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Rare earth (RE) abundances for 33 lavas ranging from picrites to differentitated basalts are reported from Sites 332, 334, and 335. Remarkably similar V-shaped relative RE fractionation patterns were observed for Holes 332A, 332B, and Site 334, with an [La/Sm]E.F (enrichment factors) averaging 1.21 and ranging only by ±0.22 for one standard deviation, yet with an absolute level of RE pattern enrichment ranging from 15 to 20× to as low as 4× chondrites (i.e., a factor of ~5). In contrast, uniform and light RE depleted patterns were observed throughout Site 335, with absolute variations occurring only over a factor of 1.5. Basalts from Site 335 are typical of normal mid-ocean ridge segments and regimes and appear to be derived from the lowvelocity layer depleted in large ionic lithophile elements (depleted low velocity layer, DLVL-derived), whereas basalts and picrites from Holes 332A, 332B, and Site 334 appear to be derived from a two-component mantle mixture (DLVL, and the Azores Mantle "Blob" enriched in light RE). Patterns with the lowest absolute enrichments in Holes 332A, 332B, and Site 334 require unusually large degrees of melting for noncumulate lavas, additional crystal accumulation at shallow depth for highly porphyritic cumulate lavas, and a relatively large amount of olivine in the mantle source. Presence of abundant spinel and unusually low FeO*/FeO* + MgO and high Cr content relative to similar lavas from the Mid-Atlantic Ridge (MAR) (40° to 30°N) are consistent with this interpretation. Secular variation of the [La/Sm]E.F. from 13 m.y.B.P. until present is shown to reflect an increase in the flux intensity of the Azores Mantle "Blob" and of its extent of overflow along the MAR axis.

Rare Earth Abundances in DSDP Sites 332, 334, and 335, and Inferences on the Azores Mantle Blob Activity with Time