Gravity anomalies and subsurface geology in the Westerwald volcanic area, Germany

The area of the present study constitutes an alkaline volcanic province in the eastern sector of the Rhenish massif. A series of gravity measurements were carried out on the volcanic fields of the Westerwald. Three-dimensional modelling and wavelength filtering processing techniques were used to analyze the gravity data. The filtered Bouguer anomaly maps show two major regional gravity features: (a) Increasing Bouguer values towards the northeastern part of the study area could be caused by lateral lithological variations within the upper crust. (2) Local negative Bouguer values in the southwest correlate with magmatic materials of intermediate type. The modelling results indicate that the volcanics of the Westerwald are underlain by two different magmatic complexes at a depth in the range 3.3–10 km with density values of 2680 and 2750 kg/m³. The densities assigned to the local igneous intrusions are in the range of 2314–2948 kg/m³ and at depths between 0.4 and 1.3 km. In the NE a diabase bed was modelled to a maximum depth of approximately 1.6 km using the assigned density of 2800 kg/m³.     

On laboratory studies of grains from outside the solar system

An overview is given of the identified surviving presolar grains in primitive meteorites. Two of these phases are discussed in more detail: (a) Presolar silicon carbide, with special emphasis on heavy element isotopic compositions which trace the slow neutron capture process (s-process) of nucleosynthesis. It is argued that there are problems either with the grain or neutron capture cross section data or with current basic understanding of heavy element nucleosynthesis, (b) Presolar diamonds, where new developments are discussed concerning the origin of the (supernova) Xenon-HL component thought to be contained within them; in addition, arguments are presented in favor of diverse carrier phases for the various Xe components observed in diamond separates.     

Geochemical demobilization of metallic pollutants in solid waste—implications for arsenic in waterworks sludges

During stabilization or demobilization of contaminants in solid waste materials, different approaches can be taken, which also can be combined: (1) sufficient long-term buffer capacity can be provided, according to the environmental conditions; (2) permeability for dissolved contaminants can be reduced by secondary mineral precipitations or by soft gels injected into the pore space of the waste body; and (3) new formations of ‘reservoir minerals' can incorporate potential pollutants in their internal structure. Emphasizing the geochemical engineering approach, two examples are presented from the field of water management, both focussing on the demobilization of arsenic species. The first example (after Driehaus, W., 1994. Arsenentfernung mit Mangandioxid und Eisenhydroxid in der Trinkwasseraufbereitung. Vol. 133, Ser. 15, VDI-Reports, Düsseldorf, 117 pp.) relates to the problems during purification of arsenic-rich raw water, suggesting the potential application of iron and manganese oxide minerals as oxidizing agents and mineral lattice structures for the elimination of arsenic. In the second example, contaminated sludges from water treatment plants were investigated for their leaching characteristics and long-term stability. A pH-stat test procedure was used to assess the leaching characteristics of metals at typical pH values. Due to the presence of iron and manganese oxides pentavalent arsenic is protected against conversion into the mobile trivalent form at neutral to low pH. Experimental data suggest that co-disposal with reducing organic matter and alkaline stabilization material or wastes could negatively influence the binding properties and, therefore, should be avoided.     

Transformation of phosphorus in the Elbe estuary

The distribution of dissolved and particle-bound phosphorus (P) was investigated in the Elbe estuary during March 1995. The forms of particulate P were studied with a sequential extraction technique. Organic P dominated particle-bound P in the outer reaches of the estuary (52%), decreased to a minimum of 21% in the turbidity zone, and increased to 33% further upstream. Fe-bound P was the second most important P species in the outer reaches (27%) and dominated in the turbidity zone (up to 57%) and upstream of the turbidity zone (up to 48%). The P:Fe ratio increased with decreasing salinity, from 0.11 in the outer reaches to about 0.22 at zero salinity. Dissolved inorganic P release from reverine suspended matter was about two to three times larger than release, from marine suspended matter and was dominated by release of Fe-bound P. Dissolved inorganic P release from marine and from riverine organic matter were of equal importance. Because marine suspended matter dominates in the estuary, this suggests riverine organic matter is remineralized much faster than marine organic matter. This is in line with the refractory nature of marine organic matter (no phytoplankton bloom) and the easily degradable character of the riverine suspended matter (phytoplankton bloom) in the Elbe estuary during March 1995.     

High Energetic Electrons Accelerated by a Coronal Shock Wave

Combined SOHO (Solar and Helisopheric Observatory) and ground based radio observations show evidently signatures of electrons accelerated by a shock wave during the event on July 9, 1996. A solar type II radio burst has been received as a signature of a coronal shock wave at 300 MHz on 9:10:54 UT. It was accompanied with electron beams appearing as type III radio bursts below 80 MHz. Simultaneously, the COSTEP (Comprehensive Suprathermal and Energetic Particle Analyzer) instrument aboard SOHO has measured enhanced electron fluxes in the range 30 keV – 3 MeV. This indicates that a coronal shock wave was able to produce high energetic electrons. A mechanism of electron acceleration up to relativistic velocities is presented and compared with the observations. The electron acceleration takes place at substructures of quasi-parallel collisionless shocks. This revised version was published online in July 2006 with corrections to the Cover Date.     

A wide-angle seismic traverse through the Variscan of southwest Ireland

A wide-angle seismic profile across the western peninsulas of SW Ireland was performed. This region corresponds to the northernmost Variscan thrust and fold deformation. The dense set of 13 shots and 109 stations along the 120  km long profile provides a detailed velocity model of the crust.
  The seismic velocity model, obtained by forward and inverse modelling, defines a five-layer crust. A sedimentary layer, 5–8  km thick, is underlain by an upper-crustal layer of variable thickness, with a base generally at a depth of 10–12  km. Two mid-crustal layers are defined, and a lower-crustal layer below 22  km. The Moho lies at a depth of 30–32  km. A low-velocity zone, which coincides with a well-defined gravity low, is observed in the central part of the region and is modelled as a Caledonian granite which intruded upper-crustal basement. The granite may have acted as a buffer to northward-directed Variscan thrusting. The Dingle–Dungarvan Line (DDL) marks a major change in sedimentary and crustal velocity and structure. It lies immediately to the north of the velocity and gravity low, and shows thickness and velocity differences in many of the underlying crustal layers and even in the Moho. This suggests a deep, pre-Variscan control of the structural development of this area. The model is compatible with thin-skinned tectonics, which terminated at the DDL and which incorporated thrusts involving the sedimentary and upper-crustal layers.     

Palaeomagnetism of the continental sector of the Cameroon Volcanic Line, West Africa

Measurement of samples from 154 sites in the continental sector of the Cameroon Volcanic Line yielded six palaeomagnetic poles, at 243.6°E, 84.6°N, α ₉₅ = 6.8°; 224.3°E, 81.2°N, α ₉₅ = 8.4°; 176.1°E, 82.0°N, α ₉₅ = 8.5°; 164.3°E, 86.4°N, α ₉₅ = 3.4°; 169.4°E, 82.6°N, α ₉₅ = 4.6° and 174.7°E, 72.8°N, α ₉₅ = 9.5°, belonging to rocks which have been dated by the K–Ar method at 0.4–0.9  Ma, 2.6  Ma, 6.5–11  Ma, 12–17  Ma, 20–24  Ma and 28–31  Ma, respectively. The results are in general agreement with other palaeomagnetic poles from Oligocene to Recent formations in Africa.
  The first three poles for rocks formed between 0.4 and 11  Ma are not significantly different from the present geographical pole. Together with other African poles for the same period, this suggests that the African continent has moved very little relative to the pole since 11  Ma. The other three poles for rocks dated between 12 and 31  Ma are significantly different from the present geographical pole, showing a 5° polar deviation from the present pole in the Miocene and 13° in the Middle Oligocene.     

Strain localization mechanisms in deep-seated layered rocks

More than 160 shear zones of the Norwegian Caledonides and Italian Southern Alps, formed under high-temperature or high-pressure conditions, are analysed with respect to mechanisms of strain localization. In metabasic rocks with a pre-existing (magmatic) layering strain localizes preferentially in mafic layers, although experiments in monomineralic rocks would predict a location in the weaker feldspar-rich layers. In addition, in some of these zones amphibole recrystallizes dynamically, whereas feldspars only show undulatory extinction. These are evidences for strength inversion between feldspars and mafic minerals. This inverse strength behaviour is caused by a reduced grain size of feldspars and sometimes amphiboles in the pre-existing mafic layers, i.e. prior to shearing. The localization of the shear zones is therefore a grain-size-sensitive process (grain-size-dependent softening), nearly independent of the composition of the deformed material. The numerous amphibole–amphibole contacts favour dynamical recrystallization by grain-boundary migration and the rare feldspar–feldspar contacts prevent or suppress the same process in feldspars. Therefore, the feigned inverse strength is mainly caused by the interaction of reduced grain size and grain-boundary effects in the original rock. This behaviour can lead to the preferential localization of shear zones in mafic layers, although they are not favourably oriented with respect to the stress system.     

Profiles and simulated exchange of H2O,O3, NO2 between the atmosphere and the HartX Scots pine plantation

Summary Vertical profiles of H₂O, CO₂, O₃, NO and NO₂ were measured during the Hartheim Experiment (HartX) to develop and calibrate a multi-layer resistance model to estimate deposition and emission of the cited gaseous species. The meteorological and gas concentration data were obtained with a 30 m high telescopic mast with 7 gas inlets located at 5 m intervals and meteorological sensors at 5, 15 and 30 m above ground; a complete gas profile was obtained every 9 min 20 s. Measured profiles were influenced by several exchange processes, namely evapotranspiration, dewfall, assimilation of CO₂ in the tree crowns, soil respiration, deposition of NO₂ and O₃ to the soil and advection of NO_x from the nearby highway. Surprisingly, no decrease in O₃ concentration was observed in the crown layer during daytime, probably due to the relatively low density of foliage elements and strong turbulent mixing.The advantage of measuring in-canopy profiles is that turbulent exchange coefficients need not be estimated as a prerequisite to obtaining vertical flux estimates. In recent years, flux-gradient relationships in canopies have been subject to many criticisms. If fluxes are calculated at several heights considering only the transfers between the turbulent air and the interacting surfaces at a certain height, and those fluxes are then integrated vertically in a subsequent step, then exchange estimates (deposition or emission) can be obtained independent of turbulent exchange conditions.Typical estimated deposition velocities calculated for a 3-day period are between 4 and 10 mm/s for NO₂ and about 4–9 mm/s for O₃ (day and night values respectively). This leads to deposition rates of about 20–40 ng N/m²s for NO₂ and about 30–40 mg O₃/m² deposited daily under the conditions encountered during HartX. Sensitivity tests done with the best available and most realistic values for model parametrization have shown that sensitivity is large with respect to the soil and cuticula resistances as well as for gas-phase ozone destruction and that more research is required to describe the effectiveness of cuticula and soil in modifying sink characteristics for NO₂ and O₃.With 12 Figures