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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Diamond - Inclusions
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcements called the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Keyword Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In an effort to make it easier for users to track down articles related to a specific topic, KRO has extracted these key words and developed a list of major key words presented in this Key Word Index to which individual key words used in the article reference have been assigned. In most of the individual Key Word Reports the references are in crhonological order, though in some such as Deposits the order is first by key word and then chronological. Only articles classified as "technical" (mainly scientific journal articles) and "media" (independent media articles) are included in the Key Word Index. References that were added in the most recent monthly update are highlighted in yellow.
Articles tagged with the keyword Diamond - Inclusions do not refer to things which diminish the quality of diamonds as defined by one of the 4C's called "clarity", as explained in diamond inclusions. These articles refer to the nature of the minerals that end up as inclusions inside a diamond. What may be the diamond buyer's curse is the scientist's bounty, for diamonds themselves beyond their carbon isotope distribution do not reveal much about the nature of the environment in which they formed. However, the chemistry of other minerals that managed to form at the same time as the diamond and ended up encased within the crystal structure of the diamond carry information about that inner part of the earth that no drill will ever penetrate. Because the pressure-temperature range under which diamonds form is known, the chemistry of inclusions are like messages in a bottle from deep within the earth. Diamond inclusions are also of great interest to diamond exploration because when it can be established that the chemical composition of certain inclusions forms only within the same pressure-temperature regime of diamonds, the presence of these minerals in a kimberlite implies the possibility of diamonds. It is only a coincidence that a garnet ended up inside a diamond whose formation is a much rarer event that that of the garnet. A chunk of rock from the diamond stability field entrained by a kimberlite magma will have many more "garnets" than diamonds. Whether one is collecting heavy minerals from till samples or extracting them from a piece of kimberlite, the chemistry of those minerals can reveal the probability of diamond content in the kimberlitic source rock. Needless to say, which "indicator minerals" are diagnostic of diamond potential is an ongoing debate.
Mineralogie des Megacristaux des Xenolithes Eclogitiques Etgranulitiques et des Inclusions Cristallines dans Les Diamants Provenant de la Kimberlite du Kasai
Ph.d. Thesis, University Cath. Louvain, Louvain-la-neuve, Belgiqu,
New dat a on the petrology of olivine lamproites of Western australia From the results of the investigation of magmatic inclusions in olivines.(Russian)
Doklady Academy of Sciences Akademy Nauk SSSR, (Russian), Vol. 284, No. 1, pp. 196-201
Diamonds from nepheline mugearite- a discussion of garnet web sterites and associated ultramafic inclusions from nepheline mugearite in the Malcha area New South WalesAust
Mineralogical Magazine, Vol. 49, No. 354, December pp. 748-751
Variations in trapping temperatures and trace elements in peridotite-suite inclusions African diamonds- evidence 2 inclusion suites implications lithosphere stratigr
Contributions to Mineralogy and Petrology, Vol. 110, No. 1, March pp. 1-15
Partitioning of high MgO, FeO, NiO, MnO and Cr2O3 between perovskite andmagnesiowustite: implications origin inclusions diamond and composition lowermantle
Proceedings of the 29th International Geological Congress. Held Japan August 1992, Vol. 1, abstract p. 48
A note on the appearance of inclusions in garnets supposedly from India and problems relating to disclosure of origin: using this as an elementary example.
The South African Gemologist, Vol. 6, No. 2, June, pp. 11-13.
An infrared investigation of inclusion bearing diamonds from the Venetia kimberlite, northern province, South Africa: implications for diamonds from craton margin se
Contributions to Mineralogy and Petrology, Vol. 144, 1, Oct. pp. 98-108.
Chemical composition, volatile components, and trace elements in melts of the Karymskii volcanic centre, Kamchatka and Golovnin a volcano, Kunashir Island....
Vladykin, N.V., Deep Seated Magmatism: its sources and plumes, pp. 104-127.
Research in fluid inclusions in minerals: current state and future outlook. Third biennial conference on fluid inclusions held Sept. 2010. discussion of papers...
The IR absorption spectrum of water in microinclusion-bearing diamonds.
Proceedings of the 10th. International Kimberlite Conference, Vol. 1, Special Issue of the Journal of the Geological Society of India,, Vol. 1, pp. 271-280.
Physicochemical parameters of the material of mantle plumes: evidence from the thermodynamic analysis of mineral inclusions in sublithospheric diamond.
Geochemistry International, Vol. 52, 11, pp. 903-911.
Russian Geology and Geophysics, Vol. 56, 1-2, pp. 211-220.
Technology
Diamond inclusions
Abstract: The formation conditions of diamond can be determined from the residual pressure of inclusions trapped within the diamond, as measured at ambient conditions, and the equations of state (EoS) of the mineral inclusion and the host diamond. The EoS parameters of the diamond and the inclusion phase are therefore critical for determining the precision and accuracy of the calculation of formation conditions of diamonds. The questions we address are (i) How precise are these calculations? and, in particular, (ii) Do we know the EoS parameters of diamond to a precision and accuracy which do not contribute significantly to uncertainties in the geological conclusions drawn from these calculations? We present a review of the most recent compressional data, simulations, and direct elastic measurements of diamond and show them to be consistent with a room-temperature bulk modulus of K0T = 444(2) GPa and a pressure derivative K = 4.0. In combination with a thermal-pressure model with parameters aV300,0 = 2.672(3) x 10- 6 K- 1 and a single Einstein temperature 0E = 1500 K, the volume variation of diamond from room conditions to pressures and temperatures exceeding those in the Earth’s transition zone is described to within the levels of uncertainty inherent in both experimental and computational determinations. For the example of olivine inclusions in diamond, these uncertainties in the diamond EoS parameters lead to uncertainties in the entrapment pressures of no more than 0.001 GPa at low temperatures and 0.008 GPa at higher temperatures.
Interface partition coefficients of trace elements in carbonate-silicate parental media for diamonds and paragenetic inclusions ( experiments at 7.0-8.5 Gpa)
Russian Geology and Geophysics, Vol. 56, 1-2, pp. 221-231.
Diamondiferous subcontinental lithospheric mantle of the northeastern Siberian Craton: evidence from mineral inclusions in alluvial diamonds. Kapchan Fold Belt Olenek Province
Abstract: In recent years we have confirmed the existence of ophiolite-hosted diamonds on Earth, which occur in mantle peridotites and podiform chromitites of many ophiolites. These diamonds differ significantly from most kimberlite varieties, particularly in their inclusions. The typical inclusions in the diamonds are Mn-rich phases, i.e., NiMnCo alloy, native Mn, MnO, galaxite, Mn olivine and Mn garnet. Ca-silicate perovskite, a typical lower mantle mineral, was identified as mineral inclusions in diamond. One occurs as a 60-nanometer, euhedral grain associated with NiMnCo alloy and graphite, while another one occurs as a 50-nanometer grain within a large inclusion containing both NiMnCo alloy and Nd-Se-Cu-S phase. By EDS the perovskite has Ca 48.3%, Si 37.7% and Mn 14.1% with oxygen. TEM diffraction data show that the inclusion has d-spacings and angles between adjacent lattice planes are consistent to the Ca-silicate perovskite with an orthorhombic structure. The only known source of such light carbon is organic material in surface sediments and the best known sources of abundant manganese are Fe-Mn-rich sediments and Mn nodules, both of which are common on the seafloor. Many parts of the modern seafloor are also covered by sediments with a continental provenance. Phases such as SiO2 and Al2O3 are not expected in mantle peridotites and must have been introduced from shallow levels. We propose that subduction of oceanic lithosphere carries C, Mn, Si, Al and REE to the transition zone or lower mantle where the material is mixed with highly reduced material, perhaps derived from greater depths. Crystallization of diamond from a C-rich fluid encapsulates the observed inclusions. The diamonds and associated minerals are incorporated into chromite grains during chromite crystallization at depth of mantle transition zone, and are carried to shallower levels by mantle convection. Accumulation of chromite grains produces podiform chromitites containing a range of exotic minerals. However, the presence of diamonds and other UHP minerals in ophiolitic peridotites indicates that such phases can persist far outside their normal stability fields.
Advances in Earth Science *** Chinese ( eng. Abstract only), Vol. 30, 3, pp. 310-322.
Mantle
Diamond inclusions
Abstract: Diamonds and their mineral inclusions are valuable for studying the genesis of diamonds, the characteristics and processes of ancient lithospheric mantle and deeper mantle. This has been paid lots of attentions by geologists both at home and abroad. Most diamonds come from lithospheric mantle. According to their formation preceded, accompanied or followed crystallization of their host diamonds, mineral inclusions in diamonds are divided into three groups: protogenetic, syngenetic and epigenetic. To determine which group the mineral inclusions belong to is very important because it is vital for understanding the data’s meaning. According to the type of mantle source rocks, mineral inclusions in diamonds are usually divided into peridotitic (or ultramafic) suite and eclogitic suite. The mineral species of each suite are described and mineralogical characteristics of most common inclusions in diamonds, such as olivine, clinopyroxene, orthopyroxene, garnet, chromite and sulfide are reviewed in detail. In this paper, the main research fields and findings of diamonds and their inclusions were described: ?getting knowledge of mineralogical and petrologic characteristics of diamond source areas, characteristics of mantle fluids and mantle dynamics processes by studying the major element and trace element compositions of mineral inclusions; ?discussing deep carbon cycle by studying carbon isotopic composition of diamonds; ?determining forming temperature and pressure of diamonds by using appropriate assemblages of mineral inclusions or single mineral inclusion as geothermobarometry, by using the abundance and aggregation of nitrogen impurities in diamonds and by measuring the residual stress that an inclusion remains under within a diamond ; ?estimating the crystallization ages of diamonds by using the aggregation of nitrogen impurities in diamonds and by determine the radiometric ages of syngenetic mineral inclusions in diamonds. Genetic model of craton lithospheric diamonds and their mineral inclusion were also introduced. In the end, the research progress on diamonds and their inclusions in China and the gap between domestic and international research are discussed.
GAC MAC Meeting Special Session SS11: Cratons, kimberlites and diamonds., abstract 1/4p.
Canada, Northwest Territories
Diamond indicators
Abstract: The Central Mackenzie Valley (CMV) area of the Northwest Territories (NWT) comprises a Phanerozoic sedimentary basin that lies between the western margin of the Slave craton and the Cordillera. Although the region is considerably outside the bounds of the exposed Slave craton, both LITHOPROBE and more recent regional-scale surface wave studies (e.g., Priestley and McKenzie, 2006) indicate the likely presence of lithospheric mantle extending into the diamond stability field. Recent work conducted by Olivut Resources Ltd. led to the discovery of 29 kimberlites in the CMV. However, the indicator mineral chemistry of discovered kimberlites does not appear to be a good match (www.olivut.ca) with those during regional till and stream sediment sampling by the Geologic Survey of Canada (GSC) and Northwest Territories Geologic Survey (NTGS) in August 2003 and July 2005. We present new geochemical data on the regional indicator minerals with the aim of obtaining geotherm and depth of mantle sampling constraints on those indicator minerals discovered to date. A statistical evaluation of the data will compare the similarities to indicator mineral chemistry with parts of the Slave craton to evaluate whether the CMV indicators may ultimately be derived from that region. In total 3600 kimberlite indicator mineral grains were picked from the 0.25-2.0 mm size fractions. Peridotitic garnet grains dominate (46%), followed by magnesium ilmenite (26%), with decreasing individual proportions >15% of chromite, low-chrome diopside, olivine, chrome-diopside and eclogitic garnet. A sub-sample of these grains (3143) were analysed by EPMA. Garnet grains classify (after Grütter et al., 2004) as 1015 (62.1%) G9, 270 (16.5%) G11, 113 (6.9%) G10, 103 (6.3%) G12, 57 (3.5%) G1, 46 (2.8%) G10D, and the remaining 31 (1.9%) as G0, G3, G3D, G4, and G5. A sub-set of garnet grains (~700) were selected for LA-ICP-MS trace element analysis. Of the grains selected 74% G9, 14% G10 (and G10D), and 8% G11, with only 4% G12 and G0 (Grütter et al., 2004). Nickel concentrations from these grains range from 2.6-168.2 ppm, with the majority (>80%) between 20-100 ppm, yielding TNi (Canil, 1999) values ranging from 643-1348°C, with the majority between ~1000-1200°C. Using a central Slave craton geothermal gradient (Hasterok and Chapman, 2011), equilibration pressures for these garnet grains range from 20-80 kbars with the majority between 40-60 kbars (120-185 km). Preliminary analysis has 581 (81%) of the erupted peridotitic mantle garnet grains plotting within the diamond stability field (Kennedy and Kennedy, 1976). Of the 128 clinopyroxene grains analysed, only a few represent garnet peridotite (lherzolite) facies KIM clinopyroxene grains following compositional screening. Thermobarometry of these grains (Nimis and Taylor, 2000), assuming they were all derived from the same lithospheric section, yields P-T arrays identical to the central Slave geotherm that was 220 km thick at the time of eruption. These results are encouraging for diamond exploration. We thank Overburden Drilling Management Ltd. for grain picking and recovery of the small diamond, SGS Lakefield Research for mounting grains, and the GSC for probing of the grains.
Abstract: Experiments on the synthesis of inclusions-bearing diamond were performed in the SiO2-((Mg,Ca)CO3-(Fe,Ni)S system at 6.3 GPa and 1650-1750 °C, using a multi-anvil high pressure apparatus of the "split-sphere" type. Diamond synthesis was realized in the "sandwich-type" experiments, where the carbonate-oxide mixture acted as a source of both CO2-dominated fluid and carbonate-silicate melt, and Fe,Ni-sulfide played a role of reducing agent. As a result of redox reactions in the carbonate-oxide-sulfide system, diamond was formed in association with graphite and Mg,Fe-silicates, coexisting with CO2-rich fluid, carbonate-silicate and sulfide melts. The synthesized diamonds are predominantly colorless or light-yellow monocrystals with octahedral habit (20-200 ?m), and polycrystalline aggregates (300-400 ?m). Photoluminescence spectroscopy revealed defects related to nickel impurity (S3 optical centers), which are characteristic of many diamonds in nature. The density of diamond crystallization centers over the entire reaction volume was ~3 × 102-103 cm? 3. The overwhelming majority of diamonds synthesized were inclusions-bearing. According to Raman spectroscopy data, diamond trapped a wide variety of inclusions (both mono- and polyphase), including orthopyroxene, olivine, carbonate-silicate melt, sulfide melt, CO2-fluid, graphite, and diamond. The Raman spectral pattern of carbonate-silicate melt inclusions have bands characteristic of magnesite and orthopyroxene (± SiO2). The spectra of sulfide melt displayed marcasite and pyrrhotite peaks. We found that compositions of sulfide, silicate and carbonate phases are in good agreement not only with diamond crystallization media in experiments, but with data on natural diamond inclusions of peridotitic and eclogitic parageneses. The proposed methodological approach of diamond synthesis can be used for experimental simulation of the formation of several types of mineral, fluid and melt inclusions, observed in natural diamonds.
Abstract: [Si-V]- is a well-known defect in diamond. It has a great potential in electronics application and also is a very important feature for gem diamond identification in separating natural from synthetic. It is common in CVD diamonds (Martineau et al., 2004), can be doped into HPHT synthetic diamonds (Sittas, et al., 1996), and also occurs in natural type IIa diamonds (Breeding and Wang, 2008). Recent study of [Si-V]- distribution (emissions at 736.6 and 736.9 nm) in HPHT synthetic diamonds confirmed that it was concentrated in the {111} growth sectors. Identical distribution pattern of Nii+, which has doublet emissions at 882.1 and 883.7 nm, was observed (Johnson et al., 2015), strongly indicating that [Si-V]- and Nii+ have the same behavior during HPHT diamond growth. However, little is known how [Si-V]- is incorporated in natural diamond lattice. In this report, we studied the distribution of [Si-V]- defect in natural diamonds and its correlation with other emissions (defects). Seven natural type IIa gem diamonds were analyzed in this study. A common feature of this group of diamonds is occurrence of euhedral olivine inclusions, which is very rare among natural type IIa diamonds and good evidence that these IIa diamonds were formed in the lithospheric mantle. Occurrence of [Si-V]- in these stones were detected among enormous natural type IIa diamonds routinely analyzed in GIA laboratories. Distribution of [Si-V]-, Nii+ and many other emissions were mapped over the table faces using various laser excitations at liquid nitrogen temperature. It was found that intensities of [Si-V]- emission varied significantly over a small area. The distribution patterns were irregular and changed from stone to stone. Distribution of Nii+ emissions showed irregular patterns, but entirely different from that of [Si-V]-. There is no correlation in spatial distribution of these two defects in natural type IIa diamonds, in drastic contract to that observed in HPHT synthetics. Possible causes of the contrast behaviors of [Si-V]- distributions in natural and HPHT synthetic diamonds, and their implications in diamond formation and gem diamond identification will be discussed.
Geophysical Research Abstracts, Vol. 19, EGRU2017-1751, April 1p.
Mantle
Diamond, inclusions, nitrogen
Abstract: A few years ago a series of iron carbides Fe3C, Fe2C, Fe7C3 and Fe23C6 (haxonite) containing up to 7.3-9.1 at.% N (N/(N+C) = 0.19-0.27) was identi?ed as inclusions in diamonds from the Juina area, Brazil in association with native iron and graphite (Kaminsky and Wirth, 2011). Subsequently nitrocarbides and carbonitrides Fe3(C,N) and Fe9(C,N)4 (nitroyarlongite) containing 12.8-18.42 at.% N (N/(N+C) = 0.37-0.60) were identi?ed in a lower-mantle microxenolith in association with ferropericlase and two post-spinel oxides Mg-Cr-Fe-O (CT phase; Mg-xieite) and Ca-Cr-O (new mineral) with an orthorhombic structure (Kaminsky et al., 2015). Recently pure nitrides Fe3N with a trigonal structure P312 and Fe2N with an orthorhombic structure Pbcn were identi?ed among mineral inclusions from diamonds in the same area. They have admixtures of Cr (0.68-1.8 at.%), Ni (0.35-0.93 at.%) and Mn (0-1.22 at.%). Fe2N contains also an admixture of 5.1-7.6 at.% Si. The nitrides associate with nitroyarlongite Fe9(N0.8C0.2)4 and iron carbide Fe7C3, which contain nanocrystals of moissanite, hexagonal 6H polytype of SiC. Fe7C3 crystallizes, in the Fe-C system, the ?rst in association with diamond at pressures starting from 130 GPa, i.e. within the lowermost mantle, the D[U+02BA] layer. Native iron and a series of nitride-carbonitride-nitrocarbide-carbides associated with Fe7C3 form as a result of in?ltration of the Fe-Ni melt from the outer core into the lowermost mantle. This melt contains up to 10 % light elements, such as C, N, O and Si, which may be the source of nitrides-carbides. The existence of nitrides in the lower mantle helps to solve the problem of ‘missing nitrogen’ in the Earth’s nitrogen balance and consider the Earth’s core as the major reservoir of nitrogen. According to calculations, the total amount of nitrogen in the Earth’s core is 9,705 ×1021 grams, and in the mantle ?500 ×1021 grams (95 % and 4.5 % of the total amount of nitrogen respectively). In such a case the average concentration of nitrogen in the Earth is ?1,710 ppm, which is similar to the concentration of nitrogen in chondrites.
European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 19147 Abstract
Technology
Diamond inclusions
Abstract: Trapping inclusions in diamonds has been used as a diagnostic to constrain diamond growth media (e.g. Navon et al., 1994; Weiss et al., 2015) in the Earth's upper mantle. Experimental works now generate inclusion-bearing diamonds from seeds in mixtures of carbonates, graphite, and silicates in the presence of excess of pure water or saline fluids (H2O-NaCl) and investigate in more details the conditions of natural diamond growth (Bureau et al., 2012; 2016). Experiments were carried at conditions compatible with the Earth's geotherm between 6-7 GPa (1300-1675°C) in multi-anvil presses at the Bayerisches Geoinstitut, Bayreuth from a few hours two a few days. Results show that within the timescale of the experiments diamond growth occurs on seeds if water and alkali-bearing carbonates are present. We show that water promotes fast diamond growth, which is favorable to the formation of inclusions. Thin sections of a few diamond seeds containing exposed inclusions were prepared using a Focus Ion Beam (about 2 to 5 µm thickness). These sections were deposited on silicon wafers and gold coated for micron-scale determination of the delta 13C isotopic compositions using the NanoSIMS 50 installed at the Muséum National d'Histoire Naturelle, Paris. Carbon isotope measurement with NanoSIMS were calibrated against a natural Ia and a synthetic IIa diamond used for diamond anvil cells, whose compositions were determined by gas-source mass spectrometry at IPGP at 3.6±0.1‰ and -20.9±0.1‰, respectively (Pinti et al., 2016). All the starting materials used for the experiments were also characterized for their delta 13C by the same technique at GEOTOP, Montréal. The isotopic composition of the new diamond grown areas were measured close to the inclusions. They exhibit a different isotopic signature than that of the starting seeds (starting diamond composition: -29.6 to -30.4±1.4‰). The new diamond signatures are falling into the range of signatures of the starting carbonates used for the experiments (- 4.8±0.1 to -16.2±0.1‰) when they are far away from the composition of the starting graphite (-26.4±0.1‰). This shows that the carbon source for diamond growth must be the carbonates present either as CO32- ions dissolved in the melt or as carbon dioxide species CO2 in the aqueous fluid and that diamond growth occurred from carbonate reduction rather that from graphite dissolved in the melt. We suggest that the presence of small discrete or isolated volumes of water-carbonate-rich fluids are necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultrahigh pressure metamorphic diamonds.
European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 1751 Abstract
Mantle
Diamond inclusions
Abstract: A few years ago a series of iron carbides Fe3C, Fe2C, Fe7C3 and Fe23C6 (haxonite) containing up to 7.3-9.1 at.% N (N/(N+C) = 0.19-0.27) was identified as inclusions in diamonds from the Juina area, Brazil in association with native iron and graphite (Kaminsky and Wirth, 2011). Subsequently nitrocarbides and carbonitrides Fe3(C,N) and Fe9(C,N)4 (nitroyarlongite) containing 12.8-18.42 at.% N (N/(N+C) = 0.37-0.60) were identified in a lower-mantle microxenolith in association with ferropericlase and two post-spinel oxides Mg-Cr-Fe-O (CT phase; Mg-xieite) and Ca-Cr-O (new mineral) with an orthorhombic structure (Kaminsky et al., 2015). Recently pure nitrides Fe3N with a trigonal structure P312 and Fe2N with an orthorhombic structure Pbcn were identified among mineral inclusions from diamonds in the same area. They have admixtures of Cr (0.68-1.8 at.%), Ni (0.35-0.93 at.%) and Mn (0-1.22 at.%). Fe2N contains also an admixture of 5.1-7.6 at.% Si. The nitrides associate with nitroyarlongite Fe9(N0.8C0.2)4 and iron carbide Fe7C3, which contain nanocrystals of moissanite, hexagonal 6H polytype of SiC. Fe7C3 crystallizes, in the Fe-C system, the first in association with diamond at pressures starting from 130 GPa, i.e., within the lowermost mantle, the D? layer. Native iron and a series of nitride-carbonitride-nitrocarbide-carbides associated with Fe7C3 form as a result of infiltration of the Fe-Ni melt from the outer core into the lowermost mantle. This melt contains up to 10 % light elements, such as C, N, O and Si, which may be the source of nitrides-carbides. The existence of nitrides in the lower mantle helps to solve the problem of 'missing nitrogen' in the Earth's nitrogen balance and consider the Earth's core as the major reservoir of nitrogen. According to calculations, the total amount of nitrogen in the Earth's core is 9,705 × 1021 grams, and in the mantle 500 × 1021 grams (95 % and 4.5 % of the total amount of nitrogen respectively). In such a case the average concentration of nitrogen in the Earth is 1,710 ppm, which is similar to the concentration of nitrogen in chondrites. References 1. Kaminsky, F. V., Wirth, R. (2011) Iron carbide inclusions in lower-mantle diamond from Juina, Brazil. Canadian Mineralogist 49(2), 555-572. 2. Kaminsky, F. V., Wirth, R., Schreiber, A. (2015) A microinclusion of lower-mantle rock and some other lower-mantle inclusions in diamond.
Abstract: Fibrous diamond growth zones can contain abundant high density fluid inclusions (HDFs) and these provide the most direct information on the source and composition of diamond-forming fluids. Four different fluid end-members have been defined; silicic, low-Mg carbonatitic, high-Mg carbonatitic, and saline. Continuous arrays exist between the silicic and low-Mg carbonatitic end-member and between the saline and high-Mg carbonatitic end-member. Different processes have been proposed to explain the two major element compositional arrays, but the origin of and relation between the various fluid end-members is still uncertain. In this study we provide new constraints on the evolution and origin of these diamond-forming fluids by combining noble gas systematics with ?13C, N concentrations, and fluid inclusion compositions.
Physics and Chemistry of Minerals, in press available, 19p.
Technology
diamond inclusions
Abstract: Elasticity is a key property of materials, not only for predicting volumes and densities of minerals at the pressures and temperatures in the interior of the Earth, but also because it is a major factor in the energetics of structural phase transitions, surface energies, and defects within minerals. Over the 40 years of publication of Physics and Chemistry of Minerals, great progress has been made in the accuracy and precision of the measurements of both volumes and elastic tensors of minerals and in the pressures and temperatures at which the measurements are made. As an illustration of the state of the art, all available single-crystal data that constrain the elastic properties and pressure–volume–temperature equation of state (EoS) of mantle-composition olivine are reviewed. Single-crystal elasticity measurements clearly distinguish the Reuss and Voigt bulk moduli of olivine at all conditions. The consistency of volume and bulk modulus data is tested by fitting them simultaneously. Data collected at ambient pressure and data collected at ambient temperature up to 15 GPa are consistent with a Mie–Grünesien–Debye thermal-pressure EoS in combination with a third-order Birch–Murnaghan (BM) compressional EoS, the parameter V0 = 43.89 cm3 mol?1, isothermal Reuss bulk modulus KTR,0=126.3(2) GPaKTR,0=126.3(2) GPa, K?TR,0=4.54(6)KTR,0?=4.54(6), a Debye temperature ?D=644(9)K?D=644(9)K, and a Grüneisen parameter ?0 = 1.044(4), whose volume dependence is described by q = 1.9(2). High-pressure softening of the bulk modulus at room temperature, relative to this EoS, can be fit with a fourth-order BM EoS. However, recent high-P, T Brillouin measurements are incompatible with these EoS and the intrinsic physics implied by it, especially that (?K?TR?T)P>0(?KTR??T)P>0. We introduce a new parameterisation for isothermal-type EoS that scales both the Reuss isothermal bulk modulus and its pressure derivative at temperature by the volume, KTR(T,P=0)=KTR,0[V0V(T)]?TKTR(T,P=0)=KTR,0[V0V(T)]?T and K?TR(T,P=0)=K?TR,0[V(T)V0]??KTR?(T,P=0)=KTR,0?[V(T)V0]??, to ensure thermodynamic correctness at low temperatures. This allows the elastic softening implied by the high-P, T Brillouin data for mantle olivine to be fit simultaneously and consistently with the same bulk moduli and pressure derivatives (at room temperature) as the MGD EoS, and with the additional parameters of ?V0 = 2.666(9) × 10?5 K?1, ?E=484(6)?E=484(6), ?T?T = 5.77(8), and ???? = ?3.5(1.1). The effects of the differences between the two EoS on the calculated density, volume, and elastic properties of olivine at mantle conditions and on the calculation of entrapment conditions of olivine inclusions in diamonds are discussed, and approaches to resolve the current uncertainties are proposed.
Earth and Planetary Science Letters, Vol. 474, pp. 215-225.
Africa, Algeria
diamond inclusions
Abstract: Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 ?m in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (?30 ?m) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.
Geochimica et Cosmochimica Acta, in press available, 23p.
Technology
diamond inclusions
Abstract: Base metal sulphide (BMS) inclusions in diamonds provide a unique insight into the chalcophile and highly siderophile element composition of the mantle. Entombed within their diamond hosts, these provide a more robust (closed system) sample, from which to determine the trace element, Re-Os and S-isotopic compositions of the mantle than mantle xenoliths or orogenic peridotites, as they are shielded from alteration during ascent to the Earth’s crust and subsequent surface weathering. However, at temperatures below 1100 °C some BMS inclusions undergo subsolidus re-equilibration from an original monosulphide solid solution (Mss) and this causes fractionation of the major and trace elements within the inclusions. Thus to study the subjects noted above, current techniques require the entire BMS inclusion to be extracted for analyses. Unfortunately, ‘flaking’ of inclusions during break-out is a frequent occurrence and hence the risk of accidentally under-sampling a portion of the BMS inclusion is inherent in current practices. This loss may have significant implications for Re-Os isotope analyses where incomplete sampling of a Re-rich phase, such as chalcopyrite that typically occurs at the outer margins of BMS inclusions, may induce significant bias in the Re-Os and 187Os/188Os measurements and resulting model and isochron ages. We have developed a method for the homogenisation of BMS inclusions in diamond prior to their break-out from the host stone. Diamonds are heated to 1100 °C and then quenched to chemically homogenise any sulphide inclusions for both major and trace elements. Using X-ray Computed Microtomography (µCT) we determine the shape and spatial setting of multiple inclusions within a host stone and crucially show that the volume of a BMS inclusion is the same both before and after homogenisation. We show that the homogenisation process significantly reduces the inherent variability of in situ analysis when compared with unhomogenised BMS, thereby widening the scope for multiple methods for quantitative analysis, even on ‘flakes’ of single BMS inclusions. Finally we show that the trace elements present in peridotite (P-type) and eclogitic (E-type) BMS are distinct, with P-type diamonds having systematically higher total platinum-group element (particularly Os, Ir, Ru) and Te and As concentrations. These distinctions suggest that the PGE and semi-metal budgets of mantle-derived partial melts will be significantly dependent upon the type(s) and proportions of sulphides present in the mantle source.
Cerantola, V., Bykova, E., Kupenko, I., Merlini, M., Ismailova, L., McCammon, C., Bykov, M., Chumakov, A.I., Petitgirard, S., Kantor, I., Svityk, V., Jacobs, J., Hanfland, M., Mezouar, M., Prescher, C., Ruffer, R., Prakapenka, V.B., Duvbovinsky, L.
Abstract: Precise dating of diamond growth is required to understand the interior workings of the early Earth and the deep carbon cycle. Here we report Sm-Nd isotope data from 26 individual garnet inclusions from 26 harzburgitic diamonds from Venetia, South Africa. Garnet inclusions and host diamonds comprise two compositional suites formed under markedly different conditions and define two isochrons, one Archaean (2.95?Ga) and one Proterozoic (1.15?Ga). The Archaean diamond suite formed from relatively cool fluid-dominated metasomatism during rifting of the southern shelf of the Zimbabwe Craton. The 1.8 billion years younger Proterozoic diamond suite formed by melt-dominated metasomatism related to the 1.1?Ga Umkondo Large Igneous Province. The results demonstrate that resolving the time of diamond growth events requires dating of individual inclusions, and that there was a major change in the magmatic processes responsible for harzburgitic diamond formation beneath Venetia from the Archaean to the Proterozoic.
Geochimica et Cosmochimica Acta, Vol. 216, pp. 335-357.
Technology
diamond inclusions - microtomography
Abstract: Base metal sulphide (BMS) inclusions in diamonds provide a unique insight into the chalcophile and highly siderophile element composition of the mantle. Entombed within their diamond hosts, these provide a more robust (closed system) sample, from which to determine the trace element, Re-Os and S-isotopic compositions of the mantle than mantle xenoliths or orogenic peridotites, as they are shielded from alteration during ascent to the Earth’s crust and subsequent surface weathering. However, at temperatures below 1100 °C some BMS inclusions undergo subsolidus re-equilibration from an original monosulphide solid solution (Mss) and this causes fractionation of the major and trace elements within the inclusions. Thus to study the subjects noted above, current techniques require the entire BMS inclusion to be extracted for analyses. Unfortunately, ‘flaking’ of inclusions during break-out is a frequent occurrence and hence the risk of accidentally under-sampling a portion of the BMS inclusion is inherent in current practices. This loss may have significant implications for Re-Os isotope analyses where incomplete sampling of a Re-rich phase, such as chalcopyrite that typically occurs at the outer margins of BMS inclusions, may induce significant bias in the Re-Os and 187Os/188Os measurements and resulting model and isochron ages. We have developed a method for the homogenisation of BMS inclusions in diamond prior to their break-out from the host stone. Diamonds are heated to 1100 °C and then quenched to chemically homogenise any sulphide inclusions for both major and trace elements. Using X-ray Computed Microtomography (µCT) we determine the shape and spatial setting of multiple inclusions within a host stone and crucially show that the volume of a BMS inclusion is the same both before and after homogenisation. We show that the homogenisation process significantly reduces the inherent variability of in situ analysis when compared with unhomogenised BMS, thereby widening the scope for multiple methods for quantitative analysis, even on ‘flakes’ of single BMS inclusions. Finally we show that the trace elements present in peridotite (P-type) and eclogitic (E-type) BMS are distinct, with P-type diamonds having systematically higher total platinum-group element (particularly Os, Ir, Ru) and Te and As concentrations. These distinctions suggest that the PGE and semi-metal budgets of mantle-derived partial melts will be significantly dependent upon the type(s) and proportions of sulphides present in the mantle source.
Acta Geologica Sinica, Vol. 91, s1, p. 32 abstract
China
diamond inclusions
Abstract: The Central Asian Orogenic Belt (CAOB) is a huge tectonic mélange that lies between the North China Craton and the Siberian Block. It is composed of multiple orogenic belts, continental fragments, magmatic and metamorphic rocks, suture zones and discontinuous ophiolite belts. Although the Hegenshan and Sartohay ophiolites are separated by nearly 3000 km and lie in completely different parts of the CAOB, they are remarkably similar in many respects. Both are composed mainly of serpentinized peridotite and dunite, with minor gabbro and sparse basalt. They both host significant podiform chromitites that consist of high-Al, refractory magnesiochromite with Cr#s [100Cr/(Cr+Al)] averaging >60. The Sartohay ophiolite has a zircon U-Pb age of ca. 300 Ma and has been intruded by granitic plutons of similar age, resulting in intense hydrothermal activity and the formation of gold-bearing listwanites. The age of the Hegenshan is not firmly established but is thought to have formed in the Carboniferous. Like many other ophiolites that we have investigated in other orogenic belts, the chromitites in these two bodies have abundant diamonds, as well as numerous super-reduced and crustal minerals. The diamonds are mostly, colorless to pale yellow, 200-300 ?m across and have euhedral to anhedral shapes. They all have low carbon isotopes (?14C = ?18 to ?29) and some have visible inclusions. These are accompanied by numerous super-reduced minerals such as moissanite, native elements (Fe, Cr, Si, Al, Mn), and alloys (e.g., Ni-Mn-Fe, Ni-Fe-Al, Ni-Mn-Co, Cr-Ni-Fe, Cr-Fe, Cr-Fe-Mn), as well as a wide range of oxides, sulfides and silicates. Grains of zircon are abundant in the chromitites of both ophiolites and range in age from Precambrian to Cretaceous, reflecting both incorporation of old zircons and modification of grains by hydrothermal alteration. Our investigation confirms that high-Al, refractory chromitites in these two ophiolites have the same range of exotic minerals as high-Cr metallurgical chromitites such as those in the Luobusa ophiolite of Tibet. These collections of exotic minerals in ophiolitic chromitites indicate complex, multi-stage recycling of oceanic and continental crustal material at least to the mantle transition zone, followed by uprise and emplacement of the peridotites into relatively shallow ophiolites.
Zeitschrfit fur Kristallographie, Vol. 231, pp. 467-473.
Technology
diamond inclusions
Abstract: We describe the experimental protocols necessary to measure the crystal structures of minerals trapped within diamonds by single-crystal X-ray diffraction to the same quality as obtained from minerals studied at ambient conditions. The results show that corrections for X-ray absorption in complex cases can be made with good precision. Comparison of the refined structure of a single-crystal olivine inclusion inside a diamond with the structure of a similar olivine held in a high-pressure diamond-anvil cell shows that data resolution, not the correction for absorption effects, is the dominant factor in influencing the quality of structures determined at high pressures by single-crystal X-ray diffraction.
Abstract: It is widely assumed that mineral inclusions and their host diamonds are ‘syngenetic’ in origin, which means that they formed simultaneously and from the same chemical processes. Mineral inclusions that, instead, were formed earlier with respect to diamonds are termed protogenetic. However, minerals can have the same age as the diamonds in that they become enclosed in and isolated from any further isotopic exchange. But this is termed ‘synchronous’ not ‘syngenetic’. Here we demonstrate conclusively the protogenesis of inclusions in diamonds, based upon data from an exceptional fragment of a diamond-bearing peridotite, its clinopyroxene and a gem-quality diamond. Clinopyroxenes in the xenolith had the same chemistry and crystallographic orientation as those for inclusions in the diamond. With our results with garnets, olivines and sulfides, we can state that a major portion of the mineral inclusions in non-coated, monocrystalline-lithospheric diamonds are protogenetic. Our discovery here presented has implications for all genetic aspects of diamond growth, including their ages.
Geochimica et Cosmochimica Acta, Vol. 232 pp. 206-224.
Technology
diamond - inclusions DFT
Abstract: Diffusivities of helium, deuterium and hydrogen have been characterized in diamond. Polished CVD diamond was implanted with either 3He, 2H, or 1H. Implanted samples were sealed under vacuum in silica glass capsules, and annealed in 1-atm furnaces. 3He, 2H and 1H distributions were measured with Nuclear Reaction Analysis. We obtain these Arrhenius relations: DHe = 4.00?×?10?15 exp(?138?±?14?kJ?mol?1/RT) m2?s?1. D2H = 1.02?×?10?4 exp(?262?±?17?kJ?mol?1/RT) m2?s?1. D1H = 2.60?×?10?4 exp(?267?±?15?kJ?mol?1/RT) m2?s?1. Diffusivities of 1H and 2H agree within experimental uncertainties, indicating little diffusive mass fractionation of hydrogen in diamond. To complement the experimental measurements, we performed calculations using a first-principles quantum mechanical description of diffusion in diamond within the Density Functional Theory (DFT). Differences in 1H and 2H diffusivities from calculations are found to be ?4.5%, reflected in differences in the pre-exponential factor. This small difference in diffusivities, despite the large relative mass difference between these isotopes, is due to the fact that the atomistic process involved in the transition along the diffusion pathway is dictated by local changes to the diamond structures rather than to vibrations involving 1H/2H. This finding is consistent with the experimental results given experimental uncertainties. In contrast, calculations for helium diffusion in diamond indicate a difference of 15% between diffusivities of 3He and 4He. Calculations of diffusion distances for hydrogen using our data yield a distance of 50??m in diamond in 300,000?years at 500?°C and ?30?min at 1400?°C. Diffusion distances for He in diamond are shorter than for H at all temperatures above ?350?°C, but differences increase dramatically with temperature because of the higher activation energy for H diffusion. For example, a 50??m diffusion distance for He would be attained in ?40 Myr at 500?°C and 400?yr at 1400?°C. For comparison, a 50??m diffusion distance for N in diamond would require nearly 1 billion years at 1400?°C. The experimental data indicate that diamonds equilibrate with ambient H and He in the mantle on timescales brief relative to most geological processes and events. However, He diffusion in diamond is slower than in any other mineral measured to date, including other kimberlite-hosted minerals. Under some circumstances, diamond may provide information about mantle He not recoverable from other minerals. One possibility is diamonds entrained in kimberlites. Since the ascent of kimberlite from the mantle to near-surface is very rapid, entrained diamonds may retain most or all of the H and He acquired in mantle environments. Calculations using reasonable ascent rates and T-t paths indicate that He diffusive loss from kimberlite-hosted diamonds is negligible for grains of 1.0-0.2?mm radius, with fractional losses <0.15% for all ascent rates considered. If the host kimberlite magma is effectively quenched in the near-surface (or is erupted), diamonds should contain a faithful record of [He] and He isotopes from the mantle source region. Preservation of H in kimberlite-hosted diamonds is less clear-cut, with model outcomes depending critically upon rates of ascent and cooling.
Geophysical Research Abstracts www.researchgate.net, Vol. 20, EGU2018-128291p. Abstract
Africa, South Africa
diamond inclusions
Abstract: Changing recycling budgets of surface materials and volatiles by subduction of tectonic plates influence the compositions of Earth’s major reservoirs and affect climate throughout geological time. Fluids play a key role in processes governing subduction recycling, but quantifying the exact fate of volatiles introduced into the mantle at ancient and recent destructive plate boundaries remains difficult. Here, we report on the role of fluids and the fate of volatiles and other elements at two very different tectonic settings: 1) at subduction settings, and 2) within the subcontinental lithospheric mantle (SCLM). We will show how olivine-hosted melt inclusions from subduction zones and mineral inclusions in diamond from the SCLM are used to reveal how changing tectonic settings influence volatile cycles with time. Melt inclusions from the complex Italian post-collisional tectonic setting are used to identify changing subduction recycling through time. The use of CO2 in deeply trapped melt inclusions instead of in lavas or volcanic gases provides a direct estimate of deep recycling, minimizing possible effects of contamination during transfer through the crust. The aim is to distinguish if increased recycling of sediments from the down-going plate at continental subduction settings results in increased deep CO2 recycling or if the increased CO2 flux results from crustal degassing of the overriding plate. Both processes likely affected climate through Earth history but could thus far not be discriminated. The study of mineral inclusions and their host diamonds from the SCLM can link changes in the cycling of carbon-rich fluids and the time and process through which the carbon redistribution took place. We use Sm-Nd isotope techniques to date the mineral inclusions and use the carbon isotope data of the host diamonds to investigate the growth conditions. I will present case-studies of peridotitic and eclogitic diamonds from three mines in Southern Africa.
Abstract: Interphase partitioning of minor elements was studied experimentally upon partial melting of model pyrolite [1] with addition of 2 wt % H2O, 10, and 15 wt % of multicomponent carbonate at 22-24 GPa and 1300-2200°C. The concentrations of minor elements were analyzed on an Agilent 7500a mass spectrometer. Phase associations included quenched melt (L), bridgmanite (Brd), CaSiO3- perovskite (CaPrv), ringwoodite (Rwd), ferropericlase (Fp), and majoritic garnet (Maj). The sequence of phase assemblages in our runs is consistent to that reported in [2] for melting of anhydrous pyrolite at 24 GPa: Fp+L, Fp+Maj+Brd(Rwd)+L, Fp+Maj+Brd(Rwd)+CaPrv. Most of minor elements, except for Sc, Cr, and Ni, are incompatible for Brd and show slight increase in partitioning coefficients from LREEs to HREEs in the H2O-bearing system. Pyrolite with carbonate is characterized by slightly higher LREE partitioning coefficients. Monovalent elements (Li, K, Cs, Rb), as well as Sr and Pb, are strongly incompatible for Brd in all systems. The similar features are observed for Fp enriched in HREEs and depleted in LREEs; all minor elements show redistribution into Fp with pressure. CaPrv is enriched in LREEs and depleted in HREEs. We applied the lattice strain model [3] for interpretation of the analytical data, which allowed us to study the behavior of minor elements as a function of P-T parameters. Our data and some previous results [4] were used for estimation of the composition of melts in equilibrium with inclusions in diamonds from the transition zone and lower mantle.
Abstract: The high amount of Fe-rich ferropericlase inclusions found in diamonds of a potential super-deep origin questions the bulk chemical model of the Earth [e.g., 1]. Although this might be due to a biased sampling of the lower mantle, it is worth to further address this discrepancy. A limiting factor of the Fe-content of the Earth´s deep mantle (TZ and lower mantle) is a correlation of the depths of the observed main mantle discontinuities with the (Fe,Mg)SiO4 phase diagram. In particular, the 520 kmdiscontinuity is related to the phase transformation of wadsleyite (assuming Fa10) to ringwoodite. The existing phase diagrams suggest a stability limit of wadsleyite ?Fa40 [e.g., 2,3], which limits the Fe-content of the Earth´s transition zone. Here we report on a discovery of Fe-rich wadsleyite grains (up to Fa56) in the high-pressure silicate melt droplets within Fe,Ni-metal in shock veins of the CB (Bencubbin-like) metal-rich carbonaceous chondrite QC 001 [4], which were identified using HR-EDX, nano-EBSD and TEM. Although the existence of such Fe-rich wadsleyite in shock veins may be due to the kinetic reasons, new theoretical and experimental studies of the stability of (Fe,Mg)SiO4 at high temperature (> 1800 K) are clearly needed. This may have significant impact on the temperature and chemical estimates of the Earth´s transition zone.
Abstract: Diamonds represent one of the few witnesses of our planet interior. They are mainly formed in the first 200 km of the lithospheric mantle, and, more rarely from the transition zone to 700 km deep. Diamonds contain a lot of information about global evolution, however their mode of formation remains poorly understood. Recent studies in high-pressure mineralogy suggest that diamonds precipitate from oxidized metasomatic fluids. The study of inclusions trapped in diamonds may provide precise information on composition, pressure, temperature and redox conditions. The aim of this study is to use the inclusions trapped in diamond as probes of the deep cycling of volatiles (C, H, halogens). Therefore, we investigate inclusions in diamonds with a systematic study of diamonds from collections. We selected 73 diamonds from three museums: National Museum of Natural History, School of Mines and Sorbonne University. The selected diamonds are studied with the help of a large range of in situ methods: RAMAN and FTIR spectrometry and X-Ray Diffraction. These analyses allow us to identify the nature of the different inclusions without damaging the gems. First results indicate silicate minerals inclusions as pyrope garnet, olivine and enstatite pyroxene. This assemblage is typical of peridotitic-type diamonds in the lithosphere.
Abstract: The oxidation state and oxygen fugacity (fO2) of Earth’s mantle exert important influences on the compositions of primary melts the speciation and mobility of carbon and sulphur, diamond formation, and the modification of subducted lithosphere [1, 2] It is generally observed that the oxygen fugacity of both cratonic and asthenospheric mantle is close to FMQ in the spinel field and that fO2 in the cratons generally decreases with depth. According to experimental studies combined with thermodynamic modelling, at depths below 180-200 km the decreasing oxygen fugacity should destabilise carbonate with all carbon at greater depths being stored as diamond [1, 3]. These pressure effects also tend to stabilise metal in the transition zone following the disproportionation of divalent iron (FeO) into Fe (metal) and Fe3+ (accommodated in garnet) [4]. To date, inclusions in diamond are the only available samples from the mantle transition zone and the lower mantle and these provide the opportunity for study of redox relationships in the deep mantle. In this study we used synchrotron Mössbauer Spectroscopy to measure Fe3+/(Fe2++ Fe3+) ratios of majoritic inclusions in diamonds from the lowermost upper mantle and the mantle transition zone for comparison with garnets from the shallow mantle. We find that there is a systematic increase with depth of the oxidation state of iron in garnets included in diamonds, with the deepest samples (~550 km depth) having Fe3+/(Fe2++ Fe3+) of up to 0.30, which is more than twice as great as in non-majoritic upper mantle garnets (< 200 km depth) [5]. When converted to oxygen fugacity these measurements imply conditions just above the stability field of metallic iron (above IW).
Contributions to Mineralogy and Petrology, doi.org:10.1007/ s00410-018-1499-5 19p.
Europe, Turkey
diamond inclusions
Abstract: The Pozanti-Karsanti ophiolite (PKO) is one of the largest oceanic remnants in the Tauride belt, Turkey. Micro-diamonds were recovered from the podiform chromitites, and these diamonds were investigated based on morphology, color, cathodoluminescence, nitrogen content, carbon and nitrogen isotopes, internal structure and inclusions. The diamonds recovered from the PKO are mainly mixed-habit diamonds with sectors of different brightness under the cathodoluminescence images. The total ?13C range of the PKO diamonds varies between ? 18.8 and ? 28.4‰, with a principle ?13C mode at ? 25‰. Nitrogen contents of the diamonds range from 7 to 541 ppm with a mean value of 171 ppm, and the ?15N values range from ? 19.1 to 16.6‰, with a ?15N mode of ? 9‰. Stacking faults and partial dislocations are commonly observed in the Transmission Electron Microscopy foils whereas inclusions are rather rare. Combinations of ( Ca0.81Mn0.19)SiO3, NiMnCo-alloy and nanosized, quenched fluid phases were observed as inclusions in the PKO diamonds. We believe that the 13C-depleted carbon signature of the PKO diamonds derived from previously subducted crustal matter. These diamonds may have crystallized from C-saturated fluids in the asthenospheric mantle at depth below 250 km which were subsequently carried rapidly upward by asthenospheric melts.
Abstract: Pyrope-almandine garnets (Mg# = 28.3-44.9, Ca# = 15.5-21.3) from a heavy mineral concentrate of diamondiferous kimberlites of the largest diamond deposit, the Yubileinaya pipe, along with kimberlite- like rocks and diamondiferous volcano-sediments of the Laptev Sea coast, have been found to contain polymineral, predominantly acicular inclusions, composed of aggregates of shrilankite (Ti2ZrO6), rutile, ilmenite, clinopyroxene, and apatite. The presence of shrilankite as an inclusion in garnets from assumed garnet-pyroxene rocks of the lower crust, lifted up by diamond-bearing kimberlite, allows it to be considered as an indicator mineral of kimberlite, which expands the possibilities when searching for kimberlite in the Arctic.
Africa, South Africa, China, United States, Canada, South America
diamond inclusions
Abstract: We present the first evidence for inclusions of ice-VII in diamonds from southern Africa, China, North- and South-America [1]. Combining synchrotron X-ray diffraction, - X-ray fluorescence and IR spectroscopy, we show the presence of ice-VII as inclusions in diamonds that have formed at depth > 410 km to about 800 km in the Earth's mantle. What is now crystalline ice-VII, a high pressure polymorph of water-ice, was component of an aqueous fluid entrapped in the diamonds that were growing in the deep mantle. Because of the confinement by the host diamonds, the inclusions retain high pressures. The same holds for inclusions of magnesian calcite, halite, and ilmenite found in the same diamond specimens. These inclusions reflect the presence of aqueous and carbonaceous fluids in the mantle transition zone and the shallow lower mantle. Using their current residual pressures and the equations of state, we can reconstruct their recovery paths [2,3]. Further, we can use the intersection of modelled recovery paths to better constrain the encapsulation pressure and temperature of these inclusions in diamonds.
Abstract: Mineral inclusions in diamonds reflect the compositional features of the diamondiferous sources so that they can provide important information of the upper mantle and even the transition zone. Since Moore and Gurney (1985) [1] found majoritic garnet inclusions in kimberlitic diamonds, the majoritic garnet inclusions have become significant samples to understand deep earth processes. According to Kiseeva et al. (2018) [2], the majoritic garnet inclusions have a ferric iron fraction (Fe3+/?Fe) increasing with depth. Recently, Xu et al. (2017) [3] discovered some majoritic garnets (from a depth of ~ 400 km) with ferric iron proportions as high as 0.81. In order to understand the origin of these Fe3+-rich garnet inclusions, the physical-chemical properties of the Fe3+-bearing garnets should be investigated. So far, no many studies have been carried out though. In this study, we performed experiments to synthesize garnets with their compositions along the grossular-andradite binary at 3 GPa and 1100 - 1200 °C, in order to investigate the effect on the physical-chemical properties of replacing Al3+ with Fe3+ on the octahedral sites of the garnet. The synthetic samples were investigated by BSE, EMPA, powder XRD and unpolarized Raman spectroscopy. The garnets had grain sizes between 20 ~ 100 um as indicated by BSI, and had generally homogenous compositions as suggested by the EMPA data. Charge balance calculations showed that most garnets had ferric iron fractions exceeding ~0.95. With an approximately linear dependence of the lattice parameters on the composition, the volume-mixing behavior should be generally ideal. We collected multiple Raman spectra from each sample, and evaluated the effects of crystal orientation and compositional heterogeneity on the Raman peak positions. Relations between the garnet compositions and Raman peak frequencies were also analyzed. Most Raman modes show linear behavior across the binary, whereas some of them do not. The reasons have been explored. According to the results of this study, we can infer that the elastic properties of the grossular-andradite binary might be linearly dependent to the composition. The Raman spectroscopic data are important for deriving some important thermodynamic data.
Journal of Geophysical Research: Solid Earth, doi: 10.1029/2018JB016012
Africa, South Africa
diamond inclusions
Abstract: Here we report the first results from elastic geobarometry applied to a kyanite inclusion entrapped within an eclogitic diamond (from Voorspoed mine, South Africa) using micro?Raman and Fourier transform infrared spectroscopy, electron microprobe analysis, ab initio calculations, and finite element modeling. Application of elastic geobarometry to very elastically anisotropic kyanite inclusions is challenging, as current models do not allow for elastic anisotropy. In order to minimize the effects of anisotropy, we have explored the effects of deviatoric stress on Raman modes via ab initio density functional theory. The results allowed us to select the Raman mode (at ca. 638 cm?1) that is the least sensitive to deviatoric stress. The shift of this band in the inclusion while still trapped within the diamond relative to the inclusion in air (once liberated) was used under hydrostatic approximation to determine a residual pressure on the inclusion of 0.184 ± 0.045 GPa and an entrapment pressure of 5.2 ± 0.3 GPa (~160 km depth) for an FTIR N?aggregation residence temperature of 1119 ± 50 °C. This is the first geothermobarometric determination for a diamond from the Voorspoed kimberlite. It overlaps with P-T estimates obtained by traditional chemical geobarometry for diamonds from other kimberlites from the Kaapvaal craton, suggesting that the hydrostatic approximation does not introduce significant errors in the geobarometric evaluation. Our protocol of Raman peak selection can be used for geobarometry of further kyanite?bearing diamonds and may provide a guide for more robust geobarometry of other types of mineral inclusions in diamonds, both eclogitic and peridotitic.
Abstract: Elastic geobarometry for host-inclusion systems can provide new constraints to assess the pressure and temperature conditions attained during metamorphism. Current experimental approaches and theory are developed only for crystals immersed in a hydrostatic stress field, whereas inclusions experience deviatoric stress. We have developed a method to determine the strains in quartz inclusions from Raman spectroscopy using the concept of the phonon-mode Grüneisen tensor. We used ab initio Hartree-Fock/Density Functional Theory to calculate the wavenumbers of the Raman-active modes as a function of different strain conditions. Least-squares fits of the phonon-wavenumber shifts against strains have been used to obtain the components of the mode Grüneisen tensor of quartz (??m1 and ?m3?) that can be used to calculate the strains in inclusions directly from the measured Raman shifts. The concept is demonstrated with the example of a natural quartz inclusion in eclogitic garnet from Mir kimberlite and has been validated against direct X-ray diffraction measurement of the strains in the same inclusion.
Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 306-7.
Mantle
diamond inclusions
Abstract: Nitrogen is one of the most common impurities in diamond, and its aggregation styles have been used as criteria for diamond classification. Pure type IaB diamonds (with 100% nitrogen in B aggregation) are rather rare among natural diamonds. The occurrence of the B center is generally associated with high temperature and a long residence time of the host diamond, which would potentially provide information on the earth’s deep interior. Seawater circulation is the unique process that shapes the surface of our planet and potentially has a profound effect on its interior due to slab subduction. In about 50 type IaB diamonds with detectable micro-inclusions submitted to GIA for screening, we found that more than 70% of them contained a typical mineral assemblage from the sublithosphere. Jeffbenite (TAPP), majorite garnet, enstatite, and ferropericlase have been observed, which could be retrograde products of former bridgmanite. CaSiO3-walstromite with larnite and titanite is the dominant phase present in approximately 40% of all diamond samples. Direct evidence from oxygen isotope ratios measured by secondary ion mass spectrometry, or SIMS, (?18OVSMOWin the range +10.7 to +12.5‰) of CaSiO3-walstromite with coexisting larnite and titanite that retrograde from CaSiO3-perovskite suggest that hydrothermally altered oceanic basalt can subduct to depths of >410 km in the transition zone. Incorporation of materials from subducted altered oceanic crust into the deep mantle produced diamond inclusions that have both lower mantle and subduction signatures. Ca(Si,Al)O3-perovskite was observed with a high concentration of rare earth elements (>5 wt.%) that could be enriched under P-Tconditions in the lower mantle. Evidence from ringwoodite with a hydroxide bond, coexisting tuite and apatite, precipitates of an NH3phase, and cohenite with trace amounts of Cl imply that the subducted brines can potentially introduce hydrous fluid to the bottom of the transition zone. In the diamonds with subducted materials, the increasing carbon isotope ratio from the core to the rim region detected by SIMS (?13C from -5.5‰ to -4‰) suggests that an oxidized carbonate-dominated fluid was associated with recycling of the subducted hydrous material. The deep subduction played an important role in balancing redox exchange with the reduced lower mantle indicated by precipitated iron nanoparticles and coexisting hydrocarbons and carbonate phases.
Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 271-2.
Global
diamond inclusions
Abstract: Through research on inclusions in diamonds over the past 50 years, a detailed picture has emerged of the mineralogical and chemical composition of diamond substrates in Earth’s mantle and of the pressure-temperature conditions during diamond formation. The exact diamond-forming processes, however, are still a subject of debate. One approach to constrain diamond-forming processes is through model calculations that aim to obtain the speciation and the carbon content of carbon-hydrogen-oxygen (CHO) fluids at particular O/(O+H) ratios and pressure-temperature conditions (using GFluid of Zhang and Duan, 2010, or other thermodynamic models of fluids). The predictions of such model calculations can then be tested against carbon and nitrogen stable isotopes and nitrogen content fractionation models, based on in situ analyses across homogenously grown diamond growth layers. Based on this approach, Luth and Stachel (2014) proposed that diamond precipitation occurs predominantly from cooling or ascending CHO fluids, composed of water with minor amounts of CO2 and CH4 (which in response to decreasing temperature may react to form diamond: CO2+ CH4 ? 2C + 2H2O). The second approach focuses on constraining the diamondforming medium by studying submicrometer fluid inclusions in fibrous-clouded and, more recently, gem diamonds. Such studies established the presence of four compositional end members of inclusions: hydrous-saline, hydrous-silicic, high-Mg carbonatitic, and low-Mg carbonatitic (e.g., Navon et al., 1988; Weiss et al., 2009). Although these fluid inclusions only depict the state of the diamond-forming medium after formation, they nevertheless provide unique insights into the major and trace-element composition of such fluids that otherwise could not be obtained. The apparent dichotomy between the two approaches—models for pure CHO fluids and actual observation of impure fluids (socalled high-density fluids) in clouded and fibrous diamonds—relates to the observation that in high-pressure and high-temperature experiments close to the melting temperature of mantle rocks, hydrous fluids contain 10–50% dissolved solid components (e.g., Kessel et al., 2015). Although at this stage the impurity content in natural CHO fluids cannot be included in numerical models, the findings for clouded and fibrous diamonds are not in conflict with the isochemical diamond precipitation model. Specifically, the fact that observed high-density inclusions are often carbonate bearing is not in conflict with the relatively reducing redox conditions associated with the O/(O+H) ratios of modeled diamond-forming CHO fluids. The model for the minimum redox stability of carbonate - bearing melts of Stagno and Frost (2010) permits fluid carbonate contents of up to about 30% at such redox conditions. Although additional data need to be obtained to build a thermodynamic model for CHO fluids with dissolved silicates and to better characterize the major and trace-element composition of high-density CHO fluids in equilibrium with typical diamond substrates (the rock types peridotite and eclogite), we already see sufficient evidence to suggest that the two approaches described above are converging to a unified model of isochemical diamond precipitation from cooling or ascending high-density CHO fluids.
Abstract: n recent years, nominal type IaAB and IIa diamonds with transient 2800 cm-1 FTIR absorption peaks arising from uncompensated boron produced under UV radiation have been reported (J. Li et al., A diamond with a transient 2804 cm-1 absorption peak, Journal of Gemmology, Vol. 35, 2016, pp. 248-252; Winter 2016 Lab Notes, pp. 412-413). The National Center of Supervision and Inspection on Quality of Gold and Silver Products recently examined a type IaB diamond that exhibited instantaneous 2803 cm-1 FTIR absorption shortly after exposure to an ultra-short-wave (< 230 nm) UV source.
Abstract: Type IIb diamonds, those defined as having trace amounts of substitutional boron, are prized for their blue colors. The famous Hope diamond is a perfect example. Besides their boron content, these rare diamonds are also characterized by their general lack of nitrogen. Little is known about how type IIb diamonds form, but they are especially intriguing because boron is often regarded as a crustal element whose presence in mantle-derived diamonds is unexpected. Despite interest in type IIb diamonds as a potential geochemical tracer of mantle processes, minimal research progress has been made to date. They are simply so rare and their color so highly valued that sample access is problematic. Even when access to type IIb diamonds is granted, these diamonds are typically free of mineral or fluid inclusions that might illuminate their geological significance (e.g. Gaillou et al. 2012; King et al. 1998).
Abstract: Diamonds are the deepest accessible “fragments” of Earth, providing records of deep geological processes. Absolute ages for diamond formation are crucial to place these records in the correct time context. Diamond ages are typically determined by dating inclusions, assuming that they were formed simultaneously with their hosts. One of the most widely used mineral inclusions for dating diamond is garnet, which is amenable to Sm-Nd geochronology and is common in lithospheric diamonds. By investigating worldwide garnet-bearing diamonds, we provide crystallographic evidence that garnet inclusions that were previously considered to be syngenetic may instead be protogenetic, i.e., they were formed before the host diamond, raising doubts about the real significance of many reported diamond “ages.” Diffusion modeling at relevant pressures and temperatures, however, demonstrates that isotopic resetting would generally occur over geologically short time scales. Therefore, despite protogenicity, the majority of garnet-based ages should effectively correspond to the time of diamond formation. On the other hand, our results indicate that use of large garnet inclusions (e.g., >100 ?m) and diamond hosts formed at temperatures lower than ?1000 °C is not recommended for diamond age determinations.
Abstract: Geophysical investigations and laboratory experiments provide strong evidence for subduction of ancient oceanic crust, and geological and mineralogical observations suggest that subducted oceanic crust is recycled into the upper mantle. This model is supported by some direct petrologic and miner-alogical evidence, principally the recovery of super-deep diamonds from kimberlites and the presence of crustal materials in ophiolitic chromitites and peridotites, but many details are still unclear. Here we report the discovery of ophiolite-hosted diamonds in the podiform chromitites of the Skenderbeu massif of the Mirdita ophiolite in the western part of Neo-Tethys. The diamonds are characterized by exceedingly light C isotopes (?13CPDB ~ -25‰), which we interpret as evidence for subduction of organic carbon from Earth's surface. They are also characterized by an exceptionally large range in ? 15Nair (-12.9‰ to +25.5‰), accompanied by a low N aggregation state. Materials sparsely included in diamonds include amorphous material, Ni-Mn-Co alloy, nanocrystals (20 × 20 nm) of calcium silicate with an orthorhombic perovskite structure (Ca-Pv), and fluids. The fluids coexisting with the alloy and Ca-Pv provide clear evidence that the diamonds are natural rather than synthetic. We suggest that the Skenderbeu diamonds nucleated and grew from a C-saturated, NiMnCo-rich melt derived from a subducted slab of ocean crust and lithosphere in the deep mantle, at least in the diamond stability field, perhaps near the top of the mantle transition zone. The subsequent rapid upward transport in channeled networks related to slab rollback during subduction initiation may explain the formation and preservation of Skenderbeu diamonds. The discovery of diamonds from the Mirdita ophiolite not only provides new evidence of diamonds in these settings but also provides a valuable opportunity to understand deep cycling of subducted oceanic crust and mantle composition.
Abstract: Diamonds growing in the Earth’s mantle often trap inclusions of fluids that are highly saline in composition. These fluids are thought to emerge from deep in subduction zones and may also be involved in the generation of some of the kimberlite magmas. However, the source of these fluids and the mechanism of their transport into the mantle lithosphere are unresolved. Here, we present experimental results showing that alkali chlorides are stable solid phases in the mantle lithosphere below 110 km. These alkali chlorides are formed by the reaction of subducted marine sediments with peridotite and show identical K/Na ratios to fluid inclusions in diamond. At temperatures >1100°C and low pressures, the chlorides are unstable; here, potassium is accommodated in mica and melt. The reaction of subducted sediments with peridotite explains the occurrence of Mg carbonates and the highly saline fluids found in diamonds and in chlorine-enriched kimberlite magmas.
www.minsocam.org/ MSA/Centennial/ MSA_Centennial _Symposium.html The next 100 years of mineral science, June 20-21, p. 21. Abstract
Mantle
diamond inclusions
Abstract: Inclusions in diamonds can tell us much of the deep and inaccessible portions of our planet including its mineralogy and the deeper effects of plate tectonics. Recently, great attention has been given in particular to those inclusions which classify their diamond hosts as “super-deep” or “sublithospheric” diamonds, which comprise only ~ 1% of the entire world diamond population (Stachel and Harris 2008). Compared to lithospheric diamonds, which form between about 120 km and 250 km depth, super-deep diamonds are believed to have formed at depths as high as 800 km. But what is the actual depth of formation of superdeep diamonds? Do they come from the Transition Zone (410-660 km depth) and Lower Mantle (below 660 km depth) or some of them form in the Upper Mantle (down to 410 km depth)? Recent advances in X-ray crystallography and theoretical understanding of mineral elasticity now allow us to answer these questions by analyzing inclusions trapped within them. Among these we can mention: jeffbenite, (Mg,Fe)3Al2Si3O12 (Nestola et al. 2016; previously known as TAPP), breyite, CaSiO3 (Brenker et al. 2018; previously known as CaSiO3-walstromite, Joswig et al. 1999, Stachel et al. 2000), ringwoodite, (Mg,Fe)2SiO4 (Pearson et al. 2014), CaSi2O5 with titanite structure (Stachel et al. 2000, Brenker et al. 2005, 2007), CaSiO3 with perovskite structure (Nestola et al. 2018). Other inclusions are typically found in super-deep diamonds but, if taken alone, they cannot be unambiguously assigned to specific depth: ferropericlase, (Mg,Fe)O, which is the most common inclusion in super-deep diamonds (e.g. Brey et al. 2004, Harte 2010), majoritic garnet, Mg3(Mg,Fe,Al,Si)2Si3O12 (Moore and Gurney 1985, Stachel et al. 2005, Walter et al. 2011), low-Ni enstatite (i.e. enstatite with very low NiO content close to 0.02 wt%, considered to be retrogressed bridgmanite, as opposed to typical Upper Mantle enstatite with 0.1-0.2 % , is, Stachel et al. 2000) and larnite, Ca2SiO4 (e.g. Brenker et al. 2005). These 9 types of inclusions are not the only ones found in super-deep diamonds, but they certainly are the most representative and abundant ones. Here, we want to provide an overview on the real significance of such important inclusions as depth markers. In particular, we will discuss which inclusion types can definitively prove a Transition-Zone or Lower-Mantle origin of super-deep diamonds, giving mineralogy a new relevance for the understanding of the deepest reaches of our planet.
www.minsocam.org/ MSA/Centennial/ MSA_Centennial _Symposium.html The next 100 years of mineral science, June 20-21, p. 22. Abstract
Mantle
diamond inclusions
Abstract: Much of the temporal record of Earth’s evolution, including its trace of plate tectonics, is blurred due to the dynamic nature of the crust-mantle system. While zircon provides the highest fidelity crustal record, diamond takes over in the mantle as the go-to mineral, capable of retaining critical information for a variety of geochemical proxies, over billion year timescales. Here we use diamond and its inclusions to tell the story of the recycling of C, N, O, H and B from the crust to various depths in Earth’s mantle. In this story, altered oceanic crust (AOC) and lithospheric mantle will play a prominent role. The carbon isotope record of diamond has long been thought to reflect the mixing of primitive mantle carbon with carbon recycled from isotopically light organic material originating from the crust. A major difficulty has been reconciling this view with the highly varied nitrogen and carbon isotope signatures in diamonds of eclogitic paragenesis, which cannot be interpreted by the same mechanism. Recent work on AOC of igneous origin (Li et al., EPSL in press) shows how isotopically varied carbon and nitrogen can be subducted to great depth and retained in spatial juxtaposition with the mafic silicate component of AOC to form the complex C-N isotope systematics observed in diamonds and the varied O isotope compositions of their inclusions. In this model a large portion of the 13C depleted carbon originated from biogenic carbonate within the AOC rather than from overlying sediments. Metamorphosed and partially devolatilized AOC will have very variable C/N ratios and highly variable nitrogen isotopes, explaining why simple two component mixing between organic matter and convecting upper mantle cannot explain the complexity of C-N isotope systematics in diamonds. Igneous AOC and its underlying altered mantle are considerably more efficient than subducted sediment at retaining their volatile inventory when recycled to transition zone and even lower mantle depths. Hence, this combination of mixing between AOC-derived volatiles and those from the convecting mantle produces the isotopic fingerprints of superdeep diamonds and their inclusions. These amazing diamonds, some worth millions of dollars, can contain pristine ultra-high pressure mineral phases never before seen in terrestrial samples. The first hydrous ringwoodite found in Earth provides evidence in support of a locally water-saturated transition zone that may result from altered oceanic lithospheric mantle foundering at that depth in the mantle. The O isotope composition of deep asthenosphere and transition zone phases document clearly crustal precursors that have interacted with the hydrosphere before residing hundreds of km deep within the Earth. Finally, spectacular blue diamonds contain boron, an element of strong crustal affinities, transported into the deep Earth along with crustal carbon, by the plate tectonic conveyor system. Diamond - such a simple mineral - and its inclusions, will continue to provide a unique, brightly illuminating light into the darkest recesses of Earth’s mantle for many years to come.
Journal of Synchrotron Radiation, Vol. 26, doi.org/10.1107 /S1600577519006854 6p. Pdf
Mantle
diamond inclusions
Abstract: Mineral inclusions in natural diamond are widely studied for the insight that they provide into the geochemistry and dynamics of the Earth's interior. A major challenge in achieving thorough yet high rates of analysis of mineral inclusions in diamond derives from the micrometre-scale of most inclusions, often requiring synchrotron radiation sources for diffraction. Centering microinclusions for diffraction with a highly focused synchrotron beam cannot be achieved optically because of the very high index of refraction of diamond. A fast, high-throughput method for identification of micromineral inclusions in diamond has been developed at the GeoSoilEnviro Center for Advanced Radiation Sources (GSECARS), Advanced Photon Source, Argonne National Laboratory, USA. Diamonds and their inclusions are imaged using synchrotron 3D computed X-ray microtomography on beamline 13-BM-D of GSECARS. The location of every inclusion is then pinpointed onto the coordinate system of the six-circle goniometer of the single-crystal diffractometer on beamline 13-BM-C. Because the bending magnet branch 13-BM is divided and delivered into 13-BM-C and 13-BM-D stations simultaneously, numerous diamonds can be examined during coordinated runs. The fast, high-throughput capability of the methodology is demonstrated by collecting 3D diffraction data on 53 diamond inclusions from Juína, Brazil, within a total of about 72 h of beam time.
Abstract: Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or quenched upon emplacement of the host kimberlite. The abundance of carbonate minerals (e.g., calcite, dolomite) and hydrous silicate minerals (e.g., phlogopite, serpentine, chlorite) within polymineralic inclusions suggests that the trapped melt was more volatile-rich than the host kimberlite now emplaced in the crust. However, the exact composition of this presumed early kimberlite melt, including the inventory of trace elements and volatiles, remains to be more narrowly constrained. For instance, one major question concerns the role of accessory alkali-halogen-phases in polymineralic inclusions, i.e., whether such phases constitute a common primary feature of kimberlite melt(s), or whether they become enriched in late-stage differentiation processes. Recent studies have shown that polymineralic inclusions react with their host minerals during ascent of the kimberlite, while being largely shielded from processes that affect the host kimberlite, e.g., the assimilation of xenoliths (mantle and crustal), degassing of volatiles, and secondary alteration. Importantly, some polymineralic inclusions within different megacryst minerals were shown to preserve fresh glass. A major conclusion of this review is that the abundance and mineralogy of polymineralic inclusions are directly influenced by the physical and chemical properties of their host minerals. When taking the different interactions with their host minerals into account, polymineralic inclusions in megacrysts can serve as useful proxies for the multi-stage origin and evolution of kimberlite melt/magma, because they can (i) reveal information about primary characteristics of the kimberlite melt, and (ii) trace the evolution of kimberlite magma on its way from the upper mantle to the crust.
Abstract: Bridgmanite (Mg,Fe)SiO3, a high pressure silicate with a perovskite structure, is dominant material in the Lower Mantle and therefore is probably the most abundant mineral in the Earth. One single-phase and two composite inclusions of (Mg,Fe)SiO3 coexisting with jeffbenite ((Mg,Fe)3Al2Si3O12), and with jeffbenite and olivine ((Mg,Fe)2SiO4) have been analyzed to identify retrograde phases of former bridgmanite in diamonds from Juina (Brazil). XRD and Raman spectroscopy have revealed that (Mg,Fe)SiO3 inclusions are orthopyroxene at ambient conditions. XRD patterns of these inclusions indicate that they consist of polycrystals. This polycrystalline textures together with high lattice strain of host diamond around these inclusions observed from EBSD may be an evidence for the retrograde phase transition of former bridgmanite. Single-phase inclusions of (Mg,Fe)SiO3 in superdeep diamonds are suggested to represent a retrograde phase of bridgmanite and fully inherit its initial chemical composition, including a high Al and low Ni contents [1,2]. The composite inclusions of (Mg,Fe)SiO3 with jeffbenite and other silicate and oxide phases may be interpreted as exsolution products from originally homogeneous bridgmanite [3]. The bulk compositions of these inclusions are rich in Al, Ti, and Fe which are similar to bridgmanite produced in experiments on the MORB composition. However, the retrograde origin of composite inclusions due to decomposition of Al-rich bridgmanite may be doubtful because each of observed phases may represent single-phase inclusions, i.e. bridgmanite and high pressure garnet (majoritic garnet), with similar compositional features.
Geochemistry International, Vol. 57, 9, pp. 964-972.
Mantle
diamond inclusions
Abstract: The paper describes mineralogical characteristics of SiO2 inclusions in sublithospheric diamonds, which typically have complicated growth histories showing alternating episodes of growth, dissolution, and postgrowth deformation and crushing processes. Nitrogen contents in all of the crystals do not exceed 71 ppm, and nitrogen is detected exclusively as B-defects. The carbon isotope composition of the diamonds varies from ?13? = -26.5 to -6.7‰. The SiO2 inclusions occur in association with omphacitic clinopyroxenes, majoritic garnets, CaSiO3, jeffbenite, and ferropericlase. All SiO2 inclusions are coesite, which is often associated with micro-blocks of kyanite in the same inclusions. It was suggested that these phases have been produced by the retrograde dissolution of primary Al-stishovite, which is also evidenced by the significant internal stresses in the inclusions and by deformations around them. The oxygen isotope composition of SiO2 inclusions in sublithospheric diamonds (?18O up to 12.9‰) indicates a crustal origin of the protoliths. The negative correlation between the ?18O of the SiO2 inclusions and the ?13C of their host diamonds reflects interaction processes between slab-derived melts and reduced mantle rocks at depths greater than 270 km.
Geochimica et Cosmochimica Acta, Vol. 266, pp. 197-212.
Russia, Urals
diamond inclusions
Abstract: The compositions of mineral inclusions from a representative collection (more than 140 samples) of diamonds from the placer deposits in the Ural Mountains were studied to examine their compositional diversity. The overwhelming majority of rounded octahedral and dodecahedral stones typical of placers contain eclogitic (E-type) mineral inclusions (up to 80%) represented by garnets with Mg# 40-75 and Ca# 10-56, including the unique high calcic “grospydite” composition, omphacitic pyroxenes containing up to 65% of jadeite, as well as kyanite, coesite, sulfides, and rutile. Peridotitic (P-type) inclusions are represented by olivine, subcalcic Cr-pyrope, chrome diopside, enstatite and magnesiochromite that are typical for diamonds worldwide. Comparing the chemical composition of olivine, pyrope and magnesiochromite in diamonds of the Urals, north-east of the Siberian platform placers and Arkhangelsk province kimberlites show striking similarity. There are significant differences only in the variations of carbon isotopic composition of the diamonds from the placers of the Urals and north-east of the Siberian platform. One typical rounded dodecahedral diamond was found to contain abundant primary oriented submicrometer-sized (<3.0?µm) octahedral fluid inclusions identified by transmission electron microscopy, which caused the milky color of the entire diamond crystal. The electron energy-loss spectrum of a singular inclusion has a peak at ?405?eV, indicating that nitrogen is present. The Raman spectra with peaks at 2346-2350?cm?1 confirmed that nitrogen exists in the solid state at room temperature. This means that fossilized pressure inside fluid inclusions may be over 6.0 GPa at room temperature, so the diamond may be considered sublithospheric in origin. However, identification of unique fluid inclusions in one typical placer diamond allows one to expand the pressure limit to at least more than 8.0 GPa. The volatile components of four diamonds from the Urals placers were analyzed by gas chromatography-mass spectrometry (GC-MS). They are represented (rel. %) by hydrocarbons and their derivatives (14.8-78.4), nitrogen and nitrogenated compounds (6.2-81.7), water (2.5-5.5), carbon dioxide (2.8-12.1), and sulfonated compounds (0.01-0.96). It is shown that high-molecular-weight hydrocarbons and their derivatives, including chlorinated, nitrogenated and sulfonated compounds, appear to be stable under upper mantle P-T conditions. A conclusion is drawn that Urals placer diamonds are of kimberlitic origin and are comparable in their high E-type/P-type inclusion ratios to those from the northeastern Siberian platform and in part to diamonds of the Arkhangelsk kimberlite province.
Parageneses of garnet inclusions in diamonds from Yakutia kimberlites based on Raman and IR spectroscopy data. Udachnaya, Zapolyarnaya, Komolskaya, Yuibeyana, Aikhal, Mir, Mayskaya.
Geology of Ore Deposits, Vol. 61, 7, pp. 606-612. pdf
Optics Express, Vol. 27, 19, pp. 27242-27255. doi.org/10.1034/ oe.27.027242
Global
diamond inclusion
Abstract: Diamond clarity refers to the absence of tiny, natural inclusions (imperfections) inside a diamond or on its surface. Almost all diamonds contain their own unique inclusions due to their natural formation process. In this paper, a new inclusion extraction approach is developed to accurately separate the regions of interest in a diamond clarity image and then identify the image features of each region. The inclusion regions can be successfully distinguished from other types of signals. The findings of the theoretical optical analysis facilitate the image processing development and also reduce its complexity and operation time. The experimental results verify the effectiveness and robustness of the proposed inclusion extraction approach. The diamond inclusions can be accurately extracted from the captured diamond clarity image. The extracted inclusions can also be converted to their actual size as seen by the naked human eye. The proposed approach is verified to be significantly less sensitive to noise than existing approaches and unaffected by the fluctuations in illumination.
Abstract: Experimentally determined major and trace element partition coefficients between majoritic garnet, clinopyroxene, and carbon dioxide-rich liquid are reported at 10 GPa and 1800 °C in a model carbonated peridotite composition in the system CaO-MgO-Al2O3-SiO2-CO2. Besides majoritic garnet, the liquid coexists with forsterite, orthopyroxene, and clinopyroxene, making melting phase relations invariant at fixed pressure and temperature conditions. Partition coefficients span a wide range of values - for instance, Sr, Nb, Ba, La, and Ce are highly incompatible in majoritic garnet, while Ca, Y, Nb, and Ho are moderately incompatible, and Lu, Si, Al, and Mg are compatible. Strong fractionation of light rare earth elements (e.g., La, Ce, Nd, Sm) and high field strength elements (e.g., Nb, Ta, Zr, Hf, Th) is seen between majoritic garnet and liquid. The experimentally determined partitioning values are used to calculate compositions of melts in equilibrium with majoritic garnet inclusions in diamonds from select localities in Brazil and Guinea. The calculated melts largely straddle those between documented carbonatites, kimberlites, and alkali basalts, low-degree mantle melting products from carbonated peridotite. This resemblance firmly suggests that majoritic garnet inclusions in diamonds from Brazil and Guinea can simply be interpreted as precipitates from such melts, thereby offering an alternative to the hypothesis that the element chemistry of such inclusions in diamonds can largely, and sometimes only, be ascribed to subducted oceanic crust, and further that, fusion of this crust may limit the terrestrial 'carbon recycling' at depths much beyond corresponding to those of Earth's transition zone.
Journal of Mineralogical and Petrological Sciences, Vol. 115, pp. 236-246. pdf
Mantle
diamond inclusions
Abstract: The genesis of CLIPPIR diamonds (Cullinan-like, large, inclusion-poor, pure, irregular, and resorbed) have attracted much interest due to their possible crystallization from metal melt in deep horizons of the earth’s mantle. These diamonds usually show a pronounced resorption and irregular morphology. The present paper reports new experimental data on the dissolution of diamond crystals at high P-T parameters in Fe-S melt containing large amounts of silicate components (5-20 wt%). The experiments were performed using a split-sphere multi-anvil apparatus (BARS) at a pressure of 4 GPa and a temperature of 1450 °C. The samples consisted of natural diamond crystals placed in mixtures of Fe, S, and kimberlite. Wide variations in dissolution rates of diamond crystals were obtained. The absence of diamond dissolution in a heterogeneous medium indicates that the amount of solid silicate phases present in metal melt plays a role in the preservation of diamonds. This study demonstrated how diamonds can be stored in natural environments due to the heterogeneity of the medium composition which could insulate diamonds from the metal-sulphide melt. The obtained results improve our understanding of processes that lead to preservation of CLIPPIR diamonds in the deep mantle.
Abstract: Mantle plumes sample the deep mantle. A limited number of geochemical endmember components can describe the isotopic and compositional variations in the ocean island basalts (OIBs), which are produced by plume volcanism. The endmembers are correlated to compositions in the OIB source regions or represent incorporation of material upon ascent. However, their actual nature and origins are still highly debated. The depths of plume sources have been proposed to be anywhere between the core-mantle boundary and the upper mantle, and need not be the same for all plume-related volcanic activities. Using a combination of synchrotron micro-X ray fluorescence and -diffraction mapping, and in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry, we show that the elemental features of HIMU-rich OIBs, such as Bermuda, St Helena, and Cook-Austral, exactly match the geochemical signature of a multiphase inclusion in a diamond. The geochemical signature in our studied diamond inclusion is markedly different from that of inclusions in lithospheric diamonds. The phases identified in the inclusion are majorite-rich garnet, ilmenite, the sodic 10Å-phase (TAP), and liebermannite. Furthermore, we show that this inclusion was entrapped at 14.5 ± 0.5 GPa (420-440 km) and 1450 ± 50 K. At the conditions of entrapment, the diamond inclusion phase assembly was garnet + ilmenite + liebermannite + clinopyroxene + stishovite + fluid. Sodic TAP is a retrograde product of reaction between clinopyroxene, stishovite, and fluid upon ascent. Its presence shows that the HIMU source is water-saturated. Entrapment in diamond indicates that the fluid also contained carbonate. The conditions of 14.5 ± 0.5 GPa and 1450 ± 50 K plot right on top of the alkaline carbonatite solidus, and match the formation of carbonatitic melt from subducted slabs plus diamond formation from reaction of carbonate with iron. In summary, our data show that the transition zone source accounts for the global HIMU endmember.
Proceedings of the National Academy of Sciences, pnas.org/cgi/doi.10.1073 /pnas.2004269117 7p. Pdf
Mantle
diamond inclusions
Abstract: The recent discovery in high-pressure experiments of compounds stable to 24-26 GPa with Fe4O5, Fe5O6, Fe7O9, and Fe9O11 stoichiometry has raised questions about their existence within the Earth’s mantle. Incorporating both ferric and ferrous iron in their structures, these oxides if present within the Earth could also provide insight into diamond-forming processes at depth in the planet. Here we report the discovery of metallic particles, dominantly of FeNi (Fe0.71Ni0.24Cu0.05), in close spatial relation with nearly pure magnetite grains from a so-called superdeep diamond from the Earth’s mantle. The microstructural relation of magnetite within a ferropericlase (Mg0.60Fe0.40)O matrix suggests exsolution of the former. Taking into account the bulk chemistry reconstructed from the FeNi(Cu) alloy, we propose that it formed by decomposition of a complex metal M oxide (M4O5) with a stoichiometry of (Fe3+2.15Fe2+1.59Ni2+0.17Cu+0.04)? = 3.95O5. We further suggest a possible link between this phase and variably oxidized ferropericlase that is commonly trapped in superdeep diamond. The observation of FeNi(Cu) metal in relation to magnetite exsolved from ferropericlase is interpreted as arising from a multistage process that starts from diamond encapsulation of ferropericlase followed by decompression and cooling under oxidized conditions, leading to the formation of complex oxides such as Fe4O5 that subsequently decompose at shallower P-T conditions.
Abstract: Majoritic garnet has been predicted to be a major component of peridotite and eclogite in Earth's deep upper mantle (>250 km) and transition zone. The investigation of mineral inclusions in diamond confirms this prediction, but there is reported evidence of other majorite-bearing lithologies, intermediate between peridotitic and eclogitic, present in the mantle transition zone. If these lithologies are derived from olivine-free pyroxenites, then at mantle transition zone pressures majorite may form monomineralic or almost monomineralic garnetite layers. Since majoritic garnet is presumably the seismically fastest major phase in the lowermost upper mantle, the existence of such majorite layers might produce a detectable seismic signature. However, a test of this hypothesis is hampered by the absence of sound wave velocity measurements of majoritic garnets with relevant chemical compositions, since previous measurements have been mostly limited to synthetic majorite samples with relatively simple compositions. In an attempt to evaluate the seismic signature of a pyroxenitic garnet layer, we measured the sound wave velocities of three natural majoritic garnet inclusions in diamond by Brillouin spectroscopy at ambient conditions. The chosen natural garnets derive from depths between 220 and 470 km and are plausible candidates to have formed at the interface between peridotite and carbonated eclogite. They contain elevated amounts (12-30%) of ferric iron, possibly produced during redox reactions that form diamond from carbonate. Based on our data, we model the velocity and seismic impedance contrasts between a possible pyroxenitic garnet layer and the surrounding peridotitic mantle. For a mineral assemblage that would be stable at a depth of 350 km, the median formation depth of our samples, we found velocities in pyroxenite at ambient conditions to be higher by 1.9(6)% for shear waves and 3.3(5)% for compressional waves compared to peridotite (numbers in parentheses refer to uncertainties in the last given digit), and by 1.3(13)% for shear waves and 2.4(10)% for compressional waves compared to eclogite. As a result of increased density in the pyroxenitic layer, expected seismic impedance contrasts across the interface between the monomineralic majorite layer and the adjacent rocks are about 5-6% at the majorite-eclogite-interface and 10-12% at the majoriteperidotite-boundary. Given a large enough thickness of the garnetite layer, velocity and impedance differences of this magnitude could become seismologically detectable.
Earth and Planetary Science Letters, Vol. 547, 10p. Pdf
Mantle
Wadsleyite, ringwoodite, majorite garnet
Abstract: The dynamics of the Earth's mantle is still poorly constrained due to the lack of understanding the transfer of matter between the upper and the lower mantle and their convective vigor. The transition zone (TZ) might play a crucial role as the interface connecting the upper to the lower mantle. Here, we examine the rheology of the main TZ minerals, wadsleyite, ringwoodite and majorite garnet based on a mineral physics approach. Using the results of lattice friction modeling and dislocation glide mobilities together with the available data on self-diffusion in the TZ minerals, we quantify their plastic deformation by diffusion and dislocation creep from theoretical plasticity models. We show that pure climb creep is expected to contribute to the plasticity of the TZ without the need of significant diffusion-related hydrolytic weakening, matching well the geophysical observations. Our model results predict that crystallographic preferred orientations (CPO) might only develop along with stress concentrations as present around cold subducting slabs which can be locally weaker than the surrounding TZ despite their lower temperatures.
Solid Earth Discussions, Vol. 5, pp. 1-75. pdf * note date
Russia, Yakutia
picroilmenites
Abstract: Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages.
High-pressure (5.5-7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1-10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10-100)/PM with La / Ybn ~ 10-25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet-spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn-Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.
Abstract: The transport of carbon into Earth’s mantle is a critical pathway in Earth’s carbon cycle, affecting both the climate and the redox conditions of the surface and mantle. The largest unconstrained variables in this cycle are the depths to which carbon in sediments and altered oceanic crust can be subducted and the relative contributions of these reservoirs to the sequestration of carbon in the deep mantle1. Mineral inclusions in sublithospheric, or ‘superdeep’, diamonds (derived from depths greater than 250 kilometres) can be used to constrain these variables. Here we present oxygen isotope measurements of mineral inclusions within diamonds from Kankan, Guinea that are derived from depths extending from the lithosphere to the lower mantle (greater than 660 kilometres). These data, combined with the carbon and nitrogen isotope contents of the diamonds, indicate that carbonated igneous oceanic crust, not sediment, is the primary carbon-bearing reservoir in slabs subducted to deep-lithospheric and transition-zone depths (less than 660 kilometres). Within this depth regime, sublithospheric inclusions are distinctly enriched in 18O relative to eclogitic lithospheric inclusions derived from crustal protoliths. The increased 18O content of these sublithospheric inclusions results from their crystallization from melts of carbonate-rich subducted oceanic crust. In contrast, lower-mantle mineral inclusions and their host diamonds (deeper than 660 kilometres) have a narrow range of isotopic values that are typical of mantle that has experienced little or no crustal interaction. Because carbon is hosted in metals, rather than in diamond, in the reduced, volatile-poor lower mantle2, carbon must be mobilized and concentrated to form lower-mantle diamonds. Our data support a model in which the hydration of the uppermost lower mantle by subducted oceanic lithosphere destabilizes carbon-bearing metals to form diamond, without disturbing the ambient-mantle stable-isotope signatures. This transition from carbonate slab melting in the transition zone to slab dehydration in the lower mantle supports a lower-mantle barrier for carbon subduction.
The American Mineralogist, Vol. 106, pp. 38-43. pdf
Mantle
perovskites, mineral inclusions
Abstract: Earth's lower mantle most likely mainly consists of ferropericlase, bridgmanite, and a CaSiO3- phase in the perovskite structure. If separately trapped in diamonds, these phases can be transported to Earth's surface without reacting with the surrounding mantle. Although all inclusions will remain chemically pristine, only ferropericlase will stay in its original crystal structure, whereas in almost all cases bridgmanite and CaSiO3-perovskite will transform to their lower-pressure polymorphs. In the case of perovskite structured CaSiO3, the new structure that is formed is closely related to that of walstromite. This mineral is now approved by the IMA commission on new minerals and named breyite. The crystal structure is triclinic (space group: P1) with lattice parameters a0 = 6.6970(4) Å, b0 = 9.2986(7) Å, c0 = 6.6501(4) Å, ? = 83.458(6)°, ? = 76.226(6)°, ? = 69.581(7)°, and V = 376.72(4) Å. The major element composition found for the studied breyite is Ca3.01(2)Si2.98(2)O9. Breyite is the second most abundant mineral inclusion after ferropericlase in diamonds of super-deep origin. The occurrence of breyite has been widely presumed to be a strong indication of lower mantle (=670 km depth) or at least lower transition zone (=520 km depth) origin of both the host diamond and the inclusion suite. In this work, we demonstrate through different formation scenarios that the finding of breyite alone in a diamond is not a reliable indicator of the formation depth in the transition zone or in the lower mantle and that accompanying paragenetic phases such as ferropericlase together with MgSiO3 are needed.
Abstract: The Carlsbad laboratory recently examined a 0.70 ct, E-color round brilliant. Infrared spectroscopy showed this to be a type IIa diamond, so we performed a variety of additional spectroscopy and imaging to verify its natural origin. This diamond also had I1 clarity due to a large inclusion under the table (figure 1). Raman analysis of the inclusions verified that this crystal was a metastable composite of the minerals wollastonite (CaSiO3) and CaSiO3-breyite (E.M. Smith et al., “The very deep origin of the world’s biggest diamonds,” Winter 2017 G&G, pp. 388-403), which indicates a sublithospheric origin. These minerals are believed to be the lower-pressure phases of CaSiO3-perovskite. Around these minerals were large disk-like graphitic fractures indicating inclusion expansion as pressures on the diamond reduced during exhumation from the mantle. The other inclusion present was unidentifiable due to its graphitic casing. Recent research of inclusions in other type II diamonds shows that many, if not most, have a superdeep origin (again, see Smith et al., 2017). This stone is one more example of diamonds forming at incredible depths of 360-750 km before being transported to near the surface.
Abstract: Inclusions can tell us a great deal about a diamond’s formation history. Inclusions such as olivine, garnet, and chromite are more common, while others such as kyanite, zircon, and corundum (Al2O3) can be quite rare. Regardless of their rarity, diamond inclusions are often quite fascinating as they trap a small bit of the deep earth that cannot otherwise be sampled.
Journal of Geophysical Research, Solid Earth, in press available, 34p.
Global
diamond inclusions
Abstract: Natural diamonds, as well as being a cherished commodity, are valuable for scientists studying the Earth's interior because they only grow at depths greater than 140 km. When diamonds grow, they may trap tiny fragments of surrounding materials as sub?millimetre defects. Study of these inclusions can provide insights into the materials and processes occurring deep inside our planet. Sub?lithospheric diamonds are a relatively rare subset of natural diamonds, believed to have grown deeper than 250 km, and are thought to be the deepest Earth materials that have been transported to the surface. Ideally, we would be able to estimate their formation depths accurately. Inclusions of majoritic garnet provide a unique opportunity for this, as their chemistry is known to change systematically with formation depth. However, this behaviour is highly complex, and previous attempts to parameterise the depth dependence of inclusion chemistries have limitations. Here we have used data science to train a "Machine Learning" algorithm that improves the accuracy of estimating the formation pressures of majoritic garnet inclusion. The approach confirms that many natural diamonds containing inclusions of majoritic garnet must have originally formed at depths of 400 - 660 km.
Nature Communications, doi.org/10.10.1038 /s41467-021-21761-9 8p. Pdf
Mantle
diamond inclusions
Abstract: The stable forms of carbon in Earth’s deep interior control storage and fluxes of carbon through the planet over geologic time, impacting the surface climate as well as carrying records of geologic processes in the form of diamond inclusions. However, current estimates of the distribution of carbon in Earth’s mantle are uncertain, due in part to limited understanding of the fate of carbonates through subduction, the main mechanism that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to reside in MgCO3 throughout much of the mantle. Experiments in this study demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work indicating that CaCO3 is more stable than MgCO3 under reducing conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.
Abstract: Inclusions are more than imperfections or clarity characteristics. They can teach us much about gemstones’ journeys and reveal otherwise inaccessible information about Earth’s formation. What stories do diamond inclusions tell about Earth’s mantle? What do rutile needles and three-phase inclusions teach us about corundum and emerald, respectively? Follow Manager of Gem Identification Nathan Renfro and Senior Manager of Research Dr. Aaron Palke as they offer an up-close look into the microworld of gems and show us how this world reveals secrets about Earth’s geologic processes at large.
Abstract: Sulfides are the most abundant inclusions in diamonds and a key tool for dating diamond formation via Re-Os isotopic analyses. The manner in which fluids invade the continental lithospheric mantle and the time scale at which they equilibrate with preexisting (protogenetic) sulfides are poorly understood yet essential factors to understanding diamond formation and the validity of isotopic ages. We investigated a suite of sulfide-bearing diamonds from two Canadian cratons to test the robustness of Re-Os in sulfide for dating diamond formation. Single-crystal X-ray diffraction (XRD) allowed determination of the original monosulfide solid-solution (Mss) composition stable in the mantle, indicating subsolidus conditions of encapsulation, and providing crystallographic evidence supporting a protogenetic origin of the inclusions. The results, coupled with a diffusion model, indicate Re-Os isotope equilibration is sufficiently fast in sulfide inclusions with typical grain size, at mantle temperatures, for the system to be reset by the diamond-forming event. This confirms that even if protogenetic, the Re-Os isochrons defined by these minerals likely reflect the ages of diamond formation, and this result highlights the power of this system to date the timing of fluid migration in mantle lithosphere.
Abstract: This study highlights the usefulness of rutile when applied for reconstruction of the metamorphic evolution of ultrahigh-pressure rocks containing diamond. Within the diamondiferous kyanite gneiss (Kokchetav massif, Northern Kazakhstan), rutile shows three distinct textural positions: (i) rounded/irregular-shaped grains in the rock matrix; (ii) monomineralic inclusions in garnet, kyanite, quartz, and zircon; and (iii) grains in polyphase inclusions within garnet and kyanite porphyroblasts. High Nb (1990-3197 ppm) and relatively low Cr (404-703 ppm) concentrations in rutile indicate its metapelitic derivation. The Zr content in rutile varies from 480 to 798 ppm and the average temperature estimates yielded by the Zr-in-rutile geothermometer for 5 GPa are 880 °C. Rutile-hosted Zn-rich (up to 1.74 wt% ZnO) staurolite is interpreted as a record of the prograde metamorphic stage formed as a result of gahnite+pyrophyllite+diaspore breakdown at 0.3-0.8 GPa, 400-450 °C. Inclusions of diamond±CO2 ± carbonate±garnet in rutile originated near the peak of metamorphism (~5 GPa and ~ 880 °C). U-Pb ID-TIMS dating of a representative rutile separate yielded a concordant age of 519 ± 1.6 Ma that is younger than the previously estimated U-Pb crystallization ages of the peak metamorphic assemblages of the Kokchetav massif (528 ± 3 Ma). The obtained age represents the timing of cooling to the closure temperature for Pb diffusion in rutile (Tc; 420-640 °C). The cooling of the rocks from the peak temperatures to Tc occurred with the rates of 27-51 °C/Ma, whereas the exhumation rates (from 880 °C and 5 GPa to 420-640 °C and 0.5-1 GPa) were 1.3-1.5 cm/year. The peak temperature estimates as well as rapid cooling and exhumation rates reported here are in agreement with published data on zircon from similar diamondiferous Kokchetav gneisses. This work demonstrates that rutile provides a beneficial tool in studies dealing with reconstruction of the metamorphic evolution of diamondiferous rocks.
Journal of Geophysical Research Physical Review B., http://doi.org/10 /1029/2020JB020 604 21p. Pdf
Mantle
diamond inclusions
Abstract: Natural diamonds, as well as being a cherished commodity, are valuable for scientists studying the Earth's interior because they only grow at depths greater than 140 km. When diamonds grow, they may trap tiny fragments of surrounding materials as sub?millimeter defects. Study of these inclusions can provide insights into the materials and processes occurring deep inside our planet. Sub?lithospheric diamonds are a relatively rare subset of natural diamonds, believed to have grown deeper than 250 km, and are thought to be the deepest Earth materials that have been transported to the surface. Ideally, we would be able to estimate their formation depths accurately. Inclusions of majoritic garnet provide a unique opportunity for this, as their chemistry is known to change systematically with formation depth. However, this behavior is highly complex, and previous attempts to parameterize the depth dependence of inclusion chemistries have limitations. Here we have used data science to train a "machine learning" algorithm that improves the accuracy of estimating the formation pressures of majoritic garnet inclusion. The approach confirms that many natural diamonds containing inclusions of majoritic garnet must have originally formed at depths of 400-660 km.
Geochemical Perspectives Letters, Vol. 17, pp. 33-38. pdf
Mantle
diamond inclusions
Abstract: Diamond inclusions sample the otherwise inaccessible archive of Earth’s deep interior. The geochemical and petrological diversity of diamond inclusions reflects either pre-metasomatic upper mantle heterogeneity or metasomatism coeval with diamond formation. We focus on the origin of lithospheric garnet and clinopyroxene inclusions by simulating metasomatic reactions between eclogitic fluids and mantle peridotites at 5 GPa, 1000 °C, and across a range of redox conditions (logfO2?=??1 to ?6 ?FMQ). Our results demonstrate that fluid-rock interaction can result in the formation of eclogitic, websteritic, and peridotitic silicates from a single fluid during a single diamond-forming metasomatic event. Ergo, the petrogenesis of diamond and their inclusions can be syngenetic, and the petrological diversity of diamond inclusions can reflect metasomatism coeval with diamond formation. Furthermore, during the metasomatism, refractory peridotite can be converted to fertile websterite which could become a pyroxenitic mantle source for oceanic basalts.
Abstract: Diamonds entrap mantle inclusions and shield them from alteration by magmatic and tectonic processes. Diamonds from Guyana are an understudied diamond suite, and the inclusions they contain provide us a window into the sub-cratonic mantle beneath northern South America. We used crystalline inclusions inside of Guyanese diamonds to infer the composition of the underlying mantle, and make estimates for its structural properties. The inclusions empirically demonstrate the long-lived, dry, and reduced nature of cratonic roots, lending evidence to the mechanism behind their preservation through time.
Abstract: Earthquakes occurring below ?300 km, especially in the mantle transition zone are some of the strongest events experienced on Earth. Deep earthquakes, whose nature and cause are poorly known, occur with regularity and are a deep and prominent result of plate tectonics. We model the paths of subducting slabs to relate pressure-temperature conditions to the experimentally determined mineralogies of the slab crust and mantle. We present a synthesis of mantle minerals included in diamonds derived from same depths as the deep earthquakes to show that fluids exist there. We show that decarbonization/melting reactions in the slab crust and dehydration reactions in the slab mantle can provide fluids to the earthquake generation regions, suggesting that fluids cause or are related to deep earthquakes.
Mantle Convection and Surface Expressions, Geophysical Monograph, No. 263, Chapter 7, pp. 179- 14p. Pdf
Mantle
inclusions, subduction, CLIPPER
Abstract: Some rare diamonds originate below the lithosphere, from depths of 300-800 km and perhaps deeper. Ongoing sublithospheric or super-deep diamond research is providing new insight into the mantle and the hidden consequences of plate tectonics. Here we highlight several advances in the past decade, stemming from the discovery of inclusions from oceanic crust at lower mantle depths; inclusions having geochemical imprints of low-degree car-bonatitic melt, possibly from subducted slabs; hydrous ringwoodite and other signs of deep water; major mantle minerals preserved in their original crystal structure, including ringwoodite and CaSiO 3-perovskite; additional diamond varieties with a super-deep origin (CLIPPIR and type IIb diamonds), greatly increasing the known prevalence and diversity of super-deep diamonds; and consistent, recurring Fe-Ni-C-S metallic melt inclusions from depths of 360-750 km. Redox freezing of oxidized, slab-derived fluid/melt upon interaction with ambient metal-saturated mantle appears to be a phenomenon broadly recorded by many super-deep diamonds. Melting of car-bonate, as well as dehydration reactions, from subducted slabs are relevant mechanisms that may generate fluid/ melt contributing to diamond growth. Fe-Ni metal, with dissolved carbon, sulfur, and other elements is also indicated as a possible diamond-forming melt. These mobile and dynamic phases are agents of chemical mass-transfer in the deep mantle.
Abstract: Defects found in diamonds are typically received as unwelcome news to the discerning jewelry shopper. But for some physicists, diamond imperfections offer a new opportunity to push the boundaries of futuristic devices that could become the backbone of tomorrow’s computers. UC San Diego Department of Physics Assistant Professor Chunhui Rita Du is a condensed matter experimentalist whose research takes advantage of impurities in diamonds. Du’s research group leverages the red, yellow and blue colors that result from diamond defects to develop sensors that can evaluate the properties of specialized materials down to the nanometer level.
AGU Advances, doi.org/10.10.1029/2021AV000434, 2p. Pdf
Mantle
diamond inclusions
Abstract: The interior of the Earth at depths greater than about 70 km is entirely devoid of earthquakes, except for a few limited regions associated with current or recent subduction. The absence of earthquakes is expected, since friction along faults becomes too great for brittle failure at these pressures. The difficult question, which has been debated for decades, is what physical process allows deep earthquakes to occur in subduction environments. Now, in a recent publication in AGU Advances, Shirey et al. (2021) provide strong evidence that fluids exist in deep subduction environments, and play a crucial role in producing deep earthquakes.
Journal of the Geological Society of India, Vol. 98, 12p. Pdf
India
chrome-diopside
Abstract: In comparison to the eastern Dharwar Craton, the mantle-derived xenocrysts/xenoliths are extremely rare or even unreported from the western Dharwar Craton, southern India. A Neoproterozoic (ca. 800-900 Ma) lamprophyre cropping out in the Mysuru area of southern India contains chrome-diopside xenocrysts (Cr2O3 content varying from 0.2-1.23 wt%) which provide important evidence about the pressure-temperature conditions and lithospheric thickness beneath the western Dharwar Craton. Studied chrome-diopsides show compositional zoning which is lacking in the liquidus phases (amphiboles and feldspars) of the lamprophyre which additionally favors a non-cognate origin of the former. Based on the compositional zoning, all the chrome-diopside xenocrysts can be divided into three groups: (i) Group I- which are euhedral and show reverse zoning with increasing Cr-content from core to rim; (ii) Group II- which are characterized by fractures and resorption textures, show complex reverse zoning and display up to three distinct compositional layers, and (iii) Group III- which evidence the reaction of chrome-diopsides with lamprophyric melt and are marked by alteration phases, such as actinolite and chlorite, together with relicts of some unaltered xenocrysts. High Cr2O3, moderate MgO and low Al2O3 content of all the three varieties of chrome-diopside suggest them to represent disaggregated xenocrysts of mantle-derived garnet peridotite. Temperature-pressure estimates for chrome-diopside xenocrysts ranges from 895-1026 °C (± 30 °C) and 32-38 kbar respectively and correspond to depth range of 106-127 km. The study reveals that lithospheric thickness during the Neoproterozoic beneath the western Dharwar craton was at least ?115 km and is similar in composition to that of the cratonic lithosphere found in the other cratonic domains.
Abstract: Major and trace element geochemistry of eclogitic mineral inclusions from Chinese diamonds are reported in this study, for the first time. Bulk major element compositions of mantle eclogite, estimated from diamond inclusions, are very close to that of MORB. All the analyzed samples exhibit evident positive Eu anomalies. Estimated bulk trace element compositions of mantle eclogite are generally parallel to that of MORB, but with deviations like enrichment in LILE and depletion in HFSE. It is proposed that the formation of mantle eclogite could be closely related to recycling of ancient oceanic crust. Other processes like (1) metasomatism by incompatible trace element rich melts; or (2) remelting and interaction with mantle peridotite, may also be involved. Coexisting of olivine with eclogitic mineral inclusions in a same diamond host, and evident trace element variations in some mineral inclusions show that some diamonds were formed by disequilibrium growth.
