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Evidencia de un antiguo depósito isotópico de osmio en la Tierra
1Geological and Environmental Sciences, 320 Lomita Mall, Stanford University, CA 94305-2115, USA. meibom@pangea.stanford.edu
Science (New York, N.Y.)
|April 20, 2002
Resumen
Los antiguos depósitos de elementos del grupo platino en el manto de la Tierra sugieren la formación temprana del núcleo interno. Los granos de iridosmina revelan proporciones extremadamente radiogénicas de isótopos de osmio, lo que apunta a interacciones núcleo-manto poco después de la acreción de la Tierra.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Geología de Isótopos Geología de Isótopos.
- Ciencias planetarias Ciencias planetarias.
Sus antecedentes:
- Los granos de iridosmina de los ofiolitos de las montañas Klamath exhiben firmas geoquímicas inusuales.
- Estos granos poseen proporciones altamente radiogénicas de isótopos de osmio (186Os/188Os) y antiguas edades de Re-Os, que van de 256 a 2644 millones de años.
- Esto sugiere la presencia de un antiguo depósito de elementos del grupo del platino con una relación supracondrítica Platino/Osmio (Pt/Os).
Objetivo del estudio:
- Para investigar el origen de los antiguos depósitos de elementos del grupo del platino.
- Explorar las implicaciones de estos reservorios para los procesos de la Tierra primitiva, específicamente la formación del núcleo.
- Para determinar si las composiciones isotópicas de iridosmina Os pueden servir como una firma del núcleo externo.
Principales métodos:
- Análisis de los granos de iridosmina de los depósitos de placer.
- Determinación de las composiciones isotópicas de osmio (Os) y renio (Re) utilizando geocronología Re-Os.
- Modelado geoquímico para evaluar los mecanismos de formación potenciales para las relaciones Pt/Os supracondríticas.
Principales resultados:
- Los granos de iridosmina muestran proporciones extremadamente radiogénicas de 186Os/188Os y una edad mínima de Re-Os de hasta 2.64 mil millones de años.
- Estos hallazgos indican la existencia de un antiguo depósito con una relación Pt/Os supra-condrítica.
- La relación Pt/Os observada es consistente con la fraccionamiento durante la cristalización del núcleo interno en el núcleo externo.
Conclusiones:
- La composición isotópica de la iridosmina Os sugiere un vínculo con el núcleo externo de la Tierra.
- Si estas composiciones isotópicas de Os son de hecho una firma del núcleo externo, implica una formación muy temprana del núcleo interno.
- El núcleo interno probablemente se formó dentro de los primeros cientos de millones de años después de la acreción de la Tierra, significativamente antes de lo que se pensaba.
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