The Palaeocene Cerro Munro tonalite intrusion (Chubut Province, Argentina): A plutonic remnant of explosive volcanism?

The Cerro Munro sub-volcanic intrusion is emplaced in the back-arc (400 km from the trench) as small sub-circular tonalite-granodiorite plutons with abundant radial porphyritic dikes. U-Pb zircon SHRIMP data give an age of crystallization of 57 Ma ± 1.4 Ma. It is located to the east of the North Patagonian Batholith (NPB) that shows a protracted and episodic magmatic history from Cretaceous to Miocene time. The NPB Palaeogene episode is characterized by the lack of magmatic activity at the arc axis, as small plutonic emplacements move to the fore-arc and back-arc. This Palaeogene tectono-magmatic episode is ruled by the detachment of the Aluk plate during the Aluk-Farallon-SAM triple junction, active at that time along northern Patagonia active margin, changing the Cretaceous ?NPB orogenic? setting to a Palaeogene ?Munro transitional? tectono-magmatic setting. Near the contacts, the tonalite contains abundant enclaves of igneous appearance and variable size from several cm to dm, described as autoliths. The study of autoliths and host tonalite reveals interesting results on the processes of fractionation in a thermally zoned magma chamber. Autoliths, and in a large extent the host tonalite, represent disguised cumulates from which a hydrous silicic liquid was extracted. Barometry calculations from mineral chemistry in both autoliths and tonalites record a shallow pressure of emplacement of 0.5 kbar. Rhyolite-dacite flows and ignimbrites, surrounding the northern contact of the Cerro Munro tonalite, may represent the exsolved liquid from the plutonic cumulates. The study by cathodoluminiscence and electron backscattered diffraction techniques from a rhyolite-hosted quartz supports this protracted history of the Cerro Munro magma chamber.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

The Palaeocene Cerro Munro tonalite intrusion (Chubut Province, Argentina): A plutonic remnant of explosive volcanism?

The Cerro Munro sub-volcanic intrusion is emplaced in the back-arc (400 km from the trench) as small sub-circular tonalite-granodiorite plutons with abundant radial porphyritic dikes. U-Pb zircon SHRIMP data give an age of crystallization of 57 Ma ± 1.4 Ma. It is located to the east of the North Patagonian Batholith (NPB) that shows a protracted and episodic magmatic history from Cretaceous to Miocene time. The NPB Palaeogene episode is characterized by the lack of magmatic activity at the arc axis, as small plutonic emplacements move to the fore-arc and back-arc. This Palaeogene tectono-magmatic episode is ruled by the detachment of the Aluk plate during the Aluk-Farallon-SAM triple junction, active at that time along northern Patagonia active margin, changing the Cretaceous ?NPB orogenic? setting to a Palaeogene ?Munro transitional? tectono-magmatic setting. Near the contacts, the tonalite contains abundant enclaves of igneous appearance and variable size from several cm to dm, described as autoliths. The study of autoliths and host tonalite reveals interesting results on the processes of fractionation in a thermally zoned magma chamber. Autoliths, and in a large extent the host tonalite, represent disguised cumulates from which a hydrous silicic liquid was extracted. Barometry calculations from mineral chemistry in both autoliths and tonalites record a shallow pressure of emplacement of 0.5 kbar. Rhyolite-dacite flows and ignimbrites, surrounding the northern contact of the Cerro Munro tonalite, may represent the exsolved liquid from the plutonic cumulates. The study by cathodoluminiscence and electron backscattered diffraction techniques from a rhyolite-hosted quartz supports this protracted history of the Cerro Munro magma chamber.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

Petrogenesis of thundereggs in Eocene rhyolite domes of central Chubut, Patagonia

Se describen los thundereggs que se encuentran en domos vitrofíricos de la caldera de Piedra Parada. Tanto las características geológicas, petrológicas como geoquímicas sugieren que estos crecen a partir de gotas de líquidos inmiscibles que se desvitrificaron como esferulitas de anortoclasa. La expansión de la fase vapor segregada al desvitrificarse las gotas inmiscibles, rompieron las esferulitas y desarrollaron grandes vesículas tapizadas por los pedazos rotos de la esferulita. El inmediato enfriamiento del resto del magma dio lugar a la formación de un domo vítreo con textura perlítica. Posteriormente, agua a baja temperatura lixivió al vidrio esferulítico y rellenó las cavidades de las vesículas y esferulitas con ópalo y/o calcedonia.Thundereggs at the glass domes of Piedra Parada Caldera are described. Their geological, petrological and geochemical characteristics suggest growth from immiscible liquid drops that devitrified as anorthoclase spherulites. The expansion of the segregated vapor phase of the devitrified immiscible drops broke the spherulites and made large vesicles lined with the broken pieces of the spherulite. Further cooling of the rest of the magma yielded a glass dome with perlitic texture. Low temperature water lixiviated the perlitic glass and spherulites, filling the cavities within the vesicles and broken spherulite with opal and/or chalcedony.Centro de Investigaciones Geológica

Petrogenesis of thundereggs in Eocene rhyolite domes of central Chubut, Patagonia

Se describen los thundereggs que se encuentran en domos vitrofíricos de la caldera de Piedra Parada. Tanto las características geológicas, petrológicas como geoquímicas sugieren que estos crecen a partir de gotas de líquidos inmiscibles que se desvitrificaron como esferulitas de anortoclasa. La expansión de la fase vapor segregada al desvitrificarse las gotas inmiscibles, rompieron las esferulitas y desarrollaron grandes vesículas tapizadas por los pedazos rotos de la esferulita. El inmediato enfriamiento del resto del magma dio lugar a la formación de un domo vítreo con textura perlítica. Posteriormente, agua a baja temperatura lixivió al vidrio esferulítico y rellenó las cavidades de las vesículas y esferulitas con ópalo y/o calcedonia.Thundereggs at the glass domes of Piedra Parada Caldera are described. Their geological, petrological and geochemical characteristics suggest growth from immiscible liquid drops that devitrified as anorthoclase spherulites. The expansion of the segregated vapor phase of the devitrified immiscible drops broke the spherulites and made large vesicles lined with the broken pieces of the spherulite. Further cooling of the rest of the magma yielded a glass dome with perlitic texture. Low temperature water lixiviated the perlitic glass and spherulites, filling the cavities within the vesicles and broken spherulite with opal and/or chalcedony.Centro de Investigaciones Geológica

Democracy Does Not Cause Growth:The Importance of Endogeneity Arguments

This article challenges recent findings that democracy has sizable effects on economic growth. As extensive political science research indicates that economic turmoil is responsible for causing or facilitating many democratic transitions, the paper focuses on this endogeneity concern. Using a worldwide survey of 165 country-specific democracy experts conducted for this study, the paper separates democratic transitions into those occurring for reasons related to economic turmoil, here called endogenous, and those grounded in reasons more exogenous to economic growth. The behavior of economic growth following these more exogenous democratizations strongly indicates that democracy does not cause growth. Consequently, the common positive association between democracy and economic growth is driven by endogenous democratization episodes (i.e., due to faulty identification)

Determinación y cuantificación de componentes mayoritarios en digeridos de rocas por electroforesis capilar con detección UV indirecta

La determinación cuantitativa de los componentes mayoritarios y minoritarios resulta fundamental para el análisis geoquímico. Habitualmente se prefiere utilizar técnicas que permitan determinar todos o la mayor parte de estos elementos en el mismo análisis. En la práctica, los métodos más utilizados para este grupo de elementos son espectrofotometría en plasma de acoplamiento inductivo (ICP-AES) y fluorescencia de rayos X (FRX).Fil: Tascon, M.. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; ArgentinaFil: Aspromonte, J. A.. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; ArgentinaFil: Cavarozzi, Claudia Ernestina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Pedemonte, Marcos Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Gagliardi, Leonardo Gabriel. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaIII Reunión Argentina de Geoquímica de la SuperficieMar del PlataArgentinaUniversidad Nacional de Mar del PlataInstituto de Geología de Costas y del Cuaternari