Konstantin Hatzipanagiotou

Evolution of boninites and island-arc tholeiites in the Pindos Ophiolite, Greece

Whole-rock geochemical and Sm/Nd isotope data are presented for a representative suite of crustal rocks from the Pindos Ophiolite in order to resolve the origin of the geochemical signature of the boninites. Comparison is made with Triassic MORB from the Avdella melange and with other ophiolitic rocks of northwestern Greece. Hydrothermal alteration results in large scatter in Sr and K and some variability in Ba, Th and U. The Pindos boninites contain high Zr and Hf with respect to REE, characteristic of many boninites. Pb, La/Sm and Nb decrease with decreasing TiO 2 from MORB to IAT, but then increase in the boninites. Nd isotopic values expressed as e Nd decrease systematically with decreasing TiO 2 , from 7–8 in IAT to 0.6–3.0 in boninites. As mantle wedge harzburgite became increasingly depleted, another magma source contributed significant amounts of Pb, REE and probably Nb. The Pb and other large-ion lithophile elements may have been transported in aqueous solutions from the subducting slab, but the REE and Nb imply an ocean-island basalt (OIB)-type source within the mantle wedge. This OIB source is a consequence of mantle plume activity during late Triassic rifting.

Listwaenite evolution in the ophiolite mélange of Iti Mountain (continental Central Greece)

Rare listwaenite occurrences with the assemblage quartz + calcite + magnetite + goethite + hematite ± talc ± ankerite have been found within the ophiolite melange of the Iti Mountain. They also contain relic Cr-spinel, and have retained mesh and hourglass textures indicating an origin from serpentinite. Geochemical investigation, using isocon analysis and assuming Ti as immobile element, reveals conservation of mass. During the listwaenite-forming metasomatic event there was influx of Si, Ca, Ba, Zr, light rare-earth elements (LREE), Ir and Pt, while Mg, Mn, heavy rare-earth elements (HREE) and Pd were removed from the system. Al, Cr, Ni and Fe tot behaved as immobile elements. The release of Mg and formation of quartz may have occurred from breakdown of the serpentine minerals at low pressure, involving very high X CO2 in the fluid phase. Two distinct fluids are thought to have been involved in the alteration process. Fractionation of REE is explained by their mobility mainly as REE-carbonate complexes, which are favoured by a CO 2 -rich and mildly alkaline fluid. Ca influx in the listwaenite is attributed to this fluid, which is likely related to the serpentinization of the peridotites. Transportation of SiO 2 , as well as of platinum-group elements (PGE), was favoured by another low-pH, highly-oxidized, saline fluid, at low temperatures. Mobility of REE probably persisted, but likely as chloride complexes. The latter fluid may have been also responsible for oxidation of Cr-spinel to goethite and of magnetite to hematite. The presence of goethite and calcite in the listwaenite account for the enrichment of LREE, given that these minerals can selectively absorb the LREE into their structures. The HREE, which were released during the breakdown of serpentine and olivine, were subsequently removed from the system. At very low temperatures the two fluids were miscible and the interaction of the acid, oxidized fluid with the calcite probably led to precipitation of Pt and Ir in the listwaenite. Direct dissolution of olivine relics has likely occurred at a late stage and further depleted the listwaenite in Mg.

Origin, evolution and radiometric dating of sub-ophiolitic metamorphic rocks from the Koziakas ophiolite (W. Thessaly, Greece)

The Koziakas ophiolitic complex is part of the western Greek ophiolitic zone of the Mesozoic Tethyan orogenic belt. Amphibolites and metasedimentary rocks that represent a sub-ophiolitic metamorphic sole underlie it. The amphibolites include MORB-type protoliths with IAT influence, suggesting a back-arc basin environment for their origin. Two amphibole K-Ar radiometric dates of the sub-ophiolitic metamorphic sole of the Koziakas ophiolite yielded ages of 174 ′ 3 Ma and 161 ′ 1 Ma. These ages are similar to those reported from the adjacent Pindos, Vourinos and Othrys ophiolitic complexes. Geothermobarometric calculations showed that the metamorphic evolution of the amphibolites occurred at around 530-650°C and 5-7kbars.

Petrographic Investigation of Microcrack Initiation in Mafic Ophiolitic Rocks Under Uniaxial Compression

This paper investigates the influence of the petrographic characteristics of mafic ophiolitic rocks on the initiation and propagation of microcracks during uniaxial compression. The microcrack patterns of a troctolite and a diorite, collected from the Pindos and Othrys ophiolites (Greece), respectively, were analysed. Thorough observation and quantification of microcracks before and after the uniaxial compression test were conducted. Combined fluorescent and polarised microscopy of polished thin sections, together with digital image analysis, indicated that the intragranular microcracks are the dominating crack type in both loaded and unloaded specimens, only in terms of their total number and length. On the other hand, the intergranular and transgranular cracks seem to grow more readily compared to the intragranular cracks, implying that the longer microcracks grow more extensively under stress. The orientation of most of the newly formed intragranular and transgranular microcracks is nearly parallel to the loading direction; however, some of the randomly oriented transgranular cracks have probably been formed during the propagation of intergranular cracks. In the troctolite, the frequency of the intragranular microcracks decreases in the olivine crystals after the uniaxial compression test due to their partial serpentinisation, which increases their resistance to brittle deformation. In the plagioclase crystals of the troctolite, microcracks are often oriented parallel to the cleavage planes, implying that such crystallographic orientations act as planes of weakness. On the contrary, the plagioclase crystals of the diorite are mainly crossed by randomly oriented microcracks, presumably due to their high degree of alteration. In the diorite, the evolution of microcracks is substantially controlled by the two perfect cleavages of amphibole. The failure of a rock occurs as a result of the growth, interaction and coalescence of a great number of pre-existing and newly formed intragranular and transgranular microcracks. The petrographic and microcrack analysis may assist in the selection of the most suitable rock type for various construction applications.

The impact of petrographic characteristics on the engineering properties of ultrabasic rocks from northern and central Greece

This paper investigates the influence of petrographic characteristics on the engineering properties of ultrabasic rocks from the Pindos, Vourinos and Koziakas ophiolites. The studied lithologies include dunites, olivine-rich harzburgites, typical harzburgites and plagioclase-bearing lherzolites. Quantitative petrographic analysis indicates that the samples display various percentages of secondary minerals. The peridotites are tested to determine the following engineering parameters: water absorption, apparent density, total porosity, point load index, Schmidt hammer value, aggregate abrasion value and polished stone value. The relationships between the petrographic features and the engineering parameters are determined using regression analysis. The micropetrographic index Irep and the ratios of secondary to primary (Se/P) and soft to hard (So/H) minerals provide significant information about the impact of ocean-floor metamorphism on the strength and durability of peridotites. The correlations indicate that the formation of secondary minerals results in mechanically weaker rocks. The polished stone value is the only engineering parameter that is positively affected by the presence of low contents of alteration products. The results also imply that Cr-spinel grains are a major determinant for the preservation of the microroughness of aggregate particles owing to their very hard nature and different mechanical behaviour compared with the surrounding silicate minerals.

Platinum-group mineral characterisation in concentrates from low-grade PGE chromitites from the Vourinos ophiolite complex, northern Greece

Abstract The Vourinos ophiolite complex, located in northern Greece, hosts various chromite deposits characterised by very low platinum-group element (PGE) grades. Total PGE (excluding Os) concentrations in the fourteen chromitite samples collected for use in this study varied from 200 to 300 ppb. Previous reports on the platinum-group minerals (PGM) from the Vourinos chromitites, obtained data by in-situ investigation on polished sections. Consequently, we used the technique of hydroseparation to study the PGM from the concentrates in the Vourinos chromitites. More specifically, we investigated two separate composite samples from Voidolakkos and Xerolivado chromitites. The Voidolakkos concentrate sample contains 74 PGM that include: laurite (Ru, Os)S2; irarsite (Ir, Ru, Rh, Pt)AsS; erlichmanite (Os, Ru)S2; ruthenium pentlandite; iridium (Ir(Os)); osmium (Os(Ir, Ru, Pt)); secondary phases composed of Ru, Os and Cu; alloys of Ir–Fe; Rh– and Ru–Ni–Fe alloys; and Os–Ir–Fe alloys. The investigation of Xerolivado concentrate sample yield 45 grains of PGM, including laurite, irarsite, erlichmanite, minor other PGE sulphides, Os–Ir–Ru alloys, iridium and secondary phases of Ru–Os alloys. PGM occur as both single and polyphase particles in both samples. The bulk of mineralisation in Voidolakkos is dominated by a finer variety (<10 μm) of PGM than the Xerolivado sample (mainly <20 μm). The former occurrence hosts considerably more altered PGM grains, less laurite and a larger variety of PGM than the latter, whereas Os–Ir alloys are present in almost equal amounts in both samples. The hydroseparation process has recovered significantly more, as well as novel, PGM grains than were known from previous in-situ mineralogical examination of single chromitite samples. Although, most of the PGM occur as free particles and in-situ textural information is lost, single grain textural evidence is observed. The mineralogical and grain size differences between the two samples may reflect styles of mineralization and indicate significant remobilization of PGE. The latter possibility is suggested by the presence of secondary PGM, which may be related to the different alteration processes that affect the Voidolakkos and Xerolivado chromitites. In summary, this study provides significant new information on the particles, grain size and associations of PGM, which are critical with respect to the petrogenesis and mineral processing of these minerals.

Crushed limestone as an aggregate in concrete production: the Cyprus case

Abstract Limestones in Cyprus are mainly quarried for the production of coarse and fine aggregates to be used in concrete. The objective of this paper is to examine the properties of crushed limestone aggregates. The petrographical and physico-mechanical properties of these aggregates are described and their suitability for concrete production is examined. The coarse crushed limestone aggregates from Cyprus have water absorption values exceeding 3.3%, which is considered high for concrete applications. Their abrasion resistance (Los Angeles) values are consistently above 23%, while their weathering coefficients generally range between 10 and 30%. The fine crushed limestone aggregates show significantly lower water absorption values (less than 2.2%) and higher weathering coefficients (above 35%) than the coarse aggregates. The weathering coefficient of crushed limestone aggregates increases with a decrease in the fraction size up to 5 mm, after which it remains fairly constant. The physico-mechanical properties of crushed limestone aggregates are distinctly variable irrespective of the fact that they belong to the same geological formation and show relatively similar petrography.

Correlations between petrographic and geometrical properties of ophiolitic aggregates from Greece

The study investigated the influence of petrographic characteristics on the geometrical properties of ultrabasic and basic ophiolitic aggregates from Greece. Quantitative petrographic analysis indicates that the studied lithologies display various percentages of secondary mineral phases. Statistical analyses indicate that the geometrical characteristics of ultrabasic rocks tend to improve as the micropetrographic index Irep, the degree of serpentinisation, the ratio of soft to hard minerals and the ratio of secondary to primary minerals decrease. The aggregate particles of the basic lithotypes tend to be more elongated and flaky when the ratio of soft to hard minerals increases. The higher flakiness and elongation index values of the ultrabasic samples are attributed to the high percentage of serpentine, the local preferred orientation of the olivine grains and the existence of oriented transgranular microcracks.RésuméL’étude a examiné l’influence des caractéristiques pétrographiques sur les propriétés géométriques des granulats d’ophiolites basiques et ultrabasiques de Grèce. Des analyses pétrographiques quantitatives ont montré la présence de pourcentages variables de phases minérales secondaires. Des analyses statistiques ont indiqué que les caractéristiques géométriques des granulats issus de roches ultrabasiques ont tendance à s’améliorer avec une décroissance de l’indice micro-pétrographique Irep, le degré de serpentinisation, le rapport minéraux tendres sur minéraux durs et le rapport minéraux secondaires sur minéraux primaires. Les granulats issus des roches basiques ont tendance à être plus allongés et aplatis lorsque le rapport minéraux tendres sur minéraux durs augmente. Les valeurs plus élevées des indices d’aplatissement et d’allongement des échantillons issus de roches ultrabasiques sont attribuées au fort pourcentage de serpentine, aux orientations préférentielles des grains d’olivine et à l’existence de microfissures trans-granulaires orientées.

Physicochemical controls on bismuth mineralization: An example from Moutoulas, Serifos Island, Cyclades, Greece

Abstract The 11.6 to 9.5 Ma Serifos pluton intruded schists and marbles of the Cycladic Blueschist unit, causing thermal metamorphism, the development of magnetite Ca-exo- and endo-skarns and the formation of low-temperature vein and carbonate-replacement ores. Potentially, the most important ores occur in the Moutoulas prospect where the mineralization in retrograde skarn and quartz veins culminated with the deposition of native bismuth. A combination of fluid inclusion microthermometry and isotope geothermometry suggests that the Moutoulas mineralization formed at a hydrostatic pressure of ~100 bars, from moderate-to-low temperature (~190–250 °C), and low-salinity (1.3–5.6 wt% NaCl equivalent) fluids. The calculated δ34SH2S compositions are consistent with the ore fluids having been derived from the Serifos pluton. Bismuth mineralization is interpreted to have occurred as a result of wall-rock interaction and mixing of a Bi-bearing ore fluid with meteoric waters. Native bismuth and bismuthinite deposited at ~200 °C, near neutral pH (6.5), low fS2 (<–16.5), and low fO2(<–44). Supergene alteration in Serifos led to the oxidation of native bismuth to bismite and bismutite.

PETROGENETIC SIGNIFICANCE OF SPINELS FROM SERPENTINISED PERIDOTITES FROM THE VERIANAOUSA OPHIOLITE

Το οφιολιθικό σύμπλeγμα της πeριοχής ανάμeσα στη Βέροια και τη Νάουσα αντιπροσωπeύeι μια διαμeλισμένη οφιολιθική eνότητα, η οποία eίναι υπeρκeίμeνη σe μία βάση που αποτeλeίται από πeτρώματα της Πeλαγονικής ζώνης και μeρικώς της υποζώνης Αλμωπίας, της ζώνης Αξιού στη βόρeια Eλλάδα. Οι μανδυακοί πeριδοτίτeς αποτeλούνται από σeρπeντινιωμένους λeρζόλιθους και χαρτσβουργίτeς, στους οποίους διeισδύeι ένα αραιό δίκτυο πυροξeνιτικών φλeβών. Οι σeρπeντινιωμένοι λeρζόλιθοι και χαρτσβουργίτeς αποτeλούνται από Al-σπινέλιους (Cr#=38.83-42.52 and Mg#=58.94- 64.77), Cr-σπινέλιους (Cr#=43.37-64.92 and Mg#=49.20-58.66) και μαγνησιοχρωμίτeς (Cr#=53.93 57.13 and Mg#=55.73-61.71). Eμφανίζουν συχνά πιο πλούσιους σe Cr πυρήνeς, οι οποίοι πeριβάλλονται από σιδηροχρωμίτη και μαγνητίτη. Οι γeωχημικές συστάσeις και η αρχική σύσταση των σπινeλίων eίναι όμοια μe πeριδοτίτeς, οι οποίοι σχηματίστηκαν σe μία ζώνη καταβύθισης. Έτσι, οι μανδυακοί πeριδοτίτeς του Οφιολιθικού Συμπλέγματος στην πeριοχή ανάμeσα στη Βέροια και τη Νάουσα αρχικά σχηματίστηκαν σe μία οπισθοτοξική λeκάνη.