Anomalías de U, Th, Zr y Hf en magmas de arco y su posible relación con la contaminación del manto, producto de la subducción de parte de la corteza continental
Cargando...
Archivos
Fecha
2017
Profesor/a Guía
Facultad/escuela
Idioma
es
Título de la revista
ISSN de la revista
Título del volumen
Editor
Universidad Andrés Bello
Nombre de Curso
Licencia CC
Licencia CC
Resumen
Numerosos estudios sugieren que parte de la composición de elementos traza en los magmas de arco, está condicionada por la corteza continental que se introduce en la cuña mantélica. Las porciones de corteza continental y sedimentos que ingresan al manto, contienen minerales accesorios capaces de albergar elementos como REE, U, Th, Pb, Ti, Nb, entre otros. En zonas de subducción continental, estos minerales podrían quedar como fases residuales luego de la fusión del material terrígeno, reteniendo los elementos mencionados.
El Complejo Plutónico Chaltén (CPCH), ubicado en la frontera Chile-Argentina en la Patagonia, representa el magmatismo de arco ocurrido en el Mioceno temprano (17-16.4 Ma), cuando se registraron altas tasas de convergencia. Dentro de este complejo, el grupo máfico Laguna Sucia (serie γ1) muestra un marcado empobrecimiento en U, Th, Zr y Hf. El objetivo principal de este estudio es determinar los procesos petrogenéticos que habrían generado la anomalía negativa en U, Th, Zr y Hf en las rocas de la serie γ1.
A partir de resultados de química y petrografía de esta serie, es posible asociar las anomalías mencionadas a la química y mineralogía de las rocas del basamento metamórfico del antearco, ya que la signatura de elementos traza de la “componente de subducción” (i.e. fundidos y fluidos generados a partir de la deshidratación y fusión del material arrastrado por la corteza subductada) evidencia anomalías negativas de Th, U, Hf y Zr.
Las rocas que conforman la serie γ1 se han generado a partir de altos grados de fraccionamiento a partir del magma primario, de hasta un 32%. La signatura de elementos traza de dicho fundido evidencia fuertes anomalías negativas de Zr y Hf, y en menor magnitud de U y Th. Con lo anterior, se sugiere que el origen de las anomalías de U, Th, Zr y Th características de la serie γ1, es previo a la génesis el magma primario, debido a la presencia de fases refractarias en el canal de subducción, procedentes de rocas metasedimentarias y de las unidades félsicas del Batolito Surpatagónico.
Numerous studies suggest that part of the composition of trace elements in arc magmas is conditioned by the continental crust that is introduced into the mantle wedge. The portions of continental crust and sediments that enter the mantle contain accessory minerals capable of capturing elements such as REE, U, Th, Pb, Ti, Nb, among others. In continental subduction zones, these minerals could remain as residual phases after terrigenous material melting, retaining the mentioned elements. The Chaltén Plutonic Complex (CHPC), located at the Chile-Argentina border in Patagonia, represents the arc magmatism occurred during early Miocene (17-16.4 Ma), when high convergence rates were recorded. Within this complex, the Laguna Sucia mafic group (γ1 series) shows marked depletion in U, Th, Zr and Hf. The main objective of this study is to determine the petrogenetic processes that would have generated the negative anomaly in U, Th, Zr and Hf in the rocks of the γ1 series. From the chemistry and petrography of this series, it is possible to relate the mentioned anomalies with the chemistry and mineralogy of the rocks of the forearc metamorphic basement, since the signature of trace elements of the "subduction component" (i.e. fluids and melts generated by dehydration and melting of the material dragged by the subducted crust) shows negative anomalies of Th, U, Hf and Zr. The rocks that include γ1 series have been generated from high degrees of fractionation from primary magma, up to 32%. The signatures of trace elements of this melted material show strong negative anomalies of Zr and Hf, and lesser of U and Th. Due to all of the above, it is suggested that the origin of the U, Th, Zr and Th anomalies characteristic of the γ1 series, is prior to the genesis of the primary magma, due to the presence of refractory phases in the subduction channel, from metasedimentary rocks and the felsic units of the South Patagonian Batholith.
Numerous studies suggest that part of the composition of trace elements in arc magmas is conditioned by the continental crust that is introduced into the mantle wedge. The portions of continental crust and sediments that enter the mantle contain accessory minerals capable of capturing elements such as REE, U, Th, Pb, Ti, Nb, among others. In continental subduction zones, these minerals could remain as residual phases after terrigenous material melting, retaining the mentioned elements. The Chaltén Plutonic Complex (CHPC), located at the Chile-Argentina border in Patagonia, represents the arc magmatism occurred during early Miocene (17-16.4 Ma), when high convergence rates were recorded. Within this complex, the Laguna Sucia mafic group (γ1 series) shows marked depletion in U, Th, Zr and Hf. The main objective of this study is to determine the petrogenetic processes that would have generated the negative anomaly in U, Th, Zr and Hf in the rocks of the γ1 series. From the chemistry and petrography of this series, it is possible to relate the mentioned anomalies with the chemistry and mineralogy of the rocks of the forearc metamorphic basement, since the signature of trace elements of the "subduction component" (i.e. fluids and melts generated by dehydration and melting of the material dragged by the subducted crust) shows negative anomalies of Th, U, Hf and Zr. The rocks that include γ1 series have been generated from high degrees of fractionation from primary magma, up to 32%. The signatures of trace elements of this melted material show strong negative anomalies of Zr and Hf, and lesser of U and Th. Due to all of the above, it is suggested that the origin of the U, Th, Zr and Th anomalies characteristic of the γ1 series, is prior to the genesis of the primary magma, due to the presence of refractory phases in the subduction channel, from metasedimentary rocks and the felsic units of the South Patagonian Batholith.
Notas
Tesis (Geólogo)
Proyecto financiado por Fondecyt 1161818
Proyecto regular UNAB N°753
Proyecto financiado por Fondecyt 1161818
Proyecto regular UNAB N°753
Palabras clave
Magmatismo, Petrogénesis, Chile, Región de Aysén del General Carlos Ibáñez del Campo