Thermal evolution of a thicker KREEP liquid layer

We consider the thermal evolution of the thickened potassium, rare earth el ement, and phosphorous (KREEP) liquid layer that extends over a significant fraction of the lunar nearside with a prescribed thickness and heat produc tion and beneath an insulting anorthosite crust: This layer represents a su bcrustal heat source beneath the Procellarum-Imbrium terrane and may be res ponsible for the localized and anomalous enrichments of highly incompatible elements in this terrane. In some models this thickened liquid layer is th e thermal source for the remelting of mare basalts and also produces the pa rent magmas of the magnesian suite. Indeed, a KREEP liquid layer thickened from 5 to 10 km with more than 200 times chondritic heat-producing elements does not continue to cool but undergoes a repeating and grows in thickness by dissolving several times its mass of anorthosite and ultramafic cumulat es. However, such a liquid layer cannot give rise to the parent magmas to t he magnesian suite,because it cannot account for the extraordinarily high i ncompatible element content, the primitive major element content, or the po sitive epsilon (nd) of the magnesian suite. This growing layer will also fo rm an impenetrable barrier to the eruption of mare basalts and is generally inconsistent with a number of geophysical constraints of the Moon, specifi cally, the existence of mascons subsequent to the basin filling by mare bas alts. A thickened KREEP liquid layer can, however, explain the asymmetry in the distribution of KREEP-rich rock on the lunar crust. Such a KREEP layer must be efficiently cooled and be quickly solidified to avoid some of the difficulties described above. A thinned anorthosite crust would allow effic ient host loss and induce crystallization of such a layer early in lunar hi story.