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Las komatiitas revelan un depósito hidráulico del manto profundo del Arqueo
Alexander V Sobolev1,2, Evgeny V Asafov2, Andrey A Gurenko3
1Université Grenoble Alpes, Institute Science de la Terre (ISTerre), CNRS, F-38041 Grenoble, France.
Nature
|April 1, 2016
Resumen
Las komatiitas arqueas entraron en erupción a altas temperaturas, con nuevas investigaciones que muestran que sus magmas contenían 0.6% de agua. Esto apoya un origen de pluma y una hidratación profunda del manto en la historia temprana de la Tierra.
Área de la Ciencia:
- Geoquímica
- Petrología
- Las primeras condiciones de la Tierra
Sus antecedentes:
- Las komatiitas arqueas son lavas ultramaficas que indican un derretimiento extremo del manto.
- Existe incertidumbre con respecto al contenido de agua de la komatiita, que afecta a la temperatura de erupción y a los modelos de origen (pluma frente a subducción).
Objetivo del estudio:
- Para estimar directamente la composición y la temperatura de cristalización de los fundidos parentales de la comatiita arqueana.
- Resolver el debate sobre el contenido de agua de la komatiita y sus implicaciones para los procesos del manto.
Principales métodos:
- Análisis de agua, elementos volátiles, principales y oligoelementos en las inclusiones fundidas dentro de la olivina de magnesio.
- Modelado geoquímico de la evolución del derretimiento y las características de la fuente.
Principales resultados:
- El fundido parental de las komatiitas de Abitibi de hace 2.700 millones de años contenía 30% de MgO, 0.6% de H2O, y estaba agotado en elementos incompatibles.
- La cristalización se inició a ~ 1,530 ° C en condiciones de reducción, evolucionando a través de la cristalización fraccionada y la asimilación de la corteza menor.
- La alta relación H2O/Ce sugiere el arrastramiento de material hidratado desde la zona de transición del manto.
Conclusiones:
- La composición de Komatiite y la baja fugacidad de oxígeno son inconsistentes con la subducción, lo que apoya un origen de penacho.
- Los resultados confirman las altas temperaturas del manto arqueo y sugieren un depósito de manto profundo e hidratado al principio de la historia de la Tierra.
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