Tectono-magmatic control on vertical dip slip basement faulting: An example from the Fennoscandian Shield

Vertical dip-slip basement faults play an important role in the evolution and structuring of the Earth's crust. The Proterozoic anorogenic rapakivi-anorthosite setting of the Fennoscandian Shield in southern Finland exhibits a widespread pattern of vertical dip-slip basement faults that are deeply eroded. The Porkkala-Mantsala (PM)-fault, located c. 30 km W of Helsinki is part of a system of crustal lineaments that closely follows the outcrop pattern of Mid-Late Proterozoic anorogenic crustal elements, such as basic dyke swarms, the outline of rapakivi granites and remnants of sediment-filled grabens. These lineaments are formed by low-grade dip-slip faults that overprint Svecofennian shear zones. Structural analysis of the PM-fault supports an interpretation in terms of reactivation of a high-grade ductile wrench zone. Successive stages of brittle deformation visible in as well the PM-fault and the Obbnäs granite demonstrate that brittle deformation in the PM-fault is coeval with the intrusion of the anorogenic Obbnäs rapakivi granite. Based on the spatial and temporal relationship of anorogenic magmatism and block faulting, a genetic relationship is proposed.     

A temperature dependent X-ray Absorption Fine Structure study of dynamic X-site disorder in almandine: a comparison to diffraction data

X-ray Absorption Fine-Structure (XAFS) measurements in the temperature range 20-473K at the Fe K-edge of synthetic almandine (Fe₃Al₂Si₃O₁₂) allow us to determine the temperature dependence of the XAFS Debye-Waller (DW) factors for each of the two crystallographically independent Fe?O bond distances (Fe(1)?O and Fe(2)?O). The vibrational anisotropy of Fe²⁺ in the dodecahedral X-site has been documented. The XAFS DW factor of the longer Fe(2)?O bond is larger and has a greater T-dependence than the shorter Fe(1)?O bond, which remains constant over the measured T range. The XAFS DW factors are compared with the uncorrelated part of the DW factors derived from a single-crystal X-ray diffraction (XRD) study on almandine and are interpreted on the basis of the Einstein model. A comparison with diffraction data shows that the shorter Fe(1)–O bond is significantly affected by correlation in the atomic displacements.     

Polynomial expansions in likelihoods for spatial data: A case study

This paper illustrates the computational benefits of polynomial representations for quantities in the likelihood function for the spatial linear model based on the power covariance scheme. These benefits include a comprehensive study of likelihoods and maximum likelihood estimators for data. For simplicity, we focus on a relatively simple covariance scheme and data observed at equal intervals along a transect; we briefly indicate how generalizations to more complicated covariance functions and higher dimensions will operate.     

Rainfall interception by trees of Pinus radiata,and Eucalyptus viminalis,in a 1300 mm rainfall area of southeastern New South Wales: I. Gross losses and their variability

Interception loss, I, was determined by continuous concurrent measurements of the canopy precipitation balances of a mature seed orchard tree of Pinus radiata, and a dominant tree of Eucalyptus viminalis at a mountainous high rainfall site (900 m a.s.l.) in Tallaganda State Forest of the Upper Shoalhaven Catchment. Approximate canopy storage capacity (Sc) of the pine was 54 l, and that of the eucalypt was 11·3 l. Gross pine I was 26·5 per cent and eucalypt I was 8·3 per cent of total incident rainfall over a period of 18 months, from June 1975 to December 1976. The exponential model that provided the best fit to overall data relating I to gross rainfall (P_g) was of good precision for the pine (r² = 0·73) but rather poor precision for the eucalypt (r² = 0·27). A consistent pattern in interception data of the two canopy types suggested that variation in I was related to change in pervasive conditions influencing rates of evaporation from wet canopies during rainfall. Multiple regression analyses confirmed that factors such as rainfall intensity and windspeed explained some of the variation in eucalypt I but little in pine I. Negative eucalypt I and corresponding low values of pine I over a wide range of P_g (up to 20 mm) suggest that capture of wind-borne precipitation (cloud, mist, or fog) had also complicated the canopy precipitation balances.     

Physico-chemical Speciation of Lead in South San Francisco Bay

The speciation of lead at a site in the South San Francisco Bay was determined using a combination of physical size fractionation and electrochemical analyses. The ‘ total dissolvable ’ Pb was 8·1 nM from analysis of an acidified unfiltered sample. The ‘ dissolved ’ Pb was equal to 0·20 nM (41 ng l⁻¹), only 2·5% of the ‘ total dissolvable ’ Pb. The difference yielded the ‘ particulate ’ Pb equal to 7·9 nM (1·6 μg l⁻¹). Results from crossflow ultrafiltration indicated that almost all (0·19 nM) of the dissolved Pb was ‘ in solution ’ [<10K nominal molecular weight (MW)] and that colloidal Pb (10K MW to 0·2 μm)accounted for onlyc. 1% of the dissolved Pb at this station. This small concentration (0·01 nM) of colloidal Pb may be attributed to the low amount of organic carbon associated with colloid size fraction as determined by dissolved organic carbon analyses.The chemical speciation of lead was determined in the dissolved sample and ultrafiltered sub-sample. Differential pulse anodic stripping voltammetry (DPASV) on a thin mercury film (TMF) rotating glassy carbon disk electrode (RGCDE) was used to distinguish the kinetically labile inorganic species (Pb′) from the Pb-chelated by organic ligands (PbL_i). Lead titration results were similar for both samples revealing that Pb′, PbL_iand excess unbound ligands were present primarily in the ultrafiltrate, rather than in the colloidal phase. The titration data can be interpreted as dissolved Pb being influenced by two classes of Pb-binding ligands. In the dissolved sample, the concentration of the stronger class of ligands was [L₁]=0·89±0·35 nM, with a conditional stability constant ofK^cond_L1,Pb′=3±1×10¹⁰M⁻¹. The weaker class was [L₂]=12·8±1·9 nM, withK^cond_L1,Pb′=4±1×10⁸ M⁻¹. The presence of these ligands, in excess of the dissolved Pb, resulted in [Pb′]=7±2 pM and [Pb²⁺]=0·3 pM (62 pg l⁻¹). While less than 2·4% of the ambient Pb was ‘ in solution ’, it existed chiefly in the form of organic complexes with [PbL₁]=0·15 nM and [PbL₂]=0·03 nM. More significantly, there were large concentrations of unchelated Pb-binding ligands, (L_i′), available to buffer the free Pb²⁺concentration in the event of perturbations in dissolved Pb.     

Numerical simulation of the Valentine's day storm during the 1990 winter icing and storms project

This paper discusses numerical simulation of the first day of the 1990 winter icing and storms project's (WISP) Valentine's day storm (VDS) case with the Purdue mesoscale model (PMM) and comparison of the results to aircraft, satellite, radiometer and other observations. This situation is marked by many observations of supercooled liquid water (SLW) contents of 0.2 g m⁻³ to 0.3 g m⁻³ by the WISP research aircraft. The PMM was initialized with the ECMWF analysis for 13 February 1990 at 0000 GMT and used to make an 18-h forecast with output every 6 h. This paper focuses on comparison of the forecast to observations made at about 1800 GMT since the aircraft encountered significant amounts of SLW during its flight between 1723 GMT and 1928 GMT. Dual channel radiometer, satellite visible imagery, and other observational data sources are also utilized. For this study, the PMM includes a new stable cloud parameterization that is discussed here. In it, cloud water and ice are explicitly calculated while rain and snow are implicitly handled. Between 0 and − 40 °C, cloud water and cloud ice can coexist; the conversion of cloud water to cloud ice is governed by the depositional growth rate of ice crystals whose concentration is diagnosed on the basis of temperature. After accounting for precipitation, a saturation adjustment is done to remove either supersaturated vapor or subsaturation in the presence of cloud drops. In mixed phase conditions, both saturation vapor pressure and the apportionment of condensate into ice or liquid are on a mass-weighted basis according to the existing amounts of ice and liquid or on the basis of temperature if there is neither.     

Amphibolitization of metagabbros in the Scottish Highlands

Abstract Compositions of actinolite, hornblende and cummingtonite, together with pyroxene and plagioclase, are studied in basic intrusions in the Dalradian of north-east Scotland, and the Glen Scaddle complex in the West Moine. Amphibolitization is due to influx of water from the country rocks. Pyroxene compositions are found to have adjusted to the regional metamorphic environment. Owing to the difficulty of diffusion of Al and Si, calcic amphiboles are zoned and commonly contain quartz blebs. Discontinuities in zoning give rise to actinolite-hornblende pairs. Compared with north-east Scotland, disequilibrium is less strong in the Glen Scaddle area: in the latter, plagioclase compositions have been greatly changed, Na partition between hornblende and plagioclase is close to equilibrium, the maximum Al content of hornblende is lower and zoning patterns are more consistent. The Fe/Mg ratio in calcic amphiboles varies with Al content, while approaching equilibrium partition with other minerals. Both zoning patterns and Fe/Mg partition with cummingtonite suggest that Fe/Mg of the calcic amphiboles increases more strongly with increasing (Al^vi+Fe³⁺) than can be explained simply by substitution of Al,Fe³⁺ for Mg on M2. Model reactions for amphibole formation are constructed. Cummingtonite formed at lower chemical potential of CaO than actinolite: Ca was exchanged for Mg,Fe between orthopyroxene-derived and clinopyroxene-derived local systems. Both cummingtonite and actinolite were formed because of kinetic constraints, as intermediate reaction products: actinolite-hornblende pairs represent disequilibrium. This work suggests that many occurrences of actinolite with hornblende, where the minerals are zoned, may also be due to diffusion kinetics.