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Un límite agudo entre la litosfera y la astenosfera fotografiado debajo del este de América del Norte
Catherine A Rychert1, Karen M Fischer, Stéphane Rondenay
1Department of Geological Sciences, Brown University, Box 1846, Providence, Rhode Island 02912, USA. Catherine_Rychert@Brown.edu
Nature
|July 29, 2005
Resumen
El límite entre la litosfera y la astenosfera es más agudo de lo esperado, lo que sugiere que el derretimiento parcial o los volátiles, no solo la temperatura, debilitan la astenosfera. Estas imágenes sísmicas revelan información clave sobre la dinámica del manto de la Tierra.
Área de la Ciencia:
- La geofísica es la geofísica.
- Sismología Sismología Sismología.
- La tectónica es la tectónica.
Sus antecedentes:
- La tectónica de placas se basa en el movimiento de la litosfera sobre la astenosfera.
- La naturaleza de la frontera entre la litosfera y la astenosfera es crucial para comprender las diferencias de resistencia mecánica.
- Los gradientes de velocidad sísmica en este límite proporcionan información sobre las propiedades físicas y químicas.
Objetivo del estudio:
- Para investigar la nitidez del límite entre la litosfera y la astenosfera utilizando datos sísmicos.
- Para restringir las propiedades físicas y químicas responsables de las características del límite.
- Diferenciar entre los mecanismos de debilitamiento térmico y los mecanismos de debilitamiento por composición o fusión.
Principales métodos:
- Análisis de las fases sísmicas convertidas en el este de América del Norte.
- Imagen de gradientes de velocidad sísmica en la base de la litosfera.
- Cuantificación de la caída de la velocidad de la onda de cizallamiento en intervalos de profundidad específicos.
Principales resultados:
- Se observó un fuerte gradiente de velocidad sísmica en el límite litosfera-astenosfera (profundidad de 90-110 km).
- La velocidad de la onda de cizallamiento cayó un 3-11% en 11 km o menos.
- Este límite agudo es inconsistente con un gradiente puramente térmico.
Conclusiones:
- La astenosfera probablemente contiene un pequeño porcentaje de fusión parcial o está enriquecida con volátiles.
- Estos factores, más que solo la temperatura, explican la debilidad de la astenosfera.
- Los hallazgos refinan los modelos del flujo del manto y la tectónica de placas.
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