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Movimiento ultrarrápido de la fuente a la superficie de la fusión en los arcos de las islas de la sistemática

S Turner¹, P Evans, C Hawkesworth

¹Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK. simon.turner@bristol.ac.uk

Science (New York, N.Y.)

|May 19, 2001

Resumen

Las lavas de arco de isla muestran mayores excesos de radio-226 que otras rocas volcánicas, lo que indica la introducción mediante la subducción de fluidos de placas. Este rápido transporte sugiere que la segregación de la fusión del manto y la formación de canales ocurren rápidamente.

Área de la Ciencia:

La geoquímica es la geoquímica.
La geoquímica de los isótopos es la geoquímica de los isótopos.
Petrología del manto Petrología del manto

Sus antecedentes:

Las lavas de arco de isla exhiben firmas geoquímicas únicas, incluidos niveles elevados de radio-226 (226Ra).
Estos excesos son notablemente más altos que los que se encuentran en los basaltos de la cresta oceánica media (MORB) o los basaltos de las islas oceánicas (OIB).

Objetivo del estudio:

Para investigar el origen de los excesos de radio-226 en lavas de arco de isla.
Para restringir las escalas de tiempo del transporte de fusión y los procesos del manto en las zonas de subducción.

Principales métodos:

Análisis de las proporciones de radio-226 y torio-230 en lavas primitivas y diferenciadas de arco de isla.
Correlación de las relaciones 226Ra/230Th con las composiciones de los elementos principales y oligoelementos (por ejemplo, Ba/Th).

Principales resultados:

Las lavas de arco de isla muestran excesos significativos de 226Ra, que exceden los de MORB y OIB.
Las proporciones iniciales más altas de 226Ra/230Th se observan en las lavas más primitivas, que se correlacionan con altas proporciones de Ba/Th.
Los excesos de radio-226 disminuyen con el aumento de la diferenciación magmática.

Conclusiones:

Los fluidos de placas subducidas son la fuente probable de enriquecimiento de 226Ra en la base de la columna de fusión del manto.
La preservación de la señal 226Ra implica un transporte rápido a la superficie (cientos de años).
Las velocidades promedio de fusión están restringidas a aproximadamente 1000 metros por año, lo que indica una rápida segregación de la fusión del manto y la formación de canales.

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