Mobility and H2O loss from fluid inclusions in natural quartz crystals

Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples. Received: 17 November 1998 / Accepted: 16 April 1999     

Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany

 Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany) confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by a model that couples the advective–dispersive transport in the fractures with the molecular diffusion exchange in the matrix. For the scale of the tests (maximum distance of 225 m), an approximation was used in which the influence of adjacent fractures is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone obtained from the tracer tests is about 1.5×10^–2 m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10^–7 m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms the dominant role of the fault zones as collectors of water and conductors of fast flow. Received, April 1997 Revised, January 1998, August 1998 Accepted, August 1998     

A Density Correction for Lagrangian Particle Dispersion Models

Current Lagrangian particle dispersion models, used to simulate the dispersion of passive tracers in the turbulent planetary boundary layer (PBL), assume that the density is constant within the PBL. In deep PBLs, where the density at the boundary-layer top may be lower by more than 20% than at the surface, this assumption leads to errors in the tracer concentrations on the order of 10%. In the presence of a vertical wind shear, this also leads to inaccurate calculations of the horizontal tracer transport. To remove this deficiency, a Langevin equation is presented that contains a density correction term. The effect of the density correction is studied using data from a large-scale tracer experiment. It is found that for this experiment, the main effect of the density correction is an increase in the surface tracer concentrations, whereas the horizontal tracer transport patterns remain largely unaffected.     

The Transport Time pdf for a Simple Turbulent Flow

In a turbulent fluid, the time a particle needs to travel from a point source to the observation point, can be considered as a random variable. It is shown that the probability density function (pdf) for this random variable is determined by the Lagrangian particle position pdf. The characteristics of the transport time pdf are discussed for the simple case of a turbulent fluid moving with a constant mean velocity.     

The cosmic‐ray exposure history of the Twannberg iron meteorite (IIG)

The Twannberg iron meteorite is one out of only six members of the group IIG. The combined noble gas and radionuclide data obtained in this new systematic study indicate that Twannberg with its ~570 recently recovered specimens was a large object with a preatmospheric radius in the range of ~2 m, which corresponds to ~250 × 10³ kg. The cosmic‐ray exposure age for Twannberg is 182 ± 45 Ma. The most surprising result is the long terrestrial age of T_terr =  ka, which is unexpected considering the humid conditions in Switzerland. However, this age is in accord with glaciation events, indicating that the less shielded samples from Mt. Sujet were found close to the position of the original strewn field, whereas the samples from Gruebmatt and Twannbach, which are from more shielded positions, were glacially transported to the east–northeast during the second last ice age (185–130 ka ago) from an original position west of Mt. Sujet.     

Geomorphological investigations and luminescence dating in the southern part of the Khangay and the Valley of the Gobi Lakes (Central Mongolia)

Geomorphological investigations in the catchment area of the Baydragiyn river along the southern slope of the Khangay and in the Valley of the Gobi Lakes in western Mongolia provide evidence for Late Quaternary glaciations and lake‐level changes. Thermoluminescence (TL) and infrared optically stimulated luminescence (IRSL) dating of aeolian and colluvial sediments from the central Khangay place the sediments that overlie fluvial and glaciofluvial terraces in the Holocene. An age of 21 ka is determined for a sand deposit overlying the terrace that is related to the last glacial ice‐margin. Lacustrine sediments from higher beach lines in the Valley of the Gobi Lakes provide evidence for a slightly more humid period around 1.5 ka, and a larger extent of the lakes in the Early Holocene at about 8.5 ka, as also reported from other parts of Central Asia. Remnants of lacustrine sediments buried by alluvial gravel, and indicating a huge palaeolake in the basin of the Orog Nuur, however, date to the early stage of the last glaciation around 70 ka. Copyright © 2001 John Wiley & Sons, Ltd.     

Chemistry and oxygen isotopic composition of cluster chondrite clasts and their components in LL3 chondrites

Cluster chondrites are characterized by close‐fit textures of deformed and indented chondrules, taken as evidence for hot chondrule accretion (Metzler 2012 ). We investigated seven cluster chondrite clasts from six brecciated LL3 chondrites and measured their bulk oxygen isotopic and chemical composition, including REE, Zr, and Hf. The same parameters were measured in situ on 93 chondrules and 4 interchondrule matrix areas. The CI‐normalized REE patterns of the clasts are flat, showing LL‐chondritic concentrations. The mean chemical compositions of chondrules in clasts and other LL chondrites are indistinguishable and we conclude that cluster chondrite chondrules are representative of the normal LL chondrule population. Type II chondrules are depleted in MgO, Al₂O₃ and refractory lithophiles (REE, Zr, Hf) by factors between 0.65 and 0.79 compared to type I chondrules. The chondrule REE patterns are basically flat with slight LREE < HREE fractionations. Many chondrules exhibit negative Eu anomalies while matrix shows a complementary pattern. Chondrules scatter along a correlation line with a slope of 0.63 in the oxygen 3‐isotope diagram, interpreted as the result of O‐isotope exchange between chondrule melts and ¹⁸O‐rich nebular components. In one clast, a distinct anticorrelation between chondrule size and δ¹⁸O is found, which may indicate a more intense oxygen isotope exchange by smaller chondrules. In some clasts the δ¹⁸O values of type I chondrules are correlated with concentrations of SiO₂ and MnO and anticorrelated with MgO, possibly due to the admixture of a SiO₂‐ and MnO‐rich component to chondrule melts during oxygen isotope exchange. Two chondrules with negative anomalies in Sm, Eu, and Yb were found and may relate their precursors to refractory material known from group III CAIs. Furthermore, three chondrules with strong LREE > HREE and Zr/Hf fractionations were detected, whose formation history remains to be explained.     

Benthic marine litter in four Gulfs in Greece,Eastern Mediterranean; abundance,composition and source identification

The types, abundance, distribution and sources of benthic marine litter found in four Greek Gulfs (Patras, Corinth, Echinades and Lakonikos) were studied using bottom trawl nets. Mean distribution and weight densities range between 72–437 Item/km² and 6.7–47.4 kg/km². Litter items were sorted into material and usage categories. Plastic litter (56%) is the most dominant material category followed by metal (17%) and glass (11%). Beverage packaging (32%) is the dominant usage category followed by general packaging (28%) and food packaging (21%). Based on the typological results three dominant litter sources were identified; land-based, vessel-based and fishery-based. Application of factor analysis (R- and Q-mode) conducted on both material and usage litter datasets confirmed the existence of the three dominant litter sources. Q-mode analysis further resulted in the quantification of the litter sources; land-based ones provided the majority (69%) of the total litter items followed by vessel-based (26%) and fishery-based (5%) sources. Diverse environmental parameters influence significantly these amounts among the four Gulfs.     

Isotopic offsets in throughfall and stemflow may have small effects on estimates of winter precipitation fractions

Forest canopies alter the amount and isotopic composition of precipitation reaching the forest floor. Thus retention, evaporation and transport processes in forest canopies, and their effects on water isotopes, are key to understanding forest water cycling. Using a two-year isotope dataset from a mixed beech/spruce forest in Zurich, Switzerland, we assessed the isotopic offsets between precipitation, throughfall and stemflow. We also analysed how these offsets affect estimates of the fraction of soil water that is derived from winter precipitation. Throughfall was typically enriched in heavy isotopes compared to precipitation, but isotopically lighter than stemflow, with average δ²H of −64.3 ‰, −59.9 ‰ and − 56.3 ‰ in precipitation, throughfall and stemflow, respectively. The differences between beech and spruce were rather small compared to the seasonal differences in precipitation isotopes. Isotopic offsets between precipitation and throughfall/stemflow were smaller during the spring and summer months (March through August) than during fall and winter (September through February). Bulk and mobile soil waters at 10 and 40 cm showed smaller seasonal variations than those in precipitation, throughfall and stemflow, and were isotopically lighter than recent precipitation, with the largest offsets occurring during the summer months (June through August) for bulk soil waters. Thus, bulk soil waters at both depths contain a mixture of precipitation from previous events and seasons, with over-representation of isotopically lighter winter precipitation. Mobile soil waters were more similar to recent precipitation than bulk soil waters were. Throughfall isotopes were slightly heavier than precipitation isotopes, resulting in different sinusoidal fits for seasonal isotopic cycles in precipitation and throughfall. These differences lead to small underestimates in the fraction of soil water originating from winter precipitation, when open-field precipitation rather than throughfall is used as the input data. Together our results highlight the importance of isotope measurements in throughfall and stemflow for the assessment of precipitation seasonality and water cycling across forested landscapes.