Phases Of Origin Research Articles

U [sbnd]Pb dating of Fe-rich phases using a sequential leaching method

A sequential leaching method was developed for U Pb dating of Fe-rich phases which uses a series of successively stronger acids. The method was applied to date Fe-rich phases of magmatic origin in the Kinsman Quartz Monzonite, New Hampshire, USA, and of sedimentary origin in the Dales Gorge Member of the Brockman Iron Formation, Hamersley basin, Australia. Using the composition of major element released by the acid leaching and combining it with X-ray and SEM analyses of the residues we were able to identify the relatively pure phases released and use these samples for dating. Magnetite separates from the Kinsman Quartz Monzonite yielded U Pb age of 372 ± 34 Ma, which is consistent with Sm Nd and a Rb Sr isochron ages determined in previous studies. Leached whole-rock samples of the Brockman Iron Formation yielded a 207Pb 206Pb age of 2213 ± 250 Ma which agrees with previously determined Pb Pb, Sm Nd, and Rb Sr isochron ages. This age is interpreted as the time of redistribution of U and Pb associated with the Fe-rich phases during regional metamorphism. While the potential of the sequential leaching method is demonstrated, more work is needed in order to improve the precision of the data. This requires further investigation of the nature of the pure phases.

Occurrence, abundance and origin of minerals in coals and coal ashes

The mineralogy of coal and coal ash samples from a wide variety of deposits worldwide has been studied by X-ray diffractometry, light microscopy, SEM, TEM, and DTA-TGA methods. The common major minerals identified in the crystalline matter of coals are quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasionally dolomite, ankerite, siderite, Fe oxyhydroxides and sulphates. A number of minor and especially accessory minerals are also present. The modes of occurrence and some genetic peculiarities of the minerals found are described and summarized. Minerals and phases of probable detrital origin include mainly silicates, volcanic glass, oxyhydroxides and phosphates. Authigenic minerals of syngenetic origin may be sulphides, clay minerals, carbonates and rarely sulphates and phosphates. Epigenetic minerals, formed by the infiltration of low-temperature hydrothermal solutions, may include sulphides, carbonates, sulphates, clay minerals, quartz, chlorides, and probably alkaline-earth hydroxides and zeolites. The alteration products of detrital and authigenic minerals may be Fe and Al oxyhydroxides, sulphates, kaolinite, illite, chlorite, muscovite, zeolites and calcite. The behaviour of these minerals and phases during low- and high-temperature ashing is also discussed.

Effect of eutectic phases on the fracture behavior of high-strength castable aluminum alloys

High-strength castable aluminum alloys have a lower plasticity and fracture toughness than deformable alloys. This is associated for the most part with the morphology and the nature of the distribution of phases of eutectic origin, which are always present in their structure. The factors affecting the fracture of high-strength castable aluminum alloys are considered in the present work.

Petrology and geochemistry of the Passa Quatro alkaline complex, southeastern Brazil

The Passa Quatro alkaline complex is formed by strongly undersaturated, felsic intrusive and subvolcanic rocks (nepheline-syenites and phonolites). The abundance and fractionation of alkali feldspar, together with lesser amounts of femic phases, generates a suite which tends, as a whole, to become peralkaline and nepheline-enriched. Variation diagrams indicate, however, strong scatter of the data, reflecting non-homogeneous distribution of major and accessory phases and, probably, slightly different liquid lines of descent. Judging from the absence of restitic phases of crustal origin and other petrologic features, these rocks are probably products of extreme fractionation from basanitic magmas. On the basis of potassic affinity and initial 87Sr/ 86Sr isotopic ratios (0.70505), these rocks closely resemble other alkaline complexes of the Rio de Janeiro littoral belt, confirming provincialism in the Meso-Cenozoic alkaline province of eastern continental Brazil.

An electroluminescence study of stabilization reactions in the oxygen-evolving complex of Photosystem II

The stabilization of the photosynthetic charge separation in Photosystem II by secondary reactions was studied using chlorophyll luminescence induced by electric field pulses in a suspension of preilluminated osmotically swollen chloroplasts. This ‘electroluminescence’ was measured as a function of the delay time between illumination and field pulse, and as a function of the number of preilluminating flashes. The result is a survey of, in principle, all stabilization and deactivation processes beyond the state Z + Q − A , which is formed within the approx. 20 μs time resolution of the method. Most of these could be identified with known secondary electron transfer reactions. A 20-fold stabilization with a half-time of 330 μs is attributed to Q − A reoxidation. No further stabilization at the acceptor side seemed to occur and no flash number dependence was detected, although a normal Q B /Q − B oscillation was found in ultraviolet absorbance. With regard to the donor side, the data are consistent with the known S-state-dependent Z + reduction times and indicate values of 9, 5 and 65 for the equilibrium constants associated with this reaction on the transitions S 1 →S 2 , S 2 →S 3 and S 3 →S 0 (O 2 ) respectively. Z + reduction was found to be electrogenic and exposed to about 5% of the membrane potential. An 0.1 s phase in S 0 is attributed to oxygen release. S 2 and S 3 are further stabilized in two phases of unknown origin with half-times of 15 ms and 0.4 s, followed by a final 20 s phase attributed to deactivation. In S 1 , Z + reduction was probably hidden in an unresolved fast phase present on all transitions, but in addition a 350 μs phase was found, which might be related to proton release. In nearly 20% of the Photosystem II reaction centers electron transfer beyond Q − A was inhibited. In these centers Z + reduction appeared to take about 1 ms and charge recombination followed in phases of about 8, 80 and 800 ms half-time.

Evidence of mantle metasomatism and heterogeneity from peridotite inclusions of northeastern Brazil and Paraguay

Textural-petrographic features, major and trace elements and mineral chemistry are reported for spinel-peridotite xenoliths from northeastern Brazil (NE-suite) and Paraguay (PY-suite). Variation trends defined by bulk rock and mineral chemistry are consistent with the effects of variable degree of high-pressure melting for both suites. The PY-suite strongly differs from the NE-suite by its very high contents of incompatible elements. This different whole-rock chemistry is related to the presence of glassy-microcrystalline blebs which are interpreted as remains of pre-existing hydrous phases of metasomatic origin. The difference between the two suites is also recorded in the chemistry of pyroxenes and spinels, which develop along different variation patterns. Although the suites partially overlap in their ranges of mg opx (Mg/(Fe 2+ + Fe 3+) ratio in orthopyroxenes), the PY-suite is, on the average, more mg opx rich (residual) than the NE-suite. Within the PY-suite a rough positive correlation exists between degree of residuality and degree of metasomatic effects. The sharp differences between the NE-suite and the PY-suite imply mantle heterogeneity on regional scale, whereas the variability within each suite is essentially related to different degrees of melting and/or metasomatism and imply mantle heterogeneity on local scale.

Compartmentation and Mobility of Flamprop and its Metabolites in Leaf Slices of Oats

Leaf slices of oats were loaded with 14C-flamprop ((1)–2(N-Benzoyl-3-chloro-4-fluoranilino) propionic acid) for 24 h. At this time, extensive metabolism to polar conjugates had occurred. Compartmental analysis was carried out and the composition of radioactivity in each of the efflux compartments was determined. Efflux of total radioactivity was described by three kinetically distinct transport phases of cellular origin. Flamprop itself was present in three pools, two of which were readily removed by washing the slices in buffer. The third pool was only released by extraction with an organic solvent. The efflux of flamprop conjugates followed a completely different pattern. They were only very slowly removed by the washing procedure, demonstrating that conjugation has a marked effect on mobility. One group of conjugates could be almost completely washed from the tissue following disruption of cellular membranes by a freeze/thaw procedure, indicating that immobility of this group was due to partition behind an impermeable membrane. The other group of conjugates could be only partially removed by this procedure, the remainder being released by extraction with an organic solvent.

The constitution of the chromium-niobium-silicon system

The constitutional diagram of the alloy system Cr-Nb-Si has been investigated for a 1000°C section, as well as some of the properties of the alloys. X-ray diffraction analysis has been used upon argon arc melted alloys. Some modifications are proposed to the known Cr-Si binary system. (The Nb-Si side had already been dealt with in a previous paper, the Cr-Nb side in a concurrent one.) The ternary diagram presented is highly complex, involving, in addition to eleven phases of binary origin, five new ternary compounds; three of the latter possess considerable homogeneity ranges: one is a new Laves phase, another a βNb 5Si 3 isomorph, stabilised to lower temperatures through Cr addition. Melting points and oxidation resistance of the alloys are given, and the latter property, though limited to a 1000°C, 1-h survey, indicates promising areas for further study.