Aubrites and diogenites: Trace element clues to their origin

We have analyzed by RNAA 25 aubrite and 9 diogenite samples for 13 to 29 siderophile, volatile, and lithophile trace elements. Both meteorite classes show a typically igneous siderophile element pattern, with Ir, Os, Re, Ge more depleted than Au, Ni, Pd, Sb. But aubrites tend to have about 10 × higher abundances (10^?3 ? 10 ^{? 4} × Cl for the first 4 and 10^?2?10^?3 × Cl for the last 4 siderophiles), apparently reflecting smaller metal/silicate distribution coefficients at lowerf(O₂), or less complete segregation of metal. Se is surprisingly abundant in aubrites (up to 0.4 × Cl), but Te is less so ($\text{Se}\text{Te}\text{? 5 × Cl}$), apparently due to its stronger siderophile character. Other volatiles (Ag, Zn, In, Cd, Bi, T1) show depletions intermediate between lunar dunite and the Earth's mantle.Of 7 aubrites analyzed for REE (Ce, Nd, Eu, Tb, Yb, Lu), 6 are depleted in REE (0.08?0.5 × Cl) and 5 show negative Eu anomalies (the exceptions are Bishopville and Mt. Egerton silicate). This supports an igneous origin, as already noted by Boynton and Schmitt (1972). No samples of the complementary, basaltic and feldspathic rocks have been found thus far, but one of our samples of Khor Temiki dark is a candidate for the basalt. It is 5?7 × enriched in REE and only slightly less so in Rb, Cs, and U. Though shocked and enriched in siderophiles to ~0.05 × Cl, it apparently represents a new meteorite class.Three diogenites analyzed for REE show very diverse patterns, from strongly depleted in light REE for Tatahouine (Ce = 0.01 × Cl) to flat for Garland (~2.5 × Cl). The data confirm the trends found by Fukuokaet al. (1977) as well as their interpretations.Factor analysis shows several parallel groupings for aubrites and diogenites: siderophiles (Re, Ir, Os, Pd, Ge), chalcophiles (Se, Te), volatiles (Ag, In, Tl) and incompatibles (U, REE, and Cs or Rb). But there are some differences for elements such as Ni, Sb, Cd, Bi, Au, and Zn, most of which behave more sensibly in aubrites than in diogenites.Several element pairs that differ greatly in volatility (Cs-U, Ge-Ir) correlate closely in aubrites, in approximately Cl-chondrite proportions. These correlations, and other lines of evidence, suggest strongly that aubrites originated by igneous processes in their parent body, not by direct nebular condensation. The source material may have resembled EL chondrites in oxidation state and depletion of refractories, metal, and volatiles.     

Zur Baugeschichte der Ardennen: Eine Antwort an F. Geukens

Ohne Zusammenfassung     

A parameterized model for the evolution of isotopic heterogeneities in a convecting system

Laboratory experiments are used to illustrate how steady convective flows, while efficient at stirring an initial heterogeneity within a single cell, do not produce dispersal of heterogeneous material over scales large compared to the depth. Long-range dispersal requires that the flow be time dependent on a time scale comparable to the overturn time. Convection in an internally heated layer has this property and numerical solutions are used to study the way in which it disperses a set of neutrally buoyant particles that were initially confined to a small space. The horizontal dispersal of these particles is reasonably well represented by an effective diffusivity of 0.3 cm²/s for a Rayleigh number of 10⁶. The concept of an effective diffusivity is then applied to the isotopic evolution of the Sm-Nd and Rb-Sr systems with spatial variations generated by horizontal variations in degree of melting 1.8×10⁹ years ago. The present-day average ε value one would measure in such a system depends on the average degree of melting, the amplitude and length scale of variations in partial melt, and the effective diffusivity assumed. Especially in the case of Nd the differences in average ε value between a uniform and a spatially variable (but with the same average) melting case can be significant. The range of ε values about the average is controlled by the competing effects of generation by the differences in enrichment factor and decay due to the effective diffusivity.     

Zum Sauerstoffhaushalt der Gewässer der Feldberger Seenplatte an Hand ausgewählter sommerlicher Tiefenprofile seit 1924 und 1962 Teil 3: Scharteisen,Wasch-See,Dolgener See

This paper presents the depth profiles of 1951 … 1980 for the Scharteisen, the investigations of the last years for the Wasch lake and the Dolgen lake, for the oxygen regime with the representation of the oxygen concentration, transparency, water temperature and the upper limit of the occurrence of hydrogen sulphide. The profiles demonstrate the eutrophication having occurred for the Scharteisen and the present state for the three lakes. The general situation of the drainage areas and the causes to be derived from it concerning changes of the water quality as well as possible measures and aims of sanitations are discussed. Also the most important data are given on the hydrography of these waters and on their utilization for obtaining drinking water and by fishery up to now.     

In situ oxygen,magnesium, and silicon isotopic compositions of the FUN inclusion Vigarano 1623-5

Oxygen, magnesium, and silicon isotopic abundances in Vigarano 1623-5 were studied using secondary ion mass spectrometry to investigate correlations between isotopic and petrologic properties of this unique forsterite-bearing FUN inclusion. Vigarano 1623-5 displays large, correlated mass-dependent fractionation effects, tightly linked to mineralogy within distinct petrologic units of the inclusion. The pyroxene-rich and melilite-rich interior parts of the inclusion display highly mass-fractionated isotopic compositions of oxygen, magnesium, and silicon, consistent with Rayleigh distillation during evaporation of a melt with initial oxygen composition close to a solar composition. However, the chemical composition, enriched in magnesium and silicon, suggests a precursor already fractionated by prior melt evaporation. A discontinuous igneous rim was produced by a flash-melting event followed by isotopic exchange in the rim melilite with planetary-like oxygen, mechanical fragmentation, and reassembly with an accretionary rim of heterogeneous materials. Al-rich minerals in 1623-5 show evidence for having crystallized with live ²⁶Al but at less than the “canonical” level of most CV calcium-aluminum-rich inclusions. However, well-defined ²⁶Al-²⁶Mg isochrons are not found and temporal implications are ambiguous.     

Investigation of the Coronal Magnetic Field Using a Type II Solar Radio Burst

The type II solar radio burst recorded on 13 June 2010 by the Hiraiso Solar Observatory Radio Spectrograph was employed to estimate the magnetic-field strength in the solar corona. The burst was characterized by a well-pronounced band splitting, which we used to estimate the density jump at the shock and Alfvén Mach number using the Rankine–Hugoniot relation. We convert the plasma frequency of the type II burst into height [R] in solar radii using an appropriate density model, and then we estimated the shock speed [V _s], coronal Alfvén velocity [V _A], and the magnetic-field strength at different heights. The relative bandwidth of the band splitting was found to be in the range 0.2?–?0.25, corresponding to a density jump of X=1.44?–?1.56, and an Alfvén Mach number of M _A=1.35?–?1.45. The inferred mean shock speed was on the order of V≈667 km?s^?1. From the dependencies V(R) and M _A(R) we found that the Alfvén speed slightly decreases at R≈1.3?–?1.5 R_⊙. The magnetic-field strength decreases from a value between 2.7 and 1.7 G at R≈1.3?–?1.5 R_⊙, depending on the coronal-density model employed. Our results are in good agreement with the empirical scaling by Dulk and McLean (Solar Phys. 57, 279, 1978) and Gopalswamy et al. (Astrophys. J. 744, 72, 2012). Our results show that the type II band-splitting method is an important tool for inferring the coronal magnetic field, especially when independent measurements are made from white-light observations.     

Growth of accretionary wedges and pulsed ophiolitic mélange formation by successive subduction of trench‐parallel volcanic elevations

Fault‐bounded coherent belts alternating with belts of mélanges are common in accretionary wedges and are usually interpreted as a result of imbrication along subduction zone megathrusts. Using the Neoproterozoic/early Cambrian Blovice accretionary complex (BAC), Bohemian Massif, as a case example, we present a new model for the origin of alternating belts through the repetition of several cycles of (1) offscraping and deformation of trench‐fill sediments to form the coherent units, interrupted by (2) arrival and subduction of linear, trench‐parallel volcanic elevations. The latter process leads to an increase in the wedge taper, triggering mass‐wasting and formation of olistostromes. At the same time, ophiolitic mélanges form by disruption of an upper part of the volcanic ridge and incorporation of the disrupted ocean‐floor succession into the olistostromes. Specifically, the BAC represents a complete section across an accretionary wedge and records three such major pulses of ophiolitic mélange formation through subduction of an outboard back‐arc basin.     

Sources,Distribution and Behavior of Major and Trace Elements in a Complex Karst Lake System

Sources and distribution of major and trace elements were investigated in the Plitvice Lakes, a pristine cascade hydrological system of sixteen karst lakes situated in a sparsely populated area of the central Croatia. Water and surface sediment samples from 17 locations, including springs, tributaries and lakes, were analyzed for the content of 22 elements by high-resolution inductively coupled mass spectrometry. Principal component analysis of the collected data set showed that different springs and tributaries displayed distinct multielemental compositions, reflecting primarily the differences in their corresponding geological backgrounds. It was shown that the springs situated in the Upper and Middle Jurassic dolomite bedrock represented the main source of several trace elements, including some toxic metals (Cd, Zn, Ni and Tl), to the Plitvice Lakes system. The concentrations of most of the trace elements (Mn, Fe, Al, Cd, Zn, Cu, Ni, Pb, Co, Cr and Tl) showed decreasing spatial trends in the downstream direction, from sources to the lakes. Such a distribution was interpreted to be a consequence of an efficient removal of the dissolved elements in the lentic parts of the system, mainly by co-precipitation with authigenic calcite and Mn oxides. Nevertheless, most of the elements in the lake sediments were highly correlated with Al, which indicated their prevalent association with terrigenic material. It was shown that the multicascade system of the Plitvice Lakes had an enhanced autopurification efficiency regarding the elimination of most of the trace metals from the aqueous phase.     

Modeling compositional compressible two-phase flow in porous media by the concept of the global pressure

We derive a new formulation for the compositional compressible two-phase flow in porous media. We consider a liquid–gas system with two components: water and hydrogen. The formulation considers gravity, capillary effects, and diffusivity of each component. The main feature of this formulation is the introduction of the global pressure variable that partially decouples the system equations. To formulate the final system, and in order to avoid primary unknowns changing between one-phase and two-phase zones, a second persistent variable is introduced: the total hydrogen mass density. The derived system is written in terms of the global pressure and the total hydrogen mass density. The system is capable of modeling the flows in both one and two-phase zones with no changes of the primary unknowns. The mathematical structure is well defined: the system consists of two nonlinear parabolic equations, the global pressure equation, and the total hydrogen mass density equation. The derived formulation is fully equivalent to the original one. Numerical simulations show ability of this new formulation to model efficiently the phase appearance and disappearance.     

Redox-dependent removal of 27 organic trace pollutants: compilation of results from tank aeration experiments

The biodegradation of various wastewater-derived organic trace pollutants occurring in different aquatic compartments of the environment was previously reported to be influenced by the prevailing redox conditions. However, comparative studies on the redox-dependent degradation behavior of organic trace pollutants are scarce. The objective of the study presented herein, was to compile and evaluate data from several comparable previous tank experiments, thus, providing an overview on the redox-dependent removal of a total of 27 wastewater-derived trace compounds, including phenazone type compounds, antimicrobials, ß-blockers, psychoactive drugs and sulfonamides. Removal rate constants were fitted assuming first-order degradation kinetics. Six compounds were identified to be removed solely under oxic, three compounds solely under anoxic conditions. Others persisted under all experimental conditions, while some were removed under both oxic and anoxic conditions.