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| Titel |
Fractional ultrabasic-basic evolution of upper-mantle magmatism: Evidence from xenoliths in kimberlites, inclusions in diamonds and experiments |
| VerfasserIn |
Yuriy Litvin, Anastasia Kuzyura |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141280
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| Publikation (Nr.) |
 EGU/EGU2017-4773.pdf |
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| Zusammenfassung |
| Ultrabasic peridotites and pyroxenites together with basic eclogites are the upper-mantle in
situ rocks among xenoliths in kimberlites. Occasionally their diamond-bearing varieties have
revealed within the xenoliths. Therewith the compositions of rock-forming minerals
demonstrate features characteristic for primary diamond-included minerals of peridotite and
eclogite parageneses (the elevated contents of Cr-component in peridotitic garnets and
Na-jadeitic component in eclogitic clinopyroxenes). High-pressure experimental study of
melting equilibria on the multicomponent peridotie-pyroxenite system olivine Ol –
orthopyroxene Opx – clinopyroxene Cpx – garnet Grt showed that Opx disappeared
in the peritectic reaction Opx+L→Cpx (Litvin, 1991). As a result, the invariant
peritectic equilibrium Ol+Opx+Cpx+Grt+L of the ultrabasic system was found to
transform into the univariant cotectic assemblage Ol+Cpx+Grt+L. Further experimental
investigation showed that olivine reacts with jadeitic component (Jd) with formation of
garnet at higher 4.5 GPa (Gasparik, Litvin, 1997). Study of melting relations in
the multicomponent system Ol – Cpx – Jd permits to discover the peritectic point
Ol+Omph+Grt+L (where Omph – omphacitic clinopyroxene) at concentration 3-4 wt.%
Jd-component in the system. The reactionary loss of Opx and Ol makes it possible to
transform the 4-phase garnet lherzolite ultrabasic association into the bimineral
eclogite assemblage. The regime of fractional Ol, Cpx and Grt crystallization must be
accompanied by increasing content of jadeitic component in residual melts that
causes the complete “garnetization of olivine”. In the subsequent evolution, the melts
would have to fractionate for basic SiO2-saturated compositions responsible for
petrogenesis of eclogite varieties marked with accessory corundum Crn, kyanite
Ky and coesite Coe. Both the peritectic mechanisms occur in regime of fractional
crystallization. The sequence of the upper-mantle fractional ultrabasic-basic magmatic
evolution and petrogenesis may be controlled by the following melting relations:
from Ol, Opx, L field to cotectic curve Ol, Opx, Cpx, L, peritectic point Ol, Opx,
Cpx, Grt, L (loss of Opx), cotectic curve Ol, (Cpx+Jd), Grt, L, peritectic point Ol,
(Cpx→Omph), Grt, L (loss of Ol), divariant field Omph,Grt,L, cotectic curve Ky, Omph,
Grt, L, eutectic point Ky,Coe,Omph, Grt,L, subsolidus assemblage Ky,Coe,Omph,
Grt.
The fractional ultrabasic-basic evolution of the upper-mantle silicate-carbonate-carbon
melts-solutions, which are responsible for genesis of diamond-and-inclusions associations
and diamond-bearing peridotites and eclogites, follows the similar physico-chemical
mechanisms (Litvin et al., 2016). This is illustrated by fractional syngenesis diagram for
diamonds and associated minerals which construction is based on evidence from high
pressure experiments.
References
Gasparik T., Litvin Yu.A (1997). Stability of Na2Mg2Si2O7 and melting relations on the
forsterite – jadeite join at pressures up to 22 GPa. Eur, J. Mineral. 9(2), 311-326.
Litvin Yu.A. (1991). Physico-Chemical Study of Melting of Materials from the Deep
Earth. Moscow: Nauka. 312 p.
Litvin Yu.A., Spivak A.V., Kuzyura A.V. (2016). Fundamentals of the mantle-carbonatite
concept of diamond genesis, Geochemistry Internat. 34(10), 839-857. |
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