On the Metamorphic Modification of Cr-Spinel Compositions From the Ultrabasic Rocks of the Pindos Ophiolite Complex (Nw Greece)

Kapsiotis, Argyrios; Tsikouras, Basilios; Grammatikopoulos, Tassos; Karipi, Sofia; Hatzipanagiotou, H.

doi:10.12681/bgsg.16719

Cited by 11 publications

(8 citation statements)

References 15 publications

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“…The cores of the Cr-bearing spinels present in podiform chromitites are very stable over a wide range of metamorphic conditions and tend to preserve their primary magmatic composition. However, alteration processes, such as serpentinization and regional metamorphism, usually modify the chemical composition of their external parts (Evans & Frost 1975;Burkhard 1993;Barnes 2000;Mellini et al 2005;Arai et al 2006;Kapsiotis et al 2007). Depending on the degree of alteration, secondary magnetite, Cr-magnetite or other Fe-Cr spinel phases (e.g.…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and magnetism of Fe-Cr spinel series minerals from podiform chromitites and dunites from Tąpadła (Sudetic ophiolite, SW Poland) and their relationship to palaeomagnetic results of the dunites

Kądziałko-Hofmokl

Delura

Bylina

et al. 2008

Geophysical Journal International

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S U M M A R YThis paper presents the mineralogy and magnetic properties of two varieties of chromitite, sampled in the same exposure of a serpentinite massif regarded to be a fragment of the Sudetic ophiolite. The varieties differ mineralogically and magnetically. One of them, labelled TaA and altered to a low degree according to scanning electron microscope (SEM) and microprobe results, comprises an unaltered Al-Cr spinel core, some secondary chromite and less abundant Cr-magnetite. It has a high magnetic susceptibility and natural remanence (NRM), and its dominating magnetic phase is ferrichromite with T b /T c of about 530 • C occurring in grains in the single domain (SD) + pseudo-single domains (PSDs) and superparamagnetic (SP) states. The second variety, labelled TaB, is highly altered and comprises, apart from Al spinel, two kinds of secondary chromites that do not differ much from the primary Al spinel and no Cr-magnetites. This chromitite variety does not reveal one well defined T b /T c , but a series ranging between 200 and 450 • C, their grain sizes correspond to the SD + SP domain states. The same pattern was observed in chromitite TaA after annealing in air at a temperature of 700 • C. Dunites associated with the chromitites contain, apart from magnetite, chromite grains. The majority of specimens reveal magnetic characteristics similar to the TaA-like variety, but in some specimens TaB-like characteristics were also observed. A standard palaeomagnetic study performed earlier on the dunites showed that their NRM has three components-Lower Devonian carried by magnetite, Permian and Tertiary-Recent. The results presented here lead us to conclude that the latter two are carried by ferrichromites similar to those found in the TaA and TaB chromitites.

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Section: Introductionmentioning

confidence: 99%

Mineralogy and magnetism of Fe-Cr spinel series minerals from podiform chromitites and dunites from Tąpadła (Sudetic ophiolite, SW Poland) and their relationship to palaeomagnetic results of the dunites

Kądziałko-Hofmokl

Delura

Bylina

et al. 2008

Geophysical Journal International

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“…Metamorphism of greenschist to lower amphibolite facies substantially modifies the primary spinel composition through infiltrating metamorphic fluids (Wylie et al 1987;Barnes 2000). In spinels, the Cr-spinel core compositions equilibrated with ferritchromite and/or magnetite are usually attributed to greenschist compared to lower amphibolite facies metamorphism (Barnes 2000;Kapsiotis et al 2007;Farahat 2008;Aswad et al 2011). The relative proportion of trivalent ions i.e., Cr 3+ , Al 3+ and Fe 3+ in spinels is not modified up to lower amphibolite metamorphic grade and therefore can be used to estimate the metamorphic grade experienced by the host peridotites (Barnes 2000).…”

Section: Low-temperature Metamorphic Implications On Spinel Compositionmentioning

confidence: 99%

“…According to Barnes (2000) and Kapsiotis et al (2007), due to greenschist to lower amphibolite grade metamorphism, Cr-spinels of mantle peridotites alter to magnetite and/or ferritchromite along grain margins and fractures as these are the only sites for metamorphic fluid interaction. The complete replacement of primary Cr-spinel grains with magnetite commonly occurs at mid to higher amphibolite grade metamorphism of host peridotites (Farahat 2008).…”

Section: Low-temperature Metamorphic Implications On Spinel Compositionmentioning

confidence: 99%

Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications

2019

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The present study focuses on the chemical modification of a Cr-spinel from the Suru Valley ophiolitic peridotites exposed near Trespone Village of Kargil district, Ladakh Himalaya. The Suru Valley peridotite is partially serpentinised with the preservation of the spinel and relics of olivine and pyroxene. These peridotites contain characteristic red-brown spinel grains of corroded grain boundaries. While analysing these grains for mineral chemistry, compositional variation was observed with Cr-rich cores rimmed by Cr-poor compositions. Secondary spinel compositions, i.e., ferritchromite and magnetite were observed along the margins and cracks of primary Cr-spinel grains. The primary Cr-spinel cores are identified as Cr-rich and are characterised by higher values of Cr 3+ # (0.5-0.6) and lower values of Al 3+ # (0.42-0.54). From primary spinel cores to altered rims it was observed that Cr 3+ # and Fe 3+ # increase while Mg 2+ # decreases due to Mg 2+-Fe 2+ and Al 3+-Fe 3+ exchange with surrounding silicates of host peridotite during alteration. On the basis of present spinel mineral chemistry, metamorphic alteration conditions were transitional between greenschist and lower amphibolite similar to most of the Neo-Tethyan ophiolite peridotites.

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“…The Pindios massif as southern continuation of Albanian western ophiolitic belt contains a few of Al-rich chromite occurrances (Economou-Eliopolis and Vacandios, 1995) any of them are metamorphoused (Kapsiotis et al, 2007).…”

Section: Vourinos Massifmentioning

confidence: 99%

On the Relatively Compositional Homogeneity of Albanian Eastern Ophiolitic Belt

Cina

2017

geosociety

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On the Metamorphic Modification of Cr-Spinel Compositions From the Ultrabasic Rocks of the Pindos Ophiolite Complex (Nw Greece)

Abstract: Serpentinites and serpentinised ultramafic rocks from the Pindos ophiolite complex, northwestern Greece, contain Cr-spinel

Cited by 11 publications

References 15 publications

Mineralogy and magnetism of Fe-Cr spinel series minerals from podiform chromitites and dunites from Tąpadła (Sudetic ophiolite, SW Poland) and their relationship to palaeomagnetic results of the dunites

Mineralogy and magnetism of Fe-Cr spinel series minerals from podiform chromitites and dunites from Tąpadła (Sudetic ophiolite, SW Poland) and their relationship to palaeomagnetic results of the dunites

Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications

On the Relatively Compositional Homogeneity of Albanian Eastern Ophiolitic Belt

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