Composition of the Cayley formation at Apollo 16 as inferred from impact melt splashes

摘要: Chemical data for impact melt splashes (IMS) collected at the Apollo 16 landing site show that Ni concentrations and FeO-Ni, Cr-Ni, Co-Ni correlations are consistent with a chondritic meteoritic component present levels between approximately 1.5 11 wt %. Like soils, IMS intermediate in composition to rocks. The chemical two main compositional groups. Group A (28 samples) chemically distinct from local soils very similar mixtures of anorthosite low-Sc VHA (LScVHA) Calculated meteorite-free basis, their average Sc concentration, La/Sc, MgO/Sc, TiO2/MgO ratios, mg′ value 6.1 ug/g, 1.94, 9800, 0.066, 0.74, respectively. B (seven have equivalents among soils. Five samples mature central southern parts site; more 67601 67941 North Ray Crater. Generally, enriched anorthositic norite (67215) or thereof as compared IMS. MgO, subgroup five 9.3 1.41, 5780, 0.124, 0.66, corresponding values 7.5 1.04, 7400, 0.090, 0.71, (and most soils) minor high-Ti not If this is mare basalt, its concentration 1.6 seven been dated by rare gas methods all 2 m.y. exposure ages, an age generally associated South These potentially likely quenched volume produced impact. signature impacting projectile chondritic, 7.3 large, coherent sheets terrestrial impacts, represented homogeneous respect target lithologies. Target lithologies Crater, which host rocks IMS, include anorthosite, LScVHA rocks, HScVHA dimict breccias. With exception 61016, portion analyzed breccias has composition, implying dimensional scales LScVHA-type do extend 1–10 cm scale observed difference surface part implies stratigraphic variation dominant type rock within Cayley Formation. mixing-model results model dominate layer. layer beneath. penetrated both layers, types traceable ejecta material. Its was formed primarily lower give That also sampled indicated affinities composition. Away reflecting soil development Estimated compositions TiO2, Sc, La 0.69 7.1 % 10.5 21.2 respectively, 0.38 5.9 11.8 subsurface An estimated Descartes Formation 0.25 3.5 7.7 2.2 KREEPy, magnesian, less aluminous than