Genesis and tectonic implications of podiform chromitites in the metamorphosed ultramafic massif of Dobromirtsi (Bulgaria)

Gonzáléz-Jiménez, José María; Locmelis, Marek; Белоусова, Е. А.; Griffin, William L.; Gervilla, Fernando; Kerestedjian, Thomas; O’Reilly, Suzanne Y.; Pearson, Norman J.; Sergeeva, Ivanina

doi:10.1016/j.gr.2013.09.020

Cited by 74 publications

(54 citation statements)

References 86 publications

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“…These features are not indicative of zircons that derive from the sedimentary lid or the cumulate pile of a downgoing slab undergoing amphibolite-facies metamorphism [68]. Xenocrystic zircons have been described from several chromitite occurrences over the globe [21][22][23][24][25][26]. We note that recycled zircons from the Tibetan (Luobusa, Dongqiao), Semail (Oman) and Ray-Iz (Urals) chromitites have complex internal structures and co-occur with various combinations of super-reducing ultrahigh-pressure (SuR-UHP) minerals without showing resetting of their U-Pb ages [22,26].…”

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

et al. 2016

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Several small chromium (Cr) ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] and mid-ocean ridge basalts (MORBs). Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite) locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe 3+ # generally increase (0.68-0.87, 0.78-0.88 and 0.55-0.80, respectively), whereas from the core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe 3+ # generally decrease (0.45-0.74 and ≤0.51, correspondingly). The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (≤30 µm), subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains) were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL) images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO 2 intermediate to mafic source. Combined micro-textural and minerochemical data repeat the possibility of zircon derivation from limited volumes of high-T fluids emanating from the gabbroic intrusions. Once zircon is precipitated in cracks, it may be altered to Ca-rich Zr-bearing silicate phases (i.e., armstrongite, calciocatapleiite). Almost all zircons in these samples show evidence of gains in solvent compounds (CaO, Al 2 O 3 and FeO) possibly due to re-equilibration with late deuteric fluids.

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Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

et al. 2016

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“…Compositional variability in terms of major elements is very common in accessory chromites in primary ultramaficmafic igneous rocks and their altered counterparts (Irvine 1965(Irvine , 1967Jackson 1969;Roeder et al 1979). Compositional variability may arise due to (a) sub-solidus reequilibration of the chromite with the surrounding silicate minerals or an interstitial melt (Hamlyn and Keays 1979;Scowen et al 1991;Rollinson 1995;Mondal et al 2006), (b) oxidation and alteration of chromites during serpentinization of the host rock and its subsequent metamorphism (Bliss and Maclean 1975;Evans and Frost 1975;Loferski and Lipin 1983;Burkhard 1993;Abzalov 1998) and (c) during retrograde metamorphism, by the action of reducing fluids, as observed in podiform chromitites from different ultramafic massifs of the central and eastern Rhodope metamorphic complex in southern Bulgaria (Gervilla et al 2012;González-Jiménez et al 2013;Colás et al 2014).…”

Section: Chromitementioning

confidence: 99%

“…Chromites in massive chromitites commonly retain primary compositions in terms of major elements and can thus be used to deduce the parental melt composition and the probable tectonic setting of the chromitite deposits (e.g., Mondal et al 2006, references therein). However, metamorphosed chromites from massive chromitites within ophiolites may be altered in terms of their minor and trace elements (e.g., González-Jiménez et al 2013Colás et al 2014). The study of chromitite deposits in Archean greenstone belts helps to reveal the nature of the mantle and the tectonic processes prevalent in the Archean.…”

Section: Introductionmentioning

confidence: 99%

“…In situ trace-element analysis using laser ablation ICP-MS (LA-ICPMS) has revolutionized petrogenetic studies as one can investigate the minerals of interest without interference from the surrounding phases (e.g., Dare et al 2009Dare et al , 2011Dare et al , 2012Pagé and Barnes 2009;González-Jiménez et al 2013Pagé et al 2012;Colás et al 2014). Compared to major elements in chromites, the trace elements are more sensitive to parameters like temperature and oxygen fugacity, and they therefore show larger variations during partial melting and fractional crystallization (Dare et al 2009;González-Jiménez et al 2013.…”

Section: Introductionmentioning

confidence: 99%

“…Compared to major elements in chromites, the trace elements are more sensitive to parameters like temperature and oxygen fugacity, and they therefore show larger variations during partial melting and fractional crystallization (Dare et al 2009;González-Jiménez et al 2013. The trace elements that enter the trivalent (Cr, Al, Fe 3+ ) octahedral site of the spinel structure, e.g., Ti, Ga, V and Co, are particularly sensitive to these processes.…”

Section: Introductionmentioning

confidence: 99%

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Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic–mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

Mukherjee

Mondal

Gonzáléz-Jiménez

et al. 2015

Contrib Mineral Petrol

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LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe 3+ # versus Ti/Fe 3+ # diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on majorelement characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic-mafic plutonic rocks in the Nuggihalli greenstone belt. AbstractThe 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic-mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite-trondhjemite-granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)-peridotite-pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30-500 m; width ≈2-15 m) are hosted by the serpentinite-peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78-86 and moderate Mg# (100 Mg/ (Mg + Fe 2+ )) of 45-55. In situ trace-element analysis Communicated by Timothy L. Grove. Electronic supplementary materialThe online version of this article (

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Alteration of chromitites from the Voidolakkos and Xerolivado mines, Vourinos ophiolite complex, Greece: implications for deformation-induced metamorphism

Kapsiotis

2014

Geol. J.

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Chromitites, associated with upper mantle spinel peridotites from the Voidolakkos and Xerolivado districts, located in the Vourinos ophiolite complex, northwestern continental Greece, were re‐investigated with respect to their structural and textural mode of occurrence, as well as their compositional signatures. They include variably deformed banded and podiform chromitite bodies made up of massive, semi‐massive, nodular, anti‐nodular, schlieren and disseminated chromian spinel. Chromitites have suffered intense shearing that was more severe in all but disseminated textured ore. Deformation has partly produced elongation of chromian spinel nodules and widespread protocataclastic zones within chromitites. The examined deposits are composed of magnesiochromite that shows a quite restricted range of Cr# [Cr/(Cr + Al)] values varying between 0.76 and 0.83, whereas Mg# [Mg/(Mg + Fe2+)] ranges from 0.55 to 0.67 accompanied by relatively low content in TiO2 (<0.15 wt.% on average). Compositional data indicate that these high‐Cr chromitite bodies crystallized from melts of boninitic affinities that have been compositionally modified after reaction with depleted harzburgite, followed by interaction with relatively undifferentiated low SiO2 melts within an intertwined system of dunite channels in the mantle wedge below the fore‐arc region of a supra‐subduction zone (SSZ). Magnesiochromite displays limited textural modification, being scarcely transformed to an opaque spinel phase along grain boundaries and fracture walls. The opaque spinel phase is characterized by elevated Cr# (0.76–0.97), relatively low Mg# (0.33–0.63) and low Fe3+# (≤0.14) and corresponds to ferrian chromite. Microscopic studies revealed that ferrian chromite is paragenetically associated with clinochlore even in unaltered chromitite specimens and the degree of serpentinization does not correlate with the frequency and abundance of alteration effects on magnesiochromite. Therefore, it is supported that regional metamorphism prior to serpentinization was responsible for the formation of the ferrian chromite–clinochlore association. In addition, magnesiochromite alteration was systematically recorded only in variably sheared chromitites displaying protocataclastic brecciation, thus it can be claimed that metamorphism was mainly governed by deformation mechanisms, which took place during the transition from ductile to semi‐brittle conditions. Ferrian chromite can be locally erratically enriched in MnO and ZnO, which is attributed to a Mn‐ and Zn‐bearing, slightly acid post‐magmatic fluid that invaded the chromitites across weakness zones. Overall, the data suggest that after magnesiochromite equilibration with the intergranular olivine, both phases were partly replaced by ferrian chromite and clinochlore, respectively, during a brief, fluid assisted episode of retrogade metamorphism that took place within a temperature interval between 700 and 300 °C, before ocean‐floor alteration. Copyright © 2014 John Wiley & Sons, Ltd.

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Genesis and tectonic implications of podiform chromitites in the metamorphosed ultramafic massif of Dobromirtsi (Bulgaria)

Cited by 74 publications

References 86 publications

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic–mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

Alteration of chromitites from the Voidolakkos and Xerolivado mines, Vourinos ophiolite complex, Greece: implications for deformation-induced metamorphism

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