Dho 1180

Lunar Mingled Breccia
(basalt-bearing fragmental regolith breccia
predominantly feldspathic)

standby for dhofar 1180 photo
Found January 18, 2005
18° 54′ 52′ N., 54° 20′ 42′ E. A single elongated fusion-crusted stone, weighing 115.2 g, was found by Michael Farmer while searching for meteorites in Oman. A section of the meteorite was submitted to Northern Arizona University (T. Bunch and J. Wittke) and Washington University in Seattle (R. Korotev) for analysis and classification, and Dhofar 1180 was determined to be a lunar meteorite unpaired to any other lunar find.

Preliminary studies have determined that Dhofar 1180 is a polymict breccia comprised primarily of clasts consisting of feldspathic anorthositic material consistent with a highlands origin. Fe-enriched, chemically zoned, mafic mineral inclusions, which constitute ~33% of the breccia, are thought to represent late-stage fractionation products of a mare basalt. The Ti content of these minerals are consistent with very-low-Ti mare basalts. All of these components show evidence of a slight preferred orientation. In addition, clasts of granulite and crystalline impact-melt breccias are present, as well as grains of olivine, pyroxene, and anorthite (Zhang and Hsu, 2006). This breccia is a rare mixture of mare material and feldspathic highlands material that is similar to that found in Calcalong Creek and Y-983885, although Dhofar 1180 is less magnesian and contains a much lower abundance of incompatible elements (no KREEP was identified). The clasts identified in Dhofar 1180 consist primarily of ferroan anorthosites, together with more mafic gabbroic anorthosites, anorthositic gabbros, norites, troctolites, olivine gabbros, and impact-melt breccias (Bunch et al., 2006; Korotev et al., 2009).

Diverse glasses of both mafic and feldspathic composition are present, with and without mineral inclusions, which are consistent with multiple impact events. Other glasses resemble regolith agglutinates. Based on these observations it was inferred by Zhang and Hsu (2009) that NWA 1180 had a regolith origin. They found that some glasses are consistent with a highly fractionated mare basalt component. One P-rich glass clast initially described as KREEP has been more accurately described as a granite–quartz-monzogabbro immiscible liquid by Korotev et al., (2009). With its Fe-rich mafic clasts and comparatively low Th abundance of 0.7–0.9 ppm, the host rock likely originated on the lunar nearside from a location distant from the PKT region, and from a location distinct from any previously studied lunar rock.

In a diagram comparing Sc vs. Sm for the lithologies of the FHT, PKT, SPA, and maria, NWA 1180 plots as a mixture of feldspathic highlands material containing ~33% mare basalt (Korotev et al., 2009). However, a petrographic analysis of NWA 1180 determined that a mare basalt component was very rare, and therefore, they proposed that the low Sm and intermediate Fe and Sc contents of NWA 1180 are actually the consequence of a mafic, KREEP-poor component derived from plutonic rocks of the FHT. In light of that finding, the use of the term ‘mingled’, typically used to describe the ternary mixture of FHT, PKT, and maria commonly found in the Apollo samples, might not be strictly accurate for this meteorite.

During a subsequent trip to the find area in February of 2005, Eric Olson found a small 3.1 g paired stone lying within 100 feet of the site of the original stone, and the following day Michael Farmer found two additional small paired stones weighing 2.04 and 0.78 grams. The specimen of Dhofar 1180 pictured above is a 0.304 g full slice, while the photo below shows an in situ photo of the complete 115 g main mass.

standby for dhofar 1180 photo
Photo courtesy of M. Farmer

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