Plagioclase saturation in lunar high-titanium basalt

High-titanium basalt collected at the Apollo 11 site was sparsely porphyritic on eruption. Phenocrysts of anorthite are reported for the first time, and were present with a few phenocrysts of olivine, pigeonite, augite, ilmenite and spinel in the liquid. That liquid has a composition which closely resembles the average rock at the site, and also closely resembles new analyses of the liquids produced in equilibrium with anorthite, olivine, pigeonite, augite, ilmenite and spinel in melting experiments at low pressure on samples 10020, 10062 (which are the first of the more abundant low-potassium group lava to have been studied). We deduce that the Apollo 11 basalt was erupted with the temperature and composition of a liquid in cotectic equilibrium at low pressure with these six phenocryst mineral species. This condition is a mandatory consequence of the hypothesis that the lunar maria are slowly consolidated giant lava lakes. It is incompatible with the hypothesis that these mare surface basalts, are unaltered partial melts extracted from the deep lunar interior. Attention is drawn to the consequences of the nearly eutectic character of the crystallization of the high-titanium basalts.