[PPS07-P13] The systematic investigations of high-pressure minerals in lunar basaltic meteorites
Keywords:Moon, Lunar mare basalt, High-pressure minerals
NWA 032 consisted of a basaltic portion and a small amount of breccia. Olivine, Ca-pyroxene, and low-Ca pyroxene occurred as phenocrysts in the basaltic portion. The matrix was filled with spherulitic textures consisting of plagioclase and Ca-pyroxene. Several shock-melt veins and melt-pockets occurred in the basaltic portion. Several olivine grains next to the shock-met veins have transformed into ringwoodite. The estimated shock pressure is ~13 GPa at least. The petrological and mineralogical features of NWA 479 were similar to those of NWA 032. Olivine grains entrained in the shock-melt veins dissociated into bridgmanite + (Mg, Fe)O. The estimated shock pressure is ~23 GPa at least. NWA 4898 showed the basaltic texture. Olivine occurred as phenocrysts. The matrix portion consisted mainly of Ca-pyroxene and plagioclase. A trace amount of silica minerals was entrained in the shock-melt veins. Some silica minerals in the shock-melt veins were stishovite. Ca-pyroxene next to the shock-melt veins dissociated into ahrensite, pyroxene-glass, and (probably) silicate titanite. The estimated shock pressure is ~9 GPa at least. NWA 2977 showed a gabbroitic texture and consisted mainly of olivine, low-Ca pyroxene, Ca-pyroxene, and plagioclase. Olivine grains next to or entrained in the shock-melt veins have transformed into ringwoodite. The estimated shock pressure is ~16 GPa at least. Two third of NWA 2727 was breccia and the other was gabbroitic. The gabbroitic portion consisted of olivine, low-Ca pyroxene, Ca-pyroxene, and plagioclase. The breccia portion included silica besides the fragments of the gabbroitic portions. Silica minerals entrained in the shock-melt veins or melt-pockets have transformed into coesite. The estimated shock pressure is ~3 GPa at least.
The shock-induced melting textures were observed in all investigated lunar mare basalt samples. Although the high-pressure polymorphs of olivine, Ca-pyroxene, and silica minerals were identified, the high-pressure polymorphs of plagioclase, which are abundant in other shocked meteorites, were not identified. In addition to previous studies [1–3], the present study reveals that many kinds of high-pressure polymorphs occur in the lunar mare basalt, implying that most lunar mare basalts have experienced the heavy impact events.
 Ohtani E. et al. PNAS 108, 463–46, 2011.
 Miyahara M. et al. NatureGeosci 4:1737, 2013.
 Kayama M. et al. Sci.Adv. 4: eaar4378, 2018.