The Petrology of Lunar Breccia 15445 and Petrogenetic Implications

Lunar breccia 15445, collected near the rim of Spur Crater, contains iron-rich olivine and ortho-pyroxene mineral clasts and two types of white lithic clasts. The dominant type (Type A) is composed principally of anorthite - magnesian orthopyroxene and appears to be a low-pressure cumulate from a magnesian, high-Al basalt. A minor type (Type B) is composed of olivine + chrome pleonaste + aluminous orthopyroxene + minor plagioclase. Type B clasts have affinities to terrestrial spinel peridotites and have a REE pattern unique for the moon. Considerations of the observed mineralogy and the trace element geochemistry suggest that garnet was originally a phase in this peridotite but was subsequently lost during subsolidus reequilibration. Hence, Type B clasts provide indirect evidence for the existence of garnet in the lunar interior.