Carbonaceous Inclusions Research Articles

Low carbon isotope ratios in apatite: An unreliable biomarker in igneous and metamorphic rocks

Carbon isotope ratios of apatite have been used to interpret the source of carbon in magmas and metamorphic fluids, using the assumption that carbon isotope fractionations between phases are small in igneous and metamorphic systems. Measured carbon isotope fractionations between co-existing apatite and calcite from igneous, metaigneous, and metasedimentary rocks are large and variable (Δ 13C = 2.3 to 20.8‰), reflecting variability in δ 13C(Ap) sampled by combustion. This result indicates that carbon isotopes in apatite sampled by common techniques (combustion, ion microprobe, step-heating) do not have a straightforward interpretation. These data suggest that the low- δ 13C values in apatite that have previously been used as indicators of biological activity may be the result of the carbon isotope fractionation systematics of apatite, rather than a reflection of incorporation of organic carbon. This unusual fractionation behavior may require reconsideration of the significance of low- δ 13C carbonaceous inclusions in apatite from ≥ 3.8 Ga metamorphic rocks from Akilia Island, Greenland.

TEM studies and the shock history of a “mysterite” inclusion from the Krymka LL chondrite

Abstract— The microstructure and composition of the matrix of one carbonaceous inclusion (K1) in the Krymka LL3.1 chondrite were studied using transmission electron microscopy (TEM). K1 has previously shown an enigmatic nature and similarities with volatile‐rich, fine‐grained, dark inclusions of Krymka called “mysterite.”In the present study, four minerals were identified by TEM. Olivine, pyroxene, and pyrrhotite typically have grain sizes of one micrometer; graphite occurs as flakes of a similar size. Olivine shows a moderately high dislocation density most probably caused by shock. Pyroxene shows coexisting ortho‐ and clinoenstatite lamellae that probably originated from shear stress after a shock event or from the rapid cooling of the protoenstatite stability field. However, we demonstrate that in this case, a shock trigger is more likely. Pyrrhotite in the studied sample occurs as a 4C monoclinic superstructure. The graphite flakes in the fragment are well crystallized, as can be seen by discrete spots in the diffraction pattern. In graphite, the degree of crystallization increases with the metamorphic grade. Based on the microstructure of this mineral we conclude that after a first moderate shock event, the residual temperature between 300 °C and 500 °C led to thermal metamorphism. A second shock event, possibly at excavation from the parent body, is responsible for the shock features observed in olivine, pyroxene, and graphite.

Silicate-silicate liquid immiscibility and graphite ribbons in Libyan desert glass

Transmission electron microscopic (TEM) investigation of the dark (brown or bluish) streaks occurring in Libyan Desert Glass reveals the common presence of small glass spherules. The spherules, mostly 100 nm in size, are homogeneously dispersed within the silica-glass matrix. The complete absence of electron diffraction effects confirms their amorphous nature. The spherules are Al-, Fe- and Mg-enriched with respect to the surrounding silica matrix and their (Mg + Al + Fe) : Si ratio is close to 1.The silica-glass matrix and amorphous spherules form an emulsion texture (i.e., globules of one glass in a matrix of another glass), which originates from silicate-silicate liquid immiscibility. This texture has also been observed in other impact-derived glasses.The silica glass also contains carbonaceous inclusions consisting of 5–50 nm thick, polygonalized graphite ribbons that form closed structures up to 200 nm in diameter.These observations are in agreement with an impact origin for Libyan Desert Glass.

Plutonium-244 fission xenon in carbonaceous inclusions of primitive meteorites

A total of 13 samples of diamond separates studied so far, all contain excess 244Pu fission xenon. On the other hand, none of the SiC separates contains excess 244Pu fission xenon, while 5 out of 10 samples of graphite separates studied so far contain excess 244Pu fission xenon.

Tensile strength and fracture surface characterization of Hi-Nicalon™ SiC fibers

Dimensional, tensile strength and fracture surface characterizations were carried out for a particular batch of Hi-Nicalon™ SiC fiber. In general, filaments with larger cross-sectional areas (equivalent diameters) had lower strengths than filaments with smaller cross-sectional areas. A cyclic variation of fiber diameter along filament lengths was discovered with a repeat distance of about 16-cm and a maximum rate of change of about ±0.6 μm/ cm . During tensile tests at room temperature, fracture originated at critical flaws that typically consisted of internal pores or carbonaceous inclusions. Well-demarcated mirror and hackle regions usually surrounded the critical flaws. With a few exceptions, the critical flaw size ( a c) was linearly related to the mirror size ( r m) by a c≈0.33 r m. From fracture mechanics principles, values for the average mirror constant ( A m) and effective fracture toughness for this batch of Hi-Nicalon™ fiber were estimated to be 2.99±0.33 and 1.1±0.2 MPa m 1/2, respectively.

Dispersed Organic Matter in Riphean Carbonate–terrigenous Sediments of the Kuzha Complex (Bashkirian Uplift, Southern Urals)

Regularities of the localization of dispersed organic matter in rhythmitic and carbonate members of the upper sequence of the Biktimir Formation were revealed by studying sections of the Middle Riphean sediments within the eastern limb of the Yurmatau Anticlinorium. This work presents the quantitative estimation of Corg content in lithological rock types and morphostructural features of carbonaceous inclusions and sulfide mineralization. The sedimentogenic–biogenic nature of organic matter and indications of gold mineralization in the host sedimentary rocks were revealed.

Oxygen isotopic abundances in calcium- aluminum-rich inclusions from ordinary chondrites: implications for nebular heterogeneity.

The oxygen isotopic compositions of two calcium-aluminum-rich inclusions (CAIs) from the unequilibrated ordinary chondrite meteorites Quinyambie and Semarkona are enriched in 16O by an amount similar to that in CAIs from carbonaceous chondrites. This may indicate that most CAIs formed in a restricted region of the solar nebula and were then unevenly distributed throughout the various chondrite accretion regions. The Semarkona CAI is isotopically homogeneous and contains highly 16O-enriched melilite, supporting the hypothesis that all CAI minerals were originally 16O-rich, but that in most carbonaceous chondrite inclusions some minerals exchanged oxygen isotopes with an external reservoir following crystallization.

Producing Clay-Coated Quartz Powders for Semidry Pressing of Wall Ceramics

ABSTRACTThis paper discusses the potential of mechanochemical activation of low grade raw materials with carbonaceous inclusions to achieve high-quality building ceramics. The procedure proposed enabled us to produce clay-coated quartz powders thus facilitating further processing steps of semidry pressing and firing of the bricks, tiles and flagstones.

An appraisal of stepped heating release of fluid inclusion CO 2 for isotopic analysis: A preliminary to δ 13C characterisation of carbonaceous vesicles at the nanomole level

An appraisal of stepped heating methods for the extraction and isolation of fluid inclusion CO 2 for carbon stable isotope ratio analysis indicates that the magnitude of the system blank, and thus its influence on the resulting data, has been considerably underestimated in previous studies. The problem derives largely from the unmodified application of stepped combustion techniques originally developed for the removal of terrestrial organic matter from extraterrestrial samples. In particular, the presence of heated Pt in the sample extraction chamber, as reported in the literature, is shown to have a serious deleterious effect on the analysis of small (sub-micromole) samples. If the extracted gases are not exposed to this combustion catalyst, the magnitude of the system blank is substantially reduced. Furthermore, excellent agreement is then generally obtained between fluid inclusion δ 13C values determined after either stepped heating or crushing of the host mineral as the fluid extraction procedure. The release of a low temperature carbon component during stepped heating, and characterised invariably by a δ 13C value of ca. −25%, is in accord with earlier studies and is attributed to surficial contamination by ubiquitous, airborne particulates of biological origin. Effective discrimination between this source of CO 2 and that derived from palaeofluid inclusions is fundamental to accurate isotopic characterisation of the latter. Application of the revised stepped heating procedure to the extraction of hydrothermal fluid inclusion CO 2 from single quartz grains (∼10–20 mg), for carbon stable isotope analysis by static vacuum mass spectrometry, is reported. Under optimum conditions, and where the isotopic composition of the sample gas is enriched in '3C by less than ∼20%0 relative to the associated procedural blank, 2–3 nmol of sample gas may be analysed with an attendant extraneous (blank) contribution to the δ 13C value that is less than the optimal analytical precision of the measurement (∼±1%0, at the 1σ level). Further progress in the application of ultra-high sensitivity mass spectrometric techniques to accurate δ 13C analysis of carbonaceous fluid inclusion components, particularly coexisting CO 2 and methane, is dependent on proper assessment of the associated blanks and the rigorous control thereof.

Evidence for life on Earth before 3,800 million years ago.

It is unknown when life first appeared on Earth. The earliest known microfossils (approximately 3,500 Myr before present) are structurally complex, and if it is assumed that the associated organisms required a long time to develop this degree of complexity, then the existence of life much earlier than this can be argued. But the known examples of crustal rocks older than 3,500 Myr have experienced intense metamorphism, which would have obliterated any fragile microfossils contained therein. It is therefore necessary to search for geochemical evidence of past biotic activity that has been preserved within minerals that are resistant to metamorphism. Here we report ion-microprobe measurements of the carbon-isotope composition of carbonaceous inclusions within grains of apatite (basic calcium phosphate) from the oldest known sediment sequences--a approximately 3,800-Myr-old banded iron formation from the Isua supracrustal belt, West Greenland, and a similar formation from the nearby Akilia island that is possibly older than 3,850 Myr. The carbon in the carbonaceous inclusions is isotopically light, indicative of biological activity; no known abiotic process can explain the data. Unless some unknown abiotic process exists which is able both to create such isotopically light carbon and then selectively incorporate it into apatite grains, our results provide evidence for the emergence of life on Earth by at least 3,800 Myr before present.

Deep penetration of sedimentary fluids in basement rocks from southern Norway: Evidence from hydrocarbon and brine inclusions in quartz veins

This paper presents evidence for fluid flow and fluid-rock interaction at upper crustal levels within the crystalline basement of southern Norway. In the high-grade Modum Complex postmetamorphic veins of quartz occur in association with albitisation of metagabbros and metasediments. Pressure-temperature conditions for the formation of these veins are in the range 250–300°C and ca. 1–2 kbar. Primary and pseudosecondary fluid inclusions in the quartz veins show two fluids: (1) hydrocarbon ± C0 2 inclusions and (2) aqueous inclusions with variable salinities. Dark carbonaceous solid inclusions are also present. The hydrocarbon inclusions are methane dominated (ca. 80–100 mot%), and the presence of higher, complex hydrocarbons is demonstrated. The aqueous inclusions in the metagabbro-hosted veins show more saline compositions than the metasediment-hosted veins. A salinity range of ca. 23-0 wt% NaCl eq is found. Some of the aqueous inclusions may contain NaHCO 3. Crush-leach analyses of inclusion fluids show Na-Ca-K-CI dominated compositions, with Na⪢Ca>K. Hydrocarbon-poor concentrates yield Br/Cl ratios close to seawater, while hydrocarbon-rich concentrates show higher values. The types and chemistry of the hydrocarbons in these veins indicate a biogenic origin of the hydrocarbon fluids. The inclusion fluids are interpreted as derived from an overlying sedimentary basin in late Precambrian or Permian times. The veining is interpreted as the deep expression of the percolation of basinal fluids into the metamorphic basement during crustal extension.

Laser damage testing of CVD-grown diamond windows

Laser-induced damage threshold (LIDT) measurements have been made on bulk polycrystalline (BP) CVD diamond plates using 0.532, 1.06 and 10.6 μm radiation and compared with measurements on natural type IIa diamond samples. Using 10.6 μm radiation, damage thresholds for BP CVD diamond have been measured as 5.6–12.7 MW mm −2 (29–66 J cm −2) using a 50 ns laser spike. These values compare with measurements in type IIa diamond of 12.5–18.5 MW mm −2 made in this study, and values of 3.5–40 MW mm −2 reported elsewhere. The LIDTs measured show a strong correlation with bulk absorption, which is significant at 0.532 μm, and with sample surface finish, but poor correlation with the carbonaceous inclusions found in the samples. Extrapolation from the d.c. dielectric breakdown threshold to the time domain of interest would suggest that, in both current CVD diamond and type IIa single-crystal natural diamond, the damage threshold is being substantially reduced by material or sample imperfections.

Accessory phases in aubrites: spectral properties and implications for asteroid 44 Nysa

The reflectance spectra of meteoritic metal, meteoritic troilite and the CR carbonaceous chondrite EET87770 have been measured in order to investigate the causes of the spectral differences between the surface of the E-class asteroid 44 Nysa and the opaque free fraction of the Happy Canyon aubrite meteorite. The data indicate that the spectral differences require the presence on Nysa's surface of a small amount of a spectrally red sloped material, of which metal and troilite are the most reasonable candidates, and a material possessing absorption bands near 0.9μm and 1.8μm. A material similar to the carbonaceous chondrite inclusions found in some aubrites can provide a match to the 0.9μm feature and perhaps the 1.8μm feature. The required abundances of these components depends on whether they are areally distributed or intimately mixed with an enstatite rich material. Based on the petrologic associations seen in aubrites and a series of simulated mineral mixtures, an intimate mixture of 69–92% enstatite and 1–11% metal + troilite and an areal component of 7–20% carbonaceous chondrite type material can provide a reasonable match to the 0.3–2.6μm spectrum of Nysa.

Carbonaceous chondrites—I. Characterization and significance of carbonaceous chondrite (CM) xenoliths in the Jodzie howardite

Mineralogical, chemical, textural, and isotopic studies of the abundant carbonaceous inclusions in the Jodzie howardite are consistent with CM characteristics. These CM xenoliths show regolith alteration on a level comparable to the Murray and Murchison meteorites but less than Nogoya, flow-oriented development of phyllosilicates and ‘poorly characterized phases’, and partial oxidation of sulfides. Temperature-programmed pyrolysis mass spectrometry (25°–1400°C) indicates that gas release patterns of volatiles and hydrocarbon components and percent contents of N(0.15), C(2.3) and S(2.4) are typical of CM meteorites. Release of significant amounts of SO 2 is attributed to the thermal breakdown of ‘poorly characterized phases’ (Fe-Ni-C-S-O) that formed during low temperature aqueous alteration in the CM parent body. Noble gas abundances are well within the reported range of CM meteorites. The fact that the Ne composition is typical for ‘solar’ values and the isotopic structure of Xe is ‘planetary’ argues that these gases were entrapped by different mechanisms. Cosmic ray exposure ages for the xenoliths ( 3He, 5 × 10 6; 21Ne, 6.7 × 10 6; 38Ar, 6.9 × 10 6 yr) agree with the reported exposure age for the eucritic host. Volatile abundances, presence of intact organic molecules, and phyllosilicates in the CM xenoliths preclude regolith temperatures in excess of 200°C after CM incorporation. Mixing of the host and xenoliths probably occurred during a low-velocity collision of main belt asteroids.

A carbonaceous inclusion from the Krymka LL-chondrite: noble gases and trace elements

A black inclusion from the Krymka LL3 chondrite was analyzed for 20 trace elements and five noble gases, by radiochemical neutron activation and mass spectrometry. The trace element pattern somewhat resembles that of C1 or C2 chondrites, but with several unique features. Elements of nebular condensation T ≳ 1000 K (U, Re, Os, Ir, Ni, Pd, Au, Sb and Ge) are essentially undepleted, as in C1 chondrites, but Re Ir is 1.49 × higher than the characteristic Cl value. Among elements condensing below 1000 K, Cs, Se, Te, and In are depleted to approximately C2 levels (~0.6 × C1), whereas Ag, Bi, Tl are enriched to ~ 1.6 × C1. Such enrichments are thought to be characteristic of late nebular condensates. The noble-gas pattern also is unique. Gas contents are higher than in C1s, by factors of 2.6 to 19 for Ne through Xe. The Ar 36 Xe 132 ratio of 500 is higher than mean values for C1s or C2s (109 or 89) and exceeds even the highest value seen in C3Os, 420, whereas the He 4 Ne 20 ratio of 62 is much lower than the values for C1s and C2s (200–370). The Xe 129 Xe 132 and Xe 136 Xe l32 ratios of 1.040 and 0.320 resemble those of C1 chondrites, and seem to imply typical proportions of radiogenic Xe 129 and ‘fissiogenic’ xenon. It appears that the inclusion represents a new primitive meteorite type, similar to C-chondrites, but probably a late condensate from a region of higher nebular pressure.

Foreign inclusions in stony meteorites—III. Rare gases and oxygen isotopes in a carbonaceous chondritic xenolith in the Plainview gas-rich chondrite

Measurements of oxygen and rare gas isotopes in a carbonaceous xenolithic inclusion in the Plainview H5 chondrite indicate that the xenolith and Plainview host are of two distinct meteorite types, and that no isotopic exchange has taken place between the two materials since their juxtaposition. The oxygen isotope analysis of the xenolith yields δ- 18O value of 6.5 ± 0.1 % relative to SMOW, a value similar to that of carbonaceous chondrites (C2). Rare gas contents of the xenolith are also similar to those of carbonaceous chondrites. The radiation ages of the xenolith ( 2.9 ± 0.4 Myr ) and the host ( 2.8 ± 0.4 Myr ) are identical. Analyses of the rare gases in a sample of the host material adjacent to the xenolith show that Plainview is gas-rich, i.e., it contains large amounts (52,300 ± 10 −8 cm 3 STP/g 4He) of solar-type trapped gases. We speculate that carbonaceous chondritic material may be more prevalent in the asteroid belt than previously suspected.

Carbonaceous inclusions, sulfides, and 'fossil gas bubbles' of presumably biologic origin associated with rafted erratics in Huronian (Precambrian) glacial-lake argillites

Carbonaceous inclusions, sulfides, and 'fossil gas bubbles' of presumably biologic origin associated with rafted erratics in Huronian (Precambrian) glacial-lake argillites

Zur genese des kohligen materials im meteoriten von Tieschitz

A carbonaceous inclusion in a chondrule and a carbonaceous fragment from the Tieschitz meteorite are described. Electronmicroprobe analyses of that material and of the carbonaceous matrix are compared with analyses of carbonaceous chondrites. This comparison shows that the carbonaceous material from the Tieschitz meteorite probably is a residual material of the chondrule-forming process. Therefore it is depleted mostly in magnesium and iron if compared with the carbonaceous chondrites. There is also a high probability that the Tieschitz carbonaceous material had suffered some alterations after agglomeration which are thought to be caused by a hydrothermal or pneumatolytic activity on the Tieschitz parent body.

Metamorphic Rocks of the Sea Floor between Start Point and Dodman Point, S.W. England

As part of the programme of study of the geology of the western approaches initiated at Bristol by Prof. W. F. Whittard (Whittard, 1962) information has been accumulated concerning the distribution and nature of the metamorphic rocks exposed in a series of inliers between Start Point in the east and Dodman Point in the west.Early dredgings in this area were described by Worth (1908). Six core samples and two dredgings of metamorphic rocks are listed by Hill & King (1953). Mica schist in situ is recorded by Holme (1953). Various cruises in R.V. ‘Sarsia’ from 1957 onwards have yielded seventeen cores and further dredged samples. Additional material, collected from the exposed parts of the Eddystone reefs or obtained by diving at critical localities, has become available through the kindness of members of the staff of the Marine Biological Laboratory at Plymouth.Sixteen cores and eight dredged samples serve to demarcate an area of schistose rocks, extending some 24 miles from east to west and 7 miles in maximum width from north to south, off the southernmost part of Devon (Fig. 1). These rocks, with an exception to be noted, compare closely with those exposed on land, between Bolt Tail and Start Point, south of a well defined east-west boundary (Ussher, 1904; Tilley, 1923). There are examples of quartz-muscovite-chlorite schists precisely like the Start Mica-schists and Bolt Mica-schists described by Tilley. Albite porphyroblasts, in a rock dredged near East Rutts (Fig. I, 1262) which is transitional to Tilley's ‘schists of composite origin’, show well the contorted swarms of carbonaceous inclusions which he describes (1923, p. 180).

A petrofabric analysis of Carrara marble

It is desirable in experiments on rock deformation to use rocks with a simple, homogeneous and isotropic structure. It was thought that Carrara marble would be a suitable rock for such experiments, and this paper describes the results of a fabric analysis of the rock. An attempt is made at giving a dynamic interpretation of the rather complex fabric. According to this interpretation the rock has passed through at least three tectonic phases although the principal stress directions throughout two of these phases appear to have remained fairly constant with respect to the later developed plane of carbonaceous inclusions which can be seen in hand specimens. There is only a weak preferred orientation of crystal axes, and in this sense the rock may therefore be regarded as reasonably isotropic.