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Impactos gigantes y el origen y evolución de los continentes
Tim E Johnson1,2, Christopher L Kirkland3, Yongjun Lu4,5
1School of Earth and Planetary Sciences, the Institute for Geoscience Research, Timescales of Mineral Systems Group, Curtin University, Perth, Western Australia, Australia. tim.johnson@curtin.edu.au.
Nature
|August 10, 2022
Resumen
Los continentes de la Tierra se formaron en tres etapas, influenciados por impactos gigantes y alteraciones hidrotermales. El análisis de antiguos cristales de circón revela los primeros procesos que dieron forma al Cratón de Pilbara.
Área de la Ciencia:
- Geociencia, específicamente la geología y la geoquímica precámbricas.
- Ciencia planetaria, centrada en las primeras condiciones de la Tierra y la formación de continentes.
Sus antecedentes:
- La Tierra es única en poseer continentes, pero su origen y evolución siguen siendo poco conocidos.
- El Cratón Pilbara en Australia Occidental es un remanente crítico y bien conservado de la corteza continental temprana de la Tierra del Eón Arcaico (hace 4.0-2.5 mil millones de años).
Objetivo del estudio:
- Para aclarar la formación y evolución del Cratón de Pilbara, proporcionando información sobre el desarrollo temprano de la corteza continental.
- Investigar el papel de los impactos gigantes y los procesos hidrotermales en la formación de los continentes nacientes.
Principales métodos:
- Análisis de las composiciones de isótopos de oxígeno (δ18O) en cristales de circón magmáticos fechados del Cratón de Pilbara.
- Correlación de grupos de edad de circón y firmas isotópicas con eventos geológicos como impactos gigantes y alteración de la corteza.
Principales resultados:
- Los circones de hace 3.6-3.4 mil millones de años (Ga) muestran el submanto δ18O, lo que indica la cristalización de magmas evolucionados que interactúan con la corteza basáltica alterada hidrotermalmente, probablemente provocada por impactos gigantes.
- Un segundo cúmulo de circón en 3.4 Ga coincide con la evidencia de impactos gigantes, lo que sugiere su influencia continua.
- Los circones de etapa posterior (3.4-3.0 Ga y <3.0 Ga) revelan la cristalización de magmas derivados del núcleo continental en evolución y el posterior reciclaje de rocas de la corteza, respectivamente.
Conclusiones:
- La formación de la corteza continental en el Cratón de Pilbara ocurrió en tres etapas distintas, fuertemente influenciadas por impactos de meteoritos y alteración hidrotermal oceánica.
- Las primeras etapas involucraron una fusión superficial impulsada por impactos, lo que condujo a la formación de un núcleo máfico-ultramáfico.
- Las etapas posteriores involucraron el reciclaje de rocas superficiales, contribuyendo al desarrollo de la corteza continental moderna.
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