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1.
Insoluble organic matter (IOM) has been obtained from two carbonaceous chondrite meteorites and subjected to analysis by laser desorption mass spectrometry (LDMS) using standard operating conditions that were optimized for fullerene detection (3-6 μJ pulses at 337 nm focused to a spot size of approximately 100 μm in diameter). The preparation process yields no free C60 in the IOM, and other experiments suggest that this material does not contain appreciable amounts of fullerenes. Nevertheless, a pronounced high-mass envelope is observed in LDMS, extending from 720 amu to about 4000 amu, with peaks spaced apart every 24 amu (corresponding to the gain or loss of C2 units). We attribute this high-mass envelope to the existence of various fullerene molecules. The present work demonstrates that these fullerene molecules are created by the laser desorption laser ionization process under typical laser conditions used for studying free fullerenes in organic solvent extracts of natural samples (toluene and 1,2,4-trichlorobenzene). The implications of this false positive detection of fullerene molecules on the reports of fullerenes in other meteoritic samples have been investigated by introducing IOM into typical fullerene extraction procedures and examining the LDMS results. We found that IOM is capable of producing false positive signals in these experiments. The effect of ambient laboratory contamination producing fullerene signals is also described. It is found that extensive centrifugation of the meteoritic extracts is able to reduce the observed fullerene envelope, which points to an association of this envelope with IOM particulates that have passed through the filtering steps. We suggest the exercise of extreme caution in interpreting fullerene data from LDMS experiments.  相似文献   

2.
Andesitic pillow lavas containing biogenic, solid bitumen (SB) are a constituent of a Neoproterozoic volcanosedimentary sequence (Teplá-Barrandian unit, Bohemian Massif) in the Mítov area of the Czech Republic. A black shale formation that is crosscut by these andesitic basalts is 565 Ma old. Carbon disulfide extracts of two powdered samples of SB contain 0.2 and 0.3 ppm of C60, respectively, as determined by high-pressure liquid chromatography. The peak assignment based on retention time is fully supported by high-resolution electron ionization mass spectrometry (EI-MS). No C70 was detected, nor was C60 found in two other SB samples from this locality. Other investigated carbonaceous samples from Bohemia (coals and anthracites of Upper Paleozoic age and anthraxolite, graphitoids, and graphite of Upper Proterozoic age) did not contain fullerenes at concentrations above the detection limit of 0.01 ppm. The absence of C60 in these samples was confirmed by EI-MS. The proposed mechanism of fullerene formation involves a primary algal phase, generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series, and their high-temperature transformation related to the extrusion of basalt. An important feature for fullerene conservation was the enclosure of fullerenes in SB with a structure similar to glasslike carbon, where the fullerene was protected against oxidation.  相似文献   

3.
Fullerenes have been detected in carbonaceous chondrite meteorites and in breccia samples from meteorite impact craters, but questions have been raised about contradictory results from similar samples and the sensitivities and accuracies of different analytical methods. We analyzed samples from three impact craters and detected C60 in samples from several locations; we also observed differences in the detection capabilities of various analytical techniques used in the search for fullerenes. The presence of C60 in rocks from the Onaping Formation of the Sudbury impact crater was confirmed. Low levels of C60 were also detected for the first time in samples from the Gardnos (Norway) and Ries (Germany) impact structures.We detected C60 in these samples using surface-enhanced laser desorption/ ionization (SELDI), but the related technique of microprobe laser-desorption, laser-ionization mass spectrometry (μL2MS) did not observe C60 above detection limits. We attribute the absence of μL2MS signal to aggregate formation caused by phthalic acid esters, which appear to easily contaminate samples either during storage or demineralization in plastic containers. The μL2MS technique is incapable of detecting aggregated C60, but aggregation does not suppress detection in SELDI. Phthalate-induced aggregation did, however, enhance SELDI detection of C60 in some cases, and we suggest that this enhancement may help explain previously reported differences in C60 detection from natural samples between laser desorption mass spectrometry (LDMS, a technique analogous to SELDI that has detected fullerenes in meteorite and impact breccia samples) and high-pressure liquid chromatography (HPLC). This work highlights the effects of phthalates and other indigenous compounds or contaminants on certain mass spectrometric techniques and lends support to the idea that several complementary analytical methods should be employed to investigate complex natural samples.  相似文献   

4.
Higher fullerenes(C84,C90,C92,C94 and C96) were successfully isolated from the Soxhlet extract of the synthetical "Graphote Smokes" soot(GS sample) by using a big Cosmosil Buckysep(Phenomenex) column(250 mm × 10 mm) with a large injection.The fractions isolated have been determined by high performance liquid chro-matography(HPLC) and laser desorption mass spectrometry(LDMS).It is found that there are different fullerenes molecules in different fractions with retention time.The result indicates that fullerenes do exist in GS samples.Also,it excludes the suspicion to some extent that fullerene molecules might be generated by the laser desorption process in the LDMS.In addition,it also provides the experimental basis for the study of natural higher fullerenes and might be helpful to figure out the question if higher fullerenes do exist in the natural samples.  相似文献   

5.
Sediment cores were collected from deep-water areas of Lake Chenghai, China in June 1997. The vertical profile of 137Cs activity gives reliable geochronological results. The results also indicate that sediment accumulation rates in deep-water areas of Lake Chenghai were relatively constant in recent decades, averaging 0.43 g cm− 2 y− 1, despite a variable organic carbon influx. 210Pbeq (= 226Ra) activity was relatively constant also, with an average value of 54.3 ± 3.2 Bq kg− 1. Vertical profiles of 210Pbex (= 210Pbtotal − 226Ra) decreased exponentially, resulting in somewhat lower sediment accumulation rates (0.3 g cm− 2 y− 1). These lower rates are likely less reliable, as the relatively large fluctuations in 210Pbex activities correlate closely to the organic carbon (Corg) content of the sediments. For example, the vertical profile of 210Pbex activity displays peaks at mass depths of 3.7-4.7 g cm− 2 (10-12 cm) and 10-11 g cm− 2(25-28 cm), similar to the maxima in the vertical profile of Corg. This phenomenon must be related to the delivery of particulate organic matter (POM) from the water to the sediments, or to watershed soil erosion. Since the mean atomic ratios of Horg / Corg and Corg / Norg in Lake Chenghai sediments are 5.5 and 7.0, respectively, indicating that POM was predominantly derived from the remains of authigenic algae, this eliminates watershed erosion rates as a primary control on lake sedimentation rates as resolved by 210Pbex. Sedimentation fluxes (F(Corg)) of particulate organic carbon since 1970 varied between 60 to 160 g m− 2 y− 1, and appeared to closely influence variations in 210Pbex concentrations. For example, sedimentation fluxes of 210Pbex (F(210Pbex)) showed maxima in the years 1972-1974 and 1986-1989, likely reflecting historical variations of lake biological productivity or carbon preservation.  相似文献   

6.
Methane and CO2 emissions from the two most active mud volcanoes in central Japan, Murono and Kamou (Tokamachi City, Niigata Basin), were measured in from both craters or vents (macro-seepage) and invisible exhalation from the soil (mini- and microseepage). Molecular and isotopic compositions of the released gases were also determined. Gas is thermogenic (δ13CCH4 from −32.9‰ to −36.2‰), likely associated with oil, and enrichments of 13C in CO2 (δ13CCO2 up to +28.3‰) and propane (δ13CC3H8 up to −8.6‰) suggest subsurface petroleum biodegradation. Gas source and post-genetic alteration processes did not change from 2004 to 2010. Methane flux ranged within the orders of magnitude of 101-104 g m−2 d−1 in macro-seeps, and up to 446 g m−2 d−1 from diffuse seepage. Positive CH4 fluxes from dry soil were widespread throughout the investigated areas. Total CH4 emission from Murono and Kamou were estimated to be at least 20 and 3.7 ton a−1, respectively, of which more than half was from invisible seepage surrounding the mud volcano vents. At the macro-seeps, CO2 fluxes were directly proportional to CH4 fluxes, and the volumetric ratios between CH4 flux and CO2 flux were similar to the compositional CH4/CO2 volume ratio. Macro-seep flux data, in addition to those of other 13 mud volcanoes, supported the hypothesis that molecular fractionation (increase of the “Bernard ratio” C1/(C2 + C3)) is inversely proportional to gas migration fluxes. The CH4 “emission factor” (total measured output divided by investigated seepage area) was similar to that derived in other mud volcanoes of the same size and activity. The updated global “emission-factor” data-set, now including 27 mud volcanoes from different countries, suggests that previous estimates of global CH4 emission from mud volcanoes may be significantly underestimated.  相似文献   

7.
The solubility and incorporation mechanisms of water in synthetic and natural MgAl2O4 spinel have been investigated in a series of high-pressure/temperature annealing experiments. In contrast to most other nominally anhydrous minerals, natural spinel appears to be completely anhydrous. On the other hand, non-stoichiometric Al-rich synthetic (defect) spinel can accommodate several hundred ppm water in the form of structurally-incorporated hydrogen. Infrared (IR) spectra of hydrated defect spinel contain one main O-H stretching band at 3343-3352 cm−1 and a doublet consisting of two distinct O-H bands at 3505-3517 cm−1 and 3557-3566 cm−1. IR spectra and structural refinements based on single-crystal X-ray data are consistent with hydrogen incorporation in defect spinel onto both octahedral and tetrahedral O-O edges. Fine structure of O-H bands in IR spectra can be explained by partial coupling of interstitial hydrogen with cation vacancies, or by the effects of Mg-Al disorder on the tetrahedral site. The concentration of cation vacancies in defect spinel is a major control on hydrogen affinity. The commercial availability of large single crystals of defect spinel coupled with high water solubility and similarities in water incorporation mechanisms between hydrous defect spinel and hydrous ringwoodite (Mg2SiO4) suggests that synthetic defect spinel may be a useful low-pressure analogue material for investigating the causes and consequences of water incorporation in the lower part of Earth’s mantle transition zone.  相似文献   

8.
Raman spectroscopy is a powerful method for the determination of CO2 densities in fluid inclusions, especially for those with small size and/or low fluid density. The relationship between CO2 Fermi diad split (Δ, cm−1) and CO2 density (ρ, g/cm3) has been documented by several previous studies. However, significant discrepancies exist among these studies mainly because of inconsistent calibration procedures and lack of measurements for CO2 fluids having densities between 0.21 and 0.75 g/cm3, where liquid and vapor phases coexist near room temperature.In this study, a high-pressure optical cell and fused silica capillary capsules were used to prepare pure CO2 samples with densities between 0.0472 and 1.0060 g/cm3. The measured CO2 Fermi diad splits were calibrated with two well established Raman bands of benzonitrile at 1192.6 and 1598.9 cm−1. The relationship between the CO2 Fermi diad split and density can be represented by: ρ = 47513.64243 − 1374.824414 × Δ + 13.25586152 × Δ2 − 0.04258891551 × Δ3 (r2 = 0.99835, σ = 0.0253 g/cm3), and this relationship was tested by synthetic fluid inclusions and natural CO2-rich fluid inclusions. The effects of temperature and the presence of H2O and CH4 on this relationship were also examined.  相似文献   

9.
The alkenone unsaturation index UK′37 has been applied to reconstruct past temperature changes in both marine and lacustrine systems. However, few studies have addressed whether the relative abundance of the C37:4 alkenone to the total C37 production (%C37:4) can reflect surface salinity changes in lacustrine systems. Here we present long-chain C37 alkenone distribution patterns in surface sediments from Lake Qinghai, China. Surface sediments were sampled over a large range of surface salinity changes (1.7-25 g/l) within Lake Qinghai and its surrounding lakes, while temperature differences at these sampling locations should be relatively small. We have found that %C37:4 varies from 15% to 49% as surface salinity decreases. We tentatively describe this %C37:4-salinity link with a general linear regression: %C37:4 = 53.4 (±7.8) − 1.73 (±0.45) × S (n = 28, r2 = 0.62), although step-wise %C37:4 changes in response to salinity variation may exist. UK′37 values vary between 0.10 and 0.16 at these sites and the inferred range of lake water temperature changes is ∼2-3 °C, suggesting that UK′37 largely reflects temperature signal across a large salinity range, consistent with previous findings that UK′37 can indicate temperature changes over a large diversity of environmental settings. We have also found that UK′37 values are correlated with salinity changes (r2 = 0.4), and thus cannot exclude potential temperature effect on %C37:4 and salinity effect on UK′37 in this study. However, even extreme estimates of temperature differences within the lake are still unable to explain the observed %C37:4 changes. We therefore suggest that %C37:4 could be used to infer past lake salinity changes at a regional scale.  相似文献   

10.
The late Holocene environmental history of the Lesotho highlands, southern Africa, is poorly understood with few detailed studies to date. At Likoaeng, Senqu Valley, Lesotho, a 3 m stratified sedimentary sequence from an open-air archaeological site records vegetation development for the period 3400-1070 cal. BP. Phytolith analyses and bulk sediment organic matter δ13C indicate that C4 grassland dominated the lower part of the sequence until approximately 2960 cal. BP when there was a switch to C3 Pooid grassland (2960-2160 cal. BP). Also noted was a change from hunting mainly bovids to a dominance of fishing at the site. The change in grassland type and archaeological subsistence strategies corresponds with an episode of neoglacial cooling and the expansion of Alpine sourgrasses into lower altitudes. From 2160 to 1600 cal. BP grassland became a mix of C3 and C4 types and by 1600-1070 cal. BP there was a return to C4 dominated grassland. During this latter phase there was a reversal from fishing to hunting again (and eventually some keeping of domestic livestock) at the site. These data outline the vegetation response to latitudinal shifts of frontal systems, and relatively strong atmospheric circulation variability, perhaps underpinned by variations of polar water into the Benguela Current during the late Holocene.  相似文献   

11.
Four nearly pure MgAl2O4 spinels, of both natural and synthetic occurrence, have been studied by means of X-ray single crystal diffraction and FTIR spectroscopy in order to detect their potential OH content. Absorption bands that can be assigned to OH incorporated in the spinel structure were only observed in spectra of a non-stoichiometric synthetic sample. The absorption intensity of two bands occurring at 3350 and 3548 cm−1 indicate an OH content of 90 ppm H2O. Based on correlations of OH vibrational frequencies and O-H?O distances, the observed absorption bands correspond to O-H?O distances of 2.77 and 2.99 Å, respectively, which is close to the values obtained by the structure refinements for VIO-Ounsh (2.825 Å) and IVO-O (3.001 Å). This indicates that one probable local position for hydrogen incorporation is the oxygens coordinating a vacant tetrahedral site. The present spectra demonstrate that the detection limit for OH in Fe-free spinels is in the range 10-20 ppm H2O. However, at appreciable Fe2+ levels, the detection of OH bands becomes hampered due to overlap with strong absorption bands caused by electronic d-d transitions in Fe2+ in the tetrahedral position.  相似文献   

12.
The Western Slope of the Songliao Basin is rich in heavy oil resources (>70 × 108 bbl), around which there are shallow gas reservoirs (∼1.0 × 1012 m3). The gas is dominated by methane with a dryness over 0.99, and the non-hydrocarbon component being overwelmingly nitrogen. Carbon isotope composition of methane and its homologs is depleted in 13C, with δ13C1 values being in the range of −55‰ to −75‰, δ13C2 being in the range of −40‰ to −53‰ and δ13C3 being in the range of −30‰ to −42‰, respectively. These values differ significantly from those solution gases source in the Daqing oilfield. This study concludes that heavy oils along the Western Slope were derived from mature source rocks in the Qijia-Gulong Depression, that were biodegraded. The low reservoir temperature (30–50 °C) and low salinity of formation water with neutral to alkaline pH (NaHCO3) appeared ideal for microbial activity and thus biodegradation. Natural gas along the Western Slope appears mainly to have originated from biodegradation and the formation of heavy oil. This origin is suggested by the heavy δ13C of CO2 (−18.78‰ to 0.95‰) which suggests that the methane was produced via fermentation as the terminal decomposition stage of the oil.  相似文献   

13.
Gas was sampled regionally, including by drilling into faults, in the South Kanto gas-field around Tokyo Bay, Japan. Gas samples were collected from cores in a gas sampling container immediately after drilling. A value of δ13C1 = −44.3‰ was obtained for gas in the container and δ13C1 = −36.3‰ for seeping gas in a fault zone. However, typical CH4 in this dissolved-in-water gas-field is mainly depleted in 13C, and δ13C1 values range from −66‰ to −68‰ owing to microbial degradation of organic material. 13C-rich CH4 is so far uncommon in the South Kanto gas-field. Seepages were observed from the surface along the north–south fault zone. The natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m. Gas seepages were not observed below a depth of 40 m. Gas rises along the fault zone dissolved-in-groundwater up to the shallow region and then separates from the groundwater. 13C-rich CH4 (adsorbed CH4) was found to have desorbed from drilled mudstone core samples taken at depths of 1400–1900 m in the main gas-production strata. Similarly, 13C-rich CH4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the Tokyo region. It also appears in the spring-water of spa wells, originating at a depth of 1200–1500 m along a tectonic line. Methane generated by microbial degradation of organic material through CO2 reduction in the South Kanto gas-field mainly originates as biogenic gas mixed with a small amount of 13C-rich CH4, derived from thermogenic gas without oil components in strata. It is assumed that 12C-rich CH4 is easily detached from core or pore water through gas production, whereas 13C-rich CH4 is strongly adsorbed on the surfaces of particles. The 13C-rich CH4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the Kanto region.  相似文献   

14.
Bulk-rock chlorine content and isotopic composition (δ37Cl) were determined in oceanic serpentinites, high-pressure metaperidotites and metasediments in order to gain constraints on the global chlorine cycle associated with hydrothermal alteration and subduction of oceanic lithosphere. The distribution of insoluble chlorine in oceanic serpentinites was also investigated by electron microprobe. The hydrothermally-altered ultramafic samples were dredged along the South West Indian Ridge and the Mid-Atlantic Ridge. The high-pressure metamorphic samples were collected in the Western Alps: metaperidotites in the Erro-Tobbio unit and metasediments in the Schistes Lustrés nappe.Oceanic serpentinites show relatively large variations of bulk-rock Cl contents and δ37Cl values with mean values of 1105 ± 596 ppm and −0.7 ± 0.4‰, respectively (n = 8; 1σ). Serpentines formed after olivine (meshes) show lower Cl content than those formed after orthopyroxene (bastites). In bastites of two different samples, Cl is positively correlated with Al2O3 and negatively correlated with SiO2. These relationships are interpreted as reflecting preferential Cl-incorporation into the bastite structure distorted by Al (substituted for Si) rather than different alteration conditions between olivine and orthopyroxene minerals. High-pressure metaperidotites display relatively homogeneous Cl contents and δ37Cl values with mean values of 467 ± 88 ppm and −1.4 ± 0.1‰, respectively (n = 7; 1σ). A macroscopic high-pressure olivine-bearing vein, formed from partial devolatilization of serpentinites at ∼2.5 GPa and 500-600 °C, shows a Cl content and a δ37Cl value of 603 ppm and −1.6‰, respectively. Metasediments (n = 2) show low whole-rock Cl contents (<15 ppm Cl) that did not allow Cl isotope analyses to be obtained.The range of negative δ37Cl values observed in oceanic serpentinites is likely to result from water-rock interaction with fluids that have negative δ37Cl values. The homogeneity of δ37Cl values from the high-pressure olivine-bearing vein and the metaperidotite samples implies that progressive loss of Cl inherited from oceanic alteration throughout subduction did not significantly fractionate Cl isotopes. Chlorine recycled in subduction zones via metaperidotites should thus show a range of δ37Cl values similar to the range found in oceanic serpentinized peridotites.  相似文献   

15.
The influence of citrate and phthalate on Co coprecipitation with calcite was investigated using a combination of batch experiments, Fourier-transform infra-red (FT-IR) spectroscopy, and thermogravimetric analysis (TGA) over a wide range of precipitation rates. Steady-state growth conditions (at constant [Ca], [Co], DIC, and pH) were generally achieved within 3-5 h, after which Co(II) partitioning into calcite was evaluated. Only minor differences are observed in the partition coefficient (Kd) trends with and without citrate and phthalate as a function of calcite precipitation rate except at very low rates. Slight inhibition of calcite growth is observed in the presence of citrate or phthalate, which can be attributed to adsorption at surface sites. TGA curves for samples coprecipitated with citrate show a significant mass loss between 375 and 550 °C, whereas the weight-loss curves for the Co-phthalate coprecipitates are indistinguishable from those of the organic-free Co coprecipitates. This indicates that citrate is incorporated into calcite during calcite crystallization, whereas phthalate is excluded. FT-IR spectra for the sample with citrate show a broad absorption in the range 3700-3100 cm−1, which is attributable to water molecules coordinated to citrate coprecipitated with calcite. The preferential incorporation of citrate over phthalate likely reflects differences in both aqueous speciation and conformation of the carboxylate groups. This new finding may provide new insight to the factors that control the behavior of macromolecules and their incorporation into the structure of calcium carbonate during biomineralization.  相似文献   

16.
The relationship between stable isotope composition (δ13C and δ18O) in seawater and in larval shell aragonite of the sea scallop, Placopecten magellanicus, was investigated in a controlled experiment to determine whether isotopes in larval shell aragonite can be used as a reliable proxy for environmental conditions. The linear relationship between δ13CDIC and δ13Caragonite (r2 = 0.97, p < 0.0001, RMSE = 0.18) was:
δ13CDIC=1.15(±0.05)∗δ13Caragonite-0.85(±0.04)  相似文献   

17.
δ13C values of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate organic C (POC) together with δ18O and δ2H values of water, δ34S values of dissolved SO4, and major ion concentrations were measured in the Murray River and its tributaries between November 2005 and April 2007 to constrain the origins and behaviour of riverine C. δ13CDIC values in the Murray River vary between −9.5 and −4.7‰ with a range of <3‰ within any sampling round. δ13CDIC values of the tributaries are −11.0‰ to −5.1‰. DIC concentrations of the Murray River increase from ∼25 mg/L in the middle and upper reaches of the river to 45–55 mg/L in the lower reaches. However, the mass ratio of DIC as a proportion of the total dissolved solids (TDS) decreases from ∼0.6–0.7 in the headwaters to ∼0.2–0.3 in the lower reaches of the river, with similar downstream changes in DIC/Cl ratios. This precludes simple evaporative concentration of DIC and is interpreted as the river evading CO2; this interpretation is consistent with pCO2 values that are in the range 550–11,200 ppm volume (ppmv), which are far higher than those in equilibrium with the atmosphere (∼360 ppmv). The δ13CDIC values are similar to those that would be produced by the weathering of marine limestone (δ13C ∼ 0‰). However, the lack of marine limestones cropping out in the Murray–Darling Basin and the relatively uniform δ13CDIC values of the Murray River (even in upland reaches where the dominant rock types are metamorphosed silicates and granites) make this unlikely. Rather the high pCO2 values and δ13CDIC values are best explained by a combination of mineralisation of low δ13C organic C and evasion to the atmosphere. The rate of these two processes may attain near steady state and control both DIC concentrations and δ13C values.  相似文献   

18.
Different analytical techniques were used to find the most reliable and economic method for determining the labile fraction of C in biochar. Biochar was produced from pine, poplar and willow (PI, PO and WI, respectively) at two temperatures (400 and 550 °C) and characterised using spectroscopic techniques [solid state 13C nuclear magnetic resonance spectroscopy (NMR)], molecular markers [pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS)], thermogravimetry (TG), elemental composition and wet oxidation (potassium permanganate and potassium dichromate). Short term incubation (110 h) of an A horizon from an Umbrisol amended with the biochar samples at two doses (7.5 and 15 t ha−1) was also carried out to provide supplementary information on the influence of biochar-soil interaction on CO2 evolution. Spectroscopic analysis demonstrated that the degree of biochar carbonisation was influenced by the type of feedstock and heating conditions and followed the order WI-400 < PI-400 ∼ WI-550 ∼ PO-400 < PO-550 < PI-550. The thermo-labile fraction of the biochar samples, estimated from TG, ranged between 21% and 49%. The fraction of total C oxidised with potassium permanganate (Cper/Ctotal) was <50 g kg−1 in all cases, whereas potassium dichromate (Cdichro/Ctotal) oxidation efficiency ranged between 180 and 545 g kg−1. For each type of feedstock, the highest values of either chemically or thermally degradable C corresponded to the biochar produced at low temperature. Results indicate that low cost methodologies, such as dichromate oxidation and TG, reflected the degree of biochar carbonisation, and could therefore be used to estimate the labile fraction of C in biochar.  相似文献   

19.
We present detailed petrographic surveys of apatite grains in association with carbonaceous material (CM) in two banded iron formations (BIFs) from the Paleoproterozoic of Uruguay and Michigan for comparison with similar mineral associations in the highly debated Akilia Quartz-pyroxene (Qp) rock. Petrographic and Raman spectroscopic surveys of these Paleoproterozoic BIFs show that apatite grains typically occur in bands parallel to bedding and are more often associated with CM when concentrations of organic matter are high. Carbonaceous material in the Vichadero BIF from Uruguay is generally well-crystallized graphite and occurs in concentrations around 0.01 wt% with an average δ13Cgra value of −28.6 ± 4.4‰ (1σ). In this BIF, only about 5% of apatite grains are associated with graphite. In comparison, CM in the Bijiki BIF from Michigan is also graphitic, but occurs in concentrations around 2.4 wt% with δ13Cgra values around −24.0 ± 0.3‰ (1σ). In the Bijiki BIF, more than 78% of apatite grains are associated with CM. Given the geologic context and high levels of CM in the Bijiki BIF, the significantly higher proportion of apatite grains associated with CM in this rock is interpreted to represent diagenetically altered biomass and shows that such diagenetic mineral associations can survive metamorphism up to the amphibolite facies.Isotope compositions of CM in muffled acidified whole-rock powders from the Akilia Qp rock have average δ13Cgra values of −17.5 ± 2.5‰ (1σ), while δ13Ccarb values in whole-rock powders average −4.0 ± 1.0‰ (1σ). Carbon isotope compositions of graphite associated with apatite and other minerals in the Akilia Qp rock were also measured with the NanoSIMS to have similar ranges of δ13Cgra values averaging −13.8 ± 5.6‰ (1σ). The NanoSIMS was also used to semi-quantitatively map the distributions of H, N, O, P, and S in graphite from the Akilia Qp rock, and relative abundances were found to be similar for graphite associated with apatite or with hornblende, calcite, and sulfides. These analyses revealed generally lower abundances of trace elements in the Akilia graphite compared to graphite associated with apatite from Paleoproterozoic BIFs.Graphite associated with hornblende, calcite, and sulfides in the Akilia Qp rock was fluid-deposited at high-temperature from carbon-bearing fluids, and since this graphite has similar ranges of δ13Cgra values and of trace elements compared to graphite associated with apatite, we conclude that the Akilia graphite in different mineral associations formed from the same source(s) of CM. Collectively our results do not exclude a biogenic origin of the carbon in the Akilia graphite, but because some observations can not exclude graphitization of abiogenic carbon from CO2- and CH4-bearing mantle fluids, there remain ambiguities with respect to the exact origin of carbon in this ancient metasedimentary rock. Accordingly, there may have been several generations of graphite formation along with possibly varying mixtures of CO2- and CH4-bearing fluids that may have resulted in large ranges of δ13Cgra values. The possibility of fluid-deposited graphite associated with apatite should be a focus of future investigations as this may prove to be an alternative pathway of graphitization from phosphate-bearing fluids. Correlated micro-analytical approaches tested on terrestrial rocks in this work provide insights into the origin of carbon in ancient graphite and will pave the way for the search for life on other ancient planetary surfaces.  相似文献   

20.
The high-pressure behavior of three synthetic amphiboles crystallized with space group P21/m at room conditions in the system Li2O–Na2O–MgO–SiO2–H2O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ANa B(Na x Li1 − x Mg1) CMg5 Si8 O22(OH)2 with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching infrared spectra can be assigned to two non-equivalent O–H dipoles in the P21/m structure, bonded to the same local environment M1M3Mg3–OH–ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P21/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared spectra collected for amphibole B(Na0.2Li0.8Mg1) in the frequency range 50 to 1,400 cm−1 also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph.  相似文献   

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