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| Titel |
High-pressure 13C-diamond-forming reaction of decomposition of Na213CO3 melt at 20 - 60 GPa |
| VerfasserIn |
N. Solopova, A. Spivak, I. Kupenko, Yu. Litvin, L. Dubrovinsky |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058910
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| Zusammenfassung |
| The available analytical data on mineralogy of syngenetic inclusions in superdeep diamonds
from the Juina area (Brazil) provided important information on the general chemical
composition of the parental medium for the host diamonds and included minerals. Carbonate
micro- and nano-inclusions of calcite CaCO3, dolomite CaMgCO3, nyerereite Na2Ca(CO3)2,
and nahcolite NaHCO3 were identified among the heterogeneous suite of primary inclusions.
Chemical and PT conditions of syngenetic formation of the superdeep diamonds and mineral
inclusions therein may be discovered using high-pressure experiments focused onto study of
chemical stability of carbonate components, involved into the diamond-forming processes,
and their melts.
We studied high-pressure high-temperature behavior of sodium carbonate Na2CO3 in
laser-heated diamond anvil cells. A starting material was a pure Na213CO3 mixed with
platinum powder in ratio approximately 20:1. The mixture was loaded into high-pressure
chamber between two layers of pure Na213CO3. Platinum powder acts as an absorber of the
NIR laser light. Re gaskets of 200 μm in thickness were pre-indented to about 30 μm
in thickness, then holes of about 130 μm in diameter were drilled in the gasket
centres. The samples were compressed between diamond anvils with 250-μm culets at
room temperature to pressures between 20 and 60 GPa. Ruby balls placed inside
the pressure chamber were used as the pressure calibrants. After quenching, the
samples were studied by Raman spectroscopy using Dilor XY Raman spectrometer
and Ar+ ion laser (514.5 nm, Coherent Innova 300). Using 13C-carbonate we can
unambiguously distinguish carbon phases produced in course of experiments as results of
decomposition of carbonate and avoid a possible contamination from 12C-diamond
anvils.
High-pressure melting of sodium carbonate is congruent within the 20 – 60 GPa pressure
interval. Formation of 13C-diamond was detected after heating sodium carbonate
melt at 34.5 GPa and higher temperature 2400 K. In the sample heated at 33 GPa
and 2600 K, we found a broad G-band at 1545 cm-1 (12C -graphite originated,
probably, from diamond anvils) and a sharp band at 1315 cm-1 (newly formed
13C-diamond). The bands correspond to mixture of graphite and diamond with isotopic
13C:12C ratio about 1:1. The 13C -diamond was synthesized, evidently, due to the
reaction of decomposition of sodium carbonate melt with formation of dense fluid
phase CO2 decomposed with liberation of elemental carbon. Further studies of
CaCO3 are in progress in order to determine a melting curve and decomposition
boundary of sodium carbonate melt, as well as PT-parameters of its phase stability
region.
This work was funded by grants of President of RF MK-913.2011.5, FPP
2011-1.3.1-151-006_6 and RFBR 10-05-00654, 11-05-00401. |
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