Basaltic Lunar Meteorites
There is compositional, petrographic, and cosmic-ray-exposure evidence that many of the basaltic lunar meteorite stones are related to each other, that is, that they are paired. Some are paired in the conventional sense - they are different fragments with different names of a single meteoroid. Others appear to be from different meteoroids that were ejected from the Moon by a common impact. Such meteorites are said to be "launch paired" or "source-crater paired." Launch pairing cannot be proved with certainty, but we assume that meteorites that are (1) found too far apart on Earth to be terrestrially paired but that (2) are compositionally and mineralogically similar and (3) were ejected from the Moon at the same time are probably launch paired (e.g., Nishiizumi et al. 2006).
We present some of the compositional evidence for pairing here. For this discussion, we include all meteorite stones with >12% FeO as "basaltic."
The figure above is a complicated plot that only a trace-element geochemist could love!
In basalts, scandium (Sc) is carried mainly by pyroxene and cobalt (Co) by olivine. The NWA 773 stones, particularly the olivine gabbro cumulate (OGC) lithology (green symbols), have low Sc/Co because they are rich in olivine. The YAMM stones (below), with little or no olivine, have high Sc/Co.
The NWA 773 basaltic magma apparently derived from a mantle source that was particularly depleted in plagioclase. As a consequence, all the stones of the NWA 773 clan are depleted in elements that are carried mainly by plagioclase - sodium (see FeO-Na2O plot below), strontium, and europium (Eu). The NWA 773 stones have high Sm/Eu because Eu is low, not because samarium (Sm) is high (see FeO-Sm plot below; also; Jolliff et al., 2003).
In the plots presented here, each circular geometric symbol represents a small (20-30 mg) subsample from one of the NWA-773 clan of lunar meteorite stones. The overlap of the olivine-phyric basalt (OPB), ferrobasalt (FB), breccia (brx), and the OGC lithologies among the different stones and mutual difference of all the NWA-773-clan samples from other basaltic lunar meteorites is one argument that NWA 773, 2700, 2727, 2977, 3160, 3170, 3333, 6950, 7007, 8127, and Anoual are all paired, despite the lithologic (rock type) diversity among the stones. The letters and numbers each represent the mean composition of other basaltic lunar meteorite stones.
The plots show several things:
NNL meteorites. The 6 LAP basalt stones [symbols 1-6], which are mutually paired (all from one meteoroid), are indistinguishable from each other in composition. NWA 4734 is indistiguishable from the 6 LAP stones. The two meteorites are almost certainly launch paired. NWA 032 and NWA 479, which are paired with each other, are also mutually indistinguishable. Meteorite NWA 032/479 is similar to meteorites LAP and NWA 4734. NWA 032/479 may be part of the launch pair group (Ziegler et al., 2005; see below). In other words two or three different rocks were ejected from the Moon by a single impact. One landed in Antarctica, the other 2 in northwestern Africa.
YQNE meteorites. Yamato 793274 and Yamato 981032 are paired stones. EET 87521 and EET 96008 are paired stones. It is likely that these two meteorites along with QUE 94281 and NWA 4884 - the YQNE meteorites - are mutually launch paired (Arai & Warren, 1999; Korotev et al., 2003; Korotev et al., 2009). All are breccias containing some highlands material. The variation in concentrations, for example, of Fe and Sc (below) among the stones reflects variation in the ratio of mare basalt and anorthosite.
YAMM meteorites. Asuka 881757 and Yamato 793169 have long been considered to be launch paired (Warren & Kallemeyn, 1993; Thalmann et al., 1996). MIL 05035, which is texturally similar to Asuka and compositionally similar to both Asuka 881757 and Yamato 793169, is likely part of the launch-pair group (Zeigler et al., 2007). MET 01210 is a breccia that may contain some feldspathic material. It appears to also be part of the YAMM launch-pair group on the basis of mineral and bulk composition (Arai et al., 2005; Zeigler et al., 2007). The data presented here are consistent with the launch-pairing hypothesis in that the composition of MET 01210 is consistent with a mixture of YAM material and material of the feldspathic highlands.
Other basaltic lunar meteorites. On the basis of the plots presented here, there is no strong reason to believe that Dhofar 287, NEA 003, NWA 3136, NWA 4898, NWA 8632, or Kalahari 009 are related to any of the other basaltic lunar meteorites.
Arai T. and Warren P. H. (1999) Lunar meteorite Queen Alexandra Range 94281: Glass compositions and other evidence for launch pairing with Yamato 793274. Meteoritics & Planetary Science 34, 209-234.
Arai T., Misawa K. and Kojima H. (2005) A new lunar meteorite MET 01210: Mare breccia with a low-Ti ferrobasalt (abstract). In Lunar and Planetary Science XXXVI, abstract no. 2361, Lunar and Planetary Institute, Houston.
Jolliff B. L., Korotev R. L., Zeigler R. A., Floss C., and Haskin L. A. (2003) Northwest Africa 773: Lunar mare breccia with a shallow-formed olivine-cumulate component, very-low-Ti (VLT) heritage, and a KREEP connection. Geochim. Cosmochim. Acta 67, 4857–4879.
Korotev R. L., Jolliff B. L., Zeigler R. A., and Haskin L. A. (2003) Compositional constraints on the launch pairing of three brecciated lunar meteorites of basaltic composition, Antarctic Meteorite Research 16, 152–175.
Korotev R. L, Zeigler R. A., Jolliff B. L., Irving A. J., and Bunch T. E. (2009) Compositional and lithological diversity among brecciated lunar meteorites of intermediate iron composition. Meteoritics & Planetary Science 44, 1287–1322.
Nishiizumi K., Hillegonds D. J., and Welten K. C. (2006) Exposure and terrestrial histories of lunar meteorites LAP 02205/02224/02226/02436, MET 01210, and PCA 02007 (abstract), In Lunar and Planetary Science XXXVII, abstract no. 2369, Lunar and Planetary Institute, Houston.
Thalmann C., Eugster O., Herzog G. F., Klein J., Krähenbühl U., Vogt S., and Xue S. (1996) History of lunar meteorites Queen Alexandra Range 93069, Asuka 881757, and Yamato 793169 based on noble gas isotopic abundances, radionuclide concentrations, and chemical composition. Meteoritics & Planetary Science 31, 857-868.
Warren P. H. and Kallemeyn G. W. (1993) Geochemical investigations of two lunar mare meteorites: Yamato-793169 and Asuka-881757. Proc. NIPR Symp. Antarct. Meteorites 6, 35-57. Nat. Inst. Polar Res., Tokyo.
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.
Zeigler R. A., Korotev R. L., and Jolliff B. L. (2007) Petrography, geochemistry, and pairing relationships of basaltic lunar meteorite stones NWA 773, NWA 2700, NWA 2727, NWA 2977, and NWA 3160 (abstract). In Lunar and Planetary Science XXXVIII, abstract no. 2109, 38th Lunar and Planetary Science Conference, Houston.