Dimitrios Kostopoulos | National & Kapodistrian University of Athens (original) (raw)
Papers by Dimitrios Kostopoulos
EGU General Assembly Conference Abstracts, Apr 1, 2017
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...
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 ...
Geologica Balcanica, Jun 30, 2001
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 &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...
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...
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...
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...
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...
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
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
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. ...
EGU General Assembly Conference Abstracts, Apr 1, 2017
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...
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 ...
Geologica Balcanica, Jun 30, 2001
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...
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...
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...
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...
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...
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
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
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. ...
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.
