Origin of Lunar Basalts

A long-standing paradigm for the origin of lunar mare basalts has been that they are the late products (~3.3 to 3.7 Ga) of remelting of a deep cumulate pile that was formed from the solidifcation of a 400 km deep, global magma ocean between 4.4 and 4.3 Ga. A unique class of lunar mare magmas, the ultramafic glasses provide key evidence of the conditions and processes that led to the cumulate remelting. Our research involves determination of the conditions that led to remelting in the moon's interior. This is accomplished by starting with high-pressure, high-temperature experiments that provide evidence of the conditions of ultramafic glass production. The work is beginning to provide a resolution of the question of the origin of the lunar mare basalts, which have remained enigmatic. The lunar ultramafic magmas are produced deep in the moon's interior and as they rise through the shallow crust on their ascent to the moon's surface they remelt and variably interact with the shallow cumulate pile. Work with graduate student Lindy Elkins indicates that an important driving mechanism for the early stages of cumulate remelting may have been the giant impacts that occurred during the ~3.9 Ga late heavy bombardment.