BULK-COMPOSITIONAL STUDY OF THREE DHOFAR LUNAR METEORITES: ENIGMATIC SIDEROPHILE ELEMENT RESULTS FOR DHOFAR 026

We report some of the first bulk analysis data for three new lunar meteorites found in Oman, during December, 1999 and January, 2000. The analyzed samples are: 1) Dhofar 025, a 104 mg aliquot from a larger powder from the Vernadsky Institute; 2) Dhofar 026, a 57 mg chip (post-pulverization mass), also from the Vernadsky Institute; and 3) Dhofar 081, a 421 mg chip, donated by the Institut fur Mineralogie (Berlin). A combination of INAA and fused-bead electron-probe analysis has been employed. Because our study only commenced a short time ago, some of our data (Table 1) are still preliminary. In general, our data for diagnostic parameters such as Fe/Mn confirm the lunar provenance of all three meteorites. An admittedly imprecise analysis by Greshake et al. [1] indicated that Dhofar 081 has an uncommonly low Fe/Mn ratio, by lunar standards. Our data confirm an extraordinarily low Fe/Mn (63); literature data for 16 other lunar meteorites average 72.1± 4.3 (1σ). Nonetheless, all other signs clearly indicate that Dhofar 081 is an anorthositic breccia of lunar highland origin. The petrology of Dhofar 025 and 026, as well as additional bulk-chemical data, are presented in companion abstracts [2-4]. Dhofar 025 is compositionally a typical (e.g., Smand Th-poor) lunar meteoritic regolith breccia [4]. Dhofar 026 is dominated by a single textural domain, its poikilitic impact-meltproduced groundmass [2]. However, an intriguing feature of this impact melt breccia is the survival of scattered igneous-textured spherules, typically ~100 μm across. As illustrated in Fig. 1 (transmitted light), the rock appears texturally heterogeneous on scales of mm to cm. Greshake et al. [1] have classified Dhofar 081 as a fragmental breccia. This choice seems correct. However, this sample’s complex and unusual texture is difficult to pigeonhole. Its texture is completely unlike that of Dhofar 026. Dhofar 081 (Fig. 2) contains a great variety of small lithic clasts (mostly fine-grained impact-melt breccia) set in a groundmass remarkably rich in swirly glass (schlieren), often brownish in color. No obvious regolith components (glass spherules, intact agglutinates) are discernible. Noble gas contents [1] are low, but virtually the same as in MAC88105, which is by all accounts a regolith (albeit, immature regolith) breccia. In any case, Dhofar 081 appears to be another thoroughly polymict lunar meteorite, which is probably at least roughly representative of the composition of its highland source region. All three Dhofar lunar meteorites have probably been compositionally altered to some degree during their residence in the desert. This alteration is most obvious in Dhofar 025, where the Sr content is more than 10 times higher than the typical concentration in unweathered but otherwise similar lunar highland regolith samples. Lesser, but still significant Sr contamination is also present in Dhofar 026 and 081. Our (preliminary) results for Ba in Dhofar 026 and especially Dhofar 025 also indicate contamination. However, the preservation of troilite and FeNi metal in Dhofar 026 appears good [3], so we can reasonably suppose that most elements, including siderophile elements, have not been radically altered. Dhofar 081 is easily the most pure-anorthositic