Suchergebnisse

{ESP}Se estudiaron las propiedades físicas y ópticas, los politipos, la composición química y la paragénesis de las micas de las pegmatitas de elementos raros Santa Elena y El Peñón. La primera es de tipo complejo, subtipo petalita y la segunda de tipo berilo subtipo berilo-columbita-fosfato: ambas pertenecen al distrito El Quemado, el más septentrional de la Provincia Pegmatítica Pampeana. Las micas son muscovitas, muscovitas litíferas, formas intermedias y lepidolitas. Las muscovitas s.I. tienen estructura 2 M, y una composición con bajos contenidos de Mn, Li, Rb, Cs, Tl e Y, un espécimen puede ser clasificado como 'muscovita rosa'. Las lepidolitas s.I. tienen estructuras del politipo 2 M, más algunas difracciones del politipo 1 M o 2 M, y comprenden algunas micas dioctaédricas y otras trioctaédricas. Son más ricas en SiO2, MnO, CaO, Li2O, Rb2O, Cs, Tl, Y y P que las muscovitas. La evolución geoquímica de las micas muestra una tendencia general con relaciones K/Rb decrecientes con la diferenciación y correlación negativa de esta relación con los contenidos de cesio, talio, itrio, litio y manganeso, en algunos casos (itrio) prácticamente lineal. Las micas litíferas de la pegmatita de subtipo petalita habrían cristalizado aproximadamente a una P de 2 a 3 kbar y a 350-400ºC, en el campo de estabilidad de espodumeno, bajo un incremento de la actividad ( ) HF, KF y LiF. Las micas de la pegmatita de subtipo berilo-columbita-fosfato habrían cristalizado en el mismo rango de P y T un poco más alta, de una fracción pobre en litio cosanguínea, pero no comagmática, con la que originó la pegmatita litífera. ; {ENG}This study describes the physical and optical properties, polytypism, chemical composition and paragenesis of a Li-Al-bearing mica suite from the northernmost pegmatite field of Pampean Pegmatite Province. The micas are from two possible cogenetic rare-element pegmatites: Santa Elena, a complex-type, petalite subtype pegmatite, and El Peñón, a beryl-type, beryl-columbite-phosphate subtype pegmatite. The micas are muscovite, lithian muscovite, mixed forms and lepidolite. The muscovite s.I. has 2 M, structure and chemistry with comparatively low contents of Mn, Li, Rb, Cs, Ti and Y; one specimen could be classified as a 'rose muscovite'. The lepidolite and mixed forms have 2 M, dominant polytypism with some scarce X-ray reflections of 1 M or 2 M, polytypes. They are higher in SiO2, MnO, CaO, Li2O, Rb2O, Cs, Ti, Y and P. Li2O ranges between 3,71 and 4,73%, and Rb2O from 0,29 to 2,53%. The geochemical evolution of the micas, illustrated by K/Rb versus lithium, manganeso, cesium, thallium and ytrium diagrams, shows a differentiation trend similar to micas from other LCT pegmatite fieids. The inferred crystallization path has evolved approximately around 2-3 kbar and 350-400ºC, in the stability field of spodumene, in a H2O-saturated environment, under increasing HF, KF and LiF activities.

Twenty years ago the first publications began to appear in Argentina of a loosely confederated group of writers, leftist in political persuasion, who took strident exception in culture to both the old oligarchic tradition and to the parvenu peronista establishment. During the years of the peronista government, the writers and intellectuals who supported Perón had been successful in imposing their own persuasions on the universities and publishing media at the expense of the old guard, represented by the literary supplements, Sur, the Academia Argentina de Letras, and the Jockey Club. The young leftists born around 1920 had been snubbed by the old-time writers and persecuted by the peronista regime. Their emergence as a loosely unified assertion of leftist political and cultural values, supported by a similar affirmation in postwar Europe, is a major literary phenomenon in mid-century Argentia.

This volume examines the ways different countries around the world have responded to rising numbers of mobile citizens. Complete with detailed case studies, it provides a groundbreaking and global analysis of emigration and diaspora policies in the 21st century. First, an introduction considers factors that determines a state's policy choices. It draws on rich empirical material to present readers with information on the determinants of policy definition and implementation, reactions to emigration, and converging and diverging trends. Next, the volume offers detailed case studies from 15 countries around the world, including Argentia, Vietnam, Senegal, the Russian Federation, Denmark, and Turkey. Coverage for each country critically analyzes its emigration or diaspora policies as well as how these policies affect its mobile citizens. The contributors also place the policies in context and explore the consequences of pertinent rules and provisions. In addition, a conclusion presents a comparative analysis of all case studies as well as details a set of best practices. Emigration and immigration are two sides of the same c oin that every country experiences and, in one way or the other, must face. This book offers readers a new look on diaspora and emigration governance across the globe and explores the future paradigm of reactions to emigration.

Of the family of war conferences the Atlantic meeting between Roosevelt and Churchill in August 1941, has been a neglected relation. It has been covered in general histories but only one substantial account of the conference has appeared to date. This state of affairs is regrettable given the intrinsic importance of some of the issues which were raised at Argentia and the fact that T. A. Wilson's account,The First Summit, was written before some of the official records were released. However, though there is a need for an overall review of the conference, this paper has the modest goal of reconsidering the economic questions which resulted in point four of the Atlantic Charter. The reasons for a new account of the genesis and formulation of the main economic provisions of the joint declaration are three-fold. First, the context of economic discussions in which the conference took place has never been adequately described; consequently the reasoning behind certain decisions, as well as some of the nuances of the talks, have been misunderstood. Secondly, the injudicious character of Welles' proposals for point four and the nature of America's diplomatic defeat at the hands of the British have never been properly explained. Finally, it has not previously been detected that Churchill evaded full consultation with his Cabinet and ignored some of their advice which, ironically, resulted in a less serious set-back for American economic goals than would otherwise have been the case.