Mg and Fe-rich carbonate–silicate high-density fluids in cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia) (original) (raw)
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High-Mg carbonatitic microinclusions in some Yakutian diamonds—a new type of diamond-forming fluid
Lithos, 2009
The composition of microinclusions in 26 fibrous cubic and coated diamonds from the Daldyn-Alakit kimberlite field, Yakutia were studied using EPMA and FTIR and the carbon isotopic composition of 4 of the diamonds was studied using SIMS. Fifteen diamonds carry carbonatitic high-density fluids (HDFs) with high MgO content (17-28 wt.%) whereas the MgO content of fluids in other diamonds does not exceed 14 wt.%. We propose that the two groups are distinct and evolved separately. The low-Mg suite is similar to previously reported carbonatitic to silicic HDFs from Africa and Brazil. The high-Mg suite is carbonatitic, but its composition is distinct from previously defined end-members. As the MgO content decreases from 28 to 17 wt.%, CaO, Na 2 O, K 2 O and Cl also decrease while the silica, Al 2 O 3 , TiO 2 and P 2 O 5 contents remain constant. Additionally, the water band in the FTIR spectra of high-Mg HDFs is wider relative to the water band in the spectra of low-Mg carbonatitic HDFs. By combining EPMA and FTIR data, we have constrained the major element composition of the high-Mg carbonatitic end-member, which comprises 78 wt.% carbonates, 9% silicates, 6% water, 5% apatite and 2% halides. The composition of the high-Mg suite is closer to that of near-solidus melts of fertile carbonate peridotites and harzburgites. Thus, it should be possible to produce the Mg-rich HDF either by incipient melting, or by cooling and crystallization of a proto-kimberlitic melt at depth. However, the peridotitic system alone cannot explain the high alkali and Cl content of the fluids. We suggest that the elevated alkali and Cl content of the high-Mg carbonatites are related to interaction of carbonate peridotite with saline fluids, or of peridotite with chloridecarbonate melts. The major element composition of the high-Mg carbonatitic HDF is dominated by the lowfraction melts of the peridotite while the content of potassium and other incompatible elements is influenced by the contribution of the saline or carbonatitic fluids.
Minerals, 2019
The microinclusions in cuboid diamonds from Ebelyakh River deposits (northeastern Siberian craton) have been investigated by FIB/TEM techniques. It was found that these microinclusions have multiphase associations, containing silicates, oxides, carbonates, halides, sulfides, graphite, and fluid phases. The bulk chemical composition of the microinclusions indicates two contrasting growth media: Mg-rich carbonatitic and Al-rich silicic. Each media has their own specific set of daughter phases. Carbonatitic microinclusions are characterized by the presence of dolomite, phlogopite, apatite, Mg, Fe-oxide, KCl, rutile, magnetite, Fe-sulfides, and hydrous fluid phases. Silicic microinclusions are composed mainly of free SiO2 phase (quartz), high-Si mica (phengite), Al-silicate (paragonite), F-apatite, Ca-carbonates enriched with Sr and Ba, Fe-sulfides, and hydrous fluid phases. These associations resulted from the cooling of diamond-forming carbonatitic and silicic fluids/melts preserved i...
The trace element composition of silicate inclusions in diamonds: a review
Lithos, 2004
On a global scale, peridotitic garnet inclusions in diamonds from the subcratonic lithosphere indicate an evolution from strongly sinusoidal REE N , typical for harzburgitic garnets, to mildly sinusoidal or ''normal'' patterns (positive slope from LREE N to MREE N , fairly flat MREE N -HREE N ), typical for lherzolitic garnets. Using the Cr-number of garnet as a proxy for the bulk rock major element composition it becomes apparent that strong LREE enrichment in garnet is restricted to highly depleted lithologies, whereas flat or positive LREE -MREE slopes are limited to less depleted rocks. For lherzolitic garnet inclusions, there is a positive relation between equilibration temperature, enrichment in MREE, HREE and other HFSE (Ti, Zr, Y), and decreasing depletion in major elements. For harzburgitic garnets, relations are not linear, but it appears that lherzolite style enrichment in MREE -HREE only occurs at temperatures above 1150 -1200 jC, whereas strong enrichment in Sr is absent at these high temperatures. These observations suggest a transition from melt metasomatism (typical for the lherzolitic sources) characterized by fairly unfractionated trace and major element compositions to metasomatism by CHO fluids carrying primarily incompatible trace elements. Melt and fluid metasomatism are viewed as a compositional continuum, with residual CHO fluids resulting from primary silicate or carbonate melts in the course of fractional crystallization and equilibration with lithospheric host rocks.
Russian Geology and Geophysics, 2011
The first data are presented on the compositions of microinclusions in fibrous diamonds from the Ebelyakh placers, northeastern Siberian Platform. Their fluid/melt microinclusions are of silicate or carbonate compositions. In general, the trace element patterns for the microinclusions correspond to kimberlites and carbonatites. The major-element composition differs significantly; for example, the microinclusions are considerably enriched in K and Na. In two of the studied diamonds, the microinclusion compositions differ considerably in the cores and rims. In one of them, the composition of the medium changes from chloride-carbonate to predominantly carbonate (sample HI-90); in the other one, from carbonate to silicate (sample HI-98). Similar carbon isotope characteristics of diamonds with microinclusions of two contrasting media might suggest their crystallization from a mantle reservoir with the same carbon isotope characteristics. The geochemical features of the microinclusions in the placer diamonds revealed their relationship with protokimberlitic carbonate-silicate fluids. Such fluids might result from the metasomatic interaction of volatiles and/or the low-degree partial melting of peridotite and eclogite substrates.
Diamonds and the Geology of Mantle Carbon
Reviews in Mineralogy and Geochemistry, 2013
Coated diamond in (a) is an optical photomicrograph, plane light courtesy Ofra Klein-Bendavid. Diameter of diamond is 1 cm. Coated diamond (b) from the Congo (alluvial) is a catholuminescence (CL) image (Used by permission of Elsevier Limited, from Kopylova et al. (2010) Earth and Planetary Science Letters, Vol. 291, Fig. 1, p. 128). Dots indicate positions of analyzed inclusions, scale bar is 0.6 mm. Diamonds in (c) and (d) are from Orapa, Botswana. They are both about 6 mm across. The color CL images show multiple growth histories with significant resorption in (c) after a first stage of growth. Note the very thin growth rings in (d). Diamonds (e) and (f) are gray-scale CL images of sub-lithospheric diamonds from the Collier 4 kimberlite pipe, Juina field, Brazil (Used by permission of Springer, from Bulanova et al. (2010) Contributions to Mineralogy and Petrology, Vol. 160, Figs. 3d,e, p. 493). Diamond in (e) is about 3 mm on the long axis. Note the irregular zoning in both diamonds.
Silicate and carbonate melt inclusions associated with diamonds in deeply subducted carbonate rocks
Earth and Planetary Science Letters, 2006
Deeply subducted carbonate rocks from the Kokchetav massif (Northern Kazakhstan) recrystallised within the diamond stability field ( P = 4.5À6.0 GPa; T c 1000 8C) and preserve evidence for ultra high-pressure carbonate and silicate melts. The carbonate rocks consist of garnet and K-bearing clinopyroxene embedded in a dolomite or magnesian calcite matrix. Polycrystalline magnesian calcite and polyphase carbonate-silicate inclusions occurring in garnet and clinopyroxene show textural features of former melt inclusions. The trace element composition of such carbonate inclusions is enriched in Ba and light rare earth elements and depleted in heavy rare earth elements with respect to the matrix carbonates providing further evidence that the inclusions represent trapped carbonate melt. Polyphase inclusions in garnet and clinopyroxene within a magnesian calcite marble, consisting mainly of a tight intergrowth of biotite + K-feldspar and biotite + zoisite + titanite, are interpreted to represent two different types of K-rich silicate melts. Both melt types show high contents of large ion lithophile elements but contrasting contents of rare earth elements. The Ca-rich inclusions display high REE contents similar to the carbonate inclusions and show a general trace element characteristic compatible with a hydrous granitic origin. Low SiO 2 content in the silicate melts indicates that they represent residual melts after extensive interaction with carbonates. These observations suggest that hydrous granitic melts derived from the adjacent metapelites reacted with dolomite at ultra high-pressure conditions to form garnet, clinopyroxene -a hydrous carbonate melt -and residual silicate melts. Silicate and carbonate melt inclusions contain diamond, providing evidence that such an interaction promotes diamond growth. The finding of carbonate melts in deeply subducted crust might have important consequences for recycling of trace elements and especially C from the slab to the mantle wedge. D 2005 Elsevier B.V. All rights reserved.