Podiform chromitites of the Tari-Misaka ultramafic complex, southwestern Japan, as mantle-melt interaction products

Arai, Shoji; Yurimoto, H.

doi:10.2113/gsecongeo.89.6.1279

Cited by 298 publications

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“…One of the most accepted mechanisms of chromite crystallization to form large volumes of chromitites in ophiolitic mantle rocks invokes chromitite formation by melt-rock interaction. According to this model, chromitites represent the filling of magmatic conduits [53] and formed by reaction between ascending mantle melts and country-rock residual peridotite [54][55][56][57][58]. The same mechanism can be applied to the formation of the Alapaevsk chromitites.…”

Section: Chromite Composition and Silicate Inclusion: Their Applicatimentioning

confidence: 99%

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

et al. 2016

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An electron microprobe study has been carried out on platinum-group minerals, accessory phases, and chromite in several chromite deposits of the Alapaevsk ophiolite (Central Urals, Russia) namely the Bakanov Kluch, Kurmanovskoe, Lesnoe, 3-d Podyony Rudnik, Bol'shaya Kruglyshka, and Krest deposits. These deposits occur in partially to totally serpentinized peridotites. The microprobe data shows that the chromite composition varies from Cr-rich to Al-rich. Tiny platinum-group minerals (PGM), 1-10 µm in size, have been found in the chromitites. The most abundant PGM is laurite, accompanied by minor cuproiridsite and alloys in the system Os-Ir-Ru. A small grain (about 20 µm) was found in the interstitial serpentine of the Bakanov Kluch chromitite, and its calculated stoichiometry corresponds to (Ni,Fe) 5 P. Olivine, occurring in the silicate matrix or included in fresh chromite, has a mantle-compatible composition in terms of major and minor elements. Several inclusions of amphibole, Na-rich phlogopite, and clinopyroxene have been identified. The bimodal Cr-Al composition of chromite probably corresponds to a vertical distribution in the ophiolite sequence, implying formation of Cr-rich chromitites in the deep mantle, and Al-rich chromitites close to the Moho-transition zone, in a supra-subduction setting. The presence of abundant hydrous silicate inclusions, such as amphibole and phlogopite, suggests that the Alapaevsk chromitites crystallized as a result of the interaction between a melt enriched in fluids and peridotites. Laurite and cuproiridsite are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at high temperatures. The sulfur fugacity was relatively high to allow the precipitation of Ir-bearing sulfides, but below the Os-OsS 2 buffer. The alloys in the system Os-Ir-Ru are classified as secondary PGM, i.e., formed at low temperature during the serpentinization process. The (Ni,Fe) 5 P phase is the first occurrence of a Ni-phosphide in terrestrial samples. Its composition indicates that it may be a new mineral. However, the small size has, so far, prevented a crystallographic study to support this conclusion.

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Section: Chromite Composition and Silicate Inclusion: Their Applicatimentioning

confidence: 99%

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

et al. 2016

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“…The breakdown of orthopyroxene in harzburgite plays an essential role in precipitation of chromitite as one of sources of its Cr and Al (Arai, 1997). There seems to be a consensus that the podiform chromitite is formed by melt/ harzburgite reaction with subsequent melt mixing at the uppermost mantle (Arai and Yurimoto, 1994;Zhou et al, 1994). The frequent presence of primary inclusions of hydrous minerals (pargasite and phlogopites) within chromian spinel of podiform chromitite (e.g., Lorand and Ceuleneer, 1989) indicate its low -pressure, i.e., upper mantle, origin within the stability field of these hydrous minerals (e.g., < 3 GPa for pargasite; Niida and Green, 1999).…”

Section: Low-pressure Generation Of Podiform Chromititesmentioning

confidence: 99%

“…1a). The podiform chromitite and dunite envelope have been interpreted as a shallowseated (uppermost mantle) product of harzburgite/melt reaction and related melt mixing (e.g., Arai and Yurimoto, 1994;Zhou et al, 1994;Arai and Abe, 1995). However, this has been seriously questioned and re -examined by discovery of diamond and other ultrahigh -pressure (UHP) minerals from podiform chromitites (e.g., Robinson et al, 2004;Trumbull et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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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“…Although the genesis of mantle-hosted Cr-rich ophiolitic chromitites is still a matter of debate, the most recent interpretations for their formation point to a mechanism of melt-peridotite reaction within conduits in the upper mantle (Arai & Yurimoto 1994, Zhou et al 1996. Experimental studies also suggest that chromitites can form from hydrous melts saturated in chromian spinel and olivine (Matveev & Ballhaus 2002).…”

Section: Origin and Tectonic Setting Of The Pindos Chromititesmentioning

confidence: 99%

“…Since sudden changes in T (of the order of 100°C) in the upper mantle are not likely to occur, fluctuations in f(S 2 ) and f(O 2 ) are more likely responsible for the development of reverse zoning in the crystallizing laurite (Gervilla et al 2005). Changes in f(S 2 ) and f(O 2 ) may be caused by magma mingling in the upper mantle (Arai & Yurimoto 1994, Zhou et al 1996 or by assimilation of Si-rich rocks by a primitive melt (Bédard & Hébert 1998). Mixing of two melts with different activities of silica (one differentiated and one primitive) in turbulent magmas in conduits can promote a continuous increase in T and decrease in f(S 2 ), which can explain the reverse pattern of zoning in laurite (González-Jiménez et al 2009).…”

Section: Origin Of the Inverse Zoning In Laurite And Conditions Of Almentioning

confidence: 99%

Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

Kapsiotis

Grammatikopoulos

Tsikouras

et al. 2009

The Canadian Mineralogist

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The chromitites of the Milia area in the Pindos ophiolite complex, in Greece, were investigated for their platinum-group mineral (PGM) content. The chromitites are massive, more rarely disseminated in texture and occur as small pods. They are composed of magnesiochromite crystals with Cr# [Cr/(Cr + Al)] between 0.80 and 0.84, and Mg# [Mg/(Mg + Fe 2+ )] between 0.54 and 0.72. The total platinum-group-element (PGE) contents in chromitites are relatively low (≤170 ppb), although they may locally be higher (up to 1059 ppb). The IPGE (Os, Ir and Ru) predominate over the PPGE (Rh, Pt and Pd). The PGM assemblage, consistent with the geochemical data, is dominated by laurite and Os-Ir-Ru alloys that occur both as single and composite grains, generally less than 15 mm in size. Laurite has a wide range of Os-for-Ru substitution [Ru/(Ru + Os): 0.42-0.99], whereas primary alloys are enriched in Ru (up to 73.80 wt.%). Some laurite crystals exhibit an anomalous pattern of zoning. Such zoning requires an inversion of the normal T-f(S 2 ) trend in magmatic systems, and is herein considered to be due to postmagmatic processes. Some Ru-rich alloy grains contain relatively high Rh and Pt abundances, similar to those of residual sulfides in mantle peridotites. This feature suggests that these alloys may represent residual PGM phases from earlier episodes of melt extraction from the severely depleted mantle unit of the Pindos ophiolite complex. Combined compositional data indicate that the Milia chromitites formed from a hydrous boninitic melt in a suprasubduction-zone environment.Keywords: chromitites, platinum-group minerals (PGM), laurite, alloys, ophiolites, Pindos, Greece. Certains grains d'alliages riches en Ru contiennent des teneurs relativement élevées en Rh et Pt, tout comme les sulfures résiduels de péridotites du manteau. Ces grains d'alliage pourraient donc représenter des MGP résiduels après l'extraction antérieure de liquide silicaté, laissant un manteau très stérile dans le complexe ophiolitique de Pinde. Les données combinées sur la composition indiquent que les chromitites de Milia se sont formées à partir d'une magma hydraté boninitique dans un milieu au dessus de la zone de subduction.(Traduit par la Rédaction)

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Podiform chromitites of the Tari-Misaka ultramafic complex, southwestern Japan, as mantle-melt interaction products

Cited by 298 publications

References 0 publications

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

Possible recycled origin for ultrahigh-pressure chromitites in ophiolites

Chromian Spinel Composition and Platinum-Group Element Mineralogy of Chromitites From the Milia Area, Pindos Ophiolite Complex, Greece

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