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Diamonds from the Rio Sorriso placer in the Juina area, Mato Grosso State, Brazil, contain mineral inclusions of ferropericlase associated with MgSiO3, CaSiO3, magnesite, merrillite, and other minerals. The ferropericlase inclusions in Rio Sorriso diamonds are resolved into two distinct genetic and compositional groups: (1) protogenetic, high-Ni and low-Fe (Ni = 8270–10,660 ppm; mg# = 0.756–0.842) ferropericlases, and (2) syngenetic, low-Ni and high-Fe (Ni = 600–3050 ppm; mg# = 0.477–0.718) ferropericlases. Based on the crystallographic orientation relationships between natural ferropericlase inclusions and host diamonds, high-Ni and low-Fe ferropericlases originate in the upper part of the lower mantle, while low-Ni and high-Fe ferropericlases, most likely, originate in the lithosphere. Mineral inclusions form the ultramafic lower-mantle (MgSiO3, which we suggest as bridgmanite, CaSiO3, which we suggest as CaSi-perovskite, and high-Ni and low-Fe ferropericlase) and lithospheric (CaSiO3, which we suggest as breyite, Ca(Si,Ti)O3, and low-Ni and high-Fe ferropericlase) associations. The presence of magnesite and merrillite inclusions in association with ferropericlase confirmed the existence of a deep-seated carbonatitic association. Diamonds hosting high-Ni and low-Ni ferropericlase have different carbon-isotopic compositions (δ13C = −5.52 ± 0.75‰ versus −7.07 ± 1.23‰ VPDB, respectively). It implies the carbon-isotopic stratification of the mantle: in the lower mantle, the carbon-isotopic composition tends to become isotopically heavier (less depleted in 13C) than in lithospheric diamonds. These regularities may characterize deep-seated diamonds and ferropericlases not only in the Juina area of Brazil but also in other parts of the world. [ABSTRACT FROM AUTHOR]

A suite of coated diamonds from the International'naya (n = 63) and Mir (n = 5) kimberlite pipes (Mirny field, Siberian craton) was studied to track the most recent metasomatic events in the sub-continental lithospheric mantle (SCLM). The diamonds consist of two contrasting domains: an older monocrystalline core, and a younger fibrous coat, the latter of which formed just prior to the kimberlite eruption. Microinclusions in the coats indicate two types of growth media: (i) dominant, silicic to low-Mg carbonatitic high-density fluids (HDFs), and (ii) minor, high-Mg carbonatitic HDFs. Eclogitic mineral inclusions were identified in the cores of the diamonds containing silicic to low-Mg carbonatitic HDFs in the coats, while peridotitic mineral inclusions were found in the cores of the diamonds with high-Mg carbonatitic HDFs in the coats. The chemistry of the high-Mg carbonatitic HDFs suggests that they originated from partial melting of a carbonated peridotite. Major components and trace-element patterns of most silicic to low-Mg carbonatitic HDFs support an eclogitic source with accessory rutile and variable ratios of CO2/H2O. In many coats, the HDFs evolve from silicic to more carbonatitic, and rarely from carbonatitic to more silicic. The scenario of both evolutionary trends could have involved the passage of peridotite-derived carbonatitic HDFs into eclogites, which triggered their partial melting, followed by the appearance of immiscible, highly silicic and Ca-rich carbonatitic fluids/melts. The immiscible fluids evolved toward a single-silicate–carbonate melt, whose cooling resulted in the precipitation of silicate minerals. [ABSTRACT FROM AUTHOR]

Merrillite, ideally Ca18Na2Mg2(PO4)14 (Dana No: 38.03.04.04; Strunz No: 08.AC.45), an analog to synthetic tricalcium phosphate β-Ca3(PO4)2, was identified as an inclusion in lower-mantle diamonds from the Rio Soriso area, Brazil. It was associated with former bridgmanite, CaSi- and CaTi-perovskites, and ferropericlase. This is the first report of merrillite in a terrestrial environment; previously, it was known only in meteorites and lunar rocks. The compositions of merrillite vary in different localities; the Rio Soriso sample was enriched in SO3 (2.03 wt%). Merrillite from lower-mantle diamonds may be a retrograde phase of the tuite [γ-Ca3(PO4)2]. Owing to their crystal structures, both merrillite and tuite may be important potential hosts for rare earth elements (REE) and large ion lithophile elements (LILE), including Sr and Ba, in the deep Earth. The find of merrillite suggests a larger variety of mineral species in the lower mantle than previously assumed. [ABSTRACT FROM AUTHOR]

In the present work, diamonds with yellow cores and a slightly colored or colorless rims have been studied. Three groups of crystals that differ in spectroscopic features have been identified. In the crystals of the first group, the heterogeneity in color is due to the variation in nitrogen concentration, which is present as the simplest low-temperature nitrogen C center. Absorption spectra of the first group display peaks at wavenumbers 1344 and 1332 cm-1 of C and C+ centers, respectively. The second group also exhibits higher nitrogen concentrations in the form of C centers in the colored zone. However, the concentration of nitrogen in the form of high temperature C-centers, and the total nitrogen content is higher at the periphery of crystals. The FTIR absorption spectra of this group display both 1344 and 1332 cm-1 peaks. Crystals of the third group do not contain C centers. The 1332 cm-1 and the A center bands are observed in the FTIR absorption spectra. In the photoluminescence spectra of the colored zone of the third group, the bands S1 and S2 have been found and the doublet lines 883 and 885 nm of the simplest Ni-containing centers. Previously unobserved systems with zerophonon lines at 799.5, 819.6, 869.5 and 930 nm lines have been registered in the photoluminescence spectra of the third group under 787 nm excitation. It is hereby proposed that this luminescence is due to Ni-containing centers. In the third group of crystals, Ni seems to stabilize C+ centers and hence the coloring of crystal zones is consistent with Ni impurity distribution. Crystals of each group have distinct sources: the first group is from Yubileinaya pipe, the second from the placers of North Yakutia with unknown primary sources and the third from the Uralian deposits. [ABSTRACT FROM AUTHOR]

The paper presents new data on the internal structure of super-deep (sublithospheric) diamonds from Saõ-Luiz river placers (Brazil) and from alluvial placers of the northeastern Siberian platform (Yakutia). The sublithospheric origin of these diamonds is supported by the presence of mineral inclusions corresponding to associations of the transition zone and lower mantle. The features of morphology and internal structure have been studied by optical and scanning electron microscopy (SEM), cathodoluminescence topography (CL), and electron backscatter diffraction (EBSD) techniques. Diamonds typically have complicated growth histories displaying alternating episodes of growth, dissolution, and post-growth deformation and crushing processes. Most crystals have endured both plastic and brittle deformation during the growth history. Abundant deformation and resorption/growth features suggest a highly dynamic growth environment for super-deep diamonds. High temperatures expected in the transition zone and lower mantle could explain the plastic deformations of super-deep diamonds with low nitrogen content. [ABSTRACT FROM AUTHOR]

Five typical coated diamonds (from Udachnaya, Yubileynaya, and Aikhal kimberlite pipes) with untypically low microinclusion abundances and four monocrystalline diamonds (Udachnaya, Mir, Nyurbinskaya pipes) that exhibit thin intermediate microinclusion-bearing zones were examined in details for growth structures, characteristic infrared absorption and photoluminescence, and composition of microinclusions. The internal structures of diamonds of both types imply that fluid inclusions entrapment in diamonds does not necessarily relate to the terminal stage of rapid fibrous growth. Instead, nitrogen aggregation state in some diamonds showed that both fibrous coats and inclusion-bearing layers might experience an annealing during mantle residence long enough to pre-date the ultimate kimberlite eruption, whereas the diamonds with internal inclusion-bearing zones also experienced later protracted history of monocrystalline growth. The presence of chloride-carbonate-silicate fluids/melts in monocrystalline diamonds indicate their generation from media generally similar to that observed in some fibrous diamonds. However, the composition of these metasomatizing fluids is different for the mantle beneath Udachnaya (mostly carbonatitic) and other pipes (Aikhal, Yubileynaya, Mir; variable abundance of silicic high-density fluids). The abundance of silica-rich fluids record either a heterogeneous distribution of eclogites in the subcontinental lithospheric mantle, or the operation of silica-rich slab-derived fluids. The inclusion abundance as well as the type of growth (fibrous or monocrystalline) is considered to be controlled by the volume of fluid fluxes; in this case, fluid consumption leads to decreasing growth rates, diminishing inclusion entrainment and stability of layered octahedrons. The detected minor compositional variations of high-density fluids in these diamonds may be due to local scale thermal perturbation in the host source and/or limited chemical heterogeneity of the parental fluid. The high amount of chlorides in high-density fluids from monocrystalline diamonds provide a new evidence for compositions of fluids/melts acting as primary metasomatic agent in the deep mantle of Siberian craton. [ABSTRACT FROM AUTHOR]

Cuboid diamonds are particularly common in the placers of the northeastern Siberian platform, but their origin remains unclear. These crystals usually range in color from dark yellow to orange and, more interestingly, are characterized by unusual low aggregated nitrogen impurities (non-aggregated C-center), suggesting a short residence time and/or low temperatures at which they have been stored in the mantle. In order to track possible isotopic signature that could help deciphering cuboid diamond's crystallization processes, δ13C values, δ15N values, and nitrogen concentrations have been determined in situ in three samples using secondary ion mass spectrometry (SIMS), whereas nitrogen aggregation states have been determined by FTIR spectroscopy. The samples fall out of the δ13C vs. δ15N field of canonical mantle composition. Different scales of carbon and nitrogen fractionation may produce the observed variations. Alternatively, mixing mantle and crustal material would obscure initial co-variations of δ13C values with δ15N or nitrogen content. [ABSTRACT FROM AUTHOR]

Notable within-crystal variability of mineralogical and geochemical properties of single natural diamonds are commonly attributed to changing chemistry of parental fluids, sources of carbon and redox conditions of diamond precipitation. A distinct type of compositional heterogeneity (mixed-habit structure) is well-known to occur in diamonds as well as in many other minerals due to purely 'structural' reasons that are unequal crystal chemistry of crystallographically different faces and selective absorption and fractionation of impurities between adjacent growth pyramids. Based on the combined cathodoluminescence, Fourier-transformed infrared spectroscopy and photoluminescence spectroscopy, study of nine diamond crystals with different growth histories and external morphology, but all showing mixed-habit patterns at different growth stages, we show that mixed-diamonds may grow in closed system conditions or with a slowly decreasing growth rate from a media with a much lower impurity content than previously thought. Intracrystal nitrogen distribution seems to be a function of growth rate even in the cases of unusual impurity partitioning between growth sectors. Generally poor with IR-active hydrogen at moderate nitrogen aggregation parameters, studied diamonds likely resemble the low hydrogen content from the growth medium that, for cubic diamonds, was typically suggested hydrogen-rich and a crucial factor for growth of cubic and mixed-habit diamonds. We also show that mixed-habit diamond growth may occur not only in peridotitic suite but also in an extended field of geochemical affinities from high-Ni to low-Ni or maybe even Ni-free environments, such as pyroxenitic or eclogitic. [ABSTRACT FROM AUTHOR]

Microinclusions of high-density fluids (HDF's) occur in cloudy diamonds from the Mir and Internatsionalnaya kimberlite pipes (Malobotuobia kimberlite field, Siberian platform). These HDFs are of typical high-Mg carbonatitic composition; a few diamonds contain microinclusions that define a low-Mg carbonatitic to silicic trend. The observed variations are interpreted as resulted from mixing of two contrasting fluids derived from the partial melting mainly of carbonated peridotite (the high-Mg carbonatitic HDFs) and eclogite (silica-rich HDFs and HDFs with high Ca/(Ca + Mg + Fe)). Immiscibility of carbonatitic and silica-rich fluids provides a possible mechanism for the co-existence of the observed HDFs but needs further proof. The uniform carbon isotope composition of cloudy diamonds with high-Mg carbonatitic microinclusions from both kimberlite pipes implies a single peridotitic source. [ABSTRACT FROM AUTHOR]

We report cloudy micro- and nano-inclusions in a superdeep diamond from São-Luiz, Brazil which contains inclusions of ferropericlase (Mg, Fe)O and former bridgmanite (Mg, Fe)SiO and ringwoodite (Mg, Fe)SiO. Field emission-SEM and TEM observations showed that the cloudy inclusions were composed of euhedral micro-inclusions with grain sizes ranging from tens nanometers to submicrometers. Infrared absorption spectra of the cloudy inclusions showed that water, carbonate, and silicates were not major components of these micro- and nano-inclusions and suggested that the main constituent of the inclusions was infrared-inactive. Some inclusions were suggested to contain material with lower atomic numbers than that of carbon. Mineral phase of nano- and micro-inclusions is unclear at present. Microbeam X-ray fluorescence analysis clarified that the micro-inclusions contained transition metals (Cr, Mn, Fe, Co, Ni, Cu, Zn) possibly as metallic or sulfide phases. The cloudy inclusions provide an important information on the growth environment of superdeep diamonds in the transition zone or the lower mantle. [ABSTRACT FROM AUTHOR]

Diamonds of eclogitic assemblages are dominant in the placer diamond deposits of the northeastern Siberian platform. In this study we present new trace elements and stable isotopes (δ 13 C and δ 18 O) data for alluvial diamonds and their garnet inclusions from this locality. Cr-rich garnets of peridotitic affinity in the studied diamonds have a narrow range of δ 18 O values from 5.7‰ to 6.2‰, which is largely overlapping with the accepted mantle range. This narrow range suggests that the garnet inclusions showing different REE patterns and little variations in oxygen isotopes may have formed by different processes involving fluid/melts that, however, were in oxygen isotopic equilibrium with the mantle. The trace element composition of the eclogitic garnet inclusions supports a crustal origin for at least the high-Ca garnets, which show flat HREE patterns and in some cases a positive Eu-anomaly. High-Ca eclogitic garnets generally show heavier oxygen isotope compositions (δ 18 O 6.5–9.6‰) than what is observed in low-Ca garnets (δ 18 O 5.7–7.4‰). The variability in oxygen isotopes and trace elements is suggested to be inherited from contrasting crustal protoliths. The relationship between the high δ 18 O values of inclusions and the low δ 13 C values of the host diamonds implies that the high-Ca garnet inclusions were derived from intensely hydrated (e.g., δ 18 O > 7‰) and typically oxidised basaltic rock close to the seawater interface, and that the carbon for diamonds was closely associated with this protolith. [ABSTRACT FROM AUTHOR]

The composition of clinopyroxenes is indicative for chemical and physical properties of mantle substrates. In this study, we present the results of Raman spectroscopy examination of clinopyroxene inclusions in natural diamonds (n = 51) and clinopyroxenes from mantle xenoliths of peridotites and eclogites from kimberlites (n = 28). The chemical composition of studied clinopyroxenes shows wide variations indicating their origin in different mantle lithologies. All clinopyroxenes have intense Raman modes corresponding to metal-oxygen translation (~300–500 cm−1), stretching vibrations of bridging O-Si-Obr (ν11~670 cm−1), and nonbridging atoms O-Si-Onbr (ν16~1000 cm−1). The peak position of the stretching vibration mode (ν11) for the studied clinopyroxenes varies in a wide range (23 cm−1) and generally correlates with their chemical composition and reflects the diopside-jadeite heterovalent isomorphism. These correlations may be used for rough estimation of these compounds using the non-destructive Raman spectroscopy technique. [ABSTRACT FROM AUTHOR]

We present a new dataset on the composition of high-density fluids (HDFs) in cloudy (n = 25), coated (n = 10) and cuboid (n = 10) diamonds from the Nyurbinskaya kimberlite pipe. These diamonds represent different populations each showing distinct growth histories. The cores of coated diamonds display multiple growth stages and contrasting sources of carbon. Fibrous coats and cuboid diamonds have similar carbon isotopes and nitrogen systematics, suggesting their formation in the last metasomatic events related to kimberlite magmatism, as is common for most such diamonds worldwide. The HDFs in most of these diamonds span a wide range from low-Mg carbonatitic to hydrous silicic compositions. The major- and trace-element variations suggest that the sources for such HDFs range in composition between the depleted mantle and more fertile mantle reservoirs. Hydrous-silicic HDFs could originate from a 13C-enriched source, which originates through subduction of crustal metasedimentary material. Percolation of such HDFs through carbonated eclogites and peridotites facilitates the formation of cuboid diamonds and fibrous coats in the mantle section beneath the corresponding area of the Siberian craton. Cloudy diamonds represent an apparently older population, reflecting continuous diamond formation predominantly from high-Mg carbonatitic HDFs that caused discrete episodes of diamond precipitation. Their high Mg# and enrichment in incompatible elements support a metasomatized peridotitic source for these HDFs. [ABSTRACT FROM AUTHOR]

Kimberlites are igneous rocks that represent the deepest magmas originated from the mantle (>150 km) and typically occur within cratons. Kimberlites are hybrid rocks consisting of minerals of different origins: xenogenic minerals produced by the fragmentation of foreign mantle and crustal rocks (i.e., xenoliths and xenocrysts), primary minerals crystallized from kimberlite melt, and later minerals formed during the post-magmatic alteration of kimberlites. Garnet, chromite, ilmenite, chrome-diopside, and olivine serve as kimberlite indicator minerals because they occur in kimberlites in significantly higher quantities than diamonds. Influences of kimberlite-related melt preceding kimberlite eruption and transporting kimberlite melt caused the formation of a number of metasomatic phases in the eclogite. [Extracted from the article]

(Mg,Fe)SiO 3 bridgmanite is the dominant phase in the lower mantle; however no naturally occurring samples had ever been found in terrestrial samples as it undergoes retrograde transformation to a pyroxene-type structure. To identify retrograde phases of former bridgmanite single-phase and composite inclusions of (Mg,Fe)SiO 3 in a series of superdeep diamonds have been examined with electron microscopy, electron microprobe, Raman spectroscopy and X-ray diffraction techniques. Our study revealed that (Mg,Fe)SiO 3 inclusions are represented by orthopyroxene. Orthopyroxenes in single-phase and composite inclusions inherit initial chemical composition of bridgmanites, including a high Al and low Ni contents. In composite inclusions they coexist with jeffbenite (ex-TAPP) and olivine. The bulk compositions of these composite inclusions are rich in Al, Ti, and Fe, which are similar but not fully resembling Al-rich bridgmanite produced in experiments on the MORB composition. The retrograde origin of composite inclusions due to decomposition of Al-rich bridgmanite may be doubtful because each of observed minerals may represent coexisting HP phases, i.e. bridgmanite or ringwoodite. • Former bridgmanite is presented in diamonds as single-phase and composite inclusions. • The retrograde phase of former bridgmanite is orthopyroxene. • Composite inclusions with bridgmanite originates from UM/LM boudary. [ABSTRACT FROM AUTHOR]

The variety of morphology and properties of natural diamonds reflects variations in the conditions of their formation in different mantle environments. This study presents new data on the distribution of impurity centers in diamond type Ib-IaA from xenolith of bimineral eclogite from the Udachnaya kimberlite pipe. The high content of non-aggregated nitrogen C defects in the studied diamonds indicates their formation shortly before the stage of transportation to the surface by the kimberlite melt. The observed sectorial heterogeneity of the distribution of C- and A-defects indicates that aggregation of nitrogen in the octahedral sectors occurs faster than in the cuboid sectors. [ABSTRACT FROM AUTHOR]

Microinclusions of high-density fluids (HDFs) were studied in coated diamonds from the Udachnaya kimberlite pipe (Siberian craton, Russia). The presence of C-centers in the coats testifies to their formation shortly before kimberlite eruption, whereas the cores have much longer mantle residence in chemically different mantle substrates, i.e., peridotite-type (P-type) and eclogite-type (E-type). The carbon isotope composition indicates an isotopically homogeneous carbon source for coats and a heterogeneous source for cores. Microinclusions in the coats belong to two groups: high-Mg carbonatitic and low-Mg carbonatitic to silicic. A relationship was found between high-Mg carbonatitic HDFs and peridotitic host rocks and between low-Mg carbonatitic to silicic and eclogites. The composition of high-Mg carbonatitic HDFs with a "planed" trace-element pattern can evolve to low-Mg carbonatitic to silicic during percolation through different mantle rocks. The compositional variations of microinclusions in the coats reflect this evolution. [ABSTRACT FROM AUTHOR]

New findings of silicate-melt inclusions in two alluvial diamonds (from the Kholomolokh placer, northeastern Siberian Platform) are reported. Both diamonds exhibit a high degree of N aggregation state (60–70% B) suggesting their long residence in the mantle. Raman spectral analysis revealed that the composite inclusions consist of clinopyroxene and silicate glass. Hopper crystals of clinopyroxene were observed using scanning electron microscopy and energy-dispersive spectroscopic analyses; these are different in composition from the omphacite inclusions that co-exist in the same diamonds. The glasses in these inclusions contain relatively high SiO2, Al2O3, Na2O and, K2O. These composite inclusions are primary melt that partially crystallised at the cooling stage. Hopper crystals of clinopyroxene imply rapid cooling rates, likely related to the uplift of crystals in the kimberlite melt. The reconstructed composition of such primary melts suggests that they were formed as the product of metasomatised mantle. One of the most likely source of melts/fluids metasomatising the mantle could be a subducted slab. [ABSTRACT FROM AUTHOR]

The article examines the missing nitrogen in the deep Earth's mantle.

A series of yellow cuboid diamonds from alluvial placers in the north-eastern Siberian platform have been examined with Fourier-transform infrared (FTIR) absorption spectroscopy, photoluminescence (PL) and electron paramagnetic resonance (EPR). All crystals having characteristic FTIR spectra with predominantly C and A centres belong to mixed type IaA/Ib with small total nitrogen content (up to 330 ppm). PL is characterized by many bands with two bands related to the NV0 and NV-centres common to all the samples. The FTIR spectra are also characterized by deformation-induced 'amber' centers. Some of the yellow diamonds studied show new bands at 4272, 4548, and 5960 cm-1 instead of the bands at 4060 and 4170 cm-1 common for 'amber' centres. An EPR study has revealed the presence of OK1 centres associated with titanium impurity. The plastic deformation of the studied diamonds is expressed as a 'tatami' strain pattern in the features of their internal structure. [ABSTRACT FROM AUTHOR]

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 in microinclusions in cuboid diamonds during their ascent to the surface. The observed compositional variations indicate different origins and evolutions of these fluids/melts. [ABSTRACT FROM AUTHOR]

New spectroscopic data were obtained to distinguish the specific features of brown and pink diamonds from Internatsionalnaya kimberlite pipe (Siberian craton). It is shown that pink and brown samples differ markedly in the content and degree of aggregation of nitrogen defects. Pink diamonds generally have higher nitrogen content and a lower aggregation state compared to brown samples, which often show significant variations in nitrogen content and aggregation state between different growth zones. The 491 and 576 nm luminescent centres, which are signs of deformed brown diamonds, are absent or of low intensity in pink diamonds implying that high nitrogen content predominantly in A form in the pink diamonds had stiffened the diamonds against natural plastic deformation. The GR1 centre, formed by a neutrally charged vacancy, was observed only in pink diamonds, which may be due to their formation and storage in the mantle at lower-temperature conditions. Mineral inclusions indicate peridotitic and eclogitic paragenesis for studied brown and pink diamonds, respectively. It is suggested that brown diamonds have been formed in a primitive mantle at higher temperatures and/or stored there much longer. [ABSTRACT FROM AUTHOR]

The concentrations of major and trace elements in minerals, reconstructed whole-rock compositions of zircon-bearing equigranular eclogites from the V. Grib kimberlite pipe located within the Arkhangelsk Diamondiferous Province (North-Western Russia), and results of the U-Pb and Lu-Hf isotope analyses of zircon grains from eclogites and granulite xenoliths are reported. These data suggest that the equigranular eclogites could represent the fragments of mid-ocean-ridge basalt that were metamorphosed during Paleoproterozoic subduction at 1.7-1.9 Ga. The Hf isotope compositions of the eclogitic zircon display uniformity and indicate corresponding Hf-depleted mantle model ages of 2.2-2.3 Ga. The formation of zircon in eclogites could have resulted from interactions with metasomatic/subduction-related fluids just prior to, but associated with, Paleoproterozoic eclogite formation. A link between eclogitic zircon formation and continental lower-crustal rocks can be excluded based on differences in the Hf isotope compositions of eclogitic and granulitic zircon grains. The U-Pb upper intercept age of granulitic zircon of 2716 ± 61 Ma provides a new minimum age constraint for zircon crystallisation and granulite formation. The U-Pb ages obtained from granulitic zircon show two stages of Pb loss at 2.2-2.6 Ga and 1.7-2.0 Ga. The late Paleoproterozoic stage of Pb loss recorded in granulitic zircon is due to the intensive reworking of basement crustal rocks, which was caused by a tectonic process/subduction event associated with equigranular eclogite formation. Our data, along with evidence previously obtained from the V. Grib pipe coarse-granular eclogites, show at least two main subduction events in the lithospheric mantle of the Arkhangelsk region: the Archean (2.8 Ga) and Paleoproterozoic (1.7-1.9 Ga) subductions, which correspond to major magmatic and metamorphic events in the Baltic Shield. [ABSTRACT FROM AUTHOR]

In this study, the specific features of structural defects of type IaB diamonds from the Mir kimberlite pipe (Yakutian diamondiferous province) have been characterized using FTIR and photoluminescence spectroscopy. Mineral inclusions in these diamonds [olivine (Ol), orthopyroxene (OPx), chromite (Chr), sulphide (Sf)] correspond to associations of peridotite rocks at the base of the lithosphere. Nitrogen content in type IaB diamonds shows significant variations, suggesting different growth media and/or several growth stages. A specific feature of these diamonds is the absence or very small amount of platelets, which may be related to annealing during their long-term residence at the temperatures of the base of the lithosphere. All studied diamonds show the presence of hydrogen defects that are active in IR spectra with an intense line at 3107 cm, and additional weaker lines at 3085 and 3237 cm, which correlated with high nitrogen content. Type IaB diamonds are also characterized by the presence of nitrogen-nickel luminescence centres S2, S3 and 523.2 nm. This feature distinguishes them from superdeep diamonds with extreme nitrogen aggregation states, which clearly attest to different growth conditions and crystallization media of type IaB diamonds from the Mir kimberlite pipe. [ABSTRACT FROM AUTHOR]

Abstract: We present the results of a detailed investigation of large (18 cm long, 6.9 kg) diamondiferous eclogite xenolith from the Udachnaya kimberlite pipe. We have studied the spatial distribution of diamonds, their relationship with the matrix minerals, mineral inclusions and their major- and trace-element compositions. The xenolith is composed of pale green clinopyroxene, round garnet grains and phlogopite, and is characterized by irregular distribution of minerals and development of zones enriched in phlogopite and garnet. Minerals in diamondiferous xenoliths show major-element compositions transitional between Udachnaya eclogites and those from peridotites. The host clinopyroxene are enriched relative to pyroxenes from Group A eclogites and websterites in respect K2O and LREE. We believe that such peculiarities reflect the interaction between mantle peridotites and LREE-enriched melts. The sources of the melts are uncertain. The distribution of diamonds (1 to 5 mm in size) in the xenolith is extremely irregular: they are more abundant in the garnet- and phlogopite-enriched zones. Diamonds often make up veins and schlieren. Nitrogen aggregation characteristics suggest that the xenolith contains diamonds of at least two generations. High degrees of aggregation in colorless diamonds of the earlier generation indicates that they formed at least 1 Ga before kimberlite eruption, whereas yellow diamonds of the second generation (type IaA) were formed only a short time before kimberlite emplacement. The presence of K-Clinopyroxene, coesite, CaCO3, and high-silica mica inclusions in diamonds of the second generation, and their internal and external morphology, suggest that these diamonds crystallized during interaction of the eclogitic substrate with high-density fluids compositionally intermediate between carbonatitic and hydrous-silicic end members rich in Si, K, Ti. [Copyright &y& Elsevier]

In this paper, new main and trace elements and isotopic data are presented for 14 coarse-grained eclogite xenoliths from the V. Grib kimberlite pipe in the central part of the Arkhangelsk Diamondiferous Province. Based on reconstructed whole rock MgO content, this suite is divided into high-MgO and low-MgO varieties. Eclogitic groups have a similar range of variations in the trace element compositions of garnet, clinopyroxene and reconstructed whole rock. All eclogites show positive Eu anomalies in garnet and Sr anomalies in the whole rock. The negative correlation between the Mg#, Sr/Lu ratio and HREE in a whole rock points to upper and lower oceanic crustal rocks as a protolith for eclogites with high and low whole rock HREEs, respectively. Low-MgO eclogites with higher whole rock HREEs have the basaltic upper oceanic crustal protolith, whereas the protoliths of eclogites with lower whole rock HREEs could be of gabbroic composition from the lower oceanic crust. High-MgO eclogites could represent MgO-rich portions of oceanic crustal rocks: picritic/MgO basalt portions in the upper oceanic crust and troctolite portions in the lower oceanic crust. The Sr and Nd isotope compositions suggest a complex history of eclogites during their residence in the lithospheric mantle. Similarities in the Nd isotope compositions and two-point Sm-Nd isochron ages are evidence for re-equilibration of the Sm-Nd isotope system between the eclogite garnet and clinopyroxene via a pre-kimberlite thermal event at 396 ± 24 Ma. The subset of clinopyroxenes from four eclogites has a Sr isotope composition that plots on the isochron at an age of 2.84 Ga, which reflects the time of the subduction event and emplacement into the lithosphere and corresponds to the time of the Belomorian Eclogite Province of Baltic Shield formation. [ABSTRACT FROM AUTHOR]

The origin of high-Mg melts remains one of the most highly debated questions in igneous petrology. There are two contrasting points of view, namely, (1) melt initiation in a rising high-temperature plume, and (2) mantle melting due to fluxing by water. To address this question we determined H 2 O, CO 2 , F, Cl and S concentrations in olivine-hosted melt inclusions of high-Mg volcanic rocks of the Siberian Traps Large Igneous Province that bracket the main pulse of volcanism at about 252–250 Ma, and can be classified as melanephelinites and meimechites. Both rock types belong to the high-Ti rock series. Correcting measured H 2 O, CO 2 , F, Cl and S concentrations in homogenized primary meimechite melt inclusions to primary meimechite melt composition using experimental melt compositions resulted in corrected melt-inclusion, volatile compositions of ~3.88 wt% H 2 O, ~1477 ppm CO 2 , ~4214 ppm F, ~2.08 wt% Cl and ~2490 ppm S. These values are viewed as minimum estimates for the original volatile concentrations in the melt because of the high probability for degassing during melt crystallization and/or during experiment homogenization. Olivine-hosted homogenized melt inclusions from melanephelinites yielded lower corrected concentrations of ~1.06 wt% H 2 O, ~998 ppm CO 2 , ~3242 ppm F, ~607 ppm Cl and ~2131 ppm S. We also measured water concentrations in clinopyroxenes of melanephelinites by FTIR, obtaining values as high as 133 ppm H 2 O, which corresponds to 0.91 wt% in the melt, in general agreement with data obtained by SIMS on the olivine-hosted melt inclusions. Olivine grains from melanephelinites are characterized by evolved compositions (Fo 0.80–0.86). Extrapolation to a primitive melanephelinite melt by simple fractional crystallization suggests that it could also contain high H 2 O concentrations (up to ~ 3 wt%). Analyzed meimechite and melanephelinite whole-rock samples are characterized by trace-element patterns that are typical of mantle-derived melts and by Sr-Nd isotope ratios that exclude crustal contamination or derivation from ancient lithospheric mantle. Thus, high volatile concentrations can be attributed to sublithospheric mantle source regions. This supports the notion that high-Mg melts form by volatile fluxing of the asthenospheric mantle rather than by decompression melting under relatively dry conditions of a rising abnormally high-temperature mantle plume. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectroscopy and electron paramagnetic resonance (EPR) were used for the first time to characterize properties of superdeep diamonds from the São-Luis alluvial deposits (Brazil). The infrared measurements showed the low nitrogen content (>50 of 87 diamonds from this locality were nitrogen free and belonged to type IIa) and simultaneously the extremely high level of nitrogen aggregation (pure type IaB being predominant), which indicates that diamonds under study might have formed under high pressure and temperature conditions. In most cases, PL features excited at various wavelengths (313, 473, and 532 nm) were indicative of different growth and post-growth processes during which PL centers could be formed via interaction between vacancies and nitrogen atoms. The overall presence of the 490.7 nm, H3, and H4 centers in the luminescence spectra attests to strong plastic deformations in these diamonds. The neutral vacancy known as the GR1 center has probably occurred in a number of crystals due to radiation damage in the post-growth period. The 558.5 nm PL center is found to be one of the most common defects in type IIa samples which is accompanied by the EPR center with g-factor of 2.00285. The 536 and 576 nm vibronic systems totally dominated the PL spectra of superdeep diamonds, while none of 'normal' diamonds from the Mir pipe (Yakutia) with similar nitrogen characteristics showed the latter three PL centers. [ABSTRACT FROM AUTHOR]