Experimental petrology and petrogenesis of mare volcanics

The present review is an extension of a review of experimental studies by Kesson and Lindsley (1976) on mare basalts that determined melting relations over a range of pressure. Pressures of multiple saturation (olivine + pyroxene +/-Cr-rich spinel +/-ilmenite) are in the range of 5 to 12.5 kbar for primitive mare basalts and in the range of 18 to 25 kbar for picritic basalts. High-Ti picrites have augite in the subliquidus region at intermediate pressures where olivine is the liquidus phase, but orthopyroxene is the liquidus phase at multiple saturation. Because of the steep depth/pressure gradient in the outer portion of the moon (20 km/kbar), these pressures imply great depths of melting within the moon and some means of transporting magmas hundreds of kilometers to the surface without significant chemical modification, if both olivine and pyroxene were left in the residuum.