Study of the erosion rates in the upper Maracujá Basin (Quadrilátero Ferrífero/MG,Brazil) by the in situ produced cosmogenic 10Be method

The present work quantifies the erosive processes in the two main substrates (schists–phyllites and granites–gneisses) of the upper Maracujá Basin in the Quadrilátero Ferrífero/MG, Brazil, a region of semi‐humid tropical climate. Two measuring methods of concentration were used: (i) in situ produced ¹⁰Be in quartz veins (surface erosion rates) and (ii) ¹⁰Be in fluvial sediments (basin erosion rates). The results confirm that (i) erosion tends to be more aggressive close to the headwaters than in the lower parts of the basin and (ii) the region is now affected by dissection. Copyright © 2006 John Wiley & Sons, Ltd.     

Long-term global sea surface temperature fluctuations and their possible influence on atmospheric CO2 concentrations

Changes of atmospheric CO₂ concentration since 1958 are shown to be related to sea surface temperature changes. The largest contribution to changes arises from the Pacific equatorial upwelling region, with the Indian Ocean and Atlantic contributing only small fractions to the variance. It is hypothesized that the observed relationship is related to the nutrients that are brought up by upwelling cold water, with photosynthesis contributing to a lowering of the partial pressure of CO₂ in the sea and thus to a greater tendency for a flux from the air to the sea.Possible longer term variations of sea temperature and CO₂ are discussed.     

Spatial and temporal variations in aboveground and belowground biomass of Spartina maritima (small cordgrass) in created and natural marshes

Spartina species are commonly used for salt marsh manipulative projects, where aboveground and belowground biomasses are functional traits that play important roles, showing high spatial and temporal variations. This work analyses variations in AGB and BGB of Spartina maritima and abiotic environmental parameters along a chronosequence of six marshes created from 1997 to 2003 with disparate sediment dynamics, and adjacent natural marshes and unvegetated tidal flats. S. maritima behaved as an autogenic engineer, as its colonization of bare sediments yielded abiotic environmental changes: specifically, bed level rise accompanied by higher oxygenation and salinity. These modifications of the environment were site-specific, depending mainly on sedimentary dynamics. At the same time, abiotic environmental changes determined biomass production rates of S. maritima that were higher in more-accreting marshes; however, AGB was kept constant from early in its development (2 years). The increase in BGB with elevation seemed to be related to the inhibition of subsurface tissue development in anoxic sediments. Biomass accumulation and production varied markedly, depending on the spatial scale, indicating the relevance of the plot size chosen for the analysis of biomass of cordgrasses. Our results show that managers of salt marshes should consider sedimentary dynamics carefully when setting realistic expectations for success criteria of created and restored wetlands.     

Direct evidence of Middle Oligocene extension in the Calabria–Peloritani terrane from co-seismic faulting: the pseudotachylyte-bearing shear zones of Palmi (southern Calabria, Italy)

The Variscan crystalline basement of the Calabria–Peloritani terrane (CPT) in southern Italy was partly reworked by ductile and brittle shear zones throughout the Alpine tectonic evolution (from thickening to exhumation). Although evidence of extensional tectonics in the CPT has already been found and roughly constrained to the Oligocene onward, no attempt has ever been made to directly date brittle fault movements. Structural (meso- and micro-scale), kinematic and petrographic analyses and ⁴⁰Ar–³⁹Ar laser experiments reveal that the pseudotachylyte-bearing shear zones of the Palmi area in southern Calabria formed in response to extensional shearing ∼33.5 Ma ago and overprinted compressional tectonic structures. Results provide the first direct evidence of Middle Oligocene co-seismic faulting in the area and confirm the role of extensional tectonics in promoting the Oligocene exhumation of the Calabria basement.     

Vorticity analysis of the Palmi shear zone mylonites: new insights for the Alpine tectonic evolution of the Calabria–Peloritani terrane (southern Italy)

New microstructural data on the mylonites from the well‐exposed Palmi shear zone (southern Calabria) are presented with the aim to shed light on both the kinematics and the geometry of the southwestern branch of the Alpine belt during Eocene. In the study area, located between the Sardinia–Corsica block and the Calabria–Peloritani terrane, previous large‐scale geodynamic reconstructions suggest the presence of strike–slip or transform fault zones dissecting the southwestern branch of the Alpine belt. However, there are no field data supporting the occurrence of these structures. This paper uses vorticity analysis technique based on the aspect ratio and the long axis orientation of rigid porphyroclasts in mylonitic marbles and mylonitic granitoids, to estimate the contribution of pure and simple shear of deformation during the movement of the Palmi shear zone. Porphyroclasts aspect ratio and orientation were measured on thin sections using image analysis. Estimates of the vorticity number, W_m, indicate that the Palmi shear zone recorded general shear with a contribution of pure shear of c. 65%. Then, the Palmi shear zone can be interpreted as a segment of a left‐lateral transpressive bend along the southern termination of the Eocene Alpine front. Copyright © 2015 John Wiley & Sons, Ltd.     

Strange star candidates revised within a quark model with chiral mass scaling

We calculate the properties of static strange stars using a quark model with chiral mass scaling.The results are characterized by a large maximum mass (～ 1.6 M) and radius (～10 km).Together with a broad collection of modern neutron star models,we discuss some recent astrophysical observational data that could shed new light on the possible presence of strange quark matter in compact stars.We conclude that none of the present astrophysical observations can prove or confute the existence of strange stars.     

Trace-element study and uranium-lead dating of perovskite from the Afrikanda plutonic complex, Kola Peninsula (Russia) using LA-ICP-MS

The U-Pb geochronology of perovskite is a powerful tool in constraining the emplacement age of silica-undersaturated rocks. The trace-element and U-Pb isotopic compositions of perovskite from clinopyroxenite and silicocarbonatite from the Afrikanda plutonic complex (Kola, Russia) were determined by laser-ablation inductively-coupled mass-spectrometry (LA-ICP-MS). In addition, the Sr isotopic composition of perovskite was measured by isotope-dilution mass-spectrometry to better constrain the relations between its host rocks. Perovskite from the two rock types shows a different degree of enrichment in Na, Mg, Mn, Pb, Fe, Al, V, rare-earth elements, Zr, Hf, Th, U and Ta. The perovskite ⁸⁷Sr/⁸⁶Sr values are within analytical uncertainty of one another and fall within the range of mantle values. The ²⁰⁶Pb/²³⁸U ages (corrected for common lead using ²⁰⁷Pb-method) of perovskite from silicocarbonatite statistically yield a single population with a weighted mean of 371?±?8 Ma (2σ; MSWD?=?0.071). This age is indistinguishable, within uncertainty, to the clinopyroxenite weighted mean ²⁰⁶Pb/²³⁸U age of 374?±?10 Ma (2σ; MSWD?=?0.18). Our data are in good agreement with the previous geochronological study of the Afrikanda complex. The observed variations in trace-element composition of perovskite from silicocarbonatite and clinopyroxenite indicate that these rocks are not related by crystal fractionation. The Sr isotopic ratios and the fact that the two rocks are coeval suggest that they were either produced from a single parental melt by liquid immiscibility, or from two separate magmas derived at different degrees of partial melting from an isotopically equilibrated, but modally complex mantle source.     

Land use dynamics in Brazilian La Plata Basin and anthropogenic climate change

The La Plata Basin (LPB) is one of the most important regions for agriculture and livestock production in South America, playing a central role in the world food production and food security. Within its borders is also located the whole Brazilian Pantanal region. Identifying the most important land use sectors in LPB as well as the changes observed in the past years is fundamental to recognize which areas of the basin might be more vulnerable to climate change in order to design adaptation strategies. A general characterization of land use and livestock production of Brazilian LPB was done by using the System of Automatic Retrieving (SIDRA) of Brazilian Institute of Geography and Statistics (IBGE) platform as the major source of data. It was observed expressive increases in land areas used for temporary crops, such as soybean, sugarcane, and maize, as well as increases in poultry and swine production. These important changes in agricultural land use and livestock production are currently associated to non-climatic drivers, but this dynamic might be strongly affected by the consequences of climate change and variability, with negative socio-economic impacts for the whole region.