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| Titel |
Diamond-bearing Rocks among Mantle Xenoliths in Kimberlites as Indicatory for the Chambers of Diamond-parental Carbonatite Magma |
| VerfasserIn |
Yuriy Litvin, Anastasia Kuzyura |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094398
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| Publikation (Nr.) |
 EGU/EGU2014-9806.pdf |
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| Zusammenfassung |
| Origin of diamond-bearing peridotite and eclogite rocks in kimberlites is cleared up
using mantle-carbonatite model of diamond genesis (Litvin, 2007, 2009, 2013).
Data of analytical mineralogy of primary inclusions in diamonds and results of
physicochemical experiments on syngenetic diamond and inclusion phase relations are
co-ordinated in this model (Litvin et al., 2012). It proved that diamond-parental
media are presented by changeable carbon-saturated peridotite-carbonatite and
eclogite-carbonatite melts. The melts are capable to form not diamonds only but their
major and minor inclusions. The upper mantle is mainly composed of diamond-free
peridotites which dominate over eclogites as 9 to 5 % (Mathias et al., 1970). Howewer
diamond-bearing peridotites and eclogites occur rarely as demonstrated for S.Africa and
Yakutia (Sobolev N., 1977). Nevertheless, origin of diamond-bearing rocks belongs
to key problems of genetic mineralogy of diamond and mantle petrology due to
dissimilar physicochemical and environmental conditions of formation of comparatively
diamond-free rocks. Symptomatic that garnets included in diamond and these of
diamond-bearing eclogite are compositionally similar (Sobolev V. et al., 1972). Garnets of
diamond-bearing eclogites, inclusions in diamonds and intergrowths with them are
marked by increased Na2O content (0.10-0.22%) because of Na-majorite component
Na2MgSi5O12 (Bobrov & Litvin, 2011). Peridotitic garnets of diamond-bearing rocks,
inclusions and intergrowths are indicated by high Cr2O3 and low CaO content over
diamond-free ones. This compositional dissimilarity is compatible with formation of
diamond-bearing rocks, inclusions and intergrowths in chambers of partially melted
peridotite-eclogite-carbonatite-sulphide-carbon system of changeable composition. However,
diamond-free rocks are products of upper-mantle magmatism based on carbonatite-free
peridotite-eclogite-sulphide-carbon system. Chambers of diamond-parental carbonatite
magma may originate and evolve by: (1) metasomatic-magmatic stage resulted in partial
carbonatization of mantle peridotite under attack of K-CO2-bearing metasomatic
agents and generation of carbonate melts; (2) dissolving-magmatic stage when major
and accessory minerals of peridotite host-rock, volatiles and carbon dissolve in
carbonate melt whereas insoluble sulphide phases penetrate into melts; eventually,
completely miscible peridotite-carbonatite-carbon magma parental for diamond and
paragenetic minerals (hosting xenogenetic sulphide minerals and melts) are formed;
(3) fraction-crystallization stage (in chamber consolidated into a self-dependent
body) during natural cooling of parental magma up to solidus temperature; the
cooling activates physicochemical control that is created by PT-phase relations for the
parental magma composition, i.e., syngenesis phase diagram on a representative
polythermal section of peridotite-eclogite-carbonatite-diamond system at 7 GPa under
conditions of fractional crystallization (Litvin, 2013). Parental carbonatite melts, while
compositionally evolve under fractional crystallization, are physicochemically capable to
form diamond and sequentially minerals of peridotitic and eclogitic parageneses
(presented as primary inclusions in diamonds). Paragenetic peridotite-eclogite transition
in the course of ultrabasic-basic fractional evolution of parental melts is revealed
in physicochemical experiments as the effect of “peridotite-to-eclogite” tonnel
(Litvin, 2013). Diamond-bearing peridotite and eclogite rocks and intimate mineral
intergrowths with diamond are also formed in the chambers of diamond-parental
carbonatite magmas under these physicochemical conditions. Diamond-free rocks among
mantle xenoliths in kimberlites represent samples of the enclosing host-rocks for the
chambers of diamond-parental carbonatite magma. Support: grant of the RF President
#MK-1386.2013.5, RFBR grants 12-05-33044, 13-05-00835 and 14-05-00537. |
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