Effect of confining pressure on the diffusion of HTO, 36Cl− and 125I− in a layered argillaceous rock (Opalinus Clay): diffusion perpendicular to the fabric

The through- and out-diffusion of HTO, ³⁶Cl⁻ and ¹²⁵I⁻ in Opalinus Clay, an argillaceous rock from the northern part of Switzerland, was studied under different confining pressures between 4 and 15 MPa. The direction of diffusion and the confining pressure were perpendicular to the bedding. Confining pressure had only a small effect on diffusion. An increase in pressure from 4 to 15 MPa resulted in a decrease of the effective diffusion coefficient of ∼20%. Diffusion accessible porosities were not measurably affected. The values of the effective diffusion coefficients, D_e, ranged between (5.6±0.4)×10⁻¹² and (6.7±0.4)×10⁻¹² m² s⁻¹ for HTO, (7.1±0.5)×10⁻¹³ and (9.1±0.6)×10⁻¹³ m² s⁻¹ for ³⁶Cl⁻ and (4.5±0.3)×10⁻¹³ and (6.6±0.4)×10⁻¹³ m² s⁻¹ for ¹²⁵I⁻. The rock capacity factors, α, measured were circa 0.14 for HTO, 0.040 for ³⁶Cl⁻ and 0.080 for ¹²⁵I⁻. Because of anion exclusion effects, anions diffuse slower and exhibit smaller diffusion accessible porosities than the uncharged HTO. Unlike ³⁶Cl⁻, ¹²⁵I⁻ sorbs weakly on Opalinus Clay resulting in a larger rock capacity factor. The sorption coefficient, K_d, for ¹²⁵I⁻ is of the order of 1–2×10⁻⁵ m³ kg⁻¹. The effective diffusion coefficient for HTO is in good agreement with values measured in other sedimentary rocks and can be related to the porosity using Archie's Law with exponent m=2.5.     

Noble gas investigations of lunar rocks 10017 and 10071

The noble gases He, Ne, Ar, Kr and Xe and also K and Ba were measured in the Apollo 11 igneous rocks 10017 and 10071, and in an ilmenite and two feldspar concentrates separated from rock 10071. Whole rock K/Ar ages of rocks 10017 and 10071 are (2350 ± 60) × 10⁶ yr and (2880 ± 60) × 10⁶ yr, respectively. The two feldspar concentrates of rock 10071 have distinctly higher ages: (3260 ± 60) × 10⁶ yr and (3350 ± 70) × 10⁶ yr. These ages are still 10 per cent lower than the Rb/Sr age obtained by Papanastassiouet al. (1970) and some Ar⁴⁰ diffusion loss must have occurred even in the relatively coarse-grained feldspar.The relative abundance patterns of spallation Ne, Ar, Kr and Xe are in agreement with the ratios predicted from meteoritic production rates. However, diffusion loss of spallation He³ is evident in the whole rock samples, and even more in the feldspar concentrates. The ilmenite shows little or no diffusion loss. The isotopic composition of spallation Kr and Xe is similar to the one observed in meteorites. Small, systematic differences in the spallation Kr spectra of rocks 10017 and 10071 are due to variations in the irradiation hardness (shielding). The Kr spallation spectra in the mineral concentrates are different from the whole rock spectra and also show individual variations, reflecting the differences in target element composition. The relative abundance of cosmic ray produced Xe¹³¹ differs by nearly 50 per cent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the Xe¹³¹ yield variability is discussed.Kr⁸¹ was measured in all the samples investigated. The Kr⁸¹/Kr exposure ages of rocks 10017 and 10071 are (480 ± 25) × 10⁶ yr and (350 ± 15) × 10⁶ yr, respectively. Exposure ages derived from spallation Ne²¹, Ar³⁸, Kr⁸³ and Xe¹²⁶ are essentially in agreement with the Kr⁸¹/Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of our sample to solar flare particles.     

大兴安岭北部甲乌拉铅锌银矿床Rb-Sr同位素测年及其地质意义

甲乌拉铅锌银矿床位于内蒙古自治区满洲里市南西150km。矿床产于中蒙古-额尔古纳兴凯造山带南东缘之得尔布干断裂北西侧。本文在甲乌拉矿床选取7件闪锌矿和6件黄铁矿样品开展了Rb-Sr定年。获得闪锌矿的Rb-Sr等时线年龄为143.0±2.0Ma(MSWD=3.2),锶同位素初始值I Sr=0.71265;黄铁矿的Rb-Sr等时线年龄为142.0±3.0Ma(MSWD=5.7),锶同位素初始值ISr=0.71267;闪锌矿与黄铁矿的Rb-Sr等时线年龄为142.7±1.3Ma(MSWD=3.8),锶同位素初始值ISr=0.71266。上述定年结果表明,甲乌拉矿床形成于早白垩世初期。甲乌拉矿床硫化物的Rb和Sr含量分别介于0.1034×10-6～7.367×10-6和1.301×10-6～7.148×10-6之间,Sr同位素初始比值(87Sr/86Sr)i介于0.71238～0.71277之间,平均值为0.71264,暗示甲乌拉矿床的成矿物质主要来源于地壳。甲乌拉矿床形成于蒙古-鄂霍茨克造山过程的后碰撞阶段。     

Extinct I129 in C3 chondrites

Eight C3 chondrites were examined by the I¹²⁹Xe¹²⁹ dating method, to see whether their IXe “ages” (better, initial $\text{I}{}^{129}\text{I}{}^{127}$ratios ≡ R₀) correlate with any other properties. The R₀'s range from 1.60 × 10^?4 to 1.09 × 10^?4, corresponding to IXe ages from 2.0 Myr before to 6.7 Myr after Murchison magnetite. Three C3O's (Lancé, Felix, Ornans) have essentially indistinguishable R₀'s of (1.41 ± 0.13) to (1.17 ± 0.10) × 10^?4; the fourth C3O, Warrenton, is undatable owing to homogenization of radiogenic and trapped Xe.Four C3V's show a distinct spread: Vigarano and Grosnaja are highest [R₀ = (1.60 ± 0.07) and (1.57 ± 0.14) × 10^?4], Mokoia is intermediate, and Kaba is lowest [R₀ = (1.38 ± 0.06) and (1.09 ± 0.10) × 10^?4]. Literature values for Allende place it near Kaba. These R₀'s correlate inversely with 4 other properties: I-, Br-, and Cd-content, and olivine composition, both percent mean deviation (PMD) and proportion of iron-poor olivine grains (≤2% fayalite).It is difficult to accept the ～9 Myr spread in R₀ as a true age, reflecting either nebular or parent-body processes. This time span is more than an order of magnitude longer than the lifetime of the solar nebula inferred from astronomical evidence. Nor does the degree of thermal metamorphism, which is slight for C3's anyway, correlate with R₀. A more plausible interpretation is that the variations in R₀ reflect mainly isotopic heterogeneity of iodine. The simplest model that accounts for the correlations with R₀ involves mixing of two iodine components in the solar nebula, associated with gas and grains, respectively. The second, of lower $\text{I}{}^{129}\text{I}{}^{127}$ ratio, predominated at later times and thus became enriched in late-formed meteorites, along with other volatiles such as Cd and Br. The low Fe content and large PMD of olivine may reflect either less metamorphism owing to shallow location in the parent body, or greater reduction of Fe²⁺ during chondrule formation.     

Sulfur isotope studies in early Archaean sediments from Isua,West Greenland: Implications for the antiquity of bacterial sulfate reduction

The sulfur contents and sulfur isotope ratios (δ³⁴S) have been measured for samples collected from the Isua area of West Greenland in an effort to place narrower limits on the time of the rise of sulfate respirers during the Precambrian.The δ³⁴S values of the Isua sediments (3.7 × 10⁹ yr old) including the various facies of the banded iron-formations have their mean values close to zero %. (CDT) (±0.5%.) with a standard deviation of less than 1%.. This comes extremely close to the respective means yielded by the presumed tuffaceous amphibolites (+ 0.3 ± 0.9%.) and by the somewhat younger, between 3.1 and 3.7 ± 10⁹ yr, basaltic Ameralik dykes of the region (+ 0.6 ± 1.1%.).In view of the regional distribution of the Isua banded iron-formation sediments, the variety of environmental conditions under which the various facies were deposited and the complete absence of isotopic evidence for sulfate reducers, in contrast to the banded iron-formations of the middle Archaean (δ³⁴Svariesfrom ?20 to +20%.), it seems most unlikely that evidence for 'sulfate reducers' existed or will be found in other sediments of Isua age.The very small spread in δ³⁴S values for the Isua sediments is interpreted as due to minor fractionation during the passage of endogenic sulfur phases to their present sites of emplacement within the sedimentary succession.     

The effects of undercooling and deformation rates on the crystallization kinetics of Stromboli and Etna basalts

We have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from Stromboli (pumice from the March 15, 2007 paroxysmal eruption) and Etna (1992 lava flow). Isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate (T = 1,157–1,187 °C and $ \dot{\gamma }_{i} $ γ · i  = 4.26 s^?1 for Stromboli; T = 1,131–1,182 °C and $ \dot{\gamma }_{i} $ γ · i  = 0.53 s^?1 for Etna). Melt viscosity increased due to the decrease in temperature and the increase in crystal content. The mineralogical assemblage comprises Sp + Plg (dominant) ± Cpx with an overall crystal fraction (?) between 0.06 and 0.27, increasing with undercooling and flow conditions. Both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process. Plagioclase nucleation incubation time strongly decreases with increasing ΔT and flow, while slow diffusion-limited growth characterizes low ΔT—low deformation rate experiments. Both Stromboli (high strain rate) and Etna (low strain rate) plagioclase growth rates (G) display relative small variations with Stromboli showing higher values (4.8 ± 1.9 × 10^?9 m s^?1) compared to Etna (2.1 ± 1.6 × 10^?9 m s^?1). Plagioclase average nucleation rates J continuously increase with undercooling from 1.4 × 10⁶ to 6.7 × 10⁶ m^?3 s^?1 for Stromboli and from 3.6 × 10⁴ to 4.0 × 10⁶ m^?3 s^?1 for Etna. The extremely low value of 3.6 × 10⁴ m^?3 s^?1 recorded at the lowest undercooling experiment for Etna (ΔT = 20 °C) indicates that the crystallization process is growth-dominated and that possible effects of textural coarsening occur. G values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions. Stirring of the melt, simulating magma flow or convective conditions, facilitates nucleation and growth of crystals via mechanical transportation of matter, resulting in the higher J and G observed. Any modeling pertaining to magma dynamics in the conduit (e.g., ascent rate) and lava flow emplacement (e.g., flow rate, pāhoehoe–‘a‘ā transition) should therefore take the effects of dynamic crystallization into account.     

Etude par la méthode des traces nucléaires du sol de la Mer de la Fécondité (Luna 16)

Minimum track-density values have been determined in 278 feldspars (83–500 μ dia.) taken from five layers of the Luna 16 core sample. Feldspars in basaltic fragments appear to have been much less shocked than single feldspar crystals in the fines, of which 40 per cent were lost during the chemical etching. For the five layers the percentage of track-rich (solar flare irradiated) fragments, with densities > 10⁸/cm², is 98 per cent. However, for 60 per cent of the crystals (anorthite for the most) only lower limits of track-density were obtained. Single anorthites appear more highly irradiated than the feldspars in basaltic fragments, the former having a median track-density value of about 1 × 10⁹/cm² and the latter only ~2 × 10⁸/cm².Assuming an age for the basalts of Mare Fecunditatis of ~3.45 × 10⁹ yr (papanastassiou and Wasserburg, 1972), the track-density levels observed in the basaltic fragments can well be explained according to the model of Comstocket al. (1971). On the other hand, in order to account for the very high track densities observed in the Luna 16 anorthites and those reported for the Apollo 15 long drill stem by crozazet al. (1972) the model would require a rate of solar flare activity much higher during the period 4.6-3.5 × 10⁹yr than that observed today.     

Tracing quartz through the environment

Quartz, SiO₂, a pure mineral with tight crystal structure, is widespread in rocks and soil. Cosmic rays produce¹⁰Be (t _1/2=1·5×10⁶, yr) and²⁶Al (t _1/2=7·05×10⁵ yr) in quartz exposed at or near the earth’s surface. The use of accelerator mass spectrometry permits measurement of these nuclides in samples exposed at sea level for typical periods.In situ production makes interpretation relatively straightforward. Potential applications include age determination, measurement of erosion and deposition rates, and use as a tracer for continental weathering processes.     

Precision W BV R photoelectric photometry of the eclipsing system RR Lyncis

We carried out accurate ( $\sigma _{obs} \approx 0\mathop .\limits^m 003$ ) W BV R photoelectric photometry of RR Lyn and obtained light curves of this eclipsing system. Our analysis of the light curves using an iterative differential-correction method yields a self-consistent system of geometrical and physical characteristics of the two components of the system and their evolutionary states. The system's age is estimated to be t=(1.08±0.15)×10⁹ yr. Observations in all filters are fitted satisfactorily by the same geometry (r _1,2, i, e, and ω). An analysisof blanketing effects in the W, B, V, and R bands indicates that the atmospheric chemical compositions of both components of the system are peculiar: the primary shows an excess ([Fe/H]_I=0.31±0.08) and the secondary a deficit ([Fe/H]_II=?0.24±0.06) of heavy elements. This is in qualitative and quantitative agreement with the results of an earlier spectroscopic study of RR Lyn by Lyubimkov and Rachkovskaya (1995). The derived physical characteristics of RR Lyn provide evidence that the metallicity effects are probably restricted to the stellar surface layers, while their interiors have normal chemical abundances.     

Distribution of gold and rhenium between nickel-iron and silicate melts: implications for the abundance of siderophile elements on the Earth and Moon

The distribution equilibrium of Au and Re between nickel-iron and basaltic melts was studied at 1400–1600°C, using radioactive tracers. Metal/silicate distribution coefficients were 1–3 orders of magnitude higher than earlier estimates, as follows. Mauna Loa basalt—Fe₁₀Ni₉₀: D_Au = 3.3 × 10⁴, D_Re = (2.4?89) × 10⁴. Gorda Ridge basalt—Fe₁₀Ni₉₀: D_Au = (18?75) × 10⁴. Synthetic lunar basalt—Fe₇₀ Ni₃₀: D_Au≥ 2 × 10⁴, D_Re ≥ 2 × 10³. The experimental ΔG₁₈₀₀^° for the distribution of Au between nickel-iron and Mauna Loa basalt is ?40 kcal/mole, compared to a calculated value of about ?110 kcal/mole for a reaction involving simple Au³⁺ ions. Presumably the difference represents stabilization of Au(III) by complex formation with ligands such as Cl^?, H₂O, etc.Gold abundances in lunar basalts are roughly consistent with the measured D_Au, but those in terrestrial basalts are two orders of magnitude too high. This discrepancy may reflect complexing by volatiles in the Earth's upper lithosphere, as well as oxidative destruction of metal in the final stages of accretion. In the absence of a metal phase, siderophile trace elements would remain trapped in the upper mantle and crust.     

南秦岭勉略带铧厂沟火山岩锆石U-Pb年代学及地球化学研究

陕西省西南部铧厂沟火山岩以英安岩为主(～ 90vol％),夹玄武岩构造透镜体(～ 10vol％).玄武岩SiO2含量为43.6％ ～ 54.7％,具有低K、Ti,高Na、Mg的特征;稀土总量为24×10-6 ～29×10-6,中稀土轻微富集,Eu、Sr轻微正异常;具有正Rb、Ba异常及负Nb、Zr异常,LaN/YbN值为1.81 ～2.87,Th/Yb值为0.19 ～0.23,Th/Nb值为0.11 ～0.20,Nb/La值为0.26～0.70,Hf/Th值为0.50 ～ 0.67,显示亚碱性弧玄武岩的特征.英安岩SiO2含量为59.5％～ 72.3％,稀土总量较低(116×10-6～187 × 10-6),为右倾式配分模式,Eu负异常,富集大离子亲石元素(如Rb、Ba、Th、K等),亏损高场强元素(如Nb、P、Ti、Ta等),显示弧火山岩地球化学特征.获得玄武岩的锆石SHRIMP U-Pb年龄为801.7±4.7Ma (MSWD=1.18;n=12),英安岩的锆石LA-ICP-MS U-Pb年龄为802.1±5.3Ma (MSWD=1.02;n=19),二者在误差范.内一致.因此,铧厂沟火山岩是一套火山弧环境的亚碱性玄武质-英安质火山岩组合,表明新元古代曾有大洋板块向南俯冲到扬子古板块北缘之下;这套火山岩裹挟于泥盆系沉积地层中,与泥盆系地层一起,共同组成了一套由晚古生代-三叠纪勉略洋闭合所致的构造混杂岩带.     

GPS rotation and strain rates in the Baikal–Mongolia region

Current deformation in Pribaikalia, Western and Central Mongolia, and Tuva has been studied from measured horizontal GPS velocities and respective computed strain and rotation rates using 1994–2007 data of the Baikal–Mongolian GPS triangulation network.The GPS velocity field shows two main trends: an NE trend within Jonggaria, the Mongolian Altay, and the Great Lakes Valley and an SE trend in the Hangayn and eastern Gobi Altay mountains, and in the Transbaikalian block of the Amur plate. The velocity magnitudes and vectors are consistent with an SE motion of the Amur plate at a rate of ～2 mm/year.The derived strain pattern includes domains of crustal contraction and extension recognized from the magnitudes of relative strains. Shortening predominates in the Gobi and Mongolian Altay and in the Khamar-Daban Range, where it is at ?₂ = (19.2 ± 6.0)×10^?9 yr^?1 being directed northeastward. Extension domains exist in the Baikal rift and in the Busiyngol–West Hangayn area, where the crust is stretching along NW axes at ?₁ = (22.2 ± 3.1) × 10^–9 yr^–1. The eastern Hangayn dome and the Gobi peneplain on its eastern border show low and unstable strain rates. In central and northern Mongolia (Orhon–Selenge basin), shortening and extension are at similar rates: ?₂ = (15.4 ± 5.4)×10^?9 yr^?1 and ?₁ = (18.1 ± 3.1)×10^?9 yr^?1. The strain pattern changes notably in the area of the Mogod earthquake of 1967.Most of rotation throughout Central Asia is clockwise at a low rate of about Ω = 6×10^?9 deg·yr^?1. High rates of clockwise rotation are observed in the Hangayn domain (18.1 ± 5.2)×10^?9 deg·yr^?1, in the Gobi Altay (10.4 ± 7.5)×10^?9 deg·yr^?1, and in the Orhon–Selenge domain (11.9 ± 5.2)×10^?9 deg·yr^?1. Counterclockwise rotation is restricted to several domains. One is in western Tuva and northwestern Great Lakes Valley of Mongolia (Ω = 3.7×10^?9 deg·yr^?1). Two more counterclockwise rotation regions occur on both flanks of the Baikal rift: along the craton edge and in basins of Transbaikalia on the rift eastern border, where rotation rates are as high as (13.0 ± 3.9)×10^?9 deg·yr^?1, while rotation within the Baikal basin does not exceed the measurement error. Another such domain extends from the eastern Hövsgöl area to the Hangayn northern foothills, with the counterclockwise rotation at a highest rate of (16.3 ± 2.8)×10^?9 deg·yr^?1.     

Isotopic fractionation between coexisting organic carbon—carbonate pairs in Precambrian sediments

δ¹³C_org and δ¹³C_carb values of 58 coexisting organic carbon-carbonate pairs covering the whole Precambrian have yielded means of ?24.7 ± 6.0%. [PDB] and +0.9 ± 2.7%. [PDB], respectively. Accordingly, isotopic fractionation between inorganic and organic carbon in Precambrian sediments is about the same as in geologically younger rocks (Δδ ? 25%.), a slight increase displayed by the Early Precambrian pairs (Δδ ? 28%.) being probably biassed by an over-representation in this age group of samples from one single locality (nevertheless, this value still lies within the range permitted for a possible deviation). It is reasonable to assume, therefore, that the overall isotope fractionation factor governing biological fixation of inorganic carbon has been virtually constant since some 3.3 × 10⁹ yr ago.     

The age of the Stillwater complex—a comparison of U-Pb zircon and Sm-Nd isochron systematics

A zircon U-Pb age of 2713 ± 3 Myr confirms the less precise age of about 2710 Myr (corrected for new decay constants of Jaffeyet al., 1971) obtained from the same sample of zircon from the Stillwater complex chill zone (Nunes and Tilton, 1971). This age compares with Sm-Nd mineral and whole-rock isochron ages of 2701 ± 8 Myr (Depaolo and Wasserburg, 1979); or 2706 ± 8 Myr if the Lugmairet al. (1975) normalization procedure is used. The agreement of these ages to within about 0.4% indicates that the λ₁₄₇ = 0.00654 × 10^?9yr^?1 value is less than 0.8% too large relative to the U decay constants determined by Jaffeyet al. (1971) and enables more correct geological syntheses to be made when working out detailed absolute age stratigraphies using precise data from both systems.     

A Laboratory Study on Estimation of Shear Strength and Compaction Properties of Overburden Dump Material in Indian Coal Mines

The Transcaucasian intermountain area is part of the Caucasus segment of the Alpine-Mediterranean mountain belt. The continental intraplate basalts of the study area range in age from 6.10 ± 0.20 to 6.40 ± 0.20 Ma. The basalt erupted from monogenetic volcanoes are formed by lava flows and their pyroclastic equivalents. They are generally characterized by low volumes, are predominantly subalkalic with minor alkaline composition. The ultramafic xenoliths have not been identified in the basalts. The basalts may be subdivided into porphyritic and oligophyric groups. Fractional crystallization plays an important role in the petrogenesis of basalts. Almost all the studied samples showed different degrees of fractionation of olivine ± plagioclase ± clinopyroxene. No significant contamination of basalts with upper continental crustal material was confirmed by Rb/Sr and Rb/Ba ratios or by Sr, Nd isotopic and geochemical composition (⁸⁷Sr/ ⁸⁶Sr = 0.703683-0.704531±2; ¹⁴³Nd/¹⁴⁴Nd = 0.512788-0.512848 ±10; ¹⁴⁷Sm/¹⁴⁴Nd = 0.1036-0.1144 ±2-3). The studied basalts display, compared to heavy rare earth elements (HREE), highly fractionated light rare earth elements (LREE) with La/Yb=9.25-24.00. This makes them similar to ocean island basalts (OIB), which is also evidenced by Ce/Pb, La/Nb, Zr/Nb, Zr/Y ratios. The Dy/Yb-La/Yb and Yb-La/Yb and ⁸⁷Sr/⁸⁶Sr-¹⁴³Nd/¹⁴⁴Nd ratios indicating a “mixed” evolution of basalt-forming magmas. The basalt feeding magma chambers of the Transcaucasian intermountain area seem to be formed from a mixture of partial melting of Normal-MORB (Mid-Ocean Ridge Basalt) type upper mantle (garnet and spinel lherzolite) and EMII type components with strong ocean island basalts (OIB)-like signature.     

In situ observations of bubble growth in basaltic,andesitic and rhyodacitic melts

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1,100 to 1,240 °C and 0.1 MPa (1 bar), obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<60 MPa in basalt and andesite, 200 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate (G _R) ranges from 3.4 × 10^?6 to 5.2 × 10^?7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density (N _B) at nucleation ranges from 7.9 × 10⁴ mm^?3 to 1.8 × 10⁵ mm^?3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble size distribution (BSD) through time, the BSDs of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSDs may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important trigger for volatile release and explosive eruptions.     

Infrared photometry of the unique object FG Sge in 1985–2001

Our analysis of many years of infrared photometry of the unique object FG Sge indicates that the dust envelope formed around the supergiant in August 1992 is spherically symmetrical and contains compact, dense dust clouds. The emission from the spherically symmetrical dust envelope is consistent with the observed radiation from the star at 3.5–5 µm, and the presence of the dust clouds can explain the radiation observed at 1.25–2.2 µm. The mean integrated flux from the dust envelope in 1992–2001 was ～(1.0±0.2)×10^?8 erg s^?1cm^?2. The variations of its optical depth in 1992–2001 were within 0.5–1.0. The maximum density of the dust envelope was recorded in the second half of 1993 and corresponded to mean optical depths as high as unity. Several times in the interval from 1992 to 2001, the dusty material of the envelope partially dissipated and was then replenished. For example, the optical depth of the dust cloud at λ=1.25 µm during the last brigthness minimum in the J band was τ_1.25≈4.3, which is much higher than the optical depth of the dust envelope of FG Sge. During maxima of the J brightness, the mean spectral energy distribution at 0.36–5 µm can be represented as a combination of radiation from a G0 supergiant that is attenuated by a dust envelope with a mean optical depth of 0.65±0.15 and emission from the spherically symmetrical dust envelope itself, with the temperature of the graphite grains being 750±150 K. At minima of the J brightness, only radiation from the dust envelope is observed at 1.65–5 µm, with the radiation from the supergiant barely detectable at 1.25 µm. As a result, the integrated flux during J minima is almost half that during J maxima. The mean mass of the spherically symmetrical dust envelope of FG Sge in 1992–2001 was (3 ± 1) × 10^?7M_⊙. This envelope’s mass varied by nearly a factor of two during 1992–2001, in the range (2 – 4) × 10^?7M_⊙. In Autumn 1992, the mass-loss rate from the supergiant exceeded 2 × 10^?7M_⊙/yr. The average rate at which matter was injected into the envelope during 1993–2001 was 10^?8M_⊙/yr. The mean rate of dissipation of the dust envelope was about 1 × 10^?8M_⊙/yr. During 1992–2001, the supergiant lost about 8.7 × 10^?7M_⊙. The parameters of the dust envelope were relatively constant from 1999 until the middle of 2001.     

Chronology and petrogenesis of a 1.8 g lunar granitic clast:14321,1062

A study was undertaken to determine the chronology of a pristine granite clast (1062) from Apollo 14 breccia 14321 using Rb-Sr, Sm-Nd and ³⁹Ar-⁴⁰Ar methods. The genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed.Chronology: The Rb-Sr internal isochron is slightly disturbed and yields an age of 4.09 ± 0.11 AE ($\text{λ(}{}^{87}\text{Rb) = 0.0139}\text{AE}{}^{\mathrm{?1}}$) and an imprecise initial I(Sr) = 0.702 ? .008. If two data are excluded, the age becomes 4.13 ± 0.03 AE and I(Sr) = 0.698 ? .003. The whole rock and mineral separates are extremely radiogenic; they yield model ages which are relatively well-defined. The average model age is 4.12 ± 0.03 AE (relative to BABI = 0.69898). The Sm-Nd internal isochron is also slightly disturbed and gives an age of 4.11 ± 0.20 AE ($\text{λ(}{}^{147}\text{Sm) = 0.00654}\text{AE}$^?1). The ³⁹Ar-⁴⁰Ar average age of the non-magnetic fraction of the sample yields a slightly younger age of 3.88 ± 0.03 AE (K-Ar constants from Steiger and $\text{>a}\text{?}$, 1977). The concordancy of Rb-Sr and Sm-Nd internal isochrons with the Rb-Sr model age strongly suggests that the granitic clast formed at 4.1 AE ago in the shallow crust and was later excavated and brecciated about 3.88 AE ago.Petrogenesis: Isotopic and trace element data of the lunar granite show large K/La and Rb/Sr fractionations, small Sm/Nd fractionation and the distinct V-shaped REE distribution pattern at the time of crystallization. A two-stage model involving crystal fractionation followed by silicate liquid immiscibility (SLI) is proposed for lunar granite genesis. We propose that the granite can be the immiscible acidic liquid produced by SLI from a residual liquid which underwent fractionation of ca, 3% of phases with REE distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with REE contents about twice those of the 15405,85 quartz monzodiorite (QMD).The extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean. Our isotopic results and trace elements data from other workers suggest that granites, QMD and probably Mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro-granophyre associations in terrestrial layered intrusions such as the Skaergaard Intrusions.     

延边天宝山多金属矿田辉钼矿Re-Os同位素 年龄及其地质意义

延边天宝山为一大型中高温热液多金属(铅,锌,铜,钼等)矿田,是由新兴铅锌、立山铅锌铜和东风铅锌铜钼3个矿床所组成.文章在矿田地质特征研究的基础上,进行了辉钼矿Re-Os同位素体系定年研究,得到结果w(Re)为0.353～9.306 μg/g,模式年龄为174.7～200.3 Ma,加权平均值年龄为(194.6±3.9) Ma,等时线年龄为(196.6±2.5) Ma(MSWD=0.94,n=9),表明天宝山多金属矿田为早侏罗世岩浆作用及相关流体活动的产物,形成于华北板块和西伯利亚板块碰撞拼合后伸展环境,初步认为成矿物质来源主要为壳源.结合区域上已有的高精度年代学数据,将吉林省中东部山区钼成矿作用划分为2期:早侏罗世(196.6～186Ma)和中侏罗世(176.9～166.9Ma),且以中侏罗世钼矿化最为发育.     

Comparison of the acid-base behaviour and metal adsorption characteristics of a gram-negative bacterium with other strains

Thermodynamic parameters for proton and metal adsorption onto a gram-negative bacterium from the genus Enterobacteriaceae have been determined and compared with parameters for other strains of bacteria. Potentiometric titrations were used to determine the different types of sites present on bacterial cell walls. Stability constants for adsorption of Pb, Cu and Zn to specific sites were determined from batch adsorption experiments at varying pH with constant metal concentration. Titrations revealed 3 distinct acidic surface sites on the bacterial surface, with pK values of 4.3±0.2, 6.9±0.5 and 8.9±0.5, corresponding to carboxyl, phosphate and hydroxyl/amine groups, with surface densities of 5.0±0.7×10⁻⁴, 2.2±0.6×10⁻⁴ and 5.5±2.2×10⁻⁴ mol/g of dry bacteria. Only carboxyl and phosphate sites are involved in metal uptake, yielding the following intrinsic stability constants: Log K_carboxyl: Zn=3.3±0.1, Pb=3.9±0.8, and Cu=4.4±0.2, Log K_phosphoryl: Zn=5.1±0.1 and Pb=5.0±0.9. The deprotonation constants are similar to those of other strains of bacteria, while site densities are also within an order of magnitude of other strains. The similarities in surface chemistry and metal stability constants suggest that bacteria may be represented by a simple generic thermodynamic model for the purposes of modelling metal transport in natural environments. Comparison with oxide-coated sand shows that bacteria can attenuate some metals to much lower pH values.