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La transformación post-espinel en Mg2SiO4 y su relación con la discontinuidad sísmica de 660 km
1Department of Geosciences, Princeton University, Princeton, New Jersey 08544, USA. sangshim@princeton.edu
Nature
|June 1, 2001
Resumen
La discontinuidad sísmica de 660 km está vinculada a un cambio de fase mineral en el manto de la Tierra. Nuevos experimentos in situ confirman que esta transformación ocurre a la profundidad esperada, alineándose con los datos sísmicos.
Área de la Ciencia:
- La geofísica es la geofísica.
- Física de los minerales Física de los minerales
- Geoquímica de Alta Presión de Alta Presión
Sus antecedentes:
- La discontinuidad sísmica de 660 km marca un cambio significativo en las propiedades del manto de la Tierra.
- Esta discontinuidad fue tradicionalmente atribuida a la transformación post-espinel de (Mg,Fe) 2SiO4.4.
- Estudios previos in situ sugirieron que esta transformación ocurrió a presiones más bajas, desafiando su asociación con la discontinuidad de 660 km.
Objetivo del estudio:
- Para investigar la transformación de fase in situ de Mg2SiO4 a altas presiones y temperaturas.
- Para determinar las condiciones precisas de presión-temperatura de la transición post-espinel en Mg2SiO4.4.
- Para conciliar los hallazgos experimentales con las observaciones sísmicas de la discontinuidad de 660 km.
Principales métodos:
- Difracción de rayos X sincrotrón in situ.
- Calentamiento láser de doble cara en una célula de yunque de diamante.
- Estudio experimental de Mg2SiO4 a presiones que van desde 20 hasta 36 GPa.
Principales resultados:
- Se observó la transformación de fase de gamma-Mg2SiO4 a MgSiO3-perovskita y MgO (periclasa) tanto en la dirección hacia delante como en la inversa.
- Se encontró que las condiciones de presión y temperatura para esta transformación post-espinel eran consistentes con los datos sísmicos para la discontinuidad de 660 km.
- Esto contradice los hallazgos de anteriores experimentos in situ de prensas múltiples de yunque.
Conclusiones:
- La transformación post-espinel de Mg2SiO4 es consistente con la discontinuidad sísmica de 660 km.
- Las técnicas experimentales de alta presión, como las células de yunque de diamante calentadas con láser, proporcionan datos cruciales para comprender los procesos profundos de la Tierra.
- La ubicación precisa y la naturaleza de las discontinuidades del manto están mejor limitadas por estos métodos avanzados in situ.
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