Petrology of the Western Highland Province: Ancient crust formation at the Apollo 14 site

摘要: Plutonic rocks found at the Apollo 14 site comprise four lithologic suites: magnesian suite, alkali evolved lithologies, and ferroan anorthosite suite (FAN). Rocks of include troctolite, anorthosite, norite, dunite, harzburgite; they are charaterized by plagioclase ≈An95 mafic minerals with mg#s 82–92. Alkali generally have ≈An90 to ≈An40 82–40. Lithologies quartz monzodiorite, granite, felsite. Ferroan anorthosites ≈An96 45–70. Whole rock geochemical data show that most samples all cumulates little or no trapped liquid component. Norites may contain significant component, some norites represent cumulate-enriched, near-liquid compositions, similar KREEP basalt 15386. Evolved lithologies partial related fractionation (quartz monzodiorite), immiscible melts derived from these magmas (granites), impact preexisting granite (felsite). Plots whole mg# versus Ca/(Ca + Na K) a distinct gap between suggesting either parent physical processes formation. Chondrite-normalized rare earth element (REE) patterns both ranges, despite large difference in major chemistry. Current models for origin call komatiitic magma early ocean cumulates; must assimilate plagiophile elements form troctolites low pressures highly enriched component so resulting mixture has REE concentrations high-K KREEP. There as yet plausible scenarios can explain unusual requirements. We propose melting primitive lunar interior buffering ultramagnesian provides more reasonable pathway troctolites. formed crystallization compositions If is then through combined assimilation-fractional cumulates.