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La composición isotópica no condrítica del azufre del manto terrestre
J Labidi1, P Cartigny, M Moreira
1Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75005 Paris, France. labidi@ipgp.fr
Nature
|September 6, 2013
Resumen
El manto de la Tierra muestra diferentes proporciones de isótopos de azufre, desafiando la idea de una composición homogénea. Esta heterogeneidad sugiere un vínculo con la diferenciación núcleo-manto y los sedimentos subducidos, no sólo adiciones tardías.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Ciencias planetarias Ciencias planetarias.
- La geoquímica de los isótopos es la geoquímica de los isótopos.
Sus antecedentes:
- La diferenciación entre el núcleo y el manto es un evento planetario importante, que influye en la composición del manto al eliminar elementos siderófilos como el azufre.
- Se suponía que el manto de la Tierra tenía una proporción de isótopos de azufre homogéneos y condríticos ((34) S / ((32) S).
- Esta suposición apoyó los modelos de un presupuesto de azufre del manto dominado por materiales de acreción tardía.
Objetivo del estudio:
- Para investigar la composición isotópica de azufre ((34) S / ((32) S) del manto de la Tierra.
- Para determinar si las proporciones de azufre en el manto son homogéneas o heterogéneas.
- Para correlacionar los isótopos de azufre con otros trazadores isotópicos del manto y comprender su origen.
Principales métodos:
- Análisis de las proporciones de isótopos de azufre ((34) S / ((32) S) en basaltos de la cresta del océano medio de la cresta del Atlántico Sur.
- Medición de los isótopos de estroncio ((87) Sr/ ((86) Sr) y neodimio ((143) Nd/ ((144) Nd) en las mismas muestras.
- Modelado de mezcla isotópica para interpretar el origen de las heterogeneidades observadas.
Principales resultados:
- Las proporciones de isótopos de azufre del manto ((34) S / ((32) S) son heterogéneas, no homogéneas como se pensaba anteriormente.
- Estas variaciones se correlacionan directamente con las proporciones de isótopos de estroncio ((87) Sr/ (86) Sr) y neodimio ((143) Nd/ (144) Nd).
- Un extremo del manto empobrecido muestra un valor significativamente negativo de δ(34) S, inconsistente con los valores condríticos incluso con la adición de azufre superficial.
Conclusiones:
- La heterogeneidad del manto observada en los isótopos de azufre apunta a un componente reciclado, probablemente sedimentos subducidos.
- Los datos sugieren un registro de diferenciación núcleo-manto donde el núcleo tiene una relación (34) S / (32) S ligeramente más alta que las condritas.
- El presupuesto de azufre del manto conserva huellas de la diferenciación temprana núcleo-manto, a pesar de las adiciones posteriores de elementos.
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