Solar neutrino measurement with the radiochemical gallium detector (GALLEX)

The GALLEX experiment for the detection of solar neutrinos by means of a radiochemical gallium detector is operated by groups from Italy, France, Germany, Israel and the USA in the Gran Sasso underground laboratory (LNGS) near L'Aquila (Italy). It consists of (i) the technical scale tank made of glass fiber reinforced polyester fabric containing 101 tonnes (54 m³) of a highly concentrated (8 moll^–1) GaCl₃ solution; (ii) a gas sparging system for desorption of GeCl₄ which has been formed by interaction of the neutrinos with gallium according to⁷¹Ga + _e ⁷¹Ge + e^– and by addition of ca. 1 mg of a stable Ge isotope; (iii) the absorption columns for concentration of GeCl₄ into a volume of 1 l of water; (iv) the laboratory scale apparatus for conversion of GeCl₄ to GeH₄ and mixing with the counting gas Xe; (v) the counter filling station, and (vi) the low level proportional counters.Contributions of possible side reactions which have to be corrected for, e.g. by cosmic muons, fast neutrons and-emitters are discussed, as well as the purification of the target solution from long-lived (t _1/2 = 271 d) cosmogenic⁶⁸Ge. A first preliminary result after one year of solar neutrino measurement is presented. This constitutes the first direct measurement of the basic proton-proton fusion reaction in the core of the sun. This result, appreciably below the predictions of the standard solar model (SSM) (132 SNU) can be interpreted, together with the results of the chlorine and KAMIOKANDE experiments either by astrophysics or by neutrino oscillations (MSW effect). The solar neutrino measurements are continuing and a calibration experiment with a⁵¹Cr source is in preparation.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9–13 November, 1992.for the GALLEX Collaboration: P. Anselmann, W. Hampel, G. Heusser, J. Kiko, T. Kirsten, E. Pernicka, R. Plaga, U. Ronn, M. Sann, C. Schlosser, R. Wink, M. Wojcik (Max Planck Institut fur Kernphysik, Heidelberg); R. v. Ammon, K.H. Ebert, T. Fritsch, K. Hellriegel, E. Henrich, L. Stieglitz, F. Weirich (Kernforschungszentrum Karlsruhe, Institut für Heisse Chemie); M. Balata, E. Bellotti, N. Ferrari, H. Lalla, T. Stolarczyk (INFN-Laboratori Nazionali del Gran Sasso); C. Cattadori, O. Cremonesi, E. Fiorini, S. Pezzoni, L. Zanotti (Universita di Milano und INFN); F. von Feilitzsch, R. Mößbauer, U. Schanda (TU München, Garching); G. Berthomieu, E. Schatzman (Observatoire Nizza); I. Carmi, I. Dostrovsky (Weizman Institut, Rehovot); C. Bacci, P. Belli, R. Bernabei, S. d'Angelo, L. Paoluzi (Universita di Roma und INFN); S. Carbit,M. Cribier, G. Dupont, L. Gosset, J. Rich, M. Spiro, C. Tao, D. Vignaud (CEN Saclay); R.L. Hahn, F.X. Hartmann, J.K. Rowley, R.W. Stoenner, J. Weneser (Brookhaven National Laboratory).     

Ion tracks in apatite at high pressures: the effect of crystallographic track orientation on the elastic properties of fluorapatite under hydrostatic compression

Static elasticity measurements at high pressures were carried out on oriented fluorapatite single crystals, some of which contained oriented amorphous ion tracks (ITs) implanted with relativistic Au ions (2.2 GeV) from the UNILAC linear accelerator at GSI, Darmstadt. High-pressure experiments on irradiated and non-irradiated crystal sections were carried out in diamond-anvil high-pressure cells under hydrostatic conditions. In situ single-crystal diffraction was performed to determine the high-precision lattice parameters, simultaneously monitoring the widths of X-ray diffraction Bragg peaks. High-pressure Raman spectra were analyzed with respect to the frequency shift and widths of bands, which correspond to the Raman-active vibrational modes of the phosphate tetrahedra. Swift heavy ion irradiation was found to induce anisotropic lattice expansion and tensile strain within the host lattice dependent on the ion-track orientation. The relatively low Grüneisen parameter for the ν _1b(A _g) mode, which has been assigned to originate from the volume fraction of the amorphous tracks, and the γ(ν _1a)/γ(ν _1b) ratio reveals compressive strain on the amorphous ITs. The comparative compressibilities for the host lattice reveal approximately equivalent bulk moduli, but significantly different pressure derivatives (K _T = 88.4 ± 0.7 GPa, ∂K/∂P = 6.3 ± 0.3 for non-irradiated, K _T = 90.0 ± 1.7 GPa, ∂K/∂P = 3.8 ± 0.5 for irradiated samples). The axial compressibility moduli β ⁻¹ reveal significant differences, which correlate with the ion-track orientation [b_a ^{- 1} \beta_{a}^{ - 1}  = 240 ± 5 GPa, b_c ^{- 1} \beta_{c}^{ - 1}  = 361 ± 14 GPa, ∂( b_a ^{- 1} ) \left( {\beta_{a}^{ - 1} } \right) /∂P = 11.3 ± 1.2, ∂( b_c ^{- 1} ) \left( {\beta_{c}^{ - 1} } \right) /∂P = 11.6 ± 3.4 for irradiation ⊥(100); 246 ± 9 GPa, 364 ± 57 GPa, 9.5 ± 2.9, 14.7 ± 14.1 for irradiation ⊥(001), 230.7 ± 3.6 GPa, 373.5 ± 5.1 GPa, 19.2 ± 1.4, 20.1 ± 1.8 for no irradiation]. Line widths of XRD Bragg peaks in irradiated apatites confirm the strain of the host lattice, which appears to decrease with increasing pressure. By contrast, the bandwidths of Raman modes increase with pressure, and this is attributed to increasing strain gradients on the length scale of the short-range order. The investigations reveal considerable deviatoric stress on the [100]-oriented tracks due to the anisotropic elasticity, while the compression is uniform for the directions perpendicular to the tracks, which are aligned parallel to the c-axis. This difference might be considered to control the diffusion properties related to the annealing kinetics and its observed anisotropy, and hence to cause potential pressure effects on track-fading rates.     

Late Palaeozoic red beds elucidate fluvial architectures preserving large woody debris in the seasonal tropics of central Pangaea

Fluvial red beds containing anatomically preserved large woody debris shed new light on seasonally dry biomes of the Pennsylvanian–Permian transition and elucidate the concurrence of river depositional systems and vegetation. As a result, the occurrence, distribution and preservation of petrified large woody debris accumulations are considered crucial to understanding the role of arborescent vegetation in shaping fluvial environments. This study reports sizeable silicified trunks and corresponding fluvial architectures from the uppermost Pennsylvanian (upper Gzhelian) Siebigerode Formation (Kyffhäuser, central Germany). The origin, taphonomy and depositional environment of the fossil woods are elucidated by using a multidisciplinary approach including geological mapping, lithofacies analysis, sediment petrography, wood anatomical studies and microstructure analyses. Results reflect the gradual burial of a gentle basement elevation by sand-bed to gravel-bed braided rivers at the north-western margin of the perimontane Saale Basin. Facies architectures resulted from a complex interplay of syndepositional tectonics, repeated palaeorelief rejuvenation, high-frequency channel avulsion, seasonally dry climate and woody debris–sediment interactions. The alluvial influx and cut-bank erosion recruited trunks from adjacent semi-riparian slope habitats vegetated by up to 40 m tall cordaitaleans and conifers. High discharge in wide braids facilitated uncongested transport of large woody debris. Trunk entombment and initial preservation resulted from grounding on barforms, anchoring by attached roots and subsequent burial. The post-depositional two-phase silicification was influenced by hydrothermal hematite mineralization and determined a selective wood preservation pattern known as ‘pointstone’. Large woody debris-induced sedimentary structures (‘LWDISS’) are introduced as a class of sediment structures formed by the biogenic impact on terrestrial deposition.     

New measurement of melting and thermal conductivity of iron close to outer core conditions

The amount of literature on both melting and thermal conductivity of iron at Earth’s core conditions is overwhelming and the discrepancies are very large.There is a broad range of experimental techniques each of which is flawed to a certain degree,which may explain the discrepancy.In this report,we present new data using a different method for determining the phase behavior and resistivity of iron in the laser-heated diamond cell by measuring the electrical resistance of both solid and liquid iron wires.The experiment avoids some of the major flaws of previous experiments,the most important of which is the detection of the onset of melting.These measurements confirm a shallow melting curve found earlier and the resistivity data imply a trend towards low thermal conductivity in the liquid outer core.     

Seasonal climate inferences from high-resolution modern diatom data along a climate gradient: a case study

This study represents a step towards developing seasonal climate inferences by using high-resolution modern data sets. The importance of seasonal climate changes is highlighted by the instrumental record of a meteorological station close to our study site (lac du Sommet in the Laurentian Mountains, Québec, Canada): Between 1966 and 2001, May temperatures increased significantly by 3.1°C (r = 0.41, n = 35, p < 0.01) but annual mean temperatures only by 0.6°C (r = 0.21, n = 35, p > 0.05). Comparison of this instrumental record with fossil diatom assemblages in a sediment core from lac du Sommet showed that axis one of a principal component analysis (PCA) of the fossil diatoms was best correlated with wind velocity in June (r = 0.62, n = 19, p < 0.005) and that past diatom production was significantly enhanced in periods with colder July temperatures (r =  ?0.77, n = 19, p < 0.0005) and higher wind velocity in June (r = 77, n = 19, p < 0.0005). The strong impact of the spring and summer conditions on overall diatom composition and productivity suggests that seasonal lake responses to climate are more important than annual mean temperatures. However, the seasonal dynamics of diatom communities are not well understood, and seasonality is rarely inferred effectively from lake sediment studies. Our research presents a pilot study to answer a twofold question: Is it possible to identify diatom communities which are typical for warmer or colder seasonal climate using sediment traps, and if it is, can this knowledge be used to infer seasonal climate conditions from fossil diatom assemblages? To address these questions, the seasonal dynamics of diatom communities and water chemistry were studied using sediment traps and water samples at biweekly intervals in four lakes distributed along an altitudinal gradient in the Laurentian Mountains from May through October 2002. Date of ice break-up was significantly related to the diatom assemblages taken in spring and uncorrelated to other significant environmental variables. Summer water temperature, circulation of the water column and pH explained a significant part of the biological variance in summer, and total nitrogen (TN) explained most of the biological variance in autumn. To infer these variables, weighted averaging partial least squares models were applied to the seasonal data sets. Inferred ice break-up dates were significantly correlated with number of days below 0°C in April (r = 0.52, n = 19, p < 0.025), inferred circulation of the water column was significantly related to measured wind velocity in June (r = 0.64, n = 19, p < 0.005), inferred summer water temperature and inferred pH was significantly related to measured July air temperature (r = 0.50, r =  ?53, n = 19, p < 0.025) and inferred TN autumn concentrations had an inverse relationship to August temperatures (r =  ?0.53, n = 19, p < 0.01). This comparison of the historical record with diatom-inferred seasonal climate signals, based on the comparison of fossil diatom assemblages with modern sediment trap data of high temporal resolution, provides a promising new approach for the reconstruction of seasonal climate aspects in paleolimnological studies.     

Oxygen-18 enrichment in the water of a clathrate hydrate

The equilibrium constants for the fractionation of H₂¹⁸O and H₂¹⁶O between liquid and solid phases were determined by slow freezing of ice and by slow formation of the clathrate hydrate of tetrahydrofuran from liquid solution. Both systems gave α = 1.0026₈. It is likely that oxygen-18 enrichment of the water in clathrate hydrates generally is essentially the same as for ice and that the relatively high oxygen-18 content observed in pore waters from some deep-sea sediments arises from the recent presence of methane hydrate.     

Precambrian basement complexes in the North-Central Scandinavian Caledonides and their pre-Caledonian tectonic evolution

Precambrian basement lithology, as exposed in four tectonic windows of the northcentral Scandinavian Caledonides, comprises uniform sequences of metasedimentary mica schists and gneisses (Børgefjell) as well as mica schists dominated by acid metavolcanics (Bångonåive) with minor basic rocks. The major part, however, is made up of intrusive rocks. Older granites are distributed in the Børgefjell area and to the east of it, obviously related to the Svecofennian Revsund granites. Younger granodiorites/quartzsyenites, subordinate in the Børgefjellet, dominate the Bångonåive window. The Bångonåive area may be tentatively correlated with the Skellefte field, the Børgefjellet with the marine basin of Central Norrland. The younger intrusives may represent marginal parts of a post-Svecofennian orogen farther west. Caledonian deformation considerably affected the Precambrian basement in the tectonic windows, where pre-Caledonian features are only preserved in the innermost parts. A (pre-Caledonian) polyphase structural and metamorphic evolution is evident in both the Børgefjell and Bångonåive windows. Penetrative deformation and medium (?) grade metamorphism prior to acid intrusions were overprinted during succeeding lower grade phases.     

Subduction of continental margins and the uplift of high-pressure metamorphic rocks

The mechanism by which high-pressure metamorphosed continental material is emplaced at high structural levels is a major unsolved problem of collisional orogenesis. We suggest that the emplacement results from partial subduction of the continental margin which, because of its high flexural rigidity, produces a rapid change in the trajectory of the descending slab. We assume a two-fold increase in effective elastic thickness of the lithosphere as the continental margin approaches the subduction zone, and calculate the flexural profile of a thin plate for progressive downward migration of the zone of increased rigidity. We assess the effect of changes in the flexural profile on the overlying accretionary prism and mantle wedge as the continent approaches by estimating the extra stresses that are imposed on the wedge due to the bending moment exerted by the continental part of the plate. The wedges overlying the subduction zones, and the subducting slab itself, experience substantial extra compressional stress at depths of around 100 km, and extensional stress at shallower depths, as the continental margin passes through the zone of maximum curvature. The magnitudes of such extra stresses are probably adequate to effect significant deformation of the wedge and/or the descending plate, and are experienced in a time interval of less than 5 m.y. for typical subduction rates. The spatial variation of yield stresses in the region of the wedge and descending slab indicates that much of this deformation may be taken up in the crustal part of the descending slab, which is the weakest region in the deeper parts of the subduction zone. This may result in rapid upward migration of the crust of the partially subducted continental margin, against the flow of subduction. High-pressure metamorphosed terranes emplaced by the mechanism envisaged in this paper would be bounded by thrust faults below and normal faults above. Movement on the faults would have been coeval, and would have resulted in rapid unroofing of the high-pressure terranes, synchronous with arrival of the continental margin at the subduction zone and, therefore, relatively early in the history of a collisional orogen.