ALBERT

Description: We present a comprehensive major and trace element and Sr–Nd–Pb isotope dataset from the major volcanic units exposed on La Palma and show how geochemical and volcanic evolution can be linked to asthenospheric and lithospheric processes. Lavas from the northern shield (from Basal Complex to Taburiente to Bejenado volcanism, 3–4 Ma to 400 ka) become more alkalic and SiO2-undersaturated with decreasing age, but show little change in MgO-normalized trace element compositions. Their high (Nb,Ta)/U and Ba/Th but low La/Nb ratios suggest assimilation of amphibole, probably in the lithospheric mantle that was metasomatized by earlier melts. Lavas from the Cumbre Vieja unit (〈125 ka) in the southern half of La Palma are more incompatible-element enriched and probably formed through lower degrees of melting than those from the northern shield, which are nearly identical isotopically. Their Nb/U ratios are mostly within the range 47 ± 10, significantly below those of the earlier lavas. In 206Pb/204Pb versus 143Nd/144Nd, 208Pb/204Pb and 208Pb/206Pb isotope diagrams, the Basal Complex rocks and lavas from the adjacent El Hierro island form a separate trend compared with the younger subaerial La Palma lavas. Both groups share a common depleted end-member but require separate, enriched HIMU-like end-members, believed to be located within the asthenosphere. The temporal and spatial variations in the composition of La Palma and El Hierro lavas could be explained within the context of NE-directed plate motion over a zoned Canary plume. After La Palma moved away from the asthenospheric source domain of the Basal Complex, El Hierro formed above the same domain, whereas the younger units on La Palma tapped a distinct asthenospheric domain located further north. The short-lived Bejenado volcano that formed directly after the giant Cumbre Nueva sector collapse at c. 560 ka produced the isotopically most depleted lavas reported from La Palma thus far. Their compositions suggest incorporation of a depleted pyroxenitic component. The Bejenado lavas also extend to the highest Nb/U and Ba/Th and lowest La/Nb ratios of all La Palma lavas, consistent with increased melting of amphibole within the lithospheric mantle or lower crust. We propose that the collapse is related to the migration of magmatism to the south of La Palma, and led to short-term enhanced decompression melting of amphibole and pyroxenite within the lithosphere.