Δομή, τεκτονικές διεργασίες και παραμόρφωση στο Νότιο Αιγαίο

The PhD thesis explores the long-term deformation and active tectonic mechanisms that contributed to the geological evolution and the formation of the complex relief of the South Aegean Sea. Despite the geological surveys that have been conducted on the Aegean, the current state of knowledge is still in its infancy. Although it is widely accepted that the geotectonic evolution of the Aegean microplate is dominated by extension in a back-arc setting, recent geological, seismological and geodetic studies have shown that overall extension may evolve in combination with transpression or transtention. This dissertation summarizes the preexisting literature and the main deformation models that have been proposed for the Aegean and through the presentation of new bathymetric and seismic data aims to improve our understanding of the tectonic processes and deformation prevailing on the South Aegean Sea. In order to develop a geodynamic model that will explain the kinematic processes and deformation mechanisms that took place in the area, the main axis of the dissertation is structured by three main research papers, the results of which provide up-to-date information about the geodynamic evolution of the South Aegean.Η παρούσα διατριβή διερευνά τη μακροχρόνια παραμόρφωση και τους ενεργούς τεκτονικούς μηχανισμούς που συνέβαλαν στην εξέλιξη και στο σχηματισμό του πολύπλοκου ανάγλυφου του Νοτίου Αιγαίου. Παρά τις γεωλογικές έρευνες που έχουν διεξαχθεί στο Αιγαίο, μέχρι και σήμερα γνωρίζουμε πολύ λίγα για τη γεωδυναμική εξέλιξη του. Αν και είναι ευρέως αποδεκτό ότι στη γεωτεκτονική εξέλιξη της μικρο-πλάκας του Αιγαίου κυριαρχούν κυρίως οι εφελκυστικές διεργασίες παραμόρφωσης που συναντώνται σε ένα back-arc περιβάλλον (οπισθοτόξο), πρόσφατες γεωλογικές, σεισμολογικές και γεωδαιτικές μελέτες έχουν δείξει ότι η συνολικός εφελκυσμός δύναται να περιλαμβάνει και πλαγιό-συμπιεστικές και πλαγιό- εφελκυστικές διεργασίες. Η παρούσα διπλωματική εργασία συνοψίζει την προϋπάρχουσα βιβλιογραφία και τα κύρια μοντέλα παραμόρφωσης που έχουν προταθεί για το Αιγαίο και μέσω της παρουσίασης νέων βαθυμετρικών και σεισμικών δεδομένων στοχεύει στη βελτίωση της κατανόησης των τεκτονικών διεργασιών και των παραμορφώσεων που επικρατούν στο Νότιο Αιγαίο. Προκειμένου να αναπτυχθεί ένα γεωδυναμικό μοντέλο που θα εξηγεί τις κινηματικές διεργασίες και τους μηχανισμούς παραμόρφωσης που έλαβαν χώρα στην περιοχή, ο κύριος άξονας της διατριβής δομείται από τρεις κύριες ερευνητικές εργασίες, τα αποτελέσματα των οποίων παρέχουν νεότερες πληροφορίες για τη γεωδυναμική εξέλιξη του Νοτίου Αιγαίου

The Santorini-Amorgos Shear Zone: Evidence for Dextral Transtension in the South Aegean Back-Arc Region, Greece

Bathymetric and seismic data provide insights into the geomorphological configuration, seismic stratigraphy, structure, and evolution of the area between Santorini, Amorgos, Astypalea, and Anafi islands. Santorini-Amorgos Shear Zone (SASZ) is a NE-SW striking feature that includes seven basins, two shallow ridges, and hosts the volcanic centers of Santorini and Kolumbo. The SASZ initiated in the Early Pliocene as a single, W-E oriented basin. A major reorganization of the geodynamic regime led to (i) reorientation of the older faults and initiation of NE-SW striking ones, (ii) disruption of the single basin and localized subsidence and uplift, (iii) creation of four basins out of the former single one (Anafi, Amorgos South, Amorgos North, and Kinairos basins), (iv) rifting of the northern and southern margins and creation of Anydros, Astypalea North, and Astypalea South basins, and (v) uplift of the ridges. Dextral shearing and oblique rifting are accommodated by NE-SW striking, dextral oblique to strike-slip faults and by roughly W-E striking, normal, transfer faults. It is suggested here that enhanced shearing in NE-SW direction and oblique rifting may be the dominant deformation mechanism in the South Aegean since Early Quaternary associated with the interaction of North Anatolian Fault with the slab roll-back

Seismic profiles across the North Anatolian Fault in the Aegean Sea

International audienceThe North Anatolian Fault (NAF) is a >1200 km-long continental strike-slip fault system, acting as the plate boundary between Eurasia and Anatolia. West of the Yeniçaga fork in Turkey, the NAF divides in two main strands: the Main Marmara Fault crossing the Marmara Sea to the North, and a southern branch of the NAF crossing the Biga Peninsula. Both strands end in the Aegean Sea, connecting conspicuous horsetail terminations offshore eastern Greece at the North Aegean Trough and off Skyros Island. The northern Aegean Sea is therefore a key area to understand the structural evolution of the North Anatolian strike-slip fault system since its formation in the Late Miocene. Stratigraphic markers in the Aegean Sea provide optimal conditions for the study of the fault system evolution at the time scale of 105-106 years. Here we present a new set of shallow seismic reflection data crossing the NAF in the northern Aegean Sea, acquired in July 2017 onboard the R/V Tethys II (INSUCNRS/IFREMER). The penetration of the seismic signal reaches the Messinian unconformity. This new datasetallows us to investigate the sub-surface structure of the fault system and to identify key unconformities related to the formation of the horsetail terminations in the Late Pliocene-Early Pleistocene. These new elements will help to better understand the structural evolution of the NAF in the framework of back arc extension in the Aegean Sea since the Late Miocene

Searching for Neolithic sites in the Bay of Kiladha, Greece

Since the excavations at Franchthi Cave in the 1960s and 1970s, the possibility of finding a submerged Neolithic site in the Bay of Kiladha has been discussed. Initial research, based on marine geophysical survey and core sampling, brought contrasted results. Starting in 2012, new parts of the Bay were investigated, using different techniques and improved methods, such as geological-geophysical survey, further core sampling (including the finding of artefacts and anthropogenic indicators of a given date in the cores), shallow water ERT (with an adapted methodology), and underwater excavation. The combined evidence leads to a reconsideration of previous work, to the discovery of submerged structures directly off the cave, which might well be Neolithic walls, and points to the existence of two new submerged sites, one dating to the Neolithic, in the middle of the Bay, and the other to the Final Neolithic/Early Bronze Age I, at Lambayanna. The implications of these findings are discussed as well