Elardo, and 3 co-authors, reported in mid-2020 that the Moon’s Earth-facing hemisphere hosts a geochemically anomalous region, the Procellarum KREEP Terrane, which is widely thought to have provided radiogenic heat for mantle melting from ~3.9 to ~1 billion years ago. However, there is no agreement on such a link between this region and the earliest pulse of post-differentiation crust-building magmatism on the Moon at ~4.37 billion years ago; whether this early magmatism was global or regional has been debated.
The authors present results of high-temperature experiments that show the nearside geochemical anomaly may have caused asymmetric early crust building via mantle melting-point depression. Their results demonstrate that the anomalous enrichment in incompatible elements of this nearside reservoir dramatically lowers the melting temperature of the source rock for these magmas and may have resulted in 4 to 13 times more magma production under the nearside crust, even without any contribution from radioactivity.
From thermal numerical modelling, the authors show that radiogenic heating compounds this effect and may have resulted in an asymmetric concentration of post-magma-ocean crust building on the lunar nearside. Their findings suggest that the nearside geochemical anomaly has influenced the thermal and magmatic evolution of the Moon over its entire post-differentiation history.
The authors concluded that the hemispheric compositional asymmetries on the Moon began to have a dramatic effect on magma production immediately after lunar differentiation. The large concentration of heat-producing elements on the Moon’s nearside not only had the potential to act as a heat source for melting but also lowered melting temperatures at the crust–mantle interface in a way that could have produced ~4–13 times more crust-building magmas than would have occurred on the farside. The positive feedback among the amount of KREEP in a source region, KREEP’s ability to depress melting temperatures and its penchant for heat production probably resulted in asymmetric crust building on the Moon’s nearside and demonstrates the important role that KREEP and its concentration on the nearside played in the thermal and magmatic evolution of the Moon throughout its entire ~4.4Gyr history.
Managed & Built by I2M Consulting, LLC | © 2010-
