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Los polimorfos de alta presión del olivino y la discontinuidad sísmica de 660 km
Nature
|June 1, 2001
Resumen
La discontinuidad del manto de 660 km es causada por la descomposición del espinel gamma (ringwoodita). Nuevos experimentos con celdas de yunque de diamante calentadas con láser confirman que esta transición ocurre a presiones del manto terrestre, reconciliando los datos sísmicos con la física de los minerales.
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 fue atribuida a la descomposición del gamma-espinel (ringwoodita) en MgSiO3-perovskita y magnesiowüstita.
- Estudios anteriores presentaron datos contradictorios sobre la presión a la que se produce esta transición, lo que desafía los modelos establecidos de composición del manto.
Objetivo del estudio:
- Para determinar con precisión las condiciones de presión y temperatura para la descomposición de la espina gamma a una profundidad del manto de 660 km.
- Para resolver las discrepancias entre las observaciones sísmicas y los datos de física mineral con respecto a la discontinuidad de 660 km.
Principales métodos:
- Difracción de rayos X in situ utilizando una célula de yunque de diamante calentada con láser.
- Control preciso de la presión, la temperatura y las condiciones hidrostáticas.
- Análisis de las transiciones de fase gamma-Mg2SiO4 bajo condiciones de alta presión y alta temperatura.
Principales resultados:
- Gamma-Mg2SiO4 se mantiene estable hasta presiones y temperaturas equivalentes a 660 km de profundidad (24 GPa, 1.900 K).
- Los productos de descomposición se identifican como MgSiO3-perovskita y MgO (periclasa).
- Los resultados experimentales se alinean con los datos sísmicos, resolviendo discrepancias anteriores.
Conclusiones:
- La discontinuidad sísmica de 660 km es consistente con la descomposición del espinel gamma en condiciones geofísicamente relevantes.
- Las mediciones precisas de presión y temperatura son críticas para conciliar la física mineral con la sismología.
- El modelo mineralógico del manto de la Tierra está respaldado por estos hallazgos.
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