Formation of
diamond and syngenetic minerals in the mantle multi-component
silicate-carbonate-sulfide-carbon substance: the key role of carbonatites
Litvin Yu.A.*, Kuzyura
(Shushkanova) A.V.*, Bobrov A.V.**,
Vasilyev P.G.**, Okoyomova
V.Yu.**
*Institute of
Experimental Mineralogy, Chernogolovka, Russia; **Moscow State University,
Moscow, Russia.
In this work, melting phase
relations of multi-component multi-phase system composed of eclogitic omphacite
(Omph-Cpx) + garnet (Grt) assemblage,
K-Mg-Ca-carbonatite, sulfide pyrrhotite (Po) + pentlandite (Pn) + chalcopyrite
(Ccp) material and carbon (graphite, diamond) is first physico-chemically studied in
high-pressure high-temperature experiment in the context of diamond genesis. In
general [1], experimental physico-chemical research of diamond origin in the
Earths mantle calls for compositions of starting materials that are chemically
close to or reproduce important constituent parts of the multi-component diamond-parent
medium of essential chemical variability.
At present, the criterion of syngenesis
of diamonds and their primary inclusions [2] is crucial for physico-chemical
experimental untangling petrological and mineralogical details of diamond
genesis. In connection with this, ซsyngenesisป phase diagram is solely suited and
most informative. The syngenesis diagram
is taken its name from the fact that it unravels the physico-chemical ซsecretsป
of syngenetic relations between diamond and all the other solid, liquid and volatile
components and phases involved into diamond-forming processes under specific
chemical and PT physical conditions. The syngenesis diagram of the
multi-component system under study at 7.0 GPa is represented by its two-measure
pseudo binary section ซeclogite28carbonatite42sulfide30
diamondป (wt. %) where {eclogite = [(Grt: SiO2 40.00, TiO2
0.46, Al2O3 22.00, Cr2O3 0.04, FeO
20.90, MnO 0.52, MgO 9.02, CaO 8.18, Na2O 0.17)40(Omph-Cpx:
SiO2 54.80, TiO2 0.48, Al2O3 9.79,
Cr2O3 0.05, FeO 6.40, MnO 0.07, MgO 8.97, CaO 13.10, Na2O
6.70, K2O 0.30)60]}28{carbonatite = (K2CO3)50(MgCO3)25(CaCO3)25}42{sulfide
= [Po: FeS]40[Pn: (Fe, Ni)9S8]40[Ccp:
CuFeS.2)20]}30; graphite is used as starting
carbon material. Major constituent parts of the whole system under study are ซeclogite40carbonatite60
diamondป and ซsulfide diamondป systems which were taken separately for
experimental study. Two separate silicate40carbonate60
(carbonatite) diamond and sulfide - diamond syngenesis diagrams were
constructed at 7.0 GPa. The curves of diamond solubility in carbonatite and
sulfide melts under partial and complete melting of the systems are determined
and plotted as the key details of the proper diagrams. The curves (together
with solidus lines) are boundary for P-T-composition conditions of
diamond-forming phase fields and important for understanding the
physico-chemical mechanism of diamond formation.
Earlier
experimental study of the simplified silicate-carbonate-sulfide system [3, 4]
demonstrates the complete carbonate-silicate liquid miscibility as well as
complete immiscibility of homogeneous carbonate-silicate and sulfide melts
which both are effective diamond-forming media. It was also found that
syngenetic formation of diamond with silicate and carbonate minerals in
diamond-forming sulfide melt is impossible because solubility of silicate and
carbonate components in sulfide melts is critically low.
The
effect of complete immiscibility of carbonatite and sulfide melts makes
possible to superpose the both sub-system diagrams experimentally studied here
by projecting the image of one of them onto another one. As a result the
combined syngenesis diagram for the whole eclogite-carbonatite-sulfide-diamond
system is constructed. Special controlling experiments testify the validity of
the combined syngenesis diagram. The pseudo binary diagram demonstrates clearly
the interrelation between syngenesis conditions of diamond and trapped phases in
dependence of PT parameters. In accordance with temperature and composition
(pressure is constant in this case), conditions of syngenetic formation of
diamond with silicate-carbonate (carbonatite) and sulfide melts, garnet,
sulfide solid solution, clinopyroxene and carbonate minerals as well as their
assemblages go evident. Hence the syngenesis diagram reveals potential scenarios
of capturing each of the coexisting phases by growing diamond and PT conditions
for these events.
Present
experimental study is motivated by (1) a close natural association of diamond
with silicate, carbonate and sulfide minerals and melts which is identified by
thorough mineralogical study of the growth inclusions in diamond [5-9], (2)
still disputable estimation of chemical composition of diamond-parent medium
between mineralogists that is contradictory favored as predominant silicate [10,
11], metal [12, 13], carbonatite [14, 15], kimberlite [16, 17], sulfide [18, 19], C-O-H volatile [20, 21] one
and (3) the first high-pressure experimental results for melting phase
relations of extremely simplified silicate (pyrope) carbonate (aragonite)
sulfide (pyrrhotite) system under PT conditions of diamond stability [3, 4].
The
resulting data of this study as well as relevant experimental and mineralogical
data support the view [2] that multi-component carbonatite (carbonate-silicate)
melt of variable composition is of decisive importance in origin of the most
mantle-derived diamonds and their syngenetic inclusions. The heart of the diamond-parent
carbonatite medium is argued as completely miscible carbonate-silicate melt
over-saturated with dissolved elemental carbon. The carbonatite melt hosts minor
chemically variable components and phases as miscible and soluble (phosphate,
chloride, C-O-H volatile, etc) so immiscible and insoluble (sulfides, native
metals, etc). Influence of the immiscible components on PT conditions and
kinetics of diamond nucleation and crystallization in parent carbonatite melts
seems not to be essential. Influence of the soluble components may be more
perceptible but not critical because of their comparatively lowered content in parent
carbonatite melt (a steady-state of C-O-H volatile phases under mantle
conditions is of low probability).
Reliable
approximation of the parent composition is multi-component system MgO CaO -
FeO (Fe, Fe2O3) MnO Na2O K2O
Al2O3 Cr2O3 TiO2
ZrO2 - SiO2 P2O5 CuS (Cu2S)
FeS (FeS2) NiS KCl NaCl SiC CO2 (CO, CH4)
H2O C. Congruent carbonate melting, complete carbonate-silicate
liquid miscibility and high elemental carbon solubility in carbonatite melts
under conditions of diamond PT stability are key factors in formation of
diamond-parent carbonatite melt.
Process
of formation of parent medium for diamonds relates to conditions of origin of
carbonatite magma in Earths mantle. The process may begin with metasomatic
mantle peridotite carbonatization by chemically active volatile C-O-H agents of
plume origin. Ensuing formation and evolution of carbonate-silicate magma with
hosting miscible components (including carbon) and immiscible phases lead to
multi-component diamond-forming carbonatite.
Experimental
study of physico-chemical role of the components highly soluble in multi-component
diamond-parent carbonatite melts (C-O-H volatile is among them) becomes urgent.
This
study is supported by the INTAS project 05-1000008-793,RFBR grants
08-05-00110-a and 09-05-00751-a..
References:
1.
Litvin Yu.A., Butvina V.G. Diamond-forming media in the system
eclogite-carbonatite-sulfide-carbon: experiments at 6.0-8.5 GPa. Petrology.
2004. Vol. 12. P. 377-387.
2. Litvin Yu.A. High-pressure
mineralogy of diamond genesis. In Advances in High-Pressure Mineralogy
(E. Ohtani, ed.). Geological Society of America Special Paper 421. 2007. P.
83-103.
3.
Shushkanova A.V., Litvin Yu.A. Phase relations in diamond-forming
carbonate-silicate-sulfide systems on melting //Russian Geology and Geophysics.
2005. Special N.V. Sobolev vol. 46. No. 12. P. 1317-1326.
4.
Shushkanova A.V., Litvin Yu.A. Experimental evidence for liquid immiscibility
in the model system CaCO3 pyrope pyrrhotite at 7.0 GPa: the role
of carbonatite and sulfide melts in diamond genesis. The Canadian Mineralogist.
2008. Special J. Gittins vol. 46. P. 991-1005.
5. Stachel T., Harris J.W., Brey G.P. Rare and
unusual mineral inclusions in diamonds from Mwadui, Tanzania // Contributions
to Mineralogy and Petrology. 1998. Vol. 132. P. 34-47.
6. Klein-BenDavid
O., Logvinova A.M., Izraeli E.S., Sobolev N.V., Navon O. Sulphide melt
inclusions in Yubileinaya (Yakutia) diamonds// Victoria, Canada, VIII
International Kimberlite Conference Long Abstract. Mineralogical Society of
America. CD-ROM FLA_0119.
7. Taylor
L.A., Anand M. Diamonds: time capsules from the Siberian mantle // Chemie der
Erde. 2004. Vol. 64. P. 1-74.
8. Titkov
S.V., Gorshkov A.I., Zudin N.G., Ryabchikov I.D., Magazina L.O., Sivtsov A.V.
Microinclusions in dark-grey diamond crystals of octahedral habit from
kimberlites of Yakutia // Geochemistry (Geokhimia). 2006. No 11. P. 1209-1217
(in Russian).
9. Logvinova
A.M., Wirth R., Fedorova E.N., Sobolev N.V. Nanometre-sized mineral and fluid
inclusions in cloudy Siberian diamonds: new insights on diamond formation //
European Journal of Mineralogy. 2008. Vol. 20. P. 317-331.
10.
Williams A.F. The Genesis of Diamond (2 volumes). London: E. Benn Ltd. 1932.
636 p.
11.
Marakushev A.A., Pertsev N.N., Zotov I.A., Paneyakh N.A., Cherenkova A.F. Some
petrological aspects of diamond genesis // Geology of Ore Deposits (Geologia
Rudnykh Mestorojdeniy). 1995. Vol. 37. N2. P. 105-121 (in Russian).
12.
Wentorf R.H., Bovenkerk H.P. On the origin of natural diamonds // Journal of
Astrophysics. 1961. Vol. 134. P. 995-1005.
9. Chepurov
A.I., Fedorov I.I., Sonin V.M. Experimental study of diamond formation under
high PT-parameters // Geology and Geophysics (Geologia i Geophysica). 1998.
Vol. 39. No 2. P. 234-244 (in Russian).
13.
Von Eckermann H.A. Comparison og Swedish, African and Russian kimberlites In P.J. Wyllie (ed.). Ultramafic and
Related Rocks. New York: John Wiley and Sons. 1967. P. 302-312.
14.
Litvin Yu.A., Litvin V.Yu., Kadik A.A. Experimental characterization of diamond
crystallization in melts of mantle silicate-carbonate-carbon systems at 7.0 GPa
// Geochemistry International. 2008. Vol. 46. P. 531-553.
15.
Sobolev V.S. Conditions of diamond formation // Geology and Geophysics
(Geologia i Geophysica). 1964. No. 1. P. 3-20 (in Russian).
16.
Arima M., Nakayama K., Akaishi M., Yamaoka S., Kanda H. // Crystallization of
diamond from a silicate melt of kimberlite composition in high-pressure and
high-temperature experiments // Geology. Vol. 21. P. 968-970.
17.
Marks P.S. Pyrrhotite and the origin of terrestrial diamonds // Mineralogical
Magazine. 1972. Vol. 38. P. 636-638.
18.
Bulanova G.P., Griffin W.L., Ryan C.G. Nucleation environment of diamonds from
Yakutian kimberlites // Mineralogical Magazine. 1998. Vol. 62. No. 3. P.
409-419.
19. Haggerty
S.E. Diamond genesis in a multiply constrained model // Nature. 1986. Vol. 320.
P. 34-38.
20.
Sokol A.G., Palyanov Yu.N. Diamond crystallization in fluid and
carbonate-fluid systems under mantle PT parameters. Part. 2. Pecuilarities of
diamond-forming processes (analytical review of experimental data) //
Geochemistry (Geokhimia). 2004. No. 11. P. 1157-1172 (in Russian).