In the Aegean region (Cyclades–Greece), a large part of the Island of Anafi consists of exhumed high-grade metamorphic sequences (amphibolites, serpentinites and metasediments) that have been intruded by Late Cretaceous intermediate and felsic granitoids. These correspond to I-type arc-related rocks, displaying calc-alkaline geochemical affinities. Variability in their petrographic features, mineral composition and geochemistry is assigned to differentiation processes that mostly involved plagioclase and/or K-feldspar, and to a lesser extent amphibole and biotite. Mineral chemistry and geochemical results suggest that the Anafi granitoids are highly comparable with the Late Cretaceous granitoid intrusive rocks from East Crete and Donousa island. The amphibole and zircon saturation thermometry yields relatively moderate temperature crystallization conditions ($\sim$790°C) for the intermediate granitoids and lower for the felsic granitoids ($\sim$630°C). Geobarometric calculations based upon the chemistry of magnesiohornblende, as well as the normative (Qz), (Ab) and (Or) contents clearly point to shallow intrusion conditions ($\sim$2.0–6.5 kbar), corresponding to an estimated depth of crystallization of $\sim$12 ± 4 km. The thrust sheets that overly the Palaeogene flysch in Anafi (metasediments with serpentinized peridotites, amphibolites and metabasites), constitute a subducted and metamorphosed oceanic sequence. These metamorphic units likely represent a part of the Pindos–Cycladic Blueschist Unit domain that was subducted at an earlier pre-Campanian stage. In the hydrated mantle wedge, incorporation of shallow level granitoids within metamorphic units was likely facilitated via corner flow intrusion mechanisms. Following the intrusion, the granitoid rocks were exhumed in a syn-convergent setting, along with the metamorphic thrust sheets, by continuous underplating of more external units, thus, escaping penetrative ductile deformation.
Lavrion was an important silver mining district in the ancient world, exploited almost continuously from the fourth millennium BC. Its mining history is central to understanding the availability of silver, lead and copper in Greece and the Aegean through the Bronze age. This history is also relevant to the phenomenal rise of Athens in the 5th century BC. Our reassessment of the mineralisation and ancient mining history at Lavrion provides a clearer understanding of its capacity to generate wealth and the scale of its impact on Athens. Integration of new geochemical and geological data with existing information has produced outcomes that help address these two issues. Foremost is the contrasting character of mineralisation at the upper 'first' and lower 'third' contacts and their marked differences in silver content, spatial distribution and supergene alteration. Discovery of the concealed, bonanza mineralisation of the third contact at Kamariza, possibly early in the 5th century BC, followed about 3000 years of mining, which appears to have been largely restricted to discontinuous, low-grade mineralisation at the first contact. Undoubtedly, this later discovery had enduring impacts on Lavrion and Athens, and it most likely funded the trireme fleet, which brought victory over the Persians at Salamis in 480 BC.
The Lavrion area corresponds to the western part of the Attic-Cycladic metamorphic belt, in the back-arc region of the active Hellenic subduction zone. Between the Eocene and the Miocene, metamorphic rocks (mainly marbles and schists) underwent several stages of metamorphism and deformation due to collision and collapse of the Cycladic belt. Exhumation during the Miocene was accommodated by the movement of a large-scale detachment fault system, which also enhanced emplacement of magmatic rocks, leading to the formation of the famous Lavrion silver deposits. The area around the mines shows the stacking of nappes, with ore deposition mainly localized within the marbles, at marble-schist contacts, below, within, or above the detachment. The Lavrion deposit comprises five genetically-related but different styles of mineralization, a feature never observed in another ore deposit elsewhere, containing the highest number of different elements of any known mining district. The local geology, tectonic, and magmatic activity were fundamental factors in determining how and when the mineralization formed. Other key factors, such as the rise and the fall of sea level, which resulted from climate change over the last million years, were also of major importance for the subsequent surface oxidation at Lavrion that created an unmatched diversity of secondary minerals. As a result, the Lavrion deposit contains 638 minerals of which Lavrion is type-locality for 23 of them, which is nearly 12% of all known species. Apart from being famous for its silver exploitation, this mining district contains more minerals than any other district on Earth.
The bedrock of Hymittos, Attic peninsula, Greece, exposes a pair of low-angle crustal-scale ductile-then-brittle detachment faults. The uppermost detachment fault separates sub-greenschist facies phyllite and marble of a Pelagonian Zone hanging wall, from greenschist facies metasedimentary schist, calc-schist, and marble correlated to the Cycladic Blueschist Unit. A second, structurally lower detachment fault subdivides the metamorphic rocks of the Cycladic blueschist unit footwall into middle and lower units. There is a marked step in metamorphic grade between the sub-greenschist facies uppermost package, and the middle-to-upper greenschist facies middle and lower packages. A suite of new white mica 40Ar/39Ar and zircon (U-Th)/He dates indicates accommodation of deformation along these faults occurred from the late Oligocene to the late Miocene with both faults active during the middle Miocene. The structures have clear top-S/SSW kinematics determined from flanking folds, sigmoids, shear bands, stair-stepping of strain shadows on porphyroclasts, and SCC' fabrics. The ductile-to-brittle deformation of the structures, morphology of the massif, and the increase in metamorphic grade suggest these low-angle structures are part of a major, crustal-scale extensional complex, located at the northwest end of the West Cycladic Detachment System, that accommodated Miocene bivergent exhumation of Attic-Cycladic metamorphic core complexes in the central Aegean. Taken together, the above data suggest that multiple coeval detachment branches may form in areas with high strain gradients to accommodate the mechanically necessary termination of Cycladic-style detachment systems.
Triassic rift-related volcanic rocks outcrop over all mainland Greece, comprising of trachybasalts and basaltic trachyandesites. Relatively immobile to the effects of alteration processes major and trace element abundances classify the volcanics into OIB and E-MORB lavas. They have mainly been distinguished based upon their: i) LREE contents, ii) silica-saturation index (S·I.), iii) Zr/Nb and Nb/Y ratio values; iv) Th, U, and Ta contents v) geotectonic discrimination diagrams. Their geochemistry indicates that most rocks were affected by moderate to extensive differentiation processes, mostly expressed by clinopyroxene fractionation. Some of the OIB and E-MORB volcanics are considered as primitive undersaturated, displaying (low SiO2, Zr/Nb and S.I. values, enhanced CaO/Al2O3 ratios). Calculated average mantle potential temperatures are comparable (1410 °C OIB; 1370 °C E-MORB), with melt fractions estimated at 3–5% for primary OIB magmas and 6–8% for primary E-MORB magmas. An asthenospheric origin is inferred for the OIB lavas, with melting in the garnet stability field (75–95 km; 2.5–3.0 GPa), whereas E-MORB parent magmas were formed with melting in the garnet/spinel (transitional) stability field (55–70 km; 1.8–2.2 GPa). The Hellenic Triassic rift-related lavas were most likely generated and erupted after lithospheric attenuation and extension, followed by subsequent asthenospheric upwelling of the mantle. The high calculated partial melting degrees and the observed thick and voluminous lava formations account for fast-spreading of the Tethys ridge during the Triassic. Temperature results suggest that the Hellenic Triassic rift-related magmas were generated from mantle at ambient temperature, render a mantle plume-based scenario improbable.
The Lavrion district of the Attica Peninsula, Greece, exposes the West Cycladic Detachment System (WCDS), a low-angle crustal-scale extensional fault system separating tectonostratigraphic units of the Cycladic Blueschist Unit. New multiple single-grain fusion and step-heated white mica 40Ar/39Ar ages integrated with existing (U–Th)/He ages and independent paleothermometry resolves a syn- to post-orogenic deformation history. A structurally higher unit records Oligocene greenschist facies deformation that evolved into brittle conditions by the middle Miocene, and shares a similar history to Serifos at the southern end of the detachment system. The structurally lowest unit remained ductile until the late Miocene, preserving pervasive post-orogenic structures, similar to along-strike structures at the centre, deepest part of the fault. The similarities of structural styles and the timing of deformation across > 150 km of strike length of the detachment system indicates tens of kilometers of offset and extraordinary potential for correlating observations along Cycladic-style detachment systems.
The Cycladic Basement (CB) and the overlying Cycladic Blueschist Unit (CBU) are part of the Paleogene Cycladic subduction complex exposed in Miocene metamorphic core complexes in the distended back-arc of the retreating Hellenic subduction zone of the southern Aegean. While the Cenozoic tectono-metamorphic evolutions of the CB and the CBU have been the foci of numerous studies, this study presents new laser ablation inductively coupled plasma mass spectrometry bedrock and detrital zircon (DZ) U-Pb ages that place robust constraints on the presubduction tectonic, magmatic, and paleogeographic evolution of the CB. Zircon U-Pb ages of crystalline CB are $\sim$306-330 Ma, demonstrating local plutonism associated with regional voluminous, protracted Carboniferous magmatism related to Paleo-Tethys subduction. The plutons intruded the CB metasedimentary host-rock sequence, characterized by distinct Gondwanan DZ U-Pb provenance, Neoproterozoic to early Paleozoic maximum depositional ages, and synmagmatic, contact metamorphic zircon rims ($\sim$300-330 Ma). DZ U-Pb dating revealed postmagmatic Permian metasedimentary rocks ($\sim$270-295 Ma) that unconformably overlie the CB and have unimodal DZ spectra that indicate exhumation of the CB prior to Permian deposition within extensional basins, as well as mark the onset of CBU deposition prior to formation of the Pindos rift domain. These U-Pb results clarify the late Paleozoic-early Mesozoic evolution of the CB as a peri-Gondwanan terrane composed of Neoproterozoic and early Paleozoic metasedimentary rocks, intruded by voluminous Carboniferous arc magmatism, and exhumed in the Permian, prior to Triassic rifting and CBU deposition. Additionally, these data provide a chronostratigraphic framework and illuminate subduction-related juxtaposition within the CB metasedimentary sequence.
The Stypsi Cu-Mo-Au-Re prospect, Lesvos island, is a shallow porphyry-epithermal system hosted within a middle Miocene microgranite porphyry, which was emplaced along NNE-, NW- and NE-trending structures, within trachyandesites to trachydacites and felsic pyroclastics of the Stypsi caldera. The mineralization comprises three stages: Stage I is characterized by magnetite-actinolite ± quartz in transitional and banded quartz veins mostly developed within the microgranite and the surrounding lavas related to calcic-potassic and propylitic alteration of the host rocks. In the banded veins, quartz is botryoidal, suggesting crystallization from a gel. Abundant vapor-rich inclusions in the bands produce a dark grey to black color. Within the veins, magnetite, chalcopyrite, bornite and native gold were followed in time by pyrite, hematite, sphalerite and galena. Stage I mineralization was synchronous and also postdates quartz formation in the veins, since it crosscuts and/or fills vugs in the center of the veins. Sulfides are associated with various combinations of K-feldspar, actinolite, epidote, chlorite, and calcite gangue minerals. Pyrite-molybdenite-chalcopyrite (Stage II) and late intermediate sulfidation epithermal veins (Stage III) overprint earlier mineralization and alteration, and are associated with sericite-calcite and sericite-kaolinite alteration of the porphyry system and spatially associated lavas, respectively. Molybdenite is widespread in the first two mineralization stages, with Re content ranging from about 0.3 wt% in Stage I to 1.96 wt% in Stage II. A barren silicic and advanced argillic (alunite-kaolinite) lithocap, is exposed on top of the porphyry-style mineralization and is crosscut by non-mineralized high-sulfidation epithermal chalcedony-barite veins. Bulk ore analyses of surface samples from the Stypsi prospect yielded values of up to 276 ppm Mo, 978 ppm Cu, up to 0.5 g/t Au, up to 3 g/t Ag, and up to 70 ppb Pd and Re. Fluid inclusion data indicate that the Stage I transitional and banded quartz veins were deposited at 420 °C–530 °C and at pressures up to 450 bars, from boiling hydrothermal fluids. The fluid in the veins consists of a brine (40–61 wt% NaCl equiv) that coexists with a lower salinity (6–14 wt% NaCl equiv) liquid phase and a low-density vapor-rich fluid. Fluid inclusions in quartz of the Stage III intermediate-sulfidation epithermal veins are characterized by relatively low homogenization temperatures (231 °C–288 °C) and salinities (up to 1.9 wt% NaCl equiv), which was the result of subsequent dilution of the moderately saline fluids by circulating meteoric water. This study verifies earlier works suggesting that Au-enriched felsic magmas are able to crystallize Re-rich molybdenite, and that Re may also be redistributed and enriched in later stages during the deposition of porphyry-style mineralization. The Stypsi prospect ressembles in many respects (e.g., Au grades, Cu/Mo ratios, the Re content of molybdenite and the presence of ore-grade calcic-potassic alteration), other porphyry Cu-Mo-Re-Au systems hosted in calc-alkaline rocks in northeastern Aegean, Greece.
Vein-type Pb-Ni-Bi-Au-Ag mineralization at the Clemence deposit in the Kamariza and “km3” in the Lavrion area, was synchronous with the intrusion of a Miocene granodiorite body and related felsic and mafic dikes and sills within marbles and schists in the footwall of (and within) the Western Cycladic detachment system. In the Serpieri deposit (Kamariza area), a porphyry-style pyrrhotite-arsenopyrite mineralized microgranitic dike is genetically related to a garnet-wollastonite bearing skarn characterized by a similar base metal and Ni (up to 219 ppm) enrichment. The Ni–Bi–Au association in the Clemence deposit consists of initial deposition of pyrite and arsenopyrite followed by an intergrowth of native gold-bismuthinite and oscillatory zoned gersdorffite. The zoning is related to variable As, Ni, and Fe contents, indicating fluctuations of arsenic and sulfur fugacity in the hydrothermal fluid. A late evolution towards higher sulfur fugacity in the mineralization is evident by the deposition of chalcopyrite, tennantite, enargite, and galena rimming gersdorffite. At the “km3” locality, Ni sulfides and sulfarsenides, vaesite, millerite, ullmannite, and polydymite, are enclosed in gersdorffite and/or galena. The gersdorffite is homogenous and contains less Fe (up to 2 wt.%) than that from the Clemence deposit (up to 9 wt.%). Bulk ore analyses of the Clemence ore reveal Au and Ag grades both exceeding 100 g/t, Pb and Zn > 1 wt.%, Ni up to 9700 ppm, Co up to 118 ppm, Sn > 100 ppm, and Bi > 2000 ppm. The “km3” mineralization is enriched in Mo (up to 36 ppm), Ni (>1 wt.%), and Co (up to 1290 ppm). Our data further support a magmatic contribution to the ore-forming fluids, although remobilization and leaching of metals from previous mineralization and/or host rocks, through the late involvement of non-magmatic fluid in the ore system, cannot be excluded.
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.
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.
This study presents detrital zircon U-Pb analyses of 23 samples of the Cycladic Blueschist Unit (CBU) from Kea, Kythnos, and Serifos islands, as well as the Lavrion Peninsula of SE Attica. The maximum depositional ages (MDA) and age distributions of detrital zircon U-Pb dates are used to correlate metasediments between the islands considered herein and infer their provenance. Two distinct detrital zircon U-Pb age distributions are found in CBU metasediments: “Proterozoic,” comprised of >40% Neoproterozoic zircons with Triassic-Early Jurassic maximum depositional ages and “Paleozoic,” containing >30% Paleozoic zircons and yielding Late Jurassic-Cretaceous MDAs. Proterozoic affinity metasediments are rift margin deposits derived from the northern Gondwanan margin. Paleozoic metasediments are flysch sediments most probably sourced from the Internal Hellenides. This metamorphosed flysch forms a distinct marker horizon found in a similar structural position in Lavrion, Kythnos, and Serifos. Based on lithologic correlation, sediment provenance, and MDA estimates, the CBU of Kythnos is correlative to the Lavrion Schists of Attica. On the islands of Serifos and Kythnos and within the Lavrion Schists only young-on-old relationships exist between rocks based on MDA estimates.
The Aegean-west Anatolian orocline formed due to Neogene opposite rotations of its western and eastern limbs during opening of the Aegean back-arc basin. Stretching lineations in exhumed metamorphic complexes in this basin mimic the regional vertical-axis rotation patterns and suggest that the oppositely rotating domains are sharply bounded along a Mid-Cycladic lineament, the tectonic nature of which is enigmatic. Some have proposed this lineament to be an extensional fault accommodating orogen-parallel extension, while others have considered it to be a transform fault. The island of Paros hosts the only exposure of the E- to NE-trending lineations characterizing the NW Cyclades and the N-trending lineations of the SE Cyclades. Here, we show new paleomagnetic results from isotropic, ca. 16 Ma granitoids that intruded both domains and demonstrate that the trend difference resulted from post-16 Ma $\sim$90° clockwise and 10° counterclockwise rotation of the NW and SE blocks, respectively. We interpret the semiductile to brittle, low-angle, SE-dipping Elitas shear zone that accommodated this rotation difference to reflect the Mid-Cycladic lineament. We conclude a two-stage exhumation history for Paros that is consistent with regional Aegean reconstructions. Between ca. 23 and 16 Ma, the metamorphic rocks of Paros were exhumed from amphibolite-facies to greenschist-facies conditions along a top-to-the-N detachment. The Elitas shear zone then started to exhume the northwestern, clockwiserotating domain from below the southeastern, counterclockwise rotating domain since 16 Ma. From this, we infer that the Mid-Cycladic lineament is an extensional shear zone, consistent with geometric predictions that Aegean oroclinal bending was accommodated by orogennormal and orogen-parallel extension.