Rodingite with Ti- and Cr-rich vesuvianite from the Sartuohai chromium deposit, Xinjiang, China

Kobayashi, Shôichi; Kaneda, Hiroaki

doi:10.2465/jmps.081224

Cited by 10 publications

(10 citation statements)

References 11 publications

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“…), which is distinctive and consistent with its generation during the serpentinization of peridotite (e.g. Kobayashi & Kaneda, ), and the full occupancy of the X + X ′ site (high content in Ca), which is characteristic of low‐grade metamorphism (Gnos & Armbruster, ). These features are consistent with vesuvianite 0 as resulting from oceanic metasomatism.…”

Section: Discussionmentioning

confidence: 97%

Ocean floor and subduction record in the Zermatt‐Saas rodingites, Valtournanche, Western Alps

Zanoni

Rebay

Spalla

2016

Journal Metamorphic Geology

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Multiscale structural analysis and petrological modelling were used to establish the pressure‐peak mineral assemblages and pressure–temperature (P–T) conditions recorded in the rodingites of the upper Valtournanche portion of the oceanic Zermatt‐Saas Zone (ZSZ; Western Alps, northwestern Italy) during Alpine subduction. Rodingites occur in the form of deformed dykes and boudins within the hosting serpentinites. A field structural analysis showed that rodingites and serpentinites record four ductile deformation stages (D1–D4) during the Alpine cycle, with the first three stages associated with new foliations. The most pervasive fabric is S2 that is marked by mineral assemblages in serpentinite indicating pressure‐peak conditions, involving mostly serpentine, clinopyroxene, olivine, Ti‐clinohumite and chlorite. Three rodingite types can be defined: epidote‐bearing, garnet–chlorite–clinopyroxene‐bearing and vesuvianite‐bearing rodingite. In these, the pressure‐peak assemblages coeval with S2 development involve: (i) epidoteII + clinopyroxeneII + Mg‐chloriteII + garnetII ± rutile ± tremoliteI in the epidote‐bearing rodingite; (ii) Mg‐chloriteII + garnetII clinopyroxeneII ± vesuvianiteII ± ilmenite in the garnet–chlorite–clinopyroxene‐bearing rodingite; (iii) vesuvianiteII + Mg‐chloriteII + clinopyroxeneII + garnetII ± rutile ± epidote in vesuvianite‐bearing rodingite. Despite the pervasive structural reworking of the rodingites during Alpine subduction, the mineral relicts of the pre‐Alpine ocean floor history have been preserved and consist of clinopyroxene porphyroclasts (probable igneous relicts from gabbro dykes) and Cr‐rich garnet and vesuvianite (relicts of ocean floor metasomatism). Petrological modelling using thermocalc in the NCFMASHTO system was used to constrain the P–T conditions of the S2 mineral assemblages. The inferred values of 2.3–2.8 GPa and 580–660 °C are consistent with those obtained for syn‐S2 assemblages in the surrounding serpentinites. Multiscale structural analysis indicates that some ocean floor minerals remained stable under eclogite facies conditions suggesting that minerals such as vesuvianite, which is generally regarded as a low‐P phase, could also be stable in favourable chemical systems under high‐P/ultra‐high‐pressure (HP/UHP) conditions. Finally, the reconstructed P–T–d–t path indicates that the P/T ratio characterizing the D2 stage is consistent with cold subduction as estimated in this part of the Alps. The estimated pressure‐peak values are higher than those previously reported in this part of ZSZ, suggesting that the UHP units are larger and/or more abundant than those previously suggested.

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Section: Discussionmentioning

confidence: 97%

Ocean floor and subduction record in the Zermatt‐Saas rodingites, Valtournanche, Western Alps

Zanoni

Rebay

Spalla

2016

Journal Metamorphic Geology

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“…Rodingite can be formed from various protoliths such as gabbroic rocks (Coleman 1967;O'Brien and Rodgers 1973;Honnorez and Kirst 1975;Leach and Rodgers 1978;Muraoka 1985;Kobayashi and Kaneda 2010), basaltic rocks (Coleman 1967;Evans et al 1979;Barriga and Fyfe 1983) 1980). In the study area, gabbro (now metagabbro) is the only possible protolith of rodingite as no other rock types are present as dykes in the serpentinite.…”

Section: Resultsmentioning

confidence: 99%

Interplay of irreversible reactions and deformation: a case of hydrofracturing in the rodingite–serpentinite system

Nishiyama

Shiosaki

Mori

et al. 2017

Prog. in Earth and Planet. Sci.

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The interplay of irreversible reactions and deformation during regional metamorphism was analyzed in the reaction zones between rodingite and serpentinite. Rodingites are leucocratic rocks found commonly in serpentinites and are considered metasomatic products of Ca-rich fluid. Rodingites occur ubiquitously in serpentinite from the Nomo metamorphic rocks, western Kyushu, a Cretaceous accretionary complex of greenschist to epidote-amphibolite facies condition. We used the singular value decomposition (SVD) method to analyze rodingitization reactions based on mineral compositions of a rodingite sample and a possible protolith (clinopyroxene gabbro). The resultant reaction implied that the rodingite was formed due to the addition of considerable amounts of CaO and H 2 O to the protolith, whereas other components such as SiO 2 , AF (Al 2 O 3 + Fe 2 O 3 ), and FM (FeO + MgO) were conserved. The Nomo rodingites are associated with reaction zones between serpentinite. A careful study on the compositional variations of diopside and chlorite in the rodingite, serpentinite, and the reaction zones between them showed a disequilibrium crystallization of diopside in the reaction zone. Diopside shows a serrated variation in composition across the reaction zone together with disequilibrium signature within grains (composite grain consisting of Fe-rich and Fe-poor parts). These features clearly indicate that diopside crystallized in a relatively short period compared to the metamorphism by irreversible reactions. Another conspicuous feature is that perovskite occurs in some reaction zones, whereas titanite is common in rodingites; this indicates that the reaction zone is poorer in SiO 2 . The tremolite veins are typically derived from the reaction zone into serpentinite; showing this is a good example of hydrofracturing associated with the formation of the reaction zone. All the reactions obtained by the SVD method that contribute to the formation of the reaction zones consumed CaO and evolved H 2 O, strongly suggesting that the hydrofracturing is caused by a rapid increment of fluid pressure during the progression of the reactions. The reactions consumed considerable amounts of SiO 2 in the reaction zone, which is consistent with the occurrence of perovskite, and the conservation of AF and FM components.

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“…Vesuvianite single crystals with a green tone were studied by Bradshaw (1972) 47 , Groat & Hawthorne (1992) 13 and Kobayashi & Kaneda (2010) 12 , and they showed that the content of Cr 2 O 3 in vesuvianite may be as high as 6.21 wt.%, and that the chromium probably occurs at the octahedral coordination site Y3, thus giving the chromium-bearing vesuvianite single crystals their usual vivid green color. In previous studies of clinochlore with a green appearance, Cr 3+ was found to occupy the octahedral sites 48,49 .…”

Section: Discussionmentioning

confidence: 99%

“…In addition, the triangularly and/or tetrahedrally coordinated site T hosts elements like Be and B 13,14 , which accounts for the brown to black and cinnamon-red color of vesuvianite [15][16][17] .Vesuvianite is a widespread rock-forming mineral that occurs principally in contact metamorphic zones associated with limestone 18,19 , and the minerals formed in association with the vesuvianite may influence the color of the californite. As previously reported, there is a systematic dependence of the associated minerals on the grade of metamorphism and the crystallization temperature of the vesuvianite, so hydrogarnet (CaAl-CaFe 3+ series), xonotlite, natrolite-thomsonite, pectolite and calcite are associated minerals at low-grade metamorphisms (<300 °C); grossular, diopside, Mg-chlorite, prehnite, epidote and calcite at medium-grade metamorphisms (~300-500 °C); grossular, diopside, wollastonite, calcite, monticellite, melilite and quartz at higher-grade metamorphic conditions (>500 °C) 1,8,19 .The major element chemical compositions of minerals are usually assessed by using X-ray fluorescence (XRF), electron probe microanalysis (EPMA) and scanning electron microscope worked with energy dispersive X-ray spectroscopy (SEM-EDS) methods 12,20 . EPMA is applied only on polished sections or special targets.…”

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confidence: 99%

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Color and genesis of californite from Pakistan: insights from μ-XRF mapping, optical spectra and X-ray photoelectron spectroscopy

Lin

et al. 2020

Sci Rep

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four californite samples from pakistan with yellowish-green, green and reddish-brown colors were investigated by combining the methods of μ-XRf mapping, XRD, Raman spectra, optical spectra, epMA and XpS. the results show that the californite is composed mainly of microcrystalline vesuvianite and smaller amounts of clinochlore. Based on the distribution of the clinochlore, the californite can be divided into three types. the gem-quality californite is composed of microcrystalline vesuvianite and has a translucent appearance. the ordinary-quality californite contains microcrystalline vesuvianite as well as clinochlore, and it has an opaque appearance. the transitional-type has properties that are intermediate between those of gem-and ordinary-quality californite. octahedrally coordinated iron and chromium in the clinochlore reduce the transparency and contribute to the opaque green and yellowish-green colors of the californite. At sites where there is no clinochlore, cr 3+ in the octahedrally coordinated site Y3 of the vesuvianite is mainly responsible for the green tone of the californite, fe 3+ and Mn 3+ at the Y3 site contribute mainly to the yellowish-green and reddish-brown colors, respectively. the fe 2+ → fe 3+ charge transfer also occurs in vesuvianite and partly influences the appearance of the californite. the actual color of californite that lacks clinochlore is due to the synergy of cr 3+ , fe 3+ and Mn 3+ crystal field transfers at the octahedral site Y3 as well as the Fe 2+ → fe 3+ charge transfer in the vesuvianite. Vesuvianite in the californite can be assigned to the P4/n space group, and the occurrence of clinochlore reflects the fact that the californite from Pakistan formed under mediumgrade metamorphic conditions at temperatures of ~300-500 °C. The content of clinochlore provides a basis for grading the quality of the californite.Californite usually refers to a microcrystalline interlocking mineral growth with vesuvianite as the major constituent. Because of its similar appearance to jadeite, californite is often considered as jadeite, and it is commonly known as golden-green jade in Chinese jewelry market. Vesuvianite is an ortho-disilicate mineral with the general formula X 18 X4Y1Y2 4 Y3 8 T 0-5 Si 18 O 68 (O, OH, F) 10 , where the X and X4 sites are occupied by Ca, Na and rare earth elements (REE); the Y1 site by Cu 2+ , Mn 3+ , Fe 2+ and Al 3+ ; and the Y2 and Y3 sites usually by Al 3+ 1-8 . As previously reported, elements substituting at the X4, Y1, Y3 and T sites have a great influence on the appearance of vesuvianite, a vesuvianite crystal may appear gold to deep red to opaque brown-black when some of Ca at the X4 site has been substituted by REE, and the intensity of the vesuvianite color increases with increasing REE content 9 . Mn 3+ and Cu 2+ can replace Fe 3+ , Mg 2+ , Al 3+ and Fe 2+ at the square pyramidal coordination site Y1 and cause the vesuvianite crystal to present yellow or dark red appearance with a lilac hue 5,6,10,11 . Cr 3+ at the octahedrally coordinated site Y3 is r...

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Rodingite with Ti- and Cr-rich vesuvianite from the Sartuohai chromium deposit, Xinjiang, China

Cited by 10 publications

References 11 publications

Ocean floor and subduction record in the Zermatt‐Saas rodingites, Valtournanche, Western Alps

Ocean floor and subduction record in the Zermatt‐Saas rodingites, Valtournanche, Western Alps

Interplay of irreversible reactions and deformation: a case of hydrofracturing in the rodingite–serpentinite system

Color and genesis of californite from Pakistan: insights from μ-XRF mapping, optical spectra and X-ray photoelectron spectroscopy

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