Late Quaternary Marine Terraces and Tectonic Uplift Rates of the Broader Neapolis Area (SE Peloponnese, Greece)

Marine terraces are geomorphic markers largely used to estimate past sea-level positions and surface deformation rates in studies focused on climate and tectonic processes worldwide. This paper aims to investigate the role of tectonic processes in the late Quaternary evolution of the coastal landscape of the broader Neapolis area by assessing long-term vertical deformation rates. To document and estimate coastal uplift, marine terraces are used in conjunction with Optically Stimulated Luminescence (OSL) dating and correlation to late Quaternary eustatic sea-level variations. The study area is located in SE Peloponnese in a tectonically active region. Geodynamic processes in the area are related to the active subduction of the African lithosphere beneath the Eurasian plate. A series of 10 well preserved uplifted marine terraces with inner edges ranging in elevation from 8 ± 2 m to 192 ± 2 m above m.s.l. have been documented, indicating a significant coastal uplift of the study area. Marine terraces have been identified and mapped using topographic maps (at a scale of 1:5000), aerial photographs, and a 2 m resolution Digital Elevation Model (DEM), supported by extensive field observations. OSL dating of selected samples from two of the terraces allowed us to correlate them with late Pleistocene Marine Isotope Stage (MIS) sea-level highstands and to estimate the long-term uplift rate. Based on the findings of the above approach, a long-term uplift rate of 0.36 ± 0.11 mm a−1 over the last 401 ± 10 ka has been suggested for the study area. The spatially uniform uplift of the broader Neapolis area is driven by the active subduction of the African lithosphere beneath the Eurasian plate since the study area is situated very close (~90 km) to the active margin of the Hellenic subduction zone.

The dire straits of Paratethys: Gateways to the anoxic giant of Eurasia

A complex interplay of palaeoclimatic, eustatic and tectonic processes led to fragmentation and dissipation of the vast Tethys Ocean in Eocene-Oligocene times. The resulting Paratethys Sea occupied the northern Tethys region on Eurasia, grouping water masses of various subbasins, separated from each other and from the open ocean through narrow and shallow gateways and land bridges. Changes in marine gateway configuration and intra-basinal connectivity affected the regional hydrology, shifting most Paratethyan basins to extreme carbon-sink anoxic environments, anomalohaline evaporitic or brackish conditions or even endorheic lakes. Paratethys gateway restriction triggered the onset of a long-lasting (∼20 Myr) giant anoxic sea, characterised by stratified water masses and anoxic bottom water conditions, resulting in thick hydrocarbon source rocks. Here, we review the geological evolution of the “dire straits” of Paratethys that played a crucial role in the Eocene-Oligocene connectivity history of the Central Eurasian seas and we show that the main anoxic phases (Kuma and Maikop) correspond to restricted connectivity with the global ocean and a period of CO2 depletion in the atmosphere. Paratethys represents one of the largest carbon sinks of Earth's history and may thus have played a prominent role in global climate change.

Basic Role of Extrusion Processes in the Late Cenozoic Evolution of the Western and Central Mediterranean Belts

Tectonic activity in the Mediterranean area (involving migrations of old orogenic belts, formation of basins and building of orogenic systems) has been determined by the convergence of the confining plates (Nubia, Arabia and Eurasia). Such convergence has been mainly accommodated by the consumption of oceanic and thinned continental domains, triggered by the lateral escapes of orogenic wedges. Here, we argue that the implications of the above basic concepts can allow plausible explanations for the very complex time-space distribution of tectonic processes in the study area, with particular regard to the development of Trench-Arc-Back Arc systems. In the late Oligocene and lower–middle Miocene, the consumption of the eastern Alpine Tethys oceanic domain was caused by the eastward to SE ward migration/bending of the Alpine–Iberian belt, driven by the Nubia–Eurasia convergence. The crustal stretching that developed in the wake of that migrating Arc led to formation of the Balearic basin, whereas accretionary activity along the trench zone formed the Apennine belt. Since the collision of the Anatolian–Aegean–Pelagonian system (extruding westward in response to the indentation of the Arabian promontory) with the Nubia-Adriatic continental domain, around the late Miocene–early Pliocene, the tectonic setting in the central Mediterranean area underwent a major reorganization, aimed at activating a less rested shortening pattern, which led to the consumption of the remnant oceanic and thinned continental domains in the central Mediterranean area.

Structure, tectonic processes and deformation of the South Aegean Sea

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.

Southward expanding plate coupling due to variation in sediment subduction as a cause of Andean growth

Growth of the Andes has been attributed to Cenozoic subduction. Although climatic and tectonic processes have been proposed to be first-order mechanisms, their interaction and respective contributions remain largely unclear. Here, we apply three-dimensional, fully-dynamic subduction models to investigate the effect of trench-axial sediment transport and subduction on Andean growth, a mechanism that involves both climatic and tectonic processes. We find that the thickness of trench-fill sediments, a proxy of plate coupling (with less sediments causing stronger coupling), exerts an important influence on the pattern of crustal shortening along the Andes. The southward migrating Juan Fernandez Ridge acts as a barrier to the northward flowing trench sediments, thus expanding the zone of plate coupling southward through time. Consequently, the predicted history of Andean shortening is consistent with observations. Southward expanding crustal shortening matches the kinematic history of inferred compression. These results demonstrate the importance of climate-tectonic interaction on mountain building.

Shrinking of Ischia Island (Italy) from Long-Term Geodetic Data: Implications for the Deflation Mechanisms of Resurgent Calderas and Their Relationships with Seismicity

The identification of the mechanisms responsible for the deformation of calderas is of primary importance for our understanding of the dynamics of magmatic systems and the evaluation of volcanic hazards. We analyze twenty years (1997–2018) of geodetic measurements on Ischia Island (Italy), which include the Mt. Epomeo resurgent block, and is affected by hydrothermal manifestations and shallow seismicity. The data from the GPS Network and the leveling route show a constant subsidence with values up to −15 ± 2.0 mm/yr and a centripetal displacement rate with the largest deformations on the southern flank of Mt. Epomeo. The joint inversion of GPS and levelling data is consistent with a 4 km deep source deflating by degassing and magma cooling below the southern flank of Mt. Epomeo. The depth of the source is supported by independent geophysical data. The Ischia deformation field is not related to the instability of the resurgent block or extensive gravity or tectonic processes. The seismicity reflects the dynamics of the shallow hydrothermal system being neither temporally nor spatially related to the deflation.

Open System Re-Os Isotope Behavior in Platinum-Group Minerals during Laterization?

In this short communication, we present preliminary data on the Re-Os isotopic systematics of platinum-group minerals (PGM) recovered from different horizons in the Falcondo Ni-laterite in the Dominican Republic. The results show differences in the Os-isotope composition in different populations of PGM: (i) pre-lateritic PGM yield 187Os/188Os varying from 0.11973 ± 0.00134 to 0.12215 ± 0.00005 (2σ uncertainty) whereas (ii) lateritic PGM are more radiogenic in terms of 187Os/188Os (from 0.12390 ± 0.00001 to 0.12645 ± 0.00005; 2σ uncertainty). We suggest that these differences reflect the opening of the Re-Os system in individual grains of PGM during lateritic weathering. The implications of these results are twofold as they will help to (1) elucidate the small-scale mobility of noble metals in the supergene setting and therefore the possible formation of PGM at these very low temperatures, (2) better refine the Os-isotopic datasets of PGM that are currently being used for defining dynamic models of core–mantle separation, crustal generation, and fundamental plate-tectonic processes such as the opening of oceans.