Rare earth evidence concerning the origin of granites of the Isle of Skye,northwest Scotland

Eleven samples of Skye granites, two samples of Torridonian sandstone and one sample of Lewisian gneiss have been analysed for ten rare earth elements (REE) by neutron activation analysis. The granites are representative of the main granite centres and compositional types. All granites have sub-parallel light-REE-enriched patterns with chondrite-normalised Ce(Ce_N) = 78–263,Yb_N = 16–60and Ce_N/Yb_N = 2.9–8.0. REE patterns for the Lewisian gneiss and Torridonian sandstone are similar to each other, withCe_N = 32–61,Yb_N = 3–5and Ce_N/Yb_N = 8–18. These two rock types as well as the Glamaig granite have negligible Eu anomalies (Eu/Eu* > 0.9), and the other granites have Eu/Eu* in the range 0.83-0.34. The REE evidence suggests that Lewisian gneiss or Torridonian sandstone arenot suitable materials from which the granites could be derived by partial melting. The Western Red Hills granite intrusions show a systematic relation of REE content with Eu/Eu*. We suggest that the Glamaig granite is the most primitive, and was derived from a source with no Eu anomaly by fractional crystallization of a more basic magma. The later Western Red Hills granites might then have resulted from further fractional crystallization of magma with a composition like that of the Glamaig granite. The Coire Uaigneich and Eastern Red Hills granites may also be products of fractional crystallization, but from different magmas to those parental to the Western Red Hills granites. The basaltic parent magmas of the Skye granites may be “continental” tholeiites derived by interaction of basalt magma with Lewisian gneiss.     

ISO Best Practices in Reference Material Certification and Use in Geoanalysis

The International Organisation for Standardisation (ISO) has published many guides, or technical standards, of great value to analytical geochemists. Two of particular importance are Guide 33 (Uses of Certified Reference Materials) and Guide 35 (Certification of Reference Materials). Both were first developed in the 1980s and undergo regular review and updating by the Reference Materials Committee (REMCO) that operates within ISO. Recent revisions have focused on adding statistical rigour to both guides. Although this offers significant advantages for use by professional metrologists, there are consequent issues of comprehension by the analytical chemists who in fact have the greatest need of them. A major focus of Guide 35 is the development of reference material uncertainties that are in full compliance with the Guide on Measurement Uncertainty (GUM), jointly issued by ISO, IUPAC and others. Guide 35 details handling of uncertainty due to (1) degradation on the shelf and in transport, (2) sample heterogeneity and (3) inter‐method and inter‐laboratory bias, as well as within‐laboratory repeatability. The International Association of Geoanalysts has developed a protocol for reference material certification that applies Guide 35 to the specific needs of the geoanalytical community. The approach being taken by the IAG in developing GUM‐compliant uncertainties for its certified values is presented. Recommendations made in Guide 33 for how a laboratory should compare its own results with certified values in assessing laboratory accuracy are outlined. Additionally, the subject of misusing reference materials is discussed. The apparent misuse occurs because so few CRMs exist that meet critical measurement needs of geoanalytical laboratories and that also meet the rigorous metrological demands of the latest editions of the ISO Guides. All of the focus of the IAG certification programme has been to undertake certifications that would fill gaps in CRM availability and thus serve to limit this misuse.     

GeoPT2. International Proficiency Test for Analytical Geochemistry Laboratories - Report on Round 2

Results from sixty laboratories participating in GeoPT2, the international proficiency testing programme for analytical geochemistry laboratories, are reported. Compared with 71.3% in the last round, 74.6% of the reported data complied with the laboratories' selected fitness for purpose criteria.     

GeoPT5. An International Proficiency Test for Analytical Geochemistry Laboratories - Report on Round 5

Results are presented from the seventy two laboratories participating in GeoPT5, round five of the international proficiency testing programme for analytical geochemistry laboratories. The sample for round five, AMH-1 (Mount Hood andesite), was distributed during March 1999 and participating laboratories were asked to analyse the sample using their routine techniques and submit results to the steering by 15th June 1999. In this report, contributed data are listed together with the derived z-scores from which participating laboratories can assess their analytical performance. Z-scores in the range -2 to 2 are considered satisfactory. Z-score values that lie outside this range may indicate unsuspected analytical bias. The distinctive feature of the present round is that AMH-1 is a candidate reference material prepared by the USGS and it is intended that the present proficiency testing data will contribute to the reference material characterisation programme.     

Rare earth element mobility during granite alteration: Evidence from southwest England

Geochemical analyses of granitic rocks from southwest England reveal that the rare earth elements (REE) were potentially mobile during hydrothermal and supergene alteration. In particular, trivalent REE were removed from the system during K-silicate alteration, Eu was lost during sericitic alteration; all REE were lost during tourmalinization, and light REE were lost during chloritization and argillic alteration. The fluids themselves had low concentrations of REE; in only one case (chloritization) were heavy REE introduced during alteration. Analysis of separated minerals indicated that the behaviour of the REE could be partly explained in terms of their different affinities for the primary and secondary assemblages. Thermodynamic calculations indicated that REE mobility is enhanced by the presence of fluorine in the alteration fluids partly because REE form more stable complexes with F than with Cl and partly because elements such as Ti, Zr and P that form REE-bearing minor phases are themselves potentially mobile.     

Numerical simulation of evapotranspiration using a root water uptake model

The abstraction of ground water by vegetation and its influence on the behaviour of geotechnical structures such as pavements, foundations and slopes has been researched for many years. In recent years, the use of numerical methods in geotechnical engineering has rapidly increased. A major challenge for numerical modelers involves the specification of the surface flow boundary condition to model root water uptake by vegetation. The abstraction of ground water by roots is a complex process which involves the interaction of the atmosphere, vegetation and the ground. Accurate prediction of the pore water pressure changes induced by vegetation requires the development of algorithms which can mimic the process of transpiration by vegetation in the continuity equation of fluid flow. This paper presents a root water uptake model which has been coded into a finite element program that can perform coupled (mechanical and fluid flow behaviour) analyses. The input data includes rainfall, potential evapotranspiration and maximum root depth. The key features of the model are discussed first, followed by a presentation of results from a series of parametric studies.     

A numerical study of the effects of wall deformation on earth pressures

When designing any earth retaining structure it is necessary to estimate the limiting earth pressures. This is usually achieved by assuming a linear pressure distrigution and by using active and passive pressure coefficients obtained by either limit equilibrium, stress field solutions of limit analysis. These coefficients are approximate in a theoretical sense, do not distinguish between modes of wall movement, and provide no pre-failure information. In practice, wall movements are dependent on the construction method and support conditions provided. Any effect of such movements on earth pressures is therefore of practical interest. In this paper the finite element method is used to investigate the effect of the mode of wall movement on the generation of earth pressure. Both smooth and rough walls are considered. It is shown that the distribution of earth pressure is highly dependent on the assumed mode of deformation. The resultant forces on the wall are also affected, but to a lesser degree. The, effect of soil dilatation, the initial horizontal stress and the distribution of soil stiffness with depth are also examined.     

Advanced constitutive modelling of shotcrete: Model formulation and calibration

Shotcrete is one of the main support elements for tunnels constructed according to the principles of the New Austrian Tunnelling Method (NATM). In this paper, a sophisticated constitutive model for the complex mechanical and time-dependent behaviour of shotcrete is presented, which is formulated within the framework of elasto-plasticity. Two independent yield surfaces govern the material behaviour in compression and tension under multi-axial loading conditions, which is further controlled by non-linear plastic strain hardening and softening rules following uniaxial stress–strain curves. The main novelty of the model is the introduction of normalised hardening and softening parameters which enable a more realistic simulation of the shotcrete loading history. In addition, cracking of the shotcrete is treated within the smeared crack concept by applying a fracture energy approach as a regularisation technique, which eliminates the dependency of the results on the size of the elements in a finite element mesh. Furthermore, the model takes into account the gradual change of the main material properties of the shotcrete due to cement hydration during the first 28 days after spraying. Other important time effects such as creep, shrinkage and hydration temperature induced deformations at early ages are considered in the current model formulation. This paper aims to describe in detail the developed structure of the constitutive model and model calibration.     

Phylogeny of the Sepia officinalis species complex in the eastern Atlantic extends the known distribution of Sepia vermiculata across the Benguela upwelling region

Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks.