Microinclusions In Diamonds Research Articles

Phonolite-Carbonatite Liquid Immiscibility at 3–6 GPa

Liquid immiscibility plays an important role in the formation of carbonatites and associated alkaline Si-undersaturated magmas. Experiments in the sodium carbonate-aluminosilicate systems suggest that the carbonate-silicate miscibility gap is limited by crustal and shallow mantle pressures (up to 2.5 GPa). Unlike in the potassium-rich carbonate-aluminosilicate systems, the carbonate-silicate miscibility gap was established at pressures of 3.5–6 GPa. It is therefore interesting to elucidate the immiscibility range under intermediate pressures, corresponding to 100–200 km depths. Here we conducted experiments over 3–6 GPa and 1050–1500 °C in the systems corresponding to immiscible melts obtained by partial melting of carbonated pelite (DG2) at 6 GPa and 1200 °C. We found that partial melting begins with the alkali-rich carbonatite melt, while immiscible phonolite melt appears over 1050–1200 °C at 3 GPa, 1200 °C at 4.5 GPa, and 1200–1500 °C at 6 GPa. As pressure decreases from 6 to 3 GPa, Na becomes less compatible, and the concentration of the jadeite component in clinopyroxene decreases by a factor of 1.5–6. As a result, the compositions of the immiscible phonolite and carbonatite melts evolve from ultrapotassic (K2O/Na2O weight ratio = 10–14) resembling silicic and carbonatitic micro-inclusions in diamonds from kimberlites and placers worldwide to moderately potassic (K2O/Na2O = 1–2), which may correspond to phonolitic and associated carbonatitic melts of the spinel facies of the shallow mantle.

The compositional peculiarities of microinclusions in diamonds from the Lomonosov deposit (Arkhangelsk province)

The data on the composition of microinclusions in diamonds from the Lomonosov deposit are reported. The studied diamonds include coated (n = 5) and cubic (n = 5) crystals. The determined range of the degree of nitrogen aggregation (4-39 %B1) in diamonds does not support their links with kimberlite magmatism, but their short occurrence in the mantle at higher temperatures is probable as well. The composition of melt/fluid microinclusions in these samples varies from essentially carbonatitic to significantly silicate. It is shown that the content of MgO, CaO, Na2O, Cl and P2O5 decreases with increasing content of silicates and water. Different mechanisms of generation and evolution of diamond-forming media are considered to explain the observed variations.

The Compositional Peculiarities of Microinclusions in Diamonds from the Lomonosov Deposit (Arkhangelsk Province)

The Compositional Peculiarities of Microinclusions in Diamonds from the Lomonosov Deposit (Arkhangelsk Province)

Melting of H2O and CO2-bearing eclogite at 4–6 GPa and 900–1200 °C: Implications for the generation of diamond-forming fluids

Abstract Eclogites play a significant role in geodynamic processes, transferring large amounts of basaltic material and volatiles (chiefly CO2 and H2O species) into the earth's mantle via subduction. Previous studies of eclogite melting focused on two end member systems: either carbonated or hydrous eclogites. Here we focus on the hydrous carbonated eclogitic system in order to define the position of its solidus and determine the near solidus fluid and melt compositions at 4–6 GPa and 900–1200 °C. Experiments were performed on a rocking multi-anvil press. The total dissolved solids in the equilibrated fluids were analyzed following the cryogenic technique using a LA-ICP-MS. H2O and CO2 content were determined by mass balance calculations. Solid phases were chemically characterized using an EPMA. Garnet and clinopyroxene are present in all experiments, assembling the eclogitic rock. A carbonate phase was detected at all temperatures at 4 GPa and at temperatures below 1200 °C at 5 and 6 GPa. Coesite was observed at all pressures below 1200 °C. The solidus was crossed between 1000 and 1100 °C at 4 and 5 GPa. At 6 GPa we observed a relatively smooth decrease in the H2O and CO2 content of the fluid phase with rising temperature, suggesting the presence of a supercritical fluid. The second critical endpoint is thus defined in this system at ∼5.5 GPa and 1050 °C. The composition of fluids and melts reported in this study indicates that the hydrous carbonated eclogite system is a plausible source-rock for high density fluids (HDFs) found in microinclusions in diamonds, specifically for the intermediate compositions along the array spanned between low-Mg carbonatitic HDFs and hydrous-silicic ones. Our results suggest that the whole array reflects melting in a heterogeneous mantle. Melting of water-rich eclogite produces silicic HDFs, carbonate-rich zones will produce carbonatitc HDFs, while source-rocks with varying H2O/CO2 ratios produce intermediate compositions.

Homogenization of carbonate-bearing microinclusions in diamond at P–T parameters of the upper mantle

The staged high-pressure annealing of natural cubic diamonds with numerous melt microinclusions from the Internatsional’naya kimberlite pipe was studied experimentally. The results mainly show that the carbonate phases, the daughter phases in partially crystallized microinclusions in diamonds, may undergo phase transformations under the mantle P–T conditions. Most likely, partial melting and further dissolution of dolomite in the carbonate–silicate melt (homogenization of inclusions) occur in inclusions. The experimental data on the staged high-pressure annealing of diamonds with melt microinclusions allow us to estimate the temperature of their homogenization as 1400–1500°C. Thus, cubic diamonds from the Internatsional’naya pipe could have been formed under quite high temperatures corresponding to the lithosphere/asthenosphere boundary. However, it should be noted that the effect of selective capture of inclusions with partial loss of volatiles in relation to the composition of the crystallization medium is not excluded during the growth. This may increase the temperature of their homogenization significantly between 1400 and 1500°C.

Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle

Research Article| November 01, 2012 Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle A. Giuliani; A. Giuliani 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia Search for other works by this author on: GSW Google Scholar V.S. Kamenetsky; V.S. Kamenetsky 2ARC Centre of Excellence on Ore Deposits, and School of Earth Sciences, University of Tasmania, Hobart, 7001 Tasmania, Australia Search for other works by this author on: GSW Google Scholar D. Phillips; D. Phillips 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia Search for other works by this author on: GSW Google Scholar M.A. Kendrick; M.A. Kendrick 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia Search for other works by this author on: GSW Google Scholar B.A. Wyatt; B.A. Wyatt 3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia Search for other works by this author on: GSW Google Scholar K. Goemann K. Goemann 4Central Science Laboratory, University of Tasmania, Hobart, 7001 Tasmania, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information A. Giuliani 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia V.S. Kamenetsky 2ARC Centre of Excellence on Ore Deposits, and School of Earth Sciences, University of Tasmania, Hobart, 7001 Tasmania, Australia D. Phillips 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia M.A. Kendrick 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia B.A. Wyatt 3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia K. Goemann 4Central Science Laboratory, University of Tasmania, Hobart, 7001 Tasmania, Australia Publisher: Geological Society of America Received: 18 Jan 2012 Revision Received: 16 Apr 2012 Accepted: 23 Jun 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (11): 967–970. https://doi.org/10.1130/G33221.1 Article history Received: 18 Jan 2012 Revision Received: 16 Apr 2012 Accepted: 23 Jun 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. Giuliani, V.S. Kamenetsky, D. Phillips, M.A. Kendrick, B.A. Wyatt, K. Goemann; Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle. Geology 2012;; 40 (11): 967–970. doi: https://doi.org/10.1130/G33221.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mantle xenoliths sampled by kimberlite and alkali basalt magmas show a range of metasomatic styles, but direct evidence for the nature of the metasomatising fluids is often elusive. It has been suggested that carbonate-rich melts produced by partial melting of carbonated peridotites and eclogites play an important role in modifying the composition of the lithospheric mantle. These mantle-derived carbonate melts are often inferred to be enriched in alkali elements; however, alkali-rich carbonate fluids have only been reported as micro-inclusions in diamonds and as unique melts involved in the formation of the Udachnaya-East kimberlite (Yakutia, Russia). In this paper we present the first direct evidence for alkali-carbonate melts in the shallow lithospheric mantle (∼110–115 km), above the diamond stability field. These alkali-carbonate melts are preserved in primary multiphase inclusions hosted by large metasomatic ilmenite grains contained in a polymict mantle xenolith from the Bultfontein kimberlite (Kimberley, South Africa). The inclusions host abundant carbonates (magnesite, dolomite, and K-Na-Ca carbonates), kalsilite, phlogopite, K-Na titanates, and phosphates, with lesser amounts of olivine, chlorides, and alkali sulfates. Textural and chemical observations indicate that the alkali-carbonate melt likely derived from primary or precursor kimberlite magmas. Our findings extend the evidence for alkali-carbonate melts/fluids permeating the Earth mantle outside the diamond stability field and provide new insights into the chemical features of previously hypothesized melts. As metasomatism by alkali-rich carbonate melts is often reported to affect mantle xenoliths, and predicted from experimental studies, the fluid type documented here likely represent a major metasomatising agent in the Earth’s lithospheric mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The high PT stability of apatite and Cl partitioning between apatite and hydrous potassic phases in peridotite: an experimental study to 19 GPa with implications for the transport of P, Cl and K in the upper mantle

High PT experiments were performed in the range 2.5–19 GPa and 800–1,500°C using a synthetic peridotite doped with trace elements and OH-apatite or with Cl-apatite + phlogopite. The aim of the study was (1) to investigate the stability and phase relations of apatite and its high PT breakdown products, (2) to study the compositional evolution with P and T of phosphate and coexisting silicate phases and (3) to measure the Cl-OH partitioning between apatite and coexisting calcic amphibole, phlogopite and K-richterite. Apatite is stable in a garnet-lherzolite assemblage in the range 2.5–8.7 GPa and 800–1,100°C. The high-P breakdown product of apatite is tuite γ-Ca3 (PO4)2, which is stable in the range 8–15 GPa and 1,100–1,300°C. Coexisting apatite and tuite were observed at 8 GPa/1,050°C and 8.7 GPa/1,000°C. MgO in apatite increases with P from 0.8 wt% at 2.5 GPa to 3.2 wt% at 8.7 GPa. Both apatite and tuite may contain significant Na, Sr and REE with a correlation indicating 2 Ca2+=Na+ + REE3+. Tuite has always higher Sr and REE and lower Fe and Mg than apatite. Phosphorus in the peridotite phases decreases in the order Pmelt ≫ Pgrt ≫ PMg2SiO4 > Pcpx > Popx. The phosphate-saturated P2O5 content of garnet increases from 0.07 wt% at 2.5 GPa to 1.5 wt% at 12.8 GPa. Due to the low bulk Na content of the peridotite, [8]Na[4]P[8]M2+−1[4]Si−1 only plays a minor role in controlling the phosphorus content of garnet. Instead, element correlations indicate a major contribution of [6]M2+[4]P[6]M3+−1[4]Si−1. Pyroxenes contain ~200–500 ppm P and olivine has 0.14–0.23 wt% P2O5 in the P range 4–8.7 GPa without correlation with P, T or XMg. At ≥12.7 GPa, all Mg2SiO4 polymorphs have <200 ppm P. Coexisting olivine and wadsleyite show an equal preference for phosphorus. In case of coexisting wadsleyite and ringwoodite, the latter fractionates phosphorus. Although garnet shows by far the highest phosphorus concentrations of any peridotite silicate phase, olivine is no less important as phosphorus carrier and could store the entire bulk phosphorus budget of primitive mantle. In the Cl-apatite + phlogopite-doped peridotite, apatite contains 0.65–1.35 wt% Cl in the PT range 2.5–8.7 GPa/800–1,000°C. Apatite coexists with calcic amphibole at 2.5 GPa, phlogopite at 2.5–5 GPa and K-richterite at 7 GPa, and all silicates contain between 0.2 and 0.6 wt% Cl. No solid potassic phase is stable between 5 and 8.7 GPa. Cl strongly increases the solubility of K in hydrous fluids. This may lead to the breakdown of phlogopite and give rise to the local presence in the mantle of fluids strongly enriched in K, Cl, P and incompatible trace elements. Such fluids may get trapped as micro-inclusions in diamonds and provide bulk compositions suitable for the formation of unusual phases such as KCl or hypersilicic Cl-rich mica.

Chloride microinclusions in diamonds of the Siberian platform

Chloride microinclusions in diamonds of the Siberian platform

IR spectroscopy: Quantitative determination of the mineralogy and bulk composition of fluid microinclusions in diamonds

Infrared (IR) absorption was used to measure the concentration of secondary phases trapped in microinclusion-bearing diamonds. Using KBr pellets with known concentrations, we determined the IR absorptivities ( ε, AU∙l/mol∙ cm) of calcite, dolomite, magnesite, apatite, quartz, phlogopite, olivine and garnet: ε calcite1433 cm − 1 = 739, ε dolomite1442 cm − 1 = 921, ε magnesite1451 cm − 1 = 563, ε apatite1049 cm − 1 = 2590 ( ε apatite605 cm − 1 = 800), ε phlogopite1006 cm − 1 = 861, ε quartz1084 cm − 1 = 418( ε quartz800 cm − 1 = 102), ε garnet967 cm − 1 = 1049, ε olivine894 cm − 1 = 418. Using the conversion factors for a diamond matrix, the concentrations of carbonates, silicates and apatite were calculated in 13 microinclusion-bearing diamonds that were previously analyzed by electron probe micro analyses (EPMA) and IR and carry carbonatitic to silicic high density fluids (HDFs). Combining the relative abundance in the microinclusions with the composition of each mineral, we calculated the concentration of SiO 2, Al 2O 3, P 2O 5 and MgO + CaO + FeO + BaO + Na 2O of the bulk HDF. Good agreement exists between the IR calculations and the EPMA data for the same diamond. Combining our data with the absorption coefficient of water and correcting for the effect of salinity, the IR spectra show that most of the low-Mg carbonatitic to silicic HDFs have ∼ 20 wt.% water while the high-Mg carbonatitic ones carry only ∼ 10%. Our results show that IR spectroscopy alone can be used as a semi-quantitative method to determine carbonatitic to silicic HDF compositions in microinclusion-bearing diamonds. In combination with EPMA, a full characterization of the major constituents is achieved, including carbonate and water content.

Mg and Fe-rich carbonate–silicate high-density fluids in cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia)

Microinclusions in 44 cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia) show wide compositional variations. In comparison with the available worldwide database most microinclusions in diamonds from Internationalnaya define a continuous range of compositions from carbonatitic to hydrous-silicic high-density fluids (HDFs). The hydrous-silicic compositional range is reported here for the first time in Yakutian diamond-forming fluids. The hydrous-silicic end-members are rich in water, SiO 2, Al 2O 3, K 2O and P 2O 5. Carbonatitic end-members are rich in carbonate, CaO, MgO, Na 2O and FeO. Microinclusions in diamonds from Internationalnaya show a range from magnesian to extremely iron-rich compositions. There are two compositional arrays of microinclusions: (i) carbonate-rich with SiO 2 < 10 wt.% where FeO decreases without any correlation with sulfur, water, carbonate or chlorine and (ii) carbonatitic to hydrous-silicic where FeO generally decreases as SiO 2 contents increase. The trace-element patterns of the microinclusions are generally similar to those of kimberlites and carbonatites, but there are significant differences in the major elements. The relative abundance of K in the microinclusions is significantly higher. The microinclusions have smooth patterns for the LILE, normalized to a primitive mantle composition. HFSE patterns in the microinclusions show some depletion in Ti, Zr and Hf relative to Ta, Nb and Mo. Primitive mantle normalized REE patterns reveal low abundances of the heavy REE and high concentrations of light REE. The La/Dy ratio of microinclusions varies widely, decreasing from carbonatitic to hydrous-silicic compositions. A general correlation of δ 13C of diamonds with the relative abundance of carbonates in the microinclusions suggests that carbon isotope compositions are related to the evolution of the parental media. The carbonate–silicate range of high-density fluids observed in diamonds from Internationalnaya may be explained by fractional crystallization of mantle fluids/melts, or mixing between liquids with different compositions.

Volatile composition of microinclusions in diamonds from the Panda kimberlite, Canada: Implications for chemical and isotopic heterogeneity in the mantle

In order to better investigate the compositions and the origins of fluids associated with diamond growth, we have carried-out combined noble gas (He and Ar), C and N isotope, K, Ca and halogen (Cl, Br, I) determinations on fragments of individual microinclusion-bearing diamonds from the Panda kimberlite, North West Territories, Canada. The fluid concentrations of halogens and noble gases in Panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances. However, noble gas, C and N isotopic ratios ( 3He/ 4He = 4–6 Ra, 40Ar/ 36Ar = 20,000–30,000, δ 13C = −4.5‰ to −6.9‰ and δ 15N = −1.2‰ to −8.8‰) are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt (MORB) source value. The high 36Ar content of the diamonds (>1 × 10 −9 cm 3/g) is at least an order of magnitude higher than any previously reported mantle sample and enables the 36Ar content of the subcontinental lithospheric mantle to be estimated at ∼0.6 × 10 −12 cm 3/g, again similar to estimates for the MORB source. Three fluid types distinguished on the basis of Ca–K–Cl compositions are consistent with carbonatitic, silicic and saline end-members identified in previous studies of diamonds from worldwide sources. These fluid end-members also have distinct halogen ratios (Br/Cl and I/Cl). The role of subducted seawater-derived halogens, originally invoked to explain some of the halogen ratio variations in diamonds, is not considered an essential component in the formation of the fluids. In contrast, it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid–melt partitioning in forming silicic fluids, and during separation of an immiscible saline fluid.

Microinclusions in diamonds of octahedral habit from kimberlites of Shandong Province, Eastern China

Microinclusions in octahedral diamond crystals from kimberlites of Shandong Province, eastern China, have been studied with analytical scanning electron microscopy. Native iron, tungsten, and lead; Fe-Cr intermetallic compounds; polydymite; ilmenite; halite; and matlockite (PbFCl) have been identified on the crystal surfaces. Microinclusions of native iron and chrome, Fe-Cr intermetallic compounds, pentlandite, Cr-free garnet, calcite, and apatite, as well as a relatively large (100 × 270 μm) inclusion representing an intergrowth of clinopyroxene, calcite, and apatite, have been revealed on the surfaces of fresh chips of the samples. The deep geological processes that could have resulted in the formation of such unusual mineral assemblages are discussed in the light of new experimental data.

Water-related IR characteristics in natural fibrous diamonds

AbstractWater-related features were studied using infrared absorption spectroscopy in fibrous diamonds with micro-inclusions. Both OH-stretching and HOH-bending vibrations were observed. The lack of correlation between the intensities of HOH and OH bands in different samples and the complexity of the OH-stretching band indicate that a large fraction of water is present as hydroxyl groups in minerals.Heating and cooling experiments were performed to elucidate the properties of fluids in micro-inclusions in diamonds. The results of experiments at various temperatures support the presence of several water-related components in individual diamonds. These spectroscopic investigations of fibrous diamonds revealed two or more interrelated water-related components preserved in micro-inclusions. The existence of several water phases or water solutions with different salinity and solutes within one diamond crystal is possible.

TEM imaging and analysis of microinclusions in diamonds: A close look at diamond-growing fluids

Fluid-bearing microinclusions in diamonds (<1 μm) provide a unique source of information on the diamond-forming medium. Transmission electron microscopy (TEM) investigation of such microinclusions enables the detailed study of their size, external habit, internal morphology, and mineralogy, and yields information on the chemical composition and crystallography of the included phases. Here we present a detailed TEM examination of microinclusions in four fibrous diamonds from Canada and Siberia, each with a distinctive inferred original fluid composition. Most microinclusions contain multi-phase assemblages that include carbonate, halide, apatite, possible pyroxene, and high-silica mica (6.8–7.7 Si atoms per formula unit) whose composition lies along the phlogopite–Al-celadonite join. The TEM results, together with the tight range of composition detected by electron probe microanalysis (EPMA) and the volatiles detected by infrared (IR) spectroscopy, suggest that the microinclusions trapped a uniform, dense, supercritical fluid and that the crystallized minerals grew as secondary phases during cooling. Carbonates appear in all assemblages, together with either halides or silicates, indicative of the importance of carbonatitic high-density fluid during diamond growth and fluid evolution. The presence of halide-carbonate or silicate-carbonate assemblages is in agreement with the bulk composition of the microinclusions as detected by EPMA. The high K content of some microinclusions detected by EPMA cannot be accounted for by the solid phases analyzed by TEM. This discrepancy suggests that K is concentrated in the residual fluid that is lost during TEM sample preparation. In addition to microinclusions, large cavities containing amorphous phases were found in the inner parts of one Siberian and one Canadian diamond. An Al-rich phase is the most abundant, and it is accompanied by Ca-rich and Si-rich phases. These phases may be explained by amorphization of crystalline phases. A breakdown of a single melt into three immiscible components is less likely.

Multiple-mineral inclusions in diamonds from the Snap Lake/King Lake kimberlite dike, Slave craton, Canada: a trace-element perspective

Multiple inclusions of minerals in diamonds from the Snap Lake/King Lake kimberlites of the southeastern Slave craton in Canada have been analyzed for trace elements to elucidate the petrogenetic history of these inclusions, and of their host diamonds. As observed worldwide, the harzburgitic-garnet diamond inclusions (DIs) possess sinusoidal REE patterns that indicate an early depletion event, followed by metasomatism by LREE-enriched, HREE-depleted fluids. Furthermore, these fluids appear to contain appreciable concentrations of LILE and HFSE, based on the increasing abundances of these elements in the olivine inclusion that occurs at the outer portion of a diamond compared to that near the core. The compositions of these fluids are probably a mixture of hydrous-silicic melt, carbonatitic melt, and brine, similar to the compositions of micro-inclusions in diamonds reported by Navon et al. (2003). Comparison between the compositions of majoritic and normal harzburgitic garnets shows that the former are more depleted in terms of major/minor elements (higher Cr#) but significantly more enriched in the REE (up to ∼10×). This characteristic may indicate the higher susceptibility for metasomatic enrichment of previously more depleted garnets. Garnets of eclogitic paragenesis show strong LREE-depleted patterns, whereas the coexisting omphacite inclusion has relatively flat light- and middle-REE but depleted HREE. Whole-rock reconstruction from coexisting garnet and omphacite inclusions indicates that the protolith of these inclusions was probably the extrusive section of an oceanic crust, subducted beneath the Slave craton.

Fluids in Yakutian and Indian Diamonds

Studies of fluids trapped in micro-inclusions in diamonds from Africa have demonstrated the existence of a wide range of fluid compositions, spanning the full range from a carbonatitic endmember, rich in CaO, FeO, MgO, K20, and carbonates to a hydrous end-member, rich in SiO2, 1(20, A1203, and water (Schrauder and Navon, 1994). Here, we report the composition of the major oxides and volatile species of fluids trapped in six diamonds from Yakutia, and four from India.

Mantle-derived fluids in diamond micro-inclusions

Micro-inclusions in diamonds from Zaire and Botswana differ in composition from the more common large inclusions of the peridotitic or eclogitic assemblages. These sub-micrometre inclusions resemble potassic magmas in their composition, but are enriched in H_2O, CO^(2−)_3 and K_2O and depleted in MgO. This composition represents a volatile-rich fluid or melt from the upper mantle, which was trapped in the diamonds as they grew.