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Skorupa oceaniczna i ofiolity w Sudetach Środkowych w świetle rozważań tektonicznych

Cymerman Z.

Przegląd Geologiczny

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2017

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Vol. 65, nr 12

1540--1547

EN

Znosko (1981a, b) first stated the important fact that the Sowie Góry "nappe” was lying on the rocks of the Middle Sudetic Ophiolite Complex. In the light of current geophysical and tectonic data, it still remains up-to-date. Both those articles have initiated a new look at the Paleozoic tectonic evolution of the Sudetes and its surroundings. This article presents an analysis ofpotential boundaries oflithostratigraphic terranes in the Sudetes and the Fore-Sudetic Block, confirmed by the waveforms of gravity horizontal gradients. Gravimetric modelling along the selected profile 3 makes it possible to present the subsurface geological structure. Metamorphic rocks of the Sowie Góry complex can probably reach a depth of almost 5 km on the Fore-Sudetic Block. Below them are mafic and ultramafic rocks, reaching a depth of up to 12 km, which belong to the Middle-Sudetic Ophiolite Complex. The kinematic data from the Sowie Góry metamorphic complex indicate displacement with the top-to-SW and to-S, as in the Middle-Sudetic Ophiolite Complex. Controversy over the origin and the geotectonic environment of the Early Ordovician protolith of the Sowie Góry gneisses, which are probably a magma product of arc-type magmatism formed above a subduction zone of the Tornquist Ocean. The Sowie Góry terrane can be considered as a relic of the Early Ordovician Paleozoic magma arc (the so-called peri-Baltic arc). The Sowie Góry terrane was moved towards the SW and S on obducted dismembered fragments of ophiolite sequences after closing the Rheic Ocean during the Eo-Variscan orogenesis.

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Alteration of mélange-hosted chromitites from Korydallos, Pindos ophiolite complex, Greece: evidence for modification by a residual high-T post-magmatic fluid

Kapsiotis A. N.

Acta Geologica Polonica

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2014

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Vol. 64, no. 4

473--494

EN

The peridotites from the area of Korydallos, in the Pindos ophiolitic massif, crop out as deformed slices of a rather dismembered sub-oceanic, lithospheric mantle section and are tectonically enclosed within the Avdella mélange. The most sizeable block is a chromitite-bearing serpentinite showing a mesh texture. Accessory, subhedral to euhedral Cr-spinels in the serpentinite display Cr# [Cr/(Cr + Al)] values that range from 0.36 to 0.42 and Mg# [Mg/(Mg + Fe2+)] values that vary between 0.57 and 0.62, whereas the TiO2 content may be up to 0.47 wt.%. The serpentinite fragment is characterized by low abundances of magmaphile elements (Al2O3: 0.66 wt.%, CaO: 0.12 wt.%, Na2O: 0.08 wt.%, TiO2: 0.007 wt.%, Sc: 4 ppm) and enrichment in compatible elements (Cr: 2780 ppm and Ni: 2110 ppm). Overall data are in accordance with derivation of the serpentinite exotic block from a dunite that was formed in the mantle region underneath a back-arc basin before tectonic incorporation in the Korydallos mélange. Two compositionally different chromitite pods are recognized in the studied serpentinite fragment, a Cr-rich chromitite and a high-Al chromitite, which have been ascribed to crystallization from a single, progressively differentiating MORB/IAT melt. Although both pods are fully serpentinized only the Al-rich one shows signs of limited Cr-spinel replacement by an opaque spinel phase and clinochlore across grain boundaries and fractures. Modification of the ore-making Cr-spinel is uneven among the Al-rich chromitite specimens. Textural features such as olivine replacement by clinochlore and clinochlore disruption by serpentine indicate that Cr-spinel alteration is not apparently related to serpentinization. From the unaltered Cr-spinel cores to their reworked boundaries the Al2O3 and MgO abundances decrease, being mainly compensated by FeOt and Cr2O3 increases. Such compositional variations are suggestive of restricted ferrian chromite (and minor magnetite) substitution for Cr-spinel during a short-lived but relatively intense, low amphibolite facies metamorphic episode (temperature: 400–700 °C). The presence of tremolite and clinochlore in the interstitial groundmass of the high-Al chromitite and their absence from the Cr-rich chromitite matrix imply that after chromitite formation a small volume of a high temperature, post-magmatic fluid reacted with Cr-spinel, triggering its alteration.

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Geochemical peculiarities of basalts of the Trostyanets volcanogenic complex (Ukrainian Carpathians)

Stupka O., Bondar R., Poberezhskyy A.

Biuletyn Państwowego Instytutu Geologicznego

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2011

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nr 444

187--190

EN

Studies of magmatic rocks of the Triassic–Lower Cretaceous ophiolite association are of great significance for geodynamic reconstructions of the evolution of the Ukrainian Carpathians. These are almond-stone basalts, clasto-lavas of basalts, and dykes of trachytes in the complex of volcanic rocks of the Trostyanets Stream. Rocks are allochthonous and hence studies of their petrochemical and geochemical properties are of great importance. Volcanites belong to the K-Na series of rocks poor in ferrimagnesian and rich in lithophylic elements; they developed on the ensialic substratum. Results of studies of two-phase fluid inclusions in calcite indicate that the gas phase constitutes 10 to 25 vol. % and is represented by CH4 and its homologues – C2H6, C3H8 and C4H10. These data may indicate a possible formation of carbon and hydrocarbons by means of the Fischer-Tropsch reaction of hydrocarbon synthesis.

PL

Badania skał magmowych asocjacji ofiolitowej triasu–kredy dolnej mają duże znaczenie dla geodynamicznej rekonstrukcji ewolucji ukraińskich Karpat. Dotyczy to bazaltów migdałowcowych, law z klastami i dajek trachitowych w kompleksie skał wulkanicznych potoku Trostyanets. Skały są allochtoniczne, toteż bardzo ważne jest badanie ich właściwości petrochemicznych i geochemicznych. Wulkanity należą do serii skał K-Na ubogich w pierwiastki żelazo-magnezowe i litofilne; tworzyły się w podwarstwie ensialicznej. Badania dwufazowych inkluzji w kalcycie pokazały, że faza gazowa zajmuje od 10 do 25% obj. i jest reprezentowana przez CH4 i jego homologi – C2H6, C3H8 oraz C4H10. Dane te mogą wskazywać na możliwość tworzenia węgla i węglowodorów na drodze reakcji Fischer-Tropscha syntezy węglowodorów.

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The ophiolites (serpentinites) as hydrocarbon bearers on the Zrenjanin North structure

Knezevic D., Knezevic S., Dinic B., Martinovic S.

Biuletyn Państwowego Instytutu Geologicznego

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2001

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nr 396

78-79