Petrology and Geochemistry of lavas from Sal Island: Implications for the variability of the Cape Verde magmatism.

Abstract

Sal Island (Cape Verde Archipelago) preserves a magmatic history ranging from ≈ 25.6 Ma to ≈ 0.6 Ma. The chemistry of magma- tism varies from Hy-normative (Serra Negra basalts: ≈ 5 Ma) to highly SiO2-undersaturated (nephelinites and melilitites). The calculated tempera- tures of magmatic segregation are higher than those usually considered for the asthenosphere, thus endorsing the role of a mantle plume to the origin of Cape Verde magmatism. Nephelinites and melilitites are characterized by pronounced K negative anomalies which are interpreted as reflecting the interaction of plume magmas with the lithosphere. Some of the Sal lavas are characterized by low 143Nd/144Nd (down to 0.512577) - when compared with the HIMU component. These values are similar to those usually reported for the Southern Cape Verde Islands. This suggest the role of a EM1-type end-member to the magma sources of the Sal, which is for the first time evidenced from the whole rock composition of one of the Northern Cape Verde Islands.