Metasomatic products of the lunar magma ocean: The role of KREEP dissemination

摘要: The origin of the incompatible element-rich lunar component, KREEP, is in Lunar Magma Ocean (LMO). fractionated residual melt after crystallization LMO represents “urKREEP” (after Warren and Wasson, 1979). percentage this low enough to be within realm silicate liquid immiscibility (SLI). This process has ability split KREEP signature into K- REEP-Fractions, which are manifest as granite (K) phosphate phases present highland lithologies or quartz ferrotroctolite soils (REEP). We envisage a localized, but significant since only small portion urKREEP undergoes SLI. Norms experimental Apollo 15 basaltic immiscible glasses suggest that thevREEP-Fraction found highlands undergone post-SLI fractionation at least fayalite. significantly reduces density REEP-Fraction coupled with its viscosity (10–15 poise), it can percolate upward, metasomatizing crust. higher granitic (=∼30000 poise) inhibits mobility, forms “pods” lower rust (as required for VHK basalt petrogenesis). With identification KREEPy components, composition calculated. Using evidence, components may recombined give pre-SLI composition, liquid-liquid Kd's used calculate from granite. Both calculated compositions MgO Al2O3 FeO P2O5 than reported low- high-K compositions. REE abundances profiles slightly more LREE-enriched previously However, profile using concave-upwards, compared produced by recombining components. Pre-SLI whitlockite/apatite occurred prior order generate concave-upwards profile. magma fractionation. presence “superKREEPy” rock types accounted assimilation, olivine vitrophyres now modeled analyzed without inference mythical “high-Mg” component. Other, widespread rocks (e.g., 14 breccias, basalts, LKFM basalts) incorporation component. splitting identifiable lithological allows petrogenesis role evolution better understood.