Petrology, geochemistry and Sr–Nd–Pb isotopes of the volcanic rocks from Pico Island—Azores (Portugal)

Abstract

Analytical data (major, minor and trace elements) for samples from Pico Island (Azores archipelago) representative of the three volcanic complexes comprising the island demonstrate that the overwhelming majority of the rocks are basalts (∼78%), followed by subordinate hawaiites (∼20%). Only one lava flow, erupted in 1718 AD, has a more evolved character (mugearite and benmoreite). Samples define mainly a sodic alkaline series, but a few rocks show transitional and sub-alkaline characteristics. Fractional crystallization is the main process to produce the more evolved nature of the magmas, occurring within a complex plumbing system and involving liquids with different degrees of melting. Pico, like other islands of the Azores archipelago, was constructed in an intraplate tectonic setting. Compositionally, the mantle plume beneath the Azores is considered to be the result of mixing between HIMU and DM reservoirs, with a lowest contribution of an EM reservoir. The present study can contribute to a better understanding of the volcanic evolution of all the Azores islands because: (1) Pico island is the youngest island of the archipelago; (2) Pico contains an important composite volcano with a magmatic chamber in an early stage of development; (3) the archipelago is located in a complex geodynamic setting and; (4) there is no major geochemical variation between the eruptive products of the islands. Because Pico represents an early stage of volcanic island formation, its study offers (1) a direct approach to evaluate the early phases of evolution of the other islands and, (2) thereby providing a context to better assess potential hazards from any future eruptive activity at Pico.