In a paper about the interior of the Moon, it references depleted mantle sources and enriched mantle sources. Sometimes the latter is referred to as 'fertile'. What is difference between the first two?
Basically, a fertile mantle is a portion of mantle that has not experienced any melting. On the other hand, a depleted mantle has experienced partial melting, and subsequent extraction of this melt. During partial melting, some elements will preferably go in the melt while others will preferably stay in the mantle. This leaves the residual mantle with a different chemical/mineral composition, which is more refractory, i.e., less likely to melt.
So "fertile" here means "can (partially) melt", while "depleted" means "cannot melt (because already did)". Corresponding mantle rocks are usually lherzolite and harzburgite, respectively. See for instance the peridotite classification article on Wikipedia:
- Harzburgite [...] is interpreted as depleted mantle rock, from which basaltic magma has been extracted.
- Lherzolite is thought to make up much of the upper mantle [...] and is the likely source rock for basaltic magma.