Dimitrios Kostopoulos - Profile on Academia.edu (original) (raw)

Papers by Dimitrios Kostopoulos

Heat budgets of crustal and mantle rocks revealed by exchange thermometers involving cations with differing diffusivities

EGU General Assembly Conference Abstracts, Apr 1, 2017

Chemical zoning and ductility of natural garnet at lower crustal conditions: An example from the Rhodope Massif

The Kesebir-Kardamos gneiss dome in the Rhodope Massif (northern Greece – southern Bulgaria) is a... more The Kesebir-Kardamos gneiss dome in the Rhodope Massif (northern Greece – southern Bulgaria) is a late orogenic extensional structure that deformed an Alpine, synmetamorphic nappe complex containing high-pressure (HP) metamorphic rocks. Microdiamond inclusions in garnet of quartzofeldspathic rocks from one of the thrust sheets suggests equilibration at ultrahigh-pressure metamorphic conditions (P>2.5GPa). This study aims at delimiting the P-T conditions of the metamorphic evolution experienced by these rocks. Garnets (10-15% vol, pyrope: 15% grossular:10% almandine:65%) from the aforementioned quartzofeldspathic rocks are chemically zoned. Biotite and kyanite are other major phases of the rock paragenesis. Garnet-biotite-plagioclase-quartz geobarometry and garnet-biotite geothermometry confine the recorded peak conditions at ca 1.0 ±0.1 GPa and 690 ±50 oC in the stability field of kyanite. The consistency of these results with the metamorphic overprint of HP-metapelites from cent...

zone where permeability and (sulphate and chloride) salt data are correlated. At greater depth, c... more zone where permeability and (sulphate and chloride) salt data are correlated. At greater depth, continual wetting with salt and subsequent heating increases permeability and pore connectivity of the sandstone block. Salt crystallization enlarges and fractures pores, enabling the ingress and movement of soluble chloride salts. The stone's intrinsic properties (permeability and porosity) have been changed by salt weathering, ultimately leading to deterioration and accelerated stone decay.

Επιστημονική Επετηρίδα του Τμήματος Γεωλογίας (Α. Π. Θ.), 2010

More than twenty ophiolitic fragments ranging in size from meter-scale to several tens of km2 occ... more More than twenty ophiolitic fragments ranging in size from meter-scale to several tens of km2 occur strato-tectonically above the Pelagonian continental massif (mid-Neoproterozoic and Permo-Carboniferous crystalline basement plus Triassic-Jurassic platform carbonate cover) in the region between the mid-late Jurassic Mesohellenic ophiolites (rooted within the Mesohellenic Trough in the west) and the Vardar Zone ophiolites (rooted in the Vardar Zone in the east). Formerly presumed to be part of a single, initially continuous mid-upper ...

Conditions of deformation and metamorphism on Skopelos island (Greece): implications for the Cretaceous-Paleogene tectonics of the Pelagonian zone

EGUGA, Apr 1, 2018

Alpine thrusting versus late Alpine extension in the northern Aegean: an evaluation of the ductile record in the Rhodope massif

Geologica Balcanica, Jun 30, 2001

Record of Variscan Low-P/High-T metamorphism in Alpine medium-P rocks of the Pelagonian Zone, Greece

In the Early Cretaceous, obduction of the ophiolites from the Vardar ocean over the eastern Pelag... more In the Early Cretaceous, obduction of the ophiolites from the Vardar ocean over the eastern Pelagonian continental margin caused medium-P metamorphism in the pre-Alpine basement and the Alpine volcanosedimentary cover series of the Pelagonian Zone (Yarwood &amp;amp;amp;amp;amp;amp;amp;amp;amp;Dixon, 1977, Schermer et al., 1990, Perraki et al., 2003). Representative mineral assemblages are garnet-chloritoid-chlorite-kyanite-white K-mica-paragonite-rutile in Permo-Triassic pelitic metasediments from Voras and Vermion

Carbonate rocks were found in association with amphibolites and epidotites in the greenschist- to... more Carbonate rocks were found in association with amphibolites and epidotites in the greenschist- to amphibolite-facies metamorphic basement of the Pelagonian zone (Greece). The mafic rocks both include and are truncated by the carbonates, hinting to a cogenesis of siliceous and carbonatic magmas/fluids. The carbonates have an isotopic signature of δ13C ranging from -5.18 to -5.56 (‰ vs. PDB) and of δ18O from 10.68 to 11.59 (‰ vs. SMOW) giving them the geochemical characteristic of carbonatites (magmatic carbonates). Mafic rocks have high Nb and Ta concentrations, typical for alkaline basalts. Therefore, textural relationships and geochemical signals in both the silicate and carbonate rocks hint at a cogenetic, mantle origin. SHRIMP U-Pb zircon ages from a carbonate bearing amphibolite date the intrusion at 278 Ma (magmatic zircon cores), well before the metamorphic event at 118 Ma (metamorphic zircon rims). However, the concentration of rare earth elements (REE) in the carbonates, amp...

Environment of diamond formation in UHPM rocks from the Greek Rhodope: A Raman study of inclusions in zircon

The Rhodope Massif in northern Greece is a newly established ultrahigh-pressure metamorphic (UHPM... more The Rhodope Massif in northern Greece is a newly established ultrahigh-pressure metamorphic (UHPM) province in the world (Mposkos and Kostopoulos, 2001). Microscopic observations on zircons separated from a garnet gneiss revealed a simple zoned structure consisting of a somewhat rounded detrital core and a metamorphic overgrowth rim. Numerous mineral and fluid inclusions were found in the metamorphic rim especially near the interface of the two domains. We carried out a detailed laser µ-Raman spectroscopic study of the inclusions and their zircon host in both domains. Quartz and monazite were identified in the detrital core whereas diamond, albite, phengite, hematite, rutile and CO 2 gas were identified in the rim. Interestingly, albite occurs always in pockets with phengite and diamond whereas the latter two phases can occur independently. We interpret these pockets as precipitates from a melt phase at high pressures. The microdiamonds were probably formed by dissociation of CO2 ; the thus liberated oxygen was combined with iron available from the fluid / melt phase to precipitate hematite. Importantly, there is clear-cut distinction in the Raman spectra of detrital and rim zircon, with the latter being additionally characterised by a broad band at ~1332 cm-1. What is more significant is that by approaching the included diamonds the above band in zircon increases dramatically in intensity. This can either be assigned to carbon occupying interstitial sites in zircon and in all probability reflects a luminescence band or to enhanced carbon solubility in zircon (Shcheka et al., 2006), with the diamonds reflecting sites locally supersaturated in carbon. We favour the former explanation since similar bands, often associated with CO2 peaks, were also observed in inclusions in garnet for which C solubility is negligible.

The Rhodope Metamorphic Complex (RMC) in northern Greece and southern Bulgaria is a synmetamorphi... more The Rhodope Metamorphic Complex (RMC) in northern Greece and southern Bulgaria is a synmetamorphic nappe pile that developed during the Alpine-Himalayan orogen. The nappe system is deformed and forms dome-andbasin structures that indicate syn- to post-convergent exhumation. High-pressure rocks showing variable degrees of retrogression occur in the intermediate high-pressure imbricate units. We document the deformation style and present new thermobarometric and geochronological constraints for the Kesebir-Kardamos dome in the eastern RMC in an attempt to comprehend the major mechanisms involved in the exhumation of high-pressure (HP) and high-temperature (HT) rocks. Thermodynamic modeling and thermobarometry applied to the high-grade rocks from the intermediate thrust sheets of the core of the Kardamos dome suggest peak conditions at 1.2GPa and ca. 750 C. U-Pb SHRIMP dating of zircons from rocks from the same unit reveals Early Cretaceous (144 Ma) as the time of the major metamorphic...

Calculating pressure with elastic geobarometry: A comparison of different elastic solutions with application to a calc-silicate gneiss from the Rhodope Metamorphic Province

Lithos

Abstract Raman elastic geobarometry has increasingly been used complementary to metamorphic phase... more Abstract Raman elastic geobarometry has increasingly been used complementary to metamorphic phase equilibria to estimate the conditions of recrystallization in metamorphic rocks. The procedure of applying Raman elastic barometry to host-inclusion mineral systems requires several steps that involve various assumptions. One of the most essential assumptions is that the mineral host-inclusion system behaves in an elastic and reversible manner. We discuss the discrepant results obtained by different authors employing different analytical solutions for elasticity and explore the assumptions lying behind each method. Furthermore, we evaluate numerically linear and non-linear elastic solutions and show their discrepancies. Both formulations are tested against recently published experiments on quartz inclusions in garnet (QuiG) at pressures up to 3 GPa, and we find a very good agreement between calculated and experimental pressure values (within 10% relative error). We subsequently apply our new elastic geobarometer to a calc-silicate gneiss from the Rhodope Metamorphic Province (N. Greece). The results of Raman elastic barometry combined with garnet-clinopyroxene geothermometry yield eclogite-facies conditions (~720 ± 40 °C, ~1.5 ± 0.2 GPa). These results are comparable to a high-temperature metamorphic overprint deduced from phase equilibria modeling in surrounding lithologies (730 ± 40 °C, ~1.2 ± 0.1 GPa). Our findings indicate that the estimated pressure from Raman elastic barometry is consistent with a significant viscous relaxation at high temperatures. We conclude that although Raman elastic barometry is a powerful tool for pressure estimation in metamorphic rocks, its pressure estimates do not necessarily correspond to entrapment conditions. Our results are consequential for the estimates of reaction overstepping in high-grade metamorphic rocks.

Bulletin of the Geological Society of Greece

The Mesohellenic ophiolites (MHO) in the Western Hellenides are part of an oceanic slab emplaced ... more The Mesohellenic ophiolites (MHO) in the Western Hellenides are part of an oceanic slab emplaced onto Pelagonian (Pangaean) continental rocks in the mid-Jurassic with a documented NE ophiolite emplacement. Ophiolitic outliers to the east of the MHO are oceanic lithospheric fragments, not complete ophiolite bodies, preserved above exhumed Pelagonia continental rocks. As these fragments lack connection to original root zone provenance, we refer to these as the “rootless” ophiolites.Pelagonian exhumation, possibly triggered by transcurent shear along its continental margin with the Pindos basin, began by the Late Jurassic and continued into the mid-Cretaceous. Exhumation affected the emplaced oceanic slab in the following ways: i) The metamorphic facies of the basal mélange separating the ophiolite from the Pelagonian basement grades from phyllitic to schist and amphibolite-schist over the exhumed Pelagonia. ii) Ophiolitic remnants are metasomatized where in contact with the exhumed Pe...

Tectonics

We have investigated subduction-exhumation processes in the Pelagonian zone, exposed on the North... more We have investigated subduction-exhumation processes in the Pelagonian zone, exposed on the Northern Sporades islands (Aegean Sea) related to successive episodes of ocean continent and continent-continent convergence through integrating multiscale structural analysis, metamorphic petrology, and white mica 40 Ar/ 39 Ar dating. Two major progressive phases of ductile deformation are documented, which are related to distinct episodes of tectonic burial and exhumation of the Pelagonian continental margin, which was facing the Neotethys/Vardar ocean. Review of existing data sets from neighboring regions shows that both deformation phases can be correlated along strike up to the Dinarides. The first phase of tectonic burial and exhumation (D1) is characterized by NW-SE tectonic transport, greenschist facies metamorphism, and Early Cretaceous (~105-135Ma) 40 Ar/ 39 Ar white mica single fusion ages. D1 is correlated with the initial closure of the Vardar ocean by top-to-the-W to NW ophiolite obduction and the underthrusting of the Pelagonian margin below the oceanic upper plate. Underthrusting was followed by exhumation and the deposition of Late Cretaceous-Paleogene sediments. The second phase of burial and exhumation (D2) is characterized by NE-SW tectonic transport, greenschist to blueschist facies metamorphism, and latest Cretaceous-Early Eocene 40 Ar/ 39 Ar white mica ages of S 2 fabrics. Top-to-the-SW shearing is correlated with the tectonic burial of the Pelagonian zone below the Eurasian continent (Rhodopia), while top-to-the-NE shearing is attributed to subsequent extensional exhumation. D2 fabrics record low-grade P-T conditions suggesting that the decoupled cover formations exposed on Skopelos were incorporated in an accretionary wedge that formed above the subducting Pelagonian basement during Paleogene times.

Bulletin of the Geological Society of Greece

A low-P / high-T metamorphic event (andalusite-sillimanite series) of pre-Alpine age, identified ... more A low-P / high-T metamorphic event (andalusite-sillimanite series) of pre-Alpine age, identified here for the first time, has affected the metapelitic rocks of the Vernon Massif. P-T conditions of metamorphism in the western part of the Massif are estimated at -2.5 kb / 600-610°C, while in the northeastern part they are estimated to have exceeded 4.5 kb / 640°C respectively. Such P-T conditions correspond to geothermal gradients of 68°C/ km and 40°C/km for the western and the northeastern parts of the Massif respectively. The inferred steep geothermal gradients require transport of heat from deeper to shallower levels within the crust, achieved via magmatic intrusions in a continental magmatic arc setting. Alpine overprinting is characterized by P-T metamorphic conditions of ~6 kb / <350°C in the western part and ~9 kb / <570°C in the northeastern part of the Massif respectively. Low-P / high-T metamorphic rocks, occurring as klippen in the Cyclades and as blocks in the ophiol...

Lithos

Carbonatitic dykes surrounded by K-Na-fenites were discovered in the Pelagonian Zone in Greece. T... more Carbonatitic dykes surrounded by K-Na-fenites were discovered in the Pelagonian Zone in Greece. Their carbonate portions have an isotopic mantle signature of δ 13 C and δ 18 O ranging from −5.18 to −5.56 (‰ vs. VPDB) and from 10.68 to 11.59 (‰ vs. VSMOW) respectively, whereas their mafic silicate portions have high Nb, Ta and ɛ Nd values, typical of alkaline basalts. Textural relationships hint at a cogenetic intrusion of silicate and carbonate liquids that according to antithetic REE profiles segregated at shallow depths (b0.6 GPa) from a parental melt sourced deeper in the mantle. Fenites bear similar REE abundances to mafic rocks but with high Rb-Ba and low Nb-Ta values. SHRIMP II U-Pb analyses of magmatic zircon cores (δ 18 O = 7.21-7.51) from a carbonate-bearing syenitic amphibolite yielded a Permian intrusion age at 278 ± 2 Ma, considerably older than a Cretaceous (118 ± 4 Ma) greenschist overprint obtained from metamorphic zircon rims (δ 18 O = 6.78-7.02). From 300 to 175 Ma the ɛ Nd of the Pelagonian magmatism rose irregularly to more primitive values attesting to a higher increment of asthenosphere-derived melts. In this context, the carbonatite formed within a transtensional regime of an intra-Pangaea dextral transform fault that signalled the forthcoming penetrating breakoff of the supercontinent, manifested in the Permo-Triassic.

Bulletin of the Geological Society of Greece

We dated basement rocks from several localities southwest of Mt. Olympos, as well as from a local... more We dated basement rocks from several localities southwest of Mt. Olympos, as well as from a locality near the top of the mountain using the single zircon Pb/Pb evaporation technique. For the samples southwest of the mountain, the ages obtained range from ca. 280 to 290 Ma, with only a few zircon grains being around 300 Ma. By contrast, the sample from near the top of the mountain appears to be slightly younger, with ca. 270 Ma. These ages imply that the granitoids crystallized during Late Carboniferous - Early Permian times, and are therefore younger than the basement gneisses of other regions of the Pelagonian zone, which yielded zircon ages of around 300 Ma (e.g. Yarwood & Aftalion 1976, Mountrakis 1983, De Bono 1998, Engel & Reischmann 2001). However, the ages obtained in the present study are identical, within error, to the muscovite Ar-Ar cooling ages from Mt. Ossa (Lips 1998). Our geochronological data show that the magmatic evolution for this part of the basement of the Pelag...

Relation between mean stress, thermodynamic, and lithostatic pressure

Journal of Metamorphic Geology

Handling Editor: Doug Robinson Abstract Pressure is one of the most important parameters to be qu... more Handling Editor: Doug Robinson Abstract Pressure is one of the most important parameters to be quantified in geological problems. However, in metamorphic systems the pressure is usually calculated with two different approaches. One pressure calculation is based on petrological phase equilibria and this pressure is often termed thermodynamic pressure. The other calculation is based on continuum mechanics, which provides a mean stress that is commonly used to estimate the thermodynamic pressure. Both thermodynamic pressure calculations can be justified by the accuracy and applicability of the results. Here, we consider systems with low‐differential stress (<1 kbar) and no irreversible volumetric deformation, and refer to them as conventional systems. We investigate the relationship between mean stress and thermodynamic pressure. We discuss the meaning of thermodynamic pressure and its calculation for irreversible processes such as viscous deformation and heat conduction, which exhibit entropy production. Moreover, it is demonstrated that the mean stress for incompressible viscous deformation is essentially equal to the mean stress for the corresponding viscous deformation with elastic compressibility, if the characteristic time of deformation is five times longer than the Maxwell viscoelastic relaxation time that is equal to the ratio of shear viscosity to bulk modulus. For typical lithospheric rocks, this Maxwell time is smaller than c. 10,000 years. Therefore, numerical simulations of long‐term (>10 kyr) geodynamic processes, employing incompressible deformation, provide mean stress values that are close to the mean‐stress value associated with elastic compressibility. Finally, we show that for conventional systems the mean stress is essentially equal to the thermodynamic pressure. However, mean stress and, hence, thermodynamic pressure can be significantly different from the lithostatic pressure.

International Journal of Earth Sciences, 2017

Acknowledgements E.M. would like to acknowledge the Alexander S. Onassis Public Benefit Foundatio... more Acknowledgements E.M. would like to acknowledge the Alexander S. Onassis Public Benefit Foundation and the ERC starting grant (335577) for financial support. We would also like to acknowledge ETH-Zurich for covering fieldwork and analytical expenses. The scientific staff of the Center of Isotopic Research (CIR) at VSEGEI, St. Petersburg (Russian Federation) is acknowledged for their help during E.M.'s stay at St. Petersburg. Jan Pleuger is acknowledged for discussions regarding the geology of Rhodope.

Geochronology and P-T Constraints on the Exhumation History of an UHP Eclogite from Northern Greece

The recent discovery in northern Greece of metamorphosed crustal rocks units which had been trans... more The recent discovery in northern Greece of metamorphosed crustal rocks units which had been transported to depths well within the diamond stability field provide concrete proof of a hitherto unknown UHP (ultrahigh-pressure) metamorphic event in the Aegean region (Kostopoulos et al., 2000, Mposkos and Kostopoulos, 2001). We investigated in detail the P-T-t path an UHP eclogite from the Galarinos area

Gondwana-derived terranes in the northern Hellenides

Geological Society of America Memoirs, 2007

... The Circum-Rhodope belt (Kauffmann etal., 1976) is the east-ern part of the mélange zone bord... more ... The Circum-Rhodope belt (Kauffmann etal., 1976) is the east-ern part of the mélange zone bordering the Serbo-Macedonian Massif and ... 1, p. 5. Anders, B., Reischmann, T., Kostopoulos, DK, and Poller, U., 2006, The old-est rocks of Greece: First evidence ... 388 Himmerkus et al. ...

Heat budgets of crustal and mantle rocks revealed by exchange thermometers involving cations with differing diffusivities

EGU General Assembly Conference Abstracts, Apr 1, 2017

Chemical zoning and ductility of natural garnet at lower crustal conditions: An example from the Rhodope Massif

Επιστημονική Επετηρίδα του Τμήματος Γεωλογίας (Α. Π. Θ.), 2010

Conditions of deformation and metamorphism on Skopelos island (Greece): implications for the Cretaceous-Paleogene tectonics of the Pelagonian zone

EGUGA, Apr 1, 2018

Alpine thrusting versus late Alpine extension in the northern Aegean: an evaluation of the ductile record in the Rhodope massif

Geologica Balcanica, Jun 30, 2001

Record of Variscan Low-P/High-T metamorphism in Alpine medium-P rocks of the Pelagonian Zone, Greece

Environment of diamond formation in UHPM rocks from the Greek Rhodope: A Raman study of inclusions in zircon

Calculating pressure with elastic geobarometry: A comparison of different elastic solutions with application to a calc-silicate gneiss from the Rhodope Metamorphic Province

Lithos

Bulletin of the Geological Society of Greece

Tectonics

Bulletin of the Geological Society of Greece

Lithos

Bulletin of the Geological Society of Greece

Relation between mean stress, thermodynamic, and lithostatic pressure

Journal of Metamorphic Geology

International Journal of Earth Sciences, 2017

Geochronology and P-T Constraints on the Exhumation History of an UHP Eclogite from Northern Greece

Gondwana-derived terranes in the northern Hellenides

Geological Society of America Memoirs, 2007

The Fe-Mg exchange reaction between garnet and orthopyroxene is a robust geothermometer that has ... more The Fe-Mg exchange reaction between garnet and orthopyroxene is a robust geothermometer that has extensively been used to retrieve metamorphic temperatures from granulitic and peridotitic/pyroxenitic lithologies with important implications on the thermal state of the continental lithosphere. More than 800 experimental mineral pairs from both simple and complex systems were gleaned from the literature covering the P-T range 0.5-15 GPa / 800-1800 • C. Grt was treated as a senary (Py, Alm, Grs, Sps, Kno and Uv), whereas Opx as a septenary (En, Fs, Di, Hd, FeTs, MgTs and MgCrTs) solid solution. For Opx, Al in the M1 site was calculated following Carswell (1991) and Fe/Mg equipartitioning between sites was assumed. A mixing on sites model was employed to calculate mole fractions of components for both minerals. With regard to the excess free energy of solution and activity coefficients the formalism of was adopted treating both minerals as symmetric regular solutions. Calibration was achieved in multiple steps; in each step ∆S was allowed to vary until the standard deviation of the differences between experimental and calculated temperature for all experiments was minimised. The experiment with the largest absolute relative deviation in temperature was then eliminated and the process was repeated. The new thermometer reproduces the experimental data to within 50 • C and is independent of P-T-X variations within the bounds of the calibrant data set.

Apatite crystals with pyrrhotite exsolution lamellae have been found in kyanite (ky)-eclogites fr... more Apatite crystals with pyrrhotite exsolution lamellae have been found in kyanite (ky)-eclogites from the Rhodope metamorphic province (RMP), northeastern Greece. RMP is a synmetamorphic nappe stack that was formed during Jurassic-Cretaceous times and underwent extension during the early Cenozoic. Kyanite eclogites occur as boudins in orthogneisses located in the lower parts of the structurally upper unit of the RMP in Greece. These rocks have recorded an early (U)HP event followed by a metamorphic overprint at granulite-facies conditions. The (U)HP mineral assemblage is omphacite, garnet, kyanite and phengite, while rutile, apatite and zircon occur as accessories. Diopside, amphibole and biotite symplectites with plagioclase were formed upon decompression during which corundum, spinel and plagioclase symplectites were formed at the expense of kyanite at granulite-facies conditions (T~800°C, P≈1.0GPa).

ID#: 189393 Password: 887898 Meeting: FRAGILE EARTH: Geological Processes from Global to Local Sc... more ID#: 189393 Password: 887898 Meeting: FRAGILE EARTH: Geological Processes from Global to Local Scales and Associated Hazards (4-

The Rhodope Massif occupies most of northeastern Greece and southern Bulgaria and comprises high-... more The Rhodope Massif occupies most of northeastern Greece and southern Bulgaria and comprises high-grade metamorphic rocks such as metapelites with microdiamond inclusions. The (U)HP mineral paragenesis underwent extensive metamorphic overprint at granulite-facies followed by amphibolite-facies retrograde metamorphism.

The Rhodope massif in northern Greece and southern Bulgaria constitutes the hinterland of the Hel... more The Rhodope massif in northern Greece and southern Bulgaria constitutes the hinterland of the Hellenide orogen. It exposes low-and high-grade metamorphic rocks and their sedimentary cover. Kyanite eclogites from Thermes-Rhodope (northern Greece) belonging to the structurally upper unit were studied in order to constrain their metamorphic conditions. The kyanite eclogites are boudins enclosed in quartzofelspathic gneisses. They experienced a polyphase metamorphic history involving equilibration at granulite-, amphibolite-and greenschist-facies conditions successively. Textural relations reveal the successive equilibrium mineral assemblages and provide constraints that very local, domainal equilibria were attained during metamorphic evolution. Omphacite formed symplectites of diopsidic pyroxene and plagioclase during decompression while garnet formed coronas of two amphiboles (ortho-and clino-), plagioclase and magnetite. The orthoamphibole is sodic gedrite with the most sodic composition found in the literature. Symplectites of plagioclase, spinel and corundum formed at the expense of kyanite suggesting some metasomatic process. During metasomatism the mineral chemistry and the local composition of the equilibration volume were modified by diffusion processes, thus nullifying any assumption that the system was closed. Conventional geothermobarometric methods and thermodynamic modelling were combined to decipher the evolution in the rock mineral assemblages as a response to P-T conditions. Modelling revealed that the formation of sapphirine, corundum, spinel and plagioclase symplectites after kyanite is only possible during decompression at pressures less than 0.8GPa.

The Cycladic islands of Syros and Siphnos, Aegean Sea, Greece, represent subducted IAT and BABB r... more The Cycladic islands of Syros and Siphnos, Aegean Sea, Greece, represent subducted IAT and BABB remnants of the Neotethyan Pindos Ocean that formed during rifting of the southern active margin of Laurussia (Pelagonia) in the mid-Triassic, in response to northward subduction of Palaeotethys. Garnet porphyroblasts (Ø=1mm) in a glaucophane-zoisite eclogite from Kini locality on Syros are compositionally zoned and display a unique prograde heating path from a high-pressure greenschist-facies core with high X Sps and low Mg# via a blueschist-facies mantle with moderate X Sps and Mg# to an eclogite-facies rim with low X Sps and high Mg#. The outermost 35 µm of the garnet rims show flat X Sps with rapidly increasing outwards Mg#. Na-Act-Chl-Ph rimmed by Gln mark the greenschist-blueschist facies transition, whereas Pg rimmed by Omp and the incoming of Rt at the expense of Ttn signify the blueschist-eclogite facies transition.

Detrital zircon U-Pb ages of a quartzite from the Feneos locality of Peloponnesus, S. Greece, wer... more Detrital zircon U-Pb ages of a quartzite from the Feneos locality of Peloponnesus, S. Greece, were determined by LA-ICPMS. The rock classifies as a mature quartz arenite and belongs to an original shale-sandstone succession now metamorphosed into a phyllite-quartzite unit. The latter chiefly represents the External Blueschist Belt of the Hellenides widely known as the Arna or Phyllite -Quartzite (PQ) Unit. Zircon age clusters at 0.5-0.75, 0.85, 0.95-1.1, 1.75-2 and 2.4-3 Ga point at the Saharan Metacraton and the Transgondwanan Supermountain as contributing sources; the youngest concordant grain is 522 Ma old.