Estrutura e geoquí­mica das fases magmática e tardimagmática em zircões do maciço graní­tico de Peneda-Gerês (NW Pení­nsula Ibérica)

Efectuou-se um estudo da estrutura interna e composição química dos zircões de granitos do maciço de Peneda-Gerês (granitos de Gerês, Paufito, Illa e Carris) com recurso a microscópio electrónico de varrimento (MEV) e microssonda electrónica. Este estudo permitiu caracterizar as fases magmática e tardimagmática e, ainda, constatar a existência de domínios de alteração nas zonas dos cristais mais ricas em elementos vestigiais (U, Th). Esta alteração é claramente mais expressiva nos zircões mais tardios (subtipos S5, G1) do granito de Carris e traduz-se em estruturas com forma botrioidal e de cor escura em imagem de electrões retrodifundidos (MEV). A grande expressividade destes domínios de alteração nos zircões do granito de Carris, em constraste com a sua limitada expressividade em zircões dos restantes granitos do maciço de Peneda-Gerês, permite supor que este fenómeno de alteração esteja relacionado com a maior abundância de fluidos hidrotermais que afectaram domínios mais susceptíveis dos cristais de zircão. Refira-se que, espacialmente associados ao granito de Carris, ocorrem filões e filonetes quartzosos e quartzo-feldspáticos com mineralizações em volframite, molibdenite, pirite, etc, correspondendo às zonas mais mineralizadas do maciço de Peneda-Gerês.A study of the internal structure and chemical composition of zircon from the main granitic units of the Peneda-Gerês granitic massif (Gerês, Paufito, Illa and Carris granites) was undertaken. This study permitted to characterize the zircons’ magmatic and late magmatic phases and, additionally, revealed the existence of alteration domains in the zones of the zircons which are richer in trace elements (U, Th). This alteration is notoriously more expressible in the late crystallizing zircons (subtypes S5, G1) of theCarris granite and appears as botrioidal structures of dark colour in back scattered electron imagery (SEM). The important expression of this alteration in the Carris granite, in contrast to the limited expression in zircons of the other granites, permits to envisage that this alteration is associated with a greater abundance of hydrothermal fluids that affected the more susceptible domains of the zircon crystals. It should be referred that spatially associated with the Carris granite occur quartz and quartz-feldspar veins with mineralizations of wolframite, molybdenite, pyrite, etc, corresponding to the most mineralized zone of the Peneda-Gerês massif.Fundação para a Ciência e a Tecnologia (FCT) - Programa de Financiamento Plurianua

Chiral 3π\pi-exchange NN-potentials: Results for dominant next-to-leading order contributions

We calculate in (two-loop) chiral perturbation theory the local NN-potentials generated by the three-pion exchange diagrams with one insertion from the second order chiral effective pion-nucleon Lagrangian proportional to the low-energy constants $c_{1,2,3,4}$. The resulting isoscalar central potential vanishes identically. In most cases these $3\pi$-exchange potentials are larger than the ones generated by the diagrams involving only leading order vertices due to the large values of $c_{3,4}$ (which mainly represent virtual $\Delta$-excitation). A similar feature has been observed for the chiral $2\pi$-exchange. We also give suitable (double-integral) representations for the spin-spin and tensor potentials generated by the leading-order diagrams proportional to $g_A^6$ involving four nucleon propagators. In these cases the Cutkosky rule cannot be used to calculate the spectral-functions in the infinite nucleon mass limit since the corresponding mass-spectra start with a non-vanishing value at the $3\pi$-threshold. Altogether, one finds that chiral $3\pi$-exchange leads to small corrections in the region $r\geq 1.4$ fm where $1\pi$- and chiral $2\pi$-exchange alone provide a very good strong NN-force as shown in a recent analysis of the low-energy pp-scattering data-base.Comment: 11 pages, 7 figures, to be published in The Physical Review

Mechanisms of enrichment of natural radioactivity along the beaches of the Camargue, France

A field study was carried out along the Golfe du Lion, that focussed on the beaches of the Camargue, to locate the main areas where enriched U and Th are found, and to better understand the processes that concentrate radioactivity on beaches. Indeed enriched areas are observed on some Camargue beaches, where high-dose rates are recorded due to excess U and Th activity (>1000 Bq kg-1). The coastline was mapped by means of an aerial gamma survey and the results indicated that the main actinides deposits occurred in the Camargue area. This concentrating effect is possibly due to a greater sedimentary contribution from the River Rhone relative to other minor Mediterranean rivers. Across the along-shore profile, the variability in actinides observed at the eastern part of Beauduc spit is mainly explained by variations in heavy and light mineral contents. Such variability can be accounted for by redistribution of the sand caused by erosion/deposition processes occurring in the eastern part of the spit. Further parameters such as grain size and heavy minerals content were studied in connection with the distribution of U, Th and 40K in the field at a more localised level (i.e. across-shore beach profile). The <200-μm fraction contains more than 50% of the radioactivity and heavy minerals (especially zircon) are the main contributors to the high levels of external radiation. Therefore the enriched areas, where U and Th exceed 1000 Bq kg-1, presumably result from the sorting of sand grains according to their size and density. © 2006 Elsevier Ltd. All rights reserved

Morphological and geochemical study of zircons in metamorphics rocks of Ollo de Sapo, Sanabria (NW Spain).Plutonic and volcano-sedimentary protoliths

This work constitutes a combination of morphological and geochemical results of zircon populations of two typical lithologies from the Ollo de Sapo Domain in the Sanabria complex: augengneiss and schist. The combination of these methods allows us discriminating between the discussed plutonic or volcanosedimentary origin of Ollo de Sapo rocks. Results allow the assignment of a peraluminous porphyritic granite derivated from a polygenetic source as protolith of the gneiss. Zircons from the schist are more varied and their characteristics point to a volcanosedimentary protolith constituted by mainly calc-alkaline crystals. Moreover, the morphological and geochemical study of an enclave of gneis in monzodiorite shows there are at least three populations of zircons in this sample. Therefore, these methods result to be useful in order to separate different zircon populations that could be wrongly considered together in geochronological studie

Zircon morphology vs. geochemical signature in meta-volcanic rocks of the Narcea Antiform (N Spain)

In the Narcea Antiform, both Ediacaran upper volcanic series and volcanic clasts in the overlying Cambrian micro-conglomerates, show geochemistry between those of calc-alkaline and alkaline series in the TAS diagram, and a mainly calc-alkaline trend in the Zr/TiO2-Nb/Y diagram. However, zircons reveal a common high temperature nature of the crystals and have overall characteristics typical of alkaline magmas. Such an apparent contradiction can be interpreted as a result of a change in the tectonic conditions. This would account for the mixed characteristics of rocks having a calc-alkaline geochemical signature but with an alkaline mineral assemblage. Moreover, zircon morphology has turned out to be an interesting clue to resolve the petrographical and geochemical discrimination in low-grade metamorphosed paleovolcanic rock

One or two species?:On the case of Hyperolius discodactylus Ahl, 1931 and H. alticola Ahl, 1931 (Anura: Hyperoliidae)

FIGURE 6. Schematic drawing of the webbing of left hind limb for a) H. cf. alticola females, b) H. cf. discodactylus females, c) H. cf. alticola males and d) H. cf. discodactylus males. Blue lines represent the median number of free phalanges and dashed red lines represent the interquartile range. Numbers of individuals per morphotype are given.Published as part of Liedtke, H. Christoph, Hügli, Dominik, Dehling, J. Maximilian, Pupin, Fabio, Menegon, Michele, Plumptre, Andrew J., Kujirakwinja, Deo & Loader, Simon P., 2014, One or two species? On the case of Hyperolius discodactylus Ahl, 1931 and H. alticola Ahl, 1931 (Anura: Hyperoliidae), pp. 253-290 in Zootaxa 3768 (3) on page 266, DOI: 10.11646/zootaxa.3768.3.2, http://zenodo.org/record/490956