Buoyancy of Azorean magmas: Consequences on ascent, intrusion and formation of magma storage areas beneath main volcanic systems.

Objectivos

The work project present here integrates data emerging from the interpretation of data connected to the PLUSYS Project (PTDC/CTE-GIX/098836/2008) funded by FCT on the basaltic magmas erupted by fissure zones in the archipelago. In PLUSYS Project, attention is focussed on the origin and evolution of these basaltic compositions and to define their deep ascent path. Preliminary results point to exclude the occurrence of shallow-level ponding areas for these magmas and to address the evolution to fractional crystallization processes occurring in the deep lithosphere. Differently, it is well known from the existing literature, that accumulation, storage and evolution processes (i.e., fractional crystallization and magma mixing) of magmas erupted by central volcanic systems occur in shallow-level reservoirs.
Thus, here it is proposed a study of petrology of volcanic products erupted by central volcanic systems characterized by both recent-to-historic volcanic activity and seismicity (Pico Volcano in the island of Pico, Água de Pau, Furnas and Sete Cidades in the island of São Miguel, Caldeira Volcano in the island of Faial). The main objectives to be reached are:

• define the spatial location of ponding areas of magmas erupted by these volcanoes. And thus drafting the presence of possible physical discontinuities in the upper lithosphere which could act as buoyancy barrier for ascending magmas. These will provide extremely useful information in addressing local seismicity to either tectonic or magma. This will be achieved essentially by a study of microthermometry of fluid inclusions present in the mineral assemblage of collected samples, and secondarily by the definition of the thermodynamic condition of equilibrium aiming mineral phases or simulating the magma ascent path with software and comparing the obtained results with real data from petrography study;
• compute the amount of magma residing in these shallow-level reservoirs. This goal will be achieved by the analysis of the existing stratigraphic sequences of pyroclastic nature.
• evaluate the impact of mixing of magmas of different composition on degassing and buoyancy, mainly by the use of existing theoretical models on the sampled compositions.
  The working scheme presented here can be applied virtually to all volcanic systems in the world and allow to get information useful for Civil Protection aims that will be integrated with the information obtained by a well developed monitoring network.