04 Ga
40
Ar/
36
Ar= 25 ± 9
4
0
A
r/
 3
6
A
r
Fig. 3a
0
2000
4000
6000
8000
0 5 10 15 20
39
Ar/ 
36
Ar
4
0
A
r/
 3
6
A
r
MIL090034 & MIL090070
Age=3.05 ± 0.59 Ga
40
Ar/
36
Ar= -154 ± 405
Age=3.23 ± 0.31 Ga
40
Ar/
36
Ar= -23 ± 412
Fig. 3b
Fig. 4. Lower bounds on 
the relative CRE ages 
(values above arrows) 
differentiate M34 and 
M70 from M36. 


Late Bombardment of the Lunar Highlands Recorded in MIL 090034, MIL 090036 and MIL 090070 Lunar Meteorites

Late Bombardment of the Lunar Highlands Recorded in MIL 090034, MIL 090036 and MIL 090070 Lunar Meteorites

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