Close encounters of the irrational kind

Eric de Silva champions a group of early-career scientists who have been finding out more about the use of science to sell untested and often untestable devices to an unsuspecting public.     

U–Pb and Sm–Nd geochronology of amphibolites from the Curaçá Belt, São Francisco Craton, Brazil: Tectonic implications

The Curaçá terrane is part of the Itabuna–Salvador–Curaçá (I–S–C) Paleoproterozoic orogen in the São Francisco craton, northeastern Brazil, and comprises supracrustal rocks, gneisses of their probable basement, amphibolites, and mafic-ultramafic Cu-bearing bodies (including the Caraíba Cu-Mine), all affected by D₁-D₃ deformation events associated to M₁-M₃ metamorphism under high-T granulite and amphibolite facies, and assisted by G₁-G₃ tonalitic-granodioritic-granitic intrusions. U–Pb and Sm–Nd Thermal Ionization Mass Spectrometry (TIMS) isotopic data from amphibolite, tonalite, and granite, sampled in a well-known outcrop, indicate partial reset and heterogeneous modification of the original isotopic systems, attributable to deformation and metamorphism. The ages obtained from these systems agree with each other, and also with other previously published U–Pb data, and imply that 2.6 Ga is the crystallization age of the protolith of the amphibolite. Together with key structural relationships, they also indicate a 2.08–2.05 Ga interval for M₃ metamorphism, and make even a less precise age (2.2–2.3 Ga) acceptable, as it suggests contamination in the amphibolite with material in a syn-D₂ tonalite crystallized 2248 ± 36 Ma ago. The new data demonstrate the existence of Neoarchean fragments of both oceanic and continental crusts and constrain the Archean-Paleoproterozoic development of the Curaçá belt, the I–S–C orogen, and the São Francisco craton.     

Vertebrate dinoturbation from the Caturrita Formation (Late Triassic, Paraná Basin), Rio Grande do Sul State, Brazil

The Caturrita Formation is a lithostratigraphic unit that comprises the Ladinian–Eonorian sequence of the Paraná Basin. It has been interpreted as deposits of alluvial plains and meandering rivers. Purported fossil tracks found in this formation at Faxinal do Soturno County, Rio Grande do Sul State, Brazil, are concave circular-shaped structures, with a laminar deformation. Some show digitiform projections, and at least three are aligned. They are interpreted as a disruption of the substrate homogeneity caused by bioturbation of tetrapods. In some of these there is a distinct color pattern — more reddish than the surrounding substrate. This is interpreted as a result of differential diagenesis. The features remain enigmatic tracks but were probably made by prosauropod dinosaurs, the dominant terrestrial herbivore group from the end of the Triassic in Gondwana strata.     

Electric currents along earthquake faults and the magnetization of pseudotachylite veins

Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km³ of stressed igneous rocks adjacent to the fault plane can deliver 10³–10⁵ A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction.     

CDM implementation in Brazil’s rural and isolated regions: the Amazonian case

There is a growing understanding that energy services play a crucial role in underpinning efforts to achieve the UN Millennium Development Goals (MDG) and in improving the lives of poor people. Brazil remains challenged in regard to a number of social issues, notably poverty reduction in isolated areas, where access to electricity is as poor as their population. In the Amazonian region, most people have no access to electricity, or else have only a precarious supply. Due to several economic and technical reasons, many cities have old, inefficient diesel generators. In such a scenario, CDM (Clean Development Mechanism) can be an instrument both to mitigate climate change and to promote sustainable development in these remote areas, thereby contributing to the achievement of the MDGs in Brazil. However, CDM implementation in Brazil is still restricted to a few types of projects (such as sugar cane bagasse cogeneration and landfill gas use), mostly proposed by big companies and hardly ever directed to the Amazon region. The main objectives of this article are to assess the potential of CDM as a possible tool to promote electricity access to the poor rural population in the Amazonian region, and to discuss the main reasons why it has not become a reality so far.     

Paleohydrological investigation of Infernão Lake, Moji-Guaçcu River watershed, São Paulo, Brazil

A 450 cm sediment core spanning the last 3,500 years was collected from 4.6 m of water in Lake Infernão, located in the floodplain of the Moji-Guaçu River in SE Brazil, to reconstruct the wetland system (river and lake) paleohydrology. A multidisciplinary approach using isotopic (¹³C and ¹⁵N), chemical (C/N ratio and lignin derived phenols) and physical analyses (% water content and density) were used in this study. A coarse sand unit in the lower part of the core (450–417 cm) corresponds to the paleoriver. The rest of the sediment core (dark clay) shows a gradual change from a fluvial to a lacustrine environment. ¹⁴C dates from the lower part of the core (417–200 cm), demonstrate an inversion and narrow span in age (3,000–3,500 yrs B.P.) corresponding to a period of rapid fluvial sedimentation and reworking. The lake seems to have been well established only after 3,000 yrs B.P. The change from a fluvial to a lacustrine environment is inferred from the isotopic and chemical data. Sediment of the fluvial phase is characterized by higher ¹³C values, lower C and N content and a lignin content representative of woody-tissues. Sediment of the lacustrine phase show a gradual decrease in ¹³C values toward the top of the core reflecting the influence of organic carbon derived by phytoplankton and aquatic macrophytes (C₃ plants). The trend to higher C and N content and low C/N ratios also support this interpretation. The lower lignin content indicates increase contributions of non-vascular plants (phytoplankton). Similarly, the slight increase of non-woody tissues (higher C/V ratios) and the predominance of angiosperm plants (high S/V ratios) as organic matter source indicate an increase contribution of aquatic plants during the lacustrine phase. Our data presented here in addition to the geomorphological information and the available paleoclimatic scenario of pollen-inferred analyses for aquatic systems from the southeastern Brazil point to a climatic origin for this fluvial-lacustrine transition at about 3,000 yrs B.P. and to a climatic evolution leading to the present conditions and to a consequently gradual isolation of Lake Infernão from the influence of the Moji-Guaçu River.     

Petrogenesis of A-type Granitoids from the Alto Moxoto and Alto Pajeu Terranes of the Borborema Province, ne Brazil: Constraints from Geochemistry and Isotopic Composition

A-type granitoids (512 Ma) either intruded into Paleoproterozoic gneiss of the Alto Moxoto Terrane (Prata Complex and Serra da Engabelada Pluton) or into Early Neoproterozoic metavolcanic metasedimentary sequence of the Alto Pajeu Terrane (Serrote Santo Antonio Pluton), constitute a small proportion of Brasiliano (= Pan-African) granitoids in the Central Tectonic Domain of the Borborema Province, northeastern Brazil. The Prata Complex consists of syenogranites, monzogranites, mafic enclaves of diorites and norites. The felsic and mafic members are not genetically related through fractionation. Mingling and mixing were extensive processes within the Prata Complex. The granites evolution appears to have involved fractionation of alkali feldspar, biotite, apatite and sphene without significant wall-rock assimilation. The Serra da Engabelada and Serrote Santo Antonio plutons consist of biotite syenogranites, with rare mafic enclaves. The studied granitoids are dominantly metaluminous, characterized by Fe-rich biotite and Fe-hornblende. High total alkalis, Y, Nb and REE and low CaO, MgO and Sr abundances and high FeO/(FeO+MgO) ratios characterize these granitoids. Chondrite-normalized REE patterns show enriched LREE, moderate to strong negative Eu anomalies and more or less flat heavy REE.The studied granitoids and diabase from dykes and enclaves show negative eNd _(512Ma) values (-14 to -10), high incompatible elements such as LILE, HFSE and REE, suggesting important contribution of Paleoproterozoic crust. The origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust. Such isotopic signature of the diabase from the dykes also reflects a Paleoproterozoic enriched lithospheric mantle in the area. The intrusion of the studied granitoids contemporary with sub-volcanic bimodal magmatism and deposition of many Cambrian "pull-apart" basins in the north and central tectonic Domain of the Borborema Province, suggest intrusion during post-tectonic relaxation of the Brasiliano orogeny following the assembly of West Gondwana.     

The corrugation of the galactic layer

The 21-cm line intensities in a (Z, R) distribution is studied at the locus of tangential points of the inner parts of the Galaxy using both Northern and Southern data. A corrugation effect is observed in the galactic neutral hydrogen layer with an average wave length of 2 kpc and a wave amplitude of 70 pc. The patterns obtained for the I and the IV quadrant indicate that the inner and the outer parts of the spiral arms are located, respectively, below and above the galactic plane. Also, with high angular resolution the corrugation pattern suggests the existence of ‘faults’ in a geological sense in the inter arm zones. Optical studies of spatial distribution of early objects show good agreement with the neutral hydrogen results, indicating that the observed corrugation pattern is an indication of real distribution of matter in the galactic layer, and not of a kinematical effect.