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La evidencia isotópica acoplada 142Nd-143Nd para la dinámica del manto de Hadeo
Vickie C Bennett1, Alan D Brandon, Allen P Nutman
1Research School of Earth Sciences, Australian National University, Canberra ACT, 0200 Australia. vickie.bennett@anu.edu.au
Science (New York, N.Y.)
|December 22, 2007
Resumen
Las antiguas rocas de Groenlandia revelan la Tierra primitiva.
Área de la Ciencia:
- Geoquímica y Geología Isotópica.
- Historia de la Tierra Temprana y Ciencias Planetarias.
Sus antecedentes:
- Comprender la diferenciación química inicial de la Tierra es crucial para descifrar la formación de los planetas.
- Los sistemas isotópicos proporcionan herramientas poderosas para rastrear los primeros procesos geológicos.
- El sistema isotópico del neodimio (Nd), particularmente el 142Nd y el 143Nd, ofrece información sobre la evolución temprana del manto.
Objetivo del estudio:
- Para fechar directamente la formación de depósitos de silicato químicamente distintos en la Tierra temprana.
- Investigar la escala y persistencia de las heterogeneidades tempranas del manto.
- Para rastrear la posterior evolución y remezcla de estos primeros dominios del manto.
Principales métodos:
- Análisis de excesos acoplados de neodimio-142 (142Nd) y neodimio-143 (143Nd) en rocas de 3.850 millones de años de antigüedad del suroeste de Groenlandia.
- Comparación de firmas de 142Nd en rocas antiguas contemporáneas de Groenlandia y Australia Occidental (>3.600 millones de años de antigüedad).
- Utilizando la desintegración del extinto samario-146 (146Sm) y el de larga vida samario-147 (147Sm) para datar la formación temprana de reservas de silicato.
Principales resultados:
- Los datos isotópicos del neodimio datan directamente la formación de depósitos de silicato químicamente distintos dentro de los primeros 30-75 millones de años de la historia de la Tierra.
- Las diferencias en las firmas de 142Nd entre las rocas de Groenlandia y Australia Occidental revelan heterogeneidades del manto a gran escala presentes muy temprano en la historia de la Tierra.
- Estas heterogeneidades persistieron durante al menos los primeros mil millones de años, con variaciones temporales de 142Nd que indican una remezcla incompleta de dominios del manto temprano.
Conclusiones:
- El manto de la Tierra era químicamente heterogéneo desde sus primeras etapas, con distintos depósitos de silicato formándose rápidamente.
- Las firmas isotópicas conservadas en rocas antiguas proporcionan un registro directo de estos primeros procesos de diferenciación.
- La remezcla incompleta de estos primeros dominios influyó en la posterior evolución geoquímica del manto.
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