Deformation of Aegean granitic rocks

The subject of this thesis is the deformation of granitic rocks of the Attic-Cycladic metamorphic-core complex.The study of the deformation was carried out with the use of classic geological techniques (field mapping, systematic sampling, structural analysis of deformation structures in the meso- and microscopic scale).Case studies were the pre-alpine granitic orthogneisses of Paros Island the Vari Gneiss Unit of Syros Island, the quartzofeldspathic rocks of Andros Island, the granitoid rocks of Anafi Island and the late-orogenic intrusions of Tinos Paros and Naxos IslandsThe study of all these cases shed light to the formation and structural evolution of the Attic-Cycladic metamorphic core complex and the crustal scale lithospheric structures that resulted in the deformation of the studied rocks.Στην παρούσα διατριβή εξετάζεται η παραμόρφωση γρανιτικών πετρωμάτων από το χώρο της Αττικοκυκλαδικής.Μελετήθηκαν με τις κλασσικές γεωλογικές μεθόδους (γεωλογική χαρτογράφηση, λήψη μετρήσεων, συστηματική δειγματοληψία, τεκτονική ανάλυση παραμορφωτικών δομών της μεσο- και μικροσκοπικής κλίμακας παρατήρησης) οι Προαλπικοί ορθογνεύσιοι της Πάρου, οι Γνεύσιοι Βάρης της Σύρου- οι Χαλαζιοαστριούχες εμφανίσεις της Άνδρου τα Γρανιτοειδή της Ανάφης και οι υστεροτεκτονικές δεισδύσεις του Μειοκαίνου στις νήσους Τήνο, Νάξο και Πάρο.Μέσω της μελέτης της παραμόρφωσης αυτών των πετρωμάτων διαφωτίστηκε η εξέλιξη και παραμόρφωση των περιβαλλόντων μεταμορφωμένων και ιζηματογενών πετρωμάτων καθώς επίσης και η δημιουργία και εξέλιξη του Αττικοκυκλαδικού συμπλέγματος μεταμορφωμένου πυρήνα και ορισμένων από τις τεκτονικές δομές λιθοσφαιρικής κλίμακας που περιλαμβάνει

Temporal and Spatial Analysis of Flood Occurrences in the Drainage Basin of Pinios River (Thessaly, Central Greece)

Historic data and old topographic maps include information on historical floods and paleo-floods. This paper aims at identifying the flood hazard by using historic data in the drainage basin of Pinios (Peneus) River, in Thessaly, central Greece. For this purpose, a catalogue of historical flood events that occurred between 1979 and 2010 and old topographic maps of 1881 were used. Moreover, geomorphic parameters such as elevation, slope, aspect and slope curvature were taken into account. The data were combined with the Geographical Information System to analyze the temporal and spatial distribution of flood events. The results show that a total number of 146 flood events were recorded in the study area. The number of flood events reaches its maximum value in the year 1994, while October contains the most flood events. The flood occurrences increased during the period 1990–2010. The flooded area reaches its maximum value in the year 1987, and November is the month with the most records. The type of damages with the most records is for rural land use. Regarding the class of damages, no human casualties were recorded during the studied period. The annual and monthly distribution of the very high category reaches the maximum values, respectively, in the year 2005 and in June. The analysis of the spatial distribution of the floods proves that most of the occurrences are recorded in the southern part of the study area. There is a certain amount of clustering of flood events in the areas of former marshes and lakes along with the lowest and flattest parts of the study area. These areas are located in the central, southern, south-eastern and coastal part of the study area and create favorable conditions for flooding. The proposed method estimates the localization of sites prone to flood, and it may be used for flood hazard assessment mapping and for flood risk management

Antimony’s Significance as a Critical Metal: The Global Perspective and the Greek Deposits

Antimony is widely acknowledged as a critical raw material of worldwide significance, based on its recognition by many countries. According to current projections, there is an anticipated increase in the demand for antimony in the forthcoming years. An issue of significant concern within the supply chain, which poses a substantial obstacle to sustainable development, is the global unequal allocation of abundant antimony resources. Most nations exhibited a high degree of dependence on a few countries for their net imports of antimony, resulting in a notable disruption and raising concerns regarding the supply chain. In most countries, antimony exploration and exploitation have been paused for a long period due to financial constraints associated with operations and environmental concerns. Nowadays, identifying additional antimony reserves, particularly in countries that heavily rely on new technologies and use significant amounts of antimony, is imperative and presents a pressing endeavor. Greece is recognized as one of the European Union member states with identified antimony deposits and a historical record of antimony exploitation. A thorough description, examination, and re-assessment of all existing data on the deposits and occurrences of antimony in Greece is presented. Most of Greece’s antimony deposits are related to hydrothermal processes, controlled by specific tectonic structures, and associated with Cenozoic magmatism. They are classified either as simple Sb-deposits, where the primary ore is a stibnite mineral, or complex polymetallic deposits with varying contents that include antimony minerals

Physical and Anthropogenic Factors Related to Landslide Activity in the Northern Peloponnese, Greece

The geological, geomorphic conditions of a mountainous environment along with precipitation and human activities influence landslide occurrences. In many cases, their relation to landslide events is not well defined. The scope of the present study is to identify the influence of physical and anthropogenic factors in landslide activity. The study area is a mountainous part of the northern Peloponnesus in southern Greece. The existing landslides, lithology, slope angle, rainfall, two types of road network (highway-provincial roads and rural roads) along with land use of the study area are taken into consideration. Each physical and anthropogenic factor is further divided into sub-categories. Statistical analysis of landslide frequency and density, as well as frequency and density ratios, are applied and combined with a geographic information system (GIS) to evaluate the collected data and determine the relationship between physical and anthropogenic factors and landslide activity. The results prove that Plio-Pleistocene fine-grained sediments and flysch, relatively steep slopes (15°–30°) and a rise in the amount of rainfall increase landslide frequency and density. Additionally, Plio-Pleistocene fine-grained sediments and flysch, as well as schist chert formations, moderate (5°–15°) and relatively steep slopes (15°–30°), along with the amount of rainfall of >700 mm are strongly associated with landslide occurrences. The frequency and magnitude of landslides increase in close proximity to roads. Their maximum values are observed within the 50 m buffer zone. This corresponds to a 100 m wide zone along with any type of road corridors, increasing landslide occurrences. In addition, a buffer zone of 75 m or 150 m wide zone along highway and provincial roads, as well as a buffer zone of 100 m or 200 m wide zones along rural roads, are strongly correlated with landslide events. The extensive cultivated land of the study area is strongly related to landslide activity. By contrast, urban areas are poorly related to landslides, because most of them are located in the northern coastal part of the study area where landslides are limited. The results provide information on physical and anthropogenic factors characterizing landslide events in the study area. The applied methodology rapidly estimates areas prone to landslides and it may be utilized for landslide hazard assessment mapping as well as for new and existing land use planning projects

Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation

Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and ~48–56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism

Manganese metallogenesis in the Hellenic arc: Case studies from a Triassic rift-related volcaniclastic succession of the Cycladic Blueschist Unit, Greece

The Triassic volcaniclastic sequence in the Cycladic Blueschist Unit (CBU) of Greece is known to contain several occurrences of metamorphosed Mn mineralization. Despite previous literature reports, a comprehensive and holistic review of the origin of these occurrences is hitherto lacking. Here we revisit the Mn metallogenic system of the CBU through a comprehensive study of Mn mineralisation at Varnavas area, Northern Attica, and its correlation with a similar occurrence at Mparades Hill, Andros island. Manganese mineralogy at both localities is manifested in a typical high-P metamorphic silicate assemblage dominated by piemontite, spessartine garnet, and minor pyroxmangite (rhodonite). Whereas at Andros Mn-rich subdomains contain brecciated braunite micronodules, preservation of tetravalent Mn oxides in a similar nodular form is documented from Varnavas, comprising dominant todorokite along with lesser hollandite, pyrolusite, and minor Mn-bearing hematite. The contrasting Mn oxide mineralogy and comparable textural characteristics at the two sites are tentatively interpreted as the result of locally incomplete reduction of precursor Mn(IV) phases during metamorphism. Bulk Mn concentrations of the studied materials generally do not exceed the value of 10 wt% Mn, unless small-scale subsampling of Mn-rich domains is undertaken. Key geochemical characteristics of the Mn-rich rocks include low transition metal concentrations (sum of Co + Ni + Cu + Zn between 0.02 and 0.06 wt%); positive-sloping, PAAS-normalised REE spidergrams at a maximum Ndsn/Ybsn ratio of 0.3; positive Ce anomalies, albeit of variable magnitude across individual samples; and high As (up to 1930 ppm) and Ba (up to 2767 ppm) contents. A combination of structural, geochemical and mineralogical evidence from the two localities along with published results from similar occurrences elsewhere (e.g., Kythnos) suggest that Mn-oxide accumulation in the CBU is genetically linked to hydrothermal venting in a back-arc rift setting during the Triassic. The geochemical variability recorded is attributed primarily to the variable mixing of a hydrothermal-sourced, hydrogenous metalliferous component that precipitated broadly contemporaneously with the deposition of the host tuffs. Low transition metal contents coupled with substantial enrichments in elements such as Ba, As, Pb and REY, attest to the felsic/intermediate character of back-arc magmatism/volcanism and associated hydrothermal activity. Primary Mn precipitates are thought to have been in the form of tetravalent Mn assemblages, which may locally be partially preserved through metamorphism, as appears to be the case in the Varnavas occurrence. The fully oxic and hydrogenous character of the precursor Mn(IV) oxy-hydroxides is supported by the consistently positive Ce anomalies observed in practically all samples from both sites. Although the Mn concentrations and distribution of the studied assemblages are sub-economic at best, we consider possible that their geographically widespread occurrence may still hold untapped potential for future discovery of commercially viable Mn ores sensu stricto, both in the Hellenic arc and in other regions of similar geotectonic and metallogenic activity

Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation

Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and 48-56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism

Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation

Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and ~48–56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism

Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece

Retrograde metamorphic rocks provide key insights into the pressure–temperature (P–T) evolution of exhumed material, and resultant P–T constraints have direct implications for the mechanical and thermal conditions of subduction interfaces. However, constraining P–T conditions of retrograde metamorphic rocks has historically been challenging and has resulted in debate about the conditions experienced by these rocks. In this work, we combine elastic thermobarometry with oxygen isotope thermometry to quantify the P–T evolution of retrograde metamorphic rocks of the Cycladic Blueschist Unit (CBU), an exhumed subduction complex exposed on Syros, Greece. We employ quartz-in-garnet and quartz-in-epidote barometry to constrain pressures of garnet and epidote growth near peak subduction conditions and during exhumation, respectively. Oxygen isotope thermometry of quartz and calcite within boudin necks was used to estimate temperatures during exhumation and to refine pressure estimates. Three distinct pressure groups are related to different metamorphic events and fabrics: high-pressure garnet growth at ∼1.4–1.7 GPa between 500–550 ∘C, retrograde epidote growth at ∼1.3–1.5 GPa between 400–500 ∘C, and a second stage of retrograde epidote growth at ∼1.0 GPa and 400 ∘C. These results are consistent with different stages of deformation inferred from field and microstructural observations, recording prograde subduction to blueschist–eclogite facies and subsequent retrogression under blueschist–greenschist facies conditions. Our new results indicate that the CBU experienced cooling during decompression after reaching maximum high-pressure–low-temperature conditions. These P–T conditions and structural observations are consistent with exhumation and cooling within the subduction channel in proximity to the refrigerating subducting plate, prior to Miocene core-complex formation. This study also illustrates the potential of using elastic thermobarometry in combination with structural and microstructural constraints, to better understand the P–T-deformation conditions of retrograde mineral growth in high-pressure–low-temperature (HP/LT) metamorphic terranes.ISSN:1869-9510ISSN:1869-952