Petrology of the ultra-high pressure metamorphic Kimi complex in Rhodope (NE Greece). A new insight into the Alpine geodynamic evolution of Rhodope

Δεν διατίθεται περίληψηStructural, penological and geochronological work has revealed that the Rhodope metamorphic province is a synmetamorphic nappe-system of Alpine age. The Kimi complex representing the uppermost entity underwent UHP metamorphism in Lower Cretaceous (>119 Ma). Diamond inclusions in garnet porphyroblasts, exsolutions of quartz rods and rutile needles in garnet from Grt-Ky-Bt-gneisses constrain pressures >4 GPa (probably -7 GPa) and temperatures > 1000 °C, indicating subduction of continental crust into the asthenospheric mantle. The garnet-spinel peridotite of the Kimi area represents a segment of upwelling asthenosphere reequilibrated into the lithospheric mantle wedge at -2.5 GPa and 1235 °C. The spinel-garnet clinopyroxenites, associated with the peridotite, represent HP mantle cumulates crystallized from a melt at similar P-T conditions (i.e. P-2.4 GPa, T~1200°C). Decompression and cooling took place in the mantle wedge within the Cr-Spinel peridotite field up to -1.8 GPa and 900 °C. Subsequent isobaric cooling crossed the stability field of garnet peridotite. At this stage, the peridotite was tectonically emplaced into the educted underlying continental crust. Three stages of exhumation of the crustal assemblage occurred in the Kimi Complex. The first stage, from the maximum depth of -200- 220 Km to -60 Km (P-1.6 GPa, T-800 °C), is characterized by slow cooling rates, indicating rapid exhumation. The second stage, from -60 Km to -38 Km (P-1.05 GPa, T~640°C), is indicated by cooling at slow rates and is characterized by hydration and annealing reequilibration/recrystallization processes. The third stage of exhumation started between 73 and 65 Ma and is characterized by rapid uplift, continuous influx of water, intrusion of muscovite pegmatites at -20 Km depth, and finally by rapid cooling at shallow levels. The Kimi Complex reached the surface before 48-42 Ma

New constraints for the alpine HP metamorphism of the Ios basement, Cyclades, Greece

The pre-Alpine basement of the Ios Island involves large Variscan granitoid bodies intruded into metasediments that had already been metamorphosed under upper amphibolite facies conditions, as it is indicated by residual migmatitic textures and deformed muscovite pegmatites. The Alpine HP-metamorphism, documented on various cycladic islands, has, also, affected the basement rocks of Ios. Pressures of '25 Kbar and temperatures of '540 °C, are estimated for the Alpine HP event, applying the chloritoid-chlorite and garnetclinopyroxene geothermometers, and the garnet-phengite-omphacite and garnet-rutile-quartz-sphene-clinozoisite geobarometers. Garnet-hornblende geothermometry yielded temperatures of '520 °C and garnet-chlorite geothermobarometry yielded temperatures of 450 °C at 15 Kbar. This suggests that, at least the first stages of decompression were accompanied by cooling, indicating a rapid exhumation, related to tectonic processes

High pressure alpine metamorphism of the Pelagonian allochthon in the Kastania area (Southern Vermion), Greece

The Pelagonian allochthon in the Kastania area (Southern Vermion) consists of pre-alpine and alpine rocks that underwent two episodes of Alpine HP/LT metamorphism. The first episode, of Lower Cretaceous age, is represented by the mineral assemblages: Quartz-albite-microcline-phengite±garnet-clinozoisite± biotite±rutiletitanite in orthogneisses and the Kastania metagranite and garnet-chloritoid-chlorite±kyanite-white K-micaparagonite- rutile in high alumina metapelites. Pressures, were estimated at TO kbar at 500 °C, applying the phengite geobarometry and more than 22 Kbar, calculating the reaction Grt+Rt+Qtz+W®Ttn-l-Czo, occurred in the Kastania metagranite during decompression. Recrystallization at albite-epidote-amphibolite facies conditions accompanied by penetrative deformation defines the dominant mineral assemblages and textures in orthogneisses, metapelites and metabasites. The second metamorphic episode of a probable Eocene age occurred under blueschist/greenschist facies conditions and produced fine-grained phengite, stilpnomelane, green biotite and blue amphibole in orthogneisses and amphibolites

Structural evolution and exhumation history of the Rhodope UHP-HP metamorphic province (Northern Greece)

Middle/Early Alpine UHP-HP domain of the Rhodope (N'Greece) show pressures >3.6 Gpa. UHP-HP rocks have been emplaced in three major tectonic pulses: (i) At about 65->48 Ma the UHP Kimi Complex was exhumed at the surface representing the structurally uppermost UHP unit, (ii) Between > 42-30 Ma, the Sidironero, Kardamos and Kechros Complexes were exhumed underlying the Kimi Complex in the central and eastern Rhodope, respectively. They are characterized by HP-metamorphism (some parts by UHP-metamorphism), isothermal decompression and probably rapid exhumation. Exhumation tectonics involves deep level thrusting, synchronous high level extension, and successive post-thrusting extension. The post-thrusting Xanthi low angle normal detachment system extending over a distance of 100 km, from central Rhodope to eastern Rhodope, is interpreted to be responsible for a decrease in recent crustal thickness of about 20 km from central to eastern Rhodope. Lutetian (c. 48-43Ma) to Oligocene marine basins transgressed atop the Kimi Complex representing the upper plate of all detachment generations, (iii) The third exhumation pulse between 26 to 8 Ma, exhumed the Thasos/Pangeon metamorphic core complexes representing the structurally lowermost tectonic units of the Rhodope domain. Their exhumation occurred by displacements on the Miocene Strymon and Thasos detachment systems

New constraints for the alpine HP metamorphism of the Ios basement, Cyclades, Greece

The pre-Alpine basement of the Ios Island involves large Variscan granitoid bodies intruded into metasediments that had already been metamorphosed under upper amphibolite facies conditions, as it is indicated by residual migmatitic textures and deformed muscovite pegmatites. The Alpine HP-metamorphism, documented on various cycladic islands, has, also, affected the basement rocks of Ios. Pressures of '25 Kbar and temperatures of '540 °C, are estimated for the Alpine HP event, applying the chloritoid-chlorite and garnetclinopyroxene geothermometers, and the garnet-phengite-omphacite and garnet-rutile-quartz-sphene-clinozoisite geobarometers. Garnet-hornblende geothermometry yielded temperatures of '520 °C and garnet-chlorite geothermobarometry yielded temperatures of 450 °C at 15 Kbar. This suggests that, at least the first stages of decompression were accompanied by cooling, indicating a rapid exhumation, related to tectonic processes

GEOCHEMISTRY AND TECTONIC SETTING OF ECLOGITE PROTOLITHS FROM KECHROS COMPLEX IN EAST RHODOPE (N.E. GREECE)

Eclogites and partially amphibolitized eclogites from the metamorphic Kechros complex in East Rhodope are studied in order to provide the geodynamic framework for the origin of their protoliths. Geochemical evidence from whole rock major and trace element concentrations shows two distinct protolith groups. The low-Fe-Ti eclogites (Charakoma locality) have low-TiO2 content (<0.67 wt%), negative Nb anomalies, positive Sr anomalies, small negative Zr and Hf anomalies and variable enrichments in LILE (e.g. Rb and Ba). The REE patterns are characterized by strong LREE enrichment (LaN/YbN=5.45-5.81), HREE depletion (GdN/YbN=1.60-1.63) and HREE abundance within the rangeof 9-10 × chondrite. The high-Fe-Ti eclogites (Kovalo and Virsini locality) have variable Sr contents, small to moderate LILE enrichment, HREE`s similar to MORB values and absence of Nb anomalies. The REE patterns of the Kovalo and Virsini eclogites are characterized by LREE depletion and relative flat MREE HREE patterns at approximately 20-30 × chondrite concentrations. Our results suggest that the protoliths of the Low-Ti eclogites show a continental rifting tectonic environment. In contrast, the protoliths of the High-Ti eclogites indicate formation of their protoliths by partial melting in an extensional oceanic environment