Controls on the chemistry of runoff from an upland peat catchment

This study uses 2 years of data from a detailed weekly water sampling programme in a 11·4 km² upland peat catchment in the Northern Pennines, UK. The sampling comprised precipitation, soil‐water samples and a number of streams, including the basin outlet. Samples were analysed for: pH, conductivity, alkalinity, Na, K, Ca, Mg, Fe, Al, Total N, SO₄, Cl and colour. Principal component analysis (PCA) was used to identify end‐members and compositional trends in order to identify controls on the development of water composition. The study showed that the direct use of PCA had several advantages over the use of end‐member mixing analysis (EMMA) as it combines an analysis of mixing and evolving waters without the assumption of having to know the compositional sources of the water. In its application to an upland peat catchment, the study supports the view that shallow throughflow at the catotelm/acrotelm boundary is responsible for storm runoff generation and shows that baseflow is controlled by cation exchange in the catotelm and mixing with a base‐rich groundwater. Copyright © 2003 John Wiley & Sons, Ltd.     

Observations of the supernova 1985F with a new spectrograph

We present the spectrum of the supernova 1985F over the wavelength range 4600 to 10000 Å as recorded in one 200 s exposure on 16 May, 1985, when its age was estimated to bet240 days. This wideband measurement with a resolution of 20 Å was made with the new Faint Object Spectrograph on the Isaac Newton Telescope (INT) at the Observatorio del Roque de los Muchachos. Broad line features were observed for the ionsOi,Oii, andOiii, Caii, and Nai although broad H was noteably absent. This suggests type I rather than type II properties but Filippenko and Sargent (1985c) have concluded this object to be of neither type and of a new peculiar class. We have observed the Caii infra-red triplet at 8600 Å which has not been previously reported in the spectrum of SN1985F and alsoCi] at 9800 Å.     

The impact of wave loads and pore-water pressure generation on initiation of sediment transport

The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported.     

Crustal xenoliths from Calbuco Volcano,Andean Southern Volcanic Zone: implications for crustal composition and magma-crust interaction

Crustal xenoliths in the 1961 andesite flow of Calbuco Volcano, in the southern Southern Volcanic Zone (SSVZ) of the Andes, consist predominantly of pyroxene granulites and hornblende gabbronorites. The granulites contain plagioclase+pyroxene+magnetite±amphibole, and have pronounced granoblastic textures. Small amounts of relict amphibole surrounded by pyroxene-plagioclase-magnetite-glass symplectites are found in some specimens. These and similar textures in the gabbronorites are interpreted as evidence of dehydration melting. Mineral and bulk rock geochemical data indicate that the granulites are derived from an incompatible trace element depleted basaltic protolith that underwent two stages of metamorphism: a moderate pressure, high temperature stage accompanied by melting and melt extraction from some samples, followed by thermal metamorphism after entrainment in the Calbuco andesite lavas. High _Nd ^T values (+4.0 to +8.6), Nd-isotope model ages of 1.7–2.0 Ga, and trace element characteristics like chondrite normalized La/Yb< and La/Nb1 indicate that the protoliths were oceanic basalts. Similar oceanic metabasalts of greenschist to amphibolite facies are found in the Paleozoic metamorphic belt that underlies the Chilean coastal ranges. Mineral and bulk rock compositions of the gabbronorite xenoliths indicate that they are cognate, crystallizing from the basaltic andesite magma at Calbuco. Crystallization pressures for the gabbros based on total Al contents in amphibole are 6–8 kbar. These pressures point to middle to lower crustal storage of the Calbuco magma. Neither granulite nor gabbro xenoliths have the appropriate geochemical characteristics to be contaminants of Calbuco andesites, although an ancient sedimentary contaminant is indicated by the lava compositions. The presence of oceanic metabasaltic xenoliths, together with the sedimentary isotopic imprint, suggests that the lower crust beneath the volcano is analogous to the coastal metamorphic belt, which is an accretionary complex of intercalated basalts and sediments that formed along the Paleozoic Gondwanan margin. If this is the case, the geochemical composition of the lower and middle crust beneath the SSVZ is significantly different from that of most recent SSVZ volcanic rocks.     

Emplacement age and thermal footprint of the diamondiferous Ellendale E9 lamproite pipe, Western Australia

The diamondiferous Ellendale 9 (E9) pipe is a funnel-shaped maar-diatreme volcano consisting of inward-dipping tuff sequences intruded by lamproite plugs and dykes. The host rocks for the E9 pipe are Permian sandstones. The multiple lithological contacts exposed within the mined maar volcano provide a natural laboratory in which to study the effect of volcanic processes on U–Th–Pb–He systematics. Zircon from the regional sandstone and E9 lamproite display a bimodal distribution of ages on (U–Th)/He–U/Pb plots. The zircon U/Pb ages for the E9 pipe (n?=?52) range from 440 to 2,725 Ma, while the cluster of (U–Th)/He ages for the lamproite dyke zircon indicate that dyke emplacement occurred at 20.6?±?2.8 Ma, concordant with a maximum emplacement age of about ≤22 Ma from phlogopite ⁴⁰Ar/³⁹Ar. These ages indicate a xenocrystic origin for the zircon entrained in the E9 dyke. The U/Pb ages of detrital zircon from the regional sandstone host (373–3,248 Ma; n?=?41) are indistinguishable from those of the lamproite zircon xenocrysts, whereas the detrital zircon in the host sandstone yield (U–Th)/He ages from 260 to 1,500 Ma. A thermochronology traverse across the E9 lamproite dyke reveals that the zircon (U–Th)/He ages in the host sandstone have not been significantly thermally reset during dyke emplacement, even at the contact. The capability of the zircon (U–Th)/He method to distinguish deep, mantle source lithologies from upper crustal source lithologies could be used in geochemical exploration for diamonds. Pre-screening of detrital samples using etching and helium assay methods will improve the efficiency and decrease the cost of greenfields exploration.     

The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter

In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 ±0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 ±2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.     

Stress deformation properties of rock and rock discontinuities

The results of an extensive literature survey on the stress deformation properties of rock materials and rock discontinuities are summarized. The results show that: (1) for rock tested under uniaxial conditions, the range of modulus is from about 1 to 100 GN/m², and the Poisson's ratio range is from 0.02 to 0.73 (0.46 if dilatant values are excluded) with an average value of 0.20; (2) for rock tested under triaxial conditions, the effects of nonlinearity and stress-dependency of the rock modulus are minor with hard, crystalline or homogeneous rock of low porosity, but are significant in porous, clastic or closely jointed rock; (3) anisotropy of the rock modulus is demonstrated mainly by variations in the modulus number or initial stiffness, while the nonlinearity and stress-dependency parameters are fairly constant with sample orientation; (4) nonlinearity and stress-dependency of the rock Poisson's ratio may be significant depending upon the magnitude of stress changes imposed, with the nonlinearity being more significant; and (5) limited data on rock discontinuities indicate that nonlinearity and stress-dependency effects may be quite large.     

Simulations of deep pencil-beam redshift surveys

We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω₀=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130  h ⁻¹ Mpc observed by Broadhurst et al. has a priori probability well below 10⁻³.