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| Titel |
Trace elements mineral-melt partitioning in diamond-forming peridotite-carbonatite system (experimental study at 8.5 GPa) |
| VerfasserIn |
A. Kuzyura, Y. Litvin, P. Vasilisev, T. Jeffries, F. Wall |
| 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 |
250065858
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| Zusammenfassung |
| The upper mantle peridotite-carbonatite system of the model composition
[(Ol36-60Opx16Cpx12-24Grt12-24)30Carb70]99TE01represents ultra-basic parental medium
for diamond and paragenetic mineral inclusions therein. This experimental study is focused
onto geochemical behavior of trace elements (TE) during formation of diamond in
heterogeneous parental medium consisting of completely miscible carbonate-silicate melt and
peridotitic minerals which are paragenetic to diamond (olivine Ol, orthopyroxene Opx,
clinopyroxene Cpx and garnet Grt). The TE mixture consists of Li, Rb, Cs, Ba,
Th, U, Ta, Nb, La, Ce, Pb, Pr, Sr, Nd, Zr, Hf, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm,
Yb, Lu, Sc, and Zn. The trace elements were mainly introduced into the system as
oxides.
In experiments at 8.5 GPa and 1510oC, quite large (more than 100 μm) garnet,
clinopyroxenes, and olivine crystals were formed in completely miscible carbonate-silicate
(carbonatite) melts Orthopyrohene was not formed. After quenching, the melt phase was
presented as cryptocrystalline aggregate which was analyzed over areas of 10Ã10 - 100Ã100
μm size with the use of microprobe and LA-ICP-MS methods. The methods were used in
analyzing TE content in single crystalline olivine, clinopyroxene and garnet submerged into
the quenched melt.
Coefficients of inter-phase TE partitioning Kd for the coupled phases olivine-melt,
clinopyroxene-melt, garnet-melt, and olivine-garnet were calculated, based on the results of
LA-ICP-MS determination of the TE contents. Spydergram characterizing clearly the
inter-phase TE partitions is plotted.
By the spydergram, garnet and olivine are the major phases in TE inter-phase
mineral-melt partitioning for the diamond-forming peridotite-carbonatite system. The feature
is that light REE elements (La, Ce, Pr) are mainly distributed into the melt phase where as the
medium and heavy elements (Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) – into garnet (Kd
= 1 – 6).
Such heavy elements as Zr, Hf, Y, and Sc are also accumulated in garnet (Kd = 1 – 5)
where as the other elements concentrated in the completely miscible carbonate-silicate melt.
Highest Kd = 5-6 for the garnet-melt couple is in Sc and Lu cases. Olivine accumulates
intensely light TE - Li, Rb, Cs, Ba (Kd = 2.5 – 5) as well as Th, U, Pb, and Zn (Kd = 1.5 –
4.5). It was found that clynopyroxene is practically not participated in TE partitioning for the
peridotite-carbonatite system.
The new experimental data are applicable to interpretation of TE contents in
paragenetic inclusions of peridotite paragenesis in natural diamond. Support: The RF
President’s grant MK-913.2011.5, RFBR grants 10-05-00654 and 11-05-00401. |
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