Mineral inclusions in zircon from diamond-bearing marble in the Kokchetav massif, northern Kazakhstan

Ikuo Katayama, Masahito Ohta, Yoshihide Ogasawara

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

In order to constrain the metamorphic evolution of deeply subducted impure marble from the Kokchetav massif, we investigated mineral inclusions in zircon, which is known to protect ultrahigh-pressure (UHP) phases from late-stage overprinting. Consequently, diamond, coesite, diopside, garnet, phlogopite, calcite, dolomite, graphite and apatite were identified as inclusion in the zircons. Silica phases were absent in the matrix, indicating they were completely consumed by the following prograde reaction: Dolomite + 2 SiO2 = Diopside + 2 CO2. The relict of coesite inclusions in zircon indicates that prograde P-T trajectory crossed cut the quartz-coesite transition before the decarbonate reaction. Matrix diopsides contain abundant exsolved phengite lamellae, whereas the exsolution is absent in the inclusions in zircon. The diopside inclusions contain higher amounts of K2O (up to 0.56 wt%) and CaEskola component (up to 3.5 mol%) than those of the matrix (0.14 wt% and 2.1 mol%, respectively). Thus, phengite exsolution occurs in matrix pyroxene with low K2O and CaEskola components compared to inclusions in zircon. This observation indicates that decreasing K2O and CaEskola components during decompression resulted in the phengite exsolution in diopside. A trace of hydroxyl in phengite needles was perhaps initially incorporated within the precursor clinopyroxene under high-pressure conditions. The peak metamorphic P-T conditions of the impure marble are estimated to 60-80 kbar and 960-1050°C, derived from K2O solubility in diopside buffered by phlogopite and from the garnet-clinopyroxene geothermometer.

Original languageEnglish
Pages (from-to)1103-1108
Number of pages6
JournalEuropean Journal of Mineralogy
Volume14
Issue number6
Publication statusPublished - 2002 Nov
Externally publishedYes

Fingerprint

Bearings (structural)
Diamond
Calcium Carbonate
diopside
marble
diamond
Minerals
zircon
phengite
coesite
exsolution
mineral
matrix
Garnets
phlogopite
clinopyroxene
dolomite
garnet
Apatites
Quartz

Keywords

  • Coesite
  • High-KO diopside
  • Marble
  • Ultrahigh-pressure metamorphism
  • Zircon

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Mineral inclusions in zircon from diamond-bearing marble in the Kokchetav massif, northern Kazakhstan. / Katayama, Ikuo; Ohta, Masahito; Ogasawara, Yoshihide.

In: European Journal of Mineralogy, Vol. 14, No. 6, 11.2002, p. 1103-1108.

Research output: Contribution to journalArticle

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abstract = "In order to constrain the metamorphic evolution of deeply subducted impure marble from the Kokchetav massif, we investigated mineral inclusions in zircon, which is known to protect ultrahigh-pressure (UHP) phases from late-stage overprinting. Consequently, diamond, coesite, diopside, garnet, phlogopite, calcite, dolomite, graphite and apatite were identified as inclusion in the zircons. Silica phases were absent in the matrix, indicating they were completely consumed by the following prograde reaction: Dolomite + 2 SiO2 = Diopside + 2 CO2. The relict of coesite inclusions in zircon indicates that prograde P-T trajectory crossed cut the quartz-coesite transition before the decarbonate reaction. Matrix diopsides contain abundant exsolved phengite lamellae, whereas the exsolution is absent in the inclusions in zircon. The diopside inclusions contain higher amounts of K2O (up to 0.56 wt{\%}) and CaEskola component (up to 3.5 mol{\%}) than those of the matrix (0.14 wt{\%} and 2.1 mol{\%}, respectively). Thus, phengite exsolution occurs in matrix pyroxene with low K2O and CaEskola components compared to inclusions in zircon. This observation indicates that decreasing K2O and CaEskola components during decompression resulted in the phengite exsolution in diopside. A trace of hydroxyl in phengite needles was perhaps initially incorporated within the precursor clinopyroxene under high-pressure conditions. The peak metamorphic P-T conditions of the impure marble are estimated to 60-80 kbar and 960-1050°C, derived from K2O solubility in diopside buffered by phlogopite and from the garnet-clinopyroxene geothermometer.",
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