Diamond genesis,seismic structure,and evolution of the Kaapvaal-Zimbabwe craton

The lithospheric mantle beneath the Kaapvaal-Zimbabwe craton of southern Africa shows variations in seismic P-wave velocity at depths within the diamond stability field that correlate with differences in the composition of diamonds and their syngenetic inclusions. Middle Archean mantle depletion events initiated craton keel formation and early harzburgitic diamond formation. Late Archean accretionary events involving an oceanic lithosphere component stabilized the craton and contributed a younger Archean generation of eclogitic diamonds. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the Archean diamond suite.     

Eclogitic diamond formation at jwaneng: No room for a recycled component

Eclogitic diamonds have a large range of delta13C values, whereas peridotitic diamonds do not. Paired delta15N-delta13C-N variations in 40 eclogitic diamonds from the Jwaneng kimberlite in Botswana show that neither the influence of recycled biogenic carbon nor the global and primordial heterogeneity of mantle carbon are likely for the origin of the large delta13C range; the data instead support a fractionation process. It is proposed that carbonatitic mantle melts from which diamonds crystallize undergo different evolutions before diamond precipitation, when percolating through either a peridotite or an eclogite. These different evolutions, reflecting the presence or absence of olivine, can account for their respective delta13C distributions.     

Viscosity of fluids in subduction zones

The viscosities of aqueous fluids with 10 to 80 weight percent dissolved silicates have been measured at 600 degrees to 950 degrees C and 1.0 to 2.0 gigapascals by in situ observation of falling spheres in the diamond anvil cell. The viscosities at 800 degrees C range from 10(-4) to 10(0.5) pascal seconds. The combination of low viscosities with a favorable wetting angle makes silicate-rich fluid an efficient agent for material transport at low-volume fractions. Our results therefore suggest that there may be a direct relationship between the position of the volcanic front and the onset of complete miscibility between water and silicate melt in the subducting slab.     

Diamonds, Eclogites, and the Oxidation State of the Earth's Mantle

The reaction dolomite + 2 coesite --><-- diopside + 2 diamond + 2O(2) defines the coexistence of diamond and carbonate in mantle eclogites. The oxygen fugacity of this reaction is approximately 1 log unit higher at a given temperature and pressure than the oxygen fugacities of the analogous reactions that govern the stability of diamond in peridotite. This difference allows diamond-bearing eclogite to coexist with peridotite containing carbonate or carbonate + diamond. This potential coexistence of diamond-bearing eclogite and carbonate-bearing peridotite can explain the presence of carbon-free peridotite interlayered with garnet pyroxenites that contain graphitized diamond in the Moroccan Beni Bousera massif at the Earth's surface and the preferential preservation of diamond-bearing eclogitic relative to peridotitic xenoliths in the Roberts Victor kimberlite.     

Strength of diamond

The yield strength of diamond is measured under a pressure of 10 gigapascals at temperatures up to 1550 degrees C by the analysis of x-ray peak shapes on diamond diffraction lines in a powdered sample as a function of pressure and temperature. At room temperature, the diamond crystals exhibit elastic behavior with increasing pressure. Significant ductile deformation is observed only at temperatures above 1000 degrees C at this pressure. The differential yield strength of diamond decreases with temperature from 16 gigapascals at 1100 degrees C to 4 gigapascals at 1550 degrees C. Transmission electron microscopy observations on the recovered sample indicate that the dominant deformation mechanism under high pressure and temperature is crystal plasticity.     

Sintered diamond compacts with a cobalt binder

Diamond powder can be successfully cemented with cobalt. At 62 kilobars the sintering occurs over the temperature range from 1570 degrees to 1610 degrees C. The maximum microhardness of the compact ( 3000 kilograms per square millimeter on the Knoop scale) is obtained with a mixture of 20 percent cobalt (by volume) and a diamond particle size of 1 to 5 micrometers.     

Cooling history of orthopyroxenes

Order-disorder transitions between ferrous iron and magnesium in orthopyroxenes [minerals close to the composition (Fe, Mg) SiO(3)] occur rapidly between approximately 480 degrees and 1000 degrees C. Disordering and ordering have been studied experimentally. The determination of the metastable ferrous iron site occupancy in orthopyroxenes from rapidly cooled volcanic rocks provides information on the cooling rates, especially from 600 degrees to 480 degrees C.     

Growth of diamond from atomic hydrogen and a supersonic free jet of methyl radicals

The growth of small ( approximately 10-micrometer) diamond particles (on 0.1-or 0.25-micrometer seed crystals) using an effusive glow discharge nozzle for H.and a separate supersonic pyrolysis jet for .CH(3) is reported. Laser micro-Raman, scanning electron microscopy, and x-ray photoelectron spectroscopy data are presented as evidence that well-crystallized diamond is indeed formed. Resonant multiphoton ionization spectroscopy is used as a diagnostic for the gas-phase chemistry indicating that the radical sources are clean and quantitative and that there is no detectable interconversion of .CH(3) to C(2)H(2) under the conditions of the experiment. Diamond growth is found at substrate temperatures greater than or equal to 650 degrees C with no marked increase in the rate of growth up to 850 degrees C. Acetylene does not give good quality diamond under similar conditions.     

High-pressure ruby and diamond fluorescence: observations at 0.21 to 0.55 terapascal

A diamond-anvil, high-pressure apparatus was used to extend the upper pressure limit of static laboratory experiments. Shifts of the R(1) strong fluorescent line of ruby were observed that correspond to static pressures of 0.21 to 0.55 terapascal (2.1 to 5.5 megabars) at 25 degrees C. Sensitive spectroscopic techniques in the pressure range 0.15 to 0.28 terapascal were used to observe ruby and diamond fluorescence separately; these two fluorescent emissions overlap strongly at high pressures. At pressures greater than approximately 0.28 terapascal, the diamond fluorescence diminished and the ruby fluorescence reappeared strongly. Pressure was determined by extrapolation of the calibrated shift of the ruby R(1) line.     

Flotation of diamond in mantle melt at high pressure

Experiments show that diamond floats in a primitive mantle melt at around 20 gigapascals and 2360 degrees C and in a melt formed by partial melting of the transition zone at about 16 gigapascals and 2270 degrees C. These observations constrain magma densities at high pressure. Diamond precipitated or trapped in a silicate melt at the base of the transition zone or the lower mantle floats and has been accumulating in the transition zone since early in Earth's history. Thus, the transition zone could be a reservoir of diamond.     

238U/235U Systematics in terrestrial uranium-bearing minerals

The present-day (238)U/(235)U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision (238)U/(235)U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. This data set exhibits a range in (238)U/(235)U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional trends. Variation between comagmatic minerals suggests that (238)U/(235)U fractionation processes operate at magmatic temperatures. A mean (238)U/(235)U value of 137.818 ± 0.045 (2σ) in zircon samples reflects the average uranium isotopic composition and variability of terrestrial zircon. This distribution is broadly representative of the average crustal and "bulk Earth" (238)U/(235)U composition.     

Evidence of thermal metamorphism on the C, g, B, and f asteroids

Reflectance spectra (0.3 to 2.6 micrometers) of 14 C, G, B, and F asteroids and 21 carbonaceous chondrite powders are compared in detail. Only three thermally metamorphosed CM-Cl chondrites that have a weak ultraviolet absorption are shown to have close counterparts among those asteroids. Reflectance spectra of heated Murchison CM2 chondrite are compared with the average C and G type asteroid spectra. Murchison heated at 600 degrees to 1000 degrees C exhibits a similar weak ultraviolet absorption and provides the best analog for those spectra. Comparison of ultraviolet absorption strengths between 160 C, G, B, and F asteroids and carbonaceous chondrites suggests that surface minerals of most of those asteroids are thermally metamorphosed at temperatures around 600 degrees to 1000 degrees C.     

Phosphorus: an elemental catalyst for diamond synthesis and growth

As diamond-producing catalysts, 12 transition metals such as iron, cobalt, and nickel were first reported by General Electric researchers more than 30 years ago. Since then, no additional elemental catalyst has been reported. An investigation of the catalytic action of group V elements is of great interest from the viewpoint of producing an n-type semiconducting diamond crystal. In the present study, diamond was synthesized from graphite in the presence of elemental phosphorus at high pressure and temperature (7.7 gigapascals and 1800 degrees C). Furthermore, single-crystal diamond was grown on a diamond seed crystal.     

Epitaxial growth of diamond films on si(111) at room temperature by mass-selected low-energy c+ beams

Diamond films ( approximately 0.7 micrometer thick) have been epitaxially grown on Si(111) substrates at room temperature with mass-selected 120-electronvolt C(+) ions. The diamond reflections observed in x-ray diffraction are well localized at their predicted positions, indicating that (i) the diamond(111) and (220) planes are parallel to the Si(111) and (220), respectively; (ii) the diamond rotational spread around its (111) normal is approximately 1.7 degrees ; and (iii) the mosaic block size is approximately 150 A. The film growth is discussed in terms of subplantation-a shallow subsurface implantation model. This discovery is an important step toward diamond semiconductor devices.     

18O/16O, 30Si/28Si, D/H, and 13C/12C Studies of Lunar Rocks and Minerals

The delta (18)O of minerals from lunar gabbros and basalts are: plgioclases +6.06 to +6.33), pyroxenes (+5.70 to +5.95), and ilmenites (+3.85 to +4.12). The uniformity of these results indicates isotopic equilibrium in the mineral assemblages. Estimated plagioclase-ilmenite temperautres range from 1150 degrees C to 1340 degrees C. The bulk (18)/ (16)O and (30)Si/ (28)Si ratios of these lunar rocks are identical with ratios of terrestrial basalts, but the lunar glass, breccia, and dust are slightly enriched in the heavier isotopes. The lunar hydrogen (formed from solar wind) has a delta D/H of less than-873 per mil and the value may be even lower, as it is probably contaminated with terrestrial hydrogen. The delta (13)C of lunar dust and breccia is unusually high relative to reduced carbon in meteorites or on earth.     

Oxygen Isotope Fractionation between Minerals and an Estimate of the Temperature of Formation

Oxygen isotopic compositions of separated minerals from three type A and four type B rocks are very uniform. The delta(18)O values are: plagioclase, 6.20; clinopyroxene, 5.75; ilmenite, 4.45 (parts per thousand relative to Standard Mean Ocean Water). The isotopic distribution corresponds to equilibrium at 1120 degrees C. The isotopic composition of lunar pyroxenes falls within the range for pyroxenes of terrestrial mafic and ultramafic rocks, ordinary chondrites, enstatite chondrites, and enstatite achondrites, but above the range for basaltic achondrites, hypersthene achondrites, and mesosiderites. Glass isolated from the lunar soil has a delta(18)O value of 6.2, significantly richer in (18)O than the crystalline rock fragments in the soil.     

The Phase Boundary Between agr- and beta-Mg2SiO4 Determined by in Situ X-ray Observation

The stability of Mg(2)SiO(4), a major constituent in the Earth's mantle, has been investigated experimentally by in situ observation with synchrotron radiation. A cubic-type high-pressure apparatus equipped with sintered diamond anvils has been used over pressures of 11 to 15 gigapascals and temperatures of 800 degrees to 1600 degrees C. The phase stability of alpha-Mg(2)SiO(4) and beta-Mg(2)SiO(4) was determined by taking account of the kinetic behavior of transition. The phase boundary between alpha-Mg(2)SiO(4) and beta-Mg(2)SiO(4) is approximated by the linear expression P = (9.3 +/- 0.1) + (0.0036 +/- 0.0002)T where P is pressure in gigapascals and T is temperature in degrees Celsius.     

温度和叶表化学物质对松杨栅锈菌夏孢子萌发的影响

松杨栅锈菌夏孢子萌发适宜温度范围为10～24℃,最适温度20℃左右。供试的2菌株对温度有不同的依赖性。TH菌株温度适应性范围较宽,GL菌株较窄。在最适温度范围内,供试的2个菌株呈现相同的萌发动力学模式,萌发最大速率出现在4～12h,温度越高,最大萌发速率出现时间越晚,并随时间的延长,萌发速率逐渐减小。在5、30℃,萌发速率有2～3个峰值,第1峰值最大,第2、第3峰值逐渐减小或消失。26℃下峰值呈现过渡型状态,有1个较小的次高峰。供试的2菌株,TH的萌发速率较GL稍高并在出现时间上略前。最适萌发条件下,石油醚、乙醚、乙酸乙酯、正丁醇、水的卜氏杨和毛白杨提取物对松杨栅锈菌夏孢子萌发有不同的影响。毛白杨所有提取物在接种12h内,均抑制夏孢子的萌发,而卜氏杨乙醚提取物则促进夏孢子萌发,其余则抑制夏孢子萌发。所有水提取物在接种12h均表现为抑制作用。接种12～24h,2种杨树叶片正丁醇萃取物对夏孢子萌发速率均有一定程度的促进作用。     

Silicate liquid immiscibility in lunar magmas, evidenced by melt inclusions in lunar rocks

Examination of multiphase melt inclusions in 91 sections of 26 lunar rocks revealed abundant evidence of late-stage immiscibility in all crystalline rock sections and in soil fragments and most breccias. The two individual immiscible silicate melts (now glasses) vary in composition, but are essentially potassic granite and pyroxenite. This immiscibility may be important in the formation of the lunar highlands and tektites. Other inclusions yield the following temperatures at which the several minerals first appear on cooling the original magma: ilmenite (?) liquidus, 1210 degrees C; pyroxene, 1140 degrees C; plagioclase, 1105 degrees C; solidus, 1075 degrees C. The glasses also place some limitations on maximum and minimum cooling rates.     

Nanometer-size alpha-PbO(2)-type TiO(2) in garnet: A thermobarometer for ultrahigh-pressure metamorphism

A high-pressure phase of titanium dioxide (TiO(2)) with an alpha-PbO(2)-type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this alpha-PbO(2)-type TiO(2) occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of alpha-PbO(2)-type TiO(2) to rutile, the stabilization pressure of alpha-PbO(2)-type TiO(2) should be 4 to 5 gigapascals at 900 degrees to 1000 degrees C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The alpha-PbO(2)-type TiO(2) may be a useful pressure and temperature indicator in the diamond stability field.