Estudios Geológicos, Vol 70, No 2 (2014)

Composición del circón de granitos variscos del Norte de Portugal


https://doi.org/10.3989/egeol.41729.318

H. C.B. Martins
Geology Centre. Department of Geosciences Environment and Spatial Planning. Faculty of Sciences, Porto University, Portugal

J. Abreu
Geology Centre. Department of Geosciences Environment and Spatial Planning. Faculty of Sciences, Porto University, Portugal

Resumen


Se han seleccionado tres plutones graniticos variscos en el norte de Portugal para el estudio de la composición del circón. Los plutones son: Vila Pouca de Aguiar y Lavadores-Madalena con afinidad de tipo-I y el plutón de Vieira do Minho de tipo transicional I-S. Los circones se presentan en cristales euhédricos a subhédricos y tienen zonados magmáticos, concéntricos oscilatorios finos ligados principalmente a variaciones de las concentraciones del Hf, Y, U y Th. La mayoría de los cristales de circón muestran la sustitución dominante “xenotima”. Los zircones tienen relaciones Zr/Hf que varían en el rango 21–52, sin diferencias significativas entre los diferentes granitos. Estos valores son idénticos a otros granitos peralumínicos y son consistentes con circones de origen cortical. Además, las relaciones Zr/Hf coinciden con las de protolitos corticais y, en consecuencia con los propuestos en la génesis de los plutones de Vila Pouca de Aguiar y Vieira de Minho, en particular rocas metaigneas. Aunque los circones del plutón Lavadores-Madalena tienen una composicíon similar a los otros plutones, fue propuesto un origen por hibridacíon. Sin embargo la similitud química de los circones de este plutón con los otros puede tambíen sugerir un origen similar.

Palabras clave


composición de circón; elementos traza; granitos Variscos

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Referencias


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