Petrography, geochronology and source terrain characteristics of lunar meteorites Dhofar 925, 961 and Sayh al Uhaymir 449

Abstract

Dhofar (Dho) 925, 961 and Sayh al Uhaymir (SaU) 449 are brecciated lunar meteorites consisting of mineral fragments and clasts from a range of precursor lithologies including magnesian anorthositic gabbronorite granulites; crystalline impact melt breccias; clast-bearing glassy impact melt breccias; lithic (fragmental) breccias; mare basalts; and evolved (silica-rich) rocks. On the similarity of clast type and mineral chemistry the samples are likely grouped, and were part of the same parent meteorite. Phosphate Pb–Pb ages in impact melt breccias and matrix grains demonstrate that Dho 961 records geological events spanning ∼500Ma between 4.35 and 3.89Ga. These Pb–Pb ages are similar to the ages of ‘ancient’ intrusive magmatic samples and impact basin melt products collected on the lunar nearside by the Apollo missions. However, the samples’ bulk rock composition is chemically distinct from these types of samples, and it has been suggested that they may have originated from the farside South Pole-Aitken impact basin (i.e., Jolliff et al., 2008). We test this hypothesis, and conclude that although it is possible that the samples may be from the South Pole-Aitken basin, there are other regions on the Moon that may have also sourced these complex breccias.