AESTHETIC CHARACTERISTICS OF GREEK ORNAMENTAL STONES ASSOCIATED WITH MINERAL, GEOCHEMICAL AND STRUCTURAL PROPERTIES

Τα εμπορικά μάρμαρα αποτελούν υλικά που δεν απαιτούν ιδιαίτερη επεξεργασία με υψηλή οικονομική αξία για την κατασκευαστική βιομηχανία. Τα πιο σημαντικάδιακοσμητικά πετρώματα στην Ελλάδα περιλαμβάνουν ασβεστόλιθους και μάρμαρα με ιδιαίτερα ποιοτικά χαρακτηριστικά και θεωρούνται προϊόντα ιδιαίτερης εμπορικής αξίας. Σε αυτή την εργασία μελετήθηκαν εβδομήντα τρία ανθρακικά δείγματα (ασβεστόλιθοι, δολομίτες και μάρμαρα) από όλη την Ελλάδα με σκοπό να καθοριστούν τα μακροσκοπικά και πετρογραφικά χαρακτηριστικά τους και να διερευνηθεί η ορυκτοχημική τους σύσταση και η γεωχημεία τους. Τα χρώματά τους ποικίλουν από λευκό έως τεφρό, εξαιτίας του περιεχομένου τους σε ασβεστίτη και δολομίτη, μαύρο σε βιτουμενιούχους ασβεστόλιθους, κίτρινο εξαιτίας της παρουσίας οξειδίων σιδήρου και αργιλικών ορυκτών, κόκκινο εξαιτίας των οξειδίων σιδήρου και μεικτών φάσεων ασβεστίτη και σιδηρίτη, καστανοπράσινο εξαιτίας της εμφάνισης οξειδίων σιδήρου μαζί με χλωρίτη και μοσχοβίτη, προσδίδοντας σχιστότητα στο πέτρωμα. Διάσπαρτες ασβεστιτικές και δολομιτικές φλέβες, όπως επίσης και εμφάνιση άλλων ορυκτών φάσεων όπως βαρύτης, επίδοτο και μαγνητίτης συμβάλλουν στη δημιουργία ιδιαίτερωνχαρακτηριστικών που προσδίδουν μοναδική εμφάνιση. Τα χαρακτηριστικά γνωρίσματα κάθε πετρώματος εξαρτώνται σημαντικά από το είδος των ορυκτών, τη σύσταση, κοκκομετρία και κατανομή τους, τη γεωχημεία και δομή τους.Commercial marble are almost ready-to-use materials with a high economic value for the building-construction industry. The most important ornamental stones in Greece include limestone and marble with notable qualitative features and are considered products of high commercial value. In this research, seventy-three carbonate samples (limestones, dolomites and marbles) from all over Greece have been studied to determine their macroscopic and petrographic features and to investigate their mineral chemistry and geochemistry. Their colors vary from whitish to gray due to their content of calcite and dolomite, black due to bitumens, yellow due to the presence of iron oxides and clay, red due to iron oxides and mixed phases of calcite- siderite, green-brownish due to the presence of iron oxides or muscovite and chlorite, giving schistosity to the rock. Scattered calcite and dolomite veins, as well as the occurrence of other minerals such as barite, epidote and magnetite, contribute to specific features, thus making their appearance unique. The particular characteristics of each stone depend highly upon the type of minerals present, their composition, grain size and extent of aggregation, their geochemistry and structure

GEOMORPHOLOGY, SEDIMENTOLOGY AND GEOCHEMISTRY IN THE MARINE AREA BETWEEN SIFNOS AND KIMOLOS ISLANDS, GREECE

Στην ελάχιστα μελετημένη θαλάσσια περιοχή μεταξύ των νησιών Σίφνου και Κιμώλου πραγματοποιήθηκε μια εκτεταμένη ωκεανογραφική μελέτη, με σκοπό την καταγραφή της υποθαλάσσιας μορφολογίας και των χαρακτηριστικών των επιφανειακών ιζημάτων, καθώς και της πηγής προέλευσης αυτών. Έγιναν καταγραφές με πολυδεσμικό βυθόμετρο και δειγματοληψίες επιφανειακών ιζημάτων με box corer με το Ω/Κ Αιγαίο και ακολούθησαν αναλύσεις μεγέθους κόκκων, ορυκτολογίας και γεωχημείας. Ένα μεγάλο βαθυμετρικό βύθισμα εντοπίστηκε βόρεια της Κιμώλου, με μέγιστο βάθος 743 μ., που συγκεντρώνει λεπτόκοκκα ιζήματα. Η κατανομή των ιζημάτων ως προς το μέγεθος κόκκων χαρακτηρίζεται από σταδιακή μείωση του μεγέθους από νότο προς βορρά. Η ορυκτολογική σύσταση περιλαμβάνει ασβεστίτη, Mg-ασβεστίτη, αραγωνίτη, δολομίτη, χαλαζία, Κ-άστριους, πλαγιόκλαστα, αμφίβολους και αργιλικά ορυκτά. Οι κύριες ιζηματολογικές επαρχίες που αναγνωρίστηκαν είναι 1) η ρηχή περιοχή πλησίον της Κιμώλου, με υψηλό περιεχόμενο σε Si, Al, K, Rb και Ba, 2) η βαθιά περιοχή δυτικά της Σίφνου, όπου εμφανίζεται και το μεγάλο βύθισμα, που χαρακτηρίζεται από υψηλό περιεχόμενο σε Fe, Ti, Na, Mg, S, Cr, Cu, Ni, V, Zn και 3) το στενό μεταξύ Σίφνου και Κιμώλου, με υψηλότερο περιεχόμενο σε Ca, S και Sr. Στο βύθισμα αυτό, παρατηρήθηκε σημαντικός εμπλουτισμός των ιζημάτων σε μαγγάνιο, ενώ τα οξείδια του Mn φαίνεται να προσροφούν διάφορα μέταλλα.An extensive oceanographic survey was conducted in the marine area between Kimolos and Sifnos Islands, a rather poorly-studied sector of the Aegean Sea, in order to gain better understanding of submarine geomorphological features and associated sediment provenance. Multi-beam bathymetry and surface sediment sampling with a box corer were carried out on board R/V Aegaeo, followed by grain-size analysis, XRD and XRF measurements. A large circular depression was identified north of Kimolos reaching a water depth of 743 m, filled with fine grained sediments. Surface sediment distribution is characterized by gradual decrease in grain-size from silty sand to silt in a S-N direction. The mineralogical composition comprises calcite, Mgcalcite, aragonite, dolomite, quartz, K feldspars, plagioclase, amphiboles and clay minerals. Major sediment provinces identified were: (i) the shallow sector proximal to Kimolos, characterized by higher contents in Si, Al, K, Rb and Ba; (ii) the deep area west of Sifnos, including the large depression, characterized by higher contents in Fe, Ti, Na, Mg, S, Cr, Cu, Ni, V, Zn; and (iii) the south passage between Kimolos and Sifnos, which exhibits higher Ca, S, and Sr contents. Manganese enrichment was observed in and around the bathymetric depression, where Mn oxides act efficiently as scavengers of a suite of metals

Evaluation of the CO2 Storage Capacity in Sandstone Formations from the Southeast Mesohellenic trough (Greece)

This study investigates the capability of the Southeast Mesohellenic Trough (SE MHT) sandstone formations to serve as a potential reservoir for CO2 storage in response to the emerging climate change issues by promoting environmentally friendly mineral sequestration applications. Sandstone samples, for the first time, were evaluated for their petrographic characteristics, mineral chemistry, geochemical properties, as well as their petrophysical and gas adsorption properties through tests. The sandstones were tested and classified into distinct groups. The most promising site to be considered for pilot CO2 storage testing is the Pentalofos Formation locality since its sandstones display specific mineral phases with the proper modal composition to conceivably react with injected CO2, leading to the development of newly formed and stable secondary mineral phases. The gas adsorption results are also more encouraging for sandstones from this sedimentary formation. All the measured UCS (uniaxial compressive strength), Ei (bending stiffness), and ν (Poisson’s ratio) results are above those dictated by international standards to perform CO2 storage practices safely. Furthermore, the specified targeted locality from the Pentalofos Formation holds the geological advantage of being overlaid by an impermeable cap-rock formation, making it suitable for deploying CO2 mineralization practices. The demarcated area could permanently store a calculated amount of ~50 × 105 tons of CO2 within the geological reservoir by reacting with the specified mineral phases, as specified through the proposed petrographic PrP index (potential reactive phases)

Gabbroic rocks in ophiolitic occurrences from East Othris, Greece: Petrogenetic processes and geotectonic environment implications

East Othris area consists of scattered ophiolitic units, as well as ophiolitic mélange occurrences, which encompass gabbroic rocks. These rocks have been affected by low-grade ocean floor metamorphism (T < 350°C and P < 8 kbar). Based on their petrography, mineral chemistry and geochemistry gabbroic rocks have been distinguished into gabbros and diorites, with the latter being divided into two groups. Gabbros seem to have been formed from moderate to high partial melting degrees (~8-25%) of a highly depleted mantle source, while group (1) diorites have been differentiated after variable fractionation processes (up to 30%). Group (2) diorites seem to have been derived from low partial melting degrees (~3%) of a fertile or moderately depleted mantle source and with extensive fractionation processes (~50%). Geochemical results suggest that partial melting processes occurred at relatively shallow depths, in the plagioclase-spinel stability field, while amphibole chemistry data indicate shallow level crystallization. Chondrite and PM-normalized patterns, Th/Yb, and Nb/Th ratios as well as mineral chemistry analyses show that gabbros and group (1) diorites (with relatively low PM-normalized Nb and Ta values and negative Ti anomalies) suggest subduction processes, while group (2) diorites are MORB or BAB related. Some gabbros have been characterised as high-Mg, being compositionally similar to picrites or boninites. Variability in extent of partial melting of the mantle source and the different geotectonic environment affinities are consistent with a supra-subduction zone (SSZ) origin of the east Othris ophiolites. The fact that IAT related rocks are more abundant in east rather than in west Othris may possibly be explained by a slab rollback model retreating to the east within the Pindos oceanic basin. © 2011 Springer-Verlag

Boninitic and tholeiitic basaltic lavas and dikes from dispersed Jurassic East Othris ophiolitic units, Greece: petrogenesis and geodynamic implications

Pillow lavas, massive lava flows, and sub-volcanic dikes of tholeiitic basaltic composition are found to be members of the Vrinena, Aerino, Eretria, and Velestino dispersed Middle–Upper Jurassic ophiolitic units in East Othris. The Vrinena and Eretria ophiolitic units appear to have been emplaced onto the Pelagonian continental margin during the Upper Jurassic–Lower Cretaceous, whereas the Aerino and Velestino units seem to have been finally emplaced during post-Palaeocene times. Geochemically these are divided into two groups: Group I includes subduction-related boninites and low-Ti basalts from the Vrinena and Aerino units, and Group II high-Ti basalts show spreading-type characteristics occurring in the Eretria and Velestino units. Primary magma of the Group I volcanics appears to have been formed after high partial melting degrees (~18%) of a highly depleted harzburgitic mantle source, under relatively high temperatures (mantle potential temperature ~1372°C). Petrogenetic modelling also suggests that the primary magma of the Group II volcanics were formed after lower partial melting degrees (~7%) of a moderately depleted mantle source. The petrological and geochemical data from the East Othris dispersed and diversely emplaced ophiolitic units provide evidence of a common intra-oceanic supra-subduction zone (SSZ) origin within the Pindos oceanic strand of the Western Tethys. Specifically, Group I lavas and dikes from Vrinena seem to represent the extrusive part of an almost complete fore- to island-arc ophiolitic sequence. Dikes of Aerino most likely correspond to fore-arc magmatic material that intruded within exhumed serpentinized ultramafic rocks through a subduction channel that developed close to the slab and towards the fore-arc and the accretionary prism. The Group II volcanics either corresponded to a fore-arc magmatic expression, which extruded earlier than Group I volcanics and prior to the establishment of a mature subduction zone, or represent back-arc to island-arc magmatism that was contemporaneous to the fore-arc magmatic activity during rollback subduction. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Composition, melting and evolution of the upper mantle beneath the Jurassic Pindos ocean inferred by ophiolitic ultramafic rocks in East Othris, Greece

Large ultramafic bodies of the East Othris ophiolite in Central Greece consist of serpentinites, of harzburgite precursors, as well as serpentinized lherzolites, which have been intruded by thin dykes of olivine-rich and olivine-poor pyroxenites. They represent parts of partially altered upper mantle wedge rocks in a Mid-Late Jurassic intraoceanic subduction setting of the Pindos microocean, a western strand of the Tethyan oceanic realm. Serpentinization and rodingitization occurred during their exhumation toward the fore-arc oceanic region and accretionary prism through a subduction channel. Petrography and geochemistry show that protoliths of most serpentinites and serpentinized peridotites are harzburgites, while few are more fertile lherzolites. Petrogenetic modeling reveals that the former harzburgites correspond to highly depleted residual mantle peridotites, which formed after moderate degrees (~13–20 %) of hydrous partial melting, whereas lherzolites, being closely related to the ophiolitic mantle peridotites of West Othris, resulted after lower partial melting degrees (~7–10 %). Mineral chemistry and geochemical data from pyroxenites imply that they have been derived after crystallization of a subduction-related IAT hydrous magma that formed after moderate partial melting degrees (~14–19 %), quite similar to those that produced the harzburgites. Melting processes for the East Othris mantle peridotites occurred in the spinel-stability field, at estimated equilibrium temperatures ranging between 900 and 1,050 °C and pressures between 1.4 and 1.7 GPa, in a rather highly oxidized environment. It is estimated that the primary IAT magma, formed under relatively high temperatures with liquidus temperature at ~1,260 °C and mantle potential temperature at ~1,372 °C. Cooling rates of the shallow mantle beneath the Pindos oceanic basin, from its Mid-Triassic rift/drift phase and the subsequently developed Mid-Late Triassic short-lived intraoceanic subduction, to the Mid-Late Jurassic main subduction phase, are estimated at ~0.7 and ~1.6 °C/Ma, respectively, with the latter being considered as unusually high. © 2015, Springer-Verlag Berlin Heidelberg

Rift and intra-oceanic subduction signatures in the Western Tethys during the Triassic: The case of ultramafic lavas as part of an unusual ultramafic-mafic-felsic suite in Othris, Greece

The Triassic igneous rocks of Othris, Greece, exhibit unusual and extreme compositional variations. Abundant E-MORB and rare OIB alkaline basalts appear to be linked to NW Gondwana (Apulia) margin rifting, Pelagonian microcontinent detachment and opening of the Pindos oceanic strand at Western Tethys. They are spatially associated with wehrlites, ultramafic lavas, picrites, transitional boninites, tholeiitic basaltic andesites and calc-alkaline andesitic to rhyodacitic rocks, whose new geochemical and petrological data suggest that they were formed in a short-lived subduction system, developed shortly after rifting/opening within the Pindos ocean. OIB alkaline basalts seem to have been formed from an enriched, possibly garnet bearing mantle source, while formation of E-MORB basalts may represent partial melts (~. 20%) of an enriched mantle source. The liquidus temperature for the primary rift-related magma is estimated at ~. 1330. °C, while mantle potential temperature reached ~. 1435. °C, with ~. 14. wt.% MgO. Subduction-related rocks were produced after differentiation of primary picritic magma, generated after ~. 32% partial melting of a fertile mantle source within the newly formed mantle wedge. Temperature conditions were similar to those calculated for the rift-related primary magma, but with higher MgO contents (~. 16. wt.%). Olivine and clinopyroxene accumulation of a batch of the subduction-related primary magma led to the formation of ultramafic magma under hydrous conditions. Wehrlites represent ultramafic magma stacked at the bottom of a magma chamber. Ultramafic lavas were formed when ultramafic magma was brought to the surface, most likely with the aid of an upwelling asthenospheric E-MORB flow passing through a slab break-off or by the bottom edge of the infant slab. The remainder of the primary picritic magma underwent variable degrees of fractional crystallization forming transitional boninites and tholeiitic basaltic andesites in a front-arc setting and calc-alkaline intermediate and felsic rocks in places closer to the passive margin of the Pelagonian microcontinent. © 2012 Elsevier B.V

Subduction-related rodingites from East Othris, Greece: Mineral reactions and physicochemical conditions of formation

The partly to pervasively metasomatized doleritic and gabbroic dykes or small to medium sized bodies found in East Othris, within Mid to Late Jurassic serpentinized peridotites of ophiolitic units and ophiolitic mélange formations are classified as rodingites and can be divided into two types. Type 1 rodingites are mainly characterized by the frequent occurrence of prehnite, while Type 2 rodingites include mostly garnets and vesuvianite. Isocon analysis showed that rodingitization essentially occurred with mass and volume preservation. Desilification, depletion of alkalies, as well as Ca enrichment was more intense for the Type 2 rodingites. Al, Fe and Mg remained rather immobile, while Ti, Y, Zr and REE were variably depleted.Rodingitization took place in an intraoceanic subduction system. It occurred in three successive stages during the exhumation of the mafic-ultramafic mantle wedge rocks in a fore-arc setting within a serpentinitic subduction channel, which developed close to the slab. The incorporation of the mafic rocks to the subduction channel probably resulted after entraining a directed mantle flow towards the slab. The first stage of rodingitization formed mainly grossular, hydrogrossular, Ti- and Cr-bearing hydrogarnets and calcite under relatively acidic and mildly oxidizing physicochemical conditions, with increased CO2/H2O ratio. During the second and more extensive rodingitization stage, alkaline and reducing conditions prevailed and CO2/H2O ratio was decreased. The modeling of the mineral reactions of this stage, using the software winTWQ v. 2.34 in the CFMASH system, reveals that in Type 1 rocks prehnite replaced most of the initial garnet, while Type 2 rocks continued to be rodingitized, mostly forming grossular and/or hydrogrossular and chlorite. Hydrogrossular, instead of grossular, was crystallized from hydrous fluids under high silica activity. Type 2 rodingites underwent further rodingitization during the third stage, due to infiltration of Ca-rich hydrothermal fluids of oceanic and/or subducted slab origin, at lower temperatures and depths. This stage is characterized by the appearance of hydroandradite and vesuvianite, under alkaline and oxidizing conditions, due to very low CO2/H2O ratio and relatively high fO2. All three rodingitization stages are estimated to have occurred under relatively moderate temperature and pressure (~300 to 400°C; ~3-6kbar respectively). Locally, Type 2 rodingites show derodingitization of variable extent, forming high-variance assemblages mostly consisting of chlorite±pumpellyite. Some chlorite marginal zones in rodingite dykes may also have been developed by Mg-rich diffusional fluid flow, during this derodingitization process. © 2013 Elsevier B.V

Potential for mineral carbonation of co2 in pleistocene basaltic rocks in volos region (Central greece)

Pleistocene alkaline basaltic lavas crop out in the region of Volos at the localities of Microthives and Porphyrio. Results from detailed petrographic study show porphyritic textures with varying porosity between 15% and 23%. Data from deep and shallow water samples were analysed and belong to the Ca-Mg-Na-HCO3-Cl and the Ca-Mg-HCO3 hydrochemical types. Irrigation wells have provided groundwater temperatures reaching up to ~30◦ C. Water samples obtained from depths ranging between 170 and 250 m. The enhanced temperature of the groundwater is provided by a recent-inactive magmatic heating source. Comparable temperatures are also recorded in adjacent regions in which basalts of similar composition and age crop out. Estimations based on our findings indicate that basaltic rocks from the region of Volos have the appropriate physicochemical properties for the implementation of a financially feasible CO2 capture and storage scenario. Their silica-undersaturated alkaline composition, the abundance of Ca-bearing minerals, low alteration grade, and high porosity provide significant advantages for CO2 mineral carbonation. Preliminary calculations suggest that potential pilot projects at the Microthives and Porphyrio basaltic formations can store 64,800 and 21,600 tons of CO2, respectively. © 2019, MDPI AG. All rights reserved