Petrografía y geoquímica de roca total del grupo plutónico Gualletué, provincia de Malleco, Novena Región, Chile
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Fecha
2020
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Facultad/escuela
Idioma
es
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Universidad Andrés Bello
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Licencia CC
Licencia CC
Resumen
Las intrusiones graníticas que afloran a lo largo de la Cordillera de Lonquimay pertenecen al Grupo Plutónico
Gualletué, y constituyen parte del segmento occidental de la Cordillera de los Andes, a los 38°S. El contacto de esta unidad
con la Formación Nacientes del Biobío es marcado, incluyendo xenolitos de esta última. En zonas interiores del valle del
río Quienquén, donde aflora una gran parte del intrusivo es posible observar relaciones de intrusión entre magmas de distinta
viscosidad, a menudo acompañado de enclaves microgranulares máficos de composición diorítica. Estas rocas también
presentan evidencia de inmiscibilidad magmática, donde coexisten magmas máficos y félsicos. Las observaciones de campo
sugieren un ascenso por stopping y emplazamiento estilo diapírico para estas intrusiones. Petrográficamente, las intrusiones
muestran variaciones en su mineralogía, con rocas de grano medio a fino, y texturas poiquilíticas, consertal, gráfica, zonas
de inclusión de apatita. Además, se distinguen dos minerales máficos principales, que permite dividir el intrusivo en tres
subunidades. En base a análisis modales, se clasifican principalmente como dioritas, dioritas cuarcíferas y tonalitas, y de
manera subordinada granodioritas. Las rocas son principalmente calco-alcalinas y de composición metaluminosa a
ligeramente peraluminosa. Se clasifican como rocas de tipo I, siguiendo el desarrollo de rocas pre-colisionales. Los análisis
de roca total indican que la diferenciación ocurrió vía cristalización fraccionada. Los elementos incompatibles y las tierras
raras presentan patrones que indican que estas intrusiones derivan de la fusión de un manto enriquecido por fluidos
provenientes de la deshidratación de la placa subductada. Las dataciones K-Ar realizadas en esta unidad por diversos autores
indican una edad que varía entre el Jurásico Superior-Cretácico Superior, pero que podría acotarse al Cretácico Superior.
The granitic intrusions that outcrops along the Lonquimay Mountain Range belong to the Gualletué Plutonic Group, and constitute part of the western segment of the Andes Mountain Range, at 38 ° S. The contact of this unit with the Nacientes del Biobío Formation is marked, including xenoliths of the latter. In inland areas of the Quienquén River Valley, where a large part of the intrusive outcrops it is possible to observe an intrusion relationships between magmas of different viscosity, often accompanied by mafic microgranular enclaves of dioritic composition. These rocks also present evidence of magmatic immiscibility, where mafic and felsic magmas coexist. Field observations suggest a stopping and diapiric-style emplacement for these intrusions. Petrographically, the intrusions show variations in their mineralogy, from medium to fine grain rocks, with poikilitic, consertal, graphic textures, and apatite inclusion zones. In addition, two main mafic minerals are distinguished, which allows the intrusive to be divided into three subunits. Based on modal analysis, they are mainly classified as diorites, quartziferous diorites and tonalites, and subordinate granodiorites. The rocks are mainly calco-alkaline and have a metaluminous to slightly peraluminous composition. They are classified as type-I rocks, following the development of pre-collisional rocks. Whole-rock analyzes indicate that the differentiation occurred via fractional crystallization. Incompatible elements and rare earths elements show patterns that indicate that these intrusions derive from the melting of a mantle region enriched by subduction-related fluids. The K-Ar dating carried out in this unit by various authors indicates an age that varies between the Upper Jurassic-Upper Cretaceous, but could be limited to the Upper Cretaceous.
The granitic intrusions that outcrops along the Lonquimay Mountain Range belong to the Gualletué Plutonic Group, and constitute part of the western segment of the Andes Mountain Range, at 38 ° S. The contact of this unit with the Nacientes del Biobío Formation is marked, including xenoliths of the latter. In inland areas of the Quienquén River Valley, where a large part of the intrusive outcrops it is possible to observe an intrusion relationships between magmas of different viscosity, often accompanied by mafic microgranular enclaves of dioritic composition. These rocks also present evidence of magmatic immiscibility, where mafic and felsic magmas coexist. Field observations suggest a stopping and diapiric-style emplacement for these intrusions. Petrographically, the intrusions show variations in their mineralogy, from medium to fine grain rocks, with poikilitic, consertal, graphic textures, and apatite inclusion zones. In addition, two main mafic minerals are distinguished, which allows the intrusive to be divided into three subunits. Based on modal analysis, they are mainly classified as diorites, quartziferous diorites and tonalites, and subordinate granodiorites. The rocks are mainly calco-alkaline and have a metaluminous to slightly peraluminous composition. They are classified as type-I rocks, following the development of pre-collisional rocks. Whole-rock analyzes indicate that the differentiation occurred via fractional crystallization. Incompatible elements and rare earths elements show patterns that indicate that these intrusions derive from the melting of a mantle region enriched by subduction-related fluids. The K-Ar dating carried out in this unit by various authors indicates an age that varies between the Upper Jurassic-Upper Cretaceous, but could be limited to the Upper Cretaceous.
Notas
Memoria (Geólogo)
Palabras clave
Petrografía, Geoquímica, Chile, Malleco, Enclaves Máficos Microgranulares