Petrogenesis and Shock Metamorphism of Basaltic Lunar Meteorites Northwest Africa 4734 and 10597

Abstract

We present comprehensive compositional and mineralogical results on two basaltic lunar meteorites Northwest Africa (NWA) 4734 and NWA 10597 to constrain their igneous mineralogy and metamorphic characteristics, and examine the potential pairing relationship among them and other meteorites (e.g., basaltic lunar meteorites collected from LaPaz Icefield, Antarctica (LAPs)). NWA 4734 and NWA 10597 are low‐Ti (3.2-3.5 wt.% TiO2), low‐Al (10-12 wt.% Al2O3), low‐K (880-1,300 ppm K) mare basalts derived from evolved parental magma (Mg# (molar Mg/[Mg + Fe] x 100) = 33.6-38.3) and are mostly composed of pyroxene (52.7-55.5 vol.%), plagioclase/maskelynite (27.5-29.3 vol.%), olivine (6.7-7.6 vol.%), and late‐formed components (i.e., mesostasis). Pyroxene and olivine in these two meteorites exhibit a multimodal compositional distribution, indicating multiple generations of these mafic minerals, which correspond to different evolution phases (e.g., magma chamber, ascending, and eruption) during the solidification of the basaltic parental magma. Immiscibility played an important role in the evolution of the late‐stage melts, inducing fractionation involving Fe‐rich and Si, K‐rich melts within mesostasis. Considering the extensive partial transformation of plagioclase to maskelynite across the sections, the average shock pressure endured by NWA 4734 and NWA 10597 is probably 23-29 GPa, which is consistent with the pressure condition (below 29.8 GPa) recorded by quartz. Similar textures, bulk composition, modal mineral proportions, and mineral compositions indicate that NWA 4734, NWA 10597, and the LAPs most likely originated from the same region of the Moon and both experienced intensive shock events. Show more