Structural classification of chromite pods in southern New Caledonia

Cassard, Daniel; Nicolas, Adolphe; Rabinovitch, M.; Moutte, Jacques; Leblanc, Marc; Prinzhofer, Alain

doi:10.2113/gsecongeo.76.4.805

Cited by 162 publications

(78 citation statements)

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“…Observations on the well -preserved ophiolitic mantle section, podiform chromitites with dunite envelope are in -situ formed replacing deformed harzburgite (e.g., Cassard et al, 1981;Lago et al, 1982). This indicates the formation of some chromitites postdates the deformation of host harzburgite at the upper mantle beneath a spreading center (Cassard et al, 1981;Ceuleneer and Nicolas, 1985;Ceuleneer et al, 1988). The dunite envelope around chromitite ( Fig.…”

Section: Low-pressure Generation Of Podiform Chromititesmentioning

confidence: 87%

“…Chromitite xenoliths possibly derived from podiform body have been rarely found from the Southwest Japan arc (Arai and Abe, 1994). Observations on ophiolites indicate various stages of chromitite formation relative to surrounding mantle peridotite: some chromitite bodies (concordant chromitites) are concordant to foliation of peridotite, and others (discordant chromitites) cut the foliation (Cassard et al, 1981;Lago et al, 1982) (Fig. 1a).…”

Section: Chracteristics Of Podiform Chromititesmentioning

confidence: 99%

“…1c) or vice versa. They have been interpreted as primary igneous textures, which are solely observed in the discordant chromitite but have been obscured in the concordant one on deformation (Cassard et al, 1981).…”

Section: Chracteristics Of Podiform Chromititesmentioning

confidence: 99%

“…They occur as small pods or irregular -shaped bodies enveloped by dunite within harzburgite or less frequently within lherzolite (Cassard et al, 1981;Arai, 1997) (Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

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Possible recycled origin for ultrahigh-pressure chromitites in ophiolites

Arai

2010

Journal of Mineralogical and Petrological Sciences

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Podiform chromitites have been interpreted as cumulates by harzburgite/melt interaction and related melt mixing at the upper mantle to the Moho transition zone. Recent discovery of diamond and other ultrahigh -pressure (UHP) minerals from some podiform chromitites, especially those from Tibet, however, has raised a question about the depth of their formation. These UHP chromitites are possibly of deep recycling origin; they had been originally formed at the upper mantle before sinking down to deeper mantle, and upwelling again to the shallowest mantle by convection. Diamond is formed by reduction/oxidation of fluidal carbon species (e.g., CO 2 or CH 4 ) obtained during the convection history, and has survived oxidation because of strong encapsulation in metal alloys further included by chromian spinel. Exsolved silicates (diopside and coesite) in chromian spinel from some UHP chromitite are possibly derived from hydrous mineral inclusions in chromian spinel formed at low pressures, which have been decomposed/molten during sinking and solved in the UHP chromian spinel phase. Both the UHP chromitites and ordinary low -pressure ones could be present in the upper mantle derived from the mid -oceanic ridge, one of the main ends of the mantle upwelling flow. The mantle recycling issue unraveled through chromitite thus can be one of the targets of deep oceanic mantle drilling including the Mohole.

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Section: Low-pressure Generation Of Podiform Chromititesmentioning

confidence: 87%

Section: Chracteristics Of Podiform Chromititesmentioning

confidence: 99%

Section: Chracteristics Of Podiform Chromititesmentioning

confidence: 99%

“…They occur as small pods or irregular -shaped bodies enveloped by dunite within harzburgite or less frequently within lherzolite (Cassard et al, 1981;Arai, 1997) (Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

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Possible recycled origin for ultrahigh-pressure chromitites in ophiolites

Arai

2010

Journal of Mineralogical and Petrological Sciences

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“…Chromitites have been interpreted as melt/rock reaction products within upper mantle harzburgites (e.g., Arai and Yurimoto, 1994;Zhou et al, 1994). Ophiolitic chromitites are classified into two types, discordant and concordant, in terms of their structural attitude relative to surrounding harzburgites (Cassard et al, 1981). The generation of two types of ophiolitic chromitite is possibly related to the polygenetic nature of ophiolites: the early stage of a spreading center such as a mid -ocean ridge, and the later stage of an arc -like setting before ophiolite obduction.…”

Section: Introductionmentioning

confidence: 99%

Formation of discordant chromitite at the initiation of sub-arc mantle processes: Observations from the northern Oman ophiolite

Miura

Arai

Tamura

2014

Journal of Mineralogical and Petrological Sciences

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Discordant chromitite, one of the structural types of ophiolitic chromitite, and surrounding peridotites, were examined in the mantle section of the northern Oman ophiolite along Wadi Hilti, to constrain its origin. Spinels from chromitite and adjacent peridotites show high Cr# (= Cr/(Cr + Al) atomic ratio), around 0.65 to 0.75, indicating an arc -related feature. Clinopyroxenes from adjacent harzburgites show low HREE contents, indicating a highly depleted character. The calculated melt composition in equilibrium with clinopyroxene in the dunite envelope indicates that the chromitite and surrounding peridotites were derived from arc -related magma, such as boninite. The arc -related magma was probably generated by the flux melting of depleted mantle harzburgite on the subducted slab, in terms of incompatible element enrichment in clinopyroxene from dunite and harzburgite. The highly depleted harzburgite surrounding discordant dunite and chromitite shows transitional changes in spinel and REE chemistry toward the surrounding oceanic harzburgites. This feature indicates that pre -existing oceanic harzburgite was partially modified by arc -related magma. Discordant chromitite, dunite, and highly depleted harzburgites are probably formed at the supra -subduction zone environment just before ophiolite obduction. Such arc -related features in mantle peridotite may be produced at a young sub -arc mantle.

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Genesis of pale microgranular masses in ophiolitic chromite deposits in northern Xinjiang: Analysis of the micro‐area composition of altered minerals using LA‐ICP‐MS

Wang¹,

Xie²,

Guo³

et al. 2020

Geological Journal

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The petrographic characteristics and micro‐area composition of altered minerals in pale microgranular masses (PMMs) that were discovered in the chromite mines of northern Xinjiang, China, were studied via laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). There are six lithotypes of PMMs, namely, rodingitized vitrobasalt, gabbro‐diabase, ultramafite, tuff‐clastic rock, rodingite or skarn, and metasomatite. The texture, composition, and geochemical affinities of a series of altered minerals, such as clinopyroxenes, garnets, serpentines, and chlorites, show that the incompatible elements actively migrate with the Fe, Mg, alkali leaching losses, and Ca aggregates during the course of the alteration process. The geochemical characteristics of the major trace elements in the altered minerals are mostly influenced by the types of protoliths and minerals and have roughly inherited those properties from the protoliths. A marked difference exists between the serpentine geochemical characteristics of the major trace elements in the surrounding peridotites and the PMMs and/or metasomatite. This observation suggests that the two differences are derived from the altered protolith minerals instead of from the fluid metasomatism. Furthermore, the chlorite in the metasomatites inherits the properties of the chlorite component in the PMMs. This study examines the development of PMMs that might undergo two different mechanisms or (at least) two different periods of genesis, i.e., early ultramafic magma xenoliths and metasomatism, as indicated by the rock fabric, and late rodingitization, as indicated by the assemblage of altered minerals and the suite of geochemical affinities. The mechanism by which PMMs develop in peridotites reveals that some podiform chromite in this area may also be xenoliths that formed after chromite was captured by ultramafic magmas in early times.

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Structural classification of chromite pods in southern New Caledonia

Cited by 162 publications

References 0 publications

Possible recycled origin for ultrahigh-pressure chromitites in ophiolites

Possible recycled origin for ultrahigh-pressure chromitites in ophiolites

Formation of discordant chromitite at the initiation of sub-arc mantle processes: Observations from the northern Oman ophiolite

Genesis of pale microgranular masses in ophiolitic chromite deposits in northern Xinjiang: Analysis of the micro‐area composition of altered minerals using LA‐ICP‐MS

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