Characterisation of chromites, chromite hosted inclusions of silicates and metal alloys in chromitites from the Indo-Myanmar ophiolite belt of Northeastern India

Bidyananda, Maibam; Foley, Stephen F.; Luguet, Ambre; Jacob, Dorrit E.; Singh, Toijam Bapin; Ray, Dwijesh; Panda, D.; Keppler, Ruth

doi:10.1016/j.oregeorev.2017.05.032

Cited by 16 publications

(7 citation statements)

References 62 publications

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“…The silicate inclusions are similar to the ones observed in chromitites from other massifs in Oman (Augé, 1987;Ahmed and Arai, 2002), in other ophiolites (e.g. Johan et al, 1983Johan et al, , 2017Talkington et al, 1984;Maibam et al, 2017;Wojtulek et al, 2019), in presentday ocean floor spinels in peridotites and chromitites (Arai and matsukage, 1998;Matsukage and Arai, 1998;Tamura et al, 2014Tamura et al, , 2016, but also in chromite-rich layers in continental layered intrusions (e.g. McDonald, 1965;Ballhaus and Stumpfl, 1986;Li et al, 2005;Spandler et al, 2005;Friedrich et al, 2019).…”

Section: Geology Of the Maqsad Dunitic Transition Zonesupporting

confidence: 76%

The Chicken and Egg Dilemma Linking Dunites and Chromitites in the Mantle–Crust Transition Zone beneath Oceanic Spreading Centres: a Case Study of Chromite-hosted Silicate Inclusions in Dunites Formed at the Top of a Mantle Diapir (Oman Ophiolite)

Rospabé

Ceuleneer

Guluche

et al. 2021

Journal of Petrology

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The mantle-crust boundary beneath oceanic spreading centres is a major chemical and thermal interface on Earth. Observations in ophiolites reveal that it is underlined by a dunitic transition zone (DTZ) that can reach a few hundred meters in thickness and hosting abundant chromitite ore bodies. The dunites have been deciphered as essentially mantle-derived in most ophiolitic massifs, i.e. reactional residues of interactions between peridotite and percolating melt(s). Although both dunite and chromitite in ophiolites have been the focus of many studies, the reasons of their systematic association remain unclear. In this study we have explored the inclusion content of the chromite grains disseminated in the dunites from the DTZ exposed in the Maqsad area of the Oman ophiolite where a former asthenospheric diapir is exposed. Similarly to chromite in chromitite ore bodies, disseminated chromite grains in dunites contain a great diversity of silicate inclusions. Based on the major and minor element composition of 1794 single silicate inclusions in chromites from 285 samples of dunite and associated rocks in the DTZ, we infer that the disseminated chromites formed by a similar “metallogenic” process to the chromitites, and that, as a whole, dunites from the DTZ actually represent the low grade endmember of a single, giant ore body. The nature of the silicate inclusions (amphibole and mica among others) enclosed in chromite grains in dunites from the Maqsad DTZ precludes their crystallization from an anhydrous primitive basaltic melt, and rather calls for a crystallization from a melt hybrid between common mafic melts and more exotic Si-, Na- and volatile-rich fluids. The hybrid parent medium of both dunites and chromitites results from the interaction between an asthenospheric diapir (the MORB source), and a colder, altered lithospheric lid and hydrothermal fluids responsible for this alteration. The excess silica in the hybrid melt is provided by the incongruent dissolution of enstatite from mantle harzburgite and/or from moderate degree of partial melting of the altered gabbroic crust. The chemical composition of the silicate inclusions is more variable when enclosed in the disseminated chromites than in the chromitites, suggesting a greater variability of melts and/or fluids fractions involved in the genesis of dunites than of chromite ores. Finally, the DTZ can be viewed as a metamorphic contact aureole between episodically rising asthenospheric diapirs and formerly accreted axial lithospheric lids. Our conclusion about the chicken and egg dilemma linking dunites and chromitites beneath oceanic spreading centres (i.e. Do the chromitites form in response to the formation of dunites or conversely?) is that the mantle dunitization itself is a potential way for the release of Cr and its re-concentration as chromite ores, and that in turn the competition between orthopyroxene (+/- plagioclase) and chromite fractionation during this fluid/melt/peridotite reactional process is responsible of the great mineralogical and chemical variability of the DTZ dunites.

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Section: Geology Of the Maqsad Dunitic Transition Zonesupporting

confidence: 76%

The Chicken and Egg Dilemma Linking Dunites and Chromitites in the Mantle–Crust Transition Zone beneath Oceanic Spreading Centres: a Case Study of Chromite-hosted Silicate Inclusions in Dunites Formed at the Top of a Mantle Diapir (Oman Ophiolite)

Rospabé

Ceuleneer

Guluche

et al. 2021

Journal of Petrology

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“…First, the investigated chromite is Fe-rich (X Mg = 0.2-1.6%). The available literature data on chromites from mantle rocks or mantle-derived melts document relatively wide compositional spectra reflecting variable conditions of origin (e.g., [37][38][39]). Among these, chromites from forearc peridotites tend to be more Fe-rich but never with X Mg values < 20% [36].…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India

et al. 2018

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Mineralogical and chemical data are presented for a suite of Na–Cr-rich clinopyroxenes associated with chromite, winchite (sodium-calcium amphibole), titanite and calcite in Mg-Cr-rich silicocarbonatites from the Samalpatti carbonatite complex, Tamil Nadu, South India. The Mg-Cr-rich silicocarbonatites occur as 10–30 cm large enclaves in pyroxenites. The chemical composition of the pyroxenes differs among individual enclaves, with variable proportions of diopside, kosmochlor and jadeite-aegirine end-members. These compositions fill a previously unoccupied space in the kosmochlor-diopside-jadeite+aegirine ternary plot, indicating a distinct origin of kosmochlor-rich pyroxene compared with previous findings from diverse settings. The Na–Cr-rich clinopyroxene has low ΣREE = 9.2 ppm, with slight enrichment in LREE (LaN = 7), coupled with low HREE (YbN = 0.6), and flat HREE, paralleled by a significant fractionation of Nb/Ta (2408) and Th/U (26.5). Sodic metasomatism (fenitization) associated with either carbonatite emplacement at shallow levels or during carbonatite ascent through the upper mantle most likely was the major process operating in the area. We suggest two scenarios of the formation of Na–Cr-rich pyroxene: (1) from mantle-derived chromian mineral phases (spinel and/or garnet) through fenitization, with subsequent corrosion by growing winchite due to volatile influx; (2) via metasomatic reaction of Cr-rich garnet in mantle peridotite due to reaction with Na-rich carbonatite melt. Collectively, the appearance of kosmochlor may play an important role in deconvolving metasomatic processes, and fenitization in particular. If combined with petrologic experiments, it could improve our understanding of the origin and subsequent history of chemical signatures of carbonate-rich materials in the mantle.

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“…West of the Salin Sub-basin, the ophiolites of the Western Ophiolite Belt include harzburgites and lherzolites (Soibam et al, 2015). The ophiolitic lithologies in the Naga Hills region in the northern IMR contain abundant podiform magnesiochromite in the ultramafic host rocks (Maibam et al, 2017). Relic Cr-spinel is common relic mineral in the Jade Mines region of the Eastern Ophiolite Belt, occurring in serpentinised dunites and peridotites, and within chlorite schists in near the Tawmaw region (Hla Htay et al, 2017).…”

Section: Myanmar's Ophiolite Beltsmentioning

confidence: 99%

A multi-proxy provenance study of Eocene to Oligocene sandstones in the Salin Sub-basin, Myanmar

McNeil

Gough

Hall

et al. 2021

Journal of Asian Earth Sciences

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Characterisation of chromites, chromite hosted inclusions of silicates and metal alloys in chromitites from the Indo-Myanmar ophiolite belt of Northeastern India

Cited by 16 publications

References 62 publications

The Chicken and Egg Dilemma Linking Dunites and Chromitites in the Mantle–Crust Transition Zone beneath Oceanic Spreading Centres: a Case Study of Chromite-hosted Silicate Inclusions in Dunites Formed at the Top of a Mantle Diapir (Oman Ophiolite)

The Chicken and Egg Dilemma Linking Dunites and Chromitites in the Mantle–Crust Transition Zone beneath Oceanic Spreading Centres: a Case Study of Chromite-hosted Silicate Inclusions in Dunites Formed at the Top of a Mantle Diapir (Oman Ophiolite)

On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India

A multi-proxy provenance study of Eocene to Oligocene sandstones in the Salin Sub-basin, Myanmar

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