Cs137 gamma-ray absorption in eclogites

Summary The coefficient of the gamma-ray absorption _Cs ¹³⁷ investigated in eclogites of the Bohemian Massif varies with fresh samples from0.2477 cm ^–1 to 0.2804 cm ^–1 . Symplectite is the main factor decreasing the value of down to0.242 cm ^–1 . On the contrary, the coefficient increases with the increasing content of clinopyroxene and especially of garnet. The linear dependence of the coefficient on the density may be expressed by the equation =0.0682+0.028.     

Si in the core? New high-pressure and high-temperature experimental data

High-pressure high-temperature experiments have been carried out up to 25 GPa and 2200°C in a multianvil press on assemblages made of silicates and iron-silicon alloys. At 20 GPa, silicon is extracted from the metal phase, forming stishovite reaction rims around metal grains. The silicon content in metal has been measured by analytical electron microscopy and electron microprobe. In contrast with earlier experiments, the present data were obtained by using silicon-rich metal alloys as starting materials instead of studying incorporation of silicon in initially silicon-free metal. As in most of previous studies carried out below 25 GPa, the silicon content in liquid metal increases with increasing pressure and with decreasing oxygen fugacity. The oxygen fugacity in most experiments was calculated by using two independent buffers: iron/?stite (IW) and SiO₂/Si, allowing to link consistently the Fe contents in silicates, the Si contents in metal and the temperatures of the experiments. At oxygen fugacities 4 log units below IW, silicates are in equilibrium with Si-rich metallic alloys (up to 17 wt% of Si in metal at 20 GPa and 2200°C). Extrapolation to 2 log units below IW leads to less than 0.1 wt% Si in the metal phase. Presence of several wt% of silicon in the Earth’s core thus requires highly reduced initial materials that, if equilibrated at conditions relevant to small planets, should already contain significant amount of silicon dissolved in metal.     

A New Mapping Protocol for Laser Ablation (with Fast-Funnel) Coupled to a Time-of-Flight Mass Spectrometer (LA-FF-ICP-ToF-MS) for the Rapid,Simultaneous Quantification of Multiple Minerals

Although in situ analysis by LA-ICP-MS is considered a rapid technique with minimal sample preparation and data reduction, mapping areas of millimetres in size using a small beam (< 15 μm) can be time consuming (several hours) when a quadrupole ICP-MS is used. In addition, fully quantitative imaging using internal standardisation by LA-ICP-MS is challenging in samples with more than one mineral phase present due to varying ablation rates. A new protocol for the quantification of multiple coexisting phases, mapped at a rate of about 12 mm² h^-1 and a resolution of 12 μm × 12 μm per pixel, is presented. The protocol allows mapping of most atomic masses, ranging from ²³Na to ²³⁸U, using a time-of-flight mass spectrometer (ICP-ToF-MS, TOFWERK) connected to a 193 nm excimer laser. A fast-funnel device was successfully used to increase the aerosol transport speed, reducing the time usually required for mapping by a factor of about ten compared with a quadrupole ICP-MS. The lower limits of detection for mid and heavy masses are in the range 0.1–10 μg g^-1, allowing determination of trace to ultra-trace elements. The presented protocol is intended to be a routine analytical tool that can provide greater access to the spatial distribution of major and trace elements in geological materials.     

Triploporella ? edgelli n. sp., a new Dasycladalean alga from the Lower Cretaceous of Lebanon

The Dasycladalean assemblage of the Jezzinian strata (uppermost Barremian–lowermost Aptian) of Lebanon consists of two organo‐genera and eight genera with eleven species, including eight Triploporellaceae. Although Triploporella marsicana (Praturlon, 1964) was reported by Saint‐Marc from the same interval, it is not found in our material. However, a lookalike, which is herein described as Triploporella ? edgelli n. sp., is identified. This new species has cyst‐containers within the primary segments of its laterals but, because it lacks calcified secondary segments, it is left in open nomenclature.     

The effects of longitudinal variations in valley geometry and wood load on flood response

We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m³ ha⁻¹. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m³ ha⁻¹. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd.     

Compositional evolution of grossular garnet from leucotonalitic pegmatite at Ruda nad Moravou, Czech Republic; a complex EMPA, LA-ICP-MS, IR and CL study

Five distinct paragenetic, morphological and compositional types of grossular garnet (G1, G2, G3, G4, G5) were distinguished within the individual (sub)units of the zoned leucotonalitic pegmatite cutting serpentinized lherzolite with rodingite dikes at ??ár near Ruda nad Moravou, Staré Město Unit, Northern Moravia. Detailed study using Electron Microprobe Analysis, Laser Ablation Inductively Coupled Plasma Mass Spectrometry, Cathodoluminiscence and Infrared Spectroscopy revealed distinct compositional trends in major, minor and trace elements. The contents of Fe³⁺, Mn, Mg and Ti increase from early garnet (G1) in the outermost grossular subunit through the interstitial garnet (G2) in the leucocratic subunit to graphic intergrowths of quartz+garnet (G3) in the coarse-grained unit. Then these constituents decrease in inclusions of garnet (G4) from the blocky unit and large crystals of garnet (G5) from the quartz core. Some trace elements (V, Ni, Y) exhibit the same trends, only Be evidently increases in garnet from border zone to the centre. Fluorine has negative correlation with Fe³⁺ as well as some trace elements (Ta, Pb). Concentrations of H₂O in garnets, up to 0.22 wt.% H₂O, are comparable with spessartine-almandine garnets from the Rutherford No. 2 pegmatite, Virginia, and grossular garnets from high-temperature calc-silicate rocks (skarns). Water contents correlate positively with Fe³⁺, but inversely with F. The use of water contents in garnet to elucidate the fluctuations of activity of H₂O during the pegmatite formation is only limited; the incorporation of hydrous defects seems to be controlled instead by crystal-structural constraints. However, the sum of all volatile components (H₂O + F) increases about twice from the outermost subunit to the centre of the pegmatite body.     

Exploring and Visualizing Stakeholder Value Regimes in the Context of Peri-Urban Park Planning

Abstract

Peri-urban zones are an emerging issue in the analysis of urban areas as social-ecological systems. This work presents a process of developing support tools for local planning and decision-making, which were used to facilitate discussion between stakeholders about planning a future peri-urban park in the south of Prague, Czech Republic. Sociological methods were employed to describe and visualize the attitudes, communication patterns and value regimes of involved stakeholders. The research developed and tested an approach to map the distribution of stakeholder value regimes related to the study area and demonstrated its capability in facilitating communication between stakeholders. The output maps can serve as practical support tools and provide efficient means during the search for consensus on a form of shared governance in the future peri-urban park.