Title:

Reconstruction of the Terceira Magma Plumbing System

A volcanic plumbing system consists of a plexus of pools and pathways of crystal mush and magma that supply the overlying volcano. Partial melts from the Earth’s mantle supply the magma and heat to sustain most volcanic plumbing systems, but within the plumbing system, the magma begins to cool and crystallize minerals. The early crystallizing mineral, clinopyroxene, can record the temperature and pressure of the magma body at the time of crystallization, and these conditions can be extracted from the crystal through thermobarometric calculations. Using LA-ICP-MS elemental analyses we developed a new approach to thermobarometry coupled with Ti diffusion to reconstruct the magma plumbing system of Terceira Island of the Azores Archipelago. The thermobarometric calculations suggest that crystallization occurs at pressures between 400-560 Mpa and 640-675 Mpa, 12-14 km and 20 km respectively. The Ti diffusive re-equilibration within the clinopyroxenes suggest crystal residence times between 2000 and 3000 years prior to eruption. Terceira consists of a tiered magma plumbing system, with a large magma body where crystallization predominately takes place at 20 km deep and subsequent smaller magma bodies at 12-14 km deep. With the success of this new approach using LA-ICP-MS to obtain the required data for thermobarometric calculations coupled with trace element diffusion, we look to develop this method further at more complex volcanic systems.

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