Geochemical processes and petrogenetic evolution of rodingite dykes in the ophiolite complex of Othrys (Central Greece)

Tsikouras, Basilios; Karipi, Sofia; Rigopoulos, Ioannis; Perraki, Maria; Pomonis, Panagiotis; Hatzipanagiotou, Konstantin

doi:10.1016/j.lithos.2009.06.013

Cited by 49 publications

(25 citation statements)

References 74 publications

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“…Massive chromitites occur as podiform, lenticular or irregular ore bodies in serpentinized dunites within harzburgites. Triassic flood basalts underlying the Othrys ophiolite nappe 34 were collected in Edipsos, Agrilia and six smaller areas. Chromitites, peridotites and basalts were also collected from the Vourinos ophiolite, considered one of the typical ophiolite complexes worldwide, as it includes a nearly undisturbed complete sequence.…”

Section: Methodsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

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Section: Methodsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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“…The high Mg# of the neoblastic pyroxenes suggests crystallisation from a nearly primitive magma, which may also account for the whole-rock high Mg# and Ni of the websterite. High pressure (> 1.5 GPa) melting of refractory lherzolites or clinopyroxene-bearing harzburgites is required and can be triggered from variations in the CO2 and H2O contents in the mantle wedge, which may have been fluxed from the subducted Pelagonian sediments [86,87], to produce carbonatitic or picriticankaramitic melts [88][89][90]. Ankaramitic melts are highly magnesian as boninites and are produced at around 1300-1350 °C, at 40-70 km depth [90].…”

Section: Origin Of Ol-orthopyroxenite and Websteritementioning

confidence: 99%

New Occurrence of Pyroxenites in the Veria-Naousa Ophiolite (North Greece): Implications on Their Origin and Petrogenetic Evolution

et al. 2017

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Abstract:The Veria-Naousa ophiolite represents a dismembered unit in north Greece, which includes variably serpentinised lherzolite and harzburgite, locally intruded by a sparse network of dykes or thin layers of websterite and olivine-orthopyroxenite composition. The websterite and the olivine-orthopyroxenite show abundant petrographic and geochemical evidence (relic olivines with mantle affinities, Cr-rich spinels, low Al 2 O 3 , depletions in incompatible elements, and concave upwards rare earth element patterns) that they comprise replacive bodies from refractory subarc mantle precursors. The occurrence of these pyroxenites in dykes implies that channelled percolation of melts account for their replacive character. High CaO/Al 2 O 3 , low Zr and crystallisation of diopside suggest that a melt of ankaramitic/carbonatitic composition percolated in lherzolite replacing porphyroclastic olivine and forming the pyroxenes in the websterite. At a shallower level, harburgites were impregnated by boninitic melts (inferred by U-shape rare earth element patterns and very rich in Cr spinels) triggering the replacement of porphyroclastic olivine by orthopyroxene for the formation of olivine-orthopyroxenite. These peritectic replacements of olivine commonly occur in a mantle wedge regime. The peculiar characteristics of the Veria-Naousa pyroxenites with LREE and compatible elements enrichments resemble the subarc pyroxenites of Cabo Ortegal implying a similar environment of formation. Whole-rock and mineralogical (spinel and clinopyroxene) compositions are also in favour of a backarc to arc environment. It is recommended that the evolution of the Veria-Naousa pyroxenites record the evolution of the subarc region and the opening of a backarc basin in a broad SSZ setting in the Axios Zone of eastern Greece.

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“…Li et al, 2004;Tsikouras et al, 2009;Koutsovitis et al, 2013 Most garnets are hydroandradites, while there are some small sized Cr-bearing hydrogarnets crystals (Cr2O3= 10.34wt.%). Li et al (2008) explains the formation of hydrogarnet with clinopyroxene and water participation in the reaction with plagioclase, whereas Cr-bearing hydrogarnets formation is related with Cr release from serpentinites (Li et al, 2004).…”

Section: Metamorphic and Metasomatic Processesmentioning

confidence: 99%