Fluid-assisted grain size reduction leads to strain localization in oceanic transform faults.

Oceanic Transform Faults are major plate boundaries representing the most seismogenic part of the mid ocean ridge system. Nonetheless, their structure and deformation mechanisms at depth are largely unknown due to rare exposures of deep sections. Here we study the mineral fabric of deformed mantle peridotites - ultramafic mylonites - collected from the transpressive Atobá ridge, along the northern fault of the St. Paul transform system in the Equatorial Atlantic Ocean. We show that, at pressure and temperature conditions of the lower oceanic lithosphere, the dominant deformation mechanism is fluid-assisted dissolution-precipitation creep. Grain size reduction during deformation is enhanced by dissolution of coarser pyroxene grains in presence of fluid and contextual precipitation of small interstitial ones, leading to strain localization at lower stresses than dislocation creep. This mechanism potentially represents the dominant weakening factor in the oceanic lithosphere and a main driver for the onset and maintenance of oceanic transform faults.

Transcranial direct-current stimulation over the motor cortex in patients suffering from anxiety and depression related to rheumatoid arthritis: Study protocol for a randomized, double-blind, placebo-controlled trial.

Rheumatoid arthritis is up to three times more prevalent in women. It is often associated with anxiety and depression, comorbidities causing psychic suffering and potentiating pain perception. It is also related to a higher risk of suicide among diagnosed patients. The high rates of discontinuation of conventional pharmacological treatments are the predominant factor in the search for new therapeutic approaches for the treatment of anxiety and depression. Transcranial direct-current stimulation (tDCS) is a promising, safe and low-cost technique that is very associative with other therapies. When applied to the primary motor cortex (M1) it can induce long-term changes in the synaptic level leading to the improvement of neuroplasticity. The primary aim of this study is to evaluate the effect of tDCS on the symptoms of anxiety and depression. The secondary aim is to evaluate the interference of tDCS on the inflammatory profile, cardiac autonomic behavior and quality of life of patients with rheumatoid arthritis. This is a randomized, double-blind, placebo-controlled clinical trial. The intervention consists of 10 consecutive sessions (once a day) applying tDCS with a 2mA current for 20 minutes. The electrode assembly on the scalp is in accordance with the International Electroencephalogram System 10-20 (EEG) and the anodal electrode is placed over the area of the primary motor cortex (M1 - C3 or C4) and the cathodal electrode on the supraorbital contralateral area (SO - Fp1 or Fp2). The analysis of continuous variables will be described by mean and standard deviation for parametric data and median and interquartile interval for nonparametric data. The evaluation of the effect of tDCS on the inflammatory profile, heart rate variability and quality of life will be obtained by the ANOVA two-way test. tDCS is expected to have a greater effect on reducing anxiety and depression symptoms compared to the placebo, being able to decrease inflammation and improve the quality of life of volunteers.

Mapping of surface radiogenic heat production from in situ gamma spectrometry and chemical data of exhumed mantle peridotites at the St. Peter and St. Paul archipelago (equatorial Atlantic).

This work presents the first mapping of the radiogenic heat production (RHP) and the respective radiogenic heat flow (RHF) of the Saint Peter and Saint Paul Archipelago (SPSPA) located at 1°N in the Equatorial Atlantic Ocean. Using radiogenic heat producing elements (RPE) we inferred a radiogenic heat production ranging 0.08-0.68 µW/m3 (Median: 0.21 µW/m3 and Geometric mean: 0.25 µW/m3) by whole-rock chemical analysis and between 0.08 and 0.48 µW/m3 (Median: 0.19 µW/m3; Geometric mean: 0.19 µW/m3) by in situ Gamma radiation spectrometry. The mean of radiogenic heat production of mylonite rocks from SPSPA (0.22 µW/m3) is significantly higher than predicted values for ultramafic rocks as those largely outcropping in the SPSPA. This is probably due to the pervasive alteration of these rocks and the incorporation of little magma fractions during mylonitization. By converse, the average surface radiogenic heat flow (49.7 µW/m2) is lower than that predicted for the oceanic lithosphere, suggesting that the upper mantle contribution to the heat flow is also low in the SPSPA region. Based on the acquired data and the peculiar tectonics of the SPSPA we propose that the lithospheric mantle around the SPSPA area is colder than that surrounding the Equatorial Atlantic region.

Semibrittle seismic deformation in high-temperature mantle mylonite shear zone along the Romanche transform fault.

Oceanic transform faults, a key element of plate tectonics, represent the first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in lithosphere. However, the thermal structure along transform faults and its effects on earthquake generation are poorly understood. Here we report the presence of a 10- to 15-kilometer-thick in-depth band of microseismicity in 10 to 34 kilometer depth range associated with a high-temperature (700° to 900°C) mantle below the brittle lithosphere along the Romanche mega transform fault in the equatorial Atlantic Ocean. The occurrence of the shallow 2016 moment magnitude 7.1 supershear rupture earthquake and these deep microearthquakes indicate that although large earthquakes occur in the upper brittle lithosphere, a substantial amount of deformation is accommodated in the semibrittle mylonitic mantle that resides at depths below the 600°C isotherm. We also observe a rapid westward deepening of this band of seismicity indicating a strong lateral heterogeneity.

Occurrence and characterization of tremolite asbestos from the Mid Atlantic Ridge.

Tremolite is one of the most common amphibole species and, in the fibrous form (i.e., characterized by crystals/particles consisting of fibres with length > 5 µm, width < 3 µm and aspect ratio > 3), one of the six asbestos minerals. Until now the attention of crystallographers has focused only on samples from continental environment. Here we report the first chemical and structural data of a tremolite asbestos found along the Mid Atlantic Ridge (MAR) at the eastern intersection of the Romanche Transform Fault (Equatorial MAR). Tremolite is associated with chlorite and lizardite and was formed through the green shale facies lower than zeolite in a predominantly fluid system. MAR tremolite asbestos shows very slight deviations from the ideal crystal structure of tremolite. Differences in cation site partitioning were found with respect to tremolite asbestos from ophiolitic complexes, attributed to the different chemical-physical conditions during the mineral formation. In particular, oceanic tremolite asbestos is enriched in Al and Na, forming a trend clearly distinct from the continental tremolites.

Seafloor evidence for pre-shield volcanism above the Tristan da Cunha mantle plume.

Tristan da Cunha is assumed to be the youngest subaerial expression of the Walvis Ridge hot spot. Based on new hydroacoustic data, we propose that the most recent hot spot volcanic activity occurs west of the island. We surveyed relatively young intraplate volcanic fields and scattered, probably monogenetic, submarine volcanoes with multibeam echosounders and sub-bottom profilers. Structural and zonal GIS analysis of bathymetric and backscatter results, based on habitat mapping algorithms to discriminate seafloor features, revealed numerous previously-unknown volcanic structures. South of Tristan da Cunha, we discovered two large seamounts. One of them, Isolde Seamount, is most likely the source of a 2004 submarine eruption known from a pumice stranding event and seismological analysis. An oceanic core complex, identified at the intersection of the Tristan da Cunha Transform and Fracture Zone System with the Mid-Atlantic Ridge, might indicate reduced magma supply and, therefore, weak plume-ridge interaction at present times.

Auto-estima da mulher idosa: uma proposta de intervenção de enfermagem à luz da Teoria de Roy / The elderly woman´s self-steem: a proposal of nursing intervention from the perspective of the Roy´s Theory

A palavra auto-estima vem sendo utilizada por tantos e de forma tão diferenciada, tornando difícil uma definição abrangente, coerente e precisa. Este estudo tem como objetivos: Analisar a auto-estima das mulheres no processo de envelhecimento, a partir da sua narrativa; Interpretar esta narrativa à luz da Teoria de Roy, em especial do modo adaptativo de autoconceito, propondo uma intervenção de Enfermagem para uma velhice saudável; Identificar as atitudes positivas e negativas das mulheres idosas, a partir do seu discurso; Descrever os mecanismos utilizados pela mulher idosa para manter-se satisfeita consigo própria; Verificar os possíveis mecanismos de enfrentamento que a mulher idosa utiliza para lidar com as dificuldades de sua vida; Propor estratégias de intervenções do Enfermeiro que contribuam para a auto-estima da mulher idosa. A população foi composta por vinte idosas, acima de sessenta anos, de um Programa de Saúde da Família de Petrópolis. A coleta de dados foi realizada no período de dezembro de 2005 a fevereiro de 2006, tendo sido interpretados à luz da teoria de Roy. Foram identificadas as seguintes categorias: I) Relacionando a auto-estima e a satisfação pessoal, com as sub-categorias Sentindo-se feliz por estar no seio da família, Percebendo-se valorizadas por ser solidária com as outras pessoas, e Sentindo-se bem por desenvolver atividades prazerosas; 2) Identificando a solidão como sentimento depreciativo à auto-estima; 3) Apreciação do corpo- Relacionando auto-estima e auto-imagem; 4) Dificuldades encontradas no cotidiano, com as sub-categorias Relacionando a auto-estima com a situação financeira, Relacionando auto-estima com a convivência intergeracional e Perda de entes queridos; 5) Encontrando na espiritualidade a sua paz interior, e, 6) Identificando o trabalho da Enfermeira como estimulador da auto-estima. Os resultados revelaram uma relação próxima e pertinente entre os achados e a teoria de Roy. A Enfermagem tem um papel fundamental n...