Lunar meteorite Queen Alexandra Range 94281: Glass compositions and other evidence for launch pairing with Yamato 793274
Authors: ARAI Tomoko , WARREN Paul H. 
Published: February 2010

Abstract— Lunar meteorite Queen Alexandra Range 94281 is remarkably similar to Yamato 793274. Pairing in the conventional Earth‐entry sense is difficult to reconcile with the 2500 km separation between the find locations for these two samples. Nonetheless, both of these regolith breccias are dominated by very‐low‐Ti (VLT) mare basalt, the pyroxenes of which feature exsolution lamellae on a remarkably coarse scale (typical lamella width = 0.5–1 μm) by mare standards. The pyroxenes also show similar compositional variations (e.g., Fe# vs. Ti# trends, which confirm parentage from VLT mare basalt). Plots using Al2O3 or FeO as a tracer of the highland component indicate indistinguishable internal mare‐highland geochemical mixing trends. The same two distinctive glass types dominate the mare glass populations of both breccias. Glass type YQ1 features 0.37–0.63 wt% TiO2, 10–17 wt% MgO, and 9–11 wt% Al2O3. Glass type YQ2 features higher TiO2 (0.99–1.22 wt%), which is inversely correlated with MgO (12.6–13.8 wt%), and nearly constant (8.8 wt%) Al2O3. All of these similarities suggest that Y‐793274 and QUE 94281 are a launch pair, which we designate YQ. Most of these similarities also extend to another mare‐breccia meteorite, Elephant Moraine 87521. However, the EET 87521 mare basalt is unusually V‐poor (∼88 μg/g), whereas the YQ mare component contains ∼166 μg/g. Queen Alexandra Range 94281 features a variety of textural domains. Discrete patches of dark matrix material appear to represent clods of mature regolith that have been mixed with a coarser, relatively immature material. Interior to a frothy fusion crust are areas of massive glass that probably formed as a splash coating on QUE 94281 when it was still on the Moon. The coarse YQ and EET 87521 pyroxene exsolution features imply relatively slow cooling in either a very shallow sill or an unusually thick (ponded) lava and/or later annealing within a cryptomare.

Mare pyroclastic glasses, including the two YQ varieties, are systematically MgO‐rich compared to crystalline mare basalts. This disparity may be a consequence of limited survival of graphite—the main fuel for explosive volcanism—during formation of the mare source regions as magma ocean cumulates. Graphite (2.2 g/cm3) survived preferentially in regions that avoided extensive early melting and thus remained MgO‐rich. An apparent bimodality in the TiO2 contents of mare volcanics, especially the pyroclastic glasses, also seems a plausible consequence of petrogenesis by remelting of magma ocean cumulates. Cumulates deposited after the magma ocean evolved to ilmenite saturation had vastly higher TiO2 contents than cumulates deposited shortly before. The YQ regolith's subequal proportions of mare and highland matter are consistent with derivation from a terrain close to a mare‐highland boundary. However, a similar mixture might also develop through vertical mixing in a cryptomare or a region of thin mare coverage. Thus, unfortunately, the YQ bulk composition is not a very useful clue to the identity of the source crater.