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| Titel |
Model of the carbonatite-kimberlite connections in the chloride-carbonate-silicate systems |
| VerfasserIn |
O. Safonov, L. Perchuk |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019338
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| Zusammenfassung |
| Kimberlitic melts are usually considered as products of gradual transition from Mg-rich
carbonatitic melts formed via partial melting of carbonatized mantle peridotites [1, 2]. On the
other hand, recent discoveries show significant contribution of alkali chlorides in the
formation of kimberlites. These are (i) melt/fluid inclusions in the kimberlitic diamonds and
olivines worldwide [3-5] and (ii) chloride-rich kimberlites of the Udachnaya-East pipe [4].
Both of them may indicate not only active role of alkalic chloride-rich liquids in incipience of
chloride-rich carbonatitic melts but also in their transformation into kimberlitic magmas.
Our experimental studies [6, 7] showed that the saturation of chloride-carbonate
liquids with silicates resulted in the formation of two immiscible melts: Cl-bearing
carbonate-silicate (CS) and chloride-carbonate (CC). This could suggest immiscible
separation of the kimberlitic melts during interaction of mantle peridotites with the
chloride-carbonate liquids. Purposeful experimental study of the chloride-carbonate liquid
interaction with peridotitic minerals and kimberlite were carried out in order to test this
suggestion.
In the system olivine-(Ca, Na2)CO3-(K, Na)Cl at 5.4 GPa exchange reactions of olivine
with the CaCO3 component of the chloride-carbonate melt results in the formation of
clinopyroxene and chloride-rich “dolomitic” melt. The higher CaCO3 content in the melt the
more intensive reactions of olivine and the larger amount of newly formed clinopyroxene.
Chlorides do not participate in “dissolution” of olivine. No CC-CS immiscibility was
observed in the run products up to temperatures 1650OC. Thus, olivine, as the only
Si-bearing component, cannot effectively saturate the chloride-carbonate liquid with silica. In
contrast, the dissolution of orthopyroxenes and/or garnets could lead to the silica saturation of
the chloride-carbonate melt and further CC-CS immiscibility [7]. Re-distribution
of carbonate and Ca from CS melt to coexisting CC results in increase of the Si
content and the Mg/Ca ratio in the carbonate-silicate melt shifting toward kimberlite
composition.
Additional experiments in the system kimberlite-(Ca, Na2)CO3-KCl at 4.8 GPa revealed
that the kimberlite-like CS melt can coexist with immiscible CC liquid at 1400-1600 |
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