Supervisors info:
Δρ. Δημήτριος Κωστόπουλος, Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Original Title:
Physicochemical parameters of active continental margin magmatism across the Aegean microplate, Greece – Geodynamic implications / Φυσικοχημικές παράμετροι μαγματισμού ενεργού ηπειρωτικού περιθωρίου διαμέσου της μικροπλάκας του Αιγαίου – Γεωδυναμικές συνέπειες
Summary:
Volcanoes are among the most interesting and imposing geological structures and have always been one of the most challenging scientific topics. Because of them, the formation of new crust, both continental and oceanic, is ensured, as well as the evolution of our planet which is a relentless work in progress. Simultaneously though, whenever an explosive or less explosive volcanic eruption occurs, the population of the surrounding areas, its properties and future in general are threatened.
In our case, the Hellenic Active Continental Margin (HACM) consists of several volcanic centers. Beginning from the ones in the Saronic Gulf, we have Sousaki/Crommyonia, Aegina, Poros, Methana and the submarine volcanic center of Pausanias in the west of Methana. The central part of the arc includes Milos, Antimilos, Kimolos, Polyegos, Santorini, Kameni and the submarine volcano of Koloumbo. As for the eastern part, there we have Nisyros, Yali, Kos and we also include the volcanic rocks of Tilos and Patmos. The active margin hosts the subduction of the oceanic part of the African lithospheric plate (eastern Mediterranean Sea) under the Eurasian plate. This geo-tectonic environment causes highly violent earthquakes and has given some of the deadliest volcanic eruptions in the past. However, even though the chemistry of the HACM is similar all along the arc, some of the volcanic centers have given significant eruptions, while the eruptions of others were relatively effusive. The question that arises, then, is what variables lead to this explosivity differentiation among the volcanic centers of the arc and what is it that determines whether future eruptivity in Santorini or Kos will probably be more violent than that of Methana or Milos?
The purpose of this thesis was to investigate the reasons why eruptability occurs in certain volcanoes and to find a way to predict it. We created a compound database that consists of numerous chemical analyses of magma and mineral samples from the entire HACM. Using that, we proceeded to calculate and determine the P – T conditions of magma storage below the arc, as well as the physicochemical conditions that control magma eruption. During this, the chemistry of all samples underwent thorough processing, so as to unfold the complexity of the melt structure and the correlation of it to eruptability. We additionally studied representative volcanic compositions of known VEI around the world. We concluded that there are four main reasons for the eruptability differentiation among the Hellenic arc: thickness of the crust, melt alkalinity, amphibole on the liquidus, and high H2O content and acid composition. Furthermore, two new diagrams are being offered, through which highly precise prediction of the explosivity index can be made, giving us a better understanding of how the Hellenic Active Continental Margin works and what potential dangers it may hold.
Keywords:
volcanoes, P-T conditions, physicochemical parameters, eruptability, volcanic explosivity index
