The Kaidun meteorite: Clasts of alkaline‐rich fractionated materials

Abstract— Clasts of alkaline (the second find in meteorites) and subalkaline rocks were found in the Kaidun meteorite. One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3–5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high‐Ca and low‐Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body. The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3–5)D is similar in some mineralogical respects to basaltic shergottites.     

Numerical modelling of stratified tidal flow over a fjord sill

Field observations of tidally driven stratified flow in the sill area of Knight Inlet (British Columbia) revealed a very complicated structure, which includes solitary waves, upstream bifurcation, hydraulic jump and mixing processes. Recent observations suggest that the flow instabilities on the plunging pycnocline at the lee side of the sill may contribute to solitary wave generation through a subharmonic interaction. The present study reports on a series of numerical experiments of stratified tidal flow in Knight Inlet performed with the help of a fine resolution fully non-linear non-hydrostatic numerical model. The model reproduces all important stages of the baroclinic tidal dynamics observed in Knight Inlet. Results demonstrate that solitary waves are generated apart from the area of hydrodynamic instability. Accelerating tidal flux forms a baroclinic hydraulic jump just above the top of the sill, whereas the bifurcations and zones of shear instabilities are formed downstream of the sill. The first baroclinic mode having the largest velocity escapes from the generation area and propagates upstream, disintegrating further into a packet of solitary waves reviling the classical “non-subharmonic” mechanism of generation. The remaining part of the disturbance (slow baroclinic modes) is arrested by tidal flow and carried away to the lee side of the obstacle, where shear instability, billows and mixing processes are developed. Some sensitivity runs were performed for different value of tidal velocity.     

The NLTE Formation of Iron Lines Used in Solar Polarimetry

We study in some detail one-dimensional NLTE effects in solar Fei lines. The lines selected are frequently used in solar polarimetry, and also in studies of line asymmetries and for abundance determinations. Our model atom for Fei–Feii–Feiii is realistic: it takes account of multiplet structure and it includes over 200 bound–bound and bound–free transitions in detail. We use very efficient iterative methods for the self-consistent solution of the kinetic and radiative transfer equations (Auer, Fabiani Bendicho, and Trujillo Bueno, 1994). We have applied these fast methods of solution because they are suitable for the investigation of 2D and 3D NLTE transfer effects with multilevel atoms, which constitutes the next step of our ongoing research project on the iron line formation problem.     

Comparative Geochemical Characteristics and Genesis of Large Polyphase Plutons in the Cores and on the Periphery of the Mongol–Okhotsk Fold Belt Magmatic Areas of Different Ages

Doklady Earth Sciences - The early Mesozoic Baga-Khentei pluton is a part of the Daurian–Khentei batholite that was formed under the impact of the Mongolian plume on the lower horizons of the...     

How Bayesian data assimilation can be used to estimate the mathematical structure of a model

In previous work, we presented a method for estimation and correction of non-linear mathematical model structures, within a Bayesian framework, by merging uncertain knowledge about process physics with uncertain and incomplete observations of dynamical input-state-output behavior. The resulting uncertainty in the model input-state-output mapping is expressed as a weighted combination of an uncertain conceptual model prior and a data-derived probability density function, with weights depending on the conditional data density. Our algorithm is based on the use of iterative data assimilation to update a conceptual model prior using observed system data, and thereby construct a posterior estimate of the model structure (the mathematical form of the equation itself, not just its parameters) that is consistent with both physically based prior knowledge and with the information in the data. An important aspect of the approach is that it facilitates a clear differentiation between the influences of different types of uncertainties (initial condition, input, and mapping structure) on the model prediction. Further, if some prior assumptions regarding the structural (mathematical) forms of the model equations exist, the procedure can help reveal errors in those forms and how they should be corrected. This paper examines the properties of the approach by investigating two case studies in considerable detail. The results show how, and to what degree, the structure of a dynamical hydrological model can be estimated without little or no prior knowledge (or under conditions of incorrect prior information) regarding the functional forms of the storage–streamflow and storage–evapotranspiration relationships. The importance and implications of careful specification of the model prior are illustrated and discussed.     

Experimental studies of Ta2O5 and columbite–tantalite solubility in fluoride solutions from 300 to 550°C and 50 to 100 MPa

It is well established that the fractionation of Li–F granitic magmas at depth leads to the accumulation of flux elements such as F and Li, and metal cations such as Ta and Nb in residual melts. However, it remains to be determined whether magmatic fractionation is sufficient to concentrate Nb and Ta into economically significant quantities, and what role hydrothermal–metasomatic processes play in the formation of such ore deposits. In the literature, reliable data about the solubility of Ta and Nb in hydrothermal solutions is missing or incomplete. This study provides a quantitative experimental estimation of the possible contribution from hydrothermal processes in Ta enrichment in cupolas of albitized and greisenized Li–F granite. Experimental studies of Ta₂O₅ and columbite–tantalite (Mn,Fe)(Nb,Ta)₂O₆ solubility were carried out in fluoride solutions consisting of HF, NaF, KF, and LiF. At low fluoride concentrations (0.01 and 0.1 m), Ta₂O₅ solubility at 550°C and 100 MPa under Co–CoO oxidizing conditions is low (near 10^?5–10^?4 m) in all fluoride solutions (HF, NaF, KF, LiF). At high fluoride concentrations (1 and 2 m) the highest Ta₂O₅ concentrations (10^?1 m) were detected in HF solutions. In KF, NaF, and LiF solutions, the Ta₂O₅ solubility is also high (10^?3–10^?2 m). The dependence of columbite–tantalite (Nb₂O₅-59 wt. %, Ta₂O₅-18 wt. %) solubility as a function of solution composition, T, and P has also been investigated. Tantalum and Nb concentrations have the highest values in HF solutions at reduced conditions (up to 10^?3 to 10^?2 m Ta in 1 m HF). In 1 m NaF solutions, the concentrations of Nb and Ta are, respectively, 2.5 and 3 orders of magnitude less than those in the 1 m HF solutions. Solubility of Ta and Nb in KF solutions has intermediate values. It is established that in NaF and KF solutions the dependence of solubility on pressure is distinctly negative. The Nb and Ta contents increase with increasing concentrations of HF and KF in solution, however, they do not change with increasing NaF concentration. In NaHCO₃, Na₂CO₃, and HCl solutions columbite–tantalite solubility is low. Even in 1 m chloride solutions the content is within the limits of 10^?5 m for Nb and 10^?6 to 10^?8 m for Ta. We conclude that hydrothermal transport of Ta and Nb is possible only in concentrated fluoride solutions.     

The Kaidun meteorite: Composition and origin of inclusions in the metal of an enstatite chondrite clast

Abstract— Metal nodules are one of the major textural components of Kaidun sample #01.3.06 EH3-4. In terms of structure, the nodules are of three types: (1) globular, (2) zoned with a massive core and globular mantle, and (3) nodules with no internal structure. The size and composition of the globules in the nodules and grains of metal of the matrix are almost identical: no greater than 20 μm and Ni, 5.95; Si, 3.33 wt%. The nodules contain small (usually <5 μm) inclusions of SiO₂; albitic glass; enstatite; roedderite; and a mixture of SiO₂ and Na₂S₂. This is the first reported occurrence of a simple sulfide of an alkaline metal in nature. The formation of the inclusions appears to be related to condensation of material onto the surfaces of metal grains. The nodules appear to have formed by aggregation of separate grains (globules) of metal, with conservation of condensates on the grain surfaces as inclusions. The inclusions probably condensed over a significant temperature range from 1400 to 600 K. The aggregation of metal grains and formation of the nodules probably occurred simultaneously with condensation.     

Cation distribution and exsolution in the Luna-20 pyroxenes as the chronological indicator of their thermal history

During the process of continuous post-crystallization cooling, the degree of phase transformation in pyroxenes (ordering and decomposition of solid solutions) is determined by the total cooling time and by cooling rates at individual stages; this degree can also be applied to the estimation of the sub-solidus cooling time of pyroxenes and of rocks, genetically associated with them (geochronometer). The degree of Fe²⁺-Mg order in distribution between theM ₁ andM ₂ sites observed in orthopyroxenes can be used as the criterion for the sub-solidus cooling rates of orthopyroxenes. A technique for approximate estimation of cooling time (rates) of orthopyroxenes in the 1000–500°C interval is suggested on the basis of an ion exchange reaction kinetic model, with the adoption of a few assumptions. X-ray structural analysis study revealed the character of the Fe²⁺-Mg intersite distribution in the M-511 and M-533 orthopyroxenes from the Luna-20 regolith; the obtainedK _D values make 0.072(T _e ^o ~ 460°C) and 0.06 (T _e ^o ~ 480°C), respectively. The corresponding evaluation of the linear cooling rate in the 1000-500°C range, as inferred by the obtained data, gave the value of 0.2–0.25° h^–1. Two features of the exosolution relate to the sub-solidus cooling rate of clinopyroxenes: the degree of phase separation by composition W_o and the exsolution scale . The monocrystal X-ray diffraction study, the transmission electron microscopy and the X-ray microprobe analysis produced the exsolution parameters for clinopyroxenes 2001-3, 2001-6 and 559 from the Luna-20 regolith: W_o 26%, 28% and 45% respectively; 300 Å, 1000 Å and 60 , respectively. The solvus temperatures (T _e) of the clinopyroxenes 2001-3 and 2001-6 make, respectively, 1100 ± 25°C and 1095 ± 45°C; the spinodal temperatures (T _s) areT _s =T _e – 50°C and represent quenching temperatures of the given pyroxenes in relation to the exsolution process. The cooling time fromT _cryst. toT _s was estimated and the value of the formal linear cooling rate was found to be ~ 90° h^–1 (2001-3) and ~ 8° h^–1 (2001-6). The average value of the pyroxene 559 sub-soldius cooling rate in the 1150–1000°C range was four orders less. The obtained data were discussed in view of the possible genesis of the studied Luna-20 pyroxenes.     

A petrological and geochemical study on time-series samples from Klyuchevskoy volcano,Kamchatka arc

To understand the generation and evolution of mafic magmas from Klyuchevskoy volcano in the Kamchatka arc, which is one of the most active arc volcanoes on Earth, a petrological and geochemical study was carried out on time-series samples from the volcano. The eruptive products show significant variations in their whole-rock compositions (52.0–55.5 wt.% SiO₂), and they have been divided into high-Mg basalts and high-Al andesites. In the high-Mg basalts, lower-K and higher-K primitive samples (>9 wt.% MgO) are present, and their petrological features indicate that they may represent primary or near-primary magmas. Slab-derived fluids that induced generation of the lower-K basaltic magmas were less enriched in melt component than those associated with the higher-K basaltic magmas, and the fluids are likely to have been released from the subducting slab at shallower levels for the lower-K basaltic magmas than for higher-K basaltic magmas. Analyses using multicomponent thermodynamics indicates that the lower-K primary magma was generated by ~13% melting of a source mantle with ~0.7 wt.% H₂O at 1245–1260?°C and ~1.9 GPa. During most of the evolution of the volcano, the lower-K basaltic magmas were dominant; the higher-K primitive magma first appeared in AD 1932. In AD 1937–1938, both the lower-K and higher-K primitive magmas erupted, which implies that the two types of primary magmas were present simultaneously and independently beneath the volcano. The higher-K basaltic magmas evolved progressively into high-Al andesite magmas in a magma chamber in the middle crust from AD 1932 to ~AD 1960. Since then, relatively primitive magma has been injected continuously into the magma chamber, which has resulted in the systematic increase of the MgO contents of erupted materials with ages from ~AD 1960 to present.     

Possible variation in methane flux caused by gas hydrate formation on the northeastern continental slope off Sakhalin Island, Russia

The Sakhalin Slope Gas Hydrate Project (SSGH) is an international collaborative effort by scientists from Japan, Korea, and Russia to investigate natural gas hydrates (GHs) that have accumulated on the continental slope off Sakhalin Island, Okhotsk Sea. From 2009 to 2011, field operations of the SSGH-09, -10, and -11 projects were conducted. GH-bearing and -free sediment cores were retrieved using steel hydro- and gravity corers. The concentrations of sulfate ions in sediment pore waters were measured to investigate sulfate concentration–depth profiles. Seventeen cores showed linear depth profiles of sulfate concentrations. In contrast, eight cores and two cores showed concave-up and -down profiles plausibly explained by sudden increase and decrease in methane flux from below, respectively, presumably caused by the formation of gas hydrate adjacent to the core sampling sites.