Trace element geochemistry at DSDP Leg 82 Holes

The recovered basalts range from those depleted in light REE (LREE) to those enriched in LREE. The two types of basalts occur together in Holes 558 and 561.

The depleted basalts have remarkably constant La/Yb, La/Sm, and La/Ti ratios and apparently derive from a large, homogeneous, mantle source underneath a segment (1200 km long) of the Mid-Atlantic Ridge. The almost twofold variation in the concentrations of incompatible trace elements in the depleted basalts is primarily due to different degrees of batch partial melting. The variation of highly to moderately incompatible elements in the Leg 82 enriched basalts can be successfully explained in terms of source mixing between depleted mantle sources and alkaline or nephelinitic magmas similar to Azores Islands magmas.