Here we analyze the chronology and statistical distribution of lunar meteorites with emphasis on the spatial and temporal distribution of lunar mare basalts. The data are mostly from the Lunar Meteorite Compendium (http://www-curator.jsc.nasa.gov/ antmet/ lmc/contents.cfm cited hereafter as Compendium) compiled by Kevin Righter, NASA Johnson Space Center, and from the associated literature. The Compendium was last modified on May 12, 2008

Basilevsky, A. T.

Neukum, G.

Nyquist, L.

NASA Technical Reports Server

LUNAR METEORITES: WHAT THEY TELL US ABOUT THE SPATIAL AND TEMPORAL DISTRIBUTION
OF MARE BASALTS. A. T. Basilevsky 1,2 , G. Neukum2
 and L. Nyquist3 . 1-Vernadsky Institute of Geochemistry and
Analytical Chemistry, RAS, Moscow, Russia atbas@geokhi.ru ; 2-Freie Universitaet Berlin, Berlin, Germany, 3-
KR/NASA Johnson Space Center, Houston, Texas 77058, USA.
1. Introduction: Here we analyze the chronology
and statistical distribution of lunar meteorites with em-
phasis on the spatial and temporal distribution of lunar
mare basalts. The data are mostly from the Lunar Meteor-
ite Compendium (http://www-curator.jsc.nasa.gov/  ant-
met/lmc/contents.cfm cited hereafter as Compendium)
compiled by Kevin Righter, NASA Johnson Space Cen-
ter, and from the associated literature. The Compendium
was last modified on May 12, 2008.
2. The data: The Lunar Meteorite Compendium cur-
rently lists 108 “stones” representing 54 meteorites.
Among the latter are identified several so-called “launch-
paired” meteorites, which are considered to be ejected
together by the same impact event but landed on Earth in
different areas. They may represent either different or
similar rock types.
In the Compendium, lunar meteorites are subdivided
into three groups: group B – mare basalts and gabbros,
group F - feldspatic (anorthositic) highland breccias, and
group M - "mingled", brecciated mixtures of these two
end-members. Of the 54 meteorites, 10 belong to group B,
30 to group F, and 14 to group M. Breccias of groups F
and M (44 meteorites in total) are presented by 4 varie-
ties: regolith breccias – 19, fragmental breccias – 12, im-
pact-melt breccias – 10, and granulitic breccias – 3.
Among the launch-paired meteorites are Yamato
793169 (B), Asuka 881757 (B), Miller Range 05035 (B),
and Meteorite Hills 01210 (M), which based on their
similarity of composition, exposure histories, and crystal-
lization ages are considered to be launched-paired [1, 2, 3,
4]. It was also suggested that meteorite NWA 032 (B) is
paired with the La Paz Ice Field basalts (B) [2]. And the
mingled meteorites, Yamato 793274/981031 (M), Ele-
phant Moraine 87521/96008 (M) and Queen Alexandra
Range 94281 (M), are also launch-paired [1, 2].
The launch-paired meteorites should be taken into ac-
count if one considers the petrological aspect of the mete-
orite source craters. The first launch-paired group consist-
ing of three group B meteorites and one group M meteor-
ite represents a mixture of mare and highland materials so
the source crater is “mingled”. The second group consist-
ing of two group B meteorites represents one “basaltic”
source crater. And the third group consisting of three
group M meteorites represents a “mingled” source crater.
So, 6 craters supplied group B meteorites, 30 craters,
group F ones, and 13 craters, group M ones. The total
number of source craters is 49.
Another subject of our analysis is the data for the ab-
solute ages of crystallization of the meteorite basalts.
Among the 10 basalts and gabbros of group B, 9 have
been isotopically dated, and among 14 mingled breccias,
basaltic clasts have been isotopically dated in 6. The re-
sults of these datings acquired mostly from the literature
cited in Compendium and partly from more recent publi-
cations, not mentioned in Compendium, are given in Ta-
ble 1 of [5] and shown here in Fig. 1.
3. Analysis of the data: We analyze the available data
along the four following lines:
3.1. Significance of regolith breccias: Regolith brec-
cias were formed within the regolith layer [e.g.,6], the
thickness of which as estimated by different techniques
varies from 3-5 m in maria to 15-35 m in highlands [6, 7].
Craters ejecting fragments of regolith breccias should not
be significantly deeper than the regolith thickness. If the
crater was significantly deeper, then its ejecta should be
dominated not with the regolith materials (including
regolith breccias), but with the components of bedrock.
Regolith breccias came from 18 of 49 source craters. This
means that more than 1/3 of the source craters were not
significantly deeper than 3-5 to 15-35 m. Keeping in mind
that depth of ejection from impact craters is ~1/10 of the
crater diameter one can conclude that these craters had
diameters not much larger than several hundreds of me-
ters. This agrees with the conclusion of [8], based on evi-
dence different from ours, and with model estimates by
[9].
3.2. Significance of mingled breccias: Source craters
of the mingled breccias had to be formed in targets com-
posed of both mare and highland materials. It is important
that 8 of 14 group M breccias are regolith breccias. The
mingled breccias could be delivered from the four geo-
logic situations: 1) a mare-highland boundary, 2) small
mare basalt ponds within highlands like those observed in
the vicinity of Orientale basin [10], 3) mare areas where
the highland material basement is at small depths, and 4)
cryptomare areas, where the highland materials overlie
ancient maria. The group M breccias derived from 13 of
49 source craters. So the mare-highland boundary (which
is narrow) and small mare ponds within highlands (which
total area is small) both look unfavorable for providing
such a large fraction of the collection. The mare areas
with shallow highland-material basement also do not look
promising, especially for the cases of regolith breccias. In
the latter cases, the mare layer should be only meters to a
few tens of meters thick, which would lead to numerous
highland islands not typical for the Moon. Cryptomaria
[11, 12] look most promising in this respect. But, if they
are the major supplier of the group M breccias this may
mean that cryptomaria are rather abundant in the lunar
highlands (14/(14+30) = 1/3 if to count meteorites, or
13/(13+30) = 1/3 if to count source craters), that about
half of them are covered with very thin highland material
https://ntrs.nasa.gov/search.jsp?R=20100001637 2019-08-30T08:32:22+00:00Z
mantles (8 of 14 mingled breccias are regolith ones), and
that the source craters of the group M breccias are mostly
within the highland domain.
3.3. Relative abundances of the meteorite source cra-
ters: If the analyzed lunar meteorite collection is a repre-
sentative sample of the near-surface part of the lunar
crust, one should expect that in this sample the relative
abundances of major petrologic types of meteorites are
proportional to the areas of these types on the lunar sur-
face. Working on this approach, one should consider not
only meteorites, but the source craters as well. We know
that the lunar maria occupy —16% of the lunar surface and
the rest is highlands [e.g., 6, 7]. So the maria vs. high-
lands areas proportion is —1:5. To calculate this propor-
tion for lunar meteorites we should take in account the
amounts of mare basalt/gabbro meteorites (B = 10), the
highland feldspatic breccias (F = 30) and mingled brec-
cias (M = 14). The latter as it was concluded above
probably derived mostly from cryptomaria, which are part
of the highlands. So, the mare- to highland-derived mete-
orites ratio is B:(F+M) = 10:(30+14) = 1:4.4, rather close
to —1:5. The abundances of source craters representing
different petrologic types are: B = 6, F = 30, and M = 13.
So B:(F+M) = 6:(30+13) = 1:7. This is not as close to the
known proportion of mare to highland areas (—1/5), but
keeping in mind that the numbers of the source craters,
and especially those craters that are sources for mare ba-
salt meteorites (only six) are small, the 1:7 ratio looks
reasonably close to 1:5 and one may conclude that the
lunar meteorites are a rather representative and random
sample of the upper part of lunar crust.
3.4. Ages of meteoritic mare basalts: Most of the me-
teoritic mare basalts have been dated by several tech-
niques. As a rule, for a given meteorite the age values
determined by the Sm-Nd, U-Pb and Rb-Sr techniques are
close, but those determined by the K-Ar technique are
often lower, probably due to loss of argon in subsequent
thermal episode(s). So, for our consideration we used
values determined by the Sm-Nd, U-Pb and Rb-Sr tech-
niques (see Fig. 1), and only in one case the K-Ar value
[13] because no other techniques were applied to this
meteorite. Fig. 1 shows what has been noted already by
other researchers [e.g., 13, 14, 15]: the meteorite mare
basalts show a time span broader than basalts sampled by
the Apollo and Luna missions. It is interesting that the
meteorite basalt ages fill the gaps in the Apollo/Luna ba-
salt age distribution (see recent summary in [16]) and
generally are in a good agreement with the mare basalt
age distribution determined by the crater count technique
[17] as was mentioned earlier by [14].
4. Conclusions: The above analysis shows:
- A significant part of the lunar meteorite source cra-
ters are smaller than hundreds of meters in diameter;
- Cryptomaria seem to be rather abundant in lunar
highlands;
- The proportions of lunar meteorites belonging to
three broad petrologic groups (mare basalt/gabbro, feld-
spatic highland breccias, mingled breccias which are a
mixture of mare and highland components) seems to be
proportional to the areal distribution of these rocks on the
lunar surface,
- The meteorite mare basalt ages show a range from
—2.5 to 4.35 Ga and fill the gaps in the Apollo/Luna basalt
age distribution.
Acknowledgments. We acknowledge Kevin Righter,
who compiled the Lunar Meteorite Compendium, which
was the starting point and became essentially the basis of
our work, and Carle Pieters, James Head and Mikhail
Figure 1. Lunar meteorite mare basalt ages of crystalliza-
tion in comparison with the Apollo/Luna mare basalt ages
and ages of lunar mare units determined by the crater
count technique [Hiesinger et al., 2003].
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Planet. Sci. 36, #2361. [4] Zeigler R. A. et al. (2007) Lu-
nar Planet. Sci. 38, #2110. [5] Basilevsky A.T. et al.
(2009) PSS, submitted. [6] Heiken G. H. et al (1991) Lu-
nar Sourcebook. A User’s Guide to the Moon, Cambridge
University Press, 736 p. [7] Wilhelms D. (1987) The Geo-
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Lunar Meteorites: What They Tell us About the Spatial and Temporal Distribution of Mare Basalts

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