Noble Gases in Terrestrial Diamonds: Preliminary Results (original) (raw)
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Noble gases in diamonds: Occurrences of solarlike helium and neon
Journal of Geophysical Research, 1987
We have measured noble gases in 17 diamond samples, mostly inclusion free, from diverse, known locations. The 'He/'He ratios are characterized by a large spread (10'), ranging from values below atmospheric to close to the solar ratio. Hlghest ratios were seen for an Australian colorless diamond composite and an Arkansas diamond. These samples also have imprecise but intriguing neon isotopic ratios, which are close to the solar value. An origin for the solarlike He and Ne in the diamond samples is unlikely to be accounted for by the presence of nucleogenic or spallogenic components. For single diamond stones a positive correlation is found between 'He/'He and 1 'C/ 12 C, possibly indicating that heavy carbon is accompanied by primordial helium. However, the He result for the Australian colorless diamond composite with low o 1 'C value requires another explanation, possibly sedimentary carbon contaminated with cosmic dust. The wide variation in 'He/' 0 *Ar ratios observed from diamond samples suggests a complex history for the source regions and the diamond crystallization processes. Results for two Australian diamond composites (colorless and colored), which came from the same kimberlite pipe, are especially notable: the colorless stones contain no radiogenic components but solarlike He and Ne isotopic ratios, whereas the colored stones are enriched in radiogenic and fissiogenic components. Seemingly the Australian diamonds crystallized in a heterogeneous environment in the mantle source region. A pair of Arkansas diamonds, believed to be from a single pipe, exhibits sim1lar anomalies. Analytical Procedures Samples Most of the diamond samples have been examined for texture and screened for inclusions by one of us (E.R.); exceptions are the industrial class and Zaire diamonds (hereafter IDn and ZAI, respectively). Samples ID1, 2, 3, and 4 were obtained commercially from a diamond dealer. ID1 is a composite of 12 small individual stones with few solid inclusions. ID2, 3, and 4 are single stones. They have significant inclusions, and their crystal form is very irregular. Five gem-quality South African individual stones were donated by De Beers Consolidated Mines, Ltd. A type I diamond was collected from the Premier pipe which is known to be of Pr'ecambrian age (1.25 b.y.) (PR1). Both type I and II diamonds were collected from the Finsch pipe (Fil and 2) and from among the De Beers, Wessel ton, Dutoitspan, and Bulfontein pipes (DEl and 2). These last five pipes are known to be of Cretaceous age (J. B. Hawthorne, De Beers, private communication, 1985). All the samples 12,507 12,508 Honda et al.: Solarlike Helium and Neon Isotopes in Diamonds ~Sapphire Viewing window Ni-slug Diamond wrapped in Ta foil Mo funnel I 0 'i' ~ 8-Cooling water Side view of basket heater Sample system 10 em
Lithos, 2019
He-NeAr compositions were determined in diamonds from the Argyle lamproite, Western Australia, to assess whether subducted material affects the noble gas budget and composition of stable old sub-continental lithospheric mantle (SCLM). Twenty diamonds (both peridotitic and eclogitic) were characterized for their carbon isotopic compositions and N abundance and aggregation from which 10 eclogitic growth zones and 5 peridotitic growth zones were analysed for their He-NeAr compositions. The eclogitic diamonds have δ 13 C values of-4.7 to-16.6‰ indicating a subduction signature, whereas the peridotitic diamonds have mantle-like compositions of-4.0 to-7.8‰. Mantle residence temperatures based on N-in-diamond thermometry showed that the eclogitic diamonds were mainly formed at 1260-1270°C or above 1300°C near the base of the lithosphere, whereas the peridotitic diamonds generally formed at lower temperatures (mostly 1135-1230°C). A noble gas subduction signature is present to various extents in the eclogitic diamonds and is inferred from a hyperbolic mixing relationship between R/Ra and 4 He and δ 13 C values concentrations with a predominance of low R/Ra values (<0.5; R/Ra = 3 He/ 4 Hesample / 3 He/ 4 Heair). In addition, low 40 Ar/ 4 He and 40 Ar/ 36 Ar ratios, high nucleogenic 21 Ne/ 4 He and low 3 He/ 22 Ne ratios are characteristic of subducted material and were found in the eclogitic diamonds. The peridotitic diamonds show generally higher R/Ra values (median 1.1 ± 1.1) and lower 4 He/ 40 Ar ratios compared to eclogitic diamonds (median 0.1 ± 0.8 R/Ra; with 7/10 samples having an average of 0.13 ± 0.14 R/Ra). The studied peridotitic diamond growth zones showed a negative correlation between R/Ra and 4 He concentrations over 2 orders of magnitude and limited variation in 3 He, that can be largely explained by radiogenic 4 He ingrowth. At low 4 He concentrations the R/Ra value is
Recycled volatiles in mantle-derived diamondsEvidence from nitrogen and noble gas isotopic data
Earth and Planetary Science Letters, 2006
Noble gas isotopic data from diamonds are commonly interpreted as a two component mixture of gases from the mantle source of mid oceanic ridge basalt (MORB) and air. The air-like component in diamonds is generally considered to have been acquired secondarily through atmospheric contamination. In a recent study [C. Gautheron, P. Cartigny, M. Moreira, J.W. Harris, C.J. Allègre, Evidence for a mantle component shown by rare gases, C and N isotopes in polycrystalline diamonds from Orapa (Botswana), Earth Planet. Sci. Lett. 240(2005) 559-572.] that involved analyses of noble gases, carbon and nitrogen, such interpretation based on noble gases is used to constrain the sources of carbon and nitrogen in diamond to be solely from the mantle.
Australian Journal of Earth Sciences, 2012
The Argyle lamproite pipe of Western Australia contains diamonds formed at depths exceeding 150 km. We undertook noble gas and carbon isotope ratio (d 13 C) analyses of three diamonds (likely of eclogitic paragenesis) from the Argyle lamproite to test for the possible presence of deeply subducted volatile components, and to further constrain the noble gas evolution of the Earth's mantle. The Argyle diamonds are characterised by mantle 3 He (with 3 He/ 4 He ratios of 0.79 R A to 0.25 R A , where R A is the atmospheric 3 He/ 4 He ratio of 1.4 6 10 -6 ), small excess Ar and Xe isotope anomalies relative to atmospheric components, and d 13 C values of -11.6 to -10.2% VPDB. These observations indicate that noble gas and carbon isotopic compositions of the mantle where the Argyle diamonds formed, represent mixtures of an intrinsic mantle component with sedimentary and atmospheric components that may have been introduced through subduction processes.
A comprehensive study of noble gases and nitrogen in “Hypatia”, a diamond-rich pebble from SW Egypt
Earth and Planetary Science Letters, 2015
This is a follow-up study of a work by Kramers et al. (2013) on a very unusual diamond-rich rock fragment found in the area of south west Egypt in the southwestern side of the Libyan Desert Glass strewn field. This pebble, called Hypatia, is composed of almost pure carbon. Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) results reveal that Hypatia is mainly made of defect-rich diamond containing lonsdaleite and multiple deformation bands. These characteristics are compatible with an impact origin on Earth and/or in space. We also analyzed concentrations and isotopic compositions of all five noble gases and nitrogen in several ~mg sized Hypatia samples. These data confirm the conclusion by Kramers et al. (2013) that Hypatia is extra-terrestrial. The sample is relatively rich in trapped noble gases with an isotopic composition being close to the Q component found in many types of meteorites. 40 Ar/ 36 Ar ratios in individual steps are as low as 0.4 ± 0.3. Cosmicray produced "cosmogenic" 21 Ne is present in concentrations corresponding to a nominal cosmic-ray exposure (CRE) age of roughly 0.1 Myr if produced in a typical meter-sized meteoroid. Such an atypically low nominal CRE age suggests high shielding in a considerably larger body. In addition to the Xe-Q composition, an excess of radiogenic 129 Xe (from the decay of short-lived radioactive 129 I) is observed (129 Xe/ 132 Xe = 1.18 +/-0.03). Two isotopically distinct N components are present, an isotopically heavy component (δ 15 N ~ +20‰) released at low temperatures and a major isotopically light component (δ 15 N ~-110‰) at higher temperatures. This disequilibrium in N suggests that the diamonds in Hypatia were formed in space rather than upon impact on Earth (δ 15 N atm = 0 ‰). All our data are broadly consistent with concentrations and isotopic compositions of noble gases in at least three different types of carbon-rich meteoritic materials: carbon-rich veins in ureilites, graphite in acapulcoites/lodranites and graphite nodules in iron meteorites. However, Hypatia does not seem to be directly related to any of these materials, but may have sampled a similar cosmochemical reservoir. Our study does not confirm the presence of exotic noble gases (e.g. G component) that led Kramers et al. (2013) to propose that Hypatia is a remnant of a comet nucleus that impacted the Earth.
Extraterrestrial, terrestrial and laboratory diamonds — Differences and similarities
Diamond and Related Materials, 2008
Characterization tools such as confocal Raman micro-spectroscopy, Laser Ablation (LA-ICP-TOF-MS) and SEM-EDS were used to characterize meteorites: primitive achondritenot classified NWA XXX ureilite found in 2006 in Morocco and the graphite nodula from the Canyon Diablo iron meteorite. The presence of diamond was confirmed in both samples. There are two kinds of meteoritic diamonds: diamonds of the sizes of microns up to millimeters are most probably of impact origin, nanodiamonds of the sizes of 1-3 nm, called presolar diamonds because of the isotopic anomalies, are believed to be formed before our Solar System was formed. There are many theories concerning presolar diamonds formation, among them: impact shock metamorphism driven by supernovae or chemical vapor deposition (CVD) from stellar outflows. We examined the properties of diamond nanopowders obtained by the PA CVD and detonation methods. Nanodiamonds obtained by the detonation method, called ultradispersed detonation diamonds (UDD), are of the same range of sizes as presolar diamonds. The results show both differences and similarities among meteoritic, terrestrial and laboratory diamonds. The comparison will help to understand the processes during presolar nanodiamonds formation.
Noble gases in metamorphic diamonds from Kokchetav massif, Kazakhstan revisited
Geochmica et Cosmochimica Acta
Keywords: noble gas isotopes metamorphic microdiamond UHPM Kokchetav subduction deep mantle convection Metamorphic diamonds from the Kokchetav massif in northern Kazakhstan are considered to have crystallized from a C-O-H fluid during ultra-high-pressure metamorphism of metasedimentary rocks subducted to 190-280 km depth. Noble gases contained in the diamonds offer great potential to constrain the noble gas state of deep mantle reservoirs. Previous studies have revealed that secondary processes during the diamond residence in the host rock drastically modified the original noble gas signature of the diamonds. However, nanometer-sized solid/fluid inclusions in the microdiamonds, which represent the former diamond-forming fluid, might preserve the noble-gas signature trapped at the time of diamond formation. We performed noble-gas analyses of the Kokchetav microdiamonds applying two gas extraction techniques: in vacuo crushing and stepwise heating. The former selectively extracts noble gases from inclusions with less noble gas extraction from the diamond lattice. Diamond crushing extracted most of the 3 He, indicating that 3 He occurs within inclusions trapped during diamond formation. The inclusion-hosted 3 He/ 4 He of (3.3-6.5)× 10 −5 is significantly higher than that of the MORB-source mantle (1.1× 10 −5 ), but close to the maximum value observed in OIBs (ca. 7 × 10 −5 ) containing noble gases enriched in a primordial component and delivered from the deep mantle by plumes. Neon isotope ratios obtained using stepwise heating also support the presence of a plume-like component. Results show that plume-like, primordial-enriched noble gases were involved in the Kokchetav microdiamond formation, implying metasomatism of the continental lithosphere by a plume prior to its subduction, or interaction of the continental slab and a fragment of the very deep mantle. The deep-mantle-derived fragment might have been delivered to the mantle wedge of the subduction channel by large-scale mantle convection originating from a deeper lower mantle source.
Carbon and Nitrogen in Mantle-Derived Diamonds
Reviews in Mineralogy and Geochemistry
Diamond types Here we focus on the C-and N-stable isotope geochemistry of mantle-derived diamonds, which include a number of subdivisions. Not considering orogenic peridotite massifs, mantlederived diamonds are transported to Earth's surface by kimberlites or, less commonly, by lamproites, ultramafic lamprophyres and, in one instance, komatiite (see Kjarsgaard et al. 2022, this volume). Under the generic term 'smooth-surfaced monocrystalline diamonds' we include smoothfaced monocrystalline diamonds that crystallized as primary octahedra, macles or cuboids and their resorption forms. All these diamonds formed prior to kimberlite activity and were therefore xenocrysts in their host kimberlite, with mantle residence times varying from several b.y. to a few hundred m.y. (Smit et al. 2022; Green et al. 2022, both this volume). The xenocrystic nature of smooth-surfaced monocrystalline diamonds is supported by advanced nitrogen aggregation states (typically Type IaAB, see Green et al. 2022, this volume) but the reverse is not true (i.e., a diamond with poorly aggregated nitrogen is not necessarily young). Based on the study of their mineral inclusions (typically about 1% of diamonds contain inclusions ≥ 100 µm in size, Stachel and Harris 2008), smooth-surfaced monocrystalline diamonds can be assigned to three particular mantle depth intervals: