Origin of K-cymrite and kokchetavite in the polyphase mineral inclusions from Kokchetav UHP calc-silicate rocks: evidence from confocal Raman imaging

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CO2‐bearing fluid inclusions coexisting with diamonds were identified in zircons from diamondiferous gneiss in the Kokchetav Massif. This discovery provides evidence for the presence of CO2 in UHP fluids and diamond formation in moderately oxidized conditions in the Kokchetav gneiss. Fluid and multiphase solid inclusions coexisting in zircons represent immiscible melt and fluid captured close to the peak metamorphic conditions for the Kokchetav UHP gneiss. Most of CO2‐bearing inclusions are CO2+H2O mixtures except for some cases when they also contain daughter phases (e.g. muscovite, calcite and quartz) tracing the presence of aqueous and solute‐rich fluids at different phases of UHP metamorphism. Decrease of pressure and temperature may have been responsible for the reduction of solutes in the CO2‐bearing fluid. The lack of CO2‐bearing inclusions in garnet porphyroblasts from diamond‐bearing gneiss, as well as the common coexistence of aqueous CO2‐bearing inclusions with calcite, testify that most likely all CO2 in fluid was consumed by the calcite‐forming reaction and hydrous melt was the only remaining growth medium during retrograde metamorphism of the Kokchetav UHPM gneisses. Neither K‐cymrite nor kokchetavite was identified among daughter phases in the hydrous melt inclusions in garnet, which indicates that they hardly could originate in a metapelitic system. Copyright © 2017 John Wiley & Sons, Ltd.

Section: Introductionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

CO₂‐bearing fluid inclusions associated with diamonds in zircon from the UHP Kokchetav gneisses

Mikhno

Musiyachenko

Shchepetova

et al. 2017

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Internal diamond morphology: Raman imaging of metamorphic diamonds

Korsakov

Toporski²,

Dieing³

et al. 2015

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Confocal 2‐D and 3‐D Raman imaging of the Kokchetav metamorphic diamonds from different rock types reveals that these diamonds have a rather complex internal morphology. The diamond shows a strong change in the position of the diamond Raman line as well as the width of this line, which could be found both in the XY and in the YZ scan. These features indicate variations in the crystalline quality of the diamond. The broadest lines are located in the center of the octahedral diamond inclusion whereas the material close to the diamond–garnet interface shows smaller line widths. These features were also found for thermochemically extracted diamond crystals, which are not armored by host mineral, and in situ for inter‐ and intragranular diamond. Furthermore, host–garnet display no evidence for broadening or up‐shift of main Raman bands, indicating very low (below detection limit) residual strain. Thus the broadening and upshift of main diamond band do not relate to residual strain in inclusion–host systems. A comparison of Raman imaging results with cathodoluminescence images reveals that the distribution of defects, which cause the cathodoluminescence of diamond crystals, can be traced by Raman imaging. The 2‐D and 3‐D Raman imaging is a very powerful tool for study of internal morphology and growth pattern of metamorphic diamond, even it is a small crystal less than 10 µm in size. The growth pattern for octahedral diamond crystals from garnet–clinozoisite gneisses were obtained for the first time by Raman imaging. Copyright © 2015 John Wiley & Sons, Ltd.

Dumortierite and tourmaline from the Barchi‐Kol diamond‐bearing kyanite gneisses (Kokchetav massif): A Raman spectroscopic study and petrological implications

Korsakov

Rezvukhina

Rezvukhin

et al. 2019

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Two minerals of boron, dumortierite and tourmaline, have been studied in a diamondiferous kyanite gneiss (Barchi‐Kol area, Kokchetav massif, Northern Kazakhstan) by Raman spectroscopy and electron microprobe (EMP) analysis. Dumortierite and tourmaline (almost pure schorl end‐member) coexist within the sample, with blue/purple dumortierite inclusions hosted by kyanite porphyroblasts and blue tourmaline crystals occurring as inclusions in garnet. Optically, dumortierite appears almost identical to kyanite host and can be easily overlooked in thin sections during optical and scanning electron microscopic observations. Both boron minerals show a very strong anisotropy, and the most prominent Raman spectra can be obtained if the electric field vector E is parallel to the c axis of the dumortierite and tourmaline crystals. The Raman spectra of the investigated dumortierite are very similar to those of the synthetic dumortierite with a pronounced excess of boron (up to 0.26 [4]B), although the EMP examination revealed only one grain of the natural dumortierite studied here to have a very low boron surplus (up to 0.03 [4]B). Neither Raman spectroscopic study nor EMP analysis detected [4]B in tourmaline. The findings of dumortierite and tourmaline in the diamondiferous gneisses provide important implications for the presence of a boron‐rich fluid or melt during subduction/exhumation processes.