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El agua y su influencia en el límite litosférico-astenosférico
David H Green1, William O Hibberson, István Kovács
1School of Earth Sciences and Centre for Ore Deposit Studies, University of Tasmania, Hobart 7001, Tasmania, Australia. David.H.Green@utas.edu.au
Nature
|September 25, 2010
Resumen
El contenido de agua en el manto superior influye significativamente en sus propiedades físicas. Los experimentos muestran que por encima de 90 km de profundidad, la descomposición de la pargasita causa una fuerte caída en el almacenamiento de agua, lo que afecta a la reología del manto y define el límite litosfera-astenosfera.
Área de la Ciencia:
- La geofísica es la geofísica.
- La geoquímica es la geoquímica.
- Petrología Experimental.
Sus antecedentes:
- La tectónica de placas de la Tierra involucra a la litosfera desacoplada de la más débil astenosfera.
- Se debate el mecanismo de formación del límite litosfera-astenosfera, con el papel del agua en la reología del manto como un factor clave.
- El agua puede debilitar los minerales del manto o inducir una fusión parcial, lo que influye en la reología.
Objetivo del estudio:
- Para investigar experimentalmente el papel del agua en el manto superior hasta 6 GPa.
- Para aclarar cómo el contenido de agua afecta a la reología del manto y la frontera litosfera-astenosfera.
Principales métodos:
- Un nuevo enfoque experimental para simular las condiciones del manto superior hasta 6 GPa.
- Análisis de lherzolita con vapor rico en agua para determinar el sólido saturado de vapor.
- Medición del contenido de agua en minerales nominalmente anhidros e identificación de sitios de almacenamiento de agua.
Principales resultados:
- La temperatura del sólido saturado de vapor para la herzolita con agua aumenta de 970°C a 1.5 GPa a 1.350°C a 6 GPa.
- La pargasita es el mineral principal de almacenamiento de agua, pero se vuelve inestable por encima de 3 GPa.
- La inestabilidad de la pargasita por encima de 3 GPa conduce a una fuerte disminución de la capacidad de almacenamiento de agua y la temperatura del sólido.
Conclusiones:
- La inestabilidad de la pargasita por encima de 3 GPa (aprox. 90 km de profundidad) causa una caída significativa en la capacidad de almacenamiento de agua del manto.
- La formación de fusión intersticial en el manto rico en agua (>180 ppm H2O) a presiones >3 GPa altera la reología del manto.
- Este proceso es crucial para definir el límite entre la litosfera y la astenosfera y coincide con el contenido de agua de las fuentes del manto astenosférico para los basaltos de la cresta oceánica media.
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