Preliminary Insights into the Petrological Processes and Magma Plumbing System of Terceira Volcano, Azores

The Azores archipelago comprises nine volcanic islands in the central North Atlantic Ocean, in the area in which the North American, Eurasian and Nubian plates meet. The complex geological setting of the archipelago is characterised by a mantle plume at the triple junction [1]. Magmatism in the Azores islands is widely believed to result from the interaction between the mantle plume and the Mid-Atlantic Ridge (MAR), which separates the Western Group islands from the Central and Eastern Groups. Terceira is the third largest island of the archipelago, located to the east of the MAR in the central group. The island consists of four central volcanoes, and is bisected by a NW-SE trending basaltic rift zone. The eruptive products of Terceira are dominated by lava flows and pyroclastic deposits which show a general evolution from basaltic to trachytic over time [2], with a mineralogy comprising varying amounts of alkali feldspar, plagioclase feldspar, olivine, clinopyroxene and minor Fe-Ti oxides. We present our preliminary data on the petrography and geochemistry (bulk-rock and mineral compositions) of samples collected around the coast and flanks of each volcano, with a focus on the application of our results in unravelling the deeper magmatic plumbing system, mantle sources and characteristics of Terceira and its evolution, particularly with respect to other Azorean islands. [1] Madeira, J. and Ribeiro, A. (1990) Tectonophysics (184): 405415; [2] DOriano C, Landi P, Pimentel A, Zanon V (2017) J Volcanol Geotherm Res (347): 4463.