Forbidden mineral assemblage coesite‐disordered graphite in diamond‐bearing kyanite gneisses (Kokchetav Massif). (31st May 2017)

• Record Type: Journal Article
• Authors: Shchepetova, Olga V.; Korsakov, Andrey; Mikhailenko, Denis; Zelenovskiy, Pavel; Shur, Vladimir; Ohfuji, Hiroaki
• Other Names: Korsakov Andrey V. guestEditor.; Marshall Craig Patrick guestEditor.
• Is Part Of: Journal of Raman spectroscopy. Volume 48:Number 11(2017)
• Page Start: 1606
• Page End: 1612
• Publication Date: 2017-05-31
• Subjects: Raman imaging -- disordered graphite -- diamond -- coesite -- UHP‐HT metamorphism; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.5167
• Languages: English
• ISSNs: 0377-0486

Abstract

Abstract : Confocal 2D and 3D Raman imaging was applied to SiO2 inclusions in kyanite porphyroblasts from diamond‐bearing kyanite gneisses of the Kokchetav Massif (Northern Kazakhstan). The study reveals a mineral assemblage of coesite‐disordered graphite which is forbidden in ultrahigh pressure‐high temperature (UHP‐HT) metamorphic complexes. Disordered graphite in coesite inclusions is optically undetectable and has been identified exclusively by Raman spectroscopy. Raman imaging of the forbidden coesite‐disordered graphite assemblage fails to detect bands assigned to fluid components (e.g. CO2, N2, CH4, H2 O liq ), but the Raman spectra of fluid inclusions in kyanite, garnet and quartz demonstrate the presence of CO2, N2, CH4, H2 O liq and disordered graphite. The disordered graphite most likely formed by precipitation from a C―O―H fluid during the retrograde stage. The fluid was entrapped by kyanite with coesite inclusions near the peak metamorphic conditions. The lack of disordered graphite around diamond crystals in our samples does not support the generally accepted origin of disordered graphite in ultra high pressure metamorphic rocks by partial diamond graphitization during exhumation. Copyright © 2017 John Wiley & Sons, Ltd. Abstract : Confocal 2D and 3D Raman imaging was applied to SiO2 inclusions in kyanite porphyroblasts from diamond‐bearing kyanite gneisses of the Kokchetav Massif (Northern Kazakhstan). The study reveals a mineral assemblage of coesite‐disordered graphite which is forbidden in ultrahigh pressure ‐ high temperature (UHP‐HT) metamorphic complexes. Disordered graphite in coesite inclusions is optically undetectable and has been identified exclusively by Raman spectroscopy.