A possible Mesoarchaean impact structure at Setlagole, North West Province, South Africa : aeromagnetic and field evidence

A 25 to 30 km wide magnetic anomaly within the >2.79 Ga granite-greenstone rocks of the northwestern Kaapvaal Craton is spatially associated with megabreccia outcrops near the village of Setlagole in the North West Province, South Africa. The breccia comprises angular to rounded ciasts of TTG gneisses, granites and granodiorites, with les.ser amounts of amphilxjlite, calc-silicate rock and banded iron-formation as well as unusual dark grey to black, irregular, centimetre- to decimetre-sized clasts that show evidence of fluidal behaviour and plastic deformation during incorporation into the breccia. The largest cla.sts reach up to several metres in size. Evidence of fluvial transport is found in rare thin sandy to gritty layers that show crude bedding and upward-fining with layers dipping gently to the northeast. The breccia matrix is highly variable but is dominated by angular mineral clasls (mainly quartz and feldspar, with subsidiary biotite, amphibole and epidote) with interstitial chlorite. The clasts show variable amounts of alteration (saussuritization, sericitization, chloritization of biotite and amphibole). The dark clasts contain angular quartz and feldspar and small biotite fragments in a cryptocrystalline chlorite-dominant matrix. Textures indicate a lower greenschist faciès metamorphic overprint. The absence of lava, dolomite or quartzite cla.sts suggests that the breccia formed prior to the deposition of the Neoarchaean Ventersdorp and Eoproterozoic Transvaal Supergroups, whereas the metamorphic grade indicates that it postdates the ca. 2.79 Ga amphibolite-facies metamorphic peak in the region. This suggests a late Mesoarchaean or early Neoarchaean (ca. 2.79 to 2.71 Ga) age for the breccia. A similar age is inferred for the magnetic anomaly based on postulated crosscutting dyke ages. Despite a comprehensive search, unequivocal shock-diagnostic microdeformation features have not yet Ixïen found in either the breccia or the highly-weathered granitic gneiss outcrops in the central parts of the anomaly. The unusual plastically-deformed dark clasts may represent chloritized mud clasts or impact melt clasts. Geochemical data on these clasts and other components of the megabreccia provide no conclusive support for a meteoritic origin, but the unparalleled comptjsition of the clasts and their high trace element abundances of Ni, Cr, V, Zn and Co relative to rocks of the Kraaipan granite-greenstone basement, sugge.sts an unusual origin for this matrix material. Given the distinctive nature of the breccia and its proximity to a large circular magnetic anomaly, it is postulated that the megabreccia could represent a mass or debris flow in a marine .setting triggered by an impact tsunami or resurge. Subsequent faulting may have led to the preferential preservation of these deposits. This interpretation of the Setlagole megabreccia and geophysical anomaly is evaluated in terms of other possible modes of origin and it is concluded that a meteoritic source best fits the available data

Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at E_p = 200 MeV. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon-nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle two-hole (2p-2h) states.Comment: Phys. Lett. B, in pres

Imaging of subsurface lineaments in the southwestern part of the Thrace Basin from gravity data

Linear anomalies, as an indicator of the structural features of some geological bodies, are very important for the interpretation of gravity and magnetic data. In this study, an image processing technique known as the Hough transform (HT) algorithm is described for determining invisible boundaries and extensions in gravity anomaly maps. The Hough function implements the Hough transform used to extract straight lines or circles within two-dimensional potential field images. It is defined as image and Hough space. In the Hough domain, this function transforms each nonzero point in the parameter domain to a sinusoid. In the image space, each point in the Hough space is transformed to a straight line or circle. Lineaments are depicted from these straight lines which are transformed in the image domain. An application of the Hough transform to the Bouguer anomaly map of the southwestern part of the Thrace Basin, NW Turkey, shows the effectiveness of the proposed approach. Based on geological data and gravity data, the structural features in the southwestern part of the Thrace Basin are investigated by applying the proposed approach and the Blakely and Simpson method. Lineaments identified by these approaches are generally in good accordance with previously-mapped surface faults

Managing job stress among nurses : what kind of job resources do we need?

Aim. This paper is a report of a study to investigate the functionality of different kinds of job resources for managing job stress in nursing. Background. There is increasing recognition that healthcare staff, and especially nurses, are at high risk for burnout and physical complaints. Several researchers have proposed that job resources moderate the relationship between job demands and job-related outcomes, particularly when there is a match between the type of demands, resources, and outcomes. Method. Based on the Demand-Induced Strain Compensation Model, cross-sectional survey data were collected between November 2006 and February 2007 by a paper-and-pencil questionnaire. The final sample consisted of 69 nurses from a Dutch nursing home (response rate 59·4%). Data were analyzed by hierarchical regression analyses. Results. High physical demands had adverse effects on both physical complaints and emotional exhaustion (i.e. burnout), unless employees had high physical resources. A similar pattern was found for high physical demands and emotional resources in predicting emotional exhaustion. The likelihood of finding theoretically-valid moderating effects was related to the degree of match between demands, resources, and outcomes. Conclusion. Job resources do not randomly moderate the relationship between job demands and job-related outcomes. Both physical and emotional resources seem to be important stress buffers for human service employees such as nurses, and their moderating effects underline the importance of specific job resources in healthcare work. Job redesign in nursing homes should therefore primarily focus on matching job resources to job demands in order to diminish poor health and ill-being