U/Pb- und K/Ar-Datierungen des Uranvorkommens Höhenstein/Oberpfalz

K/Ar dating of micas from rocks of Fichtelgebirge and the northern Oberpfalz (NE-Bavaria) covers the rather wide range from 330 to 300 Ma. In combination with Rb/Sr wholerock isochron ages of post-tektonic granites four Variscian events can be traced:

1. Regional metamorphism ～ 330 Ma,
2. Intrusion of the older post-deformative granite G1 about 320 Ma (Falkenberger Granit) followed by rapid cooling.
3. About 300 Ma ago the older mineral ages were more or less reset by the intrusion of younger granites (G2 to G4, Flossenbürger Granit) again followed by a rapid cooling.
4. Local influences later than 290 Ma are recorded by some white micas in fault gauges at least up to the middle Jurassic (< 150 Ma).

The different U-black ore types yielded strongly discordant U/Pb dates. Applying the three dimensional U/Pb-discordia plane method the following results have been obtained: the older pitchblende generation with an upper concordia intersection of 336±17 Ma can be correlated with the regional metamorphism as well as with the intrusion of the older post-deformative granites. The younger generation with 298±4 Ma is of equal age as the intrusion of the younger granites. The brannerite mineralisation which according to thin section evaluation must be still younger could be only roughly dated to 288±78 Ma. The low precision is due to low uranium concentration and high common lead contents of the samples. The lower concordia intersection ages are 0 to 7 Ma. They were obtained more precisely by dating of secondary U-minerals: 10 torbernite samples with extremely high²³⁸U/²⁰⁶Pb-ratios of 30 000 to 50 000 yielded a positive slope of the discordia which points to an age of (137±12)×10³a. The²³⁰Th/²³⁸U-activity ratio of 0.68 determined byα-spectrometry indicates an age of (130.4±5.0)×10³ a. Pyrite and chalcopyrite samples which had U-concentration of some 100 ppm and which according to thin section evaluation are younger than the brannerite showed a positive slope of the²⁰⁷Pb/²⁰⁶Pb vs.²³⁸U/²⁰⁶Pb discordia, too. They could not be dated because the²⁰⁷Pb/²⁰⁶Pb-ratios corrected for common lead contribution are lower than 0.046 (radiogenic lead of zero age). This may be explained by an addition of²⁰⁶Pb due to²²²Rn migration from the pitchblende in only a few cm distance.     

Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications

In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.
The derived ice flow velocity for Vostok Station is  2.00 m a⁻¹± 0.01 m a⁻¹  . Along the flowline of Vostok Station an extension rate of about 10⁻⁵ a⁻¹ (equivalent to 1 cm km⁻¹ a⁻¹) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a⁻¹ along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.     

Local boundary-layer development over burnt and unburnt tropical savanna: an observational study

Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo, increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site a low to moderate intensity fire, ranging between 1,000 and 3,500 kW m⁻¹, initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface, scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2^°C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating and precipitation patterns that may affect larger-scale processes such as the Australian monsoon.     

Tidal gravity variations revisited at Vostok Station, Antarctica

In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region.     

A three-dimensional method for calculating independent chemical U/Pb- and Th/Pb-ages of accessory minerals

Previous theoretical considerations on the chemical U---Th-total Pb dating method failed to distinguish between thorogenic and uranogenic lead. However, it can be shown that the data points are located on a plane in the three-dimensional ThO₂, PbO, UO₂ space. The calculation of the best-fit plane yields a slope in the ThO₂---PbO and UO₂---PbO coordinate projections, and an initial PbO value. From the two slopes, Th/Pb- and U/Pb-ages can be calculated independently.

The method described in this paper is applied to monazites from the Hercynian G4-granite of the Fichtelgebirge (Germany). Th/Pb- and U/Pb-ages were calculated at 323 ± 20 Ma and 304 ± 15 Ma, respectively. The intercept value close to zero indicates that no significant amounts of common lead are present in the monazites studied.     

Episodes of floods in Mangala Valles,Mars, from the analysis of HRSC,MOC and THEMIS images

The Mangala Valles is a 900-km long outflow channel system in the highlands adjacent to the south-eastern flank of the Tharsis bulge. This work was intended to answer the following two questions unresolved in previous studies: (1) Was there only one source of water (Mangala Fossa at the valley head which is one of the Medusae Fossae troughs or graben) or were other sources also involved in the valley-carving water supply, and (2) Was there only one episode of flooding (maybe with phases) or were there several episodes significantly separated in time. The geologic analysis of HRSC image 0286 and mapping supported by analysis of MOC and THEMIS images show that Mangala Valles was carved by water released from several sources. The major source was Mangala Fossa, which probably formed in response to magmatic dike intrusion. The graben cracked the cryosphere and permitted the release of groundwater held under hydrostatic pressure. This major source was augmented by a few smaller-scale sources at localities in (1) two mapped heads of magmatic dikes, (2) heads of two clusters of sinuous channels, and (3) probably several large knob terrain locals. The analysis of results of crater counts at more than 60 localities showed that the first episode of formation of Mangala Valles occurred ～3.5 Ga ago and was followed by three more episodes, one occurred ～1 Ga ago, another one ～0.5 Ga ago, and the last one ～0.2 Ga ago. East of the mapped area there are extended and thick lava flows whose source may be the eastern continuation of the Mangala source graben. Crater counts in 10 localities on these lava flows correlate with those taken on the Mangala valley elements supporting the idea that the valley head graben was caused by dike intrusions. Our observations suggest that the waning stage of the latest flooding episode (～0.2 Ga ago) led to the formation at the valley head of meander-like features sharing some characteristics with meanders of terrestrial rivers. If this analogy is correct this could suggest a short episode of global warming in Late Amazonian time.     

Real-time drilling mud gas monitoring for qualitative evaluation of hydrocarbon gas composition during deep sea drilling in the Nankai Trough Kumano Basin

Background

Riverine particles undergo a rapid transformation when they reach estuaries. The rapid succession of hydrodynamic and biogeochemical regimes forces the particles to flocculate, settle and enter the sediment pool. The rates and magnitudes of flocculation depend on the nature of the particles which are primarily affected by the types and quantities of organic matter (OM). Meanwhile, the OM characteristics vary widely between environments, as well as within a single environment due to seasonal climate and land use variability. We investigated the effect of the OM types and quantities through laboratory experiments using natural estuarine particles from the Mississippi Sound and Atchafalaya Bay as well as model mixtures of montmorillonite and organic molecules (i.e., biopolymers (guar/xanthan gums) and humic acid).

Results

Biopolymers promote flocculation but the magnitude depends on the types and quantities. Nonionic guar gum yields much larger flocs than anionic xanthan gum, while both of them exhibit a nonlinear behavior in which the flocculation is the most pronounced at the intermediate OM loading. Moreover, the effect of guar gum is independent of salinity whereas the effect of xanthan gum is pronounced at higher salinity. Meanwhile, humic acid does not affect flocculation at all salinity values tested in this study. These results are echoed in the laboratory manipulation of the natural estuarine particles. Flocculation of the humic acid-rich Mississippi Sound particles is unaffected by the OM, whereas that of biopolymer-rich Atchafalaya Bay particles is enhanced by the OM.

Conclusions

Flocculation is positively influenced by the presence of biopolymers that are produced as the result of marine primary production. Meanwhile, humic acid, which is abundant in the rivers that drain the agricultural soils of Southeastern United States, has little influence on flocculation. Thus, it is expected that humic acid-poor riverine particles (e.g., Mississippi River, and Atchafalaya River, to a lesser degree) may be prone to rapid flocculation and settling in the immediate vicinity of the river mouths when mixed with biopolymer-rich coastal waters. It is also expected that humic acid-rich riverine particles (e.g., Pearl River) may resist immediate flocculation and be transported further away from the river mouth.     

Fundamental constants and high‐resolution spectroscopy

Absorption‐line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine‐structure constant, α, and the proton‐to‐electron mass ratio, μ = m_p/m_e, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high‐resolution (R ≈ 60000) and high signal‐to‐noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. (2013) and Rahmani et al. (2013). A stringent bound for Δα /α is obtained for the absorber at z_abs = 1.6919 towards HE 2217‐2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in α in this system is +1.3 ± 2.4_stat ± 1.0_sys ppm if Al II λ 1670 Å and three FeII transitions are used, and +1.1 ± 2.6_stat ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on α ‐variation from an individual absorber and reveals no evidence for variation in α at the 3‐ppm precision level (1σ confidence). The expectation at this sky position of the recently‐reported dipolar variation of α is (3.2–5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δα /α at face value is not supporting this expectation but not inconsistent with it at the 3σ level. For the proton‐to‐electron mass ratio the analysis of the H₂ absorption lines of the z_abs ≈ 2.4018 damped Lyα system towards HE 0027–1836 provides Δμ /μ = (–7.6 ± 8.1_stat ± 6.3_sys) ppm which is also consistent with a null variation. The cross‐correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter‐order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrated minerals in the deposits of Aureum Chaos

Hydrated minerals have been detected in many martian chaos regions and chasmata, playing a major role in its past aqueous activity. Based on short wave infrared data from CRISM, imagery and elevation data, we identified and mapped hydrated minerals in Aureum Chaos to shed light on their stratigraphy and geological context.The Interior Layered Deposits (ILDs) display three stratigraphic units: The lowest unit shows massive and also layered, high-albedo monohydrated sulfate (MHS, best matching kieserite; 20–650 m thick) with intercalated hydroxylated ferric sulfates (HFSs, best matching jarosite) and ferric oxides. The overlying polyhydrated sulfate (PHS) is commonly layered (20–40 m thick), smooth to heavily fractured, of lower albedo and partially contains ferric oxides. Spectrally neutral, distinctly layered, and bumpy cap rock (40–300 m thick) forms the top.We found spectral and morphological similarities to Aram Chaos (PHS, MHS, ferric oxides; texture of ILD and cap rock) and Juventae Chasma (HFS). Besides, the phyllosilicate nontronite was found attributed to chaotic terrain as light toned fractured exposure and within dark, smooth mantling. The coexistence of sulfates and phyllosilicates indicates changes in the geochemistry of the aqueous environment.Since sulfates and phyllosilicates could be alteration products, the observed mineralogy presumably is not the original; conversions between PHS and MHS, MHS or PHS into jarosite, jarosite into iron oxides are considered. Due to its occurrence along mantling edges and on flat surfaces of MHS without textural differences, it appears that PHS is an alteration product of MHS, e.g. due to surface exposure. The facies and relative timing of sulfate formation remains undefined. However, two different formation models are considered. The first implies contemporaneous ILD and PHS deposition and diagenetic sulfate conversion (into MHS, iron oxides) due to overburden later on. This model is less conclusive than groundwater evaporation -the second model- due to the lack of a sharp PHS–MHS boundary that would indicate a diagenetic formation.Alternatively, the second model suggests subsequent sulfate formation. Groundwater would have penetrated into pre-existing sulfate-free ILD. The permeability and porosity of ILD material would have defined the rate of water absorption and sulfate precipitation (low in cap rock?), resulting in cementation of probably aeolian deposited ILDs. We think this model is more consistent and could explain ILD stratigraphy with the potential anhydrous cap rock on top.The surface age of chaotic terrain (late Hesperian) and mantling deposits (mid to late Amazonian) limit the ILD age and possibly the emplacement of sulfates. Phyllosilicates in the mantling are presumably allochthonous. Limiting the timing of in situ phyllosilicates is more complicated; they could be Noachian (excavated material, following the phyllosian era), or instead syn- or post-chaotic. A close spatial and temporal association of sulfates and phyllosilicates, in which nontronite represents the deep facies, and sulfates the evaporitic facies is known from Earth and is also possible and would combine groundwater alteration with the observed mineralogy.The preservation of nontronite, HFS and MHS probably reflects a relatively dry environment with intermittent aqueous activity since their emplacement.     

Trace element transport rates in subduction zones: evidence from Th, Sr and Pb isotope data for Tonga-Kermadec arc lavas

Trace element and Th, Sr and Pb isotope data for young lavas from the Tonga-Kermadec arc in the southwest Pacific suggest that geochemical variations in the lavas along the arc are linked to differences in the material being subducted beneath the arc. Lavas from the southern (Kermadec) segment of the arc have relatively radiogenic Pb isotope compositions, which reflects a contribution from subducted sediment. In contrast, much of the Pb in Tonga lavas is derived from the altered oceanic crust in the subducting Pacific Plate, and lavas from the northernmost Tonga islands of Tafahi and Niuatoputapu contain Pb and Sr derived from the subducted part of the Louisville Seamount Chain. The origin of the Pb in the lavas from these two islands can thus be traced to a point on the subducting slab, and this observation is used to estimate the rate at which trace elements are transported beneath the arc. Our calculations suggest that fluid-soluble elements such as U, Sr and Pb are transported from the subducted slab, across the mantle wedge and back to the surface in lavas over a period of approximately 2–3 Ma, and that magmas are erupted at the surface less than 350 ka after the melts are generated in the mantle wedge.