Geology Reference
In-Depth Information
15
Comparison of ANSMET
lunar meteorites to
surface and trench soil
samples from the Apollo sites
A14
(6)
10
KREEPic
A12
(12)
7
5
4
A15
(21)
3
A16
(45)
1
2
A17
(67)
A11
(5)
¥
Basaltic
¢
1
E
U
T
0.7
A16
(1)
A17
(1)
Q
0.5
P
L
0.4
M
B
I
$
0.3
Feldspathic
A
£
G
0.2
3
4
5
6
78910
FeO
T
(%)
15
20
25
Figure 6.19.
Like Figure 6.4, but comparison of ANSMET lunar meteorites, most of which are regolith breccias, to regolith (soil)
samples from the
Apollo
missions (gray fields). Most feldspathic lunar meteorites have lower concentrations of incompatible ele-
ments (Th) than the
Apollo
16 regolith. Most
Apollo
16 regolith samples plot on the dark (high-Th) part of the field. The number
in parentheses is the number of soil samples that define the field. The anomalous
Apollo
16 sample is highly immature 67711 and
the anomalous
Apollo
17 sample is 74220, the “orange glass” soil. Symbol key is in Table 6.1.
the feldspathic lunar meteorites provided a more typical
sampling of the upper crust of the feldspathic highlands,
particularly its composition, than did the
Apollo
16 sam-
ples [
Palme et al
., 1991]. Another difference between the
Apollo
16 collection and the feldspathic lunar meteorites
involves anorthosite. A common lithology of the
Apollo
16 regolith is shocked, but unbrecciated, highly feld-
spathic (>95% plagioclase) anorthosite of plutonic origin
[e.g.,
Warren
, 1990, 1993]. The ubiquity of “ferroan anor-
thosite” (
Mg'
: 50-70) at the
Apollo
16 site supports the
magma ocean model in which the Moon was mainly
molten early in its history and the anorthosite was a flo-
tation cumulate [
Warren
, 1985;
Wieczorek et al
., 2006].
Recently, large exposures of anorthosite consisting of
>99% plagioclase have been identified from orbit at
numerous locations on the lunar surface [
Ohtake et al
.,
2009]. Thus, it is curious that lithic clasts of ferroan
anorthosite are rare in feldspathic lunar meteorites
[
Korotev et al
., 2003a, 2009b]. Most lithic clasts in the
feldspathic meteorites from ANSMET and hot deserts
are granulitic and impact-melt breccias that are more
mafic than the
Apollo
16 ferroan anorthosites. The
reason for this discrepancy is not yet understood.
Perhaps the most unexpected observation about the
crust to be revealed by the feldspathic lunar meteorites
is that despite having a narrow range of normative
plagioclase abundances (72-87%; Figure 6.7), the range
in
Mg'
is large, 59-77. This observation provides a
challenge for models of crust formation [
Korotev et al
.,
2003a;
Korotev
, 2005;
Arai et al
., 2008;
Treiman et al
.,
2010;
Gross et al
., 2014].
The remaining 36% of the ANSMET lunar meteorites,
two basalts and three breccias, are of mare affinity. They
probably originate from three source craters on the
Moon, craters represented by the YQEN, YAMM, and
NNL launch-pair groups (Table 1; Figures 6.8, 6.12, and
6.13). Compositionally and texturally, the NNL group
(NWA 032/479, NWA 4734, and the LAP stones) resem-
bles basalts of the
Apollo
12 and 15 collection but are a
bit younger. The basalts and basalt clasts of the YQEN
(Yamato 793274/981031, QUE 94281, EET 87521/96008,
and NWA 4884) and YAMM (Yamato 793169, Asuka
881757, MET 01210, and MIL 05035) meteorites are dis-
tinct in several ways from any
Apollo
mare basalt, most
notably their compositions and evidence for slow cooling.
In studies in which new analytical techniques are applied
to mare basalts for the purpose of addressing planetary
issues such as formation of the Moon, water on the
