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In Jolliff et al. (2004), Korotev
et al. (2004), and Zeigler et al. (2005) we suggest,
mainly on the basis of data for the LAP
02205 stone, that LAP derives from the same source
crater on the Moon as NWA
032/479 and, in fact, may well derive from the
same basalt flow. Since completing those works, we
now have compositional (mainly trace-element) data
for 6-7 subsamples each of all 6 LAP stones as well
as the NWA 479 stone. We repeat the compositional arguments
here with all the data. We also have new data for 8
subsamples of NWA 4734.
In the plots below, each LAP point represents a subsample of 27-49 mg
in mass (mean: 35 mg), each NWA 032 point (Fagan et al., 2002) represents
a subsample of 8-23 mg (mean: 15 mg), each NWA 479 point represents a
~36-mg subsample, and each NWA 4734 point represents a 25-mg subsample.
For comparison, we also include data for Apollo 12 ilmenite basalts.
Each Apollo 12 point represents a published analysis for one of 12 basalt
samples. Among Apollo mare basalts, the Apollo 12 basalts are most similar
in composition to LAP and NWA 032/479 (Jolliff et al., 2004; Joy et al.,
2004; Mikouchi et al, 2004; Nyquist et al., 2005; Taylor & Day, 2004).
The plots show several things:
1) The six LAP stones are indistinguishable from each other in composition.
2) NWA 4734 is compositionally indistiguishable from the LAP stones.
The two meteorites are almost certainly launch paired.
3) The most Sc-rich (=olivine
poor) subsamples of NWA 032/479 overlap in composition
with the LAP/NWA 4734 subsamples.
4) Differences between average
LAP and average NWA 032/479 are comparable to the scatter
among different samples of Apollo 12 ilmenite basalt
(for example), which almost certainly all derive from
a single basalt flow.
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For a given meteorite, the scatter in the data
results mainly from sampling error - the relative proportions
of the minerals are not identical among the small subsamples.
Sc (scandium) is a trace element that resides manly in
pyroxene. Thus, the X axis of each plot is effectively
a measure of the relative pyroxene abundance. Co (cobalt)
is carried mainly by olivine. For NWA, the olivine abundance
varies considerably among the subsamples. The anticorrelation
reflects the fact that as the abundance of olivine goes
up, the abundance of pyroxene goes down.
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Cr (chromium) occurs mainly in chromite which,
in turn, occurs mainly in olivine as inclusions. NWA 032/479
is richer in olivine and chromite than LAP. That is what
we would expect if NWA derives from near the bottom of
a basalt flow where olivine accumulated by settling.
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Eu (Europium) occurs in plagioclase and in mesostasis
in lunar rocks.
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La (lanthanum) is an incompatible trace element
that occurs mainly in mesostasis (the gunk that occurs
between the grains of the major minerals, plagioclase,
pyroxene, and olivine). The principal difference between
NWA-LAP and Apollo 12 ilmenite basalts is that the meteorites
are richer in incompatible elements and have lesser concentrations
of titanium and magnesium.
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References
Day J. M. D., Taylor L. A., Floss C., Patchen
A. D., Schnare D. W., Pearson D. G. (2006) Comparative
petrology, geochemistry and petrogenesis of evolved, low-Ti
lunar mare basalt meteorites from the La Paz Icefield.
Antarctica. Geochimica et Cosmochimica Acta 70,
1581–1600.
Fagan T. J., Taylor G. J., Keil K., Bunch
T. E., Wittke J. H., Korotev R. L., Jolliff B. L., Gillis
J. J., Haskin L. A., Jarosewich E., Clayton R. N., Mayeda
T. K., Fernandes V. A., Burgess R., Turner G., Eugster
O., and Lorenzetti S. (2002) Northwest
Africa 032: Product of lunar volcanism. Meteoritics & Planetary
Science 37, 371–394.
Jolliff B. L., Zeigler R. A., and Korotev R. L. (2004) Petrography
of lunar meteorite LAP 02205, a new low-Ti basalt possibly launch paired
with NWA 032 (abstract). In Lunar and Planetary Science XXXV,
abstract no. 1438, Lunar and Planetary Institute, Houston.
Joy K. H., Crawford I. A., Russell S. S., and Kearsley A. (2004) Mineral
chemistry of LaPaz Ice Field 02205 – A new lunar basalt (abstract).
In Lunar and Planetary Science XXXV, abstract no. 1545, Lunar and Planetary
Institute, Houston.
Korotev R. L., Zeigler R. A., and Jolliff B. L. (2004) Compositional
constraints on the launch pairing of LAP 02205 and PCA 02007 with other
lunar meteorites (abstract), Lunar and Planetary Science XXXV, abstract
no. 1416, Lunar and Planetary Institute, Houston.
Mikouchi T. T., Chokai J., Arai T., Koizumi E., Monkawa A., and Miyamoto
M. (2004) LAP02205
lunar meteorite: Lunar mare basalt with similarities to the Apollo
12 ilmenite basalt (abstract). In Lunar and Planetary Science
XXXV, abstract no. 1548, Lunar and Planetary Institute, Houston.
Nyquist L. E., Shih C.-Y., Reese Y., and Bogard D. D. (2005) Age
of lunar meteorite LAP02205 and implications for impact-sampling of
planetary surfaces (abstract). In Lunar and Planetary Science XXXVI,
abstract no. 1374, Lunar and Planetary Institute, Houston.
Righter K., Brandon A.D., and Norman M.D. (2004) Mineralogy
and petrology of unbrecciated lunar basaltic meteorite LAP 02205 (abstract).
In Lunar and Planetary Science XXXV, abstract no. 1667, Lunar and Planetary
Institute, Houston.
Taylor L. A and Day J. M. D. (2005) FeNi
metal grains in La Paz mare basalt meteorites and Apollo 12 basalts (abstract).
In Lunar and Planetary Science XXXVI, abstract no. 1417, 36th Lunar
and Planetary Science Conference, Houston.
Zeigler R. A., Korotev R. L., Jolliff B.
L., and Haskin L. A. (2005) Petrology
and geochemistry of the LaPaz icefield basaltic lunar meteorite
and source-crater pairing with Northwest Africa 032. Meteoritics & Planetary
Science 40, 1073–1102.
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