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

Estimación de la actividad puzolánica de algunos áridos naturales y artificiales mediante el ensayo químico de puzolanicidad y el índice de actividad resistente

Fil: Rolny, D.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geomorfología y Suelos; ArgentinaFil: Sovarzo, L.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geomorfología y Suelos; ArgentinaFil: Couyoupetrou, L.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Recursos Minerales; ArgentinaFil: Cavarozzi, Claudia Ernestina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Cremaschi, G.. Universidad Nacional de La Plata. Facultad de Arquitectura y Urbanismo. Laboratorio de Tecnología y Gestión Habitacional; ArgentinaFil: Etcheverry, Ricardo Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Recursos Minerales; ArgentinaFil: Forte, Luis M.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geomorfología y Suelos; Argentin