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Chemical Classification of
Lunar Meteorites
LAP 02205 et al.
  
NWA 032/479, NWA 4734, and LAP 02205 et al. likely all originate from the same source crater.
All three meteorites have 3% TiO2. 

Launch Pairing of LAP, NWA 4734, and NWA 032/479

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.



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.




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.
  




Eu (Europium) occurs in plagioclase and in mesostasis in lunar rocks.
  

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.
  

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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