Alkali norite, troctolites, and VHK mare basalts from breccia 14304

Abstract

Twelve clasts were separated from breccia 14304 for consortium study: six pristine highlands rocks, two mare basalts, and four nonpristine highlands rocks. The pristine highlands rocks include representatives of the magnesian troctolite‐anorthosite and alkali suites, the two most common subgroups of the Mg suite found at the Apollo 14 site. Two troctolite clasts have olivine (∼Fo 90) and plagioclase (∼An 94) compositions similar to one group of Apollo Htroctolites. One also contains spinel (Mg′66–85). Incompatible element abundances in one are similar to those of 14305 troctolites, although the HREE (heavy rare earth elements) pattern is distinct among Apollo 14 troctolites. A dunite clast (∼Fo 89) may be an unrepresentative piece of a troctolite. Alkali lithologies include an alkali anorthosite and an alkali norite, which is a rock type not previously described. The alkali norite has a pristine igneous texture and contains inverted pigeonite (Mg′ 64), plagioclase (An82), K‐feldspar, ternary feldspar, REE‐rich phosphates, and silica. It resembles alkali gabbronorites from Apollo 14 and 67975 in mineralogy and mineral compositions. Alkali lithologies and phosphate‐bearing magnesian anorthosites from Apollo 14 may have formed from Mg‐rich magmas that assimilated various amounts of material rich in P and REE. This material could be a fractionated derivative of urKREEP. Another pristine clast from 14304 is an Mg‐gabbronorite. The two mare basalt clasts are very high potassium (VHK) basalts. They have 4 mg/g K and K/La ratios of 580 and 700. The parent magmas of VHK basalts could have formed from typical low‐Ti, high‐Al basaltic magmas by assimilation of K‐rich material. This material could also be a fractionated derivative or urKREEP. Nonpristine 14304 clasts include melt‐textured anorthosites and an augite‐rich poikilitic melt rock. The latter is probably polymict, but its major component must be an Mg‐suite gabbro.