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New results that employ Zr‐in‐rutile thermometry (ZiR) and quartz‐inclusion‐in‐garnet (QuiG) barometry constrain the P–T conditions of garnet formation in blueschists and eclogites from the island of Syros, Greece. QuiG barometry reveals that garnet from different regions across the island formed at pressures ranging from 1.1 to 1.8 GPa and ZiR thermometry on rutile inclusions in garnet constrains the minimum temperature of garnet formation to have been 475–550°C. Most importantly, there is no systematic difference in the conditions of garnet formation from different regions across the island and these results are nearly identical to those obtained from the islands of Sifnos and Ios, Greece. A model is proposed whereby the rocks from all three islands were initially metamorphosed along a relatively shallow geotherm of around 11°C/km to a depth of around 45 km and were then subjected to metamorphism along a geotherm of around 7–8°C/km, which could have been caused by either an increase in the dip of the subduction zone or an increase in the rate of subduction. Garnet formed along this steeper geotherm was accompanied by the release of significant H2O from the breakdown of chlorite over a duration of 1 Ma or less based on thermal and diffusion modeling. It is concluded that rocks from Syros, Sifnos and Ios all followed a similar, roughly counter‐clockwise prograde P–T path and that the present outcrop configuration is largely due to a complex exhumation history. Plain Language Summary: The metamorphism of rocks in subduction zones releases large quantities of H2O, which ultimately helps flux melting in the overlying mantle leading to explosive island arc volcanism and provides a trigger for large earthquakes. One of the dominant processes that produce large amounts of H2O is the formation of the mineral garnet. Here, we present results that constrain the pressure and temperature conditions for the formation of garnet from three islands in the Greek Cyclades: Syros, Sifnos, and Ios. Our results indicate that garnet formed in different rocks on all three islands in a similar subduction channel along a trajectory where the pressure increase was relatively rapid and the temperature remained nearly constant. The duration of garnet formation in the entire suite of samples is estimated to have occurred in 1 million years or less, during which time significant quantities of fluid are inferred to have been released and which most likely had a major impact on volcanism and seismicity in the region while subduction was active. Key Points: Blueschist and eclogite assemblages do not necessarily reflect equilibrium crystallizationExhumation following garnet growth must occur within 1 Ma to preserve compositional zoningThe prograde subduction P–T path in the Cyclades is concave upward with initial shallow subduction followed by near isothermal loading [ABSTRACT FROM AUTHOR]

Abstract New results that employ Zr‐in‐rutile thermometry (ZiR) and quartz‐inclusion‐in‐garnet (QuiG) barometry constrain the P–T conditions of garnet formation in blueschists and eclogites from the island of Syros, Greece. QuiG barometry reveals that garnet from different regions across the island formed at pressures ranging from 1.1 to 1.8 GPa and ZiR thermometry on rutile inclusions in garnet constrains the minimum temperature of garnet formation to have been 475–550°C. Most importantly, there is no systematic difference in the conditions of garnet formation from different regions across the island and these results are nearly identical to those obtained from the islands of Sifnos and Ios, Greece. A model is proposed whereby the rocks from all three islands were initially metamorphosed along a relatively shallow geotherm of around 11°C/km to a depth of around 45 km and were then subjected to metamorphism along a geotherm of around 7–8°C/km, which could have been caused by either an increase in the dip of the subduction zone or an increase in the rate of subduction. Garnet formed along this steeper geotherm was accompanied by the release of significant H2O from the breakdown of chlorite over a duration of 1 Ma or less based on thermal and diffusion modeling. It is concluded that rocks from Syros, Sifnos and Ios all followed a similar, roughly counter‐clockwise prograde P–T path and that the present outcrop configuration is largely due to a complex exhumation history.

This paper attempts to quantify the visual impact that certain infrastructures and buildings have on Sifnos island, a small island located in the southwestern Cyclades. Quantification of the visual effects is based on the viewshed analysis through GIS. The main element of the visibility computation method, as adopted here, is the identification of those infrastructures and buildings that are considered actors with a ‘negative’ impact on the landscape. The analysis demonstrates that zones with varying impact on landscape can be identified. Investments with ‘negative’ impact on the landscape should be directed towards areas of restricted visibility, thus minimising landscape degradation.

Equilibrium thermodynamic modelling, quartz in garnet (QuiG) Raman geobarometry, and modelling of garnet nucleation at overstepped conditions were applied to three garnet-bearing blueschists from a 1.5 km-long transect across the eclogite-blueschist unit in Sifnos, Greece, in order to evaluate the accuracy of P‒T conditions calculated via equilibrium thermodynamics. QuiG barometry uses the Raman shift of quartz inclusions in garnet to estimate the pressure of garnet nucleation and is independent of chemical equilibrium. Garnet nucleation temperatures were estimated by determining the stability field of the palaeo-assemblage inferred from garnet inclusion suites on mineral assemblage diagrams calculated in the MnNCKFMASH system and on temperatures obtained from Zr in rutile thermometry. These conditions were then compared to P‒T conditions calculated at the equilibrium garnet isograd, and the method of intersecting isopleths. The P‒T conditions calculated with intersecting garnet isopleths over- and underestimated the temperature of nucleation in samples SPH99-1a and SPH99-7, respectively, whereas they significantly underestimated nucleation pressure in SPH99-5. Nucleation of garnet in SPH99-1a at 12 kbar and ~484°C requires overstepping of ~6 kbar and a reaction affinity of 2.2 kJ mol‒1O. SPH99-5 requires overstepping of ~8 kbar with garnet reaction affinities of at least 2.0 kJ mol‒1O at 15 kbar and ~520°C. SPH99-7 requires overstepping of approximately 15 kbar and affinities of about 2.0–2.4 kJ mol‒1O at ~23 kbar and ~530°C. The geotherms calculated from SPH99-7 (~6.7°C km‒1) and SPH99-5 (9.8°C km‒1) are in accordance with previous studies. The geotherm calculated from SPH99-1a, however, is warmer (11.3°C km‒1), and could reflect changes in the rate of subduction or differences in structural position within the down-going slab. The 10 kbar pressure difference between SPH99-7 and SPH99-1a can be explained by thrusting and accretion of thin slices of underplated wedge material facilitated by slab rollback and gravitational collapse. [ABSTRACT FROM AUTHOR]

The present work analyses the effect of mineralogy, microstructure and firing temperature on the effective thermal conductivity of traditional hot processing ceramics. Samples prepared with two quartz-rich kaolinitic clays (BAR1 and BAR2), a fine kaolinitic clay (ARG) and a glaucophane-rich clay (SIF), were fired in the range between 950 and 1350 °C. The effective thermal conductivity is principally affected by the porosity of the body. Mullite further improves the thermal conductivity of BAR1 and BAR2 ceramics, while in ARG samples cristobalite is correlated with the increase in thermal conductivity. In SIF ceramics, the higher densification and the formation of spinel, pyroxene and hematite results in a higher conductivity compared to the other samples. The amorphous phase improves the ceramics' thermal conductivity since it seals voids between particles. In samples in which quartz exceeds 50 wt%, the ceramics' thermal conductivity decreases because of fissures and detachment zones formed after the α-β quartz phase transition. Finally, functional conclusions are drawn on traditional cooking pot and Medieval glass crucibles. [ABSTRACT FROM AUTHOR]

Since 35 Ma, the kinematics of the Aegean domain has been mainly controlled by the southward retreat of the African slab, inducing back-arc extension. The main structures and associated kinematics are well constrained, but the kinematics of deformation before 35 Ma, coeval with the exhumation of blueschists and eclogites of the Cycladic Blueschist Unit, is still poorly understood. The earlier Eocene syn-orogenic evolution is strongly debated and very different geometrical interpretations and kinematic histories have been proposed in the literature. This study focuses on the high-pressure and low-temperature (HP-LT) parageneses spectacularly exposed and well preserved on Sifnos Island. The new field work provides new structural constraints on the tectonic history of HP-LT units generated in the subduction zone during the Eocene. It further shows how lithological heterogeneities localize strain within an accretionary wedge and how the localisation of strain evolves through time during exhumation. We show, through new geological and metamorphic maps, cross-sections and analyses of kinematic indicators, that Sifnos is characterized by shallow-dipping shear zones reactivating weak zones due to competence contrasts or earlier tectonic contacts. Structures and kinematics associated with these shear zones, show a top-to-the-N to −NE ductile deformation. The lower part of the tectonic pile shows a downward gradient of shearing deformation and is actually a thick top-to-the-NE shear zone, which we name the Apollonia Shear Zone. Through time shearing deformation tends to localize downward, leaving the upper part of the subduction complex preserved from late deformation. The present-day shape and topography of the island is largely controlled by late brittle faults reworking the earlier ductile shear zones. Comparing with the nearby island of Syros, we propose a new tectono-metamorphic evolution of the Cycladic Blueschist Unit, which partly explains the different degrees of retrogression observed on the Cycladic Islands. [ABSTRACT FROM AUTHOR]

We use coupled zoned geochronology and thermodynamic modeling of garnet to elucidate the nature and scale of metamorphic dehydration during Eocene subduction of a quartzofeldspathic lithology from Sifnos, Greece. Two large garnet porphyroblasts were microdrilled to sample concentric growth zones, and these were dated using Sm–Nd geochronology. To put results in a geodynamic context and reveal the causes and consequences of garnet growth, we constructed thermodynamic forward models for a series of prescribed pressure–temperature ( P – T ) paths. Our data reveal three distinct phases of garnet growth: initial growth at 53.4 ± 2.6 Ma (∼0.8 GPa and ∼300 °C), followed by a period of very limited growth until a second phase, at 47.22 ± 0.36 Ma , and then a major pulse of growth, responsible for the majority of the final garnet volume, at 44.96 ± 0.53 Ma (2.06–2.19 GPa and 490–550 °C). This suggests a >2 order of magnitude acceleration in volumetric growth rate from crystal core to rim, with the final growth pulse occurring rapidly (<0.8 My), during a period of nearly isobaric heating at >75 °C/My. This final pulse was accompanied by net bulk rock dehydration of ∼0.5 wt.%. Rapid heating during early stages of exhumation in the subduction channel, or by sharp thermal gradients related to slab-mantle coupling could be causes for this pulsed metamorphism and dehydration. The garnet data thus record a concentrated pulse of dehydration and heating during the otherwise slow and continuous process of subduction. [ABSTRACT FROM AUTHOR]

The Attic-Cycladic crystalline belt in the central Aegean region records a complex structural and metamorphic evolution that documents Cenozoic subduction zone processes and exhumation. A prerequisite to develop an improved tectono-metamorphic understanding of this area is dating of distinct P-T-D stages. To evaluate the geological significance of phengite ages of variably overprinted rocks, 40Ar/39Ar and Rb-Sr analyses were undertaken on transitional blueschist-greenschist and greenschist facies samples from the islands of Syros and Sifnos. White mica geochronology indicates a large age variability (40Ar/39Ar: 41-27 Ma; Rb-Sr: 34-20 Ma). Petrologically similar samples have either experienced greenschist facies overprinting at different times or variations in ages record variable degrees of greenschist facies retrogression and incomplete resetting of isotopic systematics. The 40Ar/39Ar and Rb-Sr data for metamorphic rocks from both islands record only minor, localized evidence for Miocene ages ( c. 21 Ma) that are well documented elsewhere in the Cyclades and interpreted to result from retrogression of high-pressure mineral assemblages during lower pressure metamorphism. Field and textural evidence suggests that heterogeneous overprinting may be due to a lack of permeability and/or limited availability of fluids in some bulk compositions and that retrogression was more or less parallel to lithological layering and/or foliation as a result of, possibly deformation-enhanced, channelized fluid ingress. Published and new 40Ar/39Ar and Rb-Sr data for both islands indicate apparent age variations that can be broadly linked to mineral assemblages documenting transitional blueschist-to-greenschist- and/or greenschist facies metamorphism. The data do not record the timing of peak HP metamorphism, but may accurately record continuous (partial) resetting of isotopic systematics and/or (re)crystallization of white mica during exhumation and greenschist facies retrogression. The form of 40Ar/39Ar phengite age spectra are complex with the lowest temperature steps yielding Middle to Late Miocene ages. The youngest Rb-Sr ages suggest maximum ages of 20.6 ± 0.8 Ma (Syros) and 22.5 ± 0.6 Ma (Sifnos) for the timing of greenschist facies overprinting. The results of this study further accentuate the challenges of interpreting isotopic data for white mica from polymetamorphic terranes, particularly when mixing of populations and/or incomplete resetting of isotopic systematics occurs during exhumation. These data capture the full range of isotopic age variations in retrogressed HP rocks documented in previous isotopic studies, and can be interpreted in terms of the geodynamic evolution of the Aegean. [ABSTRACT FROM AUTHOR]

Abstract: We present a method to reconstruct the dehydration flux associated with garnet-forming reactions during subduction. Garnet-bearing blueschists from the island of Sifnos, Greece, in the Attic–Cycladic Blueschist Belt are used as a test case to extract information on the timescales of dehydration during subduction. We use garnet growth as a proxy for the net dehydration reaction. Thermodynamic (pseudosection) analysis of a mafic blueschist in this unit (representative of an altered basalt protolith) indicates that garnet grew via net reaction(s) of the form chlorite+chloritoid+glaucophane+phengite=garnet+pyroxene+lawsonite+paragonite+quartz+H2O. Garnet core and rim chemistry indicates that growth began at 2.0GPa and 460°C and ended at 2.2GPa and 560°C. The stabilization of matrix lawsonite (promoted by the bulk chemical shift of the matrix due to fractionation of the garnet and its inclusions from the system) throughout garnet growth limits the amount of water liberated from the rock over this P–T span. The average stoichiometry of the garnet-forming reaction(s) indicates an average molar production ratio of garnet to water of ~1.0:0.7. Given the 11vol.% garnet observed in the rock, this analysis indicates a loss of 0.3 to 0.4wt.% H2O from the bulk rock during garnet growth. Zoned garnet geochronology from these rocks provides a constraint on the dehydration rate from this lithology during the time span of garnet growth. Two garnet grains, roughly 1.5cm each in diameter, were microdrilled based on major element zoning contours. Three concentric growth zones were extracted from each garnet for Sm–Nd geochronology. Very low Nd concentrations in acid-cleansed garnet (0.03 to 0.09ppm) yielded very small samples (~1ng Nd) that were analyzed with TIMS using a NdO+ with Ta2O5 activator method. Untreated “garnet” powders rich in mineral inclusions from each garnet zone were also analyzed. The powders fall off of the garnet-matrix isochron, likely indicating age inheritance in the inclusions. Combining acid-cleansed garnet data from each garnet, multi-point garnet-matrix isochron ages of 46.50±0.80Ma for the core, 46.49±0.53Ma for the intermediate zone, and 46.46±0.59Ma for the rim were determined, indicating a brief growth duration of 0.04Ma with an upper bound (2 SD) on growth duration of 1.0Myr. This equates to a release of 0.3–0.4wt.% of water due to this reaction in this lithology, and heating of 100°C, in less than 1.0Myr. The short time interval represents a focused, rapid pulse of dehydration and heating within the context of the overall subduction descent timescale of ~10–20Myr. [Copyright &y& Elsevier]

Abstract: The island of Sifnos (Cyclades, Greece) is famous for its spectacular blueschist-facies rocks and eclogites. Their very well preserved high-pressure assemblages are characterized by the occurrence of Fe+3-rich minerals such as aegirine-rich pyroxene, riebeckite-rich amphibole, magnetite and deerite. Therefore, the common model system NCFMASH (Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O), in which all iron is assumed to be ferrous, is not sufficient to completely model these highly oxidized assemblages. We propose new constraints on the P–T evolution of the glaucophane schists and associated rocks from Vroulidia Bay (northern Sifnos) using P–T isochemical diagrams (pseudosections) modelled for the oxidized N(K)CFMASHO system [Na2O–(K2O)–CaO–FeO–Fe2O3–MgO–Al2O3–SiO2–H2O], and calculated using solid solution models involving Fe+3-end-members. The resulting P–T conditions could be fitted by a simple trajectory consisting of a smooth clockwise P–T loop, with two distinct high-pressure events at T =450–500 °C, P >2.0 GPa (assemblage A) and T =525–565 °C, P >2.1 GPa (assemblage B), respectively, followed by cooling and decompression. Geospeedometry based on 40Ar/39Ar data, however, allows constraint as to the duration of individual thermal excursions associated with these events. Should these limits be taken into account, the P–T envelope derived in this paper encompasses a more complex P–T history, with individual excursions that potentially involve relatively short periods of temperature increase±pressure variation. [Copyright &y& Elsevier]

Abstract: This case study on the Sifnos island, Greece, assesses the main factors controlling vegetation succession following crop abandonment and describes the vegetation dynamics of maquis and phrygana formations in relation to alternative theories of secondary succession. Field survey data were collected and analysed at community as well as species level. The results show that vegetation succession on abandoned crop fields is determined by the combined effects of grazing intensity, soil and geological characteristics and time. The analysis determines the quantitative grazing thresholds that modify the successional pathway. Light grazing leads to dominance by maquis vegetation while overgrazing leads to phryganic vegetation. The proposed model shows that vegetation succession following crop abandonment is a complex multi-factor process where the final or the stable stage of the process is not predefined but depends on the factors affecting succession. An example of the use of succession models and disturbance thresholds as a policy assessment tool is presented by evaluating the likely vegetation impacts of the recent reform of the Common Agricultural Policy on Sifnos island over a 20–30-year time horizon. [Copyright &y& Elsevier]

Zr-in-rutile thermometry on samples of blueschist from Sifnos, Greece, yields temperatures that reflect progressive crystallization of rutile from ca. 445 to 505°C with an analytical precision of + 18/−27 and ± 10°C using the electron microprobe and ± 1.5–3.5°C using the ion microprobe. Individual grains are generally homogeneous within analytical uncertainty. Different grains within a single sample record temperature differences as large 55°, although in most samples the range of temperatures is on the order of 25°. In several samples, Zr-in-rutile temperatures from grains within garnet are lower than temperatures from matrix grains, reflecting growth of rutile with increasing temperature of metamorphism. Although the specific rutile-producing reactions have not been identified, it is inferred that rutile grows from either continuous reaction involving the breakdown of lower grade phases (possibly ilmenite), or from pseudomorph reactions involving the breakdown of relic igneous precursors at blueschist-facies conditions. No systematic variation in rutile temperatures was observed across the blueschist belt of northern Sifnos, consistent with the belt having behaved as a coherent block during subduction. [ABSTRACT FROM AUTHOR]

Question: Which factors affect the spatial variation of maquis and phryganic vegetation and how can the role of human activities be estimated through degradation models. Location: Island of Sifnos, Cyclades, Greece. Methods: Data on woody vegetation, environmental conditions and intensity of human activity were collected by field survey. The vegetation data were analysed using TWINSPAN. Models based on the combination of Canonical Variate Analysis and logistic regressions were used in order to examine and describe the different pathways of maquis degradation. Results: The spatial variation of maquis and phryganic vegetation was related to both environmental and disturbance factors. The replacement of maquis by phryganic vegetation can follow two different pathways which reflect differences on the environmental conditions. However, the pathways themselves are determined by the combinations and levels of disturbance only. Conclusion: Degradation models can provide essential information on the effects of human activities on the vegetation. Maquis vegetation is relatively tolerant of disturbance, however, if disturbance exceeds certain critical thresholds, maquis is replaced by phryganic vegetation. The presence of phryganic vegetation is not always the result of maquis degradation. [ABSTRACT FROM AUTHOR]

This work presents new structural data from a high-pressure/low-temperature (HP/LT) metamorphic terrane exposed on the islands of Syros and Sifnos (Cyclades, Greece). The structure and the metamorphism of a relatively coherent HP/LT rock section were studied in order to elucidate how strain was accommodated at deep crustal levels during the formation and exhumation of HP/LT rocks. At least three deformation phases associated with eclogite- and blueschist-facies conditions (P=8–15 kbar; T=400–550 °C) were recognised. The earliest deformation fabric (S1), preserved as inclusion trails within garnet porphyroblasts, is aligned to define a sub-vertical schistosity (at present orientation), which is frequently orthogonal to the flat matrix schistosity (S2), and may indicate that deep crustal thickening involved upright folding. The currently dominant fabric in the HP rock section, S2, is usually moderately dipping and locally contains NW-trending glaucophane lineations, symmetric pressure-shadows and eclogitic boudins. The symmetric structures associated with this fabric seem to indicate coaxial vertical thinning, although the existence of non-coaxial structures out of the study area cannot be excluded. Glaucophane-bearing shear bands (S3), with top-to-NW sense of shearing, locally crosscut the earlier structures. The latest recognised fabric (D4) is scarce and often absent within the HP rocks. It is associated with top-to-NE kinematic criteria that formed at greenschist-facies conditions (P=4–7 kbar; T=400–450 °C). Based on these observations, it is suggested that partitioning of strain occurred at different crustal levels and at different times. Deep crustal deformation was governed by thickening via upright folding followed by coaxial vertical thinning, whereas non-coaxial shearing occurred when the rocks were already exhumed to relatively shallow crustal levels. The earliest fabrics (D1 to D3) pertain to Alpine orogenesis and possibly to syn-orogenic extension, whereas the latest correspond to whole-crust back-arc extension. [Copyright &y& Elsevier]

Metamorphic P–T paths provide valuable constraints on the tectonics of collisional orogens and many such paths have been deduced from analysis of chemical zoning in garnet. Inclusion barometry (e.g. quartz-in-garnet or QuiG) provides complementary and sometimes contradictory information regarding the interpretation of garnet zoning and the P–T paths derived therefrom. For example, QuiG barometry on several generations of garnet from well-characterized samples from Fall Mountain, New Hampshire, is consistent with the P–T path inferred from other methods. However, QuiG barometry is inconsistent with P–T paths inferred from garnet zoning from the Orfordville Belt (Vermont), Townshend Dam (Vermont), the Connecticut Valley Trough (Vermont), and Sifnos (Greece). New data from the Perry Mountain Formation, southeastern New Hampshire, suggests that QuiG may preserve a record of polymetamorphic events. Specifically, QuiG barometry in coticule samples is interpreted to record a previously unrecognized early medium pressure (ca. 0.9 GPa) metamorphism and a later low pressure (ca. 0.3 GPa) metamorphism. • QuiG barometry potentially provides an estimate of garnet growth conditions • QuiG barometry in some localities is consistent with peak metamorphic estimates and in some localities not • QuiG barometry suggests that some garnets grow nearly isothermally and isobarically • QuiG barometry appears to preserve entrapment conditions through multiple metamorphic events [ABSTRACT FROM AUTHOR]